Publications

Journal: Applied Thermal Engineering

Title: Experimental evaluation and optimization of the heat pipes integrated thermoelectric generator using response surface methodology

DOI: 10.1016/j.applthermaleng.2024.124599

Abstract:

In this study, integration of heat pipes with thermoelectric generators is proposed for the recovery of waste heat. Heat energy is transferred from a heat source to thermoelectric elements via heat pipes, enabling energy conversion. To dissipate excess heat from the system after conversion, additional heat pipes are positioned on the cold sides of thermoelectric elements. Cooling of the condenser sections of these heat pipes is facilitated using air flow provided by a fan. A novel approach in this study involves the innovative integration of heat pipes with thermoelectric generators. This integration provides a new pathway for optimizing waste heat recovery systems by combining advanced thermal management techniques with thermoelectric technology. Experiments conducted at different power inputs (12–42 W) and air velocities (0.4, 0.8, 1.2 m/s) determine the performance of the thermoelectric generator. Furthermore, a power usage efficiency analysis was conducted to discuss the applicability of the proposed method in electronics. At low air velocities, values below the ideal value of 1 were achieved. Experimental data were analyzed using response surface methodology to assess the impact of varying input parameters on the power output and efficiency of the thermoelectric generator. Optimization studies highlighted the importance of effectively cooling the cold side of thermoelectric elements. The highest power output and efficiency are achieved under conditions of 42 W power input, 1.2 m/s air velocity, and use of 4 heat sinks, yielding approximately 0.8 W and 2 %, respectively. Furthermore, the response surface methodology analysis indicated that the most significant effect on system outputs was the power input. Moreover, the results of this study lay the groundwork for future strategic advancements in thermoelectric generators, enhancing their role in sustainable energy solutions.

Journal: Heat Transfer Research

Title: Phase Change Materials (PCMs) for Buildings and Automotive Applications: A Review Study

DOI: 10.1615/HeatTransRes.2024053911

Abstract:

Phase change materials (PCMs) play a pivotal role in various sectors, particularly in automotive engineering, electric vehicles, and building construction. In the automotive sector, phase change materials are crucial for thermal management systems, aiding in temperature regulation of components such as batteries and engines. In electric vehicles, phase change materials are instrumental in enhancing battery performance and lifespan by effectively managing thermal loads during charging and discharging cycles, thus ensuring optimal operating conditions. These materials offer significant energy efficiency benefits by absorbing and releasing large amounts of latent heat during phase transitions, which helps in maintaining stable temperatures and reducing the load on heating and cooling systems. Additionally, PCMs contribute to sustainable building practices by enhancing thermal regulation, thereby lowering energy consumption and associated costs. This study explores the diverse applications and properties of phase change materials for improving thermal management and energy efficiency in vehicles, residences, and buildings. This research provides a comprehensive review of innovative solutions, including PCM-based heat pumps, PCM-integrated cementitious composites, and hybrid active-passive battery thermal management systems.

Journal: Heat Transfer Research

Title: Experimental investigation of horizontal solar stills using central container and transparent material as alternative to glass cover

DOI: 10.1615/HeatTransRes.2024055441

Abstract:

The increasing popularity of solar energy has spurred research aimed at enhancing the efficiency of various solar system designs. This study focuses on modifying traditional solar still systems and proposing innovative alternatives. Traditional solar stills become less practical to manufacture as their size increases because the glass cover must be held at an approximately 30° angle to ensure smooth flow of distilled water, requiring a higher elevation design on the high side of the still. To address this challenge, a wider horizontal system was developed using a specialized transparent plastic material, which reduces the brittleness risk commonly associated with glass. To further enhance efficiency, the system incorporates a surface-enhancing absorber, hemp rope in the basin, and a water-spraying mechanism on the cover. Based on the experimental results, the highest amount of distilled water collected was 79.064 g in Experiment 5. In terms of efficiency, the total thermal efficiency across all experiments was calculated, with the maximum efficiency of 4.92% obtained in Experiment 6. Additionally, the highest instantaneous efficiency (approximately 10.59%) was also achieved in Experiment 6, where hemp ropes and a spray application were used.

Journal: Heat Transfer Research

Title: EXPLORING CABIN HEATING EFFICIENCY IN ELECTRIC VEHICLES: AN EXPERIMENTAL ANALYSIS OF AIR HEATING MECHANISMS AND STRATEGIC INSULATION

DOI: 10.1615/HeatTransRes.2024055680

Abstract:

This study examines the impact of cabin heating systems on the driving range and heating performance of electric vehicles, utilizing experimental analyses conducted under cold winter conditions of Erzurum, Turkey. The ambient temperatures ranged between −8°C and −17°C during 60-min test periods. The thermal comfort was assessed by considering cabin modifications and insulation, along with the use of both the internal heating system and the external air heating system in the vehicle. The temperature difference between the cabin interior and the ambient has significantly increased with the installation of insulation materials. Results from the experiments highlighted significant positive effects of insulation material usage on heating energy ratios. The lowest heating energy ratio of 0.60% was recorded in an experiment that used only the internal heating system, without any thermal modifications or adjustments. The highest ratio, 1.70%, was recorded in an experiment where insulation materials on the floor, doors, and ceiling, along with an external heater, were utilized. Additionally, the study revealed that the internal heating system significantly influenced the vehicle range, leading to a reduction of approximately 10 km during 60 min of heating system operation. These findings underscore the crucial role of optimizing heating efficiency to enhance energy sustainability and driving range in electric vehicles.

Journal: Heat Transfer Research

Title: Performance Analysis of Alternative Compressor Cooling Techniques in Heat Pump Systems: Fan, Heat Pipe, and Peltier Applications

DOI: 10.1615/HeatTransRes.2025058001

Abstract:

The compressor, a continuously operating component in heat pumps, generates heat during operation, affecting efficiency. This study investigates the impact of various cooling methods, fan-assisted, passive cooling with heat pipes, and Peltier element cooling, on compressor performance and overall system efficiency, compared to the case without cooling. Experiments were conducted at two different voltages, 2 V and 4 V, to determine the effects of Peltier elements at different power levels. The study evaluated and discussed parameters such as the coefficient of performance (COP), entropy, enthalpy, isentropic efficiency, temperature variations, and related factors in detail. The findings highlighted the positive effects of cooling the compressor on isentropic efficiency, the thermal energy transferred from the condenser, and COP values. Among all scenarios, the use of Peltier elements yielded the best results for all parameters. However, increasing the voltage applied to the Peltier element from 2 V to 4 V caused the temperature of the hot side contacted to the environment to rise. This led to heat being transferred back to the cold side through conduction instead of being rapidly dissipated into the environment, resulting in higher compressor surface temperatures compared to the 2-V case. The highest COP value in the study was approximately 3.22, achieved with Peltier elements operating at 2 V. After accounting for the power consumption of the Peltier coolers, the COP values for experiments 1 through 5 were 2.05, 2.10, 2.12, 2.13, and 2.11, respectively.

Journal: Journal of Enhanced Heat Transfer

Title: EVALUATION OF PHOTOVOLTAIC MODULE EFFICIENCY BASED ON VARIOUS REFLECTIVE SURFACES AND ANGLE POSITIONS USING RESPONSE SURFACE METHODOLOGY

DOI: 10.1615/JEnhHeatTransf.2025057116

Abstract:

The depletion of traditional energy sources and the urgent demand for higher energy efficiency underscore the critical need for renewable energy solutions. This study explores strategies to enhance solar energy conversion efficiency by improving the performance of photovoltaic (PV) panels through the application of cost-effective and recyclable reflective materials, including Plexiglas mirror sheets and aluminum foil. By utilizing reflective materials to redirect additional sunlight onto the panels, this method enhances solar light capture and provides an accessible, cost-effective way to increase energy production. Experimental results confirm that the selected materials effectively enhance efficiency, demonstrating a measurable impact on photovoltaic panel performance. Response surface methodology (RSM) analysis highlighted that the mirror angle was the most influential parameter, with a 110° angle proving particularly effective in enhancing the energy output of the PV modules. These findings demonstrate that simple, low-cost solutions can significantly improve solar energy systems, paving the way for practical, scalable applications.

Journal: Energy for Sustainable Development

Title: Advanced mini solar still design: Spiral heating, triangular prism condensation, and comprehensive energy-exergy analysis

DOI: 10.1016/j.esd.2024.101632

Abstract:

Improving solar distillation systems is crucial in addressing water scarcity by providing a sustainable solution for clean water production, while also harnessing renewable energy to reduce environmental impact and reliance on conventional power sources. In solar still systems, salt water is typically contained in a basin, where it is heated by solar energy to produce distilled water through evaporation and condensation procedure. However, traditional systems do not allow for precise control over the temperature of the saltwater. This study introduces a novel approach by integrating a spiral type solar heater for salt water heating, which elevates the saltwater temperature to higher levels. To implement the proposed set up, the integration of a spiral-type solar heater, cotton-based materials, and a perforated pipe for delivering heated saltwater should be adopted, along with intermittent water pump operation to optimize heat absorption and evaporation efficiency. This enhancement enables more efficient condensation, which is achieved using a long triangular prism condensation unit. From the obtained results, it was revealed that the proposed mini solar still system can be modified by using cotton base materials and dripping salt water from a perforated pipe can enhance the distilled water by 138.46 %. Comparing the energy efficiency results shows a significant 128.57 % efficiency improvement, highlighting the need to optimize strategies and modifications for better solar distillation performance. Comparing the optimal experiment with the reference experiment revealed a substantial 152.63 % increase in exergy efficiency.

Journal: Sustainable Energy Technologies and Assessments

Title: Evaluating PCM heat battery as a range-saving solution for electric vehicle cabin heating

DOI: 10.1016/j.seta.2025.104270

Abstract:

In cold climates, traditional cabin heating systems that rely on the electric vehicle’s (EV) battery power consume a significant amount of energy, thus reducing the vehicle’s range. This study examines a phase change material (PCM)-based heat battery system designed to ensure thermal management in vehicle cabins while minimizing range loss. The proposed system stores heat from an external energy source using PCM and transfers it to the cabin during vehicle operation, reducing the need for conventional internal heating systems powered by the EV’s battery. Experiments were conducted on a Citroën Ami vehicle under three different scenarios: no heating, using the internal electric heating system, and employing the PCM heat battery. The results showed that using the internal heating system led to a significant reduction in vehicle range, while the PCM heat battery maintained cabin temperature and prevented additional battery consumption. In mild cold climate conditions, with outside temperatures ranging from −2 °C to 2 °C, the PCM heat battery successfully stabilized the cabin temperature over a 3-hour period. This demonstrates that the PCM heat battery system can support thermal comfort and reduce battery usage, potentially saving up to 33 % of range in cold weather.

Journal: International Journal of Numerical Methods for Heat & Fluid Flow

Title: Experimental and numerical study of a solar still with external solar heating: comparing internal condensation and air-pump-assisted external condensation in prism structures

DOI: 10.1108/HFF-11-2024-0881

Abstract:

Purpose: The purpose of this study is to develop and evaluate a novel solar still system integrating external solar heating and condensation units, comparing its performance with traditional methods through experimental and numerical analyses to optimize clean water production and energy efficiency.

Design/methodology/approach: This study involved designing a novel solar still system with an external solar heating unit and a prism-type condensation chamber. Two configurations were tested experimentally: one with internal condensation inside the prism and another with an air pump extracting vapor for external condensation. computational fluid dynamics (CFD) simulations were conducted to analyze temperature distributions and airflow dynamics in the system. Energy and exergy analyses were performed to evaluate the thermal performance and efficiency of both configurations, comparing clean water production rates and system effectiveness.

Findings: This study found that the solar still system using an air pump with external condensation significantly enhanced water production, achieving approximately 144.7% more clean water compared to the internal condensation method. Scenario 2, with the external condensation configuration, demonstrated a slight improvement in thermal efficiency (12.84%) over Scenario 1 (12.36%) and higher exergy efficiency (5.86% compared to 4.83%). CFD simulations provided insights into the temperature and air velocity distributions, highlighting the effectiveness of the external heating and condensation setup. The results demonstrate the potential of the novel system to improve clean water production while maintaining energy efficiency.

Originality/value: This study introduces a novel solar still design that integrates an external solar heating unit and an air pump-driven external condensation system, demonstrating a significant improvement in clean water production. By combining experimental results, CFD simulations and energy-exergy analyses, it provides valuable insights for optimizing solar-powered desalination systems with enhanced efficiency and sustainability.

Journal: Renewable Energy

Title: Exploring solar modified glazed balconies as energy sources for mini-split heat pumps to enhance thermal performance

DOI: 10.1016/j.renene.2025.122992

Abstract:

This study investigates the energy savings and thermal efficiency of glazed balconies with integrated heat pump systems for residential heating in cold climates. Furthermore, this study explores the integration of solar-absorbing materials on walls and floors of the balcony to enhance solar heat gain, along with the thermal benefits of a mini-split heat pump during test days. These enhancements are designed to improve energy efficiency, indoor comfort, and temperature regulation. Within the scope of the study, various evaluations such as thermal efficiency, the heat pump coefficient of performance, and temperature differences are made on different days and under different operating conditions. From the results obtained, it was observed that the thermal efficiency of the modified balcony reached 13.9 % when the mini-split heat pumps were not in operation. The COPHP values of the employed heat pump were assessed under various operational conditions. It was determined that the maximum COPHP value could surpass 3, yet the maximum average COPHP between 7:00 and 17:00 h was approximately 2.73. Consequently, this study proposes the exploration of larger sunspaces within substantial structures such as university faculties, libraries, and offices, presenting additional avenues for research. This underscores the potential for a more efficient utilization of a combination of solar energy and heat pump applications.

Journal: Sustainable Energy Technologies and Assessments

Title: Solar-assisted phase change material system for efficient cabin heating in electric vehicles under cold conditions

DOI: 10.1016/j.seta.2025.104639

Abstract:

Electric vehicles (EVs) represent a sustainable alternative to internal combustion engine vehicles; however, their limited electrochemical energy storage poses a critical challenge in cold climates, where cabin thermal conditioning can markedly diminish driving range. Conventional resistive heating systems are characterized by high energy consumption and low thermodynamic efficiency. This study introduces a solar-assisted cabin heating strategy incorporating phase change material (PCM) to address thermal management in EVs under cold ambient conditions. The system integrates a roof-mounted photovoltaic (PV) module, adaptive reflective mirrors to enhance solar irradiance capture, and a hybrid thermal storage unit comprising water and encapsulated PCM (Rubitherm RT50), which was selected due to its high latent heat capacity near the desired cabin comfort temperature, enabling efficient thermal energy storage and prolonged heat release during cold ambient conditions. Designed for the Citroën Ami electric microcar, the system operates independently of the vehicle’s traction battery, ensuring sustained cabin comfort without compromising driving range. Two experimental configurations were evaluated at ambient temperatures ranging from −2 °C to +2 °C: a water-only thermal storage scenario and a water–PCM hybrid scenario. Experimental results demonstrated that PCM incorporation significantly augmented the thermal energy storage capacity and prolonged heat release duration. Relative to the water-only configuration, the PCM-enhanced system achieved a 3.1 °C increase in cabin air temperature and a 10 °C higher outlet air temperature at the conclusion of the heating cycle. This integrated system presents a promising, energy-efficient solution for preserving EV range while ensuring occupant comfort in cold weather.

Journal: Journal of Energy Storage

Title: Thermal performance evaluation of PCM-integrated interior shading devices in building glass facades

DOI: 10.1016/j.est.2025.115614

Abstract:

This study investigates the thermal performance and energy efficiency potential of Phase Change Material (PCM)-integrated interior shading devices installed within double and triple-glazed facades. The primary aim is to explore how these systems can enhance indoor thermal comfort, reduce energy consumption, and impact natural lighting levels. A test cabin was designed to evaluate these parameters, featuring double and triple-glazed panels with integrated shading devices containing microencapsulated PCMs. The PCMs, known for their ability to store and release thermal energy through phase changes, were utilized to mitigate indoor temperature fluctuations by absorbing excess solar heat during the heating period and releasing it during the cooling period. Experimental results revealed that the combination of triple glazing, shading devices, and PCM led to significant improvements in thermal performance, reducing temperature peaks and extending the cooling period compared to systems without PCM. The integration of PCM reduced the maximum temperature difference caused by heating and cooling cycles from 26.9 °C to 20.1 °C in double-glazed windows and from 19.8 °C to 12.4 °C in triple-glazed windows. Furthermore, PCM integration was shown to delay temperature rises by acting as a thermal buffer, thus stabilizing indoor conditions and reducing the load on cooling systems. Additionally, light intensity measurements were conducted to assess the impact of the shading devices on natural daylight levels. Despite the 35 % reduction in natural lighting caused by the shading devices, the overall thermal performance and energy saving potentials were substantial, highlighting the effectiveness of PCM as a passive thermal regulation material. This study provides valuable insights into the potential of PCM-enhanced shading devices as a solution for improving energy efficiency and occupant comfort in modern buildings.

Journal: Journal of the Institute of Science and Technology

Title: Termoelektrik Buzdolaplarında Çoklu Düzenlemenin ve Elektrik Gücünün Soğutma Performansına Etkilerinin Deneysel Olarak İncelenmesi

DOI: 10.21597/jist.1519229

Abstract:

Termoelektrik (TE) soğutma teknolojisi, kompakt ve hafif yapısı ile taşınabilir soğutma sistemlerinde popüler bir çözüm sunmaktadır. Bu çalışmada, TE soğutucuların soğutma performansı ve enerji verimliliği üzerinde çeşitli tasarım parametrelerinin etkisi deneysel olarak incelenmiştir. Araştırmada, aktif modül sayısı (1 ila 3 arasında) ve uygulanan besleme gerilim (8, 10 ve 12 V) gibi kritik değişkenlerin sistem performansına etkileri deneysel olarak ele alınmaktadır. Bu deneysel parametreler farklı soğutma hacimleri için incelenerek sonuçlar detaylandırılmıştır. Ayrıca bu parametrelerin soğutma kapasitesi, sıcaklık düşümü, COP ve enerji tüketimi üzerindeki etkileşimleri ortaya koyularak, TE soğutma teknolojisinin performanslarını geliştirme yollarını araştırılmıştır. Elde edilen bulgular daha büyük soğutma hacimlerinde termodinamik açıdan daha verimli TE soğutma sistemlerinin uygulanabileceğini göstermektedir. Buna karşın küçük hacimlerde daha düşük kararlı hal sıcaklıkları elde edilmiştir. Ayrıca uygulanan besleme geriliminin geometrik parametrelere göre optimize edilmesi gerekliliği ortaya çıkmış ve en etkili soğutma yükü 10 V besleme gerilimi ve 3P modu için elde edilmiştir. Sonuç olarak, bu çalışma, termoelektrik soğutma sistemlerinin tasarımı ve işletilmesinde karşılaşılan zorlukları aşmak için kritik parametrelerin derinlemesine anlaşılmasının önemini vurgulamaktadır. Aktif modül sayısı ve uygulanan besleme geriliminin optimizasyonu, bu teknolojinin farklı uygulama alanlarına uyum sağlamasını ve enerji verimliliğini artırarak daha geniş bir kullanım potansiyeline ulaşmasını sağlayacak temel unsurlardır.

Journal: Journal of Materials Engineering and Performance

Title: Effects of Laser Powder Bed Fusion Process Parameters on Porosity, Liquid Retention, and Thermal and Surface Properties for 316L, CoCrW and Ti6Al4V Alloys

DOI: 10.1007/s11665-024-09381-y

Abstract:

Laser powder bed fusion (LPBF) offers several key advantages, including design flexibility, the ability to produce complex geometries and the fabrication of porous materials. These advantages have greatly expanded the range of applications for products manufactured using LPBF. Recently, there has been a significant increase in the use of LPBF products in thermal applications. In these applications, which involve intricate solid–fluid interface interactions, and thermal and surface properties of solids play a crucial role in heat flow interactions. This study focused on producing samples using the LPBF method with three different alloys: 316L, CoCrW and Ti6Al4V. The samples were subsequently analyzed for relative porosity, liquid retention, and thermal and surface properties. The influence of various laser process parameters, specifically energy density, on these properties was examined. The production processes conducted at various energy densities yielded porosity levels of approximately 7-32%, 2-20% and 3-16% for 316L, CoCrW and Ti6Al4V materials, respectively, in comparison with the theoretical density. Thermal conductivity values for 316L, CoCrW and Ti6Al4V samples ranged from 15.1 to 12.9, 7.9 to 7.1 and 6.1 to 5.8 W/m.K, respectively. Similarly, the average surface roughness was observed to vary in the range of 7.5-9.6, 8.3-10.5 and 8.9-10.3 μm for 316L, CoCrW and Ti6Al4V samples. Based on the obtained results, the samples were evaluated in terms of their suitability for thermal applications. Among the investigated alloys, 316L alloy is determined to have potential for thermal applications (extended surface applications, transpiration cooling, etc.) due to its efficient liquid retention feature, relatively high thermal conductivity and moderate surface roughness. Moreover, the 316L stainless steel proved to be more cost-effective, as it allowed for production at low energy density and had a relatively affordable material cost. Additionally, relatively easy porosity controlling in 316L alloy LPBF productions and leveraging its ability to fabricate porous structures hold great promise for further advancements in thermal application products.

Journal: Journal of Energy Storage

Title: Effects of microencapsulated phase change material on physico-mechanical and thermoregulation performance of lightweight geopolymer concrete with zeolite and perlite

DOI: 10.1016/j.est.2024.115225

Abstract:

This study examines impact of microencapsulated phase change material (MPCM) additives on physical and mechanical characteristics of geopolymers produced using natural zeolite and slaked lime. The binder composition consists of 90 % zeolite and 10 % slaked lime, activated with NaOH at a Na/binder ratio of 14 % by weight. Basalt-based sand and perlite were used as aggregates with a water/binder ratio of 0.60. MPCM was added in varying proportions of 8 %, 16 %, and 24 % relative to the binder weight. Samples were molded in dimensions of 50 × 50 × 50 mm and 200 × 200 × 20 mm, then cured at 95 °C for 24 h. Differential Scanning Calorimetry (DSC) outcomes presented that geopolymer composite with MPCM has a melting degree of 26.45 °C and a melting enthalpy of 17.8 J/g. Fourier Transform Infrared Spectroscopy (FTIR) results confirmed physical integration of MPCM into geopolymer structure. The study also evaluated compressive strength, ultrasound pulse velocity (UPV), dry unit weight, and microstructural properties using Scanning Electron Microscopy (SEM) and Energy Dispersive Spectroscopy (EDS). Thermoregulation performance experiments demonstrated that the MPCM-enhanced samples effectively moderated temperature fluctuations, maintaining lower temperatures for controlled heating and higher temperatures for natural cooling phases compared to the control sample. Thermal regulation capabilities of MPCM-infused geopolymers were evidenced by their property of absorbing and releasing heat, which is critical for energy-efficient building materials. Additionally, the durability and stability of the geopolymer matrix were enhanced by the uniform dispersion of MPCMs, which also improved the composite's mechanical performance. The successful integration of MPCMs highlights their potential in developing sustainable construction materials that contribute to energy savings and environmental conservation.

Journal: Energy and Buildings

Title: Enhancing thermoregulation in double glazed windows with PCMs and black films: An experimental study

DOI: 10.1016/j.enbuild.2024.115171

Abstract:

This study presents an experimental analysis of the thermoregulation characteristics of double-glazed windows integrated with phase change material (PCM) packages and black film coatings. The research focuses on varying the PCM area ratios (ARs) within the vertical glazing, specifically 15 %, 30 %, and 45 %, to evaluate their impact on thermal management and thermoregulation. The experimental setup consists of a test chamber subjected to controlled heating and cooling cycles, utilizing constant and continuous solar radiation. Temperature fluctuations and light intensity levels were recorded to assess the performance of the PCM packages, both with and without black film coatings. The results indicate that incorporating PCM into the glazed units significantly enhances thermal management by stabilizing temperature variations and delaying the attainment of steady-state conditions. The peak temperature in the test chamber with 45 % AR PCM packages during the heating period is 3.9 °C lower than that of the reference case; however, during the cooling period, temperatures remain above the reference case. This effect allows the indoor environment to maintain a temperature trend that is more aligned with thermal comfort conditions. Additionally, the application of black film coatings improved thermal absorption, leading to slightly higher temperatures (up to 2.6°C) in the PCM-filled units, but also resulted in a reduction in light transmittance. Specifically, light intensity decreased by 68 % in the 45 % AR case compared to the reference, with an additional 8–11 % reduction due to the black film coating. These findings highlight the dual role of PCM and black film in enhancing thermal comfort, while also acknowledging the trade-offs in natural lighting.

Journal: IFAC-PapersOnLine

Title: An Energy Calculation Framework Featuring Regenerative Systems in RCS/RS

DOI: 10.1016/j.ifacol.2025.09.101

Abstract:

The rapid growth of e-commerce and rising customer demand for fast, efficient order delivery have accelerated the expansion of the supply chain and logistics sectors, making warehouses essential for business success. In response, robotic compact storage and retrieval systems (RCS/RSs) have emerged as an effective solution to enhance operational flexibility, space utilization, and energy efficiency in warehouses. In these systems, robots navigate the grid to retrieve and store bins. When a bin is requested, the robot removes any obstructing bins above it, temporarily placing them on neighboring stacks before returning them to their original positions. The movement of thousands of bins daily, frequent stops, and vertical movements facilitate energy regeneration. This study introduces an energy calculation framework for RCS/RSs and examines energy regeneration in a 100 (width) × 100 (depth) × 50 (height) grid, revealing energy gains of up to 12.1% in horizontal movements (x-y-dimensions) and 26.4% in vertical movements (z-dimensions).

Journal: Gümüşhane Üniversitesi Fen Bilimleri Dergisi

Title: Cam cepheli binalarda FDM dolgulu güneş kontrol elemanlarının iç yüzey uygulamasının ışık ve ısıl performans analizi

DOI: 10.17714/gumusfenbil.1629652

Abstract:

Günümüz şartlarında insanların binalarda konfor şartlarından taviz vermeden fazla zaman geçirmesi enerji tüketim miktarının giderek artmasına sebep olmuştur. Özellikle enerji tüketiminin yoğun olduğu sektörlerden biri olan binalar, enerji tasarrufu sağlamak için alınabilecek önlemlerde belirleyici bir rol oynamaktadır. Binaların enerji verimliliğini ve çevresel sürdürülebilirliğini artırmak için dış cephe elemanları büyük bir potansiyele sahiptir. Bu çalışmada; binaların enerji verimliliğini artırmak için üç camlı cephe sistemlerin iç yüzeyinde faz değiştiren malzeme (FDM) dolgulu güneş kontrol elemanları (GKE) kullanılmasının ışık ve ısıl performans değerlendirilmesi yapılmaktadır. Deney sonuçları ile de kış mevsiminde binaların ısıtma yükünün azaltılması ve cephelerde termal direnci artırılması hedeflenmektedir. Sonuçlarda; üçlü cam sistemde GKE’nın olmadığı duruma göre, FDM dolgulu dikdörtgen profil iç GKE’nın yatayda 45o ‘de konumlandırılması durumunda termal enerji depolama ve ısıl kapasitede artış gözlenmiştir. Boş deney kabini ve içi boş GKE’ları olan durumlara göre FDM dolgulu dikdörtgen profil iç GKE’nın yatayla 45o olduğu deneyde soğuma periyotunda 40000.saniyede kabin içerisindeki hava sıcaklığında %12,2’lik bir artış gözlenmiştir. Gün ışığı değerinde ise boş deney kabini olduğu duruma göre %27 oranında azalma meydana gelmiştir. Çalışma sonuçlarının soğuk iklim bölgeleri için enerji etkin bina cephesi tasarımına rehberlik edebileceği ön görülmektedir.

Journal: Gazi Üniversitesi Mühendislik Mimarlık Fakültesi Dergisi

Title: Soğuk iklim bölgesinde bulunan LEED sertifikalı bir eğitim binasının enerji ve ekonomik performansının ulusal standartla karşılaştırılması

DOI: 10.17341/gazimmfd.1383681

Abstract:

Farklı iklim tiplerinin hâkim olduğu Türkiye’de, yüksek enerji performansı sağlayan binaların tasarımında iklim koşulları, maliyet, teknik hususlar bir arada göz önüne alınmalıdır. Soğuk iklim bölgelerinde maliyet optimum enerji seviyelerinin belirlenmesi enerji tasarrufunda önemlidir. Bu çalışmada Türkiye’nin en soğuk iklim bölgesinde (Severe Cold Region) yer alan illerden biri olan Erzurum’da LEED Silver (Leadership in Energy and Environmental Design) sertifikalı Erzurum Teknik Üniversitesi Mühendislik ve Mimarlık Fakültesi binasının enerji analizi yapılmış ve işletme sürecinde, binanın proje aşamasında öngörülen enerji performansına ulaşıp ulaşmadığının değerlendirilmiştir. Ayrıca, aynı binanın enerji tüketimi, CO2 salımı ve ekonomik kriterleri dikkate alınarak Binalarda Isı Yatlımı Yönetmeliğine uygun yapılması durumu da karşılaştırılmıştır. Önce mevcut LEED Silver sertifikalı binanın enerji simülasyonu yapılarak gerçek durumla karşılaştırılmış ve enerji tüketimleri arasındaki fark %7,3 olarak bulunmuştur. Analizlerde HAP 5.11 (Hourly Analysis Program) programı kullanılmıştır. LEED Silver sertifikasına sahip eğitim binasının ulusal standartlara göre yapılmış olması durumuna göre enerji verimliliği bakımından yaklaşık %23 ve CO2 salımın da ise %16,5 oranında avantajlı olduğu belirlenmiştir. LEED-Silver Sertifikası kriterleri kapsamında referans binaya için yapılacak olan 1153458.88 $ tutarındaki harcama, 2 yıl 9 ay sonra amorti edilecektir. Ancak inşaat metrekare birim maliyeti, üniversite kampüsünde ulusal standartlara göre yapılan diğer bir eğitim binasından ortalama %3 daha yüksektir. Bu sonuçlar enerji etkin bina tasarımında yol gösterici parametreler olarak kabul edilebilir

Journal: Journal of Thermal Analysis and Calorimetry

Title: CFD simulation and experimental analysis of cooling performance for thermoelectric cooler with liquid cooling heat sink

DOI: 10.1007/s10973-023-12682-4

Abstract:

Thermoelectric coolers are preferred in many areas because of their simple mechanism and no need for a refrigerant. In this study, an air-to-water mini thermoelectric cooler system was designed and produced. Experiments were performed by placing different numbers of thermoelectric modules on the liquid-cooling heat sink and applying different voltages. The cooling capacity and COP values of the system under different operating conditions were analyzed and discussed. In addition, the effect of fluid flow rate on system performance and temperature difference between inlet and outlet sections has been presented. The heat transfer and flow behavior of the fluid in the liquid-cooling heat sink were determined using CFD simulation methods. Moreover, the heat loss from the system was tried to be reduced by using extra foam insulation and the results were compared with single foam and the effect of the insulation on the temperature drop inside cooler was discussed. At 0.011 kg s−1 mass flow rate and 12 V voltage conditions, when the number of TE modules is increased from 1 to 3 in the TE cooler, a maximum increase of 35% in cooling load is obtained. Also, if the cases with 3 TE modules and 0.011 kg s−1 flow rate are compared in terms of cooling load, 12 V has 80% higher cooling load than 4 V. According to the numerical results, flow structures that negatively affect the heat transfer interactions and reduce the cooling performance of the TE cooler have been determined in the liquid-cooled heat exchanger. Additionally, a significant decrease in the temperature of the cooling chamber has also been achieved with additional insulation.

Journal: Heat Transfer Research

Title: Experimental and numerical study on effects of new-generation finned heat exchanger on thermal performance of thermoelectric cooling systems

DOI: 10.1615/HeatTransRes.2023048779

Abstract:

In this study, an attempt has been made to increase the efficiency of the thermoelectric refrigerator by designinig a new-generation finned heat exchanger. Surface extension, which is one of the most applied passive heat transfer enhancement techniques, was applied for this finned heat exchanger. In this application, the heat absorbed from the cooling room is transferred to the external environment more effectively. In addition, by using an external thermoelectric element (which is installed with the secondary heat exchanger), the heat exchanger cools down faster and the heat is transferred to the environment more quickly. The manufactured cooling system was tested experimentally under different working conditions, including natural and forced convection. The effects of air velocity and applied voltage to the external TE module on thermal performance were examined. Additionally, the external finned heat exchanger has been simulated and heat transfer characteristics have been evaluated using computational fluid dynamics. The lowest and highest COP values have been obtained as 0.003 and 0.011, respectively, when the external TE module has been passive. By providing 12 V for the external TE module, the lowest and highest COP values have been observed as 0.0031 and 0.0042, respectively. In addition, the importance of surface extension applications for the efficient operation of thermoelectric elements has been emphasized.

Journal: Journal of Enhanced Heat Transfer

Title: Experimental and numerical study on solar energy storage in black-covered sunspace using water-filled tin cans

DOI: 10.1615/JEnhHeatTransf.2023048545

Abstract:

In this study, the aim was to store solar energy in a sunspace room for energy savings in cold regions by using water-filled tin cans. The energy collected in the water during the sunbathing hours is transferred to the environment in the evening when the ambient air temperature suddenly drops. Additionally, the walls were covered with black material in the sunspace area to absorb maximum solar energy and then the heating performance was evaluated. In addition to experimental studies, ANSYS Fluent software (2022 R1 version) as a computational fluid dynamics (CFD) program has been used to simulate the sunspace domain in analyses. According to the obtained results, while there was a sudden drop in temperature in the ambient air after sunset, it was observed that the water temperatures in the tin cans decreased more slowly. This indicates that heat transfer from the tin cans to the ambient air occurs during the night. In addition, the effect of black surface application was shown and the differences between indoor and outdoor temperatures were evaluated. While the average temperature difference between the indoor and outdoor environment during the sunshine period without the black surface was 4.67°C, this difference increased to 9.53°C when the black surface was applied. The highest energy efficiency was achieved with the usage of the black surface, reaching a notable 58.2%.

Journal: Thermal Science and Engineering Progress

Title: Improving solar still efficiency through integration of cellulose-based water absorbers and Peltier condensation unit

DOI: 10.1016/j.tsep.2024.102475

Abstract:

This study involves a series of experiments aimed at assessing the impact of incorporating water-absorbent materials on the productivity of solar stills. It is worth mentioning that the performed experiments examine the effects of both materials and their location inside solar still unit. The solar still used for the experiments comprised a black-painted metal case and a glass layer positioned at a 30° angle relative to the horizontal. To enhance evaporation performance, a Peltier cooling module was integrated into the system. Furthermore, to prevent thermal losses and improve efficiency, the solar still case was insulated using Styrofoam material. From a scientific standpoint, the variations in this context can be ascribed to three primary variables as, integration Peltier condensation unit, use of water absorber materials like hemp and high-absorbent papers, and the incorporation of absorber dark colors. Throughout the experiments, constant test conditions were established using an artificial light source. In the reference setup, a total of 25 g of clean purified water was obtained, whereas in Case 5 (utilizing black high-absorbent papers on a triangle metal frame) and Case 6 (employing high-absorbent papers in the form of upright columns), which yielded the most efficient results, the amounts of purified water obtained were approximately 34 and 40 g, respectively. The results indicated a remarkable enhancement in thermal efficiency for Case 5 and Case 6, with approximately 29% and 45% increases, respectively, compared to the reference setup. Furthermore, a cost assessment has been conducted, demonstrating that the productivity gained through the use of internal materials contributes to improvements in cost efficiency. In comparison to the reference case, Case 6 exhibits a cost reduction for cost per liter exceeding 35%.

Journal: Wiley Interdisciplinary Reviews: Energy and Environment

Title: A comprehensive review of solar cooking systems

DOI: 10.1002/wene.516

Abstract:

This work presents an extensive and thorough examination of solar cooking systems, offering a comprehensive overview of their design, functionality, and practical implications. Through a comprehensive review of existing literature and technological advancements, the paper highlights the various types of solar cooking methods and their respective benefits. The study delves into the environmental, social, and economic advantages of solar cooking systems, presenting their potential to reduce energy demands and cooking-related challenges in diverse regions. By synthesizing a wide range of research, this review serves as a valuable resource for researchers, policymakers, and individuals interested in harnessing solar energy for sustainable and efficient cooking solutions. Additionally, this study contributes to the understanding and promotion of solar cooking as a viable and environmentally friendly alternative. It also analyzes why solar cooking systems have not become widespread and reveals the obstacles facing them.

Journal: Journal of Energy Storage

Title: Experimental study on the influence of inclination angle on phase change materials and natural convection during melting

DOI: 10.1016/j.est.2024.110769

Abstract:

Phase change materials are greatly affected by the inclination angle, which is one of the important parameters affecting natural convection during the melting process. The thermal performance of the phase-changing material was experimentally examined in this study by centrally passing a 1.21 mm diameter minichannel through it within the cylindrical casing. Water was employed as the working fluid, and RT-50 paraffin was utilized as the phase-changing material. The thermal impact of the phase-changing material during the heat transfer fluid charging process was experimentally analyzed, considering various inlet temperatures, depths, durations, and inclination angles. Additionally, Response Surface Methodology was applied to analyze the effects of the mentioned parameters on thermal performance and to establish a correlation for temperature values. The results indicated that the inclination angle greatly affects the formation and development of natural convection during the melting of pure phase change material, as well as the propagation of the solid-liquid interface and the rate of heat transfer. From the findings, at an inlet temperature of 55 °C, between 3 and 6 mm depth, max temperature change at 0° angle was 28.4 %, between 6 and 9 mm depth, max change at 0° angle was 7.51 %, and between 9 and 12 mm depth, max change at 90° angle was 30.5 %.

Journal: Desalination

Title: Experimental comparative analysis of solar system productivity and performance in water distillation: solar stills vs. parabolic dish systems

DOI: 10.1016/j.desal.2024.117402

Abstract:

This study aims to evaluate the practical suitability of two solar technologies, Solar Stills and Solar Parabolic Dishes, in meeting energy demands for various applications, including preparing distilled water and other applications. Through the analysis, solar still systems were found to be the preferred choice for distilled water production due to their ability to yield significant amounts of pure water through simple or advanced designs. Conversely, the results showed that solar parabolic dishes are more suitable for applications requiring higher temperatures, such as cooking, as they concentrate solar radiation into smaller focal points. This study presents essential information for efficient energy management in specific water treatment applications, assisting in the selection of appropriate solar technologies. The results showed that the Parabolic Dish Concentrator (PDC) achieved an impressive temperature of 96.5 °C. Nonetheless, even though these high temperatures were attained, the experiments did not lead to the production of distilled water. Based on the results, the thermal efficiency of the solar still was calculated at 5.6 % without modification and 9.4 % with the implemented modification. Conversely, the solar still's productivity witnessed a notable increase of around 66.6 % with a straightforward modification involving the incorporation of operational fans. Additionally, there was a substantial enhancement in efficiency, registering a remarkable rise of 67.8 %.

Journal: Energy and Buildings

Title: Thermal performance investigation of microencapsulated phase change material enhanced with graphene nanoplatelets in double-glazing applications

DOI: 10.1016/j.enbuild.2024.114859

Abstract:

Effective heat energy storage is crucial for thermal energy management. The utilization of latent heat storage methods is widely prevalent across various engineering applications for enhancing energy efficiency. In this study, the energy storage performances of Phase Change Materials (PCMs) achieved by incorporating graphene nanoplatelets into a microencapsulated PCM were experimentally analyzed for double-glazing applications. Changes in thermal energy storage and heat transfer performance by incorporating graphene nanoplatelets into the PCM at two different mass ratios (1 % and 0.1 %) were investigated. The results obtained from light intensity and temperature measurements, as well as thermal camera imaging, were evaluated together. The results support the contribution of graphene nanoplatelets addition to microencapsulated PCMs in enhancing thermal performance during both heating and cooling periods. Among the investigated cases, the highest mass ratio of 1 % graphene nanoplatelets addition led to a major 10 °C increase in peak temperature compared to the reference condition. In contrast, this increase in peak temperature was accompanied by a mere 14 % decrease in average light levels. This research underlines the potential of graphene-enhanced microencapsulated PCMs in optimizing thermal management systems for double-glazing applications, offering a promising pathway towards enhancing energy efficiency and thermal comfort in building environments.

Journal: Energy Sources, Part A: Recovery, Utilization, and Environmental Effects

Title: Experimental investigation on using building shower drain water as a heat source for heat pump systems

DOI: 10.1080/15567036.2020.1796845

Abstract:

Heat pumps are high-efficiency heat transfer devices with different usages, which can work by using various energy sources. This helpful device can be mixed with multiple technologies to make more efficient systems. In this study, a combination of heat pump and shower drain water is proposed to utilize wastewater deriving from the high-rise building’s bathroom. This heat pump system uses waste heat of bathroom-drained water, which is a cheap energy source compared to fossil fuel in Turkey. The mentioned heat pump system can also use wastewater from sauna, public bath, building bath, etc. to be effectively applied not only for water heating but also for space heating. In this work, it is proposed to utilize wastewater as heat source for heat pump system. In this regard a heat recovery system has been designed and combined with a heat pump system to utilize the available energy in the drained shower water. Accordingly, a wastewater gathering tank has been designed and manufactured to reuse the waste heat of the drain water. In addition, a conventional boiler has been used in the designed system to meet intended heat demand. Then the performance of the heat pump was analyzed in different wastewater temperatures. As a result, COP approximately improved by 55% when the drain water temperature increased from 15°C to 33°C. The obtained experimental results in this study showed that shower drain water thermal energy can be used successfully as a heat source for heat pump systems.

Journal: Heat Transfer Research

Title: Experimental Investigation of Heat Transfer and Pressure Drop Characteristics of Ferrofluids in the Presence of Magnetic Field and Laminar Flow Conditions

DOI: 10.1615/HeatTransRes.2023048968

Abstract:

In this study, the heat transfer performance with forced convection of two different water-based nanofluids was investigated by applying an alternating magnetic field in a minichannel. CoFe2O4−water and MnFe2O4−water nanofluids have been prepared at 0.5 vol.% and tested. The tests were carried out in a minichannel under laminar flow conditions in the Reynolds numbers range of 300−1700. Nusselt numbers of each fluid used in the experiments were calculated and compared. At the Reynolds number of 1500, the CoFe2O4−water nanofluid exhibited an increase of 12% compared to pure water, while the MnFe2O4−water nanofluid showed an increase of 4%. The Nusselt number increased in both nanofluids by applying the magnetic field to nanofluids. The highest Nusselt number obtained was 9.35 for the CoFe2O4−water nanofluid in the presence of magnetic field. While this increase was more pronounced at low Reynolds numbers, a lower rate of increase was obtained at high Reynolds numbers. In addition, the use of nanofluids significantly increased the pressure drop compared to the base fluid. While an almost 100% increase in the pressure drop was observed for the CoFe2O4−water nanofluid compared to pure water, the 65% increase for the MnFe2O4−water nanofluid was maximum. At the highest Reynolds numbers, the maximum pressure drops were determined as 3.4 kPa for the CoFe2O4−water nanofluid and 3 kPa for the MnFe2O4−water nanofluid. It was also detected that the friction factor for CoFe2O4−water and MnFe2O4−water nanofluids was 80% and 40% higher, respectively, than for the base fluid.

Journal: Renewable Energy

Title: Desalination performance evaluation of a solar still enhanced by thermoelectric modules

DOI: 10.1016/j.solener.2024.112325

Abstract:

Water scarcity is a pressing global issue, as a significant portion of the world's water resources remain salty and unsuitable for human consumption. Solar desalination has emerged as a sustainable solution to address this challenge, utilizing solar energy for water decontamination and purification. This study explores the enhancement of solar stills through the integration of thermoelectric (TE) modules, focusing on their impact on desalination performance. The optimal saltwater levels, TE module performance, and the efficiency of the system are identified in this investigation. The results of this study reveal that the integration of TE unit into solar still systems leads to a substantial increase in water production, achieving an impressive 35% improvement in productivity compared to conventional solar stills. The TE modules act as efficient cooling agents, accelerating the condensation process within the system. This improvement has substantial implications for addressing water scarcity in arid regions and providing an eco-friendly solution for freshwater production. By harnessing solar energy and advanced TE technology, the findings of this study underscore the potential of TE-enhanced solar desalination systems in providing sustainable and reliable sources of fresh water, even in areas with limited access to traditional water resources. The successful integration of TE modules into solar stills suggests a promising avenue for future research and development. Further exploration of these systems, optimization of TE module parameters, and increased utilization of renewable energy sources are all steps that can be taken to improve water production efficiency and contribute to water resource sustainability.

Journal: Journal of Energy Storage

Title: Investigation of cabin heating in electric vehicles with integrating solar cells and heat storage systems

DOI: 10.1016/j.est.2024.113782

Abstract:

In recent years, the production and usage of electric vehicles have been encouraged due to zero emissions, efficiency, and economic factors. Efficient cabin heating and thermal management in electric vehicles are crucial for enhancing passenger comfort, extending battery life, and optimizing overall energy usage, thus contributing to the sustainability and practicality of electric transportation. Heating the cabin of electric vehicles in winter has a negative effect on range. Therefore, methods are being researched to use energy efficiently without sacrificing passenger comfort and minimizing the effect on the vehicle's range. This study presents an innovative radiator design specifically crafted for Electric Vehicles (EVs), leveraging solar panels to heat water for the radiator. This system enables the vehicle to harness solar energy for heating a water tank while stationary, effectively serving as an energy storage reservoir. Upon vehicle movement, the radiator system activates to disperse the stored thermal energy throughout the cabin, ensuring superior thermal comfort. Consequently, optimizing battery range is achieved as the heating load typically leads to significant range reductions. From the obtained results in experiment 2, the results indicated that the cabin temperature rose from 3 °C to around 15 °C within a few minutes, reflecting an increase of approximately 12 °C. According to the results, this indicates that there will be a reduction in energy consumption of between 1.9 % and 3 % for a one-hour travel range in this electric vehicle. The findings of this investigation demonstrate that utilizing warm water energy storage effectively enhances cabin thermal management.

Journal: Journal of Building Engineering

Title: Utilization of recyclable aluminum cans as fins in a vertical solar air heating system: An experimental and numerical study

DOI: 10.1016/j.jobe.2022.105446

Abstract:

Heating loads cover a large portion of the total energy consumption of buildings. Solar air heating is a sustainable and low-cost alternative for heating applications instead of employing fossil energy sources. In this work, vertical solar air collectors (VSACs) have been developed to be utilized in buildings. Moreover, aluminum beverage cans have been utilized as fins to improve the effectiveness of the collector system. In the initial stage of the study, various aluminum can configurations have been analyzed numerically. Numerical findings showed that symmetric placement of aluminum cans gave better results in comparison to the hollow VSAC and VSAC with asymmetric can placement. In this regard, symmetric can configuration has been applied to the VSACs with two plenum thicknesses including 100 mm and 150 mm for experimental investigation. Experiments have been performed at two flow rates and thermal efficiencies of the tested VSACs were found between the range of 55.16–76.22%. Also, average exergy efficiency values for VSACs with higher and lower plenum thicknesses were obtained between the ranges of 8.34–8.85% and 9.84–10.36%, respectively. The overall findings of the present research exhibited successful utilization of recyclable aluminum beverage can-integrated VSACs for air heating.

Journal: Heat Transfer Research

Title: An experimental investigation to predict optimum charge of a heat pump system

DOI: 10.1615/HeatTransRes.2022044669

Abstract:

Working principles of heat pumps is an important matter from a thermodynamic point of view that has been researched from various aspects. In this study, undercharged, optimum charged, and overcharged conditions of a heat pump were investigated using R134a refrigerant. Variations in temperature, pressure, and the coefficient of performance have been evaluated and it was aimed to find out the optimum charge condition considering different parameters. According to the experimentally obtained findings, the coefficient of performance was increased by more than three times when the refrigerant amount increased from 2000 g to ~ 7300 g. The general outcomes of the present study indicated that optimum refrigerant charge amount can notably affect the performance of heat pump apparatus. It was shown that the P−h diagram of all heat pump systems depends on the working conditions and the refrigerant charge is a very important criterion that can make significant changes in the P−h diagram. It was found that, by increasing refrigerant charge, after the downtrend starts in the compressor inlet temperature, 20% refrigerant can be added to achieve the maximum COP value. Additionally, the critical point in expansion valve outlet temperature was used to find the optimum charge. It was revealed that if 140% refrigerant is added to the given refrigerant at critical point, the optimum COP value can be achieved.

Journal: Nanoscience and Technology: An International Journal

Title: Effects of nanoparticle size on properties of nanofluid and heat transfer enhancement in spiral exchanger using turbulators

DOI: 10.1615/NanoSciTechnolIntJ.2022045137

Abstract:

In energy systems that use nanofluids as heat transfer fluid, the physical properties of nanofluids are important parameters in the efficiency of various heat exchangers, including small-scale micro channels or large-scale heat exchangers. In the present work, a comprehensive study is conducted to evaluate the thermal performance of a spiral heat exchanger with ball-type turbulators using nanofluid Al2O3/water. To investigate the effect of particle dimensions on nanofluid properties, nanoparticles with sizes of 20 nm and 50 nm at a volume concentration of 2% were examined. Heat transfer rate in the heat exchanger, performance evaluation criteria, heat transfer coefficient value, pressure drop, friction factor, Reynolds-Nusselt numbers relationship and pump power for fluid circulation have been calculated. ANSYS Fluent software as a computational fluid dynamic method was utilized to analyze the spiral heat exchanger under different working conditions. It was observed that both thermal conductivity and viscosity values increased as the nanoparticle size decreased. Heat transfer coefficient analyses showed that nanofluids with 20 and 50 nm particles exhibited a maximum improvement of 30.59% and 21.53%, respectively, when compared to pure water at an inlet velocity of 0.1 m/s. Additionally, the heat exchanger with turbulator showed a maximum increase of 24.87% at an inlet velocity of 0.5 m/s compared to the heat exchanger without turbulator. Moreover, maximum heat transfer rate enhancement was found to be 14.07% when the exchanger was equipped with turbulators.

Journal: Journal of Enhanced Heat Transfer

Title: Performance analysis of thermo-electric cooling systems equipped with surface-modified and recycled nanofluids

DOI: 10.1615/JEnhHeatTransf.2022046375

Abstract:

In this research, pure water and recycled nanofluids (RNF) are utilized as heat transfer fluids in the thermoelectric cooling (TEC) system, and the effects of these fluids on the cooling performance are experimentally examined. In order to prevent nanofluid sedimentation and enhance stability, a surface modification process on Fe3O4 particles is performed. With modified Fe3O4@SiO2-mix-(CH2)3Cl@Imidazol nanoparticles, water-based nanofluids are prepared at a constant volumetric concentration. This nanofluid is used in a TEC system and recycled. The sonication time is chosen as the experimental parameter in the preparation of RNF. The RNF are subjected to ultrasonication at different time periods, including 3.5, 7, and 14 hours. The temperature drops inside the cooling chamber, coefficient of performance (COP) value of the TEC system, and dimensionless numbers, including Reynolds and Nusselt of nanofluids, are evaluated and discussed in detail. It is determined that the performance of the TEC system can be increased significantly with the usage of nanofluids. Although some deterioration in heat transfer properties is observed for the RNF, these fluids provide a significant improvement in cooling performance compared to pure water. Increasing the nanofluid flow rate increases the cooling chamber performance up to a certain level. Moreover, a significant increase in TEC chamber performance is also achieved by decreasing the temperature of the water bath in the system.

Journal: Heat Transfer Research

Title: Experimental study to evaluate effect of source temperature on COP and compressor status in water-to-air heat pumps

DOI: 10.1615/HeatTransRes.2023048436

Abstract:

Heat pump devices have been researched and analyzed from different aspects, which indicates the importance of these devices. In fact, these devices transfer heat energy effectively from one source to another by consuming power. In this work, the importance of source temperature and its effect on system performance and compressor status has been investigated. It is shown that if the temperature of the heat source is low, the refrigerant at the inlet of the compressor will be in the two-phase region, which could cause damage to the compressor. In these cases, the evaporator design can be changed as available solutions or a high-temperature heat source can be provided in the present study. On the other hand, in the two-phase region, calculating the work of the compressor with enthalpy values will be a problem and may cause a computational error in the power consumption of the compressor. The reason for this is that the enthalpy of refrigerant in the compressor cannot be obtained with two properties, i.e., temperature and pressure. This issue has been considered and the rate of computational error has been obtained. R134a refrigerant was used as circulating gas in the used water-to-air heat pump. The results obtained in the experiments performed showed that the COP value of the heat pump increased by 172% when the source temperature increased from 6°C to 34°C. As the source temperature increases, more energy is transferred to the system. This issue raises both high-pressure and low-pressure values. This increase was recorded as 34% for high pressure and 17% for low pressure when the source temperature increased from 6°C to 34°C.

Journal: International Journal of Numerical Methods for Heat & Fluid Flow

Title: Computational fluid dynamics simulation and experimental investigation of a thermoelectric system for predicting influence of applied voltage and cooling water on cooling performance

DOI: 10.1108/HFF-03-2022-0160

Abstract:

Purpose: The purpose of this paper is to experimentally and numerically investigate the cooling performance of the air-to-water thermoelectric cooling system under different working conditions.

Design/methodology/approach: An air-to-water thermoelectric cooling system was designed and manufactured according to the principle of discrete binary thermoelectric Peltier modules, and the thermal performance, heat transfer rate and average COP values were examined at different cooling water temperatures and voltages applied. Additionally, numerical simulations were performed by computational fluid dynamics approach to investigate the temperature distribution and airflow structure inside the cooling chamber.

Findings: Analyses were performed using experimental tests and numerical methods. It was concluded that, by decreasing the cooling water temperature from 20 to 5 °C, the average COP increases about 36%. The voltage analysis showed that the efficiency of the system does not always increase as the voltage rises; more importantly, the optimum voltage is different and depends on whether it is desired to increase COP or increase the cooling rate.

Originality/value: In the studies published in the field of thermoelectric cooling systems, little attention has been paid to the voltage applied and its relationship to other operating conditions. In most cases, the tests are performed at a constant voltage. In this study, several options, including applied voltage and cooling water temperature, were considered simultaneously and their effects on performance have been tested. It was found that under such studies, optimization work should be done to evaluate maximum performance in different working conditions.

Journal: Applied Thermal Engineering

Title: Experimental and numerical analysis of a grooved hybrid photovoltaic-thermal solar drying system

DOI: 10.1016/j.applthermaleng.2022.119288

Abstract:

Photovoltaic-thermal (PVT) systems are sustainable applications that allows to produce thermal and electrical energies simultaneously. In this work, a sustainable solar drying system that contains a modified PVT-air collector has been designed, numerically analyzed, manufactured and tested. In the first step of this study, four different PVT collector configurations have been numerically analyzed in order to develop a new hybrid PVT drying system. According to the numerically obtained results, outlet temperature of the PVT collector with grooved absorber, spherical turbulators and baffle configurations was higher than the outlet temperature of the unmodified collector as 15.77 %. This promising PVT collector was then fabricated and integrated with a drying chamber. The manufactured hybrid drying system has been tested under various air flow rates. The experimental findings illustrated that the average thermal efficiency and overall exergy efficiency of the PVT collector varied between 61.32 and 77.49 % and 10.65–11.17 %, respectively. In addition, mean exergy efficiency of the drying chamber was found in the range of 59.16–68.31 %. Average sustainability index values of the collector and the drying chamber was obtained between the ranges of 1.12–1.14 and 3.74–5.82, respectively. Moreover, payback period of the dryer varied between 2.98 and 3.51 years according to the economic analysis.

Journal: International Journal of Environmental Science and Technology

Title: Thermal analysis of Fe3O4/water nanofluid in spiral and serpentine mini channels by using experimental and theoretical models

DOI: 10.1007/s13762-022-04119-6

Abstract:

Heat transfer methods in small scales have been studied widely to enhance the thermal efficiency and performance of heat sinks in the field of cooling electronic devices. In this study, a comprehensive numerical investigation was conducted to evaluate thermal performance of block heat sinks for cooling electronic processors by using Nanofluid. Two different blocks including spiral and serpentine blocks were designed and tested under various working conditions using Nanofluid Fe3O4/water with a volume concentration of 0.2% and obtained results were compared to water in the term of heat transfer rate and efficiency. As one of the main aims of this study, thermophysical properties of under evaluation nanofluid were analyzed using experimental data and theoretical equation and subsequently obtained heat transfer results for all cases were discussed. ANSYS-Fluent software was utilized as a CFD method to solve the problem and perform analysis from simulation.

Journal: Microfluidics and Nanofluidics

Title: Experimental and numerical study on air-to-nanofluid thermoelectric cooling system using novel surface-modified Fe3O4 nanoparticles

DOI: 10.1007/s10404-023-02637-4

Abstract:

Peltier cooling systems are usually smaller, more portable, and relatively simpler to operate compared to conventional vapor compression cooling systems. For this reason, Peltier cooling systems are widely recommended for use in the field of cooling applications and refrigerators. These cooling systems have relatively low efficiency despite extensive operation. To solve this problem, a Peltier cooling system operated with advanced nanofluid is proposed in this study. In this cooling system, water-based Fe3O4 nanofluids were used to cool the Peltier. In order to obtain high stability in these nanofluids, the nanoparticles were synthesized chemically with surface modification processes (Fe3O4@SiO2@(CH2)3IM). By designing and manufacturing an air-to-nanofluid cooling system, the performance of Peltier cooling system was evaluated and compared to the conventional air-to-water system. The nanofluids were prepared in three different volume concentrations as 0.2%, 0.5% and 1.0% and then were examined at different working conditions. This research has been analyzed using both experimental and numerical methods. Temperature measurements and experimental COP evaluations were made in the cooling chamber. The flow structure and temperature distribution in spiral heat exchanger were closely surveyed and discussed in detail. According to the results obtained, nanofluid volumetric concentrations, inlet temperatures and mass flow rates had a significant effect on the cooling performance of the Peltier systems. It was observed that COP values decreased over time in all experiments and approach zero gradually.

Journal: Energy and Buildings

Title: Effects of double glazing, black wall, black carpeted floor and insulation on thermal performance of solar-glazed balconies

DOI: 10.1016/j.enbuild.2023.112919

Abstract:

This research was conducted to evaluate energy saving and the thermal efficiency in glazed balconies and sunspace areas. The effects of double-glazing, black walls and black carpeted floors, and insulation material on the thermal efficiency of residential balconies in the cold seasons of the year were investigated. For this purpose, the interior sun walls were covered with recycled black-painted papers, and the effect of the applied insulations on the thermal performance of the glazed balcony were investigated. In addition, a model of the glazed balcony was simulated using the ANSYS/Fluent program. By numerically analyzing the simulated model, the temperature distribution inside the balcony and the air velocity due to the natural convection in the domain volume have been visualized. It was found that the maximum thermal efficiency was achieved as 42.8 % for the case where double-glazing has been applied and walls are insulated and covered with recycled black papers. Regarding the differences between the balcony air temperature and the outdoor temperature, the temperature difference was 14 °C for the situation where all insulation measures were taken and effective absorbers were used, while this value was around 9.3 °C in the case of testing only glass window application. As a consequent, by considering larger sunspaces in large buildings such as university faculties, libraries, and offices, this study reveals more research fields to be investigated and using solar energy more efficiently.

Journal: Renewable Energy

Title: Experimental and numerical study on a novel fanless air-to-air solar thermoelectric refrigerator equipped with boosted heat exchanger

DOI: 10.1016/j.renene.2023.02.092

Abstract:

Peltier cooling systems are generally small, portable and simple in operating principle compared to conventional vapor compression cooling systems. For these reasons, Peltier cooling systems are proposed widely to use in the field. In studies on Peltier coolers presented in the literature, equipment such as pumps and fans is used and this causes noise and vibration. In order to resolve these problems and negative effects, a cooling system was designed and manufactured using completely motionless elements. Additionally, the electricity energy need of this thermoelectric cooling chamber is fully met by solar energy. This study was investigated both experimentally and numerically by using computational fluid dynamics (CFD) methods. By designing a special heat exchanger in the produced air-to-air cooler system, it has been proven that, the Peltier system can work effectively without the need for any elements such as fans. Then the effects of the voltage values applied to the system and the number of Peltier modules have been investigated. The experiments were carried out at 4 different voltage values (1.5, 2.0, 2.5 and 3.0 V) and in 3 different Peltier numbers (1, 3 and 5) in consecutive connections. According to the obtained results, the most suitable situation for reducing the temperature of the cooling chamber were obtained as the voltage was at a maximum of 3 V and the Peltier number was maximum (5 Peltiers mode), where the internal temperature of the cooling chamber decreased to 11.28 °C. It was observed that, the coefficient of performance (COP) values decreased over time in all experiments. Considering the data taken at the beginning of the experiments, the maximum COP value was obtained as 0.04 when 1 Peltier and 1.5 V voltage were applied.

Journal: International Journal of Numerical Methods for Heat & Fluid Flow 

Title: Experimental and numerical investigation of flow and thermal characteristics of aluminum block exchanger using surface-modified and recycled nanofluids

DOI: 10.1108/HFF-12-2022-0721

Abstract:

Purpose: The purpose of this study is to numerically and experimentally survey the thermal efficiency of a block-type heat exchanger operated in different working conditions by using pure water and two nanofluids as heat transfer fluids.

Design/methodology/approach: An aluminum block-type heat exchanger integrated with Peltier thermoelectric element was designed and installed to operate in a cycle, and the thermal performance of the heat exchanger, heat transfer rate, Nusselt and heat transfer coefficient variations were examined at different bath water temperatures by using recycled nanofluids. New generation surface-modified Fe3O4@SiO2-mix-(CH2)3Cl@Imidazol/water nanofluid was used as heat transfer fluid in the cycle. In addition, CFD simulation was performed using ANSYS/Fluent to investigate the temperature distribution and fluid flow structure in the used heat exchanger.

Findings: Experiments were carried out by using numerical and experimental methods. In the experiments, the operating conditions such as flow rate, volume fraction of the nanofluid and water bath temperature were changed to find the effect of each parameter on the thermal efficiency. The Reynolds number varied depending on the test conditions, which was calculated in the range of approximately 100 < Re < 350. In addition, Nusselt number and heat transfer coefficient of test fluids were very close to each other. For 0.4% nanofluid, the maximum h value was obtained as 3837.1, when the Reynolds number was measured as 314.4.

Originality/value: In the scientific articles published in the field of heat exchangers operated by nanofluids, little attention has been paid to the stability of the nanofluids and sedimentation of particles in the base fluids. In addition, in most cases, experiments were implemented using an electrical resistance as a heat source. In this research, stable surface-modified nanofluids were used as heat transfer fluids, and it was found that the Peltier thermoelectric can be used as heat sources with acceptable efficiency in flat-type heat exchangers and even non-circular channels.

Journal: Process Safety and Environmental Protection

Title: Study on a novel inclined solar water distillation system using thermoelectric module for condensation

DOI: 10.1016/j.psep.2023.07.051

Abstract:

Energy efficiency and energy conservation are critical issues today, and the use of solar energy is widely recognized as a key solution for achieving energy independence and reducing reliance on fossil fuels. In this study, a water treatment system was installed, and numerous experiments were conducted to improve energy efficiency and investigate the impact of various parameters on water distillation rates. The primary focus of this study was to increase the rate of distillation by enhancing the surface area for rapid evaporation through the use of sponge pieces, and integrating the system with a novel condensation part equipped with a mechanism that sprays water on the external heat exchanger of the thermoelectric module to increase the condensation rate. The study also examined the effects of black color on solar energy absorption, the impact of indoor fan operation on water vapor distribution, the role of insulation in reducing thermal energy losses, and the intensity of solar radiation. The results revealed that the use of sponge pieces and a thermoelectric cooler significantly increased the rate of water distillation, which was about 100.5%. Moreover, the effect of air fans on the distillation rate was observed, which increased the distillation by more than 51.1%. Overall, this study provides valuable insights into the design and optimization of solar-powered water treatment systems, highlighting the importance of energy efficiency and the potential of renewable energy sources in meeting energy needs while reducing impact on the environment.

Journal: Proceedings of the Institution of Mechanical Engineers, Part E: Journal of Process Mechanical Engineering

Title: CFD analysis and experimental investigation to determine the flow characteristics around NACA 4412 airfoil blades at different wind speeds and blade angles

DOI: 10.1177/09544089221128421

Abstract:

An aerodynamically efficient blade is one of the prime necessities to extract the maximum mechanical power from a wind turbine. A number of researches are available in the literature studying blade design and configuration to improve aerodynamic characteristics of horizontal axis wind turbines. Less attention, however, has been devoted to wind turbines in terms of simultaneous optimization of blade and airfoil angles. The present study is important for the aerodynamic design and manufacturing of wind turbine blades. In this regard, various blade angles have been numerically simulated to determine the optimum blade angle. In addition to numerical analysis, experimental tests have been done to investigate NACA 4412 blade angle. As a result of this study, it was observed that blade angle in the range of 5°–10° showed the best performance among the tested various blade angles.

Journal: Journal of Energy Storage

Title: Experimental analysis of energy storage performance of phase change materials in horizontal double-glazing applications

DOI: 10.1016/j.est.2023.108836

Abstract:

In this study, phase change material (PCM) energy storage performance was experimentally investigated for horizontal double-glazing applications. In this context, it was aimed to use PCM for energy storage in horizontal insulating glass applications, and optimize amount of PCM in the glass and the effect of the surface area it occupies on the indoor light level were analyzed. In this regard, the temperature variation in the glass with the amount of PCM was observed and the optimum amount of PCM was evaluated. The experiments were carried out on an insulated test cabin using double-glazed test elements with different PCM ratios as 0 %, 15 %, 30 %, 45 %, and 100 %. An external light source was used to create constant radiation conditions during the experiments and temperature measurements, thermal camera images, as well as light intensity measurements were taken in the test cabin. The results revealed that the increase in the energy storage capacity with the amount of PCM is limited, while the light transmittance decreases continuously due to the solid PCM shading. In other words, as the amount of used PCM increases, the energy storage capacity increases and thermal comfort conditions improve. However, this increase stopped at a certain point and a constant trend was observed. It was concluded that, this situation occurs due to the blocking of the radiation entering the indoor environment and the decrease in the radiation intensity. For the 30 % area ratio, the cooling period was extended by 450 min compared to the reference case, and longer thermal comfort conditions were provided.

Journal: 3D Printing and Additive Manufacturing

Title: Wear and thermal behavior of TiAlN thin films onto Ti6Al4V alloy manufactured by selective laser melting method

DOI: 10.1089/3dp.2021.0081

Abstract:

In this study, it was targeted to enhance the tribological and thermal properties of Ti6Al4V alloys, which were manufactured with three different build orientations and hatch spacing by using the selective laser melting (SLM) method and a traditional method (casting). In addition, the surfaces of the samples produced by these two methods were coated with the TiAlN thin film by using the cathodic arc physical vapor deposition (CAPVD) method. After the experimental investigations, the lowest wear rate was obtained for the 60–90° sample, and the highest microhardness value was measured as ∼1070 HV0.1 for the 90–45° sample. It was specified that the wear rate rose as the hatch spacing increased among the same build orientation Ti6Al4V alloys produced by SLM method. According to thermal analysis results, among the same hatch spacing values, it was determined that as the build orientation value increased, the specific heat capacity and thermal conductivity values decreased. Among the coated samples, the highest thermal conductivity and specific heat capacity values were obtained for casting samples as 5.63 (W/m·K) and 560.4 (J/kg·K), respectively.

Journal: Energy Sources, Part A: Recovery, Utilization, and Environmental Effects

Title: Exergy analysis and optimization of multiple injection parameters of a diesel engine with Taguchi method

DOI: 10.1080/15567036.2023.2242315

Abstract:

Multiple injection parameters have a significant effect on performance and emission formation in diesel engines. This study presents the optimization of these parameters with Taguchi method for different engine operating conditions. The experiments were conducted using four injections per cycle named Pilot1 (P1), Pilot2 (P2), Main (M), and Post (Po). The input parameters considered were injection timings and fuel quantities for each injection, while the output parameters were brake specific fuel consumption (BSFC) and nitrogen oxides (NOx) emissions. According to the results, the analysis of variance (ANOVA) shows that the durations of the P2 (D_P2) and Po (D_Po) and the start of the Main (SOI M) injection are very significant on BSFC and NOx emissions as independent of the engine speed. Based on contribution ratios at 1750 rpm and 2250 rpm operating conditions, D_Po is the most effective parameter on BSFC with 47.28% and 51.30%, while D_P2 has the greatest impact on NOx emissions with 37.96% and 61.80%, respectively. It is found from the optimization model obtained by using the Signal/Noise (S/N) ratios that injecting 5% of the total fuel in the post-injection phase could simultaneously improve BSFC and NOx emissions. Furthermore, the optimization model generally reduces heat loss exergy, exhaust exergy, and exergy destruction compared to the experimental values.

Journal: International Journal of Engine Research

Title: Development of optimal diesel injection strategy based on the prediction of performance and emissions using deep neural network

DOI: 10.1177/14680874211057756

Abstract:

This study aims to determine the optimal injection strategy by predicting the performance and exhaust emission parameters of a four-cylinder CRDI engine under several operating conditions. The experimental determination procedure is challenging and expensive calibration task since it requires a high number of tests. Many studies have focused on a limited level of parameters. In this study, design of experiments technique and deep neural network (DNN) modeling are used together. The experimental data set for the model is created using Taguchi L16 and L32 orthogonal arrays. The DNN model is developed to predict BSFC, NOx, HC, and CO emissions with speed, torque, injection timings and fuel quantities of each injection called as pilot1, pilot2, main, and post. In this way, it has become possible to evaluate the effects of a larger number of operating parameters in a wide range than the literature. The developed DNN model predicts the BSFC, NOx, HC, and CO with R2 0.939, 0.943, 0.963, and 0.966, respectively. Additionally, RMSE and MAE values for the model are between 0.024 and 0.048. The proposed method compared with the conventional look-up table method performs better in reducing the complexity and cost of experiments and exploration of the effects of injection parameters on engine emission and performance characteristics in a wide engine operating range. In conclusion, until 2300 rpm at specified torque (90 Nm), it is found that 70% of fuel quantity should inject in main injection to minimize BSFC and NOx emissions. The post injection quantity should be increased by reducing the amount of main injection from this operating condition on. Furthermore, it is observed that the ratios of pilot injection durations do not change with increasing engine speed, but quantity of first pilot injection is more than that of second pilot injection.

Journal: Case Studies in Thermal Engineering

Title: A novel ignition timing strategy to regulate the energy balance during the warm up phase of an SI engine

DOI: 10.1016/j.csite.2022.102602

Abstract:

The warm up characteristics of an engine have a significant impact on engine performance and exhaust emissions. In SI engines, the light-off performance of the catalytic converter is also important. One of the methods used to shorten the light off time of the catalytic converter is to retard the ignition time. When the ignition time is retarded, the temperature of the exhaust gases increases. However, in this case, the warm up performance of the engine itself may be adversely affected.

In this study, firstly, the effects of ignition timing on the energy balance during the warm up period in an SI test engine were revealed. Then, a novel ignition timing strategy was proposed in order to increase the temperature of the exhaust gases, and not to reduce the engine performance. The novel ignition timing strategy working on the principle of sequentially advanced and retarded ignition at certain intervals during the warm up period provides several advantages. When the novel ignition strategy is applied, the energy loss through the exhaust gas was increased up to 7.2% for several operating conditions, while the reduction in engine performance is eliminated. Moreover, 20% reduction in NO emission has been achieved.

Journal: Energy Conversion and Management

Title: Instantaneous energy balance and performance analysis during warm up period of a spark ignition engine under several thermal energy management strategies

DOI: 10.1016/j.enconman.2022.116102

Abstract:

Significant improvements can be obtained through different thermal energy management systems (TEMS) in internal combustion engines during warm up period. When the engine thermal energy management system works correctly, it ensures that the engine components are cooled exactly as needed, which is important in energy consumption and harmful exhaust emissions production. Additionally, thanks to the reduced warm up time, friction losses are reduced, after-treatment performance is increased, comfort conditions are improved in the passenger compartment, and the windshield quickly clears ice and condensation. However, the effects of the designed engine TEMSs on the energy balance during the warm up period should be well known. For this purpose, an experimental setup was established for not only the averages of the effects of different thermal strategies established as commonly done in the literature, but also the changes during the whole warm up process were analyzed. Then, three different TEMS were compared, and the effects of energy losses on each other were revealed. Results have shown that the warm up time can be reduced by 30 % with different engine TEMS, and thus, specific fuel consumption and CO emission can be reduced at different levels under several engine operating conditions. It was observed that when the engine coolant was not sent to the oil cooler heat exchanger during the warm up period, the thermostat opening time decreased from 252 s to 218 s. Moreover, it has been observed that the engine can reach steady state operating conditions approximately 10 % faster when the thermal energy is transferred from the exhaust gases, where a significant part of the fuel energy is lost, to the cooling water during the warm-up period.

Journal: Journal of the Brazilian Society of Mechanical Sciences and Engineering

Title: Performance analysis of air-to-water binary thermoelectric Peltier cooling systems and determination of optimum arrangement

DOI: 10.1007/s40430-022-03737-y

Abstract:

In this study, performance analysis of air-to-water thermoelectric (TE) Peltier devices was performed for optimal evaluation of double TE cooling systems and for comparison with single-type TE cooling devices. In the experimental study, binary (two-stage) Peltier systems have been examined and the desired values were obtained to compare the obtained results in terms of several parameters. For the air-to-water cooling TE setup, the highest cooling rate was observed for the binary discrete system under laboratory conditions. In terms of performance, the single Peltier device showed the highest COP value. The COP of the single Peltier setup was recorded as approximately 25% higher compared to the binary discrete systems. It has been revealed that the COP value of the consecutive binary Peltier systems is the lowest and their performance is remarkably low. Analysis was conducted to predict the flow structure and temperature distribution inside the refrigerator using the CFD simulation method. Ansys Fluent program has been used in this study to simulate the problem and good agreement has been achieved.

Journal: Sustainable Energy Technologies and Assessments

Title: Effect of heat exchanger base thickness and cooling fan on cooling performance of Air-To-Air thermoelectric refrigerator; experimental and numerical study

DOI: 10.1016/j.seta.2022.102178

Abstract:

The available statistics reveal that a significant portion of the total electrical energy in different communities is used for various heating and cooling purposes and refrigeration in the domestic and industrial sectors, which includes cooling systems in critical areas such as the food and pharmaceutical industries. In this work, air-to-air thermoelectric cooling systems have been analyzed. Experimental and numerical attempts have been made to evaluate the influence of the base thickness size of external heat exchanger on cooling performance of refrigerator. In addition, the cooling system has been operated in different working conditions and the effect of cooling fan velocity on the Coefficient of Performance (COP) value was presented. It was found revealed that, the temperature of the cooling chamber for 4.5 mm thickness dropped to 11.57 degrees C, while this temperature was 9.93 degrees C for 1.5 mm thickness. Considering the final temperatures, there was a 14% difference by reducing the thickness from 4.5 mm to 1.5 mm for the case of Vair = 7.5 external fan speed. For the numerical approach, ANSYS Fluent 16.0 software was utilized to analyze the structure of airflow inside and outside of the refrigerator in detail. As a result of Computational Fluid Dynamics (CFD) simulation temperature distribution and air velocity contours have been obtained and achieved results were discussed.

Journal: International Journal of Numerical Methods for Heat & Fluid Flow

Title: Numerical and experimental investigation of a solar absorber extension tube with turbulators for upgrading the performance of a solar dryer

DOI: 10.1108/HFF-08-2021-0565

Abstract:

Purpose: During the past several years, research and studies in the field of solar energy have been continuously increased. One of the substantial applications of solar energy is related to industrial utilization for the drying process by efficient heat transfer methods. This study aims to upgrade the overall performance of an indirect solar dryer using a solar absorber extension tube (SET) equipped with ball-type turbulators. 

Design/methodology/approach: In this work, three various SETs including hollow (SET Type 1), 6-balls (SET Type 2) and 10-balls (SET Type 3), have been simulated using Fluent software to evaluate heat transfer characteristics and flow structure along the air passage. Then, the modified solar drying system has been manufactured and tested at different configurations. 

Findings: The findings indicated that adding a SET improved the performance notably. According to the results, using turbulators in the tube has a positive effect on heat transfer. The highest overall thermal efficiency was found in the range of 51.47%-64.71% for the system with SET Type 3. The maximum efficiency increment of the system was found as 19% with the use of SET. Also, the average specific moisture extraction rate, which is a significant factor to survey the effectiveness of the dehumidification system was found between 0.20 and 0.38 kg kWh(-1). 

Originality/value: In the present study, a novel SET has been developed to upgrade the performance of the solar dehumidifier. This new approach makes it possible to improve both thermal and drying performances.

Journal: International Journal of Numerical Methods for Heat & Fluid Flow

Title: Numerical and experimental analysis of parallel-pass forced convection solar air heating wall with different plenum and absorber configurations

DOI: 10.1108/HFF-03-2021-0160

Abstract:

Purpose: Over the recent years, solar energy has received outstanding attention from researchers. Solar energy applications and related large-scale projects are increasing to meet growing global energy demand as an economical, non-polluting and renewable energy source. The purpose of this study is investigating different plenum and absorber configurations of solar air heating wall (SAHW) experimentally and numerically. 

Design/methodology/approach: In this study, various configurations of SAHW have been numerically simulated to determine the most effective design. According to the simulation results, two SAHWs with various plenum thicknesses have been fabricated and tested at different conditions. 

Findings: Numerical simulation results indicated that parallel-flow SAHWs exhibited better performance in comparison with other placements of absorber plate. Regarding to the experimentally attained results, the highest thermal efficiency was reached to 80.51%. Also, the average deviation between experimentally and numerically obtained outlet temperature is 5.5%. 

Originality/value: Considering the obtained results in the present study, designed SAHW has admissible efficiency to be used in various industrial and residential applications such as; air preheating, space heating and drying.

Journal: International Journal of Numerical Methods for Heat & Fluid Flow

Title: A comprehensive survey on utilization of hybrid nanofluid in plate heat exchanger with various number of plates

DOI: 10.1108/HFF-11-2020-0743

Abstract:

Purpose: Using suspended nanoparticles in the base fluid is known as one of the most efficient ways for heat transfer augmentation and improving the thermal efficiency of various heat exchangers. Different types of nanofluids are available and used in different applications. The main purpose of this study is to investigate the effects of using hybrid nanofluid and number of plates on the performance of plate heat exchanger. In this study, TiO2/water single nanofluid and TiO2-Al2O3/water hybrid nanofluid with 1% particle weight ratio have been used to prepare hybrid nanofluid to use in plate type heat exchangers with three various number of plates including 8, 12 and 16.

Design/methodology/approach: The experiments have been conducted with the aim of examining the impact of plates number and used nanofluids on heat transfer enhancement. The performance tests have been done at 40 degrees C, 45 degrees C, 50 degrees C and 55 degrees C set outlet temperatures and in five various Reynolds numbers between 1,600 and 3,800. Also, numerical simulation has been applied to verify the heat and flow behavior inside the heat exchangers.

Findings: The results indicated that using both nanofluids raised the thermal performance of all tested exchangers which have a various number of plates. While the major outcomes of this study showed that TiO2-Al2O3/water hybrid nanofluid has priority when compared to TiO2/water single type nanofluid. Utilization of TiO2-Al2O3/water nanofluid led to obtaining an average improvement of 7.5%, 9.6% and 12.3% in heat transfer of heat exchangers with 8, 12 and 16 plates, respectively.

Originality/value: In the present work, experimental and numerical analyzes have been conducted to investigate the influence of using TiO2-Al2O3/water hybrid nanofluid in various plate heat exchangers. The attained findings showed successful utilization of TiO2-Al2O3/water nanofluid. Based on the obtained results increasing the number of plates in the heat exchanger caused to obtain more increment by using both types of nanofluids.

Journal: Heat Transfer Research

Title: A review study on factors affecting the stability of nanofluids

DOI: 10.1615/HeatTransRes.2022041979

Abstract:

Nanofluids are suspensions of nanoparticles in a base fluid. Nanofluids that have improved thermophysical properties can be used in different applications including cooling of electronic elements, engine cooling, heat transferring in heat exchanger devices, solar water heating, domestic refrigerator-freezers, space heating, air conditioning, and many other applications. On the other hand, however, instability in nanofluids is an important obstacle to their widespread use in different energy fields. In this study, a number of research related to nanofluid stability have been comprehensively reviewed to investigate the effects of various parameters on nanofluid stability. In general, little interest has been obtained in investigating the effect of different parameters simultaneously on the stability of nanofluids. Acidity degree of the nanofluid, nanoparticles material, ultrasonication, surfactants, base fluid type, nanoparticle concentration, and surface modification of nanoparticles are among the most important technologies that are intended to increase the stability of nanofluids. This study can be considered as a useful reference for addressing the long-term stability and production of high-quality nanofluids, which is an essential demand in the field of nanofluids.

Journal: Gümüşhane University Journal of Science and Technology

Title: Effects of secondary fluid flow rate on cooling performance of vapor compression systems

DOI: 10.17714/gumusfenbil.891882

Abstract:

The vapor compression cooling devices operate on the same principle as heat pumps. In these types of machines thermal energy is transferred from the cold environment to the warmer side using provided power by the compressor. In this study, the effect of air flow rate on the cooling performance of vapor compression cooling devices has been investigated by simulating a designed system in AVL CRUISE™ M program. The simulated model is air-to-air cooling machine and refrigerant R134a was used as circulated gas inside the system. COP value of the system has been calculated in different working conditions and obtained results have been fully discussed. Accordingly, enthalpy variation in every element of the heat pump has been calculated in different working conditions and discussed on P-h diagram. This study presents a simulation method that is a practical solution method in the field of heat pumps, cooling machines and refrigerators which can be considered before installing device in order to have a proper prediction of the system performance.

Journal: Heat Transfer Research

Title: SURFACE MODIFICATION OF Fe3O4 NANOPARTICLES FOR PREPARING STABLE WATER-BASED NANOFLUIDS

DOI: 10.1615/HeatTransRes.2022044141

Abstract:

Nanofluids are known as suspension of nanoparticles in a base fluid having improved thermophysical properties, which can be used in different applications. Nanofluid stability has an important role in its thermophysical properties which can highly affect the performance of the energy systems. In the literature, thermal performances of nanofluids and heat transfer improvement studies are generally emphasized in heat exchangers and energy systems. However, the stability of nanofluids is critical for these systems. It is possible to prepare more stable nanofluids and extend the lifetime of nanofluids by performing surface modifications to nanoparticles. In this regard, the modification process method has been presented for Fe3O4 particles by examining effects of different modification processes on stability and thermophysical properties. The modified Fe3O4 nanoparticles are used to prepare water-based nanofluids with superior stability. Relevant analyses including FT-IR, XRD, EDX, TEM, and SEM analyses were performed to evaluate the properties of the synthesized nanoparticles and prepared nanofluids. Subsequently, the nanofluids with a volume concentration of 0.2% were prepared. The viscosity and thermal conductivity of samples were measured at temperatures between 20°C and 60°C to find out the effect of surface modification. Considering all performed analyses Fe3O4@SiO2-mix-(CH2)3Cl@imidazole-water nanofluid has been proposed with superior stability.

Journal: Applied Thermal Engineering

Title: Effects of surface roughness in multiple microchannels on mixed convective heat transfer

DOI: 10.1016/j.applthermaleng.2022.119102

Abstract:

It has been determined that a significant portion of the total electrical energy is consumed for different cooling and refrigeration purposes at both domestic and industrial sectors. Moreover, cooling systems are employed in a wide range of critical fields such as food industry and pharmacy. In this study, experimental and numerical approach to evaluate two different modes of thermoelectric cooler efficiency is presented. Portable thermoelectric refrigerators operated by Peltier element have been constructed, and experiments are conducted to compare efficiency of air-to-water and air-to-air thermoelectric coolers. In air-to-air mode, the Peltier device was united with heat sinks and fans on both sides. However, in air-to-water mode, a water pump and suitable water-cooled heat exchanger were used to operate in the refrigerators made of styrofoam sheets. It was revealed that, in the laboratory conditions, air-to-water mode is more efficient than air-to-air mode and COP value of the air-to-water is approximately 30–50% higher than that of air-to-air refrigerator. Moreover, ANSYS Fluent 16.0 software has been used to analyze the problem closely in detail. The problem has been simulated, and CFD results were used to visualize flow structure and heat transfer characteristics inside refrigerator box.The most widely used type of heat transfer in applications is convection heat transfer, and both natural and forced convection modes have an effect in total heat transfer to a certain extent, whether any of these modes is neglected or not. In this study, the contribution of natural and forced convection effects to total heat transfer in rectangular microchannels was investigated experimentally for determining the effect of manufacturing process -induced surface roughness in multiple microchannels fabricated using stainless steel material. The experiments were conducted with microchannel heat sinks having three different surface roughness values of 1.1 mu m, 1.8 mu m, and 3.0 mu m, three microchannel widths of 300 mu m, 500 mu m and 700 mu m and two heights of 300 mu m and 450 mu m. During the manufacturing process, surface roughness values were controlled by changing electro-erosion fabrication parameters, and detailed surface maps were generated for the microchannel heat sinks. In the ex-periments using pure water as the working fluid, constant heat flux was applied to the bottom surface of the microchannel heat sink. The experiments were conducted in the range of 10-80 Reynolds numbers to ensure mixed convection conditions. In conclusion, it was determined that surface roughness had a significant effect on mixed convective heat transfer. An increase in surface roughness from 1.1 mu m to 1.8 mu m in microchannel heat sinks with cross-sections of 300 mu m x 300 mu m, 700 mu m x 300 mu m, 300 mu m x 450 mu m, and 700 mu m x 450 mu m s led to an increase of about 24 %, 19 %, 17 %, and 13 %, respectively, in the Nusselt number. Likewise, the increase in surface roughness from 1.8 mu m to 3.0 mu m resulted in an increase of 17 %, 15 %, 14 %, and 10 %, respectively, in the Nusselt number in the same channel cross-sections. In general, an increase in hydraulic diameter led to a reduction in the effect of surface roughness on overall heat transfer. For a constant microchannel width and height, the effect of surface roughness on mixed convection could be observed only with the increase in the Grashof number. Among the eighteen microchannel heat sinks with different geometric parameters, the best heat transfer results were obtained for the smallest microchannel cross-section of 300 mu m x 300 mu m and the highest roughness value of 3.0 mu m.

Journal: Journal of Energy Storage

Title: The performance improvement of direct injection engines in cold start conditions integrating with phase change material: Energy and exergy analysis

DOI: 10.1016/j.est.2021.102895

Abstract:

The cold start problem is still one of the most significant drawbacks of diesel engines, especially in cold climates despite all technological improvements of fuel injection and control systems. Starting diesel engines becomes more difficult at low ambient air and engine block temperatures. Moreover, the production of pollutant exhaust emissions increases during the cold start and warm-up period of the engine. In this study, the thermal energy storage system (TES) with phase change materials (PCMs) has been proposed to improve the cold start and warm-up performance and exhaust emission characteristics of diesel engines. The waste heat from the engine main coolant using as the heat source is transferred to TES with integrated PCM after the warm-up period of the engine for heat storage. Then, the latent and sensible heat stored in PCM is transferred to the engine manifold to increase the temperature of intake air during cold start. The experiments have been conducted under low dead state temperature (approximate to 6 degrees C) conditions of the engine block and ambient. The experimental and energy-exergy comparison analysis results show that the cold start cranking period, CO and HC exhaust emission performances have improved by approximately 68.2%, 27.5% and 44% compared to classical engine system with the use of a designed TES, respectively. The efficiency of the strategy of increasing the intake air temperature by designing a PCM-based TES is supported by energy and exergy comparison analysis. Thermal efficiency and exergy efficiency improved in the range of 1.02%-7.45% and 0.9%-9.63%, respectively. These improvements show that the performance of a diesel engine under cold start conditions can be improved with a PCM-supported TES system.

Journal: Journal of Central South University

Title: Heat transfer enhancement of finned shell and tube heat exchanger using Fe2O3/water nanofluid

DOI: 10.1007/s11771-021-4856-x

Abstract:

Heat transfer mechanisms and their thermal performances need to be comprehensively studied in order to optimize efficiency and minimize energy losses. Different nanoparticles in the base fluid are investigated to upgrade the thermal performance of heat exchangers. In this numerical study, a finned shell and tube heat exchanger has been designed and different volume concentrations of nanofluid were tested to determine the effect of utilizing nanofluid on heat transfer. Fe2O3/water nanofluids with volume concentration of 1%, 1.5% and 2% were utilized as heat transfer fluid in the heat exchanger and the obtained results were compared with pure water. ANSYS Fluent software as a CFD method was employed in order to simulate the mentioned problem. Numerical simulation results indicated the successful utilization of nanofluid in the heat exchanger. Also, increasing the ratio of Fe2O3 nanoparticles caused more increment in thermal energy without important pressure drop. Moreover, it was revealed that the highest heat transfer rate enhancement of 19.1% can be obtained by using nanofluid Fe2O3/water with volume fraction of 2%.

Journal: Journal of Central South University

Title: Experimental investigation of effect of refrigerant gases, compressor lubricant and operating conditions on performance of a heat pump

DOI: 10.1007/s11771-021-4875-7

Abstract:

In the field of heat pumps, there are a number of parameters that affect the performance and efficiency of the apparatus, which have been the subject of studies by individual researchers in the literature. This study describes an experimental method in order to investigate the effects of some significant parameters on heat pump performance. In this regard, a laboratory heat pump setup has been utilized to operate in different working conditions for achieving an appropriate estimation to find out effects of mentioned parameters such as refrigerant type and charge amount, compressor oil viscosity, compressor cooling fan, secondary fluids temperature and flow rate. Different refrigerants have been selected and used as circulating fluid in the installed heat pump. Although this work has been devoted to a detailed attempt to recognize the effects of various parameters on the coefficient of performance (COP) value, an appropriate method has been carried out to survey the obtained results by using economic analysis. It was revealed that one of the main parameters is refrigerant charge amount which has a notable effect on COP. The temperature of the heat source was also tested and the performance of the system increased by more than 11% by employing mentioned modifications and various operating conditions. In addition, by selecting a low viscosity compressor oil, the system performance increased by 18%. This improvement is more than 6% for the case that cooling fan is installed to cool the compressor element.

Journal: Solar Energy

Title: Experimental and numerical analysis of a compact indirect solar dehumidification system

DOI: 10.1016/j.solener.2021.08.025

Abstract:

Drying foods and medicinal plants is a process with high energy consumption because high amount of energy is needed for evaporating the water from the surface of the fresh materials. Therefore, developing cost-effective and simple-structured drying systems with low energy demand is a crucial matter. In the present study, compact type solar dryers have been designed, manufactured and tested experimentally. Within this context, thermal and flow behavior of compact dryers with and without baffles have been analyzed using CFD method. Then, fabricated compact dryers have been experimented at different conditions to determine their performance. Experimental and numerical findings of this study illustrated the effective design of the developed compact solar dryers. However, compact solar dryer with baffles exhibited better performance than the solar dryer without baffles. According to the experimental results, mean specific moisture extraction rate in compact dryers with and without baffles obtained between the ranges of 0.55-0.69 and 0.47-0.62 kg/kWh, respectively. In addition, average exergy efficiency of drying chambers was attained over the range of 44.91-55.28%. Overall findings of this study indicated successfulness of a compact solar dryer which developed using simple and lightweight materials.

Journal: Renewable Energy

Title: Energy-exergy and sustainability analysis of a PV-driven quadruple- flow solar drying system

DOI: 10.1016/j.renene.2021.05.062

Abstract:

Solar energy as a clean energy source is widely investigated to find out the effective mechanisms to meet a large part of energy demand in the near future. In the present research, a square-spiral finned quadruple-flow solar collector assisted dryer has been designed, and numerically compared with finless collector. Main aim of the current work is to develop and analyze a sustainable solar drying system. In this study, different from similar works, heat transfer surface area has been enhanced by using square spiral geometry which is an unconventional fin type. According to the numerical findings, a finned quadruple-flow collector which found more efficient has been manufactured, integrated with a drying chamber and performance experiments have been conducted. In the manufactured solar dryer, a PV panel has been used to run utilized fan. CFD simulation and empirical outcomes of this research exhibited the successful design of finned quadruple-flow collector. Experimentally obtained average efficiency of quadruple-flow collector varied in the range of 73.27-78.19%. Also, mean exergy efficiency of drying chamber was found between 44.16 and 58.38%. Sustainability index and waste exergy ratio values as important factors were attained between the ranges of 1.93-2.73 and 0.52-0.56, respectively.

Journal: Renewable Energy

Title: Dehumidification of sewage sludge using quonset solar tunnel dryer: An experimental and numerical approach

DOI: 10.1016/j.renene.2021.02.158

Abstract:

In this study, it is aimed to design an efficient and sustainable solar tunnel dryer to be used in drying process of sewage sludge. In the first step of this study, heat and flow structure of three tunnel dryers including rectangular tunnel (RSTD), quonset tunnel (QSTD) and quonset tunnel with fins (QSTD/F) have been numerically surveyed to determine the effective design. Based on CFD results, quonset-type tunnel designs have been fabricated, experimentally analyzed and compared with numerical findings. In this work, different from previous studies on quonset-type solar-thermal systems, top surface of quonset geometry was made from sheet metal as an absorber to enhance heat transfer area. The drying tests have been performed in different months of the year (June and January) by applying two different air velocities to evaluate the performance of tunnel dryers at various climatic conditions. Integrating fins to the quonset tunnel had considerable positive effects on both thermal and drying performances. According to the experimental findings, specific moisture extraction rate (SMER) value was attained on June and January in the range of 0.50–0.89 and 0.39–0.65 kg/kWh, respectively. The results indicated the successfulness of quonset solar tunnel dryer design in the dehumidification process of sewage sludge.

Journal: Heat Transfer Research

Title: Numerical and experimental analysis of longitudinal tubular solar air heaters made from plastic and metal waste materials

DOI: 10.1615/HeatTransRes.2021038204

Abstract:

Recycling and reusing waste materials not only reduces environmental pollution but also contributes to the reduction of health problems and economic gain. In this study, plastic and metal materials reused in fabricating solar air heaters (SAHs) are considered. Accordingly, two tubular solar air heaters have been designed, fabricated, and experimented. The major objective of this work is to demonstrate the importance of utilizing waste materials in renewable energy-based technologies and their applicability in thermal energy production. In the first step of the analysis, the applicability of tubular-type SAHs has been studied numerically. The experiments have been conducted at two tilt angles including 90 degrees and 32 degrees and also at three flow rates including 0.012, 0.010, and 0.008 kg/s. The experimental findings showed that the efficiency of metal SAH and plastic SAH varied in the range of 36.33-50.96% and 31.60-47.06%, respectively. Also, enviro-economic costs for metal and plastic SAH were achieved as 8.02 and 7.55 $/year. Besides, the experimental results were predicted with ANN and SVM algorithms. The prediction success of the algorithms is discussed with four metrics (R-2, MAPE, RMSE, and MBE). The outcomes clearly demonstrate the successful application of this simple and cost-effective tubular-type SAH manufactured from waste materials.

Journal: Heat Transfer Research

Title: Numerical study on drag coefficient and evaluation of the flow patterns in perforated particles

DOI: 10.1615/HeatTransRes.2021038829

Abstract:

The flow regime around different shapes and surfaces has been deeply studied with numerical and experimental methods, whereas perforated particles have taken little attention among investigations. In this study, the drag coefficient and flow wake structure of spherical particles with different hole numbers and hole diameters are investigated numerically using computational fluid dynamics (CFD). In addition, the different hole numbers and sizes in the spherical model are analyzed within a wide range of Reynolds numbers. From the analysis performed it was shown that for the case when the hole number is 15 at the Re number equal to 20, the drag coefficient increases by about 0.65%, 3.76%, and 17%, when the dimensionless hole diameter is 0.02, 0.05, and 0.1, respectively. Velocity and pressure contours, streamlines, and drag coefficient histograms are discussed and compared under different flow conditions. The ANSYS Fluent 16 software is used for fluid flow analysis around and through the models mentioned.

Journal: Journal of Thermal Science

Title: Experimental Analysis and Evaluation of Thermostat Effects on Engine Cooling System

DOI: 10.1007/s11630-020-1264-8

Abstract:

Thermostat as a part of engine cooling system has a significant role in the shortening warm-up time and regulating the engine in proper temperature to approach optimal performance. Whereas, there is not adequate research on this part of the cooling system and its responsibility. Considering this gap and also being used in large scale, this study is intended to evaluate performance and reflex of the wax type thermostat in different engine working conditions. In this regard, performance of engine cooling system was investigated in various engine speeds and loads to reveal positive and negative influences of thermostat on engine cooling efficiency and engine performance. According to observed results, warm-up period and fuel consumption decrease by using a thermostat. On the other hand, however, the temperature oscillation of coolant fluid passing through engine increases sharply, which causes a disruption in the regulating engine temperature and also a possibility of the fluid boiling rises in some regions of the engine that increases the risk of damage in the engine parts. Engine temperature, fuel consumption, warm-up duration and emissions were provided and compared in two operation modes, with and without thermostat.

Journal: Journal of Thermal Analysis and Calorimetry

Title: Experimental and numerical investigation on thermoelectric coolers for comparing air-to-water to air-to-air refrigerators

DOI: 10.1007/s10973-020-09500-6

Abstract:

It has been determined that a significant portion of the total electrical energy is consumed for different cooling and refrigeration purposes at both domestic and industrial sectors. Moreover, cooling systems are employed in a wide range of critical fields such as food industry and pharmacy. In this study, experimental and numerical approach to evaluate two different modes of thermoelectric cooler efficiency is presented. Portable thermoelectric refrigerators operated by Peltier element have been constructed, and experiments are conducted to compare efficiency of air-to-water and air-to-air thermoelectric coolers. In air-to-air mode, the Peltier device was united with heat sinks and fans on both sides. However, in air-to-water mode, a water pump and suitable water-cooled heat exchanger were used to operate in the refrigerators made of styrofoam sheets. It was revealed that, in the laboratory conditions, air-to-water mode is more efficient than air-to-air mode and COP value of the air-to-water is approximately 30–50% higher than that of air-to-air refrigerator. Moreover, ANSYS Fluent 16.0 software has been used to analyze the problem closely in detail. The problem has been simulated, and CFD results were used to visualize flow structure and heat transfer characteristics inside refrigerator box.

Journal: Surfaces and Interfaces

Title: Tribological and thermal properties of plasma nitrided Ti45Nb alloy

DOI: 10.1016/j.surfin.2020.100893

Abstract:

In this study, the effects of plasma nitriding surface treatment on the structural, tribological and thermal properties of Ti45Nb Beta alloy were investigated experimentally. Plasma nitriding process of Ti45Nb alloy was performed in 25% Ar-75% N2 gas mixture, for treatment times of 1–4 hours at the temperatures of 700–750 °C. The tribological tests of the plasma nitrided alloy were performed in dry sliding conditions. Thermal property measurements were applied to the plasma nitrided samples to determine their thermal conductivity and specific heat capacity. The TiNbN2 phase was observed in the compound layer formed after the nitriding process, and the compound layer and diffusion layer thicknesses increased depending on the nitriding temperature and duration. The highest microhardness was obtained for the sample nitrided at 750 °C for 4 hours and the hardness approximately twice increased compared to the untreated alloy. Due to its high surface hardness and nitride layer with sufficient thickness, the lowest wear rate was obtained for the nitrided sample under these conditions. As a result, the most effective parameter on the wear properties of Ti45Nb alloy after nitriding was determined as the process temperature. After the plasma nitriding process, thermal conductivity, thermal diffusion and specific heat capacity values decreased due to the formation of a nitride layer on the surface with a relatively lower thermal conductivity compared to the untreated alloy.

Journal: Materiale Plastice

Title: Optimization of variables influencing the thermal conductivity and fracture strength of reinforced PMMA by using the Taguchi method

DOI: 10.37358/Mat.Plast.1964

Abstract:

How the particle size and volumetric ratio of silicon carbide (SiC) powder additions will strengthen polymethyl methacrylate (PMMA) is unclear. The purpose of this in vitro study was to optimize the reinforcement parameters of PMMA with SiC powder by using the Taguchi experimental design method. Particle size, volumetric rate, silane coupling rate, and mixing type were determined as parameters that would affect the reinforcement of PMMA with SiC powder. Using the Taguchi L9 orthogonal array, test specimens with different parameter combinations were fabricated and tested. The fracture load (in newtons) of each specimen group was recorded with the 3-point bend test. The thermal conductivity values of 60x50-mm and 3-mm-thick rectangular specimens were measured by using the Linseis THB 100 thermal conductivity unit. The thermal diffusivity values were then calculated. Thermal analysis indicated improvement in the thermal conductivity of PMMA after reinforcement with SiC. The maximum thermal diffusivity was obtained with 15% SiC powder by volume. Thermal conductivity and flexural strength increased with an increase in particle size. The maximum flexural strength value was obtained with 5% SiC powder by volume. Increasing the particle size of the filler SiC powder resulted in increased thermal conductivity and flexural strength. Increasing the SiC filler powder by volume increased the thermal conductivity of PMMA but reduced its flexural strength. This study helped determine the optimum conditions for the use of SiC powder. Knowledge of the importance of these variables will help in more effective modification of denture base resin with SiC powder to improve heat transfer without adversely affecting strength.

Journal: Heat Transfer Research

Title: Experimental and numerical study on heat transfer enhancement of home radiators by employing solar cells and fans

DOI: 10.1615/HeatTransRes.2019029250

Abstract:

In the traditional heating systems, heated water in the boiler is circulated in the home radiators to warm up the ambient temperature as an air conditioning system. Generally, in the mentioned systems, the natural convection has a key role in the heat transfer from the radiator to the surroundings. The forced convection can be also applied by using air fans, and consequently the Nusselt number will be increased, which means an increase in the efficiency and heat transfer. In this work, the air fans were placed in a sample radiator to improve the thermal efficiency. The used fans are powered by batteries, and the battery supply is charged by solar cells. The fans will be able to operate at nights when the electric energy of the solar cells has been stored in the accumulator. The problem was simulated using the ANSYS Fluent software to compare the obtained numerical results to those recorded experimentally. In numerical and experimental results, an increase in heat transfer was observed. The obtained results showed that the average heat transfer rate was improved by about 21% by using forced convention.

Journal: Heat Transfer Research

Title: Experimental optimization and investigation of compressor cooling fan in an air-to-water heat pump

DOI: 10.1615/HeatTransRes.2019030709

Abstract:

Heat pumps are seen as a highly efficient promising technology for space heating and cooling. Their efficiency has been widely studied for different types of heat pumps operating with various energy sources including air, ground, and water. However, different components of the heat pump need to be closely investigated to improve the performance of the system. This study surveys the effects of compressor cooling fan, to evaluate how a heat pump system behaves at different fan speeds. Refrigerant R134a has been used as a circulating fluid in the system. The results obtained from detailed experiments are analyzed to optimize the performance of the entire system using a compressor cooling fan, considering COP, P-h diagrams, efficiency, and thermodynamic properties. It is concluded that cooling the compressor has a remarkable effect on the thermodynamic state of refrigerant which leads to a positive influence not only on the compressor efficiency but also on the entire heat pump unit.

Journal: Solar Energy

Title: Experimental and CFD survey of indirect solar dryer modified with low-cost iron mesh

DOI: 10.1016/j.solener.2020.01.021

Abstract:

In the present work, double-pass indirect solar dryer (DPISD) and double-pass indirect solar dryer with mesh absorber modification (DPISDMA) have been designed, analyzed, manufactured and tested. The main aim of this study is improving the thermal efficiency of double-pass solar air collector by integrating iron meshes. Pepino fruit (Solarium muricatum L.) samples in two thicknesses have been used in the experimental study. Also, CFD analysis of both solar air collectors and drying chamber and quality metrics such as phenolic, total flavonoid contents and antioxidant activity have been conducted. Numerical simulation and experimental results showed that using mesh modification has positive influence on the performance of the collector. The highest value of the average efficiency of the dryer was obtained in DPISDMA for the thin sample thickness as 23.08%. According to quality analyses, the experiments which done in DPISDMA gave the best results with highest values of TPC, TFC and antioxidant activity values (p < 0.05). Drying data of the pepino fruit for different experiments were modelled according to 8 different most used mathematical models. Accordingly, the best fitted kinetics model was determined as Logarithmic model for all experiments which gave the most accurate statistical values.

Journal: Science of The Total Environment

Title: Drying municipal sewage sludge with v-groove triple-pass and quadruple-pass solar air heaters along with testing of a solar absorber drying chamber

DOI: 10.1016/j.scitotenv.2019.136198

Abstract:

Everyday a large amount of sewage sludge is produced in cities and proper and environmentally friendly municipal wastewater treatment is needed. Finding a convenient and affordable way for sewage sludge refinement to reduce environmental pollution or even utilization of sewage sludge will be a very attractive challenge for scientists. In the recent years, sustainable and renewable energy sources like solar energy are extensively utilized in different fields including heating, electricity generation, and drying applications. In this study, V-groove triple-pass (V-TPSAH) and V-groove quadruple-pass (V-QPSAH) solar air heaters have been designed, manufactured and tested for drying municipal sewage sludge. Also, two different types of drying chambers (DC-I: conventional, DC-II: solar absorber) have been integrated with each solar heater. Experimental and numerical methods have been applied to analyze the efficiency of developed solar air heater assisted drying systems. The system's performance has been tested in different working conditions to clarify the utilization potential of manufactured system. According to the experimental results solar air heater's average efficiency are in the range of 70.12-81.70%. In addition, obtained experimental findings are in line with numerical results. The outcomes of this study present the potential of using the developed systems in drying municipal sewage sludge to be used in multi purposes.

Journal: Construction and building materials

Title: Electrically conductive concrete: A laboratory-based investigation and numerical analysis approach

DOI: 10.1016/j.conbuildmat.2020.119948

Abstract:

In recent years, the application of electrically conductive concretes has been proposed as an anti-icing method on airport runways. In this work, it was aimed to evaluate usability of the nano carbon black obtained by the pyrolysis method from the waste tires and also the waste wire erosion obtained from the cutting processes for using in the electrically conductive concrete with application in airport runway anti-icing. In this regard, 36 different mixtures of the electrical conductive concretes were first investigated in the laboratory to find out general mechanical and electrical conductivity properties of the test concrete. After obtaining the result of their general characteristics, 10 different types of concrete slabs were produced. Electrothermal tests of conductive concrete slabs were carried out in a cooling chamber at -10 degrees C. A heat power within a range of 180-1315 W/m(2) has been provided for heating electrically conductive concrete slabs obtained from different mixtures and consequently an optimization method was utilized and obtained results were compared on figures and diagrams. Numerical simulation of the problem has been also carried out to find out heat flux and temperature distribution of test concretes.

Journal: Journal of Cleaner Production

Title: Testing of a novel convex-type solar absorber drying chamber in dehumidification process of municipal sewage sludge

DOI: 10.1016/j.jclepro.2020.122862

Abstract:

Each day high portion of municipal wastewater sludge is generated in cities and developing a suitable and environmentally friendly treatment technique for municipal wastewater is required. Providing a cost-effective and suitable way for sewage sludge refinement with the purpose of reducing environ-mental impacts or reutilization of sewage sludge can be an important issue for researchers. In the present study, a novel convex-type solar absorber assisted dryer has been designed for drying municipal sewage sludge. In the experimental setup, an unglazed single-pass solar air collector has been used as main air heater and integrated to the drying conventional and modified drying chambers. Experimental and CFD simulation have been used to investigate the performance of fabricated solar energy assisted dryers. Also, the effectiveness of the developed system has been analyzed in various conditions to clarify the potential of fabricated dryers. According to the results utilizing convex solar absorber led to provide high air flow rate with high temperature inside the drying chamber and consequently shortened the drying time. Experimentally obtained average energy efficiency of the modified and conventional indirect solar drying system were in the range of 32.85-47.09% and 21.32-30.45%, respectively. Moreover, the experimental results collected from CSD (conventional solar dryer) and CSASD (solar dryer with convex solar absorber) are also discussed in terms of R-2, RMSE, RRMSE, MBE, and MAPE, and a very satisfying correlation be-tween the systems CSD and CSASD is noticed with the statistical metrics. The findings of the present study demonstrate the potential of utilizing the designed dryers in drying municipal wastewater sludge.

Journal: Heat and Mass Transfer

Title: Thermodynamic analysis of a system converted from heat pump to refrigeration device

DOI: 10.1007/s00231-018-2412-5

Abstract:

In this study, an existing laboratory heat pump is converted to a refrigeration unit in order to evaluate efficiency, power consumption, pressure and temperature variations and optimal charge amount of the system in new mode using refrigerant R-407C. Refrigerant charge amount has a key role in the terms of performance, operating cost (regarding to the charge reduction and energy consumption) and environmental concerns in all heat pump and refrigeration systems, which work on the same principles. Heat pump charge amount is the subject of many research, but less studies have been done in the case of refrigerators and freezers where the system works in the transient condition, on the contrary to the heat pump units. Although this study has been devoted to a detailed attempt to examine the possibility of converting the heat pump into the refrigerator, energy aspects of the whole system and the compressor have been analyzed under different working conditions. In the installed setup, the COP value of the system is tested with charge amount between 1kg and 7kg, but obtained results show that, this value is so lower than that of heat pump unit due to restricted energy source in cooling chamber.

Journal: International Journal of Environmental Science and Technology

Title: Numerical analysis of ball-type turbulators in tube heat exchangers with computational fluid dynamic simulations

DOI: 10.1007/s13762-018-2012-4

Abstract:

In the tube heat exchangers, heat transfer enhancement by creation of turbulent flow has been investigated in a number of previous research using different turbulator forms and methods, whereas in the present work a novel ball-type turbulators is used as a new technique implementation to increase heat transfer rate by vortex generation in the flow. Numerical analysis is performed for proposed novel turbulator to probe heat and flow characteristics. Ball-type turbulators have been designed in three different ball diameters inside a tube exchanger. The effects of balls diameter, pitches and Reynolds number on the heat transfer, friction factors and also entropy generation are analyzed at four different Reynolds numbers between 5000 and 20,000. The Nusselt number and friction factor outcomes are compared with those of smooth tube under the same flow and thermal conditions to determine the heat transfer enhancement. From the numerical analysis, it is specified that the suggested turbulators generate a larger vortex flow at low Reynolds numbers, and consequently, more effective heat transfer can be obtained. Moreover, increasing the ball diameter will lead to more heat transfer rate due to the wider vortex region at behind of the ball.

Journal: Journal of Thermal Analysis and Calorimetry

Title: Experimental investigation of mixed convection heat transfer of nanofluids in a circular microchannel with different inclination angles

DOI: 10.1007/s10973-018-7463-9

Abstract:

In this study, the characteristics of mixed convection heat transfer of nanofluids in circular microchannels with 500m diameter were investigated experimentally. In the study, water and water-based SiO2 nanofluids were used as the working fluid, and volumetric particle ratios of the nanofluids were selected as 0.2 and 0.4%. The thermal conductivity and viscosity characterizations of all fluids were performed in the temperature range of 20-60 degrees C, and the characteristics related to the temperature obtained from the measurements were used in calculations. The effect of the microchannel inclination angle and particle volumetric ratio on the mixed convection heat transfer characteristics was investigated. Upon examining the results, it was revealed that the range of 13-35% of the total heat transfer was generated by the natural convection effects. Increasing the inclination angle of the test section provided an enhancement between 4 and 13% in the total heat transfer. Furthermore, the increase in the volumetric particle ratio increased both forced convection heat transfer and the natural convection heat transfer components. Adding nanosized SiO2 particles into the water caused the total heat transfer to increase from 12 to 14% for 0.2vol% and from 29 to 32% for 0.4vol%.

Journal: Heat and Mass Transfer

Title: Analysis of mixed convection heat transfer of nanofluids in a minichannel for aiding and opposing flow conditions

DOI: 10.1007/s00231-019-02638-6

Abstract:

In this study, mixed convection heat transfer characteristics of nanofluid flow in a circular minichannel were investigated experimentally. The effects of the particle volume ratio (0, 0.25, and 0.75%) and Reynolds number (200-60) on heat transfer by mixed convection were investigated for aiding and opposing flow conditions. Water and water based SiO2 nanofluids were used as working fluid in a minichannel with a diameter of 1.9 mm, and constant heat flux was applied to the outer surface of the minichannel. Temperature-dependent thermophysical properties such as thermal conductivity and viscosity, obtained by experimental measurements, were used in heat transfer calculations. Pressure based numerical computations for all experimental cases were also made by using single phase approach. The results were analyzed separately for aiding flow condition in which secondary flows originating from natural convection are in the same direction with the forced flow, and for opposing flow condition in which secondary flows are in the opposite direction with forced flow. For detailed analysis of mixed convection heat transfer, temperature contours and velocity profiles were obtained by the numerical computations which were compared and validated with the experimental results. According to the data obtained, it was determined that the addition of nanoparticles into the pure water increased the Nusselt number by around 21-64% for the aiding flow, and 18-58% for the opposing flow. The heat transfer in the aiding flow was observed to be minimum 4% and maximum 16% higher in comparison with the opposing flow condition. It was concluded that the direction of secondary flows significantly affects heat transfer.

Journal: Heat and Mass Transfer

Title: Experimental investigation of mixed convection heat transfer of ferrite-based nanofluids in multiple microchannels

DOI: 10.1007/s00231-018-2505-1

Abstract:

The objective of this study is to experimentally investigate the mixed convection heat transfer characteristics of ferrite-based (Fe2O3.NiO) nanofluids in multiple microchannel heat sinks. Two rectangular cross-sectioned microchannel heat sinks having two different heights of H=1mm and 1.8mm and a width of 300m were used. Ferrite-based nanoparticles were suspended into the pure water at two different volumetric ratios of 0.25 and 0.5%, and experiments were performed for both pure water and nanofluids. Constant heat flux was applied to the bottom wall of the microchannels by the cartridge heaters placed in heat sinks. Ferrite-based nanofluids were prepared by the two-step method, and the average size of the particles was below 20nm. The thermal conductivity and viscosity values of all fluids used in the present study were measured in a temperature range of 20-60 degrees C. Increasing the channel height from 1 to 1.8mm caused an increase in the Nusselt number about 9.4-10.7, 9.9-13.9 and 5.8-11.7% for the pure water, the 0.25 vol.% Fe2O3.NiO-water nanofluid and the 0.5 vol.% Fe2O3.NiO-water nanofluid, respectively. The addition of Fe2O3.NiO nanoparticles into the base fluid further increased the natural convection effects compared to pure water. The effects of the natural convection heat transfer in H=1.8mm were more dominant than those of H=1mm at the same Grashof number values.

Journal: Renewable Energy

Title: Comparative engine characteristics of biodiesels from hazelnut, corn, soybean, canola and sunflower oils on DI diesel engine

DOI: 10.1016/j.renene.2017.12.011

Abstract:

Biodiesel is a very popular renewable alternative fuel. Biodiesel utilization rate as an alternative fuel has been increasing in recent years due to availability, comparatively easier manufacturing process as well as superior fuel properties like non-sulphur content and storage safety. There are many articles related to properties of biodiesel and its effects on engine performance in the literature. However, the studies that compared various biodiesel samples in the same experimental system are scarce. Therefore, results obtained from different experimental systems cannot be definitely benchmarked to provide a comprehensive comparative analysis.

In this study, engine performances of five different kinds of biodiesels produced from five different vegetable oils (corn, sunflower, soybean, canola and hazelnut) were compared with each other and with diesel fuel in the same experimental system. Therefore, biodiesel samples that include different ratios of (20%, 50%, and 100%) biodiesel in diesel fuel for each biodiesel sample was prepared after biodiesels were produced by transesterification method. Every sample was used as fuel in the diesel engine. Both effective characteristics and indicated characteristics were determined for each fuel during engine test. All values were compared each other graphically. Finally, it was found that the mixture consists of 20% hazelnut biodiesel has the best performance.

Journal: Energy and Buildings

Title: A thermodynamic comparison between heat pump and refrigeration device using several refrigerants

DOI: 10.1016/j.enbuild.2018.03.037

Abstract:

Heat pumps and refrigerators are two systems with different usage, but same working principles. Generally, HPs work in steady state condition and specific thermodynamic cycle, but refrigerator or freezer apparatus have variable cycle and work in the unsteady condition.

In this study, two different data sources are gathered to analyze thermodynamic differences between two mentioned systems. Initially, an existing heat pump unit is analyzed in different working conditions with different refrigerants and then the unit is converted to a refrigeration device to compare their thermodynamic conditions and treatments.

Thermodynamic laws, COP value and efficiency, compressor power consumption, optimum charge amount, and flow rate of secondary fluid are main parameters which are considered to compare heat pump and refrigerator performances by using several refrigerants including R134a, R407c, R22, and R404a.

In the case of freezer mode, entropy reduction in compressor and COPL drop to very low values are other substantial issues discussed in this research. It was also revealed that, optimal charge amount of the freezer is 15–25% lower than that of the system when works in HP mode. Experiments showed that, in some cases COP of the heat pump was even more than 100 times greater than that of the freezer.

Journal: Waste and Biomass Valorization

Title: The Effects of Nanofilter and Nanoclay on Reducing Pollutant Emissions from Rapeseed Biodiesel in a Diesel Engine

DOI: 10.1007/s12649-017-9913-1

Abstract:

Biodiesel is a diesel fuel substitute produced from renewable resources and waste lipids that is characterized by its low-emissions. This study, presents an experimental investigation focusing on reducing NOx pollutants in biodiesel fuels by means of a novel method using nanoclay and nanofiltration together in biodiesel treatment. Rapeseed oil and methyl alcohol are converted to biodiesel by esterification method. Subsequently, nanoclay is added to the mixture to separate the nitrogen elements from the fuel. The fuel is subsequently filtered using nanofilters prior to exhaust gas analysis. The treatments are performed on biodiesel and diesel to evaluate the effects that the addition of nanoclay and nanofiltration have on the fuel. The results showed that, the nanoclay and nanofiltration significantly reduce CO and NOx pollution. In this study, filtration was also performed without nanoclay to determine the effect that nanofilters alone have on the fuel.

Journal: Mathematics and Computers in Simulation

Title: On numerical methods; optimization of CFD solution to evaluate fluid flow around a sample object at low Re numbers

DOI: 10.1016/j.matcom.2018.04.004

Abstract:

Computational fluid dynamic methods are applied to survey numerical approximations of partial differential equations. In this area, there is a wide range of numerical methodologies, algorithms, schemes, simulation strategies as well as software programs for solution.

In most experimental studies, these complicated numerical methods are used to simulate a problem without enough regard to the communication between the problem, advanced software and the nature of the solution methods. In this study, this scientific gap was considered to discuss most used numerical methodologies, their accuracy and the way numerical methods are used to solve engineering problems. In this research, governing equations and formula of numerical methods are introduced; then a 2-D sample object (cylindrical shape) is simulated in the incompressible flow as an example for simulation in CFD program (ANSYS Fluent 16). (C) 2018 International Association for Mathematics and Computers in Simulation (IMACS). Published by Elsevier B.V. All rights reserved.

Journal: Results in Physics

Title: Entropy generation of nanofluid flow in a microchannel heat sink

DOI: 10.1016/j.rinp.2018.03.013

Abstract:

Present study aims to investigate the effects of the presence of nano sized TiO2 particles in the base fluid on entropy generation rate in a microchannel heat sink. Pure water was chosen as base fluid, and TiO2 particles were suspended into the pure water in five different particle volume fractions of 0.25%, 0.5%, 1.0%, 1.5% and 2.0%. Under laminar, steady state flow and constant heat flux boundary conditions, thermal, frictional, total entropy generation rates and entropy generation number ratios of nanofluids were experimentally analyzed in microchannel flow for different channel heights of 200 mm, 300 mm, 400 mm and 500 mm. It was observed that frictional and total entropy generation rates increased as thermal entropy generation rate were decreasing with an increase in particle volume fraction. In microchannel flows, thermal entropy generation could be neglected due to its too low rate smaller than 1.10e-07 in total entropy generation. Higher channel heights caused higher thermal entropy generation rates, and increasing channel height yielded an increase from 30% to 52% in thermal entropy generation. When channel height decreased, an increase of 66%-98% in frictional entropy generation was obtained. Adding TiO2 nanoparticles into the base fluid caused thermal entropy generation to decrease about 1.8%-32.4%, frictional entropy generation to increase about 3.3%-21.6%.

Journal: Journal of Energy Engineering

Title: Influence of Refrigerant Properties and Charge Amount on Performance of Reciprocating Compressor in Air Source Heat Pump

DOI: 10.1061/(ASCE)EY.1943-7897.0000377

Abstract:

This article investigates how hydrofluorocarbon (HFC) refrigerant affects compressor operating conditions and system performance using experimental testing under different conditions. In a heat pump or refrigerator cycle, it is necessary to move the fluid in the system to achieve heating or cooling. The compressor is the responsible component in fluid movement and so is a key factor in system power consumption. For this reason, it is essential to discover ways to increase compressor energy efficiency. R404a refrigerant was selected to evaluate the influence of refrigerant on compressor performance. Compressor inlet and discharge temperatures and pressures were measured experimentally. For the tested refrigerant, compressibility factor (Z) and deviation from ideal gas behavior were analyzed cautiously to compute power consumption, isentropic work, coefficient of performance, energy and exergy state, and compressor efficiency. Also analyzed were the influence of condenser water flow rate and the effect of evaporator inlet temperature. The study discussed here provided results that can be used to enhance the performance of compressors in heating/cooling systems.

Journal: International Journal of Refrigeration

Title: Characterization of lubricating oil effects on the performance of reciprocating compressors in air-water heat pumps

DOI: 10.1016/j.ijrefrig.2016.11.017

Abstract:

Lubricating oils play several key roles in compressors, such as lubrication of the parts exposed to friction, prevention of gas leakage at the compression chamber, and cooling of the pieces heated by friction. Oil viscosity and possibility of mixing with refrigerant are the significant factors that should be considered in choosing compatible lubricants. Generally, high viscosity lubricants reduce the efficiency and lubricants with low viscosity cause to direct contact between the metal parts in the compressor. In this study, an experimental procedure has been carried out to investigate the influences of oil circulation in the compressor working with R-404a refrigerant. Although this study has been devoted to a detailed attempt to identify the effects of oil viscosity on energy consumption, an innovative way to analyze this critical parameter has been carried out in parallel with other parameters including refrigerant charge amount, condenser water flow rate and air temperature in the evaporator. The sample oils selected for experiments are SL22, SL68 and SL220. The basic nature of the lubricants and their mixtures with refrigerant, COP value, compressor efficiency and exergetic efficiency of the system has been analyzed under different working conditions. (C) 2016 Elsevier Ltd and IIR. All rights reserved.

Journal: Applied Thermal Engineering

Title: Optimization of heat transfer and efficiency of engine via air bubble injection inside engine cooling system

DOI: 10.1016/j.applthermaleng.2017.04.164

Abstract:

The advanced thermal management in the internal combustion engines has a key role in the overall performance, which directly effect on the total fuel consumption and engine exhaust emissions. Recently, a number of valuable studies have been carried out to evaluate and improve cooling system performance by using various technologies such as sliding vane rotary pump, ultimate cooling, double temperature circuits, integration, electrically-controlled valves and advanced algorithms for flexible control of the cooling system components, but, in this study an innovative strategy is presented to achieve this purpose. With a novel point of view, air-water mixture is employed to use in the cooling circuit. For this reason, at the point of coolant inlet to the engine, a constant pressure air injection mechanism was established, which can be adjusted at the desired flow rate by computer. The air injection strategy has two significant advantages. In the warm-up stage more air injection into the coolant fluid cause to a rapid heating of engine components by creating air layers around the cylinder. In the after warm-up state, however, air injection is decreased to a specified level for producing turbulence flow only in order to heat transfer enhancement and cooling purposes. Obtained results revealed that the periodic air injection by using special strategy can improve fuel economy and also decrease engine pollutant emissions.

Journal: Heat and Mass Transfer

Title: Experimental and numerical investigation of the cylindrical blade tube inserts effect on the heat transfer enhancement in the horizontal pipe exchangers

DOI: 10.1007/s00231-017-2021-8

Abstract:

In this experimental and numerical study an attempt to enhance the heat transfer rate by cylindrical blade that form turbulence flow inside the exchanger pipe is carried out. The effects of the blade geometry are also examined to investigate heat transfer rate in experimented tube inserts. Experiments are performed in different blade spacing (Sy1,2,3 = 101–216–340 mm) and various blade angles (α1,2,3 = 0°–45°–90°). The water flow rate inside the tube is adjusted in three different ranges to approach intended Reynolds numbers (Re1,2,3 = 6000–11,000–17,000). Nusselt number, Reynolds number and effect of friction factor are investigated separately. For all experiments, the increase in Nu number due to used tube inserts is recorded and compared to each other and plain tube in the related profiles. It is concluded that installed tube inserts in the heat exchanger tube, led to a significant increase in Nu number and energy saving. Among different experimented cases, using mean value in various Re numbers, the highest Nusselt number was obtained at Sy1 = 101 mm which was 24% more than that of plain tube. This value was 18.7 and 8.3% for Sy2 = 216 and Sy3 = 340 mm respectively. By this way, according results for friction factor were 0.30, 0.19 and 0.14. The presented study has been simulated by ANSYS Fluent 16 software to analyze flow behavior and heat transfer characteristics.

Journal: Applied Thermal Engineering

Title: Analysis of windbreaker combinations on steam power plant natural draft dry cooling towers

DOI: 10.1016/j.applthermaleng.2016.01.103

Abstract:

Performance of natural draft dry cooling towers is significantly affected when the wind velocity is higher than a critical level according to their design and geometry. During this type of conditions, global electricity generation of power plants using especially dry type cooling towers is substantially reduced, up to as high as 40%. In order to decrease the reduction in electricity generation of power plants, it is possible to study on the dimensions of the cooling towers. Additionally, using different types of windbreakers can reduce the effects of unfavorable operating conditions. However, the direction of the wind changes with the seasons although the prevailing wind direction is nearly the same. In this study, internal flat and combination of internal flat–external rounded windbreakers have been analyzed by using the computational fluid dynamics approach. The combination of windbreakers, which is able to move axially around the cooling tower, has been propounded to arrange the flow characteristics during the windy days. The studies on the windbreakers in the literature have been aimed to decrease the negative effects of the wind; however, the design in this study provides also an increase in the air mass flowrate due to the momentum effect of the wind.

Journal: International Journal of Heat and Mass Transfer

Title: The effect of microchannel height on performance of nanofluids

DOI: 10.1016/j.ijheatmasstransfer.2015.12.015

Abstract:

In this study, the effects of microchannel height and particle volume fraction of nanofluids on heat transfer and pressure drop characteristics are investigated experimentally. Nano sized TiO2 particles with an average diameter of 25 nm have been dispersed into the deionized water in five different particle volume fractions of 0.25%, 0.5%, 1.0%, 1.5% and 2.0%. The forced convective heat transfer experiments of nanofluids have been conducted in a microchannel, which has four different heights of 200, 300, 400 and 500 μm. A constant heat flux of 80 kW/m2 has been applied to the bottom wall of the microchannel, and the experiments have been carried out under steady state and laminar flow conditions. The results have been presented with respect to convection heat transfer coefficient and pressure drop. An increase in the microchannel height decreased the heat transfer rate and enhanced the pressure drop. It is concluded that nano sized TiO2 particles in the base fluid have provided higher heat transfer and have not caused an excessive increase in pressure drop with respect to pure water. Convection heat transfer coefficient has also increased with an increase in the volume fraction.

Journal: Applied Thermal Engineering

Title: Controlling LPG temperature for SI engine applications

DOI: 10.1016/j.applthermaleng.2015.02.059

Abstract:

In this study, the effects of the LPG temperature on the engine performance and the exhaust emission characteristics have been investigated experimentally on an SI engine. In conventional injection systems, the LPG temperature increases excessively during the phase change in pressure regulator, and reduces the engine volumetric efficiency. According to the test results, engine performance and NO emission characteristics can be improved by controlling the LPG temperature before injecting to the engine intake manifold. A new control system taking into account the results of the study has been developed and tested. In order to control the LPG temperature, the coolant flow rate in pressure regulator circuit was arranged by using a control valve activated by a PID controller unit. Results of the study showed that the engine brake power loss can be increased by about 1.85% and NO emissions can be decreased by about 2% as compared to the operation with the original LPG injection system.

Journal: Applied Thermal Engineering

Title: Controlling spark timing for consecutive cycles to reduce the cyclic variations of SI engines

DOI: 10.1016/j.applthermaleng.2015.05.042

Abstract:

Minimization of the cyclic variations is one of the most important design goal for spark-ignited engines. Primary motivation of this study is to reduce the cyclic variations in spark ignition engines by controlling the spark timing for consecutive cycles. A stochastic model was performed between spark timing and in-cylinder maximum pressure by using the system identification techniques. The incylinder maximum pressure of the next cycle was predicted with this model. Minimum variance and generalized minimum variance controllers were designed to regulate the in-cylinder maximum pressure by changing the spark timing for consecutive cycles of the test engine. The produced control algorithms were built in Lab View environment and installed to the Field Programmable Gate Arrays (FPGA) chassis. According to the test results, the in-cylinder maximum pressure of the next pressure cycle can be predicted fairly well, and the spark timing can be regulated to keep the in-cylinder maximum pressure in a desired band to reduce the cyclic variations. At fixed spark timing experiments, the COVpmax and COVimep were 3.764 and 0.677%, whereas they decreased to 3.208 and 0.533% when GMV controller was applied, respectively.

Journal: Journal of Renewable and Sustainable Energy

Title: Effects of using vortex tubes on events during cold start of a direct injection diesel engine

DOI: 10.1063/1.4798489

Abstract:

Vortex tubes use a compressed gas flow and separate it into low and high temperature regions without using any moving mechanical parts. Cold and hot exhaust flows of vortex tubes can be used for different purposes. In this study, a vortex tube was used to improve the cold start performance of a six cylinders, four stroke and direct injection diesel engine of a truck. To increase the engine intake air temperature, hot exhaust of vortex tube was introduced to the engine intake manifold. Pressured air was supplied to the vortex tube from the air tank of the compressed-air brake system of the truck. Variation in the cold starting events was observed by both in cylinder pressure data and revolution of engine crank shaft. Experiments were started when the ambient air and engine cooling fluid temperatures were at 0 °C, which is a critical temperature for cold-starting diesel engines. Experimental results showed that the cold starting performance of the engine can be successfully improved by using vortex tubes. Durations of engine starting-cranking, cranking-idling, and idling-stabling were decreased due to the increase in the intake air temperature.

Journal: Applied Thermal Engineering

Title: Engine performance, exhaust emissions, and cyclic variations in a lean-burn SI engine fueled by gasoline-hydrogen blends

DOI: 10.1016/j.applthermaleng.2011.10.039

Abstract:

The purpose of this study is to investigate the effect of adding small amounts of hydrogen to gasoline–air mixtures on the performance and exhaust emission characteristics of a spark ignition engine. Four air–fuel ratios are used ranging from stoichiometric to very lean. The amount of hydrogen added is varied from 0% to 2.14%, 5.28%, and 7.74% by volume. The test engine is operated at 2000 rpm, and measurements are made over 1000 consecutive engine cycles. From the experimental observations, the effect of hydrogen addition on (a) thermal efficiency, (b) specific fuel consumption, (c) cyclic variations of the indicated mean effective pressure (IMEP), and (d) emissions of CO, NO and unburned hydrocarbons are analyzed. The cyclic IMEP variations are analyzed using the coefficient of variation (COV) and wavelet analysis. An advantage of wavelet analysis is that it can identify the dominant modes of variability and delineate the engine cycles over which these modes may persist.

Journal: Energy Sources, Part A: Recovery, Utilization, and Environmental Effects

Title: Analysis of Combustion Stability and Its Relation to Performance Characteristics in a Compression Ignition Engine Fueled with Diesel-biodiesel Blends

DOI: 10.1080/15567030903261790

Abstract:

This article investigates the effects of using diesel-biodiesel blends on compression ignition engine performance characteristics. Combustion stability observed from in-cylinder pressure related parameters, biodiesel composition, and the fuel properties of the blends are used to analyze the variations of the characteristics. Making biodiesel from hazelnut oil is done by esterification and then experiments are conducted with the neat diesel and diesel-biodiesel blends in a four stroke naturally aspirated direct injection diesel engine. Volumetric blending ratios of biodiesel with no. 1 diesel were set at 0, 20, 40, 60, 80, and 100. It has been found that, in general, the hazel nut oil-based biodiesels behave comparably to the diesel fuel in terms of engine performance characteristics. There is no significant brake torque and power reduction, and there is a slight increase in brake specific fuel consumption when the engine is operated with diesel-biodiesel blends. The engine effective efficiency shows improvements as compared to that of the diesel fuel operating under similar conditions, especially at low blending ratios of biodiesel. The engine performance characteristics and exhaust emissions improve remarkably at B20 operations and identifying the mechanism for biodiesel blending effects is attempted.

Journal: Applied Thermal Engineering

Title: A Taguchi approach for optimization of design parameters in a tube with coiled wire inserts

DOI: 10.1016/j.applthermaleng.2011.04.022

Abstract:

This study presents the determination of the optimum values of the design parameters in a tube with equilateral triangular cross-sectioned coiled wire inserts. The effects of the design parameters such as the ratio of the distance between the coiled wire and test tube wall to tube diameter (s/D), pitch ratio (P/D), ratio of the side length of equilateral triangle to tube diameter (a/D) and Reynolds number (Re) on heat transfer and pressure drop were investigated by using Taguchi method. The Nusselt number and friction factor were considered as performance parameters. An L9(34) orthogonal array was chosen as experimental plan. The goal of this study is to reach maximum heat transfer (i.e. Nusselt number) and minimum pressure drop (i.e. friction factor). First of all, each goal was optimized, separately. Then, all the goals were optimized together, considering the priority of the goals. Contribution ratios for each parameter on the heat transfer and pressure drop were determined. Consequently, the optimum results were found to be s/D = 0.0357, P/D = 1, a/D = 0.0714 and Re = 19800.

Journal: Journal of Thermal Science and Technology (Isı Bilimi ve Tekniği Dergisi)

Title: Analysis of the thermal efficiency and cyclic variations in a SI engine under lean combustion conditions

DOI: Access link

Abstract:

There are significantly variations in cylinder pressure traces from cycle to cycle in spark ignition engines. The variations, named cyclic variations, exist even when engine is stable. Cyclic variability must be considered in the design and control of spark ignition engines and are magnified under certain engine operating conditions. In this work, effects of air excess coefficient on cyclic variability, engine performance characteristics and engine emission characteristics were investigated at lean operation conditions. The test engine is a spark ignition engine with electronically controlled fuel injectors. According to the test results, engine air excess coefficient can be increased to improve engine thermal efficiency and to decrease the harmful exhaust emissions under low load conditions without exceeding the limit of cyclic variability.

Journal: Applied Thermal Engineering

Title: Effects of ethanol-unleaded gasoline blends on cyclic variability and emissions in an SI engine

DOI: 10.1016/j.applthermaleng.2004.07.019

Abstract:

One important design goal for spark-ignited engines is to minimize cyclic variability. A small amount of cyclic variability (slow burns) can produce undesirable engine vibrations. On the other hand, a larger amount of cyclic variability (incomplete burns) leads to an increase in hydrocarbon consumption and emissions. This paper investigates the effects of using ethanol-unleaded gasoline blends on cyclic variability and emissions in a spark-ignited engine. Results of this study showed that using ethanol-unleaded gasoline blends as a fuel decreased the coefficient of variation in indicated mean effective pressure, and CO and HC emission concentrations, while increased CO2 concentration up to 10vol.% ethanol in fuel blend. On the other hand, after this level of blend a reverse effect was observed on the parameters aforementioned. The 10vol.% ethanol in fuel blend gave the best results.