Héctor González-Camarillo, Alessandro Gallo, Isabel Padilla, Carlos A. Pérez-Rábago, Charles-Alexis Asselineau, Maximina Romero, Aurora López-Delgado
2024
Abstract
The use of Fresnel lenses for solar energy concentration technology dates back to the 1950 s. These lenses feature a plano-convex optical design with a series of discontinuous convex grooves. Typically made from materials like polymethyl methacrylate, Fresnel lenses are lightweight, resistant to sunlight, thermally stable, and cost-effective.
This study presents a novel Fresnel lens-based solar furnace configuration installed at the Eduardo Torroja Institute for Construction Science in Madrid, Spain. The novelty of this work lies in the exceptional performance and operability of the facility. Experimental characterization revealed a record peak irradiance over 7 MW m−2 for an incident target power exceeding 800 W. Comparison with ray tracing simulations shows good agreement with experimental results. This setup enables high temperature experiments up to 2000 °C with rapid execution times. A fixed receiver, a shutter system and a closed-loop heliostat tracking control system allow for flexible operation up to 5000 suns and straightforward maintenance. The concentrator element costs less than 300 USD (2022) m−2, offering an economical solution to solar-powered high concentration and temperature applications. This innovative design overcomes previous operational challenges, providing a robust and economical method for high-temperature material processing and other industrial applications.
Arturo Aspiazu-Méndez, Nidia Aracely Cisneros-Cárdenas, Carlos Pérez-Rábago, Aurora M Pat-Espadas, Fabio Manzini-Poli, Claudio A Estrada
2024
Abstract
The state of Sonora, Mexico, stands as one of the leading producers of pecan nuts in the country, which are commercialized without shells, leaving behind this unused residue. Additionally, this region has abundant solar resources, as shown by its high levels of direct normal irradiance (DNI). This study contributes to research efforts aimed at achieving a synergy between concentrated solar energy technology and biomass pyrolysis processes, with the idea of using the advantages of organic waste to reduce greenhouse gas emissions and avoiding the combustion of conventional pyrolysis through the concentration of solar thermal energy. The objective of this study is to pioneer a new experimental analysis methodology in research on solar pyrolysis reactors. The two main features of this new methodology are, firstly, the comparison of temperature profiles during the heating of inert and reactive materials and, secondly, the analysis of heating rates. This facilitated a better interpretation of the observed phenomenon. The methodology encompasses two different thermal experiments: (A) the pyrolysis of pecan shells and (B) the heating–cooling process of the biochar produced in experiment (A). Additionally, an experiment involving the heating of volcanic stone is presented, which reveals the temperature profiles of an inert material and serves as a comparative reference with experiment (B). In this experimental study, 50 g of pecan shells were subjected to pyrolysis within a cylindrical stainless-steel reactor with a volume of 156 cm3, heated by concentrated radiation from a solar simulator. Three different heat fluxes were applied (234, 482, and 725 W …
NA Cisneros-Cárdenas, RA Pérez-Enciso, CA Pérez-Rábago, RA Calleja-Valdez, VM Maytorena-Soria, R García-Gutiérrez, RE Cabanillas-Lopez
2023
Abstract
This paper presents an experimental assessment of a reactor-receiver system that enables easy substitution of different receivers. The study evaluates two receivers with difference PPI sizes under various operating conditions that can withstand the use of high-temperature HTF. Environmental air was employed as the heat transfer fluid. SiC receiver with 10 and 20 PPI were tested individually, and then the heat transfer fluid. SiC receivers with 10 and 20 PPI were tested individually, and then the heat transfer surface was increased by placing an additional receiver behind (1010 and 2020 PPI). Additionally, combinations of PPI sizes were tested, such as 1020 PPI and 2010 PPI, to explore the potential effect of the orders. The authors calculated the thermal efficiency through calorimetry and compared it with similar solar concentration technologies detailed in existing literature. The results revealed that the highest temperature was achieved with the 20 PPI receiver (655 °C) compared to the other studied cases. It is established that losses are generated in the receiver due to convection and radiation, and the paper provides recommendations to improve the energy conversion efficiency.
Manterola-Villanueva Gustavo, Pérez-Rábago Carlos Alberto, Gómez-Espinoza Víctor Hugo, García-Valladares Octavio
2023
Abstract
Parabolic Trough Concentration (PTC) systems represent the best alternative for implementing solar energy in different sectors due to their reachable temperatures and maturity levels. However, there is a notably lack of normativity for evaluating the experimental thermal performance curves of these systems. For this reason, a new methodology is proposed to solve problems arising in the thermal characterization of them. This methodology allows to evaluate the system at any time of year without a two-axis tracking system, using experimental data and projections based on a ray tracing model. To validate the methodology, a PTC system was evaluated during solstices and equinoxes. Variations in experimental thermal performance response along the year caused by solar declination; were observed, reaching a maximum loss of 45% of received power and 22% in efficiency for the lowest solar altitude conditions. The ray tracing model methodology was applied to the experimental thermal performance curves obtained along the year to get the best efficiency curve. The good approximation of the projections made with this methodology helped us to consider it validated. With this method, it is also possible to easily obtain a family of curves describing the power and performance of the system throughout the year and wherever it is installed.
Irving Cruz-Robles, Jorge M. Islas-Samperio, Elisa Alonso, Alfonso J. Vázquez-Vaamonde, Carlos A. Pérez-Rábago, Claudio A. Estrada
2023
Abstract
The work explores the idea of using high-temperature solar heat in the copper smelting process; a Hybrid Central Tower system is analyzed to supply the high-temperature air for this process. The methodology was built based on the equilibrium of the smelting reactions; therefore, this analysis only account for the reactions’ energy demand. Two process schemes (process with/without using high-temperature air) and five off-gas scenarios were evaluated. Using Hybrid Central Tower systems with 13 h of Thermal Energy Storage leads to significant reductions in the annual equivalent energy consumption of the reactions (up to 22.61 %) and in the CO2 emissions of the smelting process (up to 61.4 %). The scheme that doesn’t use high-temperature air is the lower-cost option; however, with a 15 % reduction in the capital expenditure and using a discount rate of 5 %, the scheme that uses Hybrid Central Tower systems with 13 h of Thermal Energy Storage shows the similar present value costs. If a carbon price of 25 USD/tCO2e is included, the latter scheme represents the lower-cost option and the most cost-effective solution to avoid CO2 emissions.
Nidia Aracely Cisneros-Cárdenas, Rafael Cabanillas-López, Ricardo Pérez-Enciso, Guillermo Martínez-Rodríguez, Rafael García-Gutiérrez, Carlos Pérez-Rábago, Ramiro Calleja-Valdez, David Riveros-Rosas
Publicado 28 de Octubre 2021
The radiation flux distributions produced by the concentrating solar systems used to produce thermal/electrical power are usually non-homogeneous. This results in non-uniform temperature distributions on the solar receivers, causing adverse effects on the system’s overall performance. An approach to better understand the problem is to study the surfaces around the focal zone where the radiation density is homogeneous (isosurfaces), generating them from experimental data. For this, it is necessary to superimpose built volumes of the different irradiance levels using parallel planes in different directions from the focal point of a concentrator. These volumes are known as effective volumes. This study presents the model used to generate effective volume produced by a point focus concentrator, comparing it with experimental results in a direction perpendicular to the focal axis. The effective volumes were developed considering a global optical error of the system of 2.8 mrad. The set of methods used to generate effective volumes has not been previously presented in the literature. The theoretical-experimental research consisted of the combination of the camera-target method and the simulations by the ray-tracing technique. The results showed effective volumes with the highest value of 10 MW/m2 and the lowest value of 4.5 MW/m2.
Yannely Carvajal-Campos, Laura Ceballos-Mendivil, Francisco Baldenebro-López, Carlos Pérez-Rábago, Claudio A Estrada
Publicado 13 de Agosto 2019
Tantalum carbide (TaC) nanoparticles were synthesized using the IER-UNAM (HoSIER) solar furnace, which reduces polluting gas emissions and dependence on fossil fuels through the use of concentrated solar energy. TaC synthesis was performed through a carbothermal reduction method from Ta/O/C complex, using tantalum pentachloride (TaCl5) and synthesized phenolic resin as sources of tantalum and carbon, respectively, at a temperature of 1200 °C, in a reaction time of 30 min, under argon atmosphere. A solar reactor equipped with a quartz window was used, designed to work in controlled atmospheres. Complex Ta/O/C bonds and thermal decomposition were analyzed by FT-IR and TG/DSC, respectively, while the structure and morphology of TaC were analyzed by XRD, TEM, and SEM techniques. Results showed a TaC with a cubic crystalline structure, a low amount of Ta2O5 and a near-spherical ...
Alejandro Ayala-Cortés, Pedro Arcelus-Arrillaga, Marcos Millan, Camilo A. Arancibia-Bulnes, Patricio J.Valadés-Pelayo, Heidi Isabel Villafán-Vidales
Publicado 4 de Diciembre 2020
Hydrothermal processes are attractive options for the transformation of mixtures of biomass with large amounts of water, i.e. above 20wt. At hydrothermal conditions, the special properties of water makes it an attractive reaction medium to obtain several bio-based platform chemicals or fuel gases, such as hydroxymethilfurfural or fufurals, syngas, hydrogen, methane, etc. However, one of the main challenges is that a large amount of energy is required to heat reactants (mixture of water and biomass), which is usually achieved by combustion of a fraction of the bio-oil product. Therefore, to reduce this consumption, their integration with an external renewable energy source, such as concentrated solar radiation has been proposed. This approach has been recently analyzed by several research groups as an option to have sustainable and economically attractive processes. This work provides an overview of the different experimental and theoretical strategies to incorporate concentrated solar technologies into hydrothermal processing of biomass, including the main challenges of such integration for process technical feasibility.
H. Romero-Paredes, A. Santamaría-Padilla, CA Arancibia-Bulnes, HI Villafán-Vidales
Publicado 5 de noviembre 2020
El objetivo de este trabajo es la caracterización térmica de un reactor solar de cavidad multitubular (M&M) bajo radiación solar concentrada del horno solar del Instituto de Energías Renovables de la UNAM (HoSIER); concebido para realizar reacciones termoquímicas de producción de combustibles limpios como son el hidrógeno y gas de síntesis. Ha habido diversas propuestas de reactores solares, pero no se ha estudiado de manera experimental los efectos que tiene la distribución geométrica de los tubos dentro de la cavidad en su comportamiento térmico, en la inercia térmica ante los cambios de la irradiancia solar y con el flujo de aire dentro de los mismos. La caracterización se realizó en función del arreglo de los tubos en la cavidad, la estabilidad y homogeneidad de la temperatura entre los tubos y la evaluación de la inercia térmica del reactor en función de las variaciones de la irradiancia solar. Los resultados muestran que el arreglo propuesto tiene una buena estabilidad térmica y puede responder fácilmente ante cambios súbitos en la irradiancia solar. La diferencia mínima de temperatura alcanzada entre los tubos fue de 72ºC cuando la temperatura del tubo central fue de 1200ºC, equivalente a 6% de diferencia.
Carlos E. Arreola-Ramos,Omar Álvarez-Brito,Juan Daniel Macías,Aldo Javier Guadarrama-Mendoza, Manuel A. Ramírez-Cabrera,Armando Rojas-Morin,Patricio J. Valadés-Pelayo,Heidi Isabel Villafán-Vidales and Camilo A. Arancibia-Bulnes
Publicado: 27 April 2021
Reticulate porous ceramic reactors use foam-type absorbers in their operation which must fulfill two essential functions: favoring the volumetric effect and increasing the mass and heat transfer by acting as a support for the reactive materials. Heating these absorbers with highly inhomogeneous concentrate irradiation induces high thermal gradients that affect their thermal performance. Owing to the critical function of these component in the reactor, it is necessary to define a selection criterion for the foam-type absorbers. In this work, we performed an experimental and numerical thermal analysis of three partially stabilized zirconia (PSZ) foam-type absorbers with pore density of 10, 20, and 30 PPI (pores per inch) used as a volumetric absorber. A numerical model and an analytical approximation were developed to reproduce experimental results, and calculate the thermal conductivity, as well as volumetric heat transfer coefficient.
The results show that an increase in pore density leads to an increase in the temperature difference between the irradiated face and the rear face of the absorber, this occurs because when pore density increases the concentrated energy no longer penetrates in the deepest space of the absorber and energy is absorbed in areas close to the surface; therefore, temperature gradients are created within the porous medium. The opposite effect occurs when the airflow rate increases; the temperature gradient between the irradiated face and the rear face is reduced. This behavior is more noticeable at low pore densities, but at high pore densities, the effect is less relevant because the internal structure of porous absorbers with high pore density is more complex, which offers obstructions or physical barriers to airflow and thermal barriers to heat transfer.
When the steady state is reached, the temperature difference between the two faces of the absorber remains constant if the concentrate irradiation changes slightly, even changing the airflow rate. The results obtained in this work allow us to establish a selection criterion for porous absorbers that operate within solar reactors; this criterion is based on knowledge of the physical properties of the porous absorber, the environment, the working conditions, and the results expected.
Alfonso Encinas‐Vázquez, Javier Alan Quezada‐Renteria, Francisco J Cervantes, Carlos A Pérez‐Rábago, Francisco E Molina‐Freaner, Aurora M Pat‐Espadas, Claudio A Estrada
Publicado 13 de Ocgtubre 2020
The synthesis gas or hydrogen‐rich gas, at longer residence times and higher temperatures, is frequently the target of pyrolysis biomass. Biochars obtained at such conditions contain less functional groups but they are more effective for longer‐term soil C storage. The aim of this study was to elucidate the adsorption mechanisms and the effect of the ageing process on high‐temperature biochar towards lead adsorption. The biochars under study were produced from the pyrolysis of almond wood and olive tree pruning.
The almond hardwood biochar was the most susceptible to the oxidation process. This biochar exhibited higher carbon loss than the olive biochar, 22.07% and 11.76%, respectively. The adsorption process was better described by the Langmuir model and pseudo‐second order kinetics. The maximum adsorption capacity decreased from 40.3 to 24.8 mg g–1 after the oxidation process for almond‐derived biochar and remained unchanged for the olive‐biochar. Analyses demonstrated that 67% of the adsorbed Pb2+ was removed through complexation by oxygen functionalities and phosphorous compounds. After the oxidation process, this fraction accounted for only 45% of the adsorbed Pb2+, ion exchange and cation‐π being the most prominent mechanisms for the adsorption.
Diego Ramón Lobato-Peralta, Estefanía Duque-Brito, Heidi Isabel Villafán-Vidales, Adriana Longoria, P.J.Sebastian, Ana Karina Cuentas-Gallegos, Camilo Alberto Arancibia-Bulnes, Patrick U. Okoye
Publicado 28 de enero 2021
The various lignin isolation methods and pretreatments are continuously developing and thermochemical conversion of lignocellulosic biomass and tuning of the activation parameters are vital to obtaining high energy density materials. In this review, different lignin extraction methods, pretreatments, and influence of the extraction conditions on the yield and properties are presented. The thermochemical conversion of lignin-based biomass and application in supercapacitors and hydrogen storage were investigated.
The study revealed that chemical extraction via the organosolv process presents higher purity and partly preserved lignin structure compared to sulfur processes. Different parameters such as the method of extraction, the temperature, pH, resident time, and pressure greatly influences the Kappa value and yield of lignin. The potassium hydroxide (KOH) dosage as an activating agent and the activating temperature is vital to obtaining high surface area and microporosity, which enhances the lignin-based activated carbon performance towards high hydrogen storage and capacitance. Metals doping on activated carbon marginally enhance the hydrogen storage capacity and capacitance, however, reversible desorption of the adsorbed hydrogen requires a higher temperature for hydrogen storage. Besides, high metal doping reduces available surface area, collapses the cage-like structures of fullerenes, and results in lower hydrogen storage capacity of activated carbon.
The presence of heteroatoms on activated carbons enhances the performance towards high hydrogen storage and capacitance. Moreover, techno-economic and exergy-based sustainability analysis of the different lignin isolation techniques must be explored to provide valuable insights on energy and associated operational costs.
Oscar A. Jaramillo-Quintero, Royer Valentín Barrera-Peralta, Abdel Ghafour El Hachimi, Alfredo Guillén-López, Obed Pérez, Edilso Reguera, Marina Elizabeth Rincón, Jesús Muñiz
Publicado 21 de Octubre 2020
Increasing the electrochemical performance of electrode materials in sodium ion batteries (NIBs) remains a major challenge. Here, a combined experimental and theoretical investigation on the modification induced by Sb2S3 embedded in a heteroatom-doped 3D carbon matrix (CM) for efficient anodes in NIBs is presented. The structural and chemical characterization demonstrates the successful doping of 3D CM with S and Sb atoms. When evaluated as anode materials for NIBs, the heteroatom-doped nanocomposites delivered a better cycling stability and superior rate capability than those of undoped Sb2S3/CM anodes. First principle calculations were used at the Density Functional Theory level to systematically study the Sb2S3/CM and Sb2S3/heteroatom doped-CM composites, as NIBs anodes. Doping the carbon substrate by heteroatoms improved the adsorption of Sb2S3 on the matrix and allowed for ionic/covalent attraction with the Sb2S3 nanoparticle, respectively. Such results could be used to model the stabilty of the composite architectures observed in the experiment, for superior cycling stability.
Jazael Gómez, Arturo Estrada, Argelia Balbuena Ortega, Oscar Arredondo, Rocío Nava, Raul Barbosa, Dulce Capitanachi & Karen Lozano
Publicado 6 de febrero 2021
Hybrid graphemne-fiber systems could present an alternative for various industrial applications in need of large area graphene sheets. One way to produce these carbon-based structures is by subjecting an aqueous polyvinyl alcohol solution containing sodium chloride to centrifugal spinning under high humidity conditions. The developed polymer fibers are then subjected to a dehydration and carbonization process to promote the formation of the hybrid carbon structure. Potential applications of this material are highly dependent upon their conducting properties. In this work we analyzed the effect of the NaCl content and humidity conditions during the spinning process and ultimate thermal conductivity of the resultant hybrid graphene-fiber carbon systems. Results show an optimum NaCl added to the carbon precursor solution and spun at a high relative humidity (around 70%) promote the development of veils of graphene oxide multilayer that interconnect with produced fibers. We applied for the first time a thermographic method to determine the thermal conductivity of carbon mats. The thermal conductivity of the hybrid fibers increases as graphene multilayers veils expand between carbon fibers, to reach values up to 28 W m K−1.
Isaías Moreno-Cruz,Juan Carlos Castro,Omar Álvarez-Brito,Hilda B. Mota-Nava,Guillermo Ramírez-Zúñiga,José J. Quiñones-Aguilar and Camilo A. Arancibia-Bulnes
Publicado 4 de Agosto 2020
Heliostats are critical components of solar tower technology and different strategies have been proposed to reduce their costs; among them diminishing their size to reduce wind loads or linking nearby heliostats mechanically, to reduce the overall number of actuators. This document aims to describe the development of a linked array of mini-heliostats which move together in an elevation–Fresnel configuration. This configuration consists of an array of mirrors rotating around linked parallel axes, in a linear Fresnel style with an added elevation mechanism allowing all axes to incline simultaneously in the plane North–South–Zenith; that is equivalent to an array of N linked mini-heliostats moved by only two drives instead of 2N. A detailed analytical study of the Sun-tracking performance of this kind of heliostat arrays was carried out, and an 8-mirror prototype based on optical and mechanical analyses was designed, built and tested. Even though the mirrors are flat, the array produced a rather compact radiative flux distribution on the receiver. The flux distribution is compatible with a slope error of the order of 1 mrad. Peak and mean concentration ratios reached 6.89 and 3.94, respectively.
Laura G Ceballos-Mendivil, Yannely Carvajal-Campos, Judith Tánori-Córdova, Jonathan C. Luque-Ceballos, Heidi Villafán-Vidales and Claudio A. Estrada
Publicado 27 de Noviembre 2020
The use of concentrated solar energy in processing ceramic materials is an attractive route to obtain these materials with low CO2 emissions. In this work, nanostructures of monoclinic zirconia (m-ZrO2) were obtained using concentrated solar energy provided by the IER-UNAM solar furnace as a heat source. In the first stage of the process, a Zr/O/C complex was obtained by sol-gel method at a temperature of 120 °C using zirconium n-propoxide and sorbitol as precursors reagents. This complex was used in a second stage to obtain m-ZrO2 by heating it at a temperature of 1200 °C for one hour in air atmosphere. This last stage was performed in a solar furnace. Samples were analyzed by characterization techniques: FT-IR, TGA/DSC, XRD, TEM, and SEM confirming the formation of nanostructures of zirconia in monoclinic phase.
Oscar Andrés Jaramillo-Quintero, Yarimeth Ameyalli Alarcón-Altamirano, Ramses Alejandro Miranda-Gamboab, Marina Elizabeth Rincón
Publicado 19 Mayo 2020
Interfacial charge transfer is a determining factor for the development of highly efficient solar cells. In antimony-based solar cells, interfacial engineering at the absorber/electron transport material interface relies on the use of a toxic CdS interlayer. In this work, an environmental-friendly interfacial engineering approach for planar Sb2S3 solar cells was implemented by using graphene-based nanoribbons. Graphene nanoribbons (GNR) and sulfur-doped graphene nanoribbons (S-GNR) sheets were incorporated as interlayer between TiO2 and Sb2S3 films in planar Sb2S3 solar cells, resulting in an enhanced photovoltaic performance up to 4.1%. Kelvin probe and C-V measurements revealed that the improvement was related to the superior built-in voltage due to the lower work function of the graphene-based interlayers along with a suitable cascade interfacial charge transfer. More importantly, surface photovoltage transient and intensity-modulated photocurrent and photovoltage spectroscopies also demonstrated that the presence of these interlayers decreased the electron transport time and suppressed the formation of interfacial states, which in turns reduced the interfacial recombination pathways boosting the performance of the devices fabricated. Although S-doped GNR provides the best results, more work is in progress to determine the cause of increased efficiency and the lack of significant Voc increase.
Montoya De Los Santos, Hugo J.Cortina-Marrero, M.A.Ruíz-Sánchez, L.Hechavarría-Difur, F.J.Sánchez Rodríguez, Maykel Courel, Hailin Hu
Publicado 13 de Febrero 2020
#2020
In this work, an experimental and theoretical study on CH3NH3PbI3 perovskite solar cells was performed. A theoretical validation of experimental results in perovskite solar cells with efficiencies of 13.32% is presented. An optimization study which involves the spiro-OMeTAD and perovskite thickness’ influence on electrical output parameters (Voc, Jsc, FF and PCE) showed a promotion of solar cell efficiency to 15.50% under 100 nm and 400 nm for hole transport material and absorber, respectively. The importance of the diffusion length of the absorber is discussed. In order to enhance the efficiency, a study of defect density (NT) was applied at the range of 1016 cm−3 (experimental) to 1010 cm−3 (theoretical) where we achieved an efficiency of 20.26%. The present work illustrates the importance of thickness optimization and the reduction of defect density (by the improvement of the quality of processed film) to obtain a better performance of this type of solar cell. Furthermore, the relevance of the implementation of a back contact with higher work function was studied.
Carlos Fabián, Arias-Ramos, Yogesh Kumar, Paola Gabrielz Abrego-Martínez, Hailin Hu
Publicado 18 de Junio 2020
The use of controlled inert ambient to produce hybrid perovskite solar cells (PSCs) makes them less competitive towards the commercialization. Herein, progress is made with the preparation of hybrid perovskite (CH3NH3PbI3) in a high relative humidity (RH ~ 60%) ambient condition by using a mixture of ethyl acetate (EA) and 4-Tertbutyl-Pyridine (tBP) as anti-solvent. A small amount of tBP helps to form a more homogeneous perovskite surface with a higher hydrophobicity. The mixture of EA and tBP is found to be an efficient anti-solvent to extract the primary solvent and moisture in the precursor solution and form mirror-like perovskite thin films.
More than 200 perovskite solar cells, with active area of 0.1 cm2, were prepared with the perovskite thin films prepared under ambient conditions. It is showed that a small amount of tBP in EA improves consistently all the photovoltaic parameters of our PSCS, from an average efficiency of 8.64% over 113 cells with only EA as anti-solvent to 13.64% over 131 cells with EA + tBP as the anti-solvent. More than 55% of the last ones show efficiencies higher than 16%. The champion cell, recording an efficiency of 17.41% in the beginning and reaching the maximum efficiency of 18.04%, remains more than 80% of the initial efficiency after more than 180 days of storage in ambient conditions without encapsulation. The proposed method opens the possibility to fabricate highly efficient and stable perovskite solar cells under ambient condition without glove box.
Asiel N. Corpus-Mendoza, Brandon S. Cruz-Silva, Guillermo Ramirez-Zúñiga, Paola M. Moreno-Romero, Feng Liu & Hailin Hu
Publicado: 18 de Febrero 2020
Hybrid perovskite films are prepared via two-step spin coating. The impact of magnetic fields during the spin coating of the PbI2 precursor solution is assessed with atomic force microscopy and scanning electron microscopy of the obtained layers. Deeper and narrower peak–valley–peak formations are obtained in PbI2 films when the magnetic field applied and the spinning direction result in a Lorentz force that pushes the [PbI6]4− ions towards the inner area of the substrate. This produces rougher and more porous PbI2 films with an increased surface area that facilitates the infiltration of the methylammonium iodide and chloride precursor solution, thereby enhancing the formation of perovskite. Increased cell performance and more repeatable results are obtained when the PbI2 film is spin-coated under the influence of a negative magnetic field. Opposite effects are obtained when the direction of the magnetic field, and therefore the Lorentz force, is inverted. This demonstrates that a magnetic field can be used to modify the surface morphology of spin-coated thin films prepared from ionic precursor solutions.
Diana C. Martínez-Casillas, Ivan Mascorro-Gutiérrez, Maria L. Betancourt-Mendiola, Gabriela Palestino, Enrique Quiroga-González, Jojhar E. Pascoe-Sussoni, Alfredo Guillén-López, Jesús Muñiz & A. Karina Cuentas-Gallegos
Publicado:29 de Septiembre 2020
In this work, it is proven that a biochar obtained from a commercial gasifier can be used as electrode material for supercapacitors (SC). This biochar was produced at 1000 °C from corn cob wastes (GAS), and was compared to an activated biochar obtained in a traditional lab pyrolysis process (LAB). Both biochars were characterized by different physicochemical techniques, observing their amorphous nature with well-developed microporosity dependent of their pretreatment and production methodology. Furthermore, a computational modeling based on Molecular Dynamics at the ReaxFF level was also performed to elucidate the geometry of the resulting microporous structure after simulated pyrolysis. X-ray structure and pore size distribution are in agreement with those results obtained via computational simulation. Both carbon materials were electrochemically evaluated in acidic electrolyte using 3 and 2 electrode systems, obtaining capacitances of 130 F g−1 (20 mV s−1), and excellent performance compared to commercial activated carbons, with only about 10% of capacitance loss after 5000 cycles. However, GAS performance in SC was higher than activated biochar due to its higher micropore volume. This study provides a novel useful application to use gasifier residues from agricultural biomass waste for energy storage devices.
Diego Ramón Lobato-Peralta, Daniella Esperanza Pacheco-Catalán, Patricia Eugenia Altuzar-Coello, François Béguin, Alejandro Ayala-Cortés, Heidi Isabel Villafán-Vidales, Camilo Alberto Arancibia-Bulnes, Ana Karina Cuentas-Gallegos
Publicado: 7 de Agosto 2020
This work aims to propose a sustainable green process to obtain bio-derived carbons (BDCs) for utilization in supercapacitors. The process consists in carrying out solar pyrolysis to produce BDCs from abundant lignocellulosic wastes, Agave Angustifolia leaves and pruned tomato plant. Concentrated solar radiation from a high flux solar furnace was utilized to reach sample temperatures between 450 and 1564 °C in a spherical reactor. Before pyrolysis, both wastes were characterized by thermogravimetric analysis to semi-quantify cellulose and hemicellulose as well as ash content. XRD was used to determine the ash composition in both wastes, and the effect of solar pyrolysis temperature on the obtained BDCs. Additional structural properties of BDCs were analyzed by SEM, Raman spectroscopy, and physisorption.
Elemental analysis and EDAX were used to determine the chemical composition of wastes, and the effect of this on BDCs. Electrochemical properties of BDCs were analyzed by cyclic voltammetry in half cells, and those showing better performance were also tested in supercapacitor cells. Results show that BDCs from tomato plant waste have higher surface areas, with well-developed microporosity, without needing an additional activation process. This is attributed to self-activation during pyrolysis, produced by the high K and Ca content of the tomato plant pruning. Ragone plots indicate that the assembled supercapacitor cells employing the best BDCs from solar pyrolysis have specific energies and power values similar to a commercial carbon designed for supercapacitors. These results indicate that the proposed green procedure is suitable for obtaining BDCs with properties suitable for supercapacitors.
Rohini Neendoor Mohan, M.T.S.Nair, P.K.Nair
Publicado: 14 Octubre 2019
As a semiconductor of “earth-abundant” elements, Sn2S3 with a bandgap (Eg) close to 1 eV merits attention, but a method to prepare phase-pure thin film remains elusive. We report the formation of Sn2S3 thin film of 360 nm in thickness by heating chemically deposited tin sulfide thin films at 450 °C during 30–45 min in presence of sulfur at a pressure, 75 Torr of nitrogen. Energy dispersive x-ray emission spectra and grazing incidence x-ray diffraction established a reaction route for this conversion of SnS completely to Sn2S3 via an intermediate phase, SnS2. The optical bandgap of the material is 1.25 eV (indirect) and 1.75 eV (direct, forbidden). The optical absorption suggests a light-generated current density of 30 mA/cm2 for the Sn2S3 film (360 nm) as a solar cell absorber. Thin film Sn2S3 formed in 30 min heating has a p-type electrical conductivity in the dark of 1 × 10−4 Ω−1 cm−1, which increases to 3 × 10−4 Ω−1 cm−1 in 0.2 s under 800 W/m2 tungsten-halogen illumination. An estimate made for its mobility-lifetime product is, 6 × 10−6 cm2 V−1. We discuss the prospects of this material for solar cells.
Carlos A. Rodríguez-Castañeda, Paola M. Moreno-Romero, Asiel N. Corpus-Mendoza, Guillermo Suárez-Campos, Margarita Miranda-Hernández, Mérida Sotelo-Lerma, Hailin Hu
Publicado:11 de Septiembre 2020
The acid–base chemistry at the interface of zinc oxide (ZnO) and methylammonium lead tri-iodide (perovskite) leads to a proton transfer reaction that results in perovskite degradation. In perovskite solar cells (PSCs), this reaction produces low efficiency and reduces the long-term stability. In this work, an aluminum (Al) layer of 1–2 nm thickness is thermally evaporated on top of ZnO or Al3+-doped ZnO (ZnO:Al) thin films and then annealed at 450 °C for 30 min. Thermal annealing converts the surface aluminum film into a transparent and approximately 2 nm thick aluminum oxide (AlOx) layer. Also, a larger concentration of oxygen vacancies is obtained by the annealing of Al and attributed to the diffusion of Al into the ZnO surface, and the ZnO underlayer results in a more conductive material.
As a result, the chemical stability of perovskite coatings on top of AlOx-coated ZnO films is significantly enhanced, and the flat-band level of ZnO shifts 0.09 eV upwards, which improves the energetic level alignment in PSCs. This allows us to obtain ZnO:Al/AlOx-based planar PSCs that show a maximum efficiency of 16.56% with the perovskite layer prepared in ambient conditions under a relative humidity of 40–50%. After continuous illumination of about 30 min in air, ZnO-based PSCs without AlOx layer retain only 34.5% of their original efficiency, whereas those with AlOx retain about 92.5%. It is demonstrated that thermal evaporation–oxidation is an efficient method to modify the surface properties of inorganic semiconductor thin films and improves both the performance and stability of PSCs.
V.M.Maytorena, J.F.Hinojosa
Publicado 21 de Marzo 2019
The purpose of this work is to analyze the effect of non-uniform concentrated solar radiation on direct steam generation in a vertical tube of solar tower receiver. The modified RPI model was used for the conditions of critical heat flux coupled to a Eulerian two fluid model. The mathematical model was solved with CFD software. The results were validated with experimental data reported in the literature and a parametric study was carried out to determinate the effect of non-uniform concentrated solar radiation, on the steam quality, the volumetric fraction, enthalpies and temperatures of liquid and steam. Non-uniform concentrated solar fluxes favor generation of steam but produce conditions that may influence the structural durability of DSG receivers, like high axial temperature gradients and zones with temperatures above the melting temperature of stainless steel.
Tantalum carbide (TaC) nanoparticles were synthesized using the IER-UNAM (HoSIER) solar furnace, which reduces polluting gas emissions and dependence on fossil fuels through the use of concentrated solar energy. TaC synthesis was performed through a carbothermal reduction method from Ta/O/C complex, using tantalum pentachloride (TaCl5) and synthesized phenolic resin as sources of tantalum and carbon, respectively, at a temperature of 1200 °C, in a reaction time of 30 min, under argon atmosphere. A solar reactor equipped with a quartz window was used, designed to work in controlled atmospheres. Complex Ta/O/C bonds and thermal decomposition were analyzed by FT-IR and TG/DSC, respectively, while the structure and morphology of TaC were analyzed by XRD, TEM, and SEM techniques. Results showed a TaC with a cubic crystalline structure, a low amount of Ta2O5 and a near-spherical …
Lúar Moreno-Álvarez, Andrés Amat-Castrillón
Publicado: 5 de Febrero 2019
We have found the flux homogenization technique described in the paper published in volume 93, pages 115–124 (august 2016), does not provide homogenized fluxes in all out-of-focus distances of the solar receiver, but only above a certain transition distance, and that some of the numerical analysis procedures used in that document should be revised or complemented to achieve better reproducibility of the results. In addition, we also note that some statements and conclusions in that document are mistaken or formulated incorrectly, so it is necessary their correction.
Alessandro Gallo, Elisa Alonso, Carlos Pérez-Rábago, Edward Fuentealba, María Isabel Roldán
Publicado: 5 de Julio 2019
Rotary kilns are worldwide used for industrial processes that involve thermal treatments of particulate materials. However, a great amount of fossil fuels is employed in such processes. As alternative, solar rotary kilns are considered for this application due to their versatility and potential to substitute traditional fossil-fuel driven devices. In order to boost the development of this technology, efforts have to be focused on the control of the particle temperature during the treatment. In this context, a lab-scale rotary kiln was built and tested using a 7-kWe high-flux solar simulator at University of Antofagasta. It was conceived to treat particulate materials of different nature and it is able to reach temperatures higher than 800 °C under different operation strategies. Silicon carbide was selected for initial tests because it is inert, endures high temperatures (up to 1600 °C) and it has been proposed as thermal storage vector in several researches on concentrated solar power. In a first stage, the empty kiln was preheated up to about 800 °C, reaching a steady state in less than three hours and with a power of approximately 370 W entering the kiln cavity. Afterwards, 43 g of silicon carbide were introduced in the furnace and the system was heated again up to a second steady state above 800 °C. In this stage, particles showed a fast increment of their temperature and exceeded 700 °C in less than three minutes after loading. A one-dimensional transient numerical model was also developed to perform the thermal analysis of the kiln and the estimation of both the particle temperature and the system efficiency. Numerical results showed good agreement with experimental data and thermal losses could be quantified in detail. Therefore, the model was also used to predict the thermal behavior of a solar rotary kiln working in batch mode..
Adriana E. Gonzalez-Cabrera, David Riveros-Rosas, Héctor Estevez, Anayeli Ramirez, Mauro G. Valdes, Camilo A. Arancibia-Bulnes and Luis F. Zarzalejo
Publicado: 1 de Enero 2018
The importance of solar tracking systems lies in the need to optimize the amount of solar radiation on solar collectors of different types. In this work, the monthly mean daily irradiation was analyzed on a flat surface of unitary area, under different tracking schemes of the Sun, by means of the use of a numerical model. For this purpose, solarimetric data was obtained from some stations of the new Mexican Solarimetric Network, the solar irradiance incident on a flat horizontal plate was calculated. Also, the movement of some tracking systems was carried out in steps with different time intervals in order to compare it with their respective continuous movement. It was found that stepped movements report yearly incident solar irradiation values above 98% respect to continuous movement in the widest interval.
Alejandro Ayala-Cortés, Camilo Alberto Arancibia-Bulnes, Heidi Isabel Villafán-Vidales, Diego Ramón Lobato-Peralta, Diana Cristina Martínez-Casillas, and Ana Karina Cuentas-Gallegos
Publicado 25 de Julio 2019
Agave angustifolia leaves and tomato pruning biomasses were processed into carbon materials by solar pyrolysis. The influence of temperature and heating rate was studied in the physicochemical properties of the obtained biochars. The characterization techniques include elemental analyses (CHONS), physisorption to determine surface area by BET and DFT models, and capacitance values were determined by cyclic voltammetry as the electrochemical technique. It was found that for both biomasses, temperatures below 900°C are beneficial because more homogeneous and porous structures are obtained. The highest values of capacitance and surface area were obtained for tomato carbons at 450 and 600 °C, respectively.
Omar Álvareza, Armando Rojas, Arturo Barba, Camilo A. Arancibia, Jorge Álvarez, Dulce V. Melo, Carlos E. Arreola
Publicado: 30 de Diciembre 2018
This study investigates the phase transformations that can occur in an austenitic stainless steel (AISI 316) by demonstrating the appearance of δ-ferrite that is obtained in the initial heating cycles using Concentrated Solar Irradiation (CSI) at magnitudes needed to obtain the operational temperatures of central tower systems. Four AISI 316 stainless steel specimens cut from one single initial piece, were exposed to CSI in the Horno Solar de Alto Flujo Radiativo at the Universidad Nacional Autónoma de México to perform the thermal cycles. AISI 316 stainless steel is fully austenitic and is selected because it is reportedly one of the cheaper material used in CSI receivers. Monotonic tensile strength tests were performed, and it is assumed that there is no relevant effect on the mechanical behavior for the reported experiment. Phase transformations were characterized using optical microscopy, X-ray diffraction and by scanning electron microscopy analysis with an energy-dispersive X-ray spectroscopy. The appearance of δ-ferrite phase was the principal difference between CSI treated specimens, a non-treated specimen and one specimen heated by conventional method. Concentrated UV irradiation from the solar spectrum on Earth surface demonstrated to have the potential to obtain the phase transformation at a temperature near 630 °C.
C. Iriarte-Cornejo, C.A. Arancibia-Bulnes, J.F. Hinojosa, Manuel I. Peña-Cruz
Publicado:17 de Septiembre 2018
The optical characteristics of solar concentrators are key factors influencing the overall efficiency of solar power plants. For instance, heliostats need to be evaluated prior to installation and during its operation lifetime. This guarantees that the optical and thermal performance of these systems is close to design. One methodology that has gained importance due to its potential capabilities has been the Fringe Reflection Technique. This technique uses the reflection of a series of regular stripes to obtain the local slope deviations from a specular surface. Coupled to a ray tracing analysis, these slopes can be used to identify the distortion in concentrated solar spots. The enormous amount of data needed to carry out this analysis difficult its implementation at large scale. In this work, a study for determining the optimal number of sample points for heliostat surface characterization is realized. It has been found that, depending on the level of errors, the number SPFS required to reach convergence in the flux distribution profiles and intercept factors is variable. However, for the wide range of parameters considered in all cases 48 SPFS where enough to reach convergences to 1%. This is equivalent to one point per every 2.5cm of facet side length. For values of slope and canting errors up to 2mrad, half this density is sufficient.
E Anguera, CA Estrada
Publicado: 2 de Julio 2018
In this paper, we present two statistical methods to quantify the heterogeneity of the irradiance flux distribution, in a Concentrator Photovoltaic (CPV) dense-array, based on its operation and the optimization of current-matching. Preventing non-uniform flux distribution from design avoids the generation of hot spots, current mismatch and increases the overall efficiency of the system. This new approach considers the effects of the lowest irradiance values in the performance of the complete array, and its performance was corroborated by the simulations of a CPV array modelled in Matlab/Simulink; the irradiance distribution data as an input parameter was obtained from the images taken in a homogenization experiment, in the HoSIER, an 18,000 X solar furnace. The results are interpreted through the new concept of photovoltaic homogeneity, proven that the methodology successfully predicts the flux distributions, which enhances the efficiency of a series connected CPV array. Additionally, we found that the proposed methodology can also be used to optimize the electrical performance of dense-array CPV systems, working under the effects of non-uniformity illumination by rewiring the series connections into series-parallel configurations.
A Piña-Ortiz, JF Hinojosa, RA Pérez-Enciso, VM Maytorena, RA Calleja, CA Estrada
Publicado:27 de Julio 2018
In this study, a thermal analysis of a finned receiver prototype for a thermosolar tower system is presented. The experimental system consists of parallelepiped aluminum enclosure of 1.2 m high, 1.23 m wide and 0.1 m depth. At the interior, 1232 cylindrical fins with a diameter of 0.0095 m (3/8”) and 0.09 m length increases the heat transfer area up to 225%. The vertical wall receives the incoming solar concentrated radiation from a group of heliostats whilst at the interior a constant flow of water removes the absorbed energy. Experimental temperature profiles were obtained at different heights and depths and a comparison was made with numerical results obtained with the use of commercial CFD software. It was found that the maximum thermal efficiency of the receiver was 94.4 %, decreasing as the radiative flux increases.
Manuel I. Peña-Cruz,Patricio J. Valades-Pelayo,Camilo A. Arancibia-Bulnes,Carlos A. Pineda-Arellano,Iván Salgado-Tránsito, and Fernando Martell-Chavez
Publicado:10 de Octubre 2018
In this work, the seasonal and yearly optical performance of supported catalyst CPC solar photocatalytic reactors has been theoretically analyzed. A detailed model for the optical response of the anatase catalyst films is utilized, based on the characteristic matrix method, together with Monte Carlo ray tracing simulations. The catalyst is supported over glass tubes contained inside a larger glass tube that functions as receiver of the CPC reflector. Arrangements with four, five, and six tubes are considered. Overall, the four-tube scenario presents the worst performance of all, followed by the five-tube case. In general, the six-tube configuration is better. Nevertheless, important differences can be observed depending on the specific arrangement of tubes. The six-tube case surpasses the absorption rate of all the other configurations when the distance between tubes is extended. This configuration exhibits 27% increased yearly energy absorption with respect to the reference case and 47% with respect to the worst case scenario.
J. D. Macias, R. A. Gutiérrez-Razo, H. D. Garcia-Lara, F. Cervantes-Alvarez, J. Bante-Guerra, O. Ares-Muzio, H. Romero-Paredes, Noel León Rovira, C. A. Arancibia-Bulnes, H. I. Villafan-Vidales, V. Ramos-Sánchez, and J. J. Alvarado-Gil
6 de marzo 2018
Solar technology operating at elevated temperature conditions demands accurate knowledge of the optical and thermal properties of the materials involved in the construction and operation of solar collectors, reactors, and energy storages, among many others. Thermal energy storage (TES) devices involve successive melting and crystallization processes, which result in high complexity materials where the morphology, composition, and porosity could be highly non-homogeneous. In these cases, contact techniques for determining the thermal properties are highly susceptible and do not provide reliable measurements. It is under these conditions that non-contact photothermal techniques can provide superior performance, because in this case, the heat inducing source is a laser beam and the detector is usually a photodiode or a thermographic camera which are in non-contact with samples.
The materials applied as storage medium in a TES unit can be divided into four groups: metals and alloys, ceramics and glasses, polymers and elastomers, and composites that include natural materials. Soda lime silicate glass recyclable waste is a very promising material for storage medium due to its inexpensive and wide availability. In this paper, we examined soda lime silicate glass-graphite composites for use as storage medium in a TES unit. A simple one-dimensional model for thermal conductivity was developed based on equivalent thermal circuits for series-parallel composite walls, and we found that thermal conductivity values depend on the amount of graphite dispersed into the samples, the porous media, and their structure.
Aldo Javier Guadarrama-Mendoza, Heidi Isabel Villafán-Vidales, Patricio J.Valadés-Pelayoa, Camilo A. Arancibia-Bulnes, David Riveros-Rosas, Hernando Romero-Paredesc
15 de junio 2018
The numerical evaluation of the radiative heat transfer in a multichanneled solar reactor coated with ZnFe2O4 thin-film is performed by using a channel-level simulation. A ray-tracing simulation of a 25 kW solar furnace allows obtaining the radiation distribution at each channel aperture. Then a Monte Carlo ray tracing is performed to analyze the radiative heat transfer on the monolith to optimize the channel-level geometry and film thickness for maximum absorptance and more homogeneous temperature distributions. The model considers the optical properties of ZnFe2O4 films deposited on zirconia substrate, obtained through the characteristic matrix method. This approach allows accounting for important reactor design parameters and operational conditions, such as ZnFe2O4 layer thickness, incoming radiation profile, diameter and length of pores and position of the monolith in the focal zone of the solar furnace.
Elisa Alonso, Carlos Pérez-Rábago, Javier Licurgo, Alessandro Gallo, Edward Fuentealba, Claudio A. Estrada
06 de Enero 2017
Solar reactors designed and constructed for thermochemical applications present different configurations and general performance. The selection of a solar reactor that optimizes a particular process is always a difficult challenge. This work studies two types of reactor configuration by means of a comparative experimental analysis. It was employed a solar device, which is able to operate as fixed reactor with packed bed samples and as rotary kiln. The reduction of CuO into Cu2O was tested under both operation modes, due to its proved potential and interest as thermochemical storage material. It was found that heat transfer was hindered in static experiments limiting the fraction of reactive sample. Thermal gradients of about 200 °C were found in the packed bed through thermocouple and IR camera measurement. Heating rates and total fed energy must be restricted at the risk of front of the sample to melt, resulting in several operation drawbacks. In contrast, mixing conditions in rotary kilns allowed for higher heating rates and led to homogenous sample temperature. Maximum reaction yields in stationary mode did not overpass 14% while it was achieved more than 80% in rotary mode at temperatures about 860 °C. Thermal efficiencies were very limited in both operation modes due to the high thermal inertia of the solar reactor. Because rotary mode admitted much more energy, its thermal efficiency was even lower than static. A solution to increase rotary kilns thermal efficiency is working in continuous mode.
Alonso, E., Gallo, A., Roldán, M.I., Pérez-Rábago, C.A., Fuentealba, E.
12 de Enero 2017
Rotary kilns have a long history of use in classical industries. They are able to achieve high temperatures with higher thermal efficiencies than other reactor types. Their performance has been widely studied and classified according to different parameters. Since it is a well-known technology, rotary kilns have been selected for high temperature solar processes. This article initially presents a brief review of the rotary kiln technology and it focuses on the employment of these devices for thermal and thermochemical processes conducted by concentrating solar energy. Among the solar devices, a novel rotary kiln prototype for thermochemical processes is presented and compared with a static solar reactor. Finally, some practical conclusions on the design and operation of solar rotary kilns are remarked and an analysis of their main limitations is presented.
H.I.Villafán-Vidales, C.A.Arancibia-Bulnes, D.Riveros-Rosas, H.Romero-Paredes, C.A.Estradaa
15 de Noviembre 2016
Hydrogen is a promising energy carrier for transportation, domestic and industrial applications. Nowadays hydrogen is consumed basically by the chemical industry, but in long term its demand is expected to grow significantly due to emerging markets. Hence production of hydrogen with sustainable methods is a relevant issue. This work presents a review of the different CSP- aided thermochemical processes for hydrogen and syngas production. For each process, some relevant solar-tested reactor prototypes are described. In a second part, the developed solar furnaces for investigation of thermochemical process are also discussed. In addition, relevant research on hydrogen or syngas production in solar tower installations is presented. Finally the current challenges of the technology and the process for its future commercialization are also analyzed.
Elisa Alonso, CarlosPérez-Rábago, Javier Licurgo, Alessandro Gallo, Edward Fuentealba, Claudio A.Estrada
6 de Enero 2017
Solar reactors designed and constructed for thermochemical applications present different configurations and general performance. The selection of a solar reactor that optimizes a particular process is always a difficult challenge. This work studies two types of reactor configuration by means of a comparative experimental analysis. It was employed a solar device, which is able to operate as fixed reactor with packed bed samples and as rotary kiln. The reduction of CuO into Cu2O was tested under both operation modes, due to its proved potential and interest as thermochemical storage material. It was found that heat transfer was hindered in static experiments limiting the fraction of reactive sample. Thermal gradients of about 200 °C were found in the packed bed through thermocouple and IR camera measurement. Heating rates and total fed energy must be restricted at the risk of front of the sample to melt, resulting in several operation drawbacks. In contrast, mixing conditions in rotary kilns allowed for higher heating rates and led to homogenous sample temperature. Maximum reaction yields in stationary mode did not overpass 14% while it was achieved more than 80% in rotary mode at temperatures about 860 °C. Thermal efficiencies were very limited in both operation modes due to the high thermal inertia of the solar reactor. Because rotary mode admitted much more energy, its thermal efficiency was even lower than static. A solution to increase rotary kilns thermal efficiency is working in continuous mode.
Patricio J.Valadés-Pelayo, Camilo A.Arancibia-Bulnes
1 de Junio 2017
A three-dimensional transient heat transfer model is presented to predict the start-up operation of a multi-tubular cavity reactor under concentrated irradiation in a solar furnace. The reactor consists of a cavity containing nine absorber tubes, through which a suspension of CeO2 in Argon flows. An iterative splitting scheme coupling a Continuous Random Walk, a Finite Volume, and a Ray-Tracing Monte Carlo methods, is implemented to estimate the temperature gradients in the tubes and gas-particle media. The radiation heat transfer among the tubes and cavity walls is considered, as well as conduction and convection in the tubes and the particle suspension. During the initial heating stage, gradients are mainly angular, while in steady-state they are primarily axial. The former may cause tube bending or cracking, and strategies to reduce them are examined. In particular, different heating ramps were simulated, which was found to reduce these initial thermal gradients.
Patricio J.Valadés-Pelayo, Camilo A.Arancibia-Bulnes, Iván Salgado-Tránsito, Heidi I.Villafán-Vidales, Manuel I.Peña-Cruz, Antonio E.Jiménez-González
1 de Diciembre 2016
#2016
A multiscale model is presented to describe the radiation absorption field in photocatalytic reactors with supported catalyst. The characteristic matrix method is applied at the photocatalyst layer scale, and is embedded within a Monte Carlo ray tracing method, applied at the photoreactor scale. This approach allows to account for important design parameters, such as photocatalyst layer thickness, location of supporting surfaces, and incoming radiation profiles, among others. To resolve the validity of the characteristic matrix method for the description of the optical properties of the catalyst, modeled transmittance and reflectance of the supported films is compared to experimental data. This comparison is carried out for different wavelengths and film thicknesses. Afterwards, the model is applied to a solar reactor with anatase catalyst films supported on multiple surfaces.
The reactor consists of a compound parabolic concentrator with a tubular borosilicate glass receiver. Smaller glass tubes coated with the catalyst are located inside this receiver. With the developed model, a study is conducted to analyze the reactor optical performance as a function of two important design variables: film thickness and radius of the absorber tubes. The results of the model indicate directions for the improvement of the current design.
Manuel A.Ramírez-Cabrera, Patricio J.Valadés-Pelayo, Camilo A.Arancibia-Bulnes, EduardoRamos
25 de julio del 2017
In the literature for photocatalytic reaction modeling engineering, several simplified schemes applicable to ambient temperature radiative transfer for scattering media are available. A popular strategy is the Six-Flux method because it is simple and is not computer time demanding but its accuracy is not always explicit. In the present work we assess the accuracy of low order methods, including six flux case, by solving the radiative transfer equation in dimensionless form within a cubic enclosure, for i) a collimated beam and ii) a diffuse beam. Radiation enters the cube through a square window centered on one face and with an area one quarter the area of the face. The simulation considers fully absorbing walls, and isotropic scattering. The deviations of simplified models based on Discrete Ordinate or Finite Volume schemes, are compared to the mesh independent solution. The results indicate that for a collimated beam boundary condition the Six-Flux model and more refined models are moderate. The error of the total rate of energy absorbed (TREA) and that of the local volumetric rate of energy absorption (LVREA) with respect to a mesh independent solution are below 5% and 22% respectively. In contrast, it is found that for diffuse boundary conditions the Six-Flux model is very inaccurate since the corresponding errors are larger than 120%.
Camilo A.Arancibia-Bulnes, Manuel I.Peña-Cruz, Amaia Mutuberría, Rufino Díaz-Uribed, Marcelino Sánchez-González
24 de Noviembre del 2016
#2016
The optical quality of concentrators has a direct impact on the thermal efficiency of concentrating solar power plants. There is a need to evaluate the quality of the mirrors before installation and during operation. A review of the optical characterization techniques that have been developed for solar concentrators is presented. A brief description of the operation and methodology of each technique is done. The strengths and possible vulnerabilities of the techniques are also discussed. A classification of the different techniques in families according to their underlying principles of operation is proposed. Finally an analysis of the available information about the accuracy and precision of the different methods is carried out.
Juan Daniel Macias, Dallely Melissa Herrera-Zamora, Francisco Ivan Lizama-Tzec, Jose Bante-Guerra, Oscar Eduardo Arés-Muzio, Gerko Oskam, Hernando Romero-Paredes Rubio, Juan Jose Alvarado-Gil, Camilo Arancibia-Bulnes, Victor Ramos-Sánchez, and Heidi Isabel Villafán-Vidales
Publicado: 27 de junio 2017
Concentrating solar power (CSP) systems use solar absorbers to convert sunlight into thermal electric power. In CSP systems, a high reflective surface focuses sunlight onto a receiver that captures the solar energy and converts it into heat. The operation of high efficiency CSP systems involves improvements in the performance of the coatings of the solar absorption materials. To accomplish this, novel, more efficient selective coatings are being developed with high solar absorptance and low thermal losses at their operation temperature. Heat losses in a CSP system occur by three mechanisms: conduction, convection and radiation. It has been widely documented that energy losses increase with increasing operating temperature of CSP systems, and the precise knowledge of the thermophysical properties of the materials involved in CSP systems may allow us to increase the efficiency of systems.
In this work, we applied the pulsed photoradiometry technique (PPTR) to evaluate the changes in the thermophysical properties of selective coatings on a variety of substrates as a function of temperature. Three types of coatings deposited with two different techniques on three types of substrate were examined: commercial coatings based on titanium oxynitride deposited by sputtering on substrates of copper and aluminum, coatings based on black nickel deposited by electrochemical methods on substrates of steel, and coatings based on black cobalt deposited by electrochemical methods on substrates of steel and copper. Values of the thermal diffusivity and thermal conductivity were obtained in the temperature range of 25 to 550 °C. Optical reflectance measurements have been performed in order to provide an estimate of the dependence of the thermal emittance on temperature using the black body radiation theory. REFERENCES
Lara-Cerecedo L.O., Moreno-Cruz I., Pitalúa-Diaz, N., Arancibia-Bulnes, C.A.
Publicado 3 de Abril 2016
A novel modeling tool for calculation of central receiver concentrated flux distributions is presented, which takes into account drift effects. This tool is based on a drift model that includes different geometrical error sources in a rigorous manner and on a simple analytic approximation for the individual flux distribution of a heliostat. The model is applied to a group of heliostats of a real field to obtain the resulting flux distribution and its variation along the day. The distributions differ strongly from those obtained assuming the ideal case without drift or a case with a Gaussian tracking error function. The time evolution of peak flux is also calculated to demonstrate the capabilities of the model. The evolution of this parameter also shows strong differences in comparison to the case without drift.
Valades-Pelayo P.J., Romero-Paredes H., Arancibia-Bulnes C.A., Villafán-Vidales H.I.
Publicado:12 de Enero 2016
In the present study, the optimization of a multi-tubular solar thermochemical cavity reactor is carried out. The reactor consists of a cubic cavity made of woven graphite, housing nine 2.54 cm diameter tungsten tubes. A heat transfer model is developed and implemented considering high-temperature radiative transfer at steady state. The temperature distribution on the receiver tubes is determined by using a hybrid Monte Carlo-finite volume approach. The optimization aims at maximizing average tube temperature by varying tube locations. Optimal tube distributions are explored by using a custom-made stochastic, multi-parameter, global optimization algorithm. A considerable increase in average temperature as well as improvement on temperature uniformity is found in the optimized tube arrays. Patterns among the different optimal distributions are found, and general features are discussed.
Ricardo Pérez-Enciso, Alessandro Gallo, David Riveros-Rosas, Edward Fuentealba-Vidal, Carlos Pérez-Rábago
Publicado:27 de Febrero 2016
A method to achieve a uniform flux distribution with a multi-faceted point focus concentrator for laboratory tests is proposed in this work. The method can be applied to different types of receiver - thermal or photovoltaic - and no additional device is required to homogenize the flux. The technique consists in moving the receiver from the focal plane and enlarging the solar spot impinging on it. At the same time, each mirror aim-point is adjusted in order to superimpose the images that have been generated by every facet. To evaluate the method, a real multi-faceted concentrator composed of eighteen spherical mirrors was modeled in a ray-tracing software. The procedure was validated through the comparison of an image of the real solar spot on the receiver generated by three mirrors, and the simulated flux obtained the same way. This way a mean concentrator global optical error of 2.8 mrad was estimated. This value was used then for further analyses. Results show that the concentration factor can be varied in a range of 150–900 suns over a receiver diameter of up to 7 cm. Hence, according to the receiver requirements, it is possible to expand the distribution and to alter the intensity of the flux. Finally, optical parametrical analyses were carried out, from which it is inferred that good quality optics give rise to a more homogeneous solar flux on the receiver.
Julio Valle-Hernández, Hernando Romero-Paredes, Camilo A. Arancibia-Bulnes, Heidi I. Villafan-Vidales, and Gilberto Espinosa-Paredes
Publicado:31 de mayo 2016
In this paper the simulation of the thermal reduction for hydrogen production through the decomposition of cerium oxide is presented. The thermochemical cycle for hydrogen production consists of the endothermic reduction of CeO2 at high temperature, where concentrated solar energy is used as a source of heat; and of the subsequent steam hydrolysis of the resulting cerium oxide to produce hydrogen. For the thermochemical process, a solar reactor prototype is proposed; consisting of a cubic receptacle made of graphite fiber thermally insulated. Inside the reactor a pyramidal arrangement with nine tungsten pipes is housed. The pyramidal arrangement is made respect to the focal point where the reflected energy is concentrated. The solar energy is concentrated through the solar furnace of high radiative flux. The endothermic step is the reduction of the cerium oxide to lower-valence cerium oxide, at very high temperature. The exothermic step is the hydrolysis of the cerium oxide (III) to form H2 and the corresponding initial cerium oxide made at lower temperature inside the solar reactor. For the modeling, three sections of the pipe where the reaction occurs were considered; the carrier gas inlet, the porous medium and the reaction products outlet. The mathematical model describes the fluid mechanics; mass and energy transfer occurring therein inside the tungsten pipe. Thermochemical process model was simulated in CFD. The results show a temperature distribution in the solar reaction pipe and allow obtaining the fluid dynamics and the heat transfer within the pipe. This work is part of the project “Solar Fuels and Industrial Processes” from the Mexican Center for Innovation in Solar Energy (CEMIE-Sol).
H.I. Villafán-Vidales, A. Jiménez-González, A. Bautista-Orozco, C.A. Arancibia-Bulnes, C.A. Estrada.
Publicado:25 de Abril 2015
The tungsten trioxide (WO3) is a promising material with important technologic and scientific applications, due to its electrochromic, gasochromic and photochromic properties. Usually, this material is synthesized following several routes, for example, sputtering, chemical deposition, sol-gel, hydrothermal, among others. However, these methods are complicated, have long processing times and use several chemicals with the possibility of keeping undesirable impurities. In this context, concentrated solar energy is an interesting and feasible option to process materials at a low cost and without greenhouse gas emissions. In this work, a simple and green synthesis method of WO3 by using the Solar Furnace of the Renewable Energy Institute of the National University of Mexico is presented. Tungsten oxide powder is obtained by means of tungsten electrodes in a high-temperature solar reaction chamber designed to work with concentrated solar energy under controlled conditions of the gas atmosphere. The oxidation reaction was carried out for three different temperatures: 600°C, 800°C and 1000°C, and for each temperature three different oxygen molar fractions were studied: 0.33, 0.41 and 1. Some results indicate the oxygen molar fraction does not affect the phase transformation and the WO3 triclinic was the most stable phase, appearing in all the temperature ranges and concentrations. The synthesis reported in this paper is presented as a green alternative in the development of processes for the synthesis of WO3, which promote renewable energy sources with very low greenhouse gas emissions and without toxic residuals.
H.I. Villafán-Vidales, S. Abanades, M. Montiel-González, H. Romero-Paredes, C.A. Arancibia-Bulnes, C.A. Estrada.
Publicado:25 de junio 2014
A 1 kWth cavity-type solar reactor devoted to the thermal reduction of volatile oxides as part of a two-step thermochemical cycle is analyzed numerically. The thermochemical reactor consists of a vertical-axis cavity-type receiver in which the reactant is injected from the bottom in the form of an ascending rod made of a stack of zinc oxide compressed pellets undergoing thermal dissociation. A transient heat transfer model allows the simulation of the thermal behavior under real conditions for the rod of reacting particles exposed to concentrated solar radiation. The developed numerical model couples radiation, conduction and convection heat transfers to the kinetic of the reaction. The incident solar irradiation on the reactant surface is obtained using the Monte-Carlo ray tracing technique applied first to the solar concentrator and second to the reactor cavity. The model is used to predict the temperature profile from the irradiated front surface of the compressed reactant, the evolution of outlet oxygen molar flow-rate during the reduction reaction and the instantaneous thermochemical efficiency, as a function of time. The calculated results are compared with the experimentally obtained data. The agreement between experimental data and simulation related to both the temperature and the oxygen progress is fairly good with Ea = 380 kJ mol−1 and k0 = 246 × 106 mol m−2 s−1 for the kinetics of the ZnO dissociation reaction.
R. Pérez-Enciso, E. Brito-Bazan, C.A. Pérez-Rábago, C.A. Arancibia-Bulnes, D. Riveros-Rosas, C.A. Estrada.
Publicado:22 de Mayo 2014
This paper discusses the methods implemented for the solution of the drift and backlash problems in the heliostat of the High Radiative Flux Solar Furnace recently built at the Renewable Energy Institute (former Center for Energy Research) of the National University of Mexico (IER-UNAM), located at the geographical coordinates 18°50′24″ North latitude and 99°15′00″ West longitude. To solve the observed drift, several algorithms were analyzed for the calculation of the solar vector, and a closed loop through an electronic device (peephole) was implemented which makes corrections to the position of the heliostat. Using the peephole, drift heliostat decreased significantly; 70% in the horizontal direction and 63% in the vertical direction relative to the no use of peephole. The backlash was corrected by means of unbalancing the heliostat.
Elisa Alonso, Carlos Pérez-Rábago, Javier Licurgo, Edward Fuentealba, Claudio A. Estrada.
Publicado:18 de Marzo 2015
Thermochemical redox processes are currently considered one of the most promising methods for thermal storage of solar energy. Among the different types of materials available for this purpose, metal oxides allow higher operation temperatures in CSP systems. This is in agreement with the new R&D trends that focus on increasing the temperature to augment the efficiency. Copper oxide was previously proposed as a valid metal oxide for thermochemical storage. However, no demonstrative experiments had been carried out so far under solar radiation. In this work, the suitability of copper oxide was proved in a solar furnace. The employed solar reactor was a rotary kiln device with direct radiation absorption on reactive particles, which is a configuration that guarantees higher operation temperatures than other types of solar reactors. Given results include the performance of the CuO reduction in the rotary kiln under argon atmosphere and the cyclability of the pair CuO/Cu2O in air.
L.G. Ceballos-Mendivil, R.E. Cabanillas-López, J.C. Tánori-Córdova, R. Murrieta-Yescas, C.A. Pérez-Rábago, H.I. Villafán-Vidales, C.A. Arancibia-Bulnes, C.A. Estrada.
Publicado:29 de Abril 2015
Silicon carbide (SiC) has been prepared successfully using concentrated solar energy provided by the IER-UNAM solar furnace. This has led to the development of a low CO2 emissions process for the production of this material via carbothermic reduction of a silica/carbon (SiO2/C) nanocomposite, which has shown a more reactive carbon for formation of composite, being more thermally stable. Silica (obtained by a sol–gel process) and sucrose were used as precursors of silicon and carbon, respectively, at a temperature of 700 °C in controlled atmosphere (nitrogen) for the formation of the SiO2/C composite. This composite was used in a second step to obtain SiC at a temperature of 1500 °C, in argon atmosphere. The experimental setup used a Pyrex® glass spherical vessel designed to work with concentrated solar power and controlled atmospheres. The structure and morphology of the solar obtained SiC were analyzed with FTIR, XRD, TGA/DSC, SEM and TEM techniques. Results show that it is feasible to use concentrated solar energy for the synthesis of SiC. The solar SiC obtained is nanostructured and is mainly β-SiC.
M. Montiel-González, J.F. Hinojosa, H.I. Villafán-Vidales, A. Bautista-Orozco, C.A. Estrada.
Publicado: 1 de Junio 2014
In this work a theoretical and experimental study of heat transfer by natural convection and thermal radiation on a solar open cubic cavity-type receiver is presented. The theoretical study consists on solving the laminar natural convection and the surface thermal radiation on a square open cavity at one end. The overall continuity, momentum, and energy equations in primitive variables are solved numerically by using the finite-volume method and the SIMPLEC algorithm. The thermophysical properties of the fluid are considered, for the first case, as temperature dependent in all the governing equations, and for the second case, constant, except for the density at the buoyancy term (Boussinesq approximation), with the purpose of comparing the results of both theoretical models with experimentally obtained results. Numerical calculations are conducted for Rayleigh number (Ra) values in the range of 104–106. The temperature difference between the hot wall and the bulk fluid (ΔT) is varied between 10 and 400 K, and is represented as a dimensionless temperature difference (φ) for the purpose of generalization of the trends observed. Experimental results include air temperature measurements inside the receiver. These results are compared with theoretically obtained air temperatures, and the average deviation between both results is around 3.0%, when using the model with variable thermophysical properties, and is around 5.4% when using the Boussinesq approximation.
Victor H. Benitez, Jesús Pacheco-Ramirez, Nun Pitalua-Diaz
Publicado: 4 de Diciembre 2013
This paper presents the modeling and control of an array of mini-heliostats developed for a solar central tower plant facility located outside of Hermosillo, Mexico. In order to deal with the real time implementation, an algorithm to significantly reduce the error that emerges in the solar tracking requirements is presented. Heliostats are oriented to reflect solar beam to a central receiver located in top of a tower. The heliostat tracks the apparent sun position with determined periodicity. A digital controller perform the tasks of calculate the control action to drive the actuators. The real time implementation of the control action introduces numerical issues that deviates the solar ray of the desired position. Results show that the proposed control strategy is able to track the solar sun position. The controller is implemented in real time via LabVIEW computational environment and is applied in a solar tower plant facility.
V. H. Benítez Baltazar, J. H. Pacheco Ramírez, N. Pitalúa Díaz.
Publicado: 15 de Agosto 2014
A comparison was made between six turbulence models and experimental temperature profiles for the turbulent natural convection in a tilted open cubic cavity. The experimental setup consists of a cubic cavity of 1 m by side with one vertical wall receiving a constant and uniform heat flux, whereas the remaining walls are thermally insulated. The thermal fluid is air and the aperture is facing the heated wall. The temperature profiles were obtained at different heights and depths and each one consists of 10 positions inside the cavity. A commercial computational fluid dynamic software was used for the simulation and different turbulence models of k-εt and k-ω families were evaluated against experimental data. The lowest absolute average percentage difference for the experimental and numerical temperature profiles was for the rk-εt model and the highest was for the sk-ω model.
Manuel I. Peña-Cruz, Camilo A. Arancibia-Bulnes, Ana Monreal Vidal, and Marcelino Sánchez González.
Publicado:27 de Noviembre 2014
An improved tool for the shape qualification of parabolic trough mirror modules used in concentrated solar power plants was developed. The tool is based on the fringe reflection theory, in which sinusoidal fringe patterns are projected on a screen and their reflection over a specular surface is recorded by a camera. The observed distortions in the image are related directly to surface deviations from ideal geometry. Relevant aspects of the technique are its high spatial resolution (more than 1 × 106 points per mirror facet), short measurement time and easy setup. The developed tool (called FOCuS) is capable of calculating the local mirror slope deviations from its ideal design and the RMS value as a quality factor. Furthermore, the tool generates a file which can be loaded into CENER's TONATIUH ray tracing software, through a specially developed plug-in, for mirror modeling and intercept factor calculation with several tube absorber geometries.
Martha Escobar-Toledo, Camilo A. Arancibia-Bulnes, Cuitlahuac Iriarte-Cornejo, Julio Waissman, David Riveros-Rosas , Rafael E. Cabanillas and Claudio A. Estrada.
Publicado: 21 de Abril 2014
Drift is ubiquitous in heliostat fields, and may be caused by diverse geometrical inaccuracies during heliostat installation and operation. This phenomenon is studied for three important primary errors in the present paper: Angular offset in the drive mechanism, pedestal tilt, and canting error. Each error produces characteristic signatures, but there is a diversity of behavior depending on the error parameters and location of the heliostat. The variation of the extent of drift curves is studied as a function of distance, for fixed error parameters. It is found that, in general, this extent is not proportional to distance, except for far heliostats, and depends on a complicated manner on the different parameters involved. Moreover, even though the extent of drift curves becomes proportional to distance for far heliostats, the convergence is very slow, and very variable with the error parameters.
C. Iriarte-Cornejo, C.A. Arancibia-Bulnes, I. Salgado-Transito, J. Waissman, R.E. Cabanillas, C.A. Estrada.
Publicado: 5 de mayo 2014
Heliostat image drift is a common phenomenon in central receiver solar power plants. Several geometrical errors produce drift of the heliostat solar spot at receiver surface, increasing radiation spillage. A heuristic drift compensation method is proposed, based on a polynomial approximation to the drift trajectories. Results of the practical implementation of the proposed method for the control of 10 heliostats in a solar tower facility are presented. A substantial improvement of heliostat tracking is observed on the experimental tests. Because heliostat drift experimental monitoring is a time consuming task, a numerical analysis of the yearly behavior of the compensation method, based on simulations of heliostat drift, was carried out. In these simulations, the behavior of the daily RMS deviation of the concentrated solar spot centroid is evaluated for a whole year, as the polynomial correction is applied. The simulations serve also to test the effectiveness of the proposal polynomial method in a wider range of conditions. Thus, heliostats with a variety of primary error values are simulated. Random wind induced vibrations are introduced in the simulation to evaluate the effectiveness of the calibration method under noise conditions. It is found that a very effective calibration can be achieved with a few sampling events of the heliostat behavior during the year, taking only a few minutes. The RMS deviation can be reduced to values of the order of the wind induced noise level. The proposed polynomial compensation looks like a promising alternative to be implemented in heliostat fields.
Carlos Antonio Pineda Arellano, A. Jiménez González, Susana Silva Martínez, Iván Salgado-Tránsito, Cesar Pérez Franco
Publicado:31 de Agosto 2013
Atrazine is a highly persistent and carcinogenic compound used as herbicide around the world. This compound has been banned in USA and some European countries but in Mexico it is still widely used in the agriculture. In order to achieve a high mineralization of atrazine, present as active compound in the Gesaprim commercial herbicide, detoxification studies in two-compound parabolic solar reactors by means of photo-Fenton process followed by TiO2 photocatalysis was carried out. The atrazine contents in the Gesaprim solutions tested were 35 mg L−1 (19.0 mg L−1 of TOC) and 20 mg L−1 (9.5 mg L−1 of TOC). [H2O2]0/COD0 ratios of 1, 3 and 5 (1.5 × 10−3, 4.5 × 10−3 and 7.5 × 10−3 mol L−1 H2O2, respectively) were evaluated in combination with 5 mg L−1 and 10 mg L−1 Fe2+ at pH 2.8 in the photo-Fenton oxidation; whereas, in the photocatalytic process, the influence of the pH (4.8, 7.0 and 11.0) and type of TiO2 (Degussa P25 and HB) were studied with TiO2 content of 200 mg L−1. The study showed that photo-Fenton process followed by TiO2 photocatalysis produce a 72% of mineralization (for an initial TOC of 19 mg L−1) and decrease above 90% of toxicity in compliance with NMX-AA-110-1995-SCFI1 Mexican Norm. In order to established a minimum amount of chemical reagents these photodegradation processes were carried out with special emphasis on the optimization of experimental parameters such as concentrations of photocatalyst and oxidant. Atrazine mineralization was influenced by the pH of the solution, the initial concentration of hydrogen peroxide and iron ions.
C. A. Estrada Gasca
Publicado: 2 de Octubre 2013
En este trabajo se reflexiona sobre la problemática energética mundial; la finitud de las fuentes fósiles y su impacto al medio ambiente. La estructura energética mundial es no sustentable y se requiere de un cambio de paradigma energético basado en la eficiencia energética y el uso de fuentes alternas como las energéas renovables (ER). La demanda energética mundial está en continuo aumento a un ritmo de crecimiento anual del 2.47%. En un escenario al 2030 para la transformación del sistema mundial de energía, elaborado a partir del cumplimiento de nuevas políticas energéticas que consideran una economía baja en carbón para la protección del medio ambiente, todas las fuentes primarias contribuyen a satisfacer la demanda energética. De hecho, las fuentes primarias de energía que más crecen son el gas y las ER. En particular, la taza a la que las ER están creciendo y penetrando los mercados mundiales de la energía tiene una marcada similitud con la aparición de la energía nuclear en los años 1970’s y 1980’s.
México cuenta con abundantes recursos renovables y se han hecho esfuerzos importantes para avanzar en el uso de las tecnolog´ıas que aprovechan las fuentes de ER. El potencial solar del pa´ıs es realmente muy grande y el uso de las tecnologías solares que aprovechan dicho recurso es muy limitado. Se requiere, para garantizar el desarrollo sustentable en el país, que el estado mexicano se comprometa, con una visión a largo plazo, en el aprovechamiento de las ER y en el uso eficiente de la energ´ıa. Se deberán generar las políticas, los marcos legales, los incentivos económicos y los fondos de financiamiento para apoyar a la investigación científica y tecnológica y permitir el desarrollo masivo de las ER y del uso eficiente de la energ´ıa en el país.
M. Montiel Gonzalez, J. Hinojosa Palafox, C. Estrada Gasca.
Publicado 6 de Noviembre 2013
A comparison was made between six turbulence models and experimental temperature profiles for the turbulent natural convection in a tilted open cubic cavity. The experimental setup consists of a cubic cavity of 1 m by side with one vertical wall receiving a constant and uniform heat flux, whereas the remaining walls are thermally insulated. The thermal fluid is air and the aperture is facing the heated wall. The temperature profiles were obtained at different heights and depths and each one consists of 10 positions inside the cavity. A commercial computational fluid dynamic software was used for the simulation and different turbulence models of k-εt and k-ω families were evaluated against experimental data. The lowest absolute average percentage difference for the experimental and numerical temperature profiles was for the rk-εt model and the highest was for the sk-ω model.
H.I., Villafán-Vidales, Abanades, S., Arancibia-Bulnes, C.A., Riveros-Rosas, D., Romero-Paredes, H., Espinosa-Paredes, G., Estrada, C.A.
Publicado:29 de Agosto 2012
Radiative heat transfer in a 1 kW cavity-type solar reactor devoted to the thermal reduction of compressed ZnO and SnO2 powders is analyzed by a Monte Carlo ray tracing simulation. The developed model takes into account the radiative properties of the reactant particles and of the ceramic cavity walls, as well as the angular intensity distribution of the incoming concentrated solar irradiation. The model also includes the conduction heat losses through the lateral walls and the energy consumed by the endothermic chemical reaction. It is used to predict the temperature and the absorbed flux density profiles on the inner cavity walls for different main features of the reactor, concerning the dimensions of the cavity and the type of reactant. Results show that the absorbed flux density profile and the theoretical thermochemical efficiency change with the cavity aspect ratio and with the oxide reactant. The cavity with an aspect ratio of 3 and a SnO2 pellet undergoing dissociation presents the highest thermochemical efficiency. Additionally, a different configuration of the reactor design is considered, which consists in implementing a layer of reactive particles on the inner lateral cavity wall. The model highlights that this type of reactor operation with a reactant layer on the lateral cavity wall results in an improved thermochemical efficiency.
D. Riveros-Rosas, R. Castrejón-García, C. A. Arancibia-Bulnes, C. A. Pérez-Rábago, C. A. Estrada-Gasca
Publicado:14 de Diciembre 2012
A methodology for the evaluation of the specularity error of a polymeric filmoptical coating is presented. The methodology is based on the comparison of images from the sun produced by two high quality spherical mirrors, one covered with a highly specular evaporated aluminumfilm, and the second one with the polymeric film under study. This film is a commercial product known as Reflectech®. To determine the specularity error, both images are reproduced by means of ray tracing optical simulations. Those simulations use the angular brightness distribution from the sun as input, which were recorded by means of a specially developed solar scope. Significant differences are obtained between images of the sun generated by both mirrors. However, the specularity error of the coating under consideration is found to be just 0.71 mrad. This error is quite small making the polymeric coating highly appropriate for point focus concentration systems. This is illustrated by calculations for a parabolic dish concentrator.
S. L. Orozco, H. I. Villafán-Vidales, C. A. Arancibia-Bulnes
Publicado:28 de Noviembre 2011
Radiative transfer inside a slurry photocatalytic reactor with hybrid illumination from both solar radiation and lamps is examined. The local volumetric rate of photon absorption is evaluated. For this purpose, the P1 and the modified differential approximations (MDAs) are used, and results compared to a solution by the Monte Carlo method. It is found that significant differences may arise between the predictions of the above approximations and the exact results provided by the Monte Carlo simulations. The P1 approximation is very inaccurate near to the radiation entrance for the partially collimated solar radiation, although it improves, as optical depth increases. As expected, the MDA improves the results near to the boundary. Surprisingly, it turns out to be much worse than the P1 approximation at medium and large optical depths. In the case of lamp irradiation, the behavior of the MDA is the opposite; it works better at small optical depths.
A. Bassam, I. Salgado-Tránsito, I. Oller, E. Santoyo, A.E. Jiménez, J.A. Hernandez and A. Zapata.
Publicado:21 de Septiembre 2011
Artificial neural networks (ANN) were proposed as a multivariate experimental design tool for monitoring a photo-Fenton treatment of wastewaters containing a synthetic mixture of pesticides. ANN and Nelder-Mead simplex methods were used to find out the optimum operating parameters of a photo-Fenton pilot plant. ANN was developed to predict the most important operating parameters (e.g., the total organic carbon and the initial mineralization kinetic rate constants of the reactions), which determine the photo-catalytic degradation efficiency in photo-Fenton processes. Experimental measurements of temperature, pH, hydrogen peroxide (H2O2) consumption, initial concentration of Fe2+, and the AE were used as input data for the ANN learning. A feed-forward with one hidden layer, a Levenberg–Marquardt learning algorithm, a hyperbolic tangent sigmoidal transfer function and a linear transfer function were used to develop the ANN model. The best fitting of the training database was obtained with an ANN architecture constituted by seven neurons in the hidden layer. The simulated results were validated with experimental measurements, showing an acceptable agreement (R2 > 0.99). The ANN was subsequently coupled with a Nelder–Mead simplex method to obtain the optimum operating parameters of the photo-Fenton pilot plant. The H2O2 consumption was used as key variable for evaluating the optimization procedure. Errors less than 1% between simulated and experimental data were found. The obtained results showed that the use of ANN provides an excellent predictive performance tool with the additional capability to assess the influence of each operating parameter on the removal process of water pollutants.
H.I. Villafán-Vidales,C.A. Arancibia-Bulnes, S. Abanades, D. Riveros-Rosas, H. Romero-Paredes
Publicado:13 de Octubre 2011
A directly irradiated cavity solar reactor devoted to the thermal reduction of SnO2 particle-cloud is studied numerically by using the Monte Carlo method. The steady-state model solves the radiation and convection heat transfers in the semitransparent particle suspension and the chemical reaction. It was used to predict the temperature distribution and the reaction extent inside the cavity, as well as the theoretical thermochemical efficiency for different operational conditions. The simulations assume that the reactor contains a nonuniform size suspension of radiatively participating reacting SnO2 particles. The model takes into account the radiative characteristics of the particles, as well as the directional characteristics of the power distribution of the incoming concentrated solar energy. The particle concentration, the particle size, and the length of the reactor are varied. Results show that the particle temperature and the yield of the endothermic reaction are higher when the reactor is fed with a cloud of particles with average diameter of 20 μm. The maximal thermochemical efficiency reached is 10%, which corresponds to an optimal optical thickness of around 2.
H. I. Villafán-Vidales; C. A. Arancibia-Bulnes, U. Dehesa-Carrasco, H. Romero-Paredes
Publicado:28 de Noviembre 2008
Radiative heat transfer in a solar thermochemical reactor for the thermal reduction of cerium oxide is simulated with the Monte Carlo method. The directional characteristics and the power distribution of the concentrated solar radiation that enters the cavity is obtained by carrying out a Monte Carlo ray tracing of a paraboloidal concentrator. It is considered that the reactor contains a gas/particle suspension directly exposed to concentrated solar radiation. The suspension is treated as a non-isothermal, non-gray, absorbing, emitting, and anisotropically scattering medium. The transport coefficients of the particles are obtained from Mie-scattering theory by using the optical properties of cerium oxide. From the simulations, the aperture radius and the particle concentration were optimized to match the characteristics of the considered concentrator.
D. Riveros-Rosas, M. Sánchez-González, C. A. Arancibia-Bulnes, C. A. Estrada.
Publicado: 19 de Agosto 2011
It is a common practice in the development of point focus solar concentrators to use multiple identical reflecting facets, as a practical and economic alternative for the design and construction of large systems. This kind of systems behaves in a different manner than continuous paraboloidal concentrators. A theoretical study is carried out to understand the effect of the size of facets and of their optical errors in multiple facet point focus solar concentrating systems. For this purpose, a ray tracing program was developed based on the convolution technique, in which the brightness distribution of the sun and the optical errors of the reflecting surfaces are considered. The study shows that both the peak of concentration and the optimal focal distance of the system strongly depend on the size of the facets, and on their optical errors. These results are useful to help concentrator developers to have a better understanding of the relationship between manufacturing design restrictions and final optical behavior.
D. Riveros-Rosas, J. Herrera-Vázquez, C. Pérez-Rábago, C.A. Arancibia-Bulnes, S. Vázquez-Montiel, M. Sánchez-González, F. Granados-Agustín, O. Jaramillo, Estrada C.A.
Publicado: 19 de Marzo 2010
Radiative heat transfer in a solar thermochemical reactor for the thermal reduction of cerium oxide is simulated with the Monte Carlo method. The directional characteristics and the power distribution of the concentrated solar radiation that enters the cavity is obtained by carrying out a Monte Carlo ray tracing of a paraboloidal concentrator. It is considered that the reactor contains a gas/particle suspension directly exposed to concentrated solar radiation. The suspension is treated as a non-isothermal, non-gray, absorbing, emitting, and anisotropically scattering medium. The transport coefficients of the particles are obtained from Mie-scattering theory by using the optical properties of cerium oxide. From the simulations, the aperture radius and the particle concentration were optimized to match the characteristics of the considered concentrator.
P. J. Valades-Pelayo, C. A. Arancibia-Bulnes, H. Villafan-Vidales, and H. Romero-Paredes
Publicado: 31 de Mayo 2016
A multi-tubular solar thermochemical cavity reactor is proposed and the tubular array optimized. The optimized reactor design aims at operating under different temperatures and carrying out different kinds of thermochemical reactions. The radiation entering the receptacle comes from a solar concentrating system and the reactor consists of a cubic receptacle made of woven graphite, housing nine 2.54 cm diameter tungsten tubes. A model is developed and implemented considering high-temperature radiative transfer at steady state. The temperature distribution within the cavity surfaces is determined by employing a hybrid Monte Carlo-Finite Volume approach. Optimal tube distributions are explored by using a custom-made stochastic, multi-parameter, optimization algorithm. In this way, multiple global maxima are determined. Patterns among all possible optimal tube distributions within the cavity are obtained for different scenarios, by maximizing average tube temperature. From this study, practical guidelines are obtained for future application in the design of solar cavity reactors and more specifically, on the layout of multi tubular arrays to optimize radiative heat transfer.
Samaniego-Rascón, Danyela ., Arancibia-Bulnes, C., & León-Duarte, J.
Publicado: Mayo 2012
Se hizo una estimación de riesgos oculares por radiación solar concentrada en una instalación de tipo torre central destinada al aprovechamiento de energía solar. Dicha instalación es el Campo de Prueba de Helióstatos, operado conjuntamente por la Universidad Nacional Autónoma de México y la Universidad de Sonora, y recientemente inaugurado, en Hermosillo, México. La evaluación de riesgos potenciales del brillo y resplandor, originados por el receptor y las superficies de los helióstatos, fue realizada de acuerdo con la metodología propuesta en las investigaciones mas recientes. Donde, se estimaron los niveles de radiación solar concentrada mediante el software de trazo de rayos, SOLTRACE. Los niveles de radiación reflejada se comparan con los límites máximos permisibles expuestos en estudios anteriores.
Samaniego-Rascón, D., León-Duarte, J. A., & Arancibia-Bulnes, C. C.
Publicado: Octubre 2012
Se realizo una estimación de riesgos oculares por radiación solar concentrada en una instalación de tipo torre central destinada al aprovechamiento de energía solar, la cual es llamada CPH o bien Campo de Prueba de Helióstatos, operado conjuntamente por la Universidad Nacional Autónoma de México y la Universidad de Sonora, y recientemente inaugurado, en Hermosillo, México. En esta investigación efectuó un análisis representativo que muestra la situación actual de la instalación, basado en los límites máximos permisibles propuestos en estudios anteriores y posteriormente en revisión de ciertas normativas, se proponen medidas de seguridad para contrarrestar los riesgos potenciales a la salud humana.
Danyela Samaniego Rascón, Almerindo D. Ferreira, Manuel Gameiro da Silva
Publicado : Noviembre 2016
Abstract
Due to the growing motivation of countries to use renewable energy, instead of fossil fuels, for the production of electricity, the number of solar power plants had an increase in recent times. The sun as a renewable source is used by the Concentrated Solar Power systems (CSP) to achieve this goal. This process results in a considerable amount of concentrated solar radiation (visible light, infrared and ultraviolet radiation) inside and in the neighborhood of the installations. Some previous studies have addressed the possible risks for health of workers in environments where they perform activities in outdoors exposed to solar radiation. The overall purpose of this paper is to provide information about the environmental conditions in facilities using CSP technology, the effects of solar radiation in humans and the methods for the risk assessment in this type of facilities. Several standards including elements applicable to the field of occupational health in the central receiver area of solar power plants are also referred.
Danyela Samaniego Rascón, Almerindo D. Ferreira, Manuel Gameiro da Silva
Publicado: Octubre 2017
Abstract
On account of the scarcity of fossil fuels and the environmental problems arising from its use and exploitation, countries are opting for developing technologies based on renewable sources as alternatives to achieve the growing energy demand. Among the renewable energy technologies, solar energy seems to be an attractive solution. Usually solar power plants are located in sunny environments due to requirements for power generation. Meanwhile, as the ozone layer damage has been exceeding its natural restoration, a growing level of UV radiation reaches the surface of the earth where the solar industry working public will be facing new risks; among them skin risks. The present paper, focusing on the proper usage of the renewable source, aims to assess skin exposures to solar radiation within solar industry. The assessment was based on direct solar radiation measurements carried out in an experimental solar facility in Mexico. The maximum time to stay unprotected without receiving a noticeable impact on skin is calculated and security measures for solar industry workers are suggested. This research may be seen as a basic evidence of an area within solar industry with improvement opportunities and assist the development of security procedures applicable to solar energy plants' working environments.
Danyela Samaniego Rascón , Almerindo D. Ferreira , Manuel C. Gameiro da Silva , Cuitlahuac Iriarte
Publicado: Abril 2018
Abstract
Among the Concentrated Solar Power technologies, central receiver systems (CRS) is the technology moving to the forefront in market penetration. CRS requires the use of heliostats oriented toward the central receiver in order to concentrate solar radiation. The excess of light due to the reflection of the sunlight on the heliostats' surface and the brightness of the receiver are considered as possible situations of risk for the eye. The paper briefly outlines the physiological response to solar radiation subjected to momentary ocular exposures. This will be followed by the description of health impairments and the presentation of the methodology and safety doses. A case of study based on direct solar radiation measurements, is foreseen. Two scenarios were evaluated, the action of seeing directly to a heliostats' surface and the action of seeing the reflected radiation from the receiver. In the case of seeing the brightness from receiver, there exist a low potential to cause a temporary effect on the eye. Besides, a person that is looking at heliostat surface has a huge potential to present a temporary effect (after-image). The final section of the study will present and discussed the results obtained from the analysis of the case of study and provide some recommendations. The investigation aims to contribute with information directed to environmental scientists, standard developers and the solar industry that could improve/develop safety procedures directed toward the occupational health and safety within solar energy applications.
Danyela Samaniego-Rascón , Manuel C. Gameiro da Silva , Almerindo D. Ferreira , Rafael E. Cabanillas-Lopez
Publicado: Octubre 2019
Abstract
Due to production requirements, solar facilities are usually located in sunny environments where workers face hot weather. Heat is seen as an environmental and occupational hazard with its physiological effects due to high-temperature exposures. Among the heat-related effects are, dehydration, heat exhaustion, heat stroke, and death. The heat-related impairments on health could also negatively impact the performance of the workers and simultaneously, decrease their productivity. While climate change the already known effects on health could become more frequent, prevalent, and spread. The present investigation provides an analysis of the level of heat stress experienced by a worker based on Wet-bulb Globe Temperature measurements. The study was conducted at a solar energy facility in Mexico. The results show that sometimes workers develop their tasks under conditions above the alert limits of exposure. Solar workers without acclimatization and heavy workload requirements (400 kcal/h) need to rest 75% from an hour and 50% when the workload is moderate (300 kcal/h). Consequently, the percentage of work capacity was established for different scenarios. The period of risk alert during a recorded heat wave, where the worker would mainly require to stop all the physical activities, started at 6:30 am and ended at 6:50 pm. In the final section, preventive measures are suggested. This research aims to contribute with information directed to environmental scientists, standard/policy developers and the solar industry that could improve/develop safety procedures directed toward the heat-related occupational health and safety within solar energy applications under the climate change conditions.