Plenary Speakers(Alphabetical Order)

    Porous materials with nanoscale pores are widely used as gas adsorbents. Metal-organic frameworks (MOFs) are highly porous crystalline structures composed of metal nodes and organic linkers; their mesoporous structure enables them to function as excellent gas adsorbents. We are conducting research in material synthesis and functionalization, experimental measurement, and analysis to uncover the excellent gas adsorption performance of MOFs. Furthermore, with a view toward applications in heating, ventilation, and air conditioning (HVAC) technology, we are advancing theoretical and experimental research on the adsorption of water vapor and carbon dioxide in MOFs. More specifically, we are considering the application of water vapor adsorption to humidity control technologies and the application of carbon dioxide adsorption to the “hybrid compression-adsorption heat pump cycle” that we have proposed (Jubair A. Shamim, Gunjan Auti, et al., Cell Reports Physical Science 3, 101131, 2022).

    In this presentation, we discuss interesting topics related to gas adsorption in MOFs at the materials level, as well as the latest results from mechanical component testing, such as heat exchangers coated with MOFs. Regarding MOF-coated heat exchangers, we tested the water heating and cooling characteristics achieved by adsorbing and desorbing CO₂ on these heat exchangers, with the aim of developing a subcritical CO₂ heat pump (the “hybrid compression-adsorption heat pump cycle” described above). The current experimental setup is a batch operation system that alternates between adsorption and desorption; however, compared to high-pressure CO₂ vapor compression systems and to conventional adsorption heat pumps that rely on thermal regeneration, this system provides heating and cooling in a more environmentally friendly and safer manner. While the lack of continuous operation limits its immediate application, the batch-operation system serves as a test bench for validating key thermodynamic and transport processes of the continuous concept. Finally, we discuss the challenges and prospects of applying gas adsorption technology to HVAC systems, including this hybrid compression-adsorption heat pump cycle.

    This presentation examines the rapid growth of energy consumption in data centers driven by AI and generative AI, and highlights key strategies for improving energy efficiency, particularly through cooling system innovations. Energy efficiency is defined as the ratio of computational output to total energy consumption, encompassing hardware efficiency, rack performance, and facility-level metrics such as PUE. While chip efficiency has improved significantly, overall gains are limited by cooling and infrastructure constraints. Rising chip power densities further intensify the importance of advanced thermal management, which plays a key role in future energy savings in high-performance computing (HPC). The study highlights emerging cooling technologies, including advanced air cooling, immersion cooling, and two-phase systems, which can significantly reduce energy consumption and achieve PUE values below 1.1. In parallel, AI-based HVAC optimization demonstrates notable real-world savings, improving system efficiency by over 20% in field applications. Additionally, waste heat recovery is identified as a promising approach, particularly in subtropical regions, where low-grade heat can be reused through innovative systems such as liquid desiccant cooling.Overall, integrating efficient hardware, advanced cooling, intelligent control, and heat recovery is essential for sustainable data center operation in the AI era.

    In domestic refrigerators using R600a, the refrigerant has been observed to exist in a two-phase state between the condenser outlet and the expansion device inlet, even when its temperature is below the corresponding saturation temperature. This behavior deviates from conventional design assumptions, in which vapor compression refrigeration systems are expected to deliver a fully subcooled liquid at the condenser outlet. To investigate this phenomenon, a series of experiments was conducted to examine the thermodynamic state of R600a at the condenser outlet. A transparent horizontal tube with an inner diameter of 4.3 mm was installed to enable direct visualization of the refrigerant flow. The coexisting phases were separated, and the temperatures of each phase were measured individually. Visual observations, along with temperature and pressure measurements, revealed that R600a exists in a non-equilibrium two-phase state, where subcooled vapor and subcooled liquid coexist at temperatures significantly below the saturation temperature.

    To characterize this non-equilibrium condition, a set of equations was developed to estimate the specific enthalpy of the refrigerant. The proposed method showed good agreement with experimentally measured values, demonstrating its validity for describing the thermodynamic properties of R600a under such conditions.

    Additional experiments were conducted to quantify the impact of this non-equilibrium subcooled two-phase state on system performance. Compared to the conventional equilibrium subcooled state, both the condenser heat rejection and the coefficient of performance (COP) decreased when the refrigerant was in a non-equilibrium two-phase condition. These results indicate that the presence of subcooled vapor has a detrimental effect on system efficiency and should be considered in performance analyses of refrigeration systems using R600a. Furthermore, molecular dynamics (MD) simulations were performed to investigate the influence of residual air mixed with R600a. Trace amounts of air may remain in the system prior to refrigerant charging. The simulation results showed that even a small fraction of residual air can significantly reduce the saturation temperature of the mixture. This effect is considered a plausible explanation for the unexpected thermodynamic behavior of R600a observed in practical refrigeration systems.

    Owing to the rapid development of the semiconductor industry, the heat dissipation from electronic devices increases drastically with increasing device logic gate number and operation speed. The heat dissipation of a single chip doubled from 70 W in 2001 to 150 W in 2011. It doubled again from 150W in 2011 to 300W in 2016, 700 W in 2022, 1,500 W in 2025 and expected to 2,800 W in 2027. The cooling technologies have undergone changes from direct air cooling to forced convective liquid cooling and evolutionary to two-phase evaporating cooling in the past years. For resolving the high-density heat dissipation problem, it is popularly to reduce the channel size to accommodate more heat transfer area on a small heating base area and to be the so-called microchannel heat exchangers. The heat transfer performance of coolant flow in microchannel heat exchangers increased several times through the flow passage shape improvement and channel surface modification. However, the exponential growth rate of heat dissipation is much faster than the improvement in heat transfer performance of micro channel heat exchangers. It has been estimated that the reliable maximum heat flux stated in published literatures will not be able to resolve the heat dissipated from a single chip by the year of 2035. What will be the thermal solution beyond this critical moment? Are there any innovative cooling methods that can handle this extremely high flux heat dissipation? What is the ultimate solution for the high-performance AI data center cooling?