Thermal Energy Conservation System|Research|
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Thermal Energy Conversion Systems Laboratory, Department of Energy and Environmental Engineering

Heat Pump/Refrigeration Cycles

Refrigerants for heat pumps and refrigerators have a strong global warming effect compared with carbon dioxide (CO2). The global warming potentials, GWPs, of these refrigerants are several hundred-times to more than one thousand-times larger than that of CO2. Therefore, it is a global requirement that refrigerants be shifted to natural or low GWP refrigerants. In this context, the research on refrigerant properties, includeing thermophysical properties, heat transfer characteristics, and cycle performances, are essential to the design of new heat pump/refrigeration systems with natural or low GWP refrigerants. Our laboratory collaborates with Research Center for Next Generation Refrigerant Properties (NEXT-RP), International Institute for Carbon-Neutral Energy Research, Kyushu University on this issue.

Experimental set up for heat pump cycles with low GWP refrigerants

Adsorption Heat Pumps and Thermal Storage

We perform experiment of adsorption heat pump/thermal storage systems with activated carbon-ethanol pair. The commercialized adsorption chillers use water as a refrigerant and hydrophilic materials, such as silica gel and zeolite, as adsorbents. We focused on activated carbons as an adsorbent for heat pump applications because it has a large specific surface area, it adsorbs various type of refrigerant such as alcohols, hydrofluorocarbons etc., and it can be produced from a variety of orignal materials. Activated carbons can adsorb even water at a large capacity under humid conditions.
Activated carbons have a large surface area and a large micro pore volume, which asures a large adsorption uptake. On the other hand, a large porocity results in low effective thmal conductivity. In addition, high performance activated carbons are in microscale particles, which also causes several technical issues on heat transfer as well as on production of heat exchangers. Therefore, we also study a composite adsorbent to enhance the heat transfer of activated carbons.

Experimental set up for heat pump cycles with low GWP refrigerants