Abstract
Activated carbon is a suitable adsorbent for adsorption heat pumps (AHPs) with ethanol refrigerants. Although chemically activated carbon with highly developed pore structures exhibits good ethanol adsorption, the associated high production costs inhibit its practical application as an AHP adsorbent. Moreover, although physical activation can produce inexpensive activated carbon, the limited pore development limits the ethanol uptake. Recently, we developed a pressurized physical activation method that can produce activated carbon with a well-developed pore structure and characteristic pore size distribution. In this study, we investigated the applicability of the pressurized physically activated carbon as an adsorbent in activated carbon–ethanol AHP systems. Because of the large number of pressurization-induced pores of appropriate size, the pressurized physically activated carbon showed effective ethanol uptake comparable with that of chemically activated carbon on a weight basis. Furthermore, on a volume basis, the pressurized physically activated carbon, with a high bulk density, showed much higher effective ethanol uptake than chemically activated carbon. These results confirm the potential of the pressurized physically activated carbon as a relatively inexpensive high-performance adsorbent for AHP systems with ethanol refrigerants.
Highlights
Today, environmental friendliness, CO2 emission reduction, thermal energy efficiency, and thermal management are important global concerns
The adsorption heat pump (AHP) is commercially available as adsorption type refrigerators. These refrigerators are equipped with a porous adsorbent and operate based on the adsorption cooling principle proposed by Faraday in 1848.1 Unlike other types of heat pumps, adsorption heat pumps (AHPs) require almost no electricity for their operation and produce minimal vibration and noise
“effective adsorption uptake” is used to denote the difference in adsorption uptake between adsorption and regeneration conditions, as a critical index to assess the performance of AHP systems
Summary
Examples of AHP refrigerants include NH3, water, alcohol, and CO2,2–4 while porous materials such as silica gel, synthetic zeolite, and activated carbon are used as adsorbents.[5,6,7] Synthetic zeolite–water is a commercial AHP adsorbent–refrigerant combination. “effective adsorption uptake” is used to denote the difference in adsorption uptake between adsorption and regeneration (desorption) conditions, as a critical index to assess the performance of AHP systems This is because the AHP working pressure range is determined by the AHP operation temperatures (i.e., the temperatures of cooling water, the surrounding environment, and regeneration) and does not include the overall relative pressure (P/P0) range of refrigerant (0–1). Assumption of 283, 303, and 353 K for the cooling water, the surrounding environment, and regeneration temperatures, respectively Under this condition, the maximum effective ethanol uptake occurred at a carbon pore slit width of 1.6 nm.[14] Chemically activated carbon with an average pore width of 1.6 nm showed a high effective ethanol uptake of >700 mg gÀ1.14. Activation yield 1⁄2% 1⁄4 weight after activation  100 weight before activation
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