Development research on composite adsorbents applied in adsorption heat pump

A novel adsorbent design technique base on the concept of Kelvin equation was proposed to develop hydrophilic adsorbent applicable to water vapor adsorption heat pump (AHP) for high performance. In the process, the composite adsorbent was prepared after silica gel was synthesized in the pores of activated carbons by impregnating activated carbons in sodium silicate solution. Two kinds of activated carbons were tested to produce composite adsorbent and to investigate the performance by measuring the adsorption isotherms of water vapor and pore structure characteristics. All adsorption isotherms of the silica impregnated activated carbons prepared shifted to a lower region of water vapor pressure compared to those of the raw activated carbons. The volume-based amount of adsorption in the AHP operation range (φ = 0.1–0.4) for the adsorbents prepared at sodium silicate solution concentration of 10 wt.% and impregnating time of 48 h are 5.88 and 2.62 times that of the raw activated carbons (AC1 and AC2), respectively. Based on the Kelvin equation, it is clarified that the contact angle and the volume of pore radius greater than 1.2 nm decrease with the increase of sodium silicate solution concentration for the novel composite adsorbents, which contributes the isothermals shift to lower relative pressure range.