Development of a New Activated Carbon, Silica-gel and Calcium Chloride Composite Adsorbent in an Energy Efficient Solar Adsorption Cooling System

A new hydrophilic method for achieving high performance adsorbents by impregnating the macropores of activated carbon with silica-gel and calcium chloride has been proposed. In the process, a composite adsorbent was prepared by impregnating the macropores of activated carbon with sodium silicate solution and calcium chloride solution, respectively. The optimized condition was achieved when the raw activated carbon was impregnated with 10wt% silica-gel through soaking in a sodium silicate solution for 48 hours and then soaking in a 30wt% CaCl2 solution for 48 hours. TGA was used to find out the adsorption capacity at temperatures from 25°C to 400°C at the room pressure condition. 0.805 g/g of difference in equilibrium water uptake between 25°C and 115°C was recorded, showing a 324% improvement over its raw activated carbon material. Besides, the equilibrium adsorption capacity from 200Pa to 2000Pa under 27°C was recorded. With the optimum composition, the composite adsorbent can greatly enhance the average specific cooling power (SCP) of solar adsorption cooling systems to 465W/kg and the ideal coefficient of performance (COP) to 0.71 which represents a 1561% and 92% improvement over raw activated carbon, respectively. These results demonstrated that silica activated carbon/CaCl2 composite adsorbents can be a good candidate for thermal system applications driven by low temperature heat sources.