Study for the optimum uptake capacity of silica gel used in a solar adsorption chiller

Abstract

Adsorption technology is one of the alternatives to reduce the usage of fossil fuel. Among the variety of adsorbent-adsorbate pairs, silica gel and water is the most desired one due to its preferred properties. This pair is widely available, environmentally benign and can be activated with lower temperature heat source. In order to utilize silica gel-water pair in a solar heat driven adsorption chiller, one needs to study the operating conditions for the maximum utilization of the entropy of the adsorbent. Better cooling capacity is not ensured by high temperature hot flow to heat up the desorber or high pressure-gradient. Rather it depends on thermodynamic properties and on higher concentration gradient of the adsorbent. For silica gel-water pair, to increase concentration gradient in adsorption bed, temperature of the adsorption bed need to be reduced below 30°C. But, for an autonomous solar heat driven chiller it is difficult to reduce adsorption bed temperature below ambient temperature. One way to solve the problem is to reduce adsorbent mass inside the bed by distributing it in three identical beds and run the three-bed system in a series and by taking a longer pre-cooling time.