Numerical investigation of operating conditions to improve the entropy of silica gel-water driven solar adsorption chiller

Abstract

Solar powered adsorption cooling system had been investigated with different adsorbate/ adsorbent pair. This thesis deals with the numerical investigation of operating conditions to improve the entropy of silica gel water driven solar adsorption chiller. It is seen that the output of solar assisted adsorption cooler can be enhanced if the total amount of adsorbent can be distributed in multiple small adsorption beds, specially when available solar irradiance is limited. As a continuation of the study with multiple beds, the performance of a newly proposed cooling unit with 4-beds has been investigated. A new parallel system of 4-beds is considered in such a way that, when one conventional 2- bed chiller is in adsorption/ desorption mode then the other chiller is in preheat/ precool mode and the system goes on alternately. For the present case, both the systems are linked with a single evaporator and condenser. The total amount of adsorbent is distributed uniformly in four identical beds (23.5 kg/bed) resulting in a continuous evaporation and condensation process. Total 20 CPC solar thermal collectors (each of area 1.72 m2) has been considered for this study, where, one system has been connected with 10 CPC collectors and the rest were connected with the other system. However, for this new system, the performance is very much inspiring for low grade heat input. This system uses shorter cycle time (total 480s), uses 34.4 m2 of solar thermal CPC collector. Moreover, this new system produces 14 kW cyclic average cooling capacity, whereas, for the same collector area, a conventional 2-bed system produces CACC of 7.91 kW. To analyze all the things the governing equations are solved by finite difference approximation method. A cycle simulation computer program is used to analyze the better chiller performance, such as, enhanced cooling capacity (CC) and coefficient of performance (COP) are expected.