Study on Single- and Multi-Stage Adsorption Cooling Cycles Working at Sub and Above Atmospheric Conditions

This study deals with the performance analysis of single- and multi-stage adsorption cooling cycles working at partial vacuum and pressurized conditions for cooling applications. Four adsorbent-refrigerant pairs namely activated carbon fiber-ethanol, silica gel-water, Maxsorb II-R134a and Fluka-R134a pairs have been investigated. The former two pairs are deemed to be suitable for adsorption cycles working at pressures ranging from 1 to 11 kPa while the latter two are suitable for those working at above atmospheric pressure conditions typically between about 0.3 and 0.8 MPa. Invoking the adsorption isotherms of the assorted pairs, the pressure-temperature-concentration (P-T-W) diagrams have been presented. Pertaining a thermodynamic framework, the performance of both single- and multi-stage cycles in terms of specific cooling effect (SCE) and coefficient of performance (COP) has also been studied. Theoretical results show that the former two pairs i.e., the adsorption cycles working at partial vacuum pressures are suitable for surface cooling while latter two are suitable for micro cooling applications. Moreover, the multi-stage adsorption cycles can be operational at a heat source temperature below about 55°C, a region that could not be reached by any conventional adsorption cycle.