Thermodynamic analysis of adsorption refrigeration cycles

High- and mid-temperature waste heat can be recovered by using existing heat pump technologies. However, heat utilization near environmental temperatures still faces technical hurdles. Silica gel-water adsorption cycles have a distinct advantage over other systems in their ability to be driven by near-ambient temperature heat. Waste heat (above 60°C) can be exploited by using conventional silica gel-water adsorption chiller. The advanced silica-gel-water adsorption chiller can operate effectively by utilizing low-grade waste heat (~50°C) as the driving source with a cooling source of 30°C. In this paper, the effect of operating temperatures on cycle performance is discussed from the thermodynamic viewpoint. The temperature effectiveness and the entropy generation number on cycle time are analyzed. For a comparatively short cycle time, adsorber/desorber heat exchanger temperature effectiveness reaches up to 92% after only 200 sec. The entropy generation number N_s is defined by the ratio between irreversibility generated during a cycle and availability of the heat transfer fluid. The result showed that for the advanced adsorption cycle the entropy generation number N_s is smaller for hot water temperature between 45 to 55°C with a cooling source of 30°C, while for the conventional cycle N_s is smaller for hot water temperature between 65 to 75°C with the same cooling source temperature