Selection of Adsorbents for Double-Effect Adsorption Refrigeration Cycle Combined Compressor

Abstract

A system which is driven by low-grade heat around 60–90 °C is expected to enhance the use of the solar heat and waste heat. The adsorption refrigeration is capable of operating at low-grade heat while the challenge is how to increase the efficiency of current implementations of adsorption refrigerators. The double-effect cycles have higher COP than a conventional single-stage adsorption cycle because the heat generated from an adsorption process is recovered and reused as a heat source. The double-effect cycles consist of two adsorbers, and there exists freedom to select adsorbent for them. The water adsorbent isotherm of FAM was S shaped and highly dependent on adsorption pressure, and the combination of FAM will be effective for the double-effect cycle according to the adsorption pressure. However, operating temperature range of the double-effect cycles is higher than the conventional single-effect adsorption cycle; the double-effect cycles have lower COP below 80 °C because the condition of adsorption pressure at this temperature range is not suitable for any adsorbents. This study suggests using the double-effect adsorption cycles combined a compressor with a view to improving COP below 80 °C. The compressor sets up, and the adsorption pressure is controlled by compressed refrigerant vapor. The adsorption cycle can work under a lot of changes due to adjusting the adsorption pressure regardless of the external temperature like the heat source. The effect of the combination of adsorbents on adsorption cycle and installation position of a compressor is not clear. The objective of this study is to investigate the COP, SCE, and exergy efficiency of double-effect adsorption cycles with various installation position of a compressor and various adsorbent pairs FAM Z01, FAM Z02, and FAM Z05. The double-effect cycle is examined by means of the static cycle simulation assuming equilibrium stats where the cooling effect is dominated by driven heat source temperature, cooling water temperature, evaporator pressure, condenser pressure, and adsorption pressure. The results from the static cycle simulation imply that the hybrid double-effect adsorption refrigeration cycle is the efficient refrigeration cycle and can enhance the performance. For heat sources in the temperature range of 60–90 °C, the method is superior when the compressor is installed on the high-pressure side and adsorbent pair is Z02-Z01. COP amounts to 1.2, SCE amounts to 350 kJ/kg, and exergy efficiency amounts to 0.45 by supplying a minimal power consumption to the compressor. As a result, this system is expected to increase the non-utilized heat such as solar heat or waste heat utilization.