The effects of thermal and mass diffusivities on the performance of adsorption heat pumps employing zeolite synthesized on metal supports

Abstract

In order to increase the efficiency of adsorption heat pumps, an arrangement involving zeolite 4A synthesized on metal heat exchanger tubes was recently proposed and a related mathematical model was presented. In this study, the same mathematical model was employed to determine the effects of the metal type and the thermal and mass diffusivities of the adsorbent on the performance of the adsorption heat pumps. The calculations were performed for two different wall thickness values of the heat exchanger tubes and various zeolite layer thicknesses. Copper, nickel and stainless steel heat exchanger tubes were tested for their suitability to be used in the system, and the effects of the thermal and mass diffusivities related to the adsorbent were investigated in the ranges of 0.0004 to 0.0023 cm 2 s −1 and 4×10 −7 to 1×10 −5 cm 2 s −1, respectively. As a result, the diffusion coefficient was observed to be the limiting factor for the adsorption heat pumps employing the zeolite–water pair in determining the optimum thickness of the zeolite layer synthesized on metal heat exchanger tubes, while the effects of the metal type and the thermal diffusivity of the adsorbent were observed to be of trivial importance.