Dynamic modeling of the combined heat and mass transfer during the adsorption/desorption of water vapor into/from a zeolite layer of an adsorption heat pump

Abstract

This paper presents a one-dimensional model describing the combined heat and mass transfer during the adsorption/desorption of water vapor into/from a zeolite layer in a small-scale adsorption heat pump. The model is utilized to study the dynamics of both adsorption and desorption processes as well as to examine the influence of both the layer thickness and the volume of the vapor phase of the adsorber/desorber heat exchanger on their time requirements. The model equations have been numerically solved using the software packet gPROMS ( general PROcess Modeling System) [ http://www.psenterprise.com/gPROMS]. The duration of the adsorption process is found to be generally longer than that of the desorption process, depending on the zeolite layer thickness. Reducing the layer thickness by 50% results in a reduction to 25% in the duration of the adsorption process and to about 33% of the desorption process. In order to get reasonable power densities from an adsorption heat pump using zeolite layers, the layer thickness must not exceed 2.5 mm. Moreover, the volume of the vapor phase of the adsorber/desorber heat exchanger has to be minimized, in order to minimize the unavoidable losses of the coefficient of performance of the periodical adsorption heat pump due to the pre-cooling as well as the pre-heating phases.