The effects of thermal gradients in a solar adsorption heat pump utilizing the zeolite-water pair

An arrangement involving zeolite synthesized on metal wire gauzes was recently proposed to eliminate the limitations caused by insufficient heat transfer within the solar collector and a related mathematical model was presented. According to such an arrangement, zeolite 4A is envisioned to be synthesized as continuous coatings on stainless steel wire gauzes which are assumed to be placed in the collector vertically in a manner assuring a firm contact between the absorber plate and the wire gauzes. In this study, the same mathematical model is employed to determine the efficiency of the solar adsorption heat pumps under various conditions and the results are compared with those obtained by assuming the employment of a conventional arrangement leading to various amounts of thermal gradients in the solar collector. The effects of the thermal gradients on the performance of the system are investigated by taking into account the employment of zeolite 4A and zeolite 13X, and by varying the weather conditions as well as the difference between the condenser and evaporator temperatures. As a result, the presence of the thermal gradients in a solar collector is observed to decrease the COPsolar values, indicators of the efficiency of the system, to a great extent, especially when a large amount of zeolite is to be utilized. In the case of the employment of zeolite 13X, the adverse effects of thermal gradients on COPsolar are more pronounced. (C) 1999 Elsevier Science Ltd. All rights reserved.