Heat exchanger design effect on the system performance of silica gel adsorption refrigeration systems

This article presents a numerical investigation of the heat exchanger design effect on the performance of closed cycle, two-bed adsorption cooling systems with silica gel as adsorbent and water as refrigerant. It is well known that the shorter the cycle time, lower is the performance (cooling capacity and coefficient of performance). A long cycle time is responsible for lower cooling capacity. In this study, a non-dimensional switching frequency, which is inversely proportional to the cycle time, is defined and an optimum switching frequency is derived based on parametric analysis. The effect of other heat exchanger design parameters such as adsorbent number of transfer unit (NTU), bed Biot number (Bi), the heat exchanger aspect ratio (Ar) and the ratio of fluid channel radius to the adsorbent thickness (Hr), on the system performance has been investigated. The results show that the switching frequency ω, bed NTU, Ar and bed Bi have strong effects on the system performance. It is also seen that for a given set of design parameters, the system has an optimum switching frequency and the system performance will be declined seriously if the system is not operated at optimum switching frequency. The optimum switching frequency increases with the increase of NTU, Hr and with the decrease of Bi and Ar.