A novel approach to determine optimum switching frequency of a conventional adsorption chiller

This article investigates the effect of design parameters on the switching frequency of a conventional adsorption chiller with silica gel as adsorbent and water as adsorbate. It is well known that as the cycle time lengthens, the coefficient of performance (COP) rises but the cooling capacity lowers. Optimum cycle time is dependendent on the requirements of COP and cooling capacity. A novel simulation technique that introduces a profit function is employed to determine the optimum switching frequency of an adsorption refrigeration system. The results show that optimum switching frequency is very sensitive to the heat exchanger's design parameters. The design parameters are characterized by the number of transfer unit, NTU, the Biot number of adsorbent bed, Bi, the aspect ratio, AR, the ratio of the heat exchanger thickness to the radius of the fluid channel Hr, the fluid alpha number, α_f-a and the inert material alpha number, α_m-a. The optimum switching frequency increases with the increase of NTU, Hr and with the decrease of Bi, AR, α_m-a and α_f-a.