Dynamic variation of bed parameters and time optimisation of solar adsorption refrigeration system based on CFD simulation

Abstract

One major reason for the limited application of adsorption refrigeration systems is their lower refrigeration efficiency and performance compared to other alternatives. Additionally, there is limited research focused on optimizing the system performance over time. This paper presents a numerically validated thermodynamic model to analyse the effect of adsorption time on the performance efficiency enhancement of a solar adsorption refrigeration system. The adsorption rate model proposed by Sokoda and Suzuki has been used to evaluate the adsorption and desorption characteristics of water vapor on silica gel and the solar collector system has been fitted to a heat flow density equation based on measured concentrated solar heating. The water vapor adsorption capacity on silica gel as a function of temperature and pressure in the adsorption bed has been numerically evaluated during the four stages of the cooling cycle, namely adsorption, preheating, desorption, and cooling. The coefficient of performance and specific cooling power have been utilized as the major performance indicators, in the context of the influence of adsorption time on the refrigeration performance of the system. The simulation results revealed that, although increasing the adsorption time increased the system's cooling capacity, it also prolonged the cycle time and adversely affected the dynamics of preheating and desorption processes (due to increased solar input). As a result of the numerical simulation, an optimum value of adsorption time has been predicted to be 71 min corresponding to a coefficient of performance equal to 0.476 and a specific cooling power equal to 28.6 W/kg.