Numerical Simulation And Optimization Study On The Adsorbent Bed For CaCl₂-NH₃Adsorption Refrigeration System

Adsorption refrigeration, a promising technique for utilizing low-grade thermal energy, has more advantages than the vapor compressing refrigeration especially in environment protection and energy conservation. However, the longer refrigeration cycle time caused by the heat and mass transfer in the adsorbent bed constrains its widely use. Thus, how to improve the heat and mass transfer efficiency of the adsorbent bed is the key content of recent adsorption refrigeration research.In this study, the adsorbent refrigeration system uses solar energy as the main energy source, ammonia as the refrigerant and calcium chloride/expanded graphite as adsorbent. The adsorbent bed has a self-designed structure. To evaluate the performance and optimize the structure of the adsorbent bed, a numerical simulation of the desorption stage in the adsorbent bed is conducted using FLUENT software. The works and results of the study are as follows:(1) Thinking about the chemical reaction in the adsorbent bed working process and its effect on the heat transfer, the desorption reaction model is established and studied, and the heat source user-defined function is programmed in C code.(2) The structure and working characters are analyzed, and the physical and mathematical models of the adsorbent bed are established under some reasonable assumptions of the working conditions.(3) The working characters of the adsorbent bed, including temperature distribution, temperature increasing, ammonia production and refrigeration efficiency, are analyzed with the simulation results.(4) Adsorbent beds with different filling layers counts and filling diameters are analyzed on their heat transfer performance, and optimized structures are finally confirmed.(5) Adsorbent beds work with different inlet velocity are compared on heat transfer and cooling efficiency. This study provides an intuitive and simple method to study the adsorbent bed in the chemical adsorption refrigeration system. Analyzing the structure using this method can provide the theory to the optimization of the adsorbent beds.