INFLUENCE OF VARIABLE THERMAL CONDUCTIVITY AND PERMEABILITY OF ADSORBENTS ON SIMULATION: A CASE STUDY OF A TWO-STAGE FREEZING SYSTEM

Abstract

In the conventional simulation of the adsorption refrigeration performance, the constant thermal conductivity and permeability were always chosen for the construction of a mathematical model. Recent research works showed that the thermal conductivity and permeability change significantly in the adsorption and desorption processes, which means that the consequent adsorption refrigeration performance will also be influenced. In order to evaluate the influence of the variable thermal conductivity and permeability of adsorbents on the performance of adsorption refrigeration system, the variable thermal conductivity and permeability in the adsorption processes were tested for CaCl2 and BaCl2, and the two-stage adsorption refrigeration system was simulated using CaCl2 -BaCl2 -NH3 as a working pair. The simulation results for the variable thermal conductivity and permeability were compared with those for the constant thermal conductivity and permeability, as well as with experimental results. The research showed that the maximum relative error between the simulation result with variable properties and the experimental result was 9.1% for SCP, 8.3% for cooling capacity, and 12% for COP, respectively, while the maximum relative error between the simulation results with constant properties and experimental results was as high as 42.8% for SCP, 41.4% for cooling capacity, and 36% for COP, respectively. The foregoing demonstrates that the variable properties influence significantly the simulation results, and should be investigated in the first place before constructing mathematical models for chemical adsorption refrigeration systems.