A Numerical Simulation on Heat Transfer Characteristics in the Cascade Heat Exchanger of a R134a/CO2 Refrigeration System

This study focused on the phase transition of two refrigerants CO2 and R134a using the numerical simulation method. The COMSOL Multiphysics 5.3a software was used to 3D simulate CO2 condensation and R134a evaporation of a double pipe heat exchanger in a cascade refrigeration system. The simulation results indicate the heat transfer characteristics including temperature field, quality vapor, and fluid flow characteristics including velocity and pressure also. The above results are very consistent with those obtained from experiments under the same conditions. In addition, when the evaporation temperature of R134a increases, the inlet temperature and the condensation temperature of CO2 increase, respectively. Besides, the evaporation temperature of R134a increases from 3.6 °C to 4.7 °C while the CO2 condensation temperature increases from 7.9 °C to 9.7 °C and the CO2 inlet temperature increases from 58.8 °C to 63.8 °C correspondingly.