Development and validation of a microchannel evaporator model for a CO2 air-conditioning system

This paper presents an analysis/computer model to predict the performance of an evaporator for a CO2 mobile air-conditioning system. Based on the finite volume method, the model has been developed using mass and energy conservation equations, with emphasis placed on the refrigerant-side heat transfer and pressure drop characteristics. Moreover, the pressure losses both in the headers and at the port inlet of the microchannel tube were also considered. The in-tube refrigerant flow was divided into two-phase region and superheated region, and both dry and wet conditions were considered. Using the newly developed refrigerant-side heat transfer and pressure drop correlations, the model can predict the performance of evaporator with a reasonable accuracy compared with the experimental data. The errors of RMS for cooling capacities and refrigerant-side pressure drops were ±1.9% and ±12.3%, respectively. Furthermore, the effects selecting different refrigerant-side heat transfer and pressure drop models on the performance of evaporator were discussed. The program can be used to analyze and design a CO2 microchannel evaporator.