Effect of heat conduction through the fins of a microchannel serpentine gas cooler of transcritical CO₂ system

This paper presents results of an experimental study to investigate the effect of conduction through the fins on the capacity of a serpentine gas cooler. The gas cooler was a part of a transcritical CO₂ system which was operated in A/C mode. The capacity of the gas cooler was carefully measured in the chamber which simulated the outdoor condition with the original heat exchanger. In order to experimentally validate the conduction effect on the capacity, some sections of the fins, where the conduction was most significant, were cut by EDM (Electrical Discharge Machining). The capacity of the heat exchanger, after cutting fins, was measured in the same chamber at nearly identical test conditions as before cutting. Gas cooler capacity was improved up to 3.9% by cutting the fins, and temperature difference between refrigerant exit and air inlet for the gas cooler was reduced by 0.9-1.5 °C. The maximum uncertainty in the capacity measurements was 2.5% and the accuracy of temperature measurements was 0.1 °C. It was shown by system simulation that system COP could be improved by 5% by eliminating this severe conduction effect, as was done in this experiment. The tube surface temperature at some points of the gas cooler was measured and infrared images were taken to show the conduction effect before and after cutting fins.