STUDIES ON THE PERFORMANCE AND HEAT TRANSFER OF CO2 HEAT PUMP SYSTEM

In the air-conditioning and refrigeration industry, the efforts to protect the environment have mainly focused on carbon dioxide as an alternative refrigerant. Several devices have been proposed and studied to improve the steady-state performance of CO2 heat pump system, such as an expander, two-stage compressor and internal heat exchanger. To enhance the heat transfer characteristics, micro-fin tubes are widely used and its enhancement was quantitatively investigated in this study. The effects of the tube orientation of horizontal, vertical, and inclined arrangements are also studied. As a result, the internal heat exchanger increased COP by 7.1-9.1%, the two-stage gas injection cycle increased COP by 16.5%. Average evaporation heat transfer coefficients for micro-fin tubes were approximately 150 similar to 210% in horizontal tube, 110 similar to 210% in vertical tube, and 110 similar to 170% in inclined tube higher than those for the smooth tube.