Experimental investigation of CO2 gas cooler/condenser in a refrigeration system

Natural refrigerants including CO2 have been recognized as the most promising working fluids and have been widely applied in refrigeration systems over the last decade. Owing to its attractive thermo-physical properties and negligible environmental impact, the CO2 refrigerant can be used as a replacement for convectional HFC working fluids. Normally, CO2 refrigeration systems can be classified into three different groups as indirect, cascade and all CO2 transcritical booster structures. The CO2 booster system has some advantageous over the others in terms of functions and sizes etc. However, the performance of such system still requires further investigation and improvement. This study focused on the experimental investigation into the performance comparison of two CO2 finned-tube gas coolers/condensers with different design structures and their effects on the overall performance of a CO2 booster refrigeration system. The integrated CO2 booster refrigeration system consisted of two variable speed semi-hermetic compressors, a gas cooler/condenser, a liquid receiver, electrically operated expansion valves, a medium temperature display refrigeration cabinet and an additional water/glycol load. The refrigeration system and especially the CO2 gas cooler/condenser had been comprehensively instrumented to enable detailed monitoring of the system and the heat exchanger at different operating states. Results for the system performance were obtained and analysed for different CO2 gas coolers/condensers. The results include the effect of heat exchanger designs and fan operations on the system performance. In addition, the controls of supercritical and subcritical pressures and cooling capacity are described.