Theoretical Analysis of Transcritical Carbon Dioxide Vapor Compression Cycle

In the transcritical carbon dioxide vapor compression cycle heat is rejected in a gas cooler at supercritical pressure. At supercritical heat rejection the refrigerant temperature and pressure are independent on each other and one of the most important parameters affect on cycle performance is the pressure on the heat rejection side called the high pressure. A theoretical analysis shows the effect of high pressure, superheat, evaporator and gas cooler exit temperature, and gas cooler exit temperature approach on performance of a transcritical carbon dioxide vapor compression cycle was investigated in this study. The study defines an optimal high pressure which gives a maximum coefficient of performance and suggests that the cycle should operate at or near its optimal high pressure in order to keep its maximum coefficient of performance. The high pressure will also affect the cooling capacity and this effect can be used for boosting capacity at high ambient temperatures. The effect of gas cooler exit temperature and compressor inlet temperature on the optimal high pressure also was investigated. The study shows that the optimum high pressure is mainly a function of gas cooler exit temperature and compressor inlet temperature, while the value of the maximum coefficient of performance is dependent on the gas cooler exit and evaporating temperature. The study also indicates that the superheat of the gas at compressor inlet will have a positive effect on the coefficient of performance when operating with high heat rejection pressure at high ambient temperatures with high evaporating temperatures.