Theoretical Analysis And Experimental Investigation For Transcritical CO₂ Refrigeration Cycle

As a potential refrigerant substitute, the natural refrigerant of CO₂ has great advantages over the traditional synthesized refrigerant HCFCs and HFCs. It is of great practical significance in energy conservation and environment protection to develop transcritical CO₂ technology. Based on transcritical CO₂ experimental platform for the study, some fundamental data for the development and application of the natural refrigerant CO₂ are obtained according to theoretical analysis, experimental verification and performance optimization.The natural refrigerant of CO₂ has evident advantages in environment protection and thermodynamic property, etc; it can be solved fundamentally of refrigerant substitution problem. In this dissertation, theoretical analysis on transcritical CO₂ single stage compression refrigeration cycle is made; fairly comprehensive experimental study on the system performance is made in order to testify the influence of heat rejection pressure and evaporation temperature and gas cooler and external heat source. Results indicate that: there is an optimum high pressure to achieve the maximum COP; refrigerant charge, evaporation temperature, cooling water temperature, chilled water flow rate and temperature have a great impact on system performance, while the cooling water flow rate has no obvious effect; increase of gas cooler tube length led to better heat exchange efficiency, but effect of high pressure is not obvious; increase of gas cooler exit temperature led to a decrease in the refrigeration quantity and a increase in the compressor power consumption and a rapid increase in the optimal high pressure.Expander cycle has much higher performance than throttle cycle no matter what efficiency the expander is. Increase of expander isentropic efficiency is very important factor in updating system performance. Transcritical CO₂ two-stage compression cycle is an effective method to improve system performance and reduce power comsumption. Performances of transcritical CO₂ two-stage compression cycle are compared. Results show that two-stage compression expander cycle has a higher COP than the others; the overheating of compressor suction port has disadvantages on the system performance; the optimum inter-cooling pressure for two-stage compression cycle deviates from the geometric mean of high pressure and low pressure, but this has little effect on the system performance.In this dissertation, theoretical analysis on CO₂/NH₃ cascade refrigeration cycle is established. Results show that there is an optimum medium temperature of the evaporative condenser to achieve the maximum COP. The performance of CO₂/NH₃ cascade expander cycle with super-cooling is better than traditional R22/R13 cascade cycle and NH₃ two-stage compression cycle; the heat exchange efficiency of regenerator direct influence system performance.