Theoretical Analysis And Experimental Research On CO₂ Transcritical Two Stage Cycle

Based on international background of energy efficiency and emission reduction, the CO₂ transcritical cycle products of refrigeration air condition and heat pumps possess promising application prospect. In this dissertation, the performance comparison analysis of CO₂ transcritical two stage cycle was employed mainly by combining theoretical analysis and experimental study. Some fundamental data of investigating high efficiency and steady operation CO₂ transcritical cycle mode were obtained.On the background of three different kinds of CO₂ transcritical single stage cycle, the six kinds of CO₂ transcritical two stage cycle were analyzed and compared by thermodynamics in this dissertation. The results show that the COP of CO₂ transcritical two stage cycle with expander is better than the cycle with valve, and the performance of two stage cycle is also better than the single stage cycle. The intercooler and internal heat exchanger play an important role in developing cycle performance. As the applied fundamental research and synthetical consideration of factors of design and machining, the CO₂ transcritical two stage cycle TSCV+IC with intercooler and valve has a promising application prospect.A CO₂ two stage piston compressor was designed and machininged and the calculation of thermodynamics and kinematics were employed. The irreversible loss simulation analyses of two stage cycle indicate that the flow loss and frictional loss have the largest ratios, the leakage loss and heat transfer loss possess the smaller ratios.Due to CO₂ transcritical two stage cycle system constitutes, characteristic of supercritical and subcritical CO₂ heat transfer and pressure drop, the CO₂ gas cooler and intercooler were analysed and designed, respectively, and some significative assistance can be obtained for CO₂ exchanger.The performance comparison testing of two kinds based experiment of CO₂ transcritical single stage cycle SCV+IHX with internal heat exchanger and CO₂ transcritical single stage cycle SCV with valve were executed, respectively. At the same time, the performance of gas cooler, internal heat exchanger and tube-in-tube evaporator were testing on the experimental bench of CO₂ transcritical single stage cycle SCV+IHX and single stage cycle SCV, and the beneficial test data was provided for research on the CO₂ transcritical two stage cycle. The two stage cycle TSCV+IC and cycle TSCV+TG of CO₂ transcritical experimental results show that the refrigeration COPc and heat COPh have the optimum value with the variation of system intermediate pressure and temperature. In the given experimental condition, the maximum of refrigeration COPc and heat COPh have the same optimum intermediate pressure and temperature, respectively.In same testing condition, the performance of CO₂ transcritical two stage cycle TSCV+IC is better than the two stage cycle TSCV+TG. The heat output Qh and refrigerating output Qc of two stage cycle TSCV+IC are average 10% and 6% bigger than the cycle of TSCV+TG, and the heat COPh and refrigerating COPc are 8% and 5% higher than the cycle TSCV+TG, respectively. The theoretical analysis and experimental testing of CO₂ transcritical two stage cycle TSCV+IC and cycle TSCV+TG are anastomotic.