Optimal heat rejection pressure for transcritical CO2 refrigeration cycle with an expander

Heat rejection pressure plays an important role in designing a transcritical CO₂ refrigeration system, and it has an optimal value to maximize the system’s coefficient of performance (COP). With a thermodynamic simulation model, the optimal heat rejection pressure is studied in the paper for an expander cycle, as well as conventional throttle valve cycle. The effects of compressor efficiency, expander efficiency, gas cooler outlet temperature, and evaporation temperature on the optimal heat rejection pressure are analyzed. It is the first time for a transcritical CO₂ expander cycle that the optimal heat rejection pressure is correlated with the gas cooler outlet temperature and the evaporation temperature at given compressor efficiency and expander efficiency. The average deviation from the correlation to simulation results is less than 1.0%. The correlation provides a guideline to system development and performance optimization of a transcritical CO₂ expander cycle.     

Development and Experimental Study of CO2 Expander in CO2 Supercritical Refrigeration Cycles

Abstract

As one of the natural working fluids for the refrigeration system, CO₂ has been attracting increasing attention over the last ten years. But CO₂ has to work at the supercritical region for the so-called “condensation” process regarding the conventional refrigerants and evaporate at the two-phase region, and therefore results in larger throttling loss for the practical refrigeration application. Consequently, new technologies must be developed to improve the performance efficiency of the CO₂ transcritical cycle, and make it to be equal or closer to that of the refrigeration system with the conventional refrigerants. In this study, an expander is employed in the CO₂ transcritical cycle to replace the throttling valve, and as a result the throttling loss can be decreased significantly. The paper presents the development of a rolling piston expander and the activity items in the expander design, including the seal technology, the contact friction control, the suction design, etc. The performance experiments for the expander are conducted in the present testing system for the CO₂ transcritical cycle. The results show that the recovery power of the expander is related to the revolution speed of the expander. The efficiency of the expander prototype is observed to be about 32%.     

双管板换热器的设计与制造

根据双管板换热器的结构特点,从设计、制造、监造与使用维护方面全过程要点剖析,对主要重点进行系统性进行阐述,并与业内人士全方位交流与要点探讨。