Analytical and experimental investigation of two-phase ejector cycles using low-pressure refrigerants

refrigeration;two-phase ejector

Lawrence, Neal ; Hrnjak ; Predrag S. ; Elbel ; Stefan

关键词: refrigeration;    two-phase ejector;   

Others  :  https://www.ideals.illinois.edu/bitstream/handle/2142/42337/Neal_Lawrence.pdf?sequence=1&isAllowed=y

美国|英语

来源: The Illinois Digital Environment for Access to Learning and Scholarship

【 摘 要 】

The standard two-phase ejector cycle has received significant attention in research studiesin recent years because of its ability to improve the efficiency of refrigeration cycles. However,there are several alternate two-phase ejector cycles that have been proposed but have receivedlittle attention in two-phase ejector studies. Unlike the standard two-phase ejector cycle, thesealternate ejector cycles offer the opportunity for evaporation at multiple temperatures, and theydo not require a liquid-vapor separator, the inefficiency of which can decrease the performanceof the standard two-phase ejector cycle. Furthermore, it can be shown that the alternate ejectorcycles offer potential advantages in terms of real applications without reducing the theoreticalCOP, compared to the standard two-phase ejector cycle, warranting further research on alternatetwo-phase ejector cycles.An alternate two-phase ejector cycle was constructed and used to evaluate ejectorperformance and cycle performance improvement when compared to expansion valve cycles.R134a and R1234yf were used as the working fluids in the experimental tests. These lowpressureworking fluids offer less improvement potential with ejector cycles because of theirlower throttling loss, compared to CO2. It was found that two-phase ejectors using these lowpressureworking fluids were able to recover similar but lower fractions of the total expansionwork available for recovery, compared to two-phase ejectors using CO2. The alternate ejectorcycle was compared to an expansion valve cycle with two evaporation temperatures in order tomatch the cooling capacity in each evaporator. In this comparison, R134a showed COPimprovements of up to 8 %, and R1234yf showed COP improvements of up to 12 %. Thealternate ejector cycle was also compared to an expansion valve cycle with a single evaporationtemperature, which may be a more practical means of comparison for many applications. In thiscase, R134a showed COP improvements of up to 5 %, and R1234yf showed COP improvementsof up to 6 %. While not as high as the COP improvements that have been observed for CO2, thelow-pressure working fluids R134a and R1234yf certainly offer some noticeable COPimprovements on two-phase ejector cycles.