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Title:Analytical and experimental investigation of two-phase ejector cycles using low-pressure refrigerants
Author(s):Lawrence, Neal
Advisor(s):Hrnjak, Predrag S.; Elbel, Stefan
Department / Program:Mechanical Sci & Engineering
Discipline:Mechanical Engineering
Degree Granting Institution:University of Illinois at Urbana-Champaign
two-phase ejector
Abstract:The standard two-phase ejector cycle has received significant attention in research studies in 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 received little attention in two-phase ejector studies. Unlike the standard two-phase ejector cycle, these alternate ejector cycles offer the opportunity for evaporation at multiple temperatures, and they do not require a liquid-vapor separator, the inefficiency of which can decrease the performance of the standard two-phase ejector cycle. Furthermore, it can be shown that the alternate ejector cycles offer potential advantages in terms of real applications without reducing the theoretical COP, compared to the standard two-phase ejector cycle, warranting further research on alternate two-phase ejector cycles. An alternate two-phase ejector cycle was constructed and used to evaluate ejector performance and cycle performance improvement when compared to expansion valve cycles. R134a and R1234yf were used as the working fluids in the experimental tests. These lowpressure working fluids offer less improvement potential with ejector cycles because of their lower throttling loss, compared to CO2. It was found that two-phase ejectors using these lowpressure working fluids were able to recover similar but lower fractions of the total expansion work available for recovery, compared to two-phase ejectors using CO2. The alternate ejector cycle was compared to an expansion valve cycle with two evaporation temperatures in order to match the cooling capacity in each evaporator. In this comparison, R134a showed COP improvements of up to 8 %, and R1234yf showed COP improvements of up to 12 %. The alternate ejector cycle was also compared to an expansion valve cycle with a single evaporation temperature, which may be a more practical means of comparison for many applications. In this case, R134a showed COP improvements of up to 5 %, and R1234yf showed COP improvements of up to 6 %. While not as high as the COP improvements that have been observed for CO2, the low-pressure working fluids R134a and R1234yf certainly offer some noticeable COP improvements on two-phase ejector cycles.
Issue Date:2013-02-03
Rights Information:Copyright 2012 Neal D. Lawrence
Date Available in IDEALS:2013-02-03
Date Deposited:2012-12

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