Numerical study of high-speed two-phase ejector performance with R134a refrigerant

• Published in: International journal of heat and mass transfer 2018-11, Vol.126, p.1071-1082
• Main Authors: Baek, Sunghoon, Ko, Seungbin, Song, Simon, Ryu, Sungmin
• Format: Article
• Language: English
• Subjects: Low pressure refrigeration cycle; R134a; Two-phase ejector
• ISSN: 0017-9310; 1879-2189
• DOI: 10.1016/j.ijheatmasstransfer.2018.05.053

•We present numerical solutions of the high-speed flows inside a two-phase ejector with R134a used for low-pressure refrigeration cycles, and explain the detailed flow behavior affected by major geometric parameters of the ejector.•The results include characteristics of phase transition, compressibility effect, mass and heat transfer at interface of each phase. For example, the length of the diverging nozzle is related to maximizing the mean dynamic pressure at the nozzle exit; the nozzle exit position affects significantly the size of the recirculation bubble observed in the suction chamber which should be avoided or minimized; the entrainment performance of the ejector highly depends on the diameter and length of the mixing tube.•The numerical study can be taken as a pragmatic reference of designing the two-phase ejector with a high performance. An ejector is a passive pumping device to increase the flow rate of a motive fluid and to enhance compression of the fluid flow by geometrically induced secondary flows. In particular, the high-speed two-phase ejector has attracted attention as an alternative to the throttling valve, because by compensating the throttling loss that appears in expansion devices it has the potential to improve significantly the performance of refrigeration systems. However, flows inside the ejector are so complex that it is not easy to characterize the relevant flow and thermodynamic behaviors experimentally. In contrast, the numerical approach is relatively favorable to elucidate the relevant physics inside the ejector, and is considered useful to improve the performance of the ejector. However, there have been few relevant numerical studies, because it is challenging to resolve high-speed flows accompanied with phase transitions. In the present study, we present numerical solutions of the high-speed flows inside a two-phase ejector. An evaporation-condensation model is implemented and the real-fluid properties of refrigerant R134a are input in our RANS simulations to resolve phase transitions. Based on the validated predictive ability of our computational apparatus on the baseline model of the ejector, we present a parameter study to identify the effects of geometry variables on the entrainment performance. Our study provides specific guidelines to be considered when designing supersonic two-phase ejectors, and thus, it is expected to contribute to studies associated with supersonic two-phase ejector-equipped refrigeration system