An experimental and computational study of the flow pattern in a refrigerant ejector. Validation of turbulence models and real-gas effects

Abstract This investigation presents a study based on experimental and numerical flow pattern in a R134-a ejector. Furthermore, the entrainment ratio has also been analysed. The geometry of the ejector has a long tapered mixing chamber designed to improve pressure recovery. The numerical simulation is used to explain the flow features related with the static pressure profiles measurements, as well as a test case for the CFD validation. In this regard, an initial study has been undertaken in order to gain an insight into the CFD uncertainties in three relevant cases related to the ejector flow physics, namely turbulence modelling, real gas thermodynamics and shock-wave turbulent boundary layer interaction. The double-choked and mixed regime have been realized in this study. Both the standard k − e and the SST k − ω turbulence models show good agreement between the experimental and computed pressure profiles. Regarding the entrainment ratio prediction, it was better for the latter in the double-choked regime. However, for the mixed regime, it was found that the numerical analysis could not yield a reliable entrainment ratio value using any of the turbulence models employed, although the pressure profile was accurately computed. An explanation for this contradiction has been found in this investigation. Furthermore, the numerical analysis has helped to explain the differences found between the measured pressure profiles and the one-dimensional theory prediction.

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