Abstract
Due to the evaporating two-phase flow and the choked-flow condition, numerical analysis of flow through short-tube orifices is a complicated procedure. A comprehensive method for analyzing such flows is the two-fluid model, which does not assume equilibrium between phases. However, in all previous applications of this model, two-phase flow calculations at the entrance and vena contracta regions were eliminated. In this investigation, two additional steps were introduced to improve the accuracy of computations: (1) applying a comprehensive two-fluid model, including the effect of various two-phase flow patterns and the metastability of liquid phase; and (2) performing a two-phase analysis of the evaporating flow through the entrance and vena contracta, which involves simulation of this region as a contraction from the up-stream to the throat, and an expansion from the throat to downstream. Results showed more compatibility with experimental data in comparison with those of previous investigations for predicting the critical flow condition of common refrigerants HFC-134a, HCFC-22, and HFC-410a through short-tube orifices. In addition, the developed numerical scheme was utilized in order to develop selection charts for short-tube orifices based on the common refrigerant HFC-134a and the alternative newly released hydrofluoroolefin refrigerants HFO-1234yf and HFO-1234ze.
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