Developing adiabatic two-phase flow after an expansion valve: the effect of tube diameter and oil

The development of the adiabatic two-phase flow between an expansion valve and evaporator along a 600 mm -long glass tube in an air conditioning system has been presented in Yao and Hrnjak (2022). In this paper, the developing two-phase flow in a straight tube of 5 mm inner diameter is compared to that of the 8 mm tube in Yao and Hrnjak (2022) to examine the effect of the tube diameter. R134a with 1.3% of POE 32 is used as the working fluid. It provides a good opportunity to investigate the effect of oil on developing two-phase flow by comparing the results in this paper with Bowers and Hrnjak (2009). They have explored the developing two-phase flow after a needle valve using pure R134a. The flow patterns near the expansion device are affected by both the addition of oil and the structure of the expansion device. For the fully developed flow, the differences in flow patterns are mainly attributed to the oil. A 3D flow pattern map for developing two-phase flow is proposed in this paper. There is no similar research in the open literature to compare with. But the developed flow is compared with the flow pattern maps of Wojtan et al. (2005) and Barbieri et al. (2008).