Fundamental Understanding of Phase Change Mechanism of Refrigerant Flow in HVAC Pipe

In this present investigation an attempt has been made to simulate the refrigerant flow through pipes using Computational Fluid Dynamics (CFD) to observe liquid refrigerant R134a flashing phenomenon using multi-phase model in ANSYS Fluent. In a vehicle HVAC piping system the refrigerant flows under a certain operating condition and pipe packaging. When the vehicle is kept in idle condition there is a possibility that a local pressure drop may occur due to change in pipe configuration or change in operating conditions. This leads to phase change and it can be one of the factor which causes noise and vibrations in the refrigerant pipe. The unwanted noise created due to refrigerant fluid phase change inside HVAC pipe can be annoying to end user. Prediction of refrigerant flow noise through HVAC pipes is more challenging and a time consuming process. Also this is more important for OEM’s to predict source of noise at very early stage of vehicle development which is caused because of refrigerant phase change. In current paper, a detailed CFD simulation study has been done with a capillary tube as a start point for basic understanding of the phase change physics in refrigerant pipe. This developed competency will enable us to set a process to deploy this on an actual HVAC pipe. A two phase Eulerian multiphase flow is used as it is better suited to capture a thermal phase change phenomenon. Fluid properties have been assumed to vary as piecewise linear. A good correlation was obtained with available experimental data from Li-et-al on [1].