Computational Fluid Dynamics (CFD) Modeling of Two Phase Refrigerant Flow in Evaporator Refrigerant Distribution System
Two-Phase Flow, CFD, Refrigeration, Evaporator, computational mode
The biggest challenge in the evaporator distribution system is to maintain a uniform distribution of vapor and liquid phases in the evaporator. Uneven distribution will create poor refrigeration effect. In order to study flow distribution in the evaporator distributors, a two-phase CFD model has been developed for three different idealized distributors with various orientations of flow paths and geometrical parameters. The CFD model predicted flow maps, vapor qualities and, mass flow rates in the distributors as a function of various geometrical and inlet flow parameters. Refrigerant R134a is used as a working fluid with inlet saturation temperature 7°C with various inlet vapor qualities (0.15, 0.25, and 0.4) and mass flow rates (20 kg/hr, 80 kg/hr, and 120 kg/hr). An Eulerian model, coupled with the volume of fluid (VOF) approach has been adapted using Ansys Fluent 2019R3 version, where vapor is considered as a continuous phase with liquid droplets (200 micrometer diameter). Gravity played an important role in flow separation and the distribution. The CFD model predicted that flow distribution becomes more uniform with higher inlet vapor qualities and mass flow rate for horizontal inlet and outlet tubes. However, for vertical inlet and horizontal outlet tubes, flow distribution was found to be more uniform with lower vapor qualities which contains more liquid droplets and higher mass flow rates. This study will provide vital information to the researchers and the refrigeration industry about the cause of nonuniform distribution of refrigerant and their remedy, improving the performance of refrigeration systems. More importantly, this CFD model can be applied to a commercially available evaporator distributor systems and optimize the design by saving significant amount of time and cost compared to traditional experimental methods.