Development and experimental validation of a CFD model for PCM in a vertical triplex tube heat exchanger

Thermal energy storage in concentrated solar thermal power plants improves the dispatchability and eliminates the miss-match between the energy supply and demand. Recently, considerable attention has been made to latent heat thermal energy storage due to its high energy density per unit mass and volume at nearly constant temperature. This paper presents a computational fluid dynamics (CFD) model using ANSYS FLUENT 15.0 for phase change material (PCM) in a vertical triplex tube thermal energy storage system and its validation through experimental results. To enhance the heat transfer inside the PCM, eight fins have been incorporated between the internal and external tubes. Experiments were conducted for both freezing and melting processes. The CFD model endeavoured to simulate both the freezing and melting processes of the PCM. The inlet and outlet temperatures of the heat transfer fluid (HTF) as well as six temperature locations in the PCM were compared with the CFD results. The average effectiveness as well as the duration of the phase change process at each experimental point were compared with results from the CFD model and found to be in good agreement. The variation between the experimental and CFD for the phase change duration are within an average of 5.8% for freezing and 1.6% for melting.