Simulation of Triplex Tube Thermal Energy Storage System Using High Temperature Phase Change Material

Abstract

To increase the capacity factor of a concentrated solar thermal power plant (CSTPP) beyond the hours of sunlight, the use of thermal energy storage systems (TES) can be a promising solution. Phase change materials (PCMs) can store latent thermal energy in the course of the melting process and release it when solar energy is not available. Generally, PCMs have low thermal conductivity. One of the most commercially promising solutions is the application of an extended heat transfer surface inside the PCM container. Moreover, the distance of the heat transfer fluid (HTF) to the core of the PCM in a TES system can affect the storage performance. Accordingly, a triplex tube heat exchanger with eight fins is considered in this paper, to investigate the impact of the different velocity of HTF and different entrance pattern in a vertical PCM container. Notably, the middle enclosure of the triplex tube is filled with PCM. Numerical analysis using an enthalpy porosity technique revealed that increasing HTF velocity reduces the charging time. Also, when the HTF enters from the bottom of the container, the storage time will diminish owing to a natural convection side-effect, but if the HTF flows downward, the amount of sensible thermal energy storage is higher than in the other cases.