In the current paper, we investigated the phase change material (PCM) volume fraction for three-layers thermocline thermal energy storage (TES) tank system by using spherical capsules filled with high temperature PCM of different thermo-physical properties. A transient one-dimensional dispersion-concentric (D-C) model is modified to calculate the phase change process within capsules so as to determine the temperature distribution. Detailed characteristics of heat transfer between molten salt and the PCMs capsules are discussed, and various numerical results are presented, including the temperature distributions of molten salt and exit temperature. The results show that the volume fraction has a significant impact on the stored/recovered time energy. As the volume fraction of bottom PCM increases, the time required to discharge the thermocline TES tank increases.
Keywords thermal energy storage; concentrating solar power plants