Numerical Study to Investigate the Thickness of the PCM Layer for the Three Layers Tank for the CSP Plants

In the present study, the phase change material (PCM) layer thickness of the top and bottom PCMs change gradually with constant the middle PCM layer thickness for the three-layers thermocline thermal energy storage (TES) tank. It has been studied using spherical capsules packed with three types of PCMs with different thermophysical properties. A transient two-phase dispersion-concentric (D-C) model is used to calculate the process of phase change inside pellets to identify the temperature allocation. The method of heat transfer among molten salt and PCMs capsules is extensively discussed, with multiple numerical results shown. The results show that the thickness of the PCM layer has a high impact on the thermal performance of the TES tank. As the layer thickness of the top PCM increases, the time required to discharge the thermocline TES tank increases. The (80 % high phase change material (HPCM) -10 % intermediate phase change material (IPCM) - 10 % low phase change material (LPCM)) configuration has 14.6 %, 27.2 %, and 46.8 % higher overall efficiency than (33.3 % HPCM - 33.3 % IPCM -33.3 % LPCM) configuration, (70 % HPCM - 10 % IPCM - 20 % LPCM) configuration, and (10 % HPCM -10 % IPCM - 80 % LPCM) configuration. In contrast, the (80 % HPCM - 10 % IPCM - 10 % LPCM) configuration shows the highest capacity and utilization ratio.