Investigation on the charging process of a multi-PCM latent heat thermal energy storage unit for use in conventional air-conditioning systems

In order to improve the performance of thermal energy storage (TES) systems, a multiple phase change material (multi-PCM) based TES unit for use in conventional air-conditioning systems was studied. Three PCMs (PCM-1, PCM-2, and PCM-3) with phase change temperatures of 5.3 °C, 6.5 °C and 10 °C, respectively, were used. Water was used as the heat transfer fluid (HTF). A three-dimensional model (3D) was developed in ANSYS FLUENT to investigate the charging process of multi-PCM TES unit. In order to validate the model, an experimental system was set up. The effect of volume ratio of multi-PCM, HTF inlet temperature and flow rate on the charging process of TES unit was investigated. The simulation results indicate that TES unit using multi-PCM with volume ratio 1:2:3 intensify the charging process in comparison with using single-PCM. The total charging capacity of multi-PCM TES unit with 1:2:3 proportions was 3637.2 kJ and increased by approximately 32.22% as compared to the single-PCM. For the HTF flow rate of 0.3 kg/s, decreasing the inlet temperature of HTF sped up the charging capacity, and obviously shortened the complete charging time of TES unit. However, the HTF inlet temperature did not appreciably change the total charging capacity.