Experimental study on the charging and discharging performance of a thermal energy storage unit using low temperature phase change material

The latent heat thermal energy storage (LHTES) unit offers a versatile solution for storing waste heat and solar thermal energy across various temperature ranges. Despite its potential, limited experimental research has been conducted on LHTES units operating at low temperature ranges. This study addresses this gap by experimentally investigating the performance of an LHTES unit using water as the heat transfer fluid (HTF) and myristic acid (PCM) with a phase change temperature of 53-55 degrees C. The rectangular configuration of the TES unit was chosen for its practical advantages in industrial and residential applications, facilitating efficient space utilization and uniform thermal distribution. Experiments were conducted with various HTF volumetric flow rates (200, 300, and 400 LPH) using a constant temperature heat source. PCM and HTF temperature profiles at three segments of the TES unit were used to evaluate key parameters essential for designing a storage system, including thermodynamic analysis, Nusselt number, stratification analysis, storage/recovery efficiency, and charging/discharging efficiency. These parameters provide valuable insights into the performance of the LHTES unit. The outcomes indicate that increasing the HTF flow rate from 200 to 400 LPH decreases the charging/discharging duration by 40.73 % and 38.24 %, respectively. At the higher flow rate (400 LPH), convective mixing increases, reducing stratified layer stability. Furthermore, increasing the HTF flow rate leads to a reduction in peak Richardson numbers by 31.6 % and 27.8 % during charging/discharging, indicating a transition towards diminished stratification and increased turbulence in the HTF flow. In conclusion, while the TES unit exhibited better performance at a lower HTF flow rate (200 LPH), practical applications demand efficient fast charging and discharging. Despite this, minimal differences in efficiencies, energy, and exergy rates across flow rates suggest practical viability in various test conditions.