Evaluation on the Discharging Rate and State of Health of Paraffin/HDPE after 10,000 Thermal Cycling under Various Charging Speed

Fast-charging mode thermal energy storage (TES) can be obtained by improving the average heat transfer rate of the system.However, it leads to the risk of performance deterioration for the long-term operation.The impact of charging rate for paraffin and FS-Paraffin (form-stable paraffin) is evaluated in the present work.The heating/cooling process is repeated for 10,000 cycles with different charging rate (1℃/min, 5℃/min and 10℃/min).The performance is focused on the discharging rate and thermal decomposition.It shows that the fast-mode treatment causes a severe deceleration in the discharging speed.The lowest discharging rate of paraffin is obtained at 0.64℃/min.The FS-Paraffin is generally better to withstand from thermal deterioration.It has a suitable discharging rate (0.82℃/min) with the lowest state of health (SoH) percentage of 97.3%.It implies that the presence of polymer additive (20 wt% high-density polyethylene) for FS-Paraffin reduces the impact of fast-charging operation.Further evaluations are discussed in the article, including the impact on SoH, thermal conductivity and storing performance.The overall condition indicates that thermal deterioration likely occurred during the fast-mode operation and requires extensive protection to maintain the long-term operation of the TES material.