Experimental Study on the Effect of Different HTF Discharges to Increase Efficiency of a Latent Heat Storage System Using a Spiral Coil Heat Exchanger with Different Fins

The heat storage system (HHS) still faces the problem of void formation as a result of the supercooling phenomenon caused by the use of paraffin. This study was conducted to analyze the effect of HTF discharge variation in the HHS system on the increase of heat storage efficiency in both the charging and discharging processes. The prototype helical coil heat exchanger is designed, fabricated, and experimentally analyzed on 4 types of helical coils with different models of fin designs: finless helical coil, straight fin, branched fin, and crossed fin. The phase change material (PCM) used is 9 kg of commercial paraffin type. The heat transfer fluid (HTF) is SAE 20W40 oil which is heated to a temperature of 210 °C with the heat source coming from the heating element. The pump is used to circulate the HTF with an output of 10 mL·s⁻¹, 11 mL·s⁻¹, and 12 mL·s⁻¹. The experimental results show that the variation of the HTF flow rate affects the melting temperature, the paraffin freezing temperature, and the power efficiency of the LHS. The highest temperature absorption by paraffin was achieved by the branch fin model at 124 °C with a discharge of 11 mL·s⁻¹, and the highest temperature release in the Branch Fin at 90 °C with a discharge of 12 mL·s⁻¹. The highest effective power achieved by the branched fin model with effective power of 73 % charge and 53 % discharge occurred at a discharge of 12 mL·s⁻¹. Varying the HTF discharge makes a positive contribution to the charge/discharge pattern, so it can be used as a reference for latent heat storage models.