Abstract
Phase change materials (PCM) are preferred in thermal energy storage (TES) for their considerable heat storage capability even though it lacks thermal conductivity. The solid PCM settling at the bottom in an upright cylindrical TES unit with a helical heat transfer tube (HTT) takes a longer melting duration. Adding a short concentric helical HTT at the bottom-center is investigated to melt the solid PCM. Paraffin wax with a melting temperature of 60 °C has opted as PCM. Water is the heat transfer fluid (HTF) that passes through the outer tube circumferentially downward and then through the short inner HTT upward at 70, 75, 80 °C and 20, 25, and 30 LPH. The PCM melting is ensured through visual and spatial temperature measurements. The modification of HTT decreased the melting duration by 36.84% compared with an unmodified HTT. The fluid flow rate of 20 LPH and inlet temperature of 80 °C produced complete PCM melting in 120 min: the maximum energy efficiency of 39.32%: the exergy efficiency of 32.43%. This study helpful to design HTT for various solar applications requiring thermal storage.
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