Effect of conical coiled heat transfer fluid tube on charging of phase-change material in a vertical shell and coil type cylindrical thermal energy storage

Abstract

ABSTRACT Effective thermal energy storage is essential to overcome the intermittent availability of solar energy. A small cylindrical thermal energy storage unit is investigated to provide heat during the early morning for domestic hot water using flat plate solar water heaters. A helically coiled heat transfer tube (HTF) in cylindrical thermal storage is investigated on charging phase-change material (PCM). An acrylic cylindrical container is used to hold the PCM. HTF tube is made up of copper helical coil with and without a conical section at the bottom of the loop. The heat transfer tube at the bottom is formed into a small conical shape at the helical coil’s center. The selected PCM is paraffin wax with a melting temperature of about 60°C. The HTF temperature is maintained at 75°C at a flow rate of 0.5 kg/min to charge the PCM of 1 kg mass. Part of solid PCM at the container’s bottom was observed with a longer duration to melt entirely without a conical section of the HTF tube. The irregular temperature distribution was also observed in PCM, mainly along the vertical direction. Thus, the complete melting was achieved by a conical coiled heat transfer tube at the container’s bottom. The conical coil length of the HTF tube increased the overall length by 10%. The PCMs melting duration with a conical tube at the bottom reduced significantly by 16% and enhanced average storage effectiveness by 13.06% compared to the HTF tube without the conical coil. Abbrevations: HTF: Heat transfer fluid; LHS: Latent heat storage; PCM: Phase-change material; TES: Thermal energy storage