Experimental investigation of heat transfer characteristics in a vertical multi-tube latent heat thermal energy storage system

A vertical multi-tube thermal energy storage system using commercial phase change material (PCM) RT60 has been experimentally investigated. The selection of PCM and experimental rig configurations seek to be suitable to serve as a household thermal energy storage application for the solar energy application. PCM is filled at the annulus of the shell of the cylindrical container and the tubes while heat transfer fluid (HTF) is circulated inside tube to deliver or retrieve thermal energy to or from PCM. Five HTF tubes are configured to achieve heat transfer enhancement in this vertical latent heat thermal energy storage system. Thermocouples are installed at four horizontal cross-sections of the storage unit and at every cross-section thermocouples are positioned at different radial and angular coordinates to capture the transient temperature changes of PCM during the charging and discharging processes. HTF inlet temperature was set at 80 °C in the charging process and 10 °C in the discharging process. The same HTF volume flow rate of 20 L/min was applied in the consecutive charging and discharging processes. The comparative analysis of PCM temperature measurements along the axial, radial and angular directions was conducted. The experimental results showed that natural convection-controlled heat transfer during the charging process, while PCM solidified faster at the bottom liquid PCM region during the early stage of discharging, afterwards conduction dominated heat transfer mode. The analytical study and experimental data stated that the arrangement and positions of HTF tubes have a notable effect on the thermal response of the latent heat thermal energy storage system during the charging and discharging processes.