Experimental study on the thermal characteristics of a visualized shell-and-tube LHTES system at different endothermic and exothermic temperatures

This research developed a novel medium-temperature (up to 300 degrees C) latent heat thermal energy storage (LHTES) system, utilizing a compact shell-and-tube thermal exchange system containing spiral finned tubes, 220 kg of phase change material (PCM) was employed, enabling 44.52 MJ of heat storage, a visible window allowed to observe the phase change process and investigate the temperature variations in conjunction with thermocouples. The study analyzed the thermal traits and explored the impact of charging and discharging temperatures on the system's thermal performance.The outcomes indicated that natural convection gradually supplants heat conduction in the charging process as the primary heat transfer mechanism and a temperature stratification phenomenon emerges within the TES; during the discharging process, a contrasting behavior is observed. Employing charging-discharging temperature configurations of 290-170, 280-160, and 270-150 degrees C, the cumulative energy input to complete the cycle process is 63.59, 56.43, and 54.87 MJ, correspondingly, the released energy is 33.64, 33.41, and 33.57 MJ, yielding cycle efficiencies of 52.90, 59.20, and 61.20 %, respectively, with the charging temperature rising from 270 to 290 degrees C, storage time decreased 25.6 %, but lead to an 8.49 % decrease in heat storage efficiency, while the discharging temperature has a relatively minor influence on the system.