Thermal performance investigation of a novel medium-temperature pilot-scale latent heat storage system at different charging and discharging temperatures

Abstract

Large-capacity medium-temperature latent heat storage (LHS) systems have the potential to be extensively utilized for waste heat recovery and peak load shifting. However, the phase change behavior and mechanism of medium-temperature phase change materials (PCMs) in shell-and-tube LHS systems, as well as the impact of charging and discharging temperatures on the thermal performance, are still unclear. To address these issues and verify the reliability of the cylindrical pilot-scale LHS system, this article designed and constructed a novel cylindrical medium-temperature (up to 300 °C) LHS system with a large capacity (approximately 1 GJ) equipped with spiral and H-shaped fins. The research focused on investigating the impact of various charging and discharging temperatures on the thermal behavior of the LHS system to adapt different temperature scenarios in waste heat recovery while also analyzing the coupling effect of heat conduction and natural convection during charging and discharging and depicting the PCM liquidus based on thermocouple data. The experimental findings indicated that increasing the charging temperature could effectively shorten the charging duration, with a decrease from 5.99 h at 280 °C to 4.00 h at 300 °C, representing a reduction of 33.22%. In contrast, the impact of decreasing the discharging temperature on the discharging duration was less significant than that of increasing the charging temperature. Besides, the differences in heat transfer mechanisms between the charging and discharging processes were analyzed. In the charging process, the heat transfer was initially dominated by heat conduction, followed by natural convection. Conversely, heat conduction predominantly governed the heat transfer process in the discharging process. The heat transfer process dominated by heat conduction would increase the non-uniformity of PCM temperature on the horizontal plane, while the heat transfer process dominated by natural convection would alleviate this non-uniformity. Moreover, the accumulative stored energy under the charging temperature of 290 °C was 952.37 MJ, while the released energy under the discharging temperature of 160 °C was 648.72 MJ, which was approximately 10–200 times greater than those documented in existing studies.