Thermal performance investigation of latent heat-packed bed thermal energy storage system with axial gas injection

The latent heat-packed bed thermal energy storage system has a broad application prospect in industrial waste heat recovery and solar thermal energy collection. In this work, a novel design with axial gas injections is proposed with the examination for waste heat recovery from the spodumene calcination process. Part of the heat transfer fluid is diverted from the main inlet to the axial inlets, which leads to heat transfer enhancement due to flow rate drop and elevated temperature difference. Compared to the conventional design, axial gas injection leads to an immediate enhancement in temperature uniformity, with a maximum of 64 K decrease in temperature difference, which could reduce thermally induced damage and improve device safety. The axial design also leads to increased charging efficiency by up to 21 %, with the charging efficiency increasing with the number of axial inlets. Further investigation shows charging efficiency is inversely proportional to porosity, with porosity decreasing from 0.5 to 0.3, charging efficiency increases by 15 % at the end of charging, while the round-trip efficiency is on the contrary. Moreover, studies on heat transfer fluid show that elevated mass flow rate leads to decreased charging efficiency and improved round-trip efficiency, which is due to higher entropy generation and enhanced heat transfer rate. For a dedicated application, the packed bed needs to be optimized depending on the thermal performance, safety, and given requirements.