A novel design of discrete heat and cold sources for improving the thermal performance of latent heat thermal energy storage unit

Abstract

The low thermal conductivity of phase change materials (PCMs) severely limits the operating efficiency and flexibility of the latent heat thermal energy storage (LHTES) unit. In this study, a novel LHTES unit with discrete heat and cold sources was proposed and investigated numerically, including symmetrical and staggered arrangements with side-heat and bottom-heated LHTES units. The consecutive and simultaneous heat storage and release processes of the seven developed models were comprehensively considered and compared for the first time. The results show that with the discrete arrangement of source, the additional heat conduction effect and natural convection in the side-heated LHTES unit would be significantly improved. More importantly, the heat storage and release cycle of the side-heated and symmetrical arrangement was shortened by 49.9%, the steady-state time was advanced by 46.6%, the steady-state liquid fraction was increased by 4.2%, and the heat transfer rate was increased by 22.3%. The discrete source arrangement had no obvious improvement on the performance of the bottom-heated LHTES unit. In addition, energy analysis showed that the side-heated LHTES unit stored more sensible heat. The discrete heat and cold sources effectively improved the thermal performance and flexibility of the LHTES unit.