Liquid Metal Gallium in Metal Inserts for Solar Thermal Energy Storage: A Novel Heat Transfer Enhancement Technique

Abstract

This paper investigates the heat transfer characteristics of a prototype latent heat energy storage (LHES) system with novel metal insert design configuration. The novel thermal energy storage (TES)system consist ofa vertical cylindrical shell, a helical coil and metalinserts (MI) withliquid metal gallium(Ga), designed for LHES capacity of ~13MJ. 25 kg of D-Mannitol(DM) is investigated as a phase change material (PCM) forenergy storage and property tests were conducted on DM. PCM was cycled 1000 times and checked for suitability for long term energy storage applications. Results confirmed that the addition of MI with Ga enhanced the thermal performance of the TES system. Moreover, the vertical orientation of the shell as well as the metal inserts supported natural convection during charging cycles and acted as a nucleation sites during discharging cycles, thereby assuring rapid charging and discharging of the TES system. High thermal conductivity, low specific heat of Ga and its liquid phase atroom temperatures helped Ga act as thermal energy carriers in TES unit. Maximum power output of 0.64 kW was obtained during solidification cycle and efficiency range of 87–89% for MI configuration. The presented novel LHES design can be used with a wide range of PCM and over a different temperature range of applications, mainly for water heating, high temperature industrial waste heat recovery and solar thermal applications.