Exploration of phase change material melt front during latent heat thermal energy storage charging

Abstract

Latent Heat Thermal Energy Storage (LHTES) is a technology that utilises the phase change energy of a material to store energy and is used in multiple engineering disciplines. The use of this technology at high temperatures presents new material challenges that need to be considered. The exploration of Phase Change Material (PCMs) melting phenomena was completed with finite volume methods to model advection-diffusion interactions of different PCM classes undergoing pure substance melting. This study modelled a two-dimensional system with heat flux elicited by an isothermal wall – producing a melt front in the PCM. The investigation focussed on retention of a Solid Salt Barrier (SSB) between the liquid PCM and the storage tank wall. The importance of such a barrier is to mitigate the corrosion between the liquid PCM and the containment vessel. Results reveal the possibility of SSB retention through the adaptation of a LHTES system aspect ratio. A thermal storage inefficiency via unmelted PCM has been demonstrated and quantified when an SSB is maintained. Through varying geometry and PCM choice (carbonate, fluoride, and chloride eutectics), it was also shown that SSB retention is possible; however, when optimising the rate of internal enthalpy change, the corresponding aspect causes the SSB protected wall to be insignificant compared to exposed surfaces at the top and base. This paper provides insight into the implications of aspect ratio choice for thermal energy storage tank designs; as well, suggestions are made regarding exploration of divergent geometries to greater utilise the PCM energy storage capacity available in SSB systems.