Morphological evolution of mushy zone and effect of mushy zone constant during melting process

Phase change materials have attracted great attention in the field of thermal energy storage (TES) owing to their high heat storage density and nearly isothermal property during phase transitions. This paper aims at probing the physics of latent TES through numerical modelling with a focus on morphological evolution of mushy zone and influence of mushy zone constant (Amush) during melting process. Mushy zone refers to a two-phase mixed region appearing between solid phase and liquid phase under non-isothermal solid-fluid phase change conditions, while Amush comes from a damping term of momentum equations in the enthalpy-porosity model to simulate fluid flow within the mushy zone. In the present study, the melting of lauric acid in a simple rectangular TES container has been modelled numerically, and our predictions have been validated in comparison with experimental results from the literature [12]. It has been found that the morphological evolution of mushy zone, including the marching speed and the overall thickness variation, is strongly relevant to the local heat transfer mechanisms, both heat conduction and natural convection. In addition, our results also indicate that Amush is a critical parameter for performance prediction of mushy zone phase-change processes. A higher Amush value generally corresponds to a slower PCM melting process, mainly because it implies larger flow resistance and weaker natural convection within the mushy zone. Further experimental work and theoretical analysis are ongoing to capture microscopic morphological evolutions and determine appropriate Amush values for modelling mushy zone phase change processes.