Solid/liquid phase change in presence of natural convection: A thermal energy storage case study

Solid/liquid phase change process has received great attention for its capability to obtain high energy storage efficiency. In order to analyze these systems, undergoing a solid/ liquid phase change, in many situations the heat transfer process can be considered conduction-dominated. However in the past years, it has been shown that natural convection in the liquid phase can significantly influence the phase change process in terms of temperature distributions, interface displacement and energy storage. In this paper a procedure to analyze systems undergoing liquid/solid phase change in presence of natural convection in the liquid phase based on the utilisation of a commercial computer code (FLUENT), has been developed. This procedure is applied to the study of a cylinder cavity heated from above and filled with a phase change material. It was found that when the coupling with the environment, even if small, is considered, natural convection in the liquid phase occurs. The numerical results are then compared with available experimental data. The analysis shows that the agreement between numerical and experimental results is significantly improved when the results are obtained considering the presence of circulation in the liquid phase instead of considering the process only conduction-dominated. Furthermore, some interesting features of the flow field are presented and discussed.