EXPERIMENTAL VALIDATION of MUSHY ZONE CONSTANT for MODELING of SOLIDIFICATION/MELTING for THERMAL ENERGY STORAGE APPLICATIONS

The thermal energy storage (TES) systems use phase change materials (PCM's) for storage and release of thermal energy. A lot of research is being conducted in recent times for fast, efficient storage and release of thermal energy using phase change materials in order to utilize the vast amount of latent heat available at constant temperature during phase change process. The numerical modeling for solidification and melting of PCM is employed in various commercial software and applied for different applications which include the solidification or melting. In the numerical simulation of phase change process, the solidification and melting are modelled using enthalpy-porosity method developed some researchers previously. The mushy zone constant is an important factor in this method which is used in the governing equations as a source term to model the melt front. The aim of this study is to determine the role of mushy zone constant on the solidification/melting behavior of phase change material numerically and validate the results with the experiments. The melting behavior of PCM is studied in this paper. The experimental setup consisting of a cubical container of dimensions 3 3 3 filled with PCM was considered. The box was heated from one side and insulated from other sides so that the heat supplied is transferred to the PCM to melt it completely. The melting behavior of PCM was observed by capturing images at specific time intervals with the help of a camera. The camera was placed in such a way with minimum parallax error. These results are validated with previous numerical study in which the mushy zone constant was varied from 104 to 106 to determine the optimum value. The PCM used in this study is a paraffin wax material having a melting point of 48 C. The propagation of melt front is plotted at different time steps and validated with the numerical results. The propagation of melt front is observed to be different for each of the mushy zone constant values. It was observed that the melting for higher values of mushy zone constant is observed to be similar to the experiment for the initial part of melting. Also, the melting rate speeds up and is observed to be similar to melting in the lower values of mushy zone constant. This paper aims to be a starting point to determine the optimum mushy zone constant for different factors affecting the melting behavior such as different materials, temperature difference.