Modeling of PCM melting: Analysis of discrepancy between numerical and experimental results and energy storage performance

In this work, a comprehensive analysis of constrained melting of phase change material (PCM) is performed to identify the reasons for the discrepancy of numerical predictions. To identify this, models are proposed by accounting various experimental geometrical details. The predictions are compared and validated with the available experimental results. The results indicated a substantial influence of accounting geometrical details for reducing the difference between the numerical predictions and the experimental data. Further, the global and the local thermal and flow behavior during PCM melting, and their influence on heat storage is described. It is observed that the thermally induced flow patterns followed by formation of stratified layers aid in achieving improved heat storage. Moreover, undulations in the melting front and temperature fluctuations are observed due to thermal plumes and multiple counter-rotating vortices in the capsule. For evaluating the thermal performance, the stratified and the total energy storage densities, along with the thermal energy storage (TES) effectiveness, are also analyzed. At the end, for accounting different solid and liquid phase properties, a new physically consistent mathematical formulation of the conservative form of the energy equation is proposed. Simulation using this advanced model has shown further improvement in the predictions.