Scale analysis and experimental results of a solid/liquid phase-change thermal energy storage system

A detailed experimental study has been carried out to evaluate the heat transfer performance of a solid/liquid phase-change thermal energy storage system. The phase-change material (PCM) and metal foam are contained in a vertically oriented test cylinder that is cooled or heated at its outside boundary, resulting in radially inward melting, respectively. Detailed quantitative time-dependent volumetric temperature distributions and melt-front motion and shape data were obtained. As the PCM melts, the interface moves away from the surface of the heat source/sink, and a thermal resistance layer is built up, resulting in a reduced heat transfer rate and/or increased temperature difference between the system to be cooled (or heated) and the PCM. The phase-change medium was 99% pure eicosane, with a melting temperature of 36.5°C. Results have been generalized to apply to any low-Stefan number PCM. A heat transfer scale analysis was used in order to help in interpretation of the data and development of heat transfer correlations. In the scale analysis, conduction heat transfer in the solid and natural convection heat transfer in liquid were considered. Comparison of experimental data with scale-analysis predictions of the solid-liquid interface position and temperature distribution was performed.