Numerical evaluation of thermal energy storage rate in planar and cylindrical phase change material composites

Efficient design of high-performance phase change material (PCM) composites remains challenging, due to a lack of understanding regarding the relationships between the performance characteristics, and relevant design parameters. In this work, we adopt the effective composite approximation, as justified through experimental validation, and numerically investigate the effects of individual design variables on the thermal energy storage rate into phase change material composites under a constant temperature boundary condition. We isolate and describe the impact of (1) geometry, (2) volume fraction of metal, (3) time, (4) material thermophysical properties, and (5) the magnitude of the thermal boundary condition on the heat absorption rate normalized by heated area, by volume, and by mass of the active composite PCM. Finally, we assess the accuracy of the quasi-steady state approximation, as well as a modified version of the quasi-steady state approximation, which incorporates a term for sensible heating. These results are used to illustrate key relationships and trends which affect the volume fraction of metal in a composite PCM which maximizes the thermal energy storage rate across different performance metrics.