Numerical study of thermally optimized metal structures in a Phase Change Material (PCM) enclosure

•Optimization was applied to redesign conductive metal structure in a PCM enclosure.•Dynamic thermal behaviours of the PCM melting process was investigated numerically.•Effects of metal structure, metal volume fraction and orientation were characterized.•Tree shape structures improved overall heat diffusion to enhance PCM melting.•Orientation of the PCM enclosure plays an important role in enhancing PCM melting. Embedding metal fins into PCMs to improve the thermal conductance of PCM enclosure is widely used in the thermal management of mobile electronics. This paper presented the application of a density-based structure optimization method to redesign the conductive metal structure for better heat diffusion from a concentrated heat source into a PCM enclosure. Two plate fin heat sink structured PCM enclosures with the metal volume fractions of 20% and 30% were the baselines, and the optimized tree shape structures with the similar metal volume fractions of 18.7% and 27.6% were generated for comparison. A transient numerical model based on the Volume of Fluid (VOF) and enthalpy-porosity methods was built to investigate the dynamic thermal behaviors of PCM enclosures. Results illustrated that the optimized tree shape designs outperformed the baseline designs by achieving lower heat source temperature and higher melt fraction in the main PCM melting stage. Increasing metal volume fraction improved the overall thermal conductance of PCM enclosures and hence suppressed the temperature non-uniformity and lowered the heat source temperature. Upwardly orientated PCM enclosure had much better heat transfer performance than that under downward orientation due to its enhanced thermal mixing resulted from the intensified convection flows.