Abstract
This paper numerically investigated the effect of natural convection on the thermal behaviour of a PCM-based heat sink with novel tree shape conductive structures and conventional plate fin structures. Simulations were realized using a CFD model based on the enthalpy-porosity and VOF methods. Results showed that the influence of natural convection was related to the applied metal structure, orientation and metal volume fraction. Among them, orientation expressed the most significant impact on the natural convection heat transfer by affecting the flow pattern and in return the fin efficiency. Increasing metal volume fraction tended to weaken the influence of natural convection ascribed to the enhanced heat conduction and restricted convection flow. The optimized tree shape structure with a better heat conduction path and curvilinear interface promoted natural convection, by which the better thermal mixing and higher fin efficiency were achieved, and thus enhanced heat transfer. When natural convection was negligible, the tree shape structure design initially performed a better but subsequently worse heat transfer due to its higher fin efficiency but shorter contact lines. It is suggested that the optimized tree shape structure is more superior in applications where minimum conductive material is necessary and natural convection is significant.