Impact of shape of container on natural convection and melting inside enclosures used for passive cooling of electronic devices

The present paper numerically analyzes a passive cooling system using enclosures with different geometries filled with thermal conductivity-enhanced phase change material (PCM). A numerical code is developed using an unstructured finite-volume method and an enthalpy-porosity technique to solve for natural convection coupled to a solid-liquid phase change. Five geometries containing the same volume of PCM are compared while cooling the same surface. The unsteady evolution of the melting front and the velocity and temperature fields is detailed. Other indicators of cooling efficiency are monitored, including the maximum temperature reached at the cooled surface. The computational results show the high impact of varying geometry: a maximum temperature difference as high as 40 oC is observed between two of the enclosures. The best efficiency is obtained for an enclosure shifted vertically relative to the cooled surface. Other findings and recommendations are made for the design of PCM-filled enclosures. Highlights: → The shape of a PCM-filled enclosure impacts the cooling of a vertical surface. → Its relative position is of great importance also. → The best tested configuration is a slender geometry shifted vertically. → This configuration reduces the maximum temperature at the surface by 40 oC. → Part of the PCM should be placed above the surface, and none below it.