  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^{\circ}C 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.
