A novel concept to enhance the applicability of solid gallium as phase change material for heat sinks by integrating within it discretely distributed chunks of un-encapsulated PCM

Abstract

Here we disclose for the first time in the literature a new concept that augments the applicability of solid gallium as effective phase change material (PCM) for heat sinks. Gallium is known to have favorable thermo-physical features; e.g. high thermal conductivity and low melting point, hence may be used advantageously as cooling medium. Yet, it suffers from a major inherent drawback namely its limited specific heat capacity. During direct contact heat rejection from a hot source into a solid gallium block, this drawback can result in non-negligible superheating of the formed melted mushy gallium layer touching the hot source hence may lead to clear deterioration of the temperature difference that drives heat transfer from the source to the gallium body. To overcome these adverse effects, we suggest hereby integrating within the solid gallium block discretely distributed cavities filled with macro-scale chunks of un-encapsulated PCM material. The PCM will capture some of the heat dumped into gallium resulting in: (1) less superheating of melted gallium mushy layer, and (2) lower melting rate of solid gallium giving thereby a better chance for prolonged operation before the need to cut gallium off from the heat source to allow for its re-solidification for repeated use. Since gallium is used in its solid state, there is no need to use encapsulation shells to hold the PCM within gallium. This leads to less resistance in the path of heat transfer within the sink and so to better sink performance. Design precautions are taken to prevent complete melting of gallium housing the PCM, maintaining thereby PCM cavities integrity while dumping heat into gallium. The to-be-cooled source is resembled by batches of hot water brought into direct contact with the gallium. Yet, hot sources of other shapes and natures can also be used to assess the proposed concept. Experiments with volumetric percentage of PCM in the gallium of 4% are conducted. Temperature history results for both the PCM in the cavities and the solid gallium during heat dumping operation show promising role of PCM in regards to lowering sink temperatures. Further detailed testing of the concept under different PCM loading percentages and for various PCM placement configurations and arrangements within the gallium are however still planned for upcoming research work.