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A new approach using un-encapsulated discrete PCM chunks to augment the applicability of solid gallium as phase change material in thermal management applications

Al Omari, S.-A.B., Ghazal, A.M., Elnajjar, E.
Energy conversion and management 2018 v.158 pp. 133-146
direct contact, gallium, heat, management systems, melting, specific heat, temperature
Gallium is known to have favorable thermo-physical features and may be used advantageously as a phase change material in heat sinks for thermal management systems (TMS). Yet, it suffers from a major inherent drawback namely its limited specific heat that can offset its other favorable features. The aim of this work is to propose a new simple approach to circumvent such drawbacks and to enhance the applicability of solid gallium as phase change material for TMS by integrating within it discretely distributed cavities filled with chunks of un-encapsulated PCM material. Two PCM cavities arrangements were considered; structured well-defined cylindrical cavities, and randomly distributed randomly shaped cavities. Implementing PCM as proposed hereby aims at capturing some of the heat dumped from a hot source into the gallium and thereby serving two purposes: (1) reduce the gallium’s temperature and (2) reduce melting rate of gallium during phase change upon receiving heat from the source. The hot to-be-cooled source is resembled here by batches of hot water (40 and 60 ml) brought into direct contact with the solid gallium/PCM sink matrix. Two percentages of PCM loading in gallium were considered; 5% and 10% volume fraction. Results have shown that using PCM as proposed is effective in maintaining low gallium sink temperature upon receiving heat from the source. The structured configuration leads only to slight superiority of sink performance. Increasing volumetric PCM loading in gallium up to about 10% clearly improves gallium’s performance as heat sink and results in faster cooling rates as compared to the reference baseline case with only gallium without PCM. For 60 ml of hot water, the temperature drop from ∼70 °C to ∼40 was done in ∼100 s which results in 140 s time saving as compared to the reference case.