Vibration-enhanced direct contact heat exchange using gallium as a solid phase change material

This study experimentally addresses cooling hot liquid in a heat sink under mechanical vibrational excitations. We investigated vibration-enhanced direct contact heat exchange between hot water and a heat sink composed of a phase change material, solid gallium (Ga). The whole sink assembly was vibrated with a sinusoidal wave in the vertical direction. Latent heat and low melting temperature of Ga restricted the maximum temperature rise and the superheating of molten Ga between the water and the solid Ga body. The total amount of Ga melted during the heat exchange with water was measured, providing the share of latent and, in turn, sensible heat absorbed by Ga during the process. Vibration drastically enhanced the cooling rates of hot water under the tested frequencies (20 and 50 Hz) and amplitudes (0.3, 0.5 and 0.7 mm). The enhancement in water cooling was better pronounced for amplitudes higher than 0.3 mm. Under 50 Hz frequency and 0.7 mm amplitude, 99% of heat lost by water was dumped into the gallium sink and 1% was dissipated into the surrounding environment. Under static non-vibrating conditions the heat sink could only capture about 60% of the heat lost by the water. The rest was dissipated into the environment.