Room temperature liquid metal (galinstan, made up of gallium, indium and tin) is driven to oscillate by the phase change of water in the self-excited oscillating heat pipe (OHP) charged with liquid metal and water. The cross section of the channel is square with the dimension of 3×3 mm2. Liquid metal is a high-performance coolant with ultrahigh thermal conductivity (nearly 27 times higher than water). During the operation of OHP, liquid metal is pushed up by the vapor expansion in the evaporator section, and moves back by the vapor contraction and gravity effects. Then, liquid metal is driven to oscillate continuously between evaporator and condenser in the OHP. Surface tension of galinstan is 10 times higher than water, resulting in a ball shape of liquid metal in the channels. And there is a thin water film existing between liquid metal and inner surface. During the oscillating motion, liquid metal presents the characteristics of a mollusk. Soft liquid metal is extended into metal filament, or breaks up into small liquid metal balls. Then, small liquid metal balls coalesce into a long liquid metal slug, resulting in surface waves due to the released surface energy during the coalescence process. The deformation and deformation recovery of the liquid metal is the result of competition between deforming pressure forces and the reforming surface tension forces. Oscillations of liquid metal will generate flow field disturbance in the base fluid of water and further enhance the heat transfer performance in two-phase flow systems.

[This research work was supported by the National Natural Science Foundation of China under Grant No. 21606034 and Office of Naval Research under Grant No. N00014-19-1-2006.]

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