Heat Transfer Enhancement in an Oscillating Heat Pipe with Self-Dispersion Liquid Metal Micro-Droplets

Liquid metal micro- or nano-droplets in aqueous solution which can be called metallic emulsion is a novel coolant with high heat transfer capacity due to the high thermal conductivity of liquid metal. Here, we produce a liquid metal micro-droplets coolant with the mixture of galinstan, water and surfactant (sodium dodecyl benzene sulfonate, SDBS). Liquid metal is dispersed into multiple micro-droplets spontaneously by the intense generated boiling vapor bubbles in the oscillating heat pipes (OHPs) with the control of heat input. With the addition of SDBS into water, coalescence of small liquid metal droplets is reduced due to the repulsion force acting on the interfaces of liquid metal droplets by the covered surfactant molecules. The size of liquid metal droplets depends on the SDBS concentration and heat input, which is decreased with the increasing of heat input. Moreover, the base fluid has an optimum surfactant concentration of 0.4 wt. % for the well dispersion of liquid metal droplets. In this surfactant concentration, the average radius of the liquid metal droplets is in the range of 0.2 to 0.6 mm at the heat input of 260 W to 380 W. The heat transfer performance of OHPs is significantly improved by using this working fluids with liquid metal micro-droplets in comparison to pure water. The maximum reduction in thermal resistance is 27 % for an OHP with 0.4 wt. % surfactant solution and 2 g liquid metal compared to pure water-filled OHP. The innovative fluids with multiple liquid metal droplets can be used in the heat transfer devices for faster and smaller electronic components and systems.