Shape stability and flow behaviour of a phase change material based slurry in coupled fluid-thermo-electrical fields for electronic device cooling

The suitable phase transition temperature range and low electrical conductivity make fatty acid-based Phase Change Material (PCM) slurries an attractive heat transfer fluid for cooling of High–Voltage Direct Current (HVDC) electronic devices. However, their shape instability induced by external electrical field may alter their effective thermophysical properties and hence the heat transfer performance. In this work, the shape stability and flow behavior of a fatty acid droplet under a coupled fluid-thermo-electric coupled field are numerically investigated. The effects of droplet size, fluid velocity and temperature, and electrical field on the shape and energy of the droplet are evaluated. The results show that the droplet size is the major influencing factor for the shape stability. Given other conditions, the deformation ratio and the internal pressure difference of a 1 μm droplet are respectively 8 times higher and 5 times larger than a 7 μm droplet. An increase in the slurry velocity only slightly increases the particle interior pressure; given other conditions, an increase in the velocity from 0.22 m/s to 1.1 m/s only leads to an internal pressure increase by 25.77%. The electrical stress across the surface tends to squeeze the droplet into a prolate shape, offsetting the shape deformation by the shear stress and hence stabilizing the PCM slurry. The presence of the electrical field slows down the energy evolution and reduces the pressure difference inside the droplet.