Multiphase flow and heat transfer on micro/nanostructured surfaces

Abstract

Paper presented to the 10th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Florida, 14-16 July 2014.Multiphase flow and heat transfer in mini/microspaces are of significant interest for thermal management applications, where the latent heat of phase change offers an efficient method to dissipate large heat fluxes in a compact device, such as a heat spreader or a heat pipe. However, a significant challenge for the implementation of microscale phase change heat spreader is associated with micro/nano flow instabilities due to insufficient micro/nano bubble removal, leading to local liquid dry-out which severely limits the heat removal efficiency. This work will conduct a review on the challenges and opportunities that surfaces with micro/nanostructure patterned wettabilities. Bubble dynamics, fluid flow and heat transfer caused by the micro/nanostructure patterned surfaces will be reported and discussed. The effects of micro/nanostructure patterned surfaces on flow generation under a vapor bubble in a microchannel under very low Reynolds number will be demonstrated. The effects of wettability patterned surfaces on nucleation pool boiling and flow boiling heat transfer processes will be described. Bubble formation, breakup and departure are visualized and measured. Wettability patterned micro/nanostructure surfaces are manufactured on glass wafers and copper surfaces, respectively. Different surface hexagonal pattern size will be used. Indium Tin Oxide (ITO), Fluoroalkylsilanes (FAS) and Copper Oxide (CuO) will be used for glass and copper surfaces, respectively. It is found that bubble dynamics and pool boiling performance are enhanced significantly on smooth and flat surfaces combining hydrophilic and hydrophobic patterns in comparison with a hydrophilic surface. A micro/nanostructured heat spreader with asymmetrical wettability patterns will be demonstrated.