Experimental characterization of a micro-scale thin film evaporative cooling device

A MEMS-NEMS cooling device based on gas-assisted, thin-film evaporation and its experimental performance characterization are presented, aiming to dissipate large heat fluxes at low junction temperature for thermal management of hot spots in microprocessors. The salient feature of this cooling scheme that distinguishes it from other currently used microfluidic cooling techniques is an efficient combination of heat and mass transfer modes to maximize the rate of convective heat transfer and phase change via evaporation, which enable dissipation of very large heat fluxes. In order to make this possible, a thin film of coolant (~15 μm) is maintained by capillary action over the hotspot by using a thin (~10 μm) nanoporous membrane. This results in minimizing the thermal resistance offered by the thin film. In addition, jet impingement of dry air over the membrane enhances evaporation rate by reducing the mass transfer resistance for transport of vapor phase from the liquid-vapor interface to the ambient. In this paper, design and performance results obtained from experimental testing of a microfabricated device are discussed, demonstrating the heat transfer coefficients approaching 0.1 MW/m²K, while maintaining surface temperatures well below the saturation temperature of the working fluid.