Theoretical investigation on the thermal prformance of flat two-phase heat spreaders with microchannels

A detailed mathematical model of a two-phase heat spreader with axial microchannels is developed in which the fluid flow is considered along with the heat and mass transfer processes during evaporation and condensation. The model is based on the equations for the mass, momentum and energy conservation, which are written for the evaporator, adiabatic, and condenser zones. The model, which permits to simulate several shapes of microchannels, can predict the maximum heat transfer capacity of the two-phase heat spreader, the optimal fluid mass, and the temperatures and pressure gradients along the microchannel. The effect of shear stresses at the free liquid surface in a microchannel due to the frictional liquid-vapor interaction on the liquid flow is taken into consideration. The heat transfer through the liquid films in both evaporator and condenser is accounted for in the model, which is described with respect to the disjoining pressure, interfacial thermal resistance, surface roughness, and curvature. The thermal resistances of the evaporator and condenser are determined by accounting for the longitudinal distribution of the meniscus curvature, which is dependent on heat load and heat spreader inclination.