Optimal design of subcooled microchannel heat sinks with variable heat inputs

Abstract

Geometric optimization and flow parameters modelling were carried out for two-phase flow in horizontal rectangular microchannels. The flow was highly subcooled at inlet temperature of 25oC using deionized water as the cooling fluid and aluminium as the heat sink material. Velocities between 0.1 and 4.5m/s and heat fluxes between 100 and 300 W/cm2 (1x106 W/m2 and 3x106 W/m2) were used in the modelling and optimization. The subcooled boiling model in ANSYS computational fluid dynamics code was used for the velocities and heat fluxes to obtain optimal geometric and flow parameters for subcooled boiling heat transfer in two-phase flow. The code used for the simulations was validated by the available experimental data in the literature and the agreement showed the capability of CFD to predict accurately, subcooled boiling heat transfer in rectangular microchannels for cooling of microelectronic devices. Comparisons were made between two-phase flow and single-phase flow by using their optimal geometric and flow parameters, and the results clearly demonstrated the superiority of two-phase flow in optimal rectangular microchannels for removal of high heat fluxes at low Reynolds numbers. Optimal microchannel heat sink at 100 W/cm2 was used for the critical heat flux study to show the extent to which it could operate beyond the optimal heat flux, and the outcome revealed that the heat sink material would be destroyed after the safe heat flux limit of 1000 W/cm2. Temperature contours are provided to show temperature distribution in the heat sink material for two-phase and single-phase flows. The optimal Reynolds number increases as the minimized thermal resistance and peak base temperature decrease which is evident of good thermal performance of the optimal microchannels.