Experimental measurements and numerical simulations have been performed on copper and aluminum microchannel heatsinks of 300, 420, 500, and 900 &amp / #956 / m channel widths. The heatsinks have been designed specifically for use with T/R (transmit/receive) module cooling applications of military phased array radars. An analytical calculation was also performed to aid in the design methodology. Distilled water was used as the coolant with flow rates ranging from 0.50 lpm (liters per minute) to 1.00 lpm. Local heat fluxes as high as 100 W/cm2 were tested. Upon completion of the experiments, the thermally best performing specimen, the 300 &amp / #956 / m copper specimen, yielded a maximum temperature rise of 26.1 &deg / C between the heat load and coolant inlet, at a coolant flow rate of 1.00 lpm and local heat flux of 100 W/cm2, leading to a thermal resistance of 0.63 &deg / C/W. The pressure drop measured across the heatsink under these conditions was 0.030 bar. Numerical simulations were carried out using the commercial Computational Fluid Dynamics (CFD) software FLUENT&reg / . Effects of thermal interface layers and heat spreading due to the localized heat load were investigated. Simulation results for temperature were seen to agree fairly well with experimental data as long as thermal interface layers were accounted for. The study showed that the T/R modules of military phased array radars, dissipating as high as 100 W/cm2 locally, could be cooled within the limits of the harsh environmental conditions required of military applications with moderate pressure drops.

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