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To solve the heat dissipation problem of electronic devices with high heat flux hotspots, a diamond microchannel heat sink consisting of 37 parallel triangular microchannels with channel lengths of 45 mm and hydraulic diameters of 280 μm was designed. The flow boiling heat transfer characteristics of ammonia in the microchannels were investigated under high heat fluxes of 473.9-1000.4 W/cm2. Saturated flow boiling experiments with saturation temperatures of 25, 30, and 35°C and mass fluxes of 98–1200 kg/m2s were conducted, as well as subcooled flow boiling with inlet subcooling of 5°C as a comparison. The temperature and pressure drop measurements were analyzed, and the main conclusions below can be drawn. (1) At a given heat flux, the heat source temperature first decreased and then increased with the mass flux, and there existed an optimum mass flux to optimize the cooling performance of the heat sink. (2) The heat transfer performance under the saturated inlet condition was obviously better than that under the subcooled inlet condition. (3) A larger saturation temperature leaded to weakening of both the heat transfer capacity and the stability of the microchannel heat sink. Notably, with the high heat diffusion ability of the diamond substrate and the great heat transfer capacity of ammonia flow boiling in microchannels, the heat sink can achieve a heat removal capacity of up to 1000.4 W/cm2.

Flow boiling in microchannels is a promising technique for cooling high power-density electronic devices. In this study, a microchannel heat sink using ammonia as working fluid is developed, and its cooling efficiency is experimentally investigated under nonuniform high-density heat flux, which well simulates a practical heat dissipation scenario for microthermal systems. Diamond with high thermal conductivity of 1500 W/m·K is selected as the microchannel heat sink material. A total of 37 parallel triangular microchannels with aspect ratio of 5, channel length of 45 mm and hydraulic diameter of 280 μm are uniformly engineered on the diamond film by laser ablation processing. The significance of diamond substrate as a heat spreader to minimize the nonuniformity of heat flux imposed by a central hotspot is verified. The influences of heat flux and mass flux on the cooling efficiency are experimentally investigated. An optimal range of outlet vapor quality from 0.10 to 0.13 is found, within which the minimum heat source temperature can be achieved. Notably, the microchannel heat sink is capable of managing a central hotspot with heat flux of 267 W/cm2 while maintaining the heat source temperature at 53.3 °C for a mass flux of 320 kg/m2s.