A closed-loop two-phase microchannels cooling system using a micro-gear pump was built in this paper. The microchannels heat sink was made of oxygen-free copper, and 14 parallel microchannels with the dimension of 0.8mm(W)×1.5mm(D)×20mm(L) were formed by electric spark drilling followed by linear cutting which separated the channels from each other. The heat transfer performance was evaluated by the fluid temperature, the pressure drop across the micro-channels and the volumetric flow rate. Experiments were performed with refrigerant FC-72 which spanned the following conditions: initial pressure of Pin = 73 kPa, mass velocity of G = 94 – 333 kg/m2s, outlet quality of xe,out = 0 – superheat and heat flux of q= 25–140 W/cm2. The result showed that, the maximum heat flux achieved 96 W/cm2, as the heating surface temperature was kept below 85 °C and critical heat flux occurred in the condition of low flow rate. Average two-phase heat transfer coefficients increased with the heat flux at low mass flux (G = 94 and 180 kg/m2s) and all heat fluxes, high mass flux (G = 333 kg/m2s) and all heat fluxes, and moderate mass fluxes (G = 224kg/m2s) under low and moderate heat fluxes (q<110 W/cm2 for G = 224 kg/m2s), which was a feature of nucleate boiling mechanism. Pressure drop through microchannels heat sink was found to be below 4kPa.

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