A new cooling scheme is proposed where the primary working fluid flowing through it micro-channel heat sink is pre-cooled to low temperature using an indirect refrigeration cooling system. Cooling performance was explored using HFE 7100 as working fluid and four different micro-channel sizes. High-speed video imaging was employed to help explain the complex interrelated influences of hydraulic diameter, micro-channel width, mass velocity and subcooling oil cooling performance. Unlike most prior two-phase micro-channel heat sink studies, which involved annular film evaporation due high void fraction, the low coolant temperatures used in this study produced subcooled flow boiling conditions. Decreasing coolant temperature delayed the onset of boiling, reduced bubble size and coalescence effects, and enhanced CHF. Heat fluxes in excess of 700 W/cm(2) could be managed Without burnout. Premature CHF occurred at low mass velocities and was caused by vapor flow reversal toward the inlet plenum. This form of CHF was eliminated by decreasing coolant temperature and/or increasing flow rate. (c) 2008 Elsevier Ltd. All rights reserved.