Two-phase (phase-change) microchannel (MC) system is a promising technology for achieving enhanced heat removal for highdensity electronics. Yet phase-change studies in MCs with hydraulic diameters on the order of several hundred micrometers or smaller have been inconclusive. Most of earlier studies involved one specific channel design and one type of working fluid. It is thus difficult to make fair comparisons across various experimental works toward recommending the best design option for real applications under specific operating conditions. In the current work, flow boiling experiments were conducted for MC cold plates with channel widths ranging from 61 μm to 330 μm and channel height ∼ 300 μm (hydraulic diameters from ∼ 100 μm to ∼ 337 μm) and a pin-fin array cold plate with fin size and inter-spacing ∼ 150 μm. Two working fluids, deionized water at sub-atmospheric pressure (∼ 25 kPa to 45 kPa) and HFE-7100 at ambient pressure, were tested respectively. High-speed visualization facilities were employed to help understand the rapid phase-change processes inside the flow passages. Pressure drop and heat transfer characteristics of the microchannel cold plates under various heat flux and flow rate conditions were recorded and analyzed as well as boiling fluctuations. Detailed visualization results will be presented in a separate paper [Tong et al., IMECE2007-42028].

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