Thermal and Manufacturing Design Considerations for Silicon-Based Embedded Microchannel-3D Manifold Coolers (EMMCs): Part 1-Experimental Study of Single-Phase Cooling Performance With R-245fa

Abstract

High performance and economically viable cooling solutions must be developed to reduce weight and volume, allowing for a wide-spread utilization of hybrid electric vehicles. The traditional embedded microchannel cooling heat sinks suffer from high pressure drop due to small channel dimensions and long flow paths in two-dimensional (2D) plane. Utilizing direct "embedded cooling" strategy in combination with top access three-dimensional (3D) manifold strategy reduces the pressure drop by nearly an order of magnitude. In addition, it provides more temperature uniformity across large area chips and it is less prone to flow instability in two-phase boiling heat transfer. This study presents the experimental results for single-phase thermofluidic performance of an embedded silicon microchannel cold plate (CP) bonded to a 3D manifold for heat fluxes up to 300W/cm(2) using single-phase R-245fa. The heat exchanger consists of a 5x5mm(2) heated area with 25 parallel 75x150 mu m(2) microchannels, where the fluid is distributed by a 3D-manifold with four microconduits of 700x250 mu m(2). Heat is applied to the silicon heat sink using electrical Joule-heating in a metal serpentine bridge and the heated surface temperature is monitored in real-time by infrared (IR) camera and electrical resistance thermometry. The maximum and average temperatures of the chip, pressure drop, thermal resistance, and average heat transfer coefficient (HTC) are reported for flow rates of 0.1, 0.2. 0.3, and 0.37L/min and heat fluxes from 25 to 300W/cm(2). The proposed embedded microchannels-3D manifold cooler, or EMMC, device is capable of removing 300W/cm(2) at maximum temperature 80 degrees C with pressure drop of less than 30kPa, where the flow rate, inlet temperature, and pressures are 0.37L/min, 25 degrees C and 350kPa, respectively. The experimental uncertainties of the test results are estimated, and the uncertainties are the highest for heat fluxes<50 W/cm(2) due to difficulty in precisely measuring the fluid temperature at the inlet and outlet of the microcooler.