Local Heat Transfer Coefficient Measurements of Flat Angled Sprays Using Thermal Test Vehicle

Abstract

Impingement cooling methods, such as spray cooling and jet impingement have demonstrated the capability of cooling high heat flux surfaces while maintaining a low thermal resistance. Most spray cooling and jet impingement experiments attempt to measure the average heat transfer coefficient, even though it is known that heat transfer coefficients are known to change as a function of distance from the impact zone. Secondly, most experiments are done on thick uniformly heated surfaces although most electronic devices are very thin (<0.2 mm) and generate heat very non- uniformly with very large peak heat fluxes (>1000 W/cm2) over very small areas (<0.25 mm2). In this study an accurate measurement of the uniformity of the spray cooling thermal solution was attained using an Intel supplied thermal test vehicle. The heater block is a thin silicon chip (<0.25 mm thick and 7 cm2 in surface area) delivering a uniform heat flux to 70 W/cm2. The platform also has the ability to power large peak heat fluxes (>1000 W/cm2) over small areas (<0.2 5 mm2). Experiments using jet impingement with flat spray nozzles angled to the surface were conducted with water, methanol, and HFE-7000. The axial heat transfer coefficient variation was measured under uniform heat loading. Finally, the measurements are compared to modified models from the literature with good agreement.