Overview
In view of the rapid increase of microchip power densities, thermal management has become considerably more challenging and requires efforts aimed at developing a liquid-based cooling module capable of handling high heat fluxes. Four modules containing up to 120 planar ("slot") jets and a drainage channel system that prevented any cross-flow effect were tested using FC72 as test fluid. A custom-made heater resembling an actual microchip was manufactured from silicon and equipped with temperature sensors. The effects of the flow rate, the inlet liquid temperature, the gap between impinged surface and nozzle plate, and different module geometries are discussed.
Jet impingement cooling with a single jet can remove high power densities at the stagnation point, but at the price of decreasing heat transfer efficiency towards the periphery, resulting in strong temperature gradients on the cooled surfaces. To remedy this situation, single-phase submerged jet arrays have been proposed to provide high cooling performance while attaining good temperature uniformity. Typically the cooling performance of jet arrays increases with the number of nozzles, but for very large numbers of jets the performance is reduced at the periphery owing to accumulating crossflow.
Although the heat transfer performance was smaller than with single-phase cooling using microchannels, the pump power consumption was very low, rendering two-phase cooling in jet geometries a valid alternative to other cooling options. 92 W/cm2 were removed at a junction temperature of 85 ºC, and critical heat flux (CHF) was observed at 161 W/cm2 using a coolant flow of 1.46 l/min and an inlet temperature of 20 °C. The performance of jet coolers was improved further using other coolant fluids and by boiling-enhancement structures on the surfaces that would enhance heat transfer and lower the onset temperature of boiling. In the longer term, improvements of cooling may be possible by means of vapor compression refrigeration and flow boiling in multi-microchannels. These topics are being addressed in collaboration with academic institutions.
Publications
[1] M. Fabbri, A. Wetter, B. Mayer, T. Brunschwiler, B. Michel, H. Rothuizen, R. Linderman, and U. Kloter, "Microchip Cooling Module Based on FC72 Slot Jet Arrays Without Cross-Flow," 22nd ITHERM Symposium, Dallas Fort Worth, (2006).
