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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.
» Back to Single-phase,
miniaturized convective cooling
References
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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).
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IBM Research
