Abstract

Through the application of cryogenic cooling via liquid nitrogen (LN2), the power consumption of a CPU was substantially reduced. Using a digitally controlled solenoid valve and an additively manufactured cold plate, the manual process of LN2 cooling was automated for precise control of cold plate temperature. The power consumption and frequency relationship of the processor was established across three different thermal solutions to determine the effect of temperature on this relationship. It was found that power consumption of the processor decreased at lower temperatures due to a reduction in current leakage and the core voltage necessary for stable operation. This culminated in a reduction of up to 10.6% in processor power consumption for the automated solution and 20.8% for the manual LN2 solution when compared to the air cooled baseline. Due to the binary nature of the solenoid valve, flow rate was tuned via an in-line needle valve to increase thermal stability. It was found that for lower flow rates, approximately 5.0 g/s, temperatures oscillated within a range of +/- 11.5°C while higher flow rates of 10 to 12 g/s generated amplitudes as small as +/-3.5°C. Additionally, several tests measured the rate of LN2 consumption and found that the automated solution used 230% to 280% more coolant than the manual thermal solution, implying there is room for improvement in the cold plate geometry, LN2 vapor exhaust design, and coolant delivery optimization.

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