Flow boiling in an onboard variable microgap is demonstrated as a viable cooling method for multidevice electronics. The microgap is created by a bonded conformal encapsulation that delivers uniform subcooled inlet coolant flow across a multidevice layout comprising a processor and two in-line, symmetrically placed memory devices. Each device is simulated with a ceramic resistance heater on a 1:1 scale, and the heights of the devices create the variable microgap under the roof line of the encapsulation. The gap height for the processor is 0.5 mm and 1 mm for the memory devices. Parameters investigated are pressure drop, average device temperature, processor power, and coefficient of performance (COP). For inlet coolant flow first over the memory devices, the average device temperature exceeds the 95 °C limit when processor power is ∼50 W or less. For inlet flow over the processor, memory device temperatures are approximately the same over all the levels of processor and memory chip power. For processor power <30 W and an inlet coolant temperature of 25 °C, single-phase heat transfer is the dominant cooling mechanism. When processor power is >40 W, two-phase heat transfer dominates, and processor power of 120 W is reached within the 95 °C threshold. Volumetric power density across the data set is 134 to 1209 W/cm3.

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