Piezo-Actuated Enhanced Nucleate Boiling: From Saturated to Controlled Flash Regimes in Two-Phase Direct-to-Chip Cooling for Artificial Intelligence Superchips and Data Centers

Document Type

Article

Publication Date

9-1-2026

Abstract

Two-phase direct-to-chip cooling is emerging as an important thermal management pathway for the rapidly increasing thermal design powers of modern AI superchips while maintaining data center energy efficiency. This paper presents a combined passive–active approach that transitions high-performance saturated heterogeneous nucleate boiling to a stabilized and controlled flash-nucleate boiling regime using low-power piezoelectric actuation that produces feather-like in-plane and out-of-plane microvibrations of the heated surface. Experiments on microstructured copper cold plates (CPs) with dielectric fluids, at 100–140 kPa pressures, establish baseline enhanced nucleate boiling (ENB-1) performance in partial flow-boiling configurations typical of direct-to-chip flow loops. These results quantify cold-plate behavior and indicate that physics-guided modifications of the experimentally tested microstructures and flow-loop design, as modeled and proposed for further experimental testing, can substantially increase heat-transfer coefficients and critical heat flux (CHF). Activation of megahertz piezo-actuators with low-frequency modulation near antiresonance generates small microvibrations that modify nucleating bubble dynamics and their characteristic frequencies. This triggers a rapid transition to a controlled, stabilized high-pressure (400–500 kPa) heterogeneous flash-nucleate boiling regime (ENB-2), sustained at the boiling surface by “on–off” microlayer heating and acoustic streaming mechanisms. This transition from ENB-1 to ENB-2 accompanies a short-duration (tens of milliseconds) increase in interfacial mass transfer across bubble microlayers, producing transient heat extraction of 200–400 J from underneath the heated surface, that is, from the chip to the ENB-2 condenser with a sustained high pressure at the vapor exit of the cold plate. Three-dimensional transient conduction simulations predict chip-level temperature reductions of about 15–20 °C for low-thermal-inertia test vehicles and future chip implementations. Baseline experiments show nucleate boiling heat transfer with critical heat flux near 50–60 W/cm2 and a lower heat-transfer coefficient (HTC) of 1–2 W/cm2 °C. The tested and deployed architecture is amenable to further optimization to higher CHF (135–175 W/cm2 or more) and associated HTC (up to 150 W/cm2 °C) for ENB-1 and 10–20 °C cooler chips through ENB-2. Observed ENB-2 condenser performance suggests a shift from the ENB-1 condenser to a direct-contact tank/pool condenser for ENB-2, which would allow sustained waste-heat recovery from the vapor at, say, 70 °C and 400 kPa. That is, a stabilized flash-boiling regime supports lower junction temperatures, improved chip reliability, and more energy-efficient next-generation AI data centers.

Publication Title

ASME Journal of Heat and Mass Transfer

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