Acoustic Emission Signatures of Flow Boiling in a Microchannel Heat Sink

Abstract

Flow boiling in microchannel heat sinks is a promising route for next-generation electronics cooling, but its implementation is limited by interfacial instabilities, flow oscillations, vapor choking, and local dryout. Conventional diagnostics based on optical visualization, temperature, pressure, and flow-rate measurements are valuable, but they can be difficult to apply for real-time monitoring in compact or visually inaccessible cooling hardware. This work evaluates contact acoustic emission (AE) sensing as a nonintrusive diagnostic for identifying phase-change events and characterizing transient two-phase flow behavior in a microchannel heat sink. A synchronized multimodal facility was developed that combines contact AE sensing, airborne microphone measurements, thermofluidic measurements, and high-speed optical imaging under controlled heating conditions. Representative tests comparing a single-phase baseline at P = 2.2 W with a boiling case at P = 45.3 W show that boiling onset produces pronounced increases in AE amplitude and AE hit rate. The AE count-duration distribution also broadens during boiling and includes short-duration, high-count transients that are consistent with rapid interfacial motion and abrupt vapor-fraction changes. In contrast, microphone spectrograms show weaker separation between single-phase and two-phase conditions, indicating that solid-borne AE is more sensitive to confined boiling events under the tested conditions. These results establish a baseline framework for physics-informed acoustic diagnostics and machine-learning-assisted monitoring of two-phase thermal management systems.