Acoustic Signatures of Boiling Critical Heat Flux and Interfacial Instabilities

Boiling is critical to the efficient and safe operation of electronics cooling, power generation, refrigeration, water purification, and chemical processing. However, pool and flow boiling are prone to various instabilities, leading to significantly reduced heat transfer coefficients, higher pressure drop, and potential damage to equipment. The interplay of physical mechanisms, such as bubble nucleation, growth and departure, turbulent flows, capillary flows, and thermal expansion-driven flows, has limited our understanding of boiling instabilities. In this study, we use wideband acoustic emission sensing, integrated with high-speed imaging and temperature/pressure measurements, to probe the physical mechanisms that dominate critical heat flux (CHF) and flow instabilities during pool and flow boiling. The wideband AE sensing technique allows for higher sampling rates to capture high-frequency interface oscillations and the onset of CHF and flow regime transitions. The resulting acoustic signatures show significant change in dominant frequency and amplitude at CHF and help to quantify the role of liquid film, turbulent diffusion, and interfacial waves during boiling regime transitions.