Damped harmonic oscillator framework for boiling acoustics: Insights from single vapor bubble experiments

• Necking-induced liquid inrush at departure is the primary acoustic source. • Single-bubble spectra resemble those from standard multi-bubble boiling. • Gas and vapor bubbles show distinct frequency trends despite similar dynamics. • Vapor bubbles emit weaker, lower-frequency (300–500 Hz) signals than gas bubbles. • Existing models significantly overpredict acoustic frequency and damping. • New model predicts reduced stiffness, along with gas-like damping, matches experiments. Bubbles are ubiquitous in natural and engineered systems and often serve as acoustic indicators of underlying physical processes. While the acoustics of gas bubbles have been extensively studied, the mechanisms of sound generation by vapor bubbles during boiling remain poorly understood. Here, we investigate passive acoustic emissions from single vapor bubbles during near-saturated pool boiling using synchronized audio–visual diagnostics and report—for the first time—the detailed acoustic signature of the ebullition cycle. We find that bubble departure is the dominant sound-emitting event, driven by necking-induced liquid inrush that excites radial oscillations—akin to Minnaert-like resonance observed in gas bubbles detaching from underwater nozzles. However, vapor bubbles produce weaker and lower-frequency broadband signals (300–500 Hz) compared to the sharp Minnaert peaks (>1000 Hz) of gas bubbles of similar size. The vapor bubble emission range remains robust across variations in power input and persists in multi-bubble boiling, where overlapping departures and coalescence events add complexity without altering the dominant features. Analytical modeling reveals that existing formulations systematically overpredict both the natural frequency and damping of vapor bubbles, as they were derived for quiescent liquid pools. In realistic boiling, however, bubbles interact strongly with the surrounding flow field during departure, which enhances heat loss and reduces effective stiffness. To capture this effect, we propose a modified natural frequency relation that extends Prosperetti’s formulation by incorporating thermal convection in addition to evaporation–condensation. The resulting relation preserves the original parametric structure while introducing a convection parameter, S , which quantifies the relative importance of convective heat transfer. Once the dependence of S is determined by performing boiling experiments under varying pool conditions, the proposed formulation can serve as a unified relation for predicting boiling acoustics. Overall, this work presents a physics-based framework for boiling acoustics and provides a foundation for acoustic sensing and thermal management technologies.