Probing Flow Condensation with Acoustic Signatures*

Two-phase thermal management systems, with both boiling and condensation processes, offer great potential and heat transfer coefficients that are orders of magnitude higher than traditional single-phase systems. However, two-phase flows can suffer from a wide range of interfacial instabilities leading to significant thermal performance degradation. In this study, we aim to characterize dominating physical mechanisms of flow condensation, such as turbulent diffusion in annular liquid film and interfacial waves, using an integrated system of acoustic and optical sensing techniques and thermofluidic characterizations. A wideband acoustic emissions sensor and high-sensitivity accelerometer are utilized to capture acoustic and vibrational signatures that signal the onset of liquid film formation and interfacial waves during flow pattern transitions. Compared to optical imaging, wideband acoustic emission sensing allows for higher sampling rates to capture high-frequency interface oscillations critical to the flow regime transitions and works well even for condensation in opaque tubes. Acoustic features are correlated with thermofluidic processes. By relating thermal performance metrics with these dynamic signatures in acoustic regimes, we explore the ability to probe and monitor critical flow regime transitions and transport efficiency in flow condensation.