A novel non-destructive acoustic approach for investigating pool boiling phenomena

Analyzing boiling phenomena and performance within invisible boiling systems, where the interior cannot be observed, has traditionally been challenging. In this study, we propose a non-destructive approach using acoustic analysis method to figure out the boiling dynamics or performance, non-invasively. In pool boiling experiment, the acoustic emission (AE) sensor captured the emitted signals at the outside of the heater. Our analysis focused on two key aspects: single bubble characterization and multi-boiling phenomena. For single bubble, we observed that the AE signals originated from the pressure waves generated at the solid-vapor interface of the bubbles. Utilizing a finite difference method, the bubble radius was reverse calculated from the AE signals, enabling predictions up to a certain duration. Frequency analysis revealed a direct correlation between the signal frequency and the oscillation of the bubble radius. In multi-boiling phenomena, as heat flux increases, the number and intensity of AE signals rise, indicating more frequent and rapid bubble generation. A correlation was established between the AE signal counts in the 40 kHz range and the heat transfer coefficient (HTC). The AE count increased linearly with heat flux until it saturated near the critical heat flux. This correlation provided the non-destructive method to estimate the boiling HTC based on AE measurements. In conclusion, the findings offer insights into bubble dynamics, heat transfer characteristics, and the potential application for HTC estimation.