| Abstract: | Intensity and power spectral density of acoustic emission in subcooled nucleate pool boiling of water from boiling inception to the heater burnout was investigated experimentally. Platinum and Ni-Cr wires with dia. 1.0 mm or smaller were used as the heater. The measurements were performed in containers at atmospheric pressure and in a dam at pressures up to 3 atm. In the former case photographic observations of boiling bubbles were also made. The acoustic emission in boiling had frequency components up to and sometimes beyond 50 kHz; the shape of power spectral densities behaved differently for heat fluxes above and below a certain value at which the overall acoustic intensity assumed a maximum value. With the increase in heat flux the acoustic emission increased in high frequencies below this heat flux, while it became eminent in low frequencies above the same heat flux. This phenomenon is related to the transition from the region with single bubbles to the region with coalesced bubbles. Resonance-like peaks found in the measurements with containers that may depend on the container geometry were not observed in the measurements in the dam and smoother power spectral densities were obtained. |
