Early detection of localized onset of boiling

Abstract Noise measurement has been often used to detect boiling phenomena in water or other liquids. Although some acceptable correlations have been shown, no in depth study of the relationship between measurement observation and physical boiling process has been satisfactorily presented. This paper shows the results of an experimental investigation on the detection of localized onset of boiling in water on a heated fuel pin. Accelerometers placed on the pin and on the surrounding structures at appreciable distance from the boiling spot were used. A detailed analysis of the results and a comparison with the theoretical bases of boiling has been made in order to extract the actual boiling information from the structure background vibrations. The influence of pressure and temperature have corroborated the proposed relationship between the measured noise and the bubble growing and collapsing processes. The observations conducted on different structures have assessed the independance of the analysis with respect to the structure particular dynamic behaviour. The detection method is shown to be robust and capable to be applied even when accelerometers cannot be placed near the hot zone as in nuclear reactor for instance.