Experimental study on vapor bubble oscillation and boiling sound in microbubble emission boiling (MEB)

We study experimentally so-called "microbubble emission boiling (MEB), " which occurs under high subcooled conditions. We especially focus on the correlation among the heat transfer characteristics, the oscillating behaviors of the vapor bubbles on a horizontal circular heating surface, and the boiling sound in the developing and developed states of the MEB in the pool. Spatial-temporal behaviors of the vapor bubbles oscillation and characteristics of boiling sound are investigated through the Fourier spectra of the temporal variations of the oscillation obtained by high-speed imaging and the boiling sound obtained by sheathed microphone, respectively. We indicate that the vapor bubbles exhibit non-uniform oscillation in the radial direction at the early stage of the MEB, whereas they oscillate uniformly in the radial direction in phase above the heating surface at the fully developed state of the MEB. We find that the uniformity of the vapor bubbles oscillation is the essence of the heat transfer characteristics and the accompanying boiling sounds.