Investigation on interaction between an oscillating vapor film and its surrounding liquid in microbubble emission boiling

Abstract

Microbubble emission boiling (MEB) is a boiling phenomenon occurred under highly subcooled condition, which can realize a heat flux higher than critical heat flux. Owing to the complex bubble dynamics in MEB, its heat transfer mechanism remains elusive. In this study, the convection near an oscillating vapor film and its contribution to MEB are investigated experimentally and numerically. Visualization results reveal that the convection near the vapor film is enhanced with its thermal affected area being enlarged over 4-fold within 32 ms after the occurrence of MEB. Different from nucleate boiling, the vapor film attached on the heating surface oscillates rapidly in its volume, width and height in MEB, which may be one of the reasons for the formation of the strong convection. On this basis, simulations of the fluid flow and heat transfer near a stable or an oscillating vapor film were performed. Numerical results show that the oscillation of the vapor film enhances its surrounding convection obviously and improves the heat dissipated from the vapor into cold bulk over 10 times compared with that for a stable film. The above findings suggest that the convection enhanced by the vapor film oscillation plays an important role inMEB.