Interfacial Heat Transfer of Condensation Bubble with Consideration of Bubble Number Distribution in Subcooled Flow Boiling

Abstract

For predicting the void fraction distribution in subcooled flow boiling, it is necessary to measure the interfacial heat transfer coefficient—which determines the amount of condensation rate of vapor bubble—with high accuracy. In this study, the relationship among the bubble number distributions, void fraction, bubble collapse rate and phase change rate was clarified through measurement of the average interfacial heat transfer coefficient using image analysis under the condition of forced convectional subcooled flow boiling. The bubble number distributions were measured by translating bubble images observed by a high-speed camera. The bubble collapse rates were obtained by the process of bubble number. The obtained bubble collapse rates were possible to predict the decrease rate of the void fraction in low subcooling condition with high accuracy. The average heat transfer coefficient was shown to depend on the interfacial area concentration, via calculation of the average interfacial heat transfer using the obtained bubble number distribution. The developed experimental correlation of the interfacial heat transfer with the interfacial area concentration was compared with the measured value, and the interfacial heat transfer using the developed correlation equation corresponded to the measured one. A comparison with previous correlation equations for interfacial heat transfer coefficients and consideration of the bubble number distribution confirmed the applicability of the experimental correlation of the interfacial heat transfer coefficient to a boiling channel.

Keywords

• image processing
• multiphase flow
• bubble condensation
• bubble number distribution
• bubble collapse rate
• interfacial heat transfer