Bubble lift-off in forced convective subcooled boiling flow

Abstract

Bubble lift-off is different from bubble departure, and it is more suitable for the boundary condition for numerical simulation of subcooled boiling flow. A force balance analysis of a growing bubble was performed to predict the bubble lift-off size. The dimensionless form of the bubble lift-off diameter was formulated to be a function of Jacob number and Prandtl number. The modeling of bubble lift-off frequency requires careful study of bubble collapse during sliding. Forced convective subcooled boiling flow experiments were conducted in a BWR-scaled vertical upward annular channel. Water was used as the testing fluid, and the tests were performed at atmospheric pressure. A high-speed digital video camera was applied to capture the dynamics of the bubble nucleation process. Bubble lift-off diameters and lift-off frequencies were obtained from the images for a total of 92 test conditions. The bubble lift-off frequency was found to be same as the bubble departure frequency. The proposed bubble lift-off diameter model agreed well with the experimental data within the averaged relative deviation of ±33.6 %.