Bubble departure in forced convective subcooled boiling flow

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 departure frequencies were obtained from the video for a total of 92 test conditions. The departure frequency increases as the increase of inlet temperature or heat flux, or the decrease of inlet fluid velocity. A force balance analysis of a growing bubble was performed to predict the bubble departure size to be around 10-4 m. The departure frequency is modelled by taking account of transient heat conduction and bubble growth rate. Comparison with experiments suggests that departure frequency falls into two regions: subcooled region and saturate region. The proposed bubble departure frequency model agreed fairly well with the experimental data