Numerical simulation of subcooled boiling water in vertical concentric annulus under low pressure

Adopted a modified bubble departure diameter correlation based on the Unal mechanism model, a numerical simulation of subcooled boiling water under low pressure was performed on the computational fluid dynamics code CFX5.7 with user defined FORTRAN program. The water boiling flow experiments under low pressure in a vertical concentric annulus from reference were adopted to validate the modified model of bubble departure diameter. Moreover, the examination of grid independence was discussed, and the influences of the non-drag force on the radial void fraction distribution force were investigated, including lift force, turbulent dispersion force and wall lubrication force. The simulation results indicate that the models are endowed with a preferable applicability for broad test conditions. Especially, the peak void fraction at near-wall region occurs in low liquid subcooling and low mass flux, contrariwise, the peak void fraction in near-wall region never appears. which is in accordance with the experimental data. The predicted profiles of liquid velocity are close to the experimental data, but obviously differ from the prediction of vapor velocity in the near-wall region.