A Void Fraction Distribution Fast Prediction Model for Non-Axisymmetric Channels and Application to a Rod Bundle Subchannel

The void fraction distribution is crucial for the two-phase flow characteristics, the available Void fraction Distribution Fast Prediction model (VDFP) can improve the prediction accuracy of the 1D nuclear system analysis codes. In the past, one VDFP called 1D Test-Solver was developed to predict the radical void fraction distribution based on the balance of radical interfacial forces, which has a good physical ground and is suitable for a wide range of flow conditions. The computation cost of the 1D VDFP is small enough to couple with the 1D system analysis codes, and it is quite promising for the code's development in the future. However, the 1D VDFP is an axisymmetric model and is only suitable for vertical circular pipes. In this study, a 2D VDFP, which is suitable for a non-axisymmetric channel, was developed while retaining the merit of low computation cost. The axial velocity distribution was calculated based on the balance of axial differential pressure force and viscous force. The viscosity was divided into the liquid viscosity, eddy viscosity caused by the liquid shear effects and bubble agitation. The void fraction distribution was calculated based on the balance of lift force, wall lubrication force, and turbulent dispersion force. The developed VDFP model was used to predict the void fraction distribution in a rod bundle subchannel with the rod diameter of 25 mm and the rod pitch of 34 mm. Since the rod bundle subchannel is cramped, the effects of bubble geometric restriction on void fraction prediction were evaluated. The VDFP was verified by comparing the prediction results with the experimental data. For future research, VDFP should be verified and improved by more experimental data from asymmetric channels and coupled with 1D nuclear system analysis codes