Keiko Kano

Two-Phase Void Drift Phenomena in a 2 × 3 Rod Bundle: Flow Redistribution Data and Their Analysis

Abstract To improve a void drift model used in a subchannel analysis, new experimental data are obtained for air-water two-phase flows in a vertical 2 × 3 rod channel consisting of six subchannels simulating a square array boiling water reactor fuel rod bundle. The data include the axial redistributions of flow rates of both phases and void fraction in the respective subchannels. By fitting the above data with the Lahey and Moody void settling model, we have determined a void diffusion coefficient in their model. It is found that the void diffusion coefficient for slug, churn, and annular flows could be well correlated in terms of a turbulent Peclet number developed in our previous study. Furthermore, a subchannel analysis code based on a two-fluid model proposed in our previous study is examined against the present data. In the code, the void settling model is incorporated with usual conservation equations of mass and momentum. From the examination, it is found that the subchannel analysis code can predict well the data on subchannel flow and void fraction for the 2 × 3 rod channel if appropriate correlations are adopted to evaluate wall and interfacial friction forces needed in the two-fluid model.

Flow distribution and slug flow characteristics for hydraulically equilibrium air-water two-phase flows in a vertical 2×3 rod channel

To complete subchannel analysis for predicting thermal-hydraulic behavior of coolant in a BWR rod bundle channel, accurate estimation of fluid transfer between subchannels is necessary. In order to validate a prediction method, flow distributions data of gas and liquid phases are essential. But, such data reported so far are limited to those in a two-subchannel system alone. Then we have measured flow distributions of both phases and Taylor bubble velocity in a multi-subchannel system as called 2×3 rod bundle channel. It has been found that flow distributions of gas and liquid in bubble and annular flows under a hydraulically equilibrium flow condition are close to those of single-phase flow, but in slug-churn flow the distributions are different. In slug-churn flow, both superficial gas velocity and Taylor bubble velocity are higher in larger subchannel. These experimental data are presented and discussed in this paper.Copyright