Investigation of two-phase flow mixing between two subchannels. 1. Fluctuating pressure model and its experimental verification

Cross-flow between subchannels in a BWR fuel assembly has usually been estimated by three types of mixing models, namely, pressure difference, turbulent mixing and void drift, which are expressed by time-averaged flow parameters. It is important to notice that two-phase flow has an inherent time-varying nature even in the steady-state flow condition. In this paper, we attempted to express the above cross-flow phenomenon by a simple mixing model to which time-varying pressure difference was applied. To examine the validity of the model, a test using an air-water loop with a short mixing zone was conducted and compared with the prediction. Results showed that the model well estimated the experimental cross-flow data without conventional turbulent mixing and void drift model. (author)