Understanding fluid flows in the piping systems of industrial facilities is of crucial importance for their safety and operation. In accidental scenarios studied for the primary circuit of a pressurized water reactor (PWR), two-phase flows within pipes may occur, exhibiting a wide variety of regimes depending on the encountered conditions. The transitions between these different regimes (stratified, annular, slug, bubbly, etc.) under such conditions are the subject of extensive experimental and numerical research. In particular, system-scale thermohydraulic simulation codes, such as CATHARE, must accurately compute these regime transitions.
This thesis aims to improve the prediction at the system scale of two-phase flow regime transitions in horizontal or inclined pipes. The project is structured around three main objectives. The first objective seeks to better account for scaling and fluid transposition issues by investigating models that influence the stratified/intermittent and stratified/annular transitions, including interfacial friction. The second objective focuses on predicting the transition between bubbly and intermittent regimes by revisiting the modeling of bubble segregation and mixing, and by incorporating new experimental data. The third objective, directly related to the previous one, addresses the transient effects of regime transitions, particularly by exploring the use of interfacial area transport equations.
The software tools used will include the CATHARE code, while experimental data will be provided from CEA facilities and the literature.