Numerical studies of gas pull-through and liquid entrainment in gas–liquid flows through multi-branch manifolds

Abstract

Flows of air–water and saturated steam–water mixtures in a horizontal cylindrical vessel with a single or several cylindrical outlets (branches) were investigated computationally using the volume of fluid (VOF) method to separate the phases and the delayed detached eddy simulation (DDES) model to simulate turbulence. The time-dependent gas–liquid interface was resolved and the vertical distance between the interface elevation and the branch inlet was determined. The computed critical elevations at the onsets of gas pull-through (OGP) and liquid entrainment (OLE) in single-branch vessels were found to be in fair agreement with experimental values under comparable conditions. Simulations of gas–liquid flows in manifolds with three branches also predicted successfully OGP and OLE in the different branches. As an example of the applicability of the present method, we investigated a problem of interest to the CANDU nuclear reactor safety analysis, namely, the discharge of fluid through a small break at the top of a header model with 12 other branches (feeders), focusing on its dependence on the inlet flow rates.