Onset condition of gas and liquid entrainment at an inclined branch pipe on a horizontal header

An experimental and analytical investigation of onset condition of gas pull through and liquid entrainment in a single inclined branch to the arbitrary direction was performed in the present study. Since previous studies have been made only for specific angles of 0° and ±90°, it is hard to apply them to the case of branch off to the arbitrary direction. In the present study, series of experimental works was made with a horizontal header of 184 mm inner diameter with a single branch pipe which can be attached in nine different orientations of 0°, ±30°, ±45°, ±60°, ±90° angles and with two different diameters of 16.0 and 24.8 mm, respectively. Also, a simple mechanistic model is developed here based on the force balance at the top of the vortex on the surface of the stratified water. The onset condition due to the vortex breakup for the branch oriented with angle of θ   was determined as Frg(ρg/Δρ)0.5=C1((hOLE/d)+1/2(D/d)(1−sin θ))C2 and the onset condition due to the ascending film was Frg(ρg/Δρ)0.5=C1(hOLE/d)C2 which is similar to that of side branch. It was found that the present model predicted experimental data well in terms of the direction and diameter of the branch pipe. The present model and data may be useful in determination of the quality of flow through the inclined branch which is one of key parameter in the safety study of hypothetic small break loss of coolant accident in the nuclear power plant.