Experimental and theoretical investigation of liquid entrainment through small-scaled ADS-4 in AP1000

• We performed experimental and theoretical research of liquid entrainment.
• Visualization research was performed to make entrainment mechanism clear.
• Effect of entrance length is discussed.
• Effect of liquid flow is analyzed.
• Models of entrainment at T-junction were developed.

An experimental and theoretical research has been performed for liquid entrainment at T-junction consisting of hot leg and ADS-4 pipe in view of the insufficiency of existing studies. Based on visualization research, three kinds of entrainment phenomena including intermittent entrainment, stratified entrainment and annular entrainment are clearly observed, and the feature of each flow regime is summarized and recorded by high-speed camera. Also, the flow pattern map is plotted from the experimental data to indicate the transition conditions of different flow regimes. For the purpose of modeling and expanding previous research, the influence of entrance length on entrainment is discussed on the basis of two different test sections. The effect of liquid flow on onset entrainment and stable entrainment is analyzed, and experiment results show that the effect of liquid flow on entrainment through ADS-4 pipe can be neglected. Also, onset entrainment model and branch quality model are established and accord with experimental data well.