The principle of dynamic separation with T-junction having a horizontal run and a vertical branch is presented. The analysis of gas-liquid flow systems involving T-junctions is very important for applications to phase separation in gas-liquid transport pipelines, but the complexity of the multi dimensional phenomenon of dividing two-phase flow in T-junction needs special modelling. Based on the fundamental mass, momentum and energy balance equations, the mathematical model enables the prediction of phase distribution and pressure drop through the junction taking into account of the two-phase flow pattern and the flow restriction in the tee-branch. The very good agreement of the numerical simulation results with experimental data validates the mathematical modelling and leads to the conclusion that the developed computational code is a very useful tool for the flow characterization of a T-junction separator. (c) 2006 Elsevier B.V. All rights reserved.