Pressure drop in a horizontal, equal-sided, sharp-edged, combining tee junction with air–water flow

•New experimental data are reported on the two-phase pressure drop in a horizontal combining tee.•The independent parameters are identified and the influence of each parameter is quantified.•Comparison with existing models resulted in various degree of success in predicting the data.•A new empirical model was developed using a new approach for formulating the mechanical energy loss. Experiments were conducted on the two-phase pressure drop through a horizontal, equal-sided, sharp-edged, combining tee junction of diameter 37.8mm with air–water mixtures at a nominal absolute pressure of 150kPa. The new experimental data were used to assess the performance of existing models and to develop a new empirical model for the pressure-drop prediction. The experiments were conducted in a new facility with 41 pressure taps distributed over the three legs of the tee to provide accurate measurements of the pressure drop. The test matrix covered wide ranges of mixture qualities on the three sides of the junction and of distributions of liquid and gas flows between the two inlets. It is shown that previous modelling methods are not capable of consistent prediction of the data and a new empirical model is proposed based on the present data and using a new approach in formulating the irreversible component of the pressure drop. The new model produced excellent agreement with the data.