Investigations into the pressure drop and mass flow distribution of two-phase flow in rectangular T-junctions

The phase separation and pressure drop of a gas-liquid mixture flowing throuth a T-junction of equal pipe diameters (d = 50 mm) was investigated. The inlet pipe was orientated horizontally, the branch directions were horizontal and vertically upward or downward. The experiments were performed with air-water flow (0.4 < p < 1 MPa) and steam-water flow at pressures up to 10 MPa. The inlet mass flux and quality were varied in a wide range and included test parameters in the slug, annular and dispersed flow regimes. For constant inlet parameters the mass flux ratio G3/G1 between the inlet (1) and branch (3) was varied between 0 and 1. At the same time, detailed differential pressure drop measurements along the inlet, run and branch were carried out to determine the pressure drop in the T-junction. A comparison was made of different models describing the pressure difference Δpsub(1-3) between the inlet and branch and the pressure difference Δpsub(1-2) between the inlet and run on the one hand, and the experimental results, on the other hand. For the branch with upward orientation the T-junction acts as a good separator since nearly all of the gas flows through the branch. For the horizontal branch, the gas preferentially flows into the branch at high values of G3/G1. The quality ratio x3/x1 has a maximum at about G3/G1. For the downward branch the separation is strongly affected by the phase distribution in the inlet pipe; in general, gas flows predominantly into the branch at very high values of G3/G1, whereas this applies for liquid at low values. Empirical correlations have been derived to describe the phase separation for all three branch orientations. The best results of modelling Δpsub(1-2) and Δpsub(1-3) are shown by the model of Reimann-Seeger for all variations of the parameters. (orig.)