Liquid and gas velocity measurements using LDV in air–water duct flow Original Research Article

Simultaneous measurements of liquid and gas velocity have been made in an air–water two-phase flow in a rectangular vertical duct. A forward/backward scattering Laser Doppler Velocimeter (LDV) with amplitude discrimination was used to measure each of the two phasic velocities. High speed photography and hot-film anemometry were used to confirm the gas and liquid velocities respectively. Transverse velocity profiles were acquired in both bubble and slug regimes to demonstrate the application of the LDV technique over a range of flow conditions and void fractions. Experiments were performed with two bubble sizes and with slugs. With the injection of bubbles, a flattened two-phase flow mean velocity profile was observed. Results indicate that for a given gas flow the relative velocity of the bubbles increases with increasing flowing void fraction for large bubbles and the opposite trend is observed for smaller bubbles. These results are consistent with the Zuber–Findlay equation.