Measurements on wave propagation and bubble and slug velocities in cocurrent upward two-phase flow

Experiments on two-phase flow characteristics have been performed in vertical upward air-water flow through a transparent pipe system 17 m in height under atmospheric pressure. This system has been designed such that, in the first 7 m, both bubbly flow and slug flow can exist, depending on the air-and water-flow rates at the inlet, but that, owing to a decrease in pipe diameter, the flow will shift to slug flow quite easily in the upper 10 m. Experimental techniques used comprise pressure measurements with pressure transducers mounted flush to the pipe wall, light attenuation measurements with the use of two parallel laser beams 1 cm apart, and high-speed photography at 200 frames/s. With this setup, we measured both semi-steady flow parameters, such as slug frequencies and Taylor bubble rise velocities, and wave-propagation phenomena, such as the velocity of sound and of voidage waves in the two-phase medium. The results of these experiments have been compared with correlations from the literature and with simulations using the two-phase flow code SOPHY-2 (software package for hyperbolic equations) developed in housé.