A Study of Kinematic Characteristics of the Developing Region of Vertical Upward Two-Phase Flow With Co-Flowing Streams

Lack of knowledge about bubbly flow development in vertical channels is identified. An experimental setup is built for two-dimensional, two-component particle image velocimetry (PIV) and bubble shadowgraphy measurements of gas fraction, liquid-phase velocity, and gas-phase velocity profiles. Axial development of the gas phase injected coaxially into the upward water flow from a point source is explored. The developing region of two-phase flow is defined based on the axial position where the bubble core spreads over the cross section. This definition is found to be consistent with a prior work and is shown to be consistent with the behavior of the main kinematic parameters. The axial distributions of the bubble core width, gas fraction, peak liquid-phase velocity, and peak gas-phase velocity in the developing region demonstrate initially oscillatory behavior followed by an asymptotic one. The axial distribution of the liquid-phase velocity has a prominent, elongated peak closer to the gas injection level. Its position is independent of the flow conditions. The rest of the flow parameters also have prominent extremums, positions of which are independent of the flow conditions. The span of the developing region does not show significant dependence on the flow conditions. It is suggested that the pressure head, which was not changing during the experiments, could have the main influence on the mentioned extremums. Two methods of slip velocity calculations are suggested; their advantages and disadvantages are explored. Only one method is shown to capture all the aspects of the kinematics of the developing region. An attempt is made to consider gas injection from the perspective of the jet theory. It is shown that the existent methods fail to predict the main kinematic parameters and that the influence of both gas phase and liquid phase inlet parameters must be taken into account, just as is done in the developed region.