Experiments on vertical turbulent flow with millimetric bubbles, under three gravity conditions, upward, downward and microgravity flows (lg, -lg and 0g), have been performed to understand the influence of gravity upon the flow structure and the phase distribution. The mean and fluctuating phase velocities, shear stress, turbulence production, gas fraction and bubble size have been measured or determined. The results for 0g flow obtained during parabolic flights are taken as reference for buoyant lg and - lg flows. Three buoyancy numbers are introduced to understand and quantify the effects of gravity with respect to friction. We show that the kinematic structure of the liquid is similar to single-phase flow for 0g flow whereas it deviates in lg and -lg buoyant flows. The present results confirm the existence of a two-layer structure for buoyant flows with a nearly homogeneous core and a wall layer similar to the single-phase inertial layer whose thickness seems to result from a friction-gravity balance. The distributions of phase velocity, shear stress and turbulence are discussed in the light of various existing physical models. This leads to a dimensionless correlation that quantifies the wall shear stress increase due to buoyancy. The turbulent dispersion, the lift and the nonlinear effects of added mass are taken into account in a simplified model for the phase distribution. Its analytical solution gives a qualitative description of the gas fraction distribution in the wall layer.


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    Title :

    Turbulent bubbly flow In pipe under gravity and microgravity conditions


    Additional title:

    Turbulente Blasenströmung im Rohr unter Gravitations- und Mikrogravitationsbedingungen


    Contributors:

    Published in:

    Publication date :

    2012


    Size :

    47 Seiten, 18 Bilder, 4 Tabellen, 73 Quellen




    Type of media :

    Article (Journal)


    Type of material :

    Print


    Language :

    English