Dispersion of Gas Bubbles in a Two-Dimensional MHD Turbulence

The dispersion of small gas bubbles in a vertical upwards liquid metal two phase flow is investigated theoretically as well as experimentally. Local void fraction measurements are presented for a vertical sodium-argon flow with and without external magnetic field. The dispersion of an initially narrow void distribution shows this behaviour clearly: There is an overall focussing effect of the magnetic field on the void distribution, but the dispersion of gas bubbles is much more suppressed parallel to the field than perpendicular to it.
The bubble transport is modelled by a simple diffusion equation. The model takes into account that bubbles represent no passive tracer of the flow field but have an own dynamics due to their relative velocity to the liquid phase. The experimental results will be analyzed in terms of the corresponding diffusion coefficients.