Turbulent dispersion of gas bubbles in quasi-two-dimensional MHD turbulence
The transport properties of the liquid metal two-phase flow are strongly modified due to the
influence of an external magnetic field.
Experimental investigations of the gas dispersion in a turbulent channel flow have been performed
at the sodium loop of the Forschungszentrum Rossendorf
applying a transverse magnetic field and the mercury facility located at the Institute of Physics
Riga/Salaspils (Latvia) producing a magnetic field along the mean flow direction by means of a
solenoid.
Small Argon bubbles have been injected into the liquid metal flow by a rectangular test section.
A single orifice positioned in the centre of the channel cross section just at the entrance of the
flow into the magnetic field has been used to inject the gas. The local void fraction has been
measured in a distance of 300 mm (sodium flow) and 500 mm (mercury flow) downstream from the gas
injector by means of resistive probes.
Transverse magnetic field
The figures show isoplots of the cross sectional void fraction distributions obtained for growing
values of the magnetic field strength at Reynolds numbers of 9300 and 18600, respectively.
Re = 9300 Re = 18600
In the ordinary hydrodynamic case (Ha = 0) the void fraction shows a distinct tendency to a uniform
distribution over the cross sectional area. The application of a magnetic field causes a concentration
of the gas bubbles in the channel centre. This concentration process advances further with increasing
field strength indicating a significant damping of the turbulent motion.
The fact that the damping of the turbulent bubble dispersion parallel to the field lines is much
more pronounced than in the perpendicular direction reveals the anisotopic effect of the
electromagnetic force. The mass transfer properties are determined by the
quasi-two-dimensional turbulent structure of the flow.
For sufficiently large values of the magnetic interaction parameter (N ~ 800) a relaminarization of
the flow is observed. The gas phase is again isotropic and confined to a narrow channel region above
the position of gas injection.
Longitudinal magnetic field
In the longitudinal magnetic field configuration no breaking of the symmetry occurs by the applied
field. We also find a significant concentration of the gas phase with growing field strength due to
the electromagnetic damping of the turbulent fluctuations. In contrast to the transverse case the void
fraction distributions remain isotropic.
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