Investigation of liquid metal two phase flow characteristics by means of local resistivity probes and X-ray screening technique


Investigation of liquid metal two phase flow characteristics by means of local resistivity probes and X-ray screening technique

Eckert, S.; Gerbeth, G.; Guttek, B.; Stechemesser, H.; Lielausis, O.

In many technologies such as the refinement of metallic melts the injection of gas bubbles is used to drive some liquid motion, enhance transport processes or to control the rate of chemical reactions. The resulting flow structure strongly depends on two phase flow parameters such as bubble size, bubble distribution or the local void fraction. Magnetic fields can be used to control the characteristics of a liquid metal bubbly flow.
We present experimental investigations of the bubble formation in heavy liquid metals as well as the influence of external magnetic fields on the turbulent dispersion of gas bubbles and the slip ratio in liquid metal bubbly flows, respectively.

a) Bubble formation
If gas bubbles are injected into a liquid metal characterised by a large surface tension one should be care to get a good wetting between the fluid and the surface of the gas injector. Otherwise, the gas would try to spread out along this interface to form gas layers. A control of the bubble size and formation rate becomes difficult. The comparison between experiment and theoretical models describing bubble formation processes requires an ideal wetted gas injector.
The bubble formation in mercury and the eutectic alloy InGaSn has been studied by means of several methods of gas injection, for instance through single orifices or injectors made from sintered metals with a mean porosity of a few microns. X-ray measurements have been used to directly observe the resulting gas bubbles rising in the liquid metal. In the case of an single orifce the influence of electromagnetic forces on the bubble frequency has been demonstrated.

b) Turbulent bubble dispersion, slip ratio
The transport properties of small argon bubbles have been studied in turbulent upwards channel flows of sodium and mercury. The bubbles were injected by a single orifice located in the centre of the channel cross section. After a distinct distance the local void fraction and the bubble velocity has been measured by means of electrical resistivity probes. The flow has been exposed to external magnetic fields directed transverse or longitudinal to the mean flow direction.
We will present and discuss measuring results showing the effect of the magnetic field strength and direction on the horizontal gas distribution and the ratio between gas and liquid velocity.

Keywords: two-phase flow; bubbly regime; liquid metals; void fraction measurements; electric resistivity probe; X-ray imaging

  • Lecture (Conference)
    International Workshop on Measuring Techniques for Liquid Metal Flows (MTLM), Dresden, October 11-13, 1999

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Publ.-Id: 2552