Electromagnetic inspection of a two-phase flow of GaInSn and argon

In the continuous casting process, an adequate control of liquid steel flow through the submerged entry nozzle is essential for maintaining steel cleanliness and ensuring good surface quality in downstream processing. Monitoring the flow in the nozzle presents a challenge for the instrumentation system because of the high temperature environment and the limited access to the nozzle in between the tundish and the mould.In this paper, the distribution of a two-phase liquid metal/gas flow is studied by using a liquid metal laboratory model of an industrial steel caster and an inductive sensor array. The experiments were performed with the liquid eutectic alloy GaInSn as an analogue for liquid steel, which has similar conductive properties as molten steel and allows the measurements at room temperature. A scaled (approx. 1:10) experimental rig consisting of a tundish, a stopper rod, a nozzle and a mould was used. Argon gas was injected through the centre of the stopper rod and the behavior of two-phase GaInSn/argon flows was studied.The electromagnetic system used in the experiments to monitor the behavior of two-phase GaInSn/argon flows consists of an array of 8 equally spaced inductive coils arranged around the object, a data acquisition system and a host computer. The present system operates at 10 kHz and has a capture rate of 10 frames per second.The results show clearly that the injection of the argon gas is distinguishable from the single phase flow by observing the appearance of oscillation patterns. These oscillations become more dominant with the increase of the argon flow. In some cases two main oscillation patterns were present in the raw signals. In general, the signals and the reconstructed void fractions in the nozzles are highly correlated with the observed oscillations of the level height in the mould and the pressure in the nozzle.

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► An electromagnetic technique to image the two-phase flow of liquid metal/argon
► Flow in the nozzle of a laboratory model of an industrial steel caster was studied
► Different flow regimes can be identified under various conditions
► Oscillatory pattern can be seen, which is more dominant with increase in Ar flow