Experimental investigations of two-phase flows in various liquid metal processes


Experimental investigations of two-phase flows in various liquid metal processes

Shevchenko, N.; Boden, S.; Vogt, T.; Timmel, K.; Röder, M.; Eckert, S.; Gerbeth, G.

Many technical applications in metallurgy and casting rely on liquid metal two-phase flows. Gas injection is routinely applied at various stages of melt preparation and refinement to promote chemical reactions and to stir the melt for reducing temperature and/or concentration gradients together with promoting an effective removal of impurities. In continuous steel casting, argon bubbles are injected to avoid solidification and to generate desired flow patterns directing impurities to the surface. In aluminium casting, on the other hand, uncontrolled entrapment of gas bubbles may cause serious casting defects.
Multi-phase flows with a compressible disperse phase, i.e. bubbles, are a particular challenge and substantially more difficult than corresponding single-phase flows. Different length and time scales coexist even in rather generic flow configurations such as a bubble plume and the stochastic nature of both the carrier-phase turbulence and the dispersed-phase distribution needs to be accounted for. The physical and numerical models still lack sophistication as they need reliable experiments for validation. Compared to the numerous experimental studies on the movement of bubbles in transparent liquids, especially in water, the number of publications dealing with gas bubbles rising in liquid metals is small. Measurements in liquid metals are substantially more difficult but are indispensable because of the distinct differences in material properties compared to water, in particular density and surface tension. Further specific problems concern the influence of surfactants at fluid-gas interfaces. All these conditions cause the gas bubbles to behave very differently in liquid metals compared to water, in particular with respect to bubble formation, dispersion, coalescence and breakup. Substantial work is still to be done in this respect.
We present experimental activities at HZDR for investigating liquid metal two-phase flows. Ultrasonic methods and X-ray radioscopy are used for detection and characterization of gas bubbles in the liquid metal flow. A series of measurements has been conducted for the configuration of a bubble plume rising in a liquid metal. Another study is concerned with the two-phase flow in a mockup for modeling the continuous casting process of steel. A specific experimental facility was designed and constructed at HZDR for visualizing two-phase flows in the mould and the submerged entry nozzle by means of X-ray radioscopy. This setup utilizes the low melting, eutectic alloy GaInSn as model liquid and operates under isothermal conditions. First results will be presented here accompanied by statistical analysis and a discussion of the advantages and limitations of the measuring techniques applied at these experiments.

Keywords: two-phase flows; bubbles; X-ray radioscopy; Ultrasonic methods

  • Poster
    The 3rd International Symposium on Cutting Edge of Computer Simulation of Solidification, Casting and Refining (CSSCR2013), 20.-23.05.2013, Helsinki/ Stockholm, Finland/ Sweden

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Publ.-Id: 18804