A model study was carried out to elucidate bubble and liquid flow characteristics in the reactor of metals refining processes stirred by gas injection. Wood's metal with a melting temperature of 70 ЊC was used as the model of molten metal. Helium gas was injected into the bath through a centered single-hole bottom nozzle to form a vertical bubbling jet along the centerline of the bath. The bubble characteristics specified by gas holdup, bubble frequency, and so on were measured using a twoneedle electroresistivity probe, and the liquid flow characteristics, such as the axial and radial mean velocity components, were measured with a magnet probe. In the axial region far from the nozzle exit, where the disintegration of rising bubbles takes place and the radial distribution of gas holdup follows a Gaussian distribution, the axial mean velocity and turbulence components of liquid flow in the vertical direction are predicted approximately by empirical correlations derived originally for a water-air system, although the physical properties of the two systems are significantly different from each other. Under these same conditions, those turbulent parameters in high-temperature metals refining processes should thus be accurately predicted by the same empirical correlations.

No abstract

In the steelmaking and refining processes, bottom gas blowing is a widely-used method. In these systems, the gas is blown into liquid from the bottom of the vessel at a temperature lower than liquid temperature. The mechanism of heat transfer between bubbles and liquid and the effect of heat transfer on the formation of bubbles and the rising characteristics of the bubbles were investigated, using air and helium in a water model. The injection temperature of the gases was about -11 O'C. Heat transfer between bubbles and liquid was almost fully completed near the nozzle. Bubble expansion due to the heat transfer resulted in the increase of gas holdup in the radial direction. In the region far from the nozzle, the bubble characteristics accompanyingcold gas injection were the same as those initiated by an ambient temperature gas injection at the samemass flow rate.

The coherent structure of turbulence in a vertical He-Wood's metal bubbling jet formed in a cylindrical vessel was investigated using the four-quadrant classification method. Turbulent motions of molten Wood's metal flow were classified into four distinct categories: ejection (higher-momentum fluid motion, directed outward), sweep (lower-momentum fluid motion, directed inward), outward interaction (lower-momentum fluid motion, directed outward), and inward interaction (higher-momentum fluid motion, directed inward). The relative occurrence in frequency of each turbulent motion and the contributions of each turbulent motion to the axial and radial turbulence kinetic energies and Reynolds shear stress were determined. These quantities were different from their respective values in an air-water vertical bubbling jet. Such differences were found to be closely associated with the fact that the shape and size of bubbles differs significantly between the two bubbling jets. Consequently, the coherent structure of turbulence in a bubbling jet is strongly dependent on the behavior of the wake behind the bubbles.

Faculty of Engineering,In refining processes for steel and some other metals, gas is blown into molten metal from the top, the bottom or simultaneously from the top and bottom of the vessel to promote mixing and chemical reactions.Since the gas is usually injected at a temperature lower than the molten metal temperature, knowledge about the heat transfer between gas and molten metal is required to predict preciseiy the mixing effect. Present authors previously carried out cold model experiments for bottom injection to investigate the mechanism of convective heat transfer betweenbubbles and liquid, using cooled gas andwater and proposed an empirical correlation for the Nusselt number. In this paper, the mechanism of convective heat transfer betweenbubbles and molten metal was investigated using molten Wood's metal. Thefunctional relationship between the Nusselt numberand the Peclet number was the same as that for water models although the Prandtl numbers of water and Wood'smetal were much different with each other.