This article presents a review of the research into gas stirring in ladle metallurgy carried out over the past few decades. Herein, the physical modeling experiments are divided into four major areas: (1) mixing and homogenization in the ladle; (2) gas bubble formation, transformation, and interactions in the plume zone; (3) inclusion behavior at the steel-slag interface and in the molten steel; and (4) open eye formation. Several industrial trials have also been carried out to optimize gas stirring and open eye formation. Approaches for selecting criteria for scaling to guarantee flow similarity between industrial trials and physical modeling experiments are discussed. To describe the bubble behavior and two-phase plume structure, four main mathematical models have been used in different research fields: (1) the quasi-single-phase model, (2) the volume of fluid (VOF) model, (3) the Eulerian multiphase (E-E) model, and (4) the Eulerian-Lagrangian (E-L) model. In recent years, the E-E model has been used to predict gas stirring conditions in the ladle, and specific models in commercial packages, as well as research codes, have been developed gradually to describe the complex physical and chemical phenomena. Furthermore, the coupling of turbulence models with multiphase models is also discussed. For physical modeling, some general empirical rules have not been analyzed sufficiently. Based on a comparison with the available experimental results, it is found that the mathematical models focusing on the mass transfer phenomenon and inclusion behaviors at the steel-slag interface, vacuum degassing at the gas-liquid interface, dissolution rate of the solid alloy at the liquid-solid interface, and the combination of fluid dynamics and thermodynamics need to be improved further. To describe industrial conditions using mathematical methods and improve numerical modeling, the results of physical modeling experiments and industrial trials must offer satisfactory validations for the improvement of numerical modeling.

The bubbly flow and mixing conditions for gas stirring in a 50t ladle were investigated by using physical modelling and mathematical modelling. In the physical modelling, the effect of the porous plugs' configurations on the tracer homogenization was studied by using a saturated NaCl solution to predict the mixing time and a color dye to show the mixing pattern. In the mathematical modelling, the Euler-Lagrange model and species transport model were used to predict the flow pattern and tracer homogenization, respectively. The results show that, for a +/- 5% homogenization degree, the mixing time with dual plugs using a radial angle of 180 degrees is shortest. In addition, the mixing time using a radial angle of 135 degrees decreases the most with an increased flow rate. The flow pattern and mixing conditions predicted by mathematical modelling agree well with the result of the physical modelling. For a +/- 1% homogenization degree, the influence of the tracer's natural convection on its homogenization pattern cannot be neglected. This is especially true for a 'soft bubbling' case using a low gas flow rate. Overall, it is recommended that large radial angles in the range of 135 degrees 180 degrees are chosen for gas stirring in the present study when using dual porous plugs.

The gas injection in a ladle using a porous plug is simulated using both the Euler-Euler and Euler-Lagrange approaches. The effects of various forces, bubble sizes, and bubble injection frequencies on the flow pattern are modeled. For predicting axial velocity and turbulent kinetic energy, the Euler-Lagrange approach fits better than Euler-Euler approach with the measured data. In the Euler-Euler approach, differences in axial velocities and turbulent kinetic energies for various bubble sizes mainly appears in the plume zone. In the Euler-Lagrange approach, different bubble sizes with the same injection frequency have a small impact on the turbulence dissipation. Furthermore, the turbulent dispersion from the gas phase to the liquid phase has an important effect on the plume structure and spout eye formation. For both modeling, the smaller the bubble diameter is, the larger the axial velocity and turbulent kinetic dissipation are in the central zone. For the bubble coalescence and breakup, according to the comparison of two modeling approaches, the Euler-Lagrange approach is more accurate in predicting the flow pattern for gas injection with a porous plug in the ladle.

The bubble characteristic created during bottom injection in a ladle has been studied using physical modeling and mathematical modeling. The width of central plume, statistical number of bubbles, and the periodic behavior of bubble injection have been compared using a slot plug and three porous plugs with various porosities. Furthermore, the effect of the plug’s permeability on the plume structure and bubble size distribution has been predicted using the Eulerian Multiphase Model and Population Balance Model. The results show that, for the bottom blowing using a slot plug, an increased flow rate will not change the gas-liquid plume width significantly, but lead to an increased periodic behavior of bubble’s statistic amount. For the bottom blowing using porous plug, an increased flow rate results in a wider central plume, but no obvious change of the periodic characteristic of bubbles. The effect of porosity on the bubble behavior was also studied. As the porosity increases, the volume fraction of gas and the average size of bubbles at the central plume zone increases, and the width of two-phase plume decreases. Moreover, the results predicted by the mathematical modeling are consistent with those from the physical modeling. The difference between a slot plug and a porous plug in industrial applications has been analyzed theoretically. The results show that it is more beneficial to use the slot plug to create strong stirring and to reach beneficial desulfurization condition nearby the open eye, and to use the porous plug for the inclusion removal.

During secondary steelmaking, argon bubbles are often passed through molten steel to ensure a clean and homogeneous product. The behavior of the bubbles and the capacity of the bubbles to stir the melt and remove impurities depends on their size, shape, and velocity. These factors depend on the ambient pressure of the melt, the temperature and flow rate of the gas and the geometry of the gas nozzles. There have been many studies that investigate the behavior of bubbles when the melt is under atmospheric pressure, but few when the melt is held under vacuum. This makes it difficult to optimize the argon blowing process. The current study addresses this lack of knowledge by studying bubble behavior when the melt is under vacuum. Physical modeling was used to analyze the effects of the reduced pressure and nozzle diameter on the bubbles’ initial diameter and ascent behavior in a molten steel. Moreover, a multiphase fluid dynamics solver for compressible fluids called ‘compressibleInterFoam’ was validated and used. Increasing the flow rate leads to larger initial bubble diameters and more frequent bubble formation, and increasing the nozzle diameter leads to larger initial bubble diameters and less frequent bubble formation. Decreasing the subjected pressure causes the bubble diameter to increase substantially but bubbles to form less frequently. For flow rates in the range of 5.0(mL·min^-1)_STP to 2000(mL·min^-1)_STP, the bubble diameter ranges from 6.0mm to 20.0mm. The frequency of bubble generation initially increases with flow rate before reaching a constant value. During the ascent, a bubble will shed several small bubbles at the bottom to reach a constant shape. In the steel-argon system, under laminar flow conditions, the maximum bubble width under a pressure of 0.2bar is 65mm and is 58mm under a pressure of 2.0bar. As the surrounding pressure increases, the maximum size of the bubble under the steady condition will decrease. These findings can be used to determine the bubble behaviors and to optimize the conditions of argon blowing to produce steel that is sufficiently clean, while minimizing argon usage.

A coupled method of Fluid dynamics and Thermodynamics, named as Multi-zone Reaction Model, was established to simulate the flow pattern with bottom oxygen injection in a 145t electric arc furnace. The simulated maximum hot spot temperature and decarburization rate in the refining phase were compared against the data measured in the industrial operation. Moreover, the physical modeling was carried out to study the effect of nozzle size on the flow characteristics in the reaction zone. The results show, under high flow rates, the effect of nozzle size on the flow field in the reaction zone of the plume area can be neglected. The decarburization rate and hot spot temperature predicted by the modeling are consistent with the industrial measurements. The maximum hot spot temperature gradually decreases during the refining phase. The oxygen flow rate has a significant influence on the decarburization rate, hot spot temperature and average steel temperature. In terms of combined injection of O₂ and inert argon gas, for a certain O₂ flow rate, the decarburization rate increases due to the efficient mass transfer of carbon in the molten steel. Furthermore, for the replacement of argon using CO₂, it is demonstrated that as the ratio of CO₂ mass fraction increases from 0% to 40%, the maximum hot spot temperature decrease with the value of 570K, and the increment rate of average steel temperature, and the decarburization rate in the molten steel decrease with the ratio of 68%, and 81%, respectively. The endothermic reaction of CO₂ with the molten steel results in a temperature drop in the plume above the hot spot zone.