G. A. Irons

The impact of bubble dynamics on the flow in plumes of ladle water models

Bubbly plumes are widely encountered in metallurgical processes when gas is injected into liquid metals for refining purposes. Based on the experimental findings from a water model ladle, this phenomenon was simulated with a mathematical model, paying special attention to the dynamics of the bubbles in the plume. In the model, the liquid flow field is first calculated in an Eulerian frame with an estimated distribution of the void fraction. The trajectories of bubbles are then computed in a Lagrangian manner using the estimated flow field, experimentally measured information on bubble drag coefficients, lateral migration due to lateral lift forces, and variation in bubble size due to breakup. Turbulence in the two-phase zone is modeled with a modifiedk-ε model with extra source terms to account for the second phase. The computed void fraction and turbulent liquid flow field distributions are in good agreement with experimental measurements.

Settling and clustering of silicon carbide particles in aluminum metal matrix composites

The settling of 14-μm silicon carbide particles in an aluminum-silicon alloy was monitored with an electrical resistance probe to measure thein situ particle voluem fraction. The rate of settling was much greater than expected from hindered settling of single 14-μm particles. From the observed settling rate, an equivalent hydrodynamic diameter and density of clusters of particles were deduced, 38 μm and 2740 kg/m3, respectively. Other work was analyzed with the same procedure; it was concluded that if the stirring prior to settling were intense, then the clusters would be smaller than with weaker stirring. The implications for foundry practice and mechanical properties are discussed.

A Water Model Study of Impinging Gas Jets on Liquid Surfaces

Water modeling experiments were designed to observe the deformation of a liquid surface by impinging the gas jet. Video images were taken and processed in a systematic way. The important surface cavity parameters, such as depth, width, and their frequency of oscillation, were obtained. The relation between surface depression depth and the supplied gas momentum were consistent with previous findings and were extended to higher flow rates. The surface instability and the onset of splashing were observed and interpreted with the Blowing number. The wave behaviors were described qualitatively with a combination of photographic evidence and power spectral density analysis to extract the characteristic wave numbers for each gas flow rate. The analysis of the time series of the surface variables showed a connection to the attenuation of turbulence gas pressure fluctuation and the surface deformation by the gas impingement. Bath velocities were measured with a particle image velocimetry (PIV) technique. To quantify the transfer of kinetic energy from the gas to the liquid, an energy transfer index was defined and calculated with the PIV data. The index was insensitive to gas flow rate but increased with cavity width. The momentum transfer across the interface was also analyzed, and a similar cavity width dependence was found. A correlation between the cavity shape and momentum transfer was proposed.

The kinetics of molten iron desulfurization using magnesium vapor

Magnesium vapor was injected into 60 kg heats of carbon-saturated iron at 1523 K. The magnesium dissolution and desulfurization rates as well as magnesium bubble size were monitored over sulfur contents ranging from 0.0002 to 0.2 pct S. The magnesium dissolution mass transfer coefficient was found to be 0.046 ± 0.034 mm · s−1 (for 30 mm diam bubbles). Further analysis indicated that most of the desulfurization took place at magnesium sulfide inclusions present in the bath; there was good agreement between the experimental precipitation rate constant and that predicted for diffusion to the number of inclusions observed by chemical analysis and inclusion counts. The seed magnesium sulfide inclusions were probably stripped from the ascending magnesium bubbles. These particles were quickly eliminated from the melt by bubble and induction stirring, resulting in a steady-state number of inclusions. This allowed a pseudosteady-state model to be developed.

A multi-phase model for plumes in powder injection refining processes

A one-dimensional steady-state model for momentum transfer in ascending gas-liquid-powder plumes has been developed for conditions relevant to powder injection refining processes. Inter-phase transport of momentum permits the calculation of the volume fraction and velocity of the gas, liquid, and solid phases as they rise in the melt. The effects of plume geometry, initial conditions, density of the phases, head of liquid, bubble size, and powder loading and properties are assessed. Liquid velocities in gas-only injection into water compare favorably with available experimental data. Significantly lower liquid velocities are predicted in liquid metals. At solids loadings used in commercial powder injection stations, the powder is expected to have only a small effect on liquid velocity. For wire injection conditions with little gas release, liquid velocities are considerably smaller.

Solidification of particle-reinforced metal-matrix composites

The solidification behavior of ceramic particle-reinforced metal-matrix composites (MMCs) is different from that of the bare matrix, not only because of the presence of the ceramic particles, but also due to their redistribution in the melt that results in nonhomogeneous thermophysical properties. The MMCs comprised of 10-to 15-μm SiC particles of varying volume fractions, dispersed uniformly in a modified aluminum A356 alloy by the melt stirring technique, were solidified unidirectionally in a thermocouple-instrumented cylindrical steel mold. The cooling rates were continually monitored by measuring temperatures at different depths in the melt, and the solidified MMCs were sectioned into disks and chemically analyzed for SiC volume fraction. The results point out that the cooling rate increased with increasing volume fraction of SiC particles. A small increase in the bulk SiC volume fraction of the cast MMC was observed due to particle settling during solidification. A one-dimensional enthalpy model of MMC solidification was formulated, wherein particle settling occurring in the solidifying matrix was coupled to the enthalpy equation by means of the Richardson-Zaki hindered settling correlation. A comparative study of simulations with experiments suggested that the thermal response of SiC particles used in this study was similar to that of single crystals, and their presence increased the effective thermal conductivity of the composite.

Developments in modelling of gas injection and slag foaming

Abstract Gas injection into metallurgical ladles has been an active area of CFD modelling for many years. Recent work with both Eulerian and Lagrangian frameworks is presented for bottom stirring in ladle and steelmaking electric furnace configurations. Comparison with water and liquid metal results shows that the Lagrangian models provide a better representation of the systems. Slag foaming is an important phenomenon in smelting–reduction processes and electric furnace steelmaking. The void fraction in the foam is generally greater than 0.9, a regime that has received considerably less attention than bottom stirring where the local void fraction is less than 0.1. Again, it was found, by comparison with experimental data, that Lagrangian models were generally preferable over Eulerian models.

A multiphase fluid mechanics approach to gas holdup in bath smelting processes

In slag-based, smelting-reduction processes, the overflow of slag from the vessel is considered a major limitation to productivity; this phenomenon is commonly called slag foaming. While much has been learned from laboratory-scale studies of foaming, the superficial gas velocities are well below those encountered in production (centimeters per second compared to meters per second). A multiphase fluid dynamic model was developed to determine the relationship between gas velocity and void fraction (holdup) at industrial production rates. In the model, the drag between the gas and slag is balanced against the weight of the slag. Within the framework of the model, the only unknown quantity is a drag factor which can be extracted from experimental data. Values of this factor from water models, smelting-reduction converters, and other slag systems fall in a narrow range. The model can be used to estimate slag height in smelting-reduction vessels. The behavior of slags at high rates of gas injection is markedly different from foaming observed at low flow rates.

Progress in Slag Foaming in Metallurgical Processes

Professor Fruehan has been a pioneer in the fundamental understanding of slag foaming in ironmaking and steelmaking processes. Although considerable progress has been made in our understanding of the phenomena, there are still unanswered questions regarding the mechanisms in industrial processes and how to control them. At McMaster University, we have been working on conditions that are relevant to foaming in electric arc furnaces (EAFs) where these phenomena are central to modern EAF practices. This work will be reviewed and put in the context of what is known from a fundamental standpoint.

Ladle Eye Area Measurement using Multivariate Image Analysis

Abstract Despite the importance of ladle metallurgy to the overall steel making process, very little has been achieved in the way of advanced ladle control. Limited sensors are available to monitor progress during refining and current control methods involve manual procedures. This paper details a vision-based sensor for analyzing ladle eye dynamics in real time using a multivariate image analysis (MIA) technique based on principal component analysis (PCA). Predictive capabilities of the developed model are demonstrated using previously published cold model data over a wide range of operating variables. Further, preliminary work has confirmed the ability of the sensor for potential use in an industrial setting.