Kinnor Chattopadhyay

Physical Modeling of Slag ‘Eye’ in an Inert Gas-Shrouded Tundish Using Dimensional Analysis

The formation of an exposed eye in the gas-stirred metallurgical vessels such as ladle or tundish is a common observation. Although gas stirring results in proper homogenization of melt composition and temperature, the resulting exposed eye leads to higher heat losses, re-oxidation of liquid steel, and formation of inclusions. Most of the previous research related to slag eye were carried out explicitly for ladles. In the present work, a large number of experiments were performed to measure the slag eye area in full scale and one-third scale water models of an inert gas-shrouded tundish under various operating conditions. Based on the polynomial regression of experimental data, and the method of dimensional analysis, correlations for diameter of gas bubbles and plume velocity were developed. Subsequently, these results were used to obtain correlations for the slag eye area, and critical gas flow rate in an inert gas-shrouded tundish in terms of the operational parameters viz., gas flow rate, thickness of the slag and melt baths, along with the physical properties of the liquids viz., kinematic viscosity and density. It was observed that the dimensionless slag eye area can be expressed in terms of dimensionless numbers such as the density ratio, Froude number, and Reynolds number.

Tundish Open Eye Formation in Inert Gas-Shrouded Tundishes: A Macroscopic Model from First Principles

Open eye formation in tundishes can result in reoxidation of liquid steel leading to the formation of harmful inclusions. Moreover, it is also a site for heat loss, gas absorption, and slag emulsification. All these factors make it necessary to understand the fundamentals of open eye formation, which in turn will allow us to prevent or control its harmful effects. In the present study, the bubble plume regions in a ladle and tundish were compared, and it was observed that there are significant differences between the two. Moreover, a simplistic model for predicting the open eye area in tundishes for ‘thin slag’ practices was derived using the principles of conservation of mass and momentum. The proposed model was able to predict open eye areas in tundish reasonably well and was compared with other models, and experimental results.

Effect of Interphase Forces on Gas–Liquid Multiphase Flow in RH Degasser

A mathematical model was developed to study the gas–liquid flow behavior in the Ruhrstahl–Heraeus (RH) degasser by using the Euler–Euler approach, and the effects of different combinations of interphase forces on the circulation flow rate as well as the distribution of the gas volume fraction were investigated. The results showed that the model predictions correspond with the measured values. As a key factor in avoiding the gas-adhering wall effect, the virtual mass force has a tremendous impact on the circulation flow rate and distribution of the gas volume fraction. The contribution of the turbulent dispersion force on the circulation flow rate is insignificant, but it shows a significant effect on the distribution of the gas volume fraction. Furthermore, the effect of the wall lubrication force and the lift force on gas–liquid flow is negligible when compared with the virtual mass and turbulent dispersion forces.

Investigation of Eccentric Open Eye Formation in a Slab Caster Tundish

Inert gas shrouding in tundish can result in the formation of a tundish open eye (TOE) due to the presence of reversed flows on the upper surface of the tundish. Prolonged presence of open eyes promotes reoxidation of liquid steel and creates harmful inclusions, which can ultimately result in clogging of SENs. In spite of its importance, not much work has been performed on TOEs. In our series of recent works (Chattopadhyay in Modelling of Transport Phenomena for Improved Steel Quality in a Delta-Shaped Four Strand Tundish, 2011; Chattopadhyay et al. in ISIJ Int 51: 573–580, 2011; Chatterjee and Chattopadhyay in ISIJ Int 55: 1416–1424, 2015; Metall Mater Trans B 41: 508–521, 2016; Metall Mater Trans B 47: 3099–3114, 2016; Chatterjee et al. in ISIJ Int 56: 1889–1892, 2016), although substantial efforts have been made to understand the basics of TOE formation process, a lot still remains to be deciphered. The current work deals with investigating a strange phenomenon observed during tundish operations: eccentric open eye formation. It is essential to gain proper insights of this matter in order to improve the operations, enhance liquid metal cleanliness, and generate more revenues. A mathematical model was developed using ANSYS-FLUENT 16.2. The standard k-ε turbulence model and the discrete phase method, coupled with the discrete random walk model was employed. Three different causes for eccentric open eye formation viz., unbalanced throughput, biased argon injection, and misalignment of ladle shroud have been analyzed. The predicted results correspond to both water model experiments and real plant observations.

Dimensionless Analysis and Mathematical Modeling of Electromagnetic Levitation (EML) of Metals

Electromagnetic levitation (EML), a contactless metal melting method, can be used to produce ultra-pure metals and alloys. In the EML process, the levitation force exerted on the droplet is of paramount importance and is affected by many parameters. In this paper, the relationship between levitation force and parameters affecting the levitation process were investigated by dimensionless analysis. The general formula developed by dimensionless analysis was tested and evaluated by numerical modeling. This technique can be employed to design levitation systems for a variety of materials.

Applications of Electromagnetic Levitation and Development of Mathematical Models: A Review of the Last 15 Years (2000 to 2015)

Electromagnetic levitation (EML) is a contact-less, high-temperature technique which has had extensive application with respect to the investigation of both thermophysical and thermochemical properties of liquid alloy systems. The varying magnetic field generates an induced current inside the metal droplet, and interactions are created which produce both the Lorentz force that provides support against gravity and the Joule heating effect that melts the levitated specimen. Since metal droplets are opaque, transport phenomena inside the droplet cannot be visualized. To address this aspect, several numerical modeling techniques have been developed. The present work reviews the applications of EML techniques as well as the contributions that have been made by the use of mathematical modeling to improve understanding of the inherent processes which are characteristic features of the levitation system.

Modeling of Liquid Steel/Slag/Argon Gas Multiphase Flow During Tundish Open Eye Formation in a Two-Strand Tundish

Multiphase flows are frequently encountered in metallurgical operations. One of the most effective ways to understand these processes is by flow modeling. The process of tundish open eye (TOE) formation involves three-phase interaction between liquid steel, slag, and argon gas. The two-phase interaction involving argon gas bubbles and liquid steel can be modeled relatively easily using the discrete phase modeling technique. However, the effect of an upper slag layer cannot be captured using this approach. The presence of an upper buoyant phase can have a major effect on the behavior of TOEs. Hence, a multiphase model, including three phases, viz. liquid steel, slag, and argon gas, in a two-strand slab caster tundish, was developed to study the formation and evolution of TOEs. The volume of fluid model was used to track the interphase between liquid steel and slag phases, while the discrete phase model was used to trace the movement of the argon gas bubbles in liquid steel. The variation in the TOE areas with different amounts of aspirated argon gas was examined in the presence of an overlying slag phase. The mathematical model predictions were compared against steel plant measurements.

Numerical and Experimental Modeling of the Recirculating Melt Flow Inside an Induction Crucible Furnace

In the paper, a new water model of the turbulent recirculating flow in an induction furnace is introduced. The water model was based on the principle of the stirred vessel used in process engineering. The flow field in the water model was measured by means of particle image velocimetry in order to verify the model’s performance. Here, it is indicated that the flow consists of two toroidal vortices similar to the flow in the induction crucible furnace. Furthermore, the turbulent flow in the water model is investigated numerically by adopting eddy-resolving turbulence modeling. The two toroidal vortices occur in the simulations as well. The numerical approaches provide identical time-averaged flow patterns. Moreover, a good qualitative agreement is observed on comparing the experimental and numerical results. In addition, a numerical simulation of the melt flow in a real induction crucible furnace was performed. The turbulent kinetic energy spectrum of the flow in the water model was compared to that of the melt flow in the induction crucible furnace to show the similarity in the nature of turbulence.

Alternative Applications of SPL: Testing Ideas Through Experiments and Mathematical Modeling

Spent pot lining (SPL) is a well-known waste product from the aluminium electrolytic cell. The SPL generation rate is approximately 1–1.5 million tons per annum, and this is a significant environmental burden to the aluminium industry. Previous reports indicated that more than half of the total amount of SPL generated is stored in lined/ unlined sites/buildings, waiting for further treatment. At the University of Toronto, the Process Metallurgy and Modelling Group (PM2G) is working extensively to understand the chemistry of SPL and find alternate applications of SPL. Some of the potential applications of SPL conceptualized at the University of Toronto are: (a) as a flux in the non ferrous industry, (b) as an alternate to coal in ironmaking blast furnaces. Experimental and mathematical modeling techniques have been used to test these ideas, and the results are discussed in detail.

Mathematical Modeling of Molten Salt Electrolytic Cells for Sodium and Lithium Production

Sodium (Na) and Lithium (Li) are produced using molten salt electrolysis. The electrochemistry of the electrolyte is well-researched; however, there are benefits to understanding the melt flow and implications on it for cell design modifications. The basic configuration of alkali metal cells is the Downs cell. This consists of a central anode surrounded by a cathode, and this geometry was the basis for this mathematical modeling study. The behavior of gas bubbles in molten electrolyte was studied in both Na and Li cells through the use of computational fluid dynamics (CFD) techniques. The distance between the anode and the cathode was varied in the CFD model to ascertain whether strong circulatory flows would change significantly in the cell. The standard k-e turbulence model was used to mimic turbulent flow, and a two-way coupled Discrete Phase Model (DPM) was adopted to simulate flotation behavior of chlorine bubbles and liquid metal droplets. The liquid metal distribution on the free surface was predicted using the Volume of Fluid (VOF) multi-phase model.