Pierre Chapelle

Toward a Full Simulation of the Basic Oxygen Furnace: Deformation of the Bath Free Surface and Coupled Transfer Processes Associated with the Post-Combustion in the Gas Region

The present article treats different phenomena taking place in a steelmaking converter through the development of two separate models. The first model describes the cavity produced at the free surface of the metal bath by the high-speed impinging oxygen jet. The model is based on a zonal approach, where gas compressibility effects are taken into account only in the high velocity jet region, while elsewhere the gas is treated as incompressible. The volume of fluid (VOF) method is employed to follow the deformation of the bath free surface. Calculations are presented for two- and three-phase systems and compared against experimental data obtained in a cold model experiment presented in the literature. The influence on the size and shape of the cavity of various parameters and models (including the jet inlet boundary conditions, the VOF advection scheme, and the turbulence model) is studied. Next, the model is used to simulate the interaction of a supersonic oxygen jet with the surface of a liquid steel bath in a pilot-scale converter. The second model concentrates on fluid flow, heat transfer, and the post-combustion reaction in the gas phase above the metal bath. The model uses the simple chemical reaction scheme approach to describe the transport of the chemical species and takes into account the consumption of oxygen by the bath and thermal radiative transfer. The model predictions are in reasonable agreement with measurements collected in a laboratory experiment and in a pilot-scale furnace.

Experimental and Numerical Analysis of the Deformation of a Liquid Aluminum Free Surface Covered by an Oxide Layer During Induction Melting

In an induction furnace, as a result of electromagnetic forces, the free surface of a liquid aluminum bath deforms and takes the form of a dome. The oxide layer that forms spontaneously on the free surface of aluminum melts may also influence the deformation by exerting an additional friction force on the metal. A non-intrusive experimental technique—Structured Light Fringe Projection—was used to measure the complete surface deformation and its fluctuations, for a varying set of operating parameters—inductor current intensity and initial liquid metal filling level inside the crucible. For an axisymmetric geometry, numerical simulations were carried out to calculate in a single framework: (i) the electromagnetic forces using the A–V formulation, (ii) the free surface deformation using the Volume of Fluid method, and (iii) the turbulent stirring of the metal using a RANS-based k–ω model. The friction force due to the oxide layer was modeled by imposing a pseudo-wall condition on the free surface, which makes the interfacial velocity very small compared to the average liquid metal pool velocity. A marked impact on the dome height due to applied friction force is observed. Finally, comparisons between the predicted and measured domes are presented.

On the Modeling of Thermal Radiation at the Top Surface of a Vacuum Arc Remelting Ingot

Two models have been implemented for calculating the thermal radiation emitted at the ingot top in the VAR process, namely, a crude model that considers only radiative heat transfer between the free surface and electrode tip and a more detailed model that describes all radiative exchanges between the ingot, electrode, and crucible wall using a radiosity method. From the results of the second model, it is found that the radiative heat flux at the ingot top may depend heavily on the arc gap length and the electrode radius, but remains almost unaffected by variations of the electrode height. Both radiation models have been integrated into a CFD numerical code that simulates the growth and solidification of a VAR ingot. The simulation of a Ti-6-4 alloy melt shows that use of the detailed radiation model leads to some significant modification of the simulation results compared with the simple model. This is especially true during the hot-topping phase, where the top radiation plays an increasingly important role compared with the arc energy input. Thus, while the crude model has the advantage of its simplicity, use of the detailed model should be preferred.

Modeling of Inclusion Behavior in an Aluminum Induction Furnace

Crucible induction furnaces are widely used in the aluminum industry, for scrap remelting, metal treatments and casting. The operation principle results in an intense circulation within the furnace, raising a specific question with regard to inclusion dynamics within the melt, reflected by LiMCA measurements at the furnace exit. In an effort to understand the involved phenomena, a hydrodynamic model of an induction furnace was built and complemented by an inclusion module that takes into account the transport of inclusions and the interaction of inclusions with other inclusions (aggregation) or with the crucible walls. A numerical inclusion distribution has been developed that reflects the characteristics of the inclusions present in the melt. The model and results of its application are presented in this paper.

Characterization of the behaviour of the electric arc during VAR of a Ti alloy

In this paper, we report experimental results based on the direct observation of the electric arc behaviour during vacuum arc remelting of a Ti alloy. These results were obtained in a specifically instrumented industrial furnace using high speed framing camera and optical emission spectroscopy, for a current density level of the order of 10 A/cm2 and a gap length of a few centimetres. It was observed that the arc exhibits a similar operating regime to that described in the literature for the case of Inconel 718 and Zr alloy electrodes. The arc structure corresponds essentially to that of a diffuse metal vapor arc with separate and rapidly moving cathode spots. Several critical parameters of the cathode spots, including their current, size and velocity, and of the interelectrode plasma were evaluated. Also, the interactions between the arc operation and the transfer of metal drops in the interelectrode gap were investigated. Three modes of transfer of the liquid metal drops in the interelectrode gap have been identified depending on the gap length: drop falling, drip short and drop erosion induced by the cathode spots.