Numerical simulations were conducted to study the melt flow under the influence of control devices in a T-type two-strand bloom caster tundish via the open source Computational Fluid Dynamics software OpenFOAM. Three different cases were studied: a bare tundish, a tundish with two pairs of baffles, and a tundish equipped with a turbulence inhibitor and a pair of baffles. Turbulence inhibitor and baffles arrangement showed an improvement of the fluid flow characteristics, yielding lower values of dead volume and higher values of plug flow. With a turbulence inhibitor, the velocity of metal which flows directly toward the tundish floor is smaller and the turbulence kinetic energy of the melt top surface is lower than the other two arrangements.
In the steel production route, continuous casting of liquid steel is the most important process. Basically, the tundish in the continuous casting is an intermediate vessel between the ladle and the mold to distribute and supply liquid steel to different molds at an approximately constant rate (Figure
Schematic diagram of a continuous casting setup.
Since detailed knowledge of the molten steel flow is a prerequisite to any effective flow-control optimization, significant efforts have been made by researchers to investigate fluid flow phenomena in tundish systems. Estimation of the various residence time distribution (RTD) parameters via the pulse tracer addition technique has been widely used to study the fluid flow patterns in tundish system [
In the present, work fluid flow in a 30 t tundish with different flow control devices was investigated by mathematical models. In each case of study, flow characteristics, velocity patterns, RTD curves, and inclusion distribution were obtained. The objective in this work was to study the effects of the flow control devices on the fluid flow pattern and RTD curves in a T-type two-strand tundish of a bloom caster.
Figure
Physical dimensions of the tundish and the control devices.
The liquid steel flow in the continuous casting tundish can be considered to be three-dimensional, Newtonian, and incompressible turbulence. A layer of slag at the top of liquid is neglected and the melt surface is assumed to be flat. The mathematical model, which is used to simulate the melt flow inside the tundish as well as the chemical mixing process of the tracer injected by a pulse in the incoming stream, was formulated based on the solution of the three-dimensional Navier-Stokes equations, the mass transfer equation, and two equations for the
Continuity equation:
Momentum equation:
Effective viscosity
Mass transfer equation:
In the mass transfer equations,
Due to symmetry, only a half tundish from the symmetric central-longitudinal plane was chosen for this mathematical simulation. On the top surface of the bath and in symmetry planes, the fluxes of all variables were set equal to zero. No slip conditions were applied to all solid surfaces of the tundish including baffles, and interior walls of the tundish and standard wall functions were applied. The tundish exit is computationally treated as a plane, at which flow occurs at an ambient pressure. The vertical velocity profiles of the liquid steel at the inlet of the tundish were assumed to be uniform through the cross-sections and the other two velocity components were assumed to be zero. The values of
The initial condition for (
A control volume-based technique was used to convert the nonlinear governing equations to algebraic equations that can be solved numerically using the 3D mesh (Figure
3D computational mesh employed in the present model.
In this section, the fluid flow model was validated against the experimental data [
Comparison of the predicted and measured RTD curves.
A typical grid independence test (i.e., 51 × 58 × 34, 63 × 79 × 40, and 76 × 96 × 48) of the present numerical calculation was evaluated in Figure
Grid independence check of solutions in a bare tundish.
Figure
RTD curves for the three cases studied.
From the RTD curves, minimum residence time,
Table
RTD parameters in the tundish system.
Tundish configuration |
|
|
|
---|---|---|---|
Case I | 17 | 28 | 288 |
Case II | 65 | 118.8 | 259.6 |
Case III | 70 | 164.2 | 325.5 |
Volume fraction of flow for the studied cases.
Figure
Predicted metal flow field in tundish for all cases: (a) Case I, (b) Case II, and (c) Case III.
Figure
Predicted turbulent kinetic energy field in tundish for all cases: (a) Case I, (b) Case II, and (c) Case III.
A numerical study was conducted to investigate the fluid flow and residence time distribution of the T-type two-strand continuous casting tundish with and without flow control devices. The following conclusions have been drawn from the present study. The application of a pair of baffles eliminates the short circuiting phenomena in the tundish and brings down the dead volume from 54% to 24%. The employment of a TI and a pair of baffles is more effective to increase the plug fraction than a bare tundish or a tundish with just a pair of baffles, and it was found to be an optimum configuration of the two-strand tundish in the present study. With a TI, the velocity vectors directed toward the tundish floor are smaller and the turbulence kinetic energy of the liquid steel top surface is lower than the other two arrangements, which means a more stable slag-metal interface.
This work was supported by the Natural Science Foundation of China (51210007) and the National Key Technology R&D Program of China (2011BAK06B02).