Effect of flow modifiers on the fluid flow characteristics in a slab caster tundish

ABSTRACT

In a slab caster tundish, controlling liquid steel flow is of paramount importance for clean steel production. A conventional tundish design consists of a pouring box, a weir and a dam. To improve the overall performance of a 40 ton slab caster tundish, three different arrangements by incorporating additional flow modifiers have been examined. A three-dimensional steady state fluid flow model has been developed using a RANS (Reynolds-Averaged Navier-Stokes) approach. Subsequently, transient scalar-transport equations were solved to obtain the C-curve of the tundish. A different approach has been followed to evaluate the inlet boundary condition to mimic the process conditions more accurately. The CFD predictions were validated with the results of the water model. Mean residence time, dead volume fraction and flow structures have been considered for evaluating tundish performance. All the proposed configurations have shown improvements in comparison to the base case. The mean residence time of the fluid was found to be the highest for the case having two pairs of weir and dam. However, the insights derived from the flow structures specifically plug flow in zone 2 and near the tundish outlet region suggest that that having a single weir and two dams is the optimal choice.

Dans un panier de machine à couler des brames, contrôler le débit d’acier liquide est d’une importance prépondérante pour une production d’acier propre. Une conception conventionnelle d’un panier de coulée se compose d’un bassin de coulée, d’un déversoir et d’un barrage. Afin d’améliorer les performances globales d’un panier de coulée d’une machine à couler des brames de 40 tonnes, on a examiné trois dispositions différentes incorporant des modificateurs d’écoulement supplémentaires. On a développé un modèle d’écoulement de fluide tridimensionnel en régime permanent à l’aide d’une approche RANS (Reynolds-Averaged Navier-Stokes). Ensuite, on a résolu des équations de transport scalaire transitoire pour obtenir la courbe C du panier de coulée. On a suivi une approche différente pour évaluer la condition aux limites d’entrée pour imiter plus précisément les conditions du procédé. On a validé les prédictions de la DNF (dynamique des fluides numérique) avec les résultats du modèle d’eau. On a pris en compte le temps de séjour moyen, la fraction de volume mort et les structures d’écoulement pour évaluer les performances du panier de coulée. Toutes les configurations proposées ont montré des améliorations par rapport au cas de base. Il s’est avéré que le temps de séjour moyen du fluide était le plus élevé pour le cas ayant deux paires de déversoir et de barrage. Cependant, les informations dérivées des structures d’écoulement, spécifiquement l’écoulement en bouchon dans la zone 2 et près de la région de sortie du panier de coulée, suggèrent que le choix optimal consiste en un seul déversoir et deux barrages.

KEYWORDS:

• Mathematical modelling
• single strand continuous caster tundish
• residence time distribution
• flow modifier
• water modelling
• C-curve
• flow control devices
• tundish

Acknowledgements

The authors would like to express our special gratitude to their colleague, Mr. P S Srinivas, who has reviewed every version of this paper and responded with a combination of compassion and criticism. His insights were instrumental in shaping this research paper. The authors are grateful to their colleagues Dr. Vikas Singh, Mr. Ravi Wasudev Golani and Dr. Suvankar Ganguly for their support throughout the research work.

Disclosure statement

No potential conflict of interest was reported by the author(s).

List of symbols
$D_{I{W}_n}$	=	Distance between inlet and nth weir
$D_{I{D}_n}$	=	Distance between inlet and nth dam
u	=	Mean velocity
x	=	Coordinate for measure of distance
p	=	Pressure
µ	=	Co-efficient of viscosity
g	=	Acceleration due to gravity
k	=	Turbulent kinetic energy
t	=	Time (sec)
Cw	=	Concentration of water
CT	=	Concentration of tracer
Vdp	=	Volume ratio of dispersed plug flow
Vd	=	Dead volume ratio
Vm	=	Mixed volume ratio

Greek Letters
ρ	=	Density of the fluid
σ	=	Coefficients
ϵ	=	Rate of dissipation of turbulent kinetic energy
θ	=	Dimensionless Time

Subscripts
i, j, k	=	Three Cartesian coordinate directions x, y and z
t	=	Turbulence
eff	=	Effective

Abbreviations
RTD:	=	Residence Time Distribution