Effect of outlet positions and various turbulence models on mixing in a single and multi strand tundish

Jha, Pradeep Kumar; Dash, Sukanta Kumar

doi:10.1108/09615530210434296

Cited by 32 publications

(22 citation statements)

References 14 publications

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“…A larger peak value of concentration at early time indicates short-circuiting phenomena inside the tundish and contributes to the formation of large dead regions inside the tundish. A smaller peak value contributes to better mixing parameters, such as a large value of mean residence time and the ratio of mixed to dead volume inside the tundish [8][9]. It is hence anticipated that delaying the appearance of the tracer from the outlet near the inlet by closing it for some time after tracer injection may affect the fluid flow inside the tundish, and then, the mixing characteristics may be improved.…”

Section: Introductionmentioning

confidence: 99%

Numerical investigation of the effect of transitory strand opening on mixing in a multistrand tundish

Mishra

Jha

Sharma

et al. 2011

Int J Miner Metall Mater

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In a multistrand, the outlet near the inlet produces short circuiting flow. This leads to the formation of dead zones inside the tundish, and consequently, the mean residence time decreases. In the present study, numerical investigation of mixing inside a delta shaped tundish with sloping boundaries was carried out by solving the Navier-Stokes equation and employing the standard turbulence model. To decrease the dead zone volume inside the tundish, the effect of closing the outlet near the inlet for a small amount of time and further opening it on the mixing behavior of the tundish was studied. The outlets near the inlet were closed for varying amount of time, and the transient analysis of fluid flow and the tracer dispersion study were carried out to find the mixing parameters of the tundish, namely, mean residence time and the ratio of mixed to dead volume of the tundish. An optimum closure time of the near outlet has been found, which yields best mixing inside the tundish. The numerical code was validated against the experimental observation by performing the tracer dispersion study inside a multistrand tundish and the reasonably good match between the experimental and numerical results in terms of residence time distribution (RTD) curves. The results obtained from the present study confirm the strong role of choosing the right time for opening and closing the outlets to get improved characteristics for the fluid flow and mixing behavior of the tundish. The educational version of computational fluid dynamics (CFD) software PHOENICS was used to solve the governing equations and interpret the results in different forms. Nomenclature: C: Concentration of the tracer, kg·m −3 ; C av,i : Average concentration of the tracer at outlet i, kg·m −3 ; D: Derivative, s −1 ; k: Turbulent kinetic energy, m 2 ·s −2 ; MRT: Mean residence time, s; P: Pressure, kg·m −1 ·s −2 ; RTD: Residence time distribution; t: Time, s; t r : Actual mean residence time of the fluid in the vessel, s; U: Mean velocity, m·s −1 ; i j u u : Average turbulent stress, kg·m −1 ·s −2 ; V: Volume of the tundish, m 3 ; ε: Dissipation rate of turbulent kinetic energy, m 2 ·s −3 ; μ: Coefficient of viscosity, kg·m −3 ; ν: Kinematic viscosity, m 2 ·s −1 ; ρ: Density of fluid, kg·m −1 ·s −1 ; τ: Theoretical mean residence time, s.

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Section: Introductionmentioning

confidence: 99%

Numerical investigation of the effect of transitory strand opening on mixing in a multistrand tundish

Mishra

Jha

Sharma

et al. 2011

Int J Miner Metall Mater

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“…The turbulent quantities, k and ε, on the first near wall cell have been set from the equilibrium log law wall function as has been described by Jha and Dash et al [2][3][4]. The turbulent intensity at the inlet of the nozzle has been set to 2% with the inlet velocity being known and the back flow turbulent intensity at all the pressure outlet boundaries has been set to 5%.…”

Section: Governing Equationsmentioning

confidence: 99%

Prediction of entrance length and mass suction rate for a cylindrical sucking funnel

Mishra

Dash

2009

Numerical Methods in Fluids

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SUMMARYConservation equations for mass, momentum and energy have been solved numerically for a cylindrical funnel with louvers (lateral openings on the side wall of the cylindrical funnel through which air can come into it) to compute the suction rate of air into the funnel. The nozzle placed centrally at the bottom of the cylinder ejects high-velocity hot gaseous products so that atmospheric air gets sucked into the funnel. The objective of the work is to compute the ratio of the rate of mass suction to that of the mass ejected by the nozzle for different operating conditions and geometrical size of the funnel. From the computation it has been found that there exists optimum funnel diameter and optimum funnel height for which the mass suction is the highest. The protruding length of the nozzle into the funnel has almost no effect on the mass suction rate after a certain funnel height. The louvers opening area has a very high impact on the mass suction rate. The entrance length for such a sucking funnel is strikingly much lower compared with a simple cylindrical pipe having uniform flow at the inlet at same Reynolds number. A new correlation has been developed to propose the entrance length for a sucking pipe, the rate of mass suction into it and the exhaust plume temperature over a wide range of operating parameters that are normally encountered in a general funnel operations of naval or merchant ship.

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“…Details of the turbulence prescription can be found from the authors article. 20,21) The top surface of the vessel was set to a zero shear stress condition where the gas bubbles were allowed to escape. Once the solution reached steady state the tracer dispersion equation was solved where the inlet of the tracer injection point was set to mass fraction of 1 for 1 s. This was achieved in 5 equal time steps of 0.2 s each.…”

Section: Boundary Conditionsmentioning

confidence: 99%

Optimisation of the Bottom Tuyeres Configuration for the BOF Vessel Using Physical and Mathematical Modelling

et al. 2007

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An experimental perspex model of the BOF vessel was made to the scale of 1 : 6 on which mixing time measurements were done by injecting potassium chloride (KCl) at a certain point and measuring the conductivity of the solution with time. It was found that the mixing time in the vessel attained a minimum when the bottom nozzles (eight in number) were kept at a pitch circle diameter (PCD) ratio of 0.4 with combined blowing (top blowing as well as bottom blowing) but the mixing time became a minimum at a PCD of 0.5 when only bottom blowing was done. In order to get a finer position of the bottom nozzles so that the mixing time could still be minimized, a mathematical model was used (because experiment could not be done with so close placement of the nozzles in one setup) to simulate the flow in the vessel with the help of the two equation k-e turbulence model along with a discrete phase model to simulate the air bubbles being injected in to the vessel. The mathematical model could predict the mixing time in the vessel to a very good degree of accuracy when compared with the experimental observations for the PCD of 0.5. From the mathematical model it was predicted that the mixing time in the vessel could still be lowered if the bottom nozzles were placed at a PCD of 0.56 instead of 0.5.

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Effect of outlet positions and various turbulence models on mixing in a single and multi strand tundish

Cited by 32 publications

References 14 publications

Numerical investigation of the effect of transitory strand opening on mixing in a multistrand tundish

Numerical investigation of the effect of transitory strand opening on mixing in a multistrand tundish

Prediction of entrance length and mass suction rate for a cylindrical sucking funnel

Optimisation of the Bottom Tuyeres Configuration for the BOF Vessel Using Physical and Mathematical Modelling

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