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This article summarizes the outcome of research work carried out to improve the performance of the oxygen lance in the LD steelmaking process. It is stated that the lack of control of the foamy slag and the augmentation of interfacial area creation between the slag and metal are the major hindrances in running the process effectively for improved turn-down steel quality. The ineffectiveness of the existing design in producing liquid metal droplets in the presence of slag foam is explained. In order to augment the droplet generation, a new oxygen lance with a central subsonic nozzle through which flow can be controlled has been introduced and its blowing performances studied using numerical and water model studies. The jet characteristics studied in the numerical simulations show no jet coalescence. The interferences of the jets with the bath have further been analyzed by hydrodynamic model studies. It has been found that the droplet generation rate improves significantly due to the presence of the central jet. Further, it has been observed that controlling the flow rate through the central hole can be used as an effective process control tool.

Gas flows in micro-channels are, in general, theoretically treated with the Maxwell slip velocity as a boundary condition for the convection velocity at the wall. It is pointed out that wall slip is conventionally introduced in theoretical/numerical treatments of gas flows through micro-channels to obtain agreement with experimental results. In the present paper, we provide an alternative by solving the extended Navier-Stokes equations for compressible gas flows in micro-channels using the conventional no-slip velocity boundary condition for the convection velocity. Results obtained with this approach are presented and compared with experiments. It is also shown that the theoretical treatment of micro-channel gas flows using the "extended Navier-Stokes equations" also permits the phenomena such as the Knudsen paradox, to be treated in an analytical manner. Comparison with experimental data suggests that the derived analytical solution has excellent agreement up to Knudsen number of approximately 1, which shows the validity of extended Navier-Stokes equations with the conventional no-slip velocity boundary condition up to the early transition regime of micro-channel gas flows.

Submerged entry nozzle (SEN) clogging is caused by deposition of solid microinclusions present in the liquid steel and aided by stagnation and swirling velocity regimes near the bottom wall. A mathematical model has been developed to investigate steel flow within the SEN and the results obtained with k-e and Reynolds stress model (RSM) turbulence models have been compared. The existing flat SEN bottom causes stagnation of the steel flow within the nozzle and the absence of shear stress prevents the removal of inclusions. The jet from the port is narrow and focused and has two high turbulent swirls near the walls. As a remedy, a parabolic curve shaped bottom has been designed to guide the liquid steel flow and has resulted in a better flow profile and exit jet characteristics. Stagnation is absent and the jet characteristics have improved with the average jet turbulence being reduced by 33%. The study on the sufficiency of the shear stress magnitudes to remove clogging has shown that the curve bottom performs better compared with the flat bottom. The effect of casting speed variation has also been studied on these two bottom configurations. The preliminary plant trials show encouraging results. List of symbolsA inlet cross-sectional area of the nozzle at inlet, m 2 A slab cross-sectional area of the slab, m 2 C 1e ,C 2e ,C m constants in turbulence equations g acceleration owing to gravity, m s 22 G k generation of turbulent kinetic energy, Pa s 22 I turbulent intensity, % k turbulent kinetic energy, m 2 s 22 k in inlet turbulent kinetic energy, m 2 s 22 k p turbulent kinetic energy near the wall, m 2 s 22 n local coordinate normal to the wall p static pressure, N m 22 u i velocity in a particular direction, m s 21 v ref reference velocity, m s 21 v z,in SEN inlet velocity, m s 21 V resultant velocity, m s 21 V c casting speed, m min 21 y* dimensionless distance from the wall b effective area fraction of the port e turbulent kinetic energy dissipation rate, m 2 s 23 e in inlet turbulent kinetic energy dissipation rate, m 2 s 23 m dynamic viscosity, Pa s m t turbulent (eddy) viscosity, Pa s h local jet angle, deg. r density of liquid steel, kg m 23 s k ,s e constants in turbulence equations t w wall shear stress, Pa