Mixing phenomena in a RH process has been studied numerically by solving the Navier Stokes equations along with the species concentration equation in a cartesian coordinate system comprising the geometry of the ladle and the snorkel fitted to it. The solution of the species concentration equation has been utilized to compute the mixing time in the RH ladle under different flow conditions. The numerical procedure and solution algorithm has been first verified by comparing the numerically obtained tracer dispersion curve, with the actual plant measurement, which agrees fairly well with each other. Mixing time for the RH process has been computed for different downleg snorkel size, snorkel immersion depth (SID) and steel velocity within the downleg and a non-dimensional mixing time correlation has been developed for the RH ladle taking the above three pertinent input parameters into considerations. The correlated non-dimensional mixing time equation predicts fairly well the computed result as well as the actual mixing time being observed in the plant.

Continuous casting of slab caster of Tata Steel has been simulated using a three dimensional mathematical model based on considerations of fluid flow, heat transfer and solidification for better understanding of the process. Liquid metal comes in the mould by bifurcated nozzle. The principal model equations are momentum and heat balances. In various zones, different standard boundary conditions have been used. In the mould region, Savage and Prichard expression for heat flux has been used. In the spray cooling zone, heat transfer coefficient for surface cooling of the slab has been calculated by knowing the water flow rate and nozzle configuration of plant. The turbulence in the molten metal has been modelled by the Realizable k-e model. CFD software (Fluent) has been used for the solution of equations to predict the velocities in the molten pool of the slab, temperature of the entire volume of the slab, heat transfer coefficient in the mould region, heat flux in the spray and radiation region and shell thickness. The variables studied are different casting speed.KEY WORDS: slab caster; turbulence; solidification; shell profile; CFD; radiation cooling; spray cooling; heat flux; heat transfer coefficient; mathematical modelling; steel casting; realizable k-epsilon model. ISIJ International, Vol. 47 (2007), No. 3, pp. 433-442 433 © 2007 ISIJ austenite-ferrite phase transformation, which is accompanied by a sizeable volume change should not occur. To meet the above criteria, after certain length of spray cooling, the strand is allowed to be radiant cooled. The dimensions of the caster are given in Table 1. The spray zone length has been sub divided into six regions for flexibility of cooling. The first is spray ring region (Zone 0) just after the mould and having only water flow. In the narrow face of the slab, the spray ring region (Zone 0 N&S) is also having only water flow. After this region, there is no forced cooling on the narrow face. After spray ring region other spray zones are named as 1A, 1B, Zone 2, Zone 3, Zone 4 and Zone 5 as mentioned in Table 1. Slab cast should be free from surfaces and internal cracks. For a given composition of steel, solidification in the slab casting will depend on fluid flow and heat transfer in different zones. In the mould region, the total heat transfer can be easily obtained by knowing difference of temperature between the inlet and the outlet of water passing through mould cooling jacket and its flow rate. Theoretically, it is difficult to get the heat transfer along the mould length because of air gap formation between mould and slab, resistance of heat flow due to shell formation, mould plate, water-copper plate, thermal contraction of slab and mould plate, bulging due to liquid height pressure.2-6) Singh and Blazek 7) have experimentally measured the heat transfer profile along the mould length by using a bench scale casting facility. Mould was stationary, unlike the actual caster. They have shown the effect of carbon content, casting speeds, pouring practice, mou...

Experimental simulation of air bubble movement in a 1/3rd scale model slab caster mold has been done for parallel, upward and downward port submerged entry nozzle (SEN) with different water flow and air flow rates in order to study the bubble penetration depth, horizontal dispersion and the air jet angle. It has been observed that the bubble penetration depth depends more on the flow rate of water rather than that of air. The bubble penetration depth also depends on the port angle and on the "well" provided on the SEN. Below a certain critical water flow rate the flow becomes asymmetric in the slab caster mold for a given flow rate of air. SEN with a well depth may help to avoid bubble entrapment defects in the slab at the cost of higher surface disturbances on the mold. A mathematical modeling of the air bubble movement in water was also carried out for the same experimental set up where it was observed that for same air flow rate the bubble penetration depth was more for higher water flow rate confirming to the experimental findings. The experience gained from the experiment and mathematical modeling helped to fine tune the parameters at the caster so that the strike rate of ultra low carbon grade steel could be improved substantially.KEY WORDS: air bubble movement; slab caster mold; experimental simulation; mathematical modeling; bubble dispersion and penetration.

The conventional delta shaped tundish (rectangular with sloping walls) is currently used in many industries for billet caster. The effective volume in this type of tundish is significantly low and results in a lower quality of steel. In the present work, a three-dimensional mathematical model has been used to study the fluid flow characteristics in a six strand billet caster tundish whose one side is curved. The results obtained were compared with a conventional delta shaped tundish and the strong role of curvature in modifying the fluid flow characteristics is noticed. Investigations were performed to study the effect of ladle pouring point in a curved shape tundish. It was found that fluid flow characteristics can be improved by placing the ladle pouring point at the right position. Simulations have been performed for two different shapes of pouring chamber to investigate the role of curvature in the flow control devices. The results obtained confirmed the strong role of curvature to get the improved characteristics for inclusion flotation. The mathematical model has been validated by the experimental results of Singh and Koria for a single strand bare tundish.KEY WORDS: billet caster tundish; pouring chamber; plug volume; mean residence time; inclusion flotation. distance between two ladle pouring points are 200 mm. Table 2 shows all other operating parameters of the tundish. Two different shapes of flow control devices called Pouring chamber were used for the study. Mathematical Formulation and AssumptionsThe flow field in the tundish was computed by solving the continuity and momentum conservation equation in ISIJ International, Vol. 45 (2005) , Fig. 1(b).Top view of the delta shape tundish about symmetry plane for position-1 of ladle pouring point at position-1 (dimensions are similar to curved shape tundish shown in Fig. 1(a)). Fig. 1(c).Top view of the delta shape tundish in Case 6 of Table 1 for position-1 of ladle pouring point (dimensions are similar to curved shape tundish shown in Fig. 1(a)). Fig. 1(d).Top view of the delta shape tundish for Case 7 in Table 1 for position-1 of ladle pouring point (dimensions are similar to curved shape tundish shown in Fig. 1(a)). Table 1. Simulation performed for following cases. Table 2. Operating parameters of billet caster tundish with six strands. Fig. 2(a).Top view of the contour shape pouring chamber (dimensions in mm). Fig. 2(b).View of the section AB and CD shown in Fig. 2(a) of pouring chamber (all dimensions are in mm).three-dimensional. The standard k-e model was solved to incorporate the turbulence near the incoming and outgoing stream. The free surface of the liquid in the tundish was assumed to be flat and the slag depth was considered to be insignificant. Natural convection effect was neglected while computing the velocity field. The equation for dispersion of tracer in the tundish was solved to capture the variation of tracer concentration in the tundish and then RTD analysis was performed. Here, C 1 ϭ1.44, C 2 ϭ1.92, C m ϭ0.09, s C ϭ1, s k ϭ1, s...

Room temperature model studies using water to simulate 'metal' and paraffin oil (when required) as 'slag' were conducted to study the extent of mixing and the rate of mass transfer between metal and slag in the 130 t basic oxygen furnaces (BOFs) in operation in Tata Steel. Several systems of gas injection including top blowing, combined blowing and exclusive bottom purging were investigated. Similar work was undertaken in a room temperature model of an 80 t energy optimising furnace (EOF), in operation for a brief period earlier in Tata Steel. Details of the optimum blowing conditions, including the number/distribution of bottom tuyeres for the BOFs, are elaborated in the present paper. How mixing/mass transfer in an EOF compares with the BOF case(s) is also highlighted.