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A numerical analysis and a water model study of the mold region of a billet continuous caster was performed with a novel injection concept using swirling flow in the pouring tube, to control the heat and mass transfer in the continuous casting mold. The following results were found: A weak impinging flow can be observed near the corner of the mold wall, which results in the promotion of uniform heat and mass transfer all around across the plane, particularly at the casting corner. An upward flow directed from the vicinity of the nozzle outlet to the meniscus can be observed near the corner of the upper part of the mold, which leads to the active heat and mass transfer into the meniscus. A uniform velocity and heat distribution can be obtained within a short distance of 200 mm downward from the outlet of the nozzle. Quite different mold flow patterns are observed between the divergent and straight immersion nozzles. Heat and mass transport in the mold using the divergent nozzle is much more reasonable than that using the straight nozzle.

With increasingly more stringent requirements on steel quality and productivity in uphill teeming production, it is vital to attain more desirable fluid flow conditions in the filling of the mould. In this investigation, physical and mathematical modelling was carried out to study the effects of nozzle type and utilization of a swirl generator in the inlet nozzle on the flow pattern in the ingot mould during the initial filling period. Specific focus was on the effects on the resultant hump and axial velocities. Three cases were considered: 1) a straight nozzle, 2) a divergent nozzle, and 3) a divergent nozzle combined with a swirl generator. It was found that usage of the divergent nozzle, compared to the straight nozzle, resulted in a smaller hump and lower axial velocities in the bath. For the combination of divergent nozzle and swirl generator, these findings were even more pronounced, with the hump practically eliminated, and the axial velocities, as well as the turbulence at the meniscus, significantly lower. The findings of the study suggest that a divergent nozzle combined with a swirling flow generated in the nozzle could be used in the up‐hill teeming process in purpose to get calmer initial filling conditions.

With increasing requirement of steel productivity and quality in continuous casting in the conventional casting system using an immersion nozzle with side pouring holes, it is very difficult to establish a reasonable molten flow pattern. In order to overcome this difficulty, we propose a new method imparting a swirling motion to the flow in the immersion nozzle and to control the flow pattern in the mold. Obtained results are as follows:1) High amplitudes of oscillation with a period of 10 to 15 sec are observed in the outlet flow of the immersion nozzle and meniscus flow in the conventional casting system, while these phenomena are remarkably suppressed using swirling motion in the immersion nozzle, which leads to very calm and uniform flow pattern at the outlets of the immersion nozzle, in the mold and on the meniscus in the mold.2) The steady outlet flow softly impinges on the side wide face, and then turns around as a reverse flow along the other wide face describing a S-shaped curve in the cross section and clock-wise rotational flow in the vertical section. This outlet flow exerts a shearing-effect on the inner wall of the mold, leads to the considerable energy consumption and exerts a braking effect in the flow which results in suppression of self-excitation-vibration in the bulk mold flow and biased flow on the meniscus. In other words, imparting a swirling motion to the flow in the immersion nozzle, remarkably reasonable bulk mold flow can be obtained.

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Swirling flow effectiveness on controlling the bulk mold flow has been acknowledged recently, concerning the productivity of continuous casting process and its quality. From the practical viewpoint, relationship between the throughput and bulk mold flow is investigated. Following results are obtained:1) Numerical analysis fairly coincide with the experimental results for the cases: nozzle outlet, surface flow and velocity distributions along the narrow face. 2) Surface velocity decreases with increasing the axial length of the nozzle outlet, particularly in length from 20 to 60 mm. 3) For the high throughput case, considerable stable bulk mold flow can be obtained. Results and ConsiderationIt has been acknowledged that turbulence-k-e model is not appropriate for swirling flow phenomena. However, in my several studies using a water model, the calculated results using the k-e model have fairly coincided with the water-model-experiment-results as shown for several turbulent-flow-cases, within swirl-number (mean tangential velocity across the tube/mean axial velocity across the tube) of 1, even with the considerably high tangential velocity of 2 m/s in the tube. 6,7) On the other case, the calculated results using the k-e model have not coincided with the experimental results, for the case (ϭswirl numberϾ Ͼ1). 12)Namely, in the flow area within the swirl number less than 1, calculation using the k-e model is considered to be effective. Accordingly, in this study, following governing equations were used because almost applied swirl numbers are within 1. Continuity, momentum equations and Realizable k-e model are adopted at the following calculations using the FLUENT-code.13) Where the coefficients C 1 , C 2 , s k , s e , are empirical constants which have the following values C 1 ϭ1.44, C 2 ϭ1.9, s k ϭ1.0, s e ϭ1.2. Boundary conditions: wall function at solid wall; k and e are those derived from the assumption of an equilibrium boundary layer; uniform axial component velocity and radial profiles of tangential velocity described later are assumed, at the nozzle inlet; a constant pressure is assumed at exit boundary; no shear stress is assumed at the free surface; small grid spacing was employed near the domain. In order to ensure the numerical accuracy of the results, the mass and momentum equations are required to be satisfied to within 0.1% of the integrated flow of the quantity through the domain.The radial profiles of the tangential velocity at 20 mm ISIJ International, Vol. 41 (2001) downwards from the nozzle entrance, which are used in calculation, are shown in Fig. 3. Where, W is defined as a mean tangential velocity across the nozzles which correspond to radial profile of tangential velocity shown. Velocity distributions at the outlet of the nozzle for the cases without and with swirl are shown in Fig. 4. For the case without swirl, the flow goes through down and impinges on the well of bottom and rises as a reverse flow. A boundary separation between the flow and curved wall is observed at the upper par...

Swirling flow effectiveness on controlling the bulk mold flow has been acknowledged recently, concerning the productivity and its quality of continuous casting process. In this study, simple immersion nozzle without opposite face on the end of the nozzle is proposed. From the practical viewpoint, relationship between the throughput and bulk mold flow is investigated.