Numerical Optimization of Nozzle Ports to Improve the Fluidynamics by Controlling Backflow in a Continuous Casting Slab Mold

Abstract

In order to improve the fluid flow patterns inside the mold, a better understanding of the backflow phenomenon and its controlling parameters is necessary; then a mathematical simulation of the fluidynamics in the mold and the submerge entry nozzle (SEN) are carried out considering two typical nozzle designs and different modifications applied to the outlet ports. The numerical model considers isothermal three dimensional continuity and the Navier-Stokes equations in Cartesian co-ordinates, which are solved together with the k-ε standard turbulence and the Volume of Fluid (VOF) models through the volume finite method. The results show that the backflow phenomenon emerges from an inadequate SEN port design, when a boundary layer separation is generated before the steel is delivered to the mold. This separation occurs at the upper internal side of the port inducing a low pressure zone with high levels of kinetic energy dissipation, producing the backflow phenomenon. From the analysis, it is concluded that the implementation of a radius at the internal upper side of the port avoids the separation of the boundary layer, eliminating the backflow phenomenon which allows the use of the complete effective exit area of the port; this is reflected in a velocity decrease of the jets and consequently a velocity decrement of the bulk flow. Furthermore, the size of the radius controls the penetration angle of the jets, the impact point position and the meniscus deformation; which avoids the need of the inclination angle of the port.

Modeling Study of Molten Steel Turbulence Control by SEN Design Improvement in a Conventional Slab Caster

“…All these flow patterns variations could be attributed to the fact that the backflow phenomenon has disappears, and the delivering port uses now the total exit area as demonstrated previously by the numerical simulation. [12] It is important to mention that the instantaneous PIV fields for the shallow position show the presence of the typical upper roll flow; however, the upper roll flow occurrence was still intermittent and the average fields did not show it. To have a complete view of the flow patterns inside the mould, red dye tracer was performed and the results are shown in Figure 4b; it can be observed that the jets have a more symmetric flow pattern allowing better fluid feeding to the meniscus and more symmetrical lower roll flows.…”

“…Thus, the hypothesis that the jet variations have its origin on the backflow phenomenon can be established from the previous numerical results by the authors. [12] This first analysis stage ended co-validating the mathematical simulation (Figure 7b) with the PIV measurements results (Figure 7a). It is important to remark that the numerical results show the average velocity fields; for that, it is possible to observe a welldeveloped double roll flow.…”

“…This tendency could be attributed to the backflow observed and described by the mathematical analysis carried out and presented in a previous publication. [12] Focusing on the lower roll flow, it can be mentioned that it does not show a clear structure at shallow position, but at deep position shows better definition (Point 3, Figure 2). Related to the intermittency of the upper roll flow at shallow position, it is possible to associate this to the steel flow turbulence in this zone, which is correlated by the vorticity.…”

“…A pressure inlet condition is applied at the mould top (p ¼ 101 325 Pa, T ¼ 300 K) to model the effects of a system open to the atmosphere. [12] 3. Results and Discussion…”

Anchor-Shaped Design of a Submerged Entry Nozzle for the Continuous Casting of Steel

“…The quality of the steel slabs is greatly influenced by the fluid flow in the continuous casting mold [2], and the geometry of the Submerged Entry Nozzle (SEN) is the most important parameter [3] [4]. In the continuous casting mold, mold powder is added in order to prevent heat losses, provide good lubrication, and protect the molten steel from air oxidation.…”