Numerical Analysis of Thermal-driven Buoyancy Flow in the Steady Macro-solidification Process of a Continuous Slab Caster

Abstract

The role of thermal-driven buoyancy flow in the steady macro-solidification process of a continuous slab caster and its effect on the predicted flow and temperature distribution are discussed by combining the non-dimensional analysis and the predicted results obtained from a steady three-dimensional coupled fluid flow, heat transfer and macro-solidification model. Results show that the relative strength among the thermal-driven buoyancy flow, the forced flow caused by the SEN impinging jet and the fluid flow through the porous matrix of mushy-zone continuously changes. The strength of thermal-driven buoyancy flow in the mold and sub-mold zone of slab caster is dependent on the characteristic flow velocity, temperature difference and the porosity-permeability ratio relation. The convection flow caused by thermal buoyancy at liquidus temperature of steel can result in the occurrence of local turbulence. The obvious effect zone of the thermal buoyancy flow on the predicted flow and temperature is in the region where the forced flow has become inferior and the mushy porous flow does not play a dominant role.KEY WORDS: continuous slab caster; solidification; thermal-driven buoyancy flow; numerical simulation.liquid steel and solid steel is regarded as the constant value and Boussenisque's approximation is used to consider the thermal-driven buoyancy flow. 3) The low-Reynolds number k-e turbulent model of Lam and Bremhorst is utilized to consider the turbulent flow in the mold. Boundary ConditionsAll general initial and boundary conditions for simulation on a continuous slab caster have been noted in several references. 18,22) The specified coordinate and grid system for a given caster in the present study is shown in Fig. 1. The geometrical parameters and operating conditions of this caster are summarized in Table 1. The value of the Darcy coefficient is adopted in concert with the work of Seyedein et al. 18) and the values of various turbulent constants are assigned by the reference. 23)It is very difficult to determine the mold heat flux due to the existing gas gap between the mold and the shell. A simple local heat flux formulation obtained by the measurement of the mold water volume and water temperature difference between the inflow and the outflow of cooling water is employed, as given by: At the strand surface below the mold, the values of heat transfer flux from the strand surface to the environment are governed by combination of three heat-transfer mechanisms: conduction, convection and radiation. Therefore, it is very difficult to decide the combined heat-transfer coefficient and a trial and error study procedure is adopted, which can be simply outlined as follows: 1) the known spray cooling water volume obtained from the plant's database is inputted into the known empirical or semi-empirical formulations 24) to calculate the combined heat transfer coefficient in different segments of the caster; 2) the heat transfer coefficient is used as the boundary condition to obtain the calculated surface temperatu...

Three Dimensional Turbulent Fluid Flow and Heat Transfer Mathematical Model for the Analysis of a Continuous Slab Caster

“…Sussman et al 31) have solved the three-dimensional turbulent multi-phase fluid flow for behavior of the steel, argon and inclusion particles in both the water model and continuous caster. S. Qiu et al 32) have discussed the effect of thermal driven buoyancy on predicted flow and temperature obtained from a steady three-dimensional coupled fluid flow, heat transfer and macro-solidification model. Huang et al 33) have developed a turbulent three-dimensional model to simulate the transient flow behavior in the mold.…”

Thermo-fluid Mathematical Modeling of Steel Slab Caster: Progress in 21st Century

“…In absence of this effect, the recirculation loop may be under predicted by the model. 37,38) As shown in Fig. 3, thermal buoyancy role is appreciable especially in sub-mold region.…”

“…Over the periods increasingly complex models are developed to take into account various phenomena at work. Computational rigour has evolved from a symmetry modeling approach [12][13][14][15] to full domain 16) taking inherent flow asymmetries into account, from 2-dimensional (2D) 12) to 3-dimensional (3D) 16) modeling approach to correctly implement turbulence, from steady state 12,14) modeling to transient 16,17) modeling approach to capture chaotic nature of flow, from single phase flow 12,15) to multiphase flow 17) to take interaction of argon bubbles, overlying slab/mold flux layer along with solutal and thermal convections.…”

“…and have been extensively used as a first hand validation for fluid flow results. 24,[30][31][32][33][34][35][36] QIU 37) developed a validated 3D steady coupled model to resolve the thermal driven buoyancy flow. The importance of inter-dendritic convection was underlined by non-dimensional analysis.…”

Applying Finite Point Method in Solidification Modeling during Continuous Casting Process

“…[1][2][3] Simulation of solidification by solving of heat transfer equation is used to calculate the thickness of solidified shell and strand temperature profile. [4][5][6][7] The common methods for simulation of solidification are finite element method (FEM), finite difference method (FDM) and finite volume method (FVM). These methods are mesh-based methods and in these methods, the problem domain, where the partial differential governing equations are defined, is often discretized into meshes.…”