| A three-dimensional mathematical model for the simulation of vertical direct chill (DC) slab casting of aluminum alloys has been developed. The model is based on the solution of the 3D time-averaged turbulent momentum (Navier-Stokes) and energy equations. The momentum equations are modified with a Darcy-type source term to simulate motion of the melt in the mushy region. The buoyancy force term is implemented in the model through the Boussinesq approximation. The low Reynolds number k-&egr; turbulence model of Launder and Sharma is used to calculate the Reynolds stresses and the turbulent heat fluxes. A variable heat transfer coefficient is used along the ingot surface to account for the different cooling regions. The mathematical model is qualitatively and quantitatively verified by comparing the computed results with a physical water model and a real casting experiment, respectively of independent researchers. Each of the comparisons showed a good agreement. The quantitative verification of the solidification front depths is improved when the thermal buoyancy force effect is included in the model.; A parametric study has been carried on two casters of variable aspect ratio each using a different type of inlet melt distribution system. In the case of the small aspect ratio caster, the physical properties of aluminum Al-3104 are used. For this caster, the studied parameters are the casting speed, the primary cooling rate, the melt superheat and the combo-bag dimensions. Also, the effect of complete blockage of the bottom windows of the distribution bag is studied. An in-depth understanding of some behaviors of the melt flow and solidification profile in the steady state operational phase of the DC casting process is gained. For example, the roles played by the angle flow and the upward component of the vertical recirculation at the wide symmetry plane in controlling both the solidification front depth and the mushy layer thickness at the slab center are ascertained. This study has revealed the influence of the melt stream issued from the bottom window of the bag on the depth and uniformity of the solidification front. The model has successfully identified a faulty design of the short combo bag. This industrially favorite design causes what is called the reverse flow, that is, the melt from the surrounding sump enters the combo bag through the bottom window. (Abstract shortened by UMI.)... |
