A numerical simulation of the D.C. continuous casting process including nucleate boiling heat transfer

The steady-state thermal problem associated with the direct-chill continuous casting of A6063 aluminum cylindrical ingots is solved using the numerical finite element technique. Excellent correlation is demonstrated between the numerical model and experimental data from ingots cast at two different speeds. By application of the model, effective heat transfer coefficients are calculated as a function of vertical position on the outside surface of the ingot. It is shown that direct application of these coefficients to the modeling of different casting situations will produce substantial errors in the region in which heat transfer is by nucleate boiling. Using theories of nucleate boiling with forced convection and film cooling, a method is developed to calculate the external boundary conditions in the submold region of the ingot, thus making it possible for the first time to define explicitly all of the thermal boundary conditions associated with this casting configuration. These theories are incorporated into the numerical model, and a subsequent simulation shows excellent agreement with experimental data from a third ingot.