The effect of natural convection on solidification in tall tapered feeders

Abstract

Tall tapered feeders (TTFs) are used in foundry casting to supply additional molten metal to a casting, in order to overcome problems associated with shrinkage upon freezing. Due to the shape and volume of TTFs, natural convection may play a significant role in heat transfer and hence affect the progress of the solidification front. A computational model of heat transfer and fluid flow in a TTF, incorporating natural convection, is presented. The heat equation is solved in terms of temperature, rather than enthalpy. Latent heat is incorporated by an ``apparent capacity'' formulation. An iterative scheme is used to calculate the latent heat effect using the liquid fraction. Flow in the mushy zone is represented by a Darcy-like resistance term and the Navier-Stokes equations are solved using a modified operator splitting method. The approach yields an accurate solution for both flow and temperature fields. The results confirm that solidification progress is affected by convection at early times, after which conduction dominates.