A model approach for a modification of the effective heat conductivity in the turbulent melt flow simulation for 28" Si CZ crucibles is presented, which helped to overcome deficiencies in the growth interface shape prediction for industrial 300 mm Si CZ growth. The model has been incorporated into a CZ simulation tool based on the simulation software codes FEMAG for the global heat transfer and CFD-ACE for the turbulent melt flow simulation. The model predictions are compared to results from 300 mm Si CZ growth experiments with 200 kg charge weight in 28" crucibles in a growth parameter range covered by standard industrial processes. The model is an engineering approach. Nevertheless, some physical background is briefly discussed on a phenomenological basis, including results of recent model experiments. (C) 2004 Elsevier B.V. All rights reserved.