We apply numerical simulation to analyze flow structure and physical properties of sapphire melt during Kyropoulos crystal growth. The Direct Numerical Simulation (DNS) approach was used to investigate 3D features of melt convection in a lab-scale furnace. The importance to account for the effect of internal radiation inside sapphire melt is discussed. For different sets of material properties, we have investigated the effect of the Marangoni and buoyancy driving forces on the melt flow. Results of 3D unsteady modeling are discussed in detail and compared with related experimental data. (C) 2015 Elsevier Ltd. All rights reserved.