The paper presents results of numerical simulation of convective flows which exist in Ge and Si melts while growing crystals in Czochralski configuration in a rotating heat field of second order axial symmetry (L-2) The numerical simulation is based on the solution of non-stationary three-dimensional Navier-Stokes equations acid heat-transfer equations in Boussinesq approximation. The results showed that heat field rotation makes possible an efficient mixing of molten material without any mechanical tools. Trajectories of closed toroidal flows having the azimuthal component of velocity vector have been simulated in the milt. We demonstrate a novel heating concept provided by a contact-fret: control over heat-mass transfer processes in a medium of crystallization.