  The heat transfer (conductive, convective, radiative) and the related
problems (the unknown phase boundary fluid/crystal, the assessment of the
quality of the grown crystals) encountered in the melt and vapour growth of
single crystal as well as the corresponding macroscopic models are reviewed.
The importance of the adequate description of the optical crystal properties
(semitransparency, absorption, scattering, refraction, diffuse and specular
reflecting surfaces) and their effect on the heat transfer is stressed. The
problems of the code verification and validation are discussed; differences
between the crystal growth simulation codes intended for the research and for
the industrial applications are indicated.
