Influence of variable viscosity on the onset of hydrothermal waves in thermocapillary liquid bridges

The float-zone crystal-growth process is investigated in the framework of t he half-zone model. The influence of a temperature-dependent viscosity on t he axisymmetric steady thermocapillary flow, and its stability with respect to nonaxisymmetric perturbations is examined by means of a linear-stabilit y analysis. The onset of oscillatory convection is studied numerically by a mixed Chebyshev-collocation finite-difference method. Detailed calculation s have been carried out for Pr = 4 and unit aspect ratio. It is found that the temperature-dependent viscosity decreases the critical Reynolds number for the onset of three-dimensional flour. Since the threshold shift is a fu nction of the azimuthal wavenumber of the neutral mode, the critical mode m ay depend on the magnitude of the viscosity variation. MSC (1991): 76D45, 7 6E15, 76R99.