Convective flow structure in a growth ampoule

The hydrodynamic aspects of physical vapor transport processes in growth ampoules are considered experimentally. The apparatus consists of a horizontal cylinder filled with air and subjected to a constant horizontal temperature gradient. The apparatus is made transparent by using a glass cylinder coated with a thin film of SnO₂ which is used as a heater by passing a constant electrical current through it. The cylinder has inside diameter D=18.3 mm and length L=90mm. The Rayleigh number is varied between 444 and 1425. A Laser-Doppler anemometer is used to obtain the velocity field along the axis and various diameters of the cylinder. The 3-D convective structure obtained by flow visualisation and confirmed by velocity measurements is illustrated. The influence of the boundary conditions on the flow structure is examined and experimental results are compared to 2-D computations.