A 3-DIMENSIONAL ANALYSIS OF THE FLOW AND HEAT-TRANSFER FOR THE MODIFIED CHEMICAL VAPOR-DEPOSITION PROCESS INCLUDING BUOYANCY, VARIABLE PROPERTIES, AND TUBE ROTATION

A study has been made of the heat transfer, flow, and particle deposition relative to the modified chemical vapor deposition (MCVD) process. The effects of variable properties, buoyancy, and tube rotation have been included in the study. The resulting three-dimensional temperature and velocity fields have been obtained for a range of conditions. The effects of buoyancy result in asymmetric temperature and axial velocity profiles with respect to the tube axis. Variable properties cause significant variations in the axial velocity along the tube and in the secondary flow in the region near the torch. Particle trajectories are shown to be strongly dependent on the tube rotation and are helices for large rotational speeds. The component of secondary flow in the radial direction is compared to the thermophoretic velocity, which is the primary cause of particle deposition in the MCVD process. Over the central portion of the tube the radial component of the secondary flow is most important in determining the motion of the particles.