Some model problems in the laser enhanced MCVD process

Combined free and forced laminar convection in horizontal and vertical tubes with external and volumetric heating were investigated. A continuum model of a two phase flow of submicron aerosol particles and a background gas is considered. An attempt is made to increase the deposition efficiency of the aerosol particles produced by the Modified Chemical Vapor Deposition (MCVD) process in the manufacture of optical fiber preforms. It is indicated that laser heating can significantly modify temperature gradients and the thermophoretic deposition of aerosol particles in the temperature field. In the vertical tube cases, buoyant heating plays a significant role in its effect on particle trajectories. Results using the Boussinesq approximation deviate significantly from those using the perfect gas law, even when laser heating is small. Such analysis may have an important bearing on methods employed in the fabrication of optical fiber preforms.