Analysis of transport phenomena in the coating of fibers by CVD

Inorganic coated fibers produced bychemical vapor deposition find several tecl~nological applications. In this CVD process, a fiber core is mounted in a. react,or between two e1ect.rodes. Reactive gases flow over the substrate and react. near or on the fiber surface to form the desired coating. Experience has sl~o\vn that quality deposition can only be obtained over a. small range of the governing parameters: t,hese parameters are, however, difficult to control. In the present study, a mathematical model is developed for the reactor configuration under consideration. The different mass and energy transport lnechanisin are compared and their influence on the reactor performance is evaluated for horizontal reactor arrangements. Numerical results, showing sharp temperature and concentration gradient close t,o the fiber surface, suggest that heat and mass transfer in this region are controlled by conduction and diffusion mechanisnls. In the bulk region, heat, and mass transfer via the convection and conduction/diffusion ~nechanisms can be of equal inlportance. Numerical results show how bulk properties are affected by both transversal and longitudinal rolls.