Chmt;ca/ Eng ine e ring Sc ie nc e , zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA Vol. 45. No. 8. pp. 2543-2550. 1990. 0009-2509190 $3.00 + 0.00 Printed m Great Bntain 0 1990 Pergamon Press plc zyxwvut CVD REACTORS FOR THE SYNTHESIS OF INORGANIC FIBERS. zyxwvutsrqponmlkjihgfedc MODELING AND zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFE EXPERIMENTAL EVACUATION Jan H. Scholtz, Jorge E. Gatica, Hendrik J. Viljoen, Vithal Revankar and Vladimir Hlavacek Laboratory for Ceramic and Reaction Engineering Department of Chemical Engineering State University of New York at Buffalo Buffalo, New York 14260 USA ABSTRACT In this work the application of CVD technologies for coating of fibrous substrates is addressed. The transport phenomena occurring in the reactor chamber are modeled in terms of conservation laws. The resulting mathematical model is solved by means of the GFEM. Two- and preliminary three- dimensional results are reported in the actual range of experimental conditions. Based on boundary layer assumptions for the gas phase, a one-dimensional “moving boundary” model for the deposition surface is formulated. Characteristics of fibers manufactured in the laboratory are presented and model predictions are analyzed. Several design and operation problems are pinpointed and further modeling studies are outlined. KEYWORDS CVD, natural convection, fibers, modeling, numerical simulation INTRODUCTION In the last years Chemical Vapor Deposition (CVD) has been gaining in popularity, becoming a widely used process in modern technology (Blocher, 1981). Its wide range of applications includes from the manufacture of semiconductor devices (Jensen, 1987) to the production, coating and infiltration of structural fibers and composite materials (DiCarlo. 1985). Despite its widespread and routine application, the level of understanding on the interaction between the fluid dynamics of the process and the mass and energy transfer phenomena was rather limited until recent scientific contributions were published. A CVD system is simply a chemical reactor. As such, flow rates and flow patterns of reactant vapors along with substrate temperature must be carefully controlled if uniform film layers are to be obtained. Certainly, the reactor design plays a decisive role on the properties of the materials deposited. The control an&or elimination of recirculating gas patterns over the substrate as well as the improvement in the species transport to the reaction surface are essential goals pursued when designing the chambers to carry out CVD processes. In simple geometries, as the horizontal planar channel reactor, one way to attain an homogeneous distribution of the reactant concentration gradients has been to tilt the susceptor in order to obtain a constant mass transfer driving force. In vertical reactors used in the microelectronic industry the substrate is commonly rotated to expose the substrate wafer uniformly to the reacting gas stream. In more complex configurations, or applications other than microelectronics, the alternatives are not so apparent. Among the advantages exhibited by CVD technology for the coating of fibrous substrates its flexibility and potential for scale-up are the most important. Certainly, this process is suitable for scale-up to the production of long inorganic fibers. The process can be conbgurated for batch as well as continuous operation and both hot and cold wall reactor conflgurations can be used. 2543