Numerical Simulation Of Chemical Vapor Deposition Of Carbon On Graphite

Author : Himel Barua
Publisher :
ISBN 13 :
Total Pages : 152 pages
Book Rating : 4.:/5 (18 download)

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Download or read book Computational Modeling of Chemical Vapor Deposition written by Himel Barua and published by . This book was released on 2016 with total page 152 pages. Available in PDF, EPUB and Kindle. Book excerpt: The primary objective of this study is to obtain the rate of Carbon deposition by chemical vapor deposition (CVD) process for material samples hanged in CVD reactor. The samples include net of bundles of fibers, semi-opened channel cut through rectangular sample and sample with circular holes. Momentum, continuity and transport equations for chemical species within gas phase and surface reactions have been solved numerically. For numerical solution by finite-volume method ANSYS FLUENT software and for geometric modeling and finite-volume meshing ANSYS Workbench software have been used. For numerical study two approaches have been taken. The first approach is a single-step solution where the flow field in reactor including flow field near and inside the sample have been resolved simultaneously. The second approach is a two-step solution, where the model has been divided into reactor-scale model and sample-scale model, where for each one a separate numerical mesh has been generated and a corresponding set of numerical parameters has been optimized separately for each model. The former process is a straightforward one that is applicable to a sample of any linear scale; however, the approach is computationally expensive relative to the latter one. The latter approach assumes that the scale of sample is small compared to the reactor scale and the two CFD models are solved sequentially. Results obtained by one-step and two-steps approaches are similar in terms of obtained CVD rates with some discrepancy caused by use of different numerical meshes and because in the latter model there is no feedback on the reactor flow field by the sample. For fibrous samples, CVD rates are obtained at the range of volume fractions. Obtained CVD rates are near-uniform along the fiber circumference and mostly sensitive to temperature field in reactor. For rectangular model with channel samples, the CVD rate is obtained at vertical orientations of the sample along the reactor axis for suspended sample with circular holes, CVD rates are obtained along the length of the hole. Near both entrances of each circular hole, vortices are generated which block the flow entering inside the hole. Because of diminished flowrate and corresponding advection inside the hole, C deposition is lowest at the center of the hole. In terms of effect on deposition, C2H2 and CH4 plays more significant role than other species. As C2H2 directly participates in surface reactions, higher concentration of C2H2 assures higher growth rate of C. CH4 in one of the primary species with largest initial mass fraction, participates in gas-phase reactions and is responsible for production of other intermediate gas species. Higher depletion of CH4 assures higher production of C2H2 and corresponding higher C deposition. This observation is similar for all the substrates.