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Chemkin 4.1.1 Chapter 5: Chemical Mechanism Analysis One must supply a diffusion coefficient in Equation 5-2 to evaluate Da. To do this, THE Mechanism Analyzer requires the user to name a “major species” and a “carrier gas species.” Through internal calls to the TRANSPORT Subroutine Library, CHEMKIN evaluates the binary diffusion coefficient between these two species at the specified bath temperature and pressure. The user may also specify the length scale L. The default value for L is 1 cm. For each gas-phase reaction, a report is generated of k * and Da for the forward and reverse directions. In some cases, the input CHEMKIN reaction mechanism specifies the reaction to be irreversible. In these cases, the quantities k * and Da are still calculated for the reverse direction, but the numbers are enclosed in square brackets [ ] to flag these reactions as not being part of the mechanism. A uniform-dimensional rate constant of Equation 5-1 is also calculated for surface * reactions. In this case, k has units of mole • cm -2 •sec -1 f . Thus, one can make a comparison between reaction rates for surface reactions. The surface Damköhler number is defined to be Equation 5-3 Da = k f * -------------------- DG [ ] ⁄ L The equation for the surface Damköhler number differs from the equation for the gasphase Damköhler number by a factor of the length scale L. As before, it provides a measure of the relative speed of the surface reaction rate versus the molecular mass transport rate. 5.1.2 Reaction Mechanism for Diamond CVD 5.1.2.1 Project Description This user tutorial demonstrates the use of the Mechanism Analyzer model to extract a wider variety of detailed thermodynamic, chemical kinetic, and transport data from a CHEMKIN reaction mechanism. The chemistry set nominally describes a diamond CVD process and is a subset of a published mechanism, 42 but one that has now been superseded by the authors. 43 The reactions in this example, especially the surface reactions, have been contrived to demonstrate the capabilities of the Mechanism Analyzer and should not be used as a source of kinetic data for diamond deposition. 42.“Analysis of diamond growth in subatmospheric dc plasma-gun reactors.” Michael E. Coltrin and David S. Dandy, Journal of Applied Physics, 74(#9):5803 (1993). © 2007 Reaction Design 164 RD0411-C20-000-001
Chapter 5: Chemical Mechanism Analysis <strong>Tutorials</strong> <strong>Manual</strong> 5.1.2.2 Project Setup The project file is called mechanism_analyzer__diamond_cvd.ckprj. The data files used for this sample are located in the samples\mechanism_analyzer\diamond_cvd directory. This reactor diagram contains only the Mechanism Analyzer. Section 5.1.2.3 illustrates which sections of the output result from which choices on the input panels, so only brief usage instructions are provided here. The Output Control tab of the Output Control panel contains a number of selections that determine the kinds of information that will be put into the output file and XML Solution File (XMLdata.zip). At the top of the Output Control tab, there is a choice to turn All Tables On or Off. Turning All Tables On will result in a very large output file, so this is generally not recommended, except for the smallest reaction mechanisms. The usage of these controls is as follows. To obtain All output of a certain type, turn it On at the highest level. To limit the output of a certain type to specific species or reactions, turn it Off at the higher level(s), then On for the class (gas, surface or bulk) of species/reactions or by listing the specific species/reactions of interest. As an illustration of how to use the levels of choices to specify data types, consider the case of thermodynamic data tables. There are two types of data tables available: summary tables which are given at the bath gas conditions, and detailed tables which cover a range of temperatures. In this example, the Summary Thermo Tables are turned Off in general, but then back On for Species, but not for Reactions. Turning All Summary Thermo Tables On is equivalent to checking all three boxes, but is simpler. In the case of the more detailed Species Thermo Tables, they are turned Off in general, and On for the Bulk species only. In addition, on the Species-specific Data panel, Species Thermo Tables are specified for two gas phase species, CH 3 and CH 4 , plus two surface species, CH2(S) and CH(S). The results of these selections are shown in Section 5.1.2.3. For reaction information, most of the output types are turned On at the general level, so there are no entries on the Reaction-specific Data tab of the Output Control panel. The C1_ Mechanism Analyzer panel allows specification of the physically based parameters that affect the output file. The Reactor Physical Property tab allows the user to override the default values for pressure and temperature of the bath gas, as well as the ranges used for the thermodynamics and kinetics tables. The Speciesspecific Data tab allows specification of the composition of the bath gas, as well as overriding the default definitions for the carrier gas and major species. No entries are made on the Cluster Properties, Solver, or Continuations panels for this problem. 43.The authors now prefer the mechanism in: “A simplified analytical model of diamond growth in direct current arcjet reactors.” David S. Dandy and Michael E. Coltrin, Journal of Materials Research, 10(#8):1993 (1995). Private communication, M. E. Coltrin, Feb. 1998. RD0411-C20-000-001 165 © 2007 Reaction Design
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Chemkin 4.1.1 Contents Table of Con
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Tutorials Manual 4.1.1 Figures List
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Chemkin 4.1.1 1 1 Introduction The
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Chemkin 4.1.1 2 2 Combustion in Gas
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Chapter 2: Combustion in Gas-phase
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Chemkin 4.1.1 3 3 Catalytic Process
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