A simplified analytical model of diamond growth in direct current arcjet reactors

1995 ◽  
Vol 10 (8) ◽  
pp. 1993-2010 ◽  
Author(s):  
David S. Dandy ◽  
Michael E. Coltrin
Keyword(s):  
Direct Current ◽  
Defect Density ◽  
Chemical Vapor ◽  
Quantitative Agreement ◽  
Chemical Kinetic ◽  
Operating Conditions ◽  
Diamond Growth ◽  
Simplified Model ◽  
Flow Models ◽  
Wide Range

A simplified model of a direct current arcjet-assisted diamond chemical vapor deposition reactor is presented. The model is based upon detailed theoretical analysis of the transport and chemical processes occurring during diamond deposition, and is formulated to yield closed-form solutions for diamond growth rate, defect density, and heat flux to the substrate. In a direct current arcjet reactor there is a natural division of the physical system into four characteristic domains: plasma torch, free stream, boundary layer, and surface, leading to the development of simplified thermodynamic, transport, and chemical kinetic models for each of the four regions. The models for these four regions are linked to form a single unified model. For a relatively wide range of reactor operating conditions, this simplified model yields results that are in good quantitative agreement with stagnation flow models containing detailed multicomponent transport and chemical kinetics. However, in contrast to the detailed reactor models, the model presented here executes in near real-time on a computer of modest size, and can therefore be readily incorporated into process control models or global dynamic loop simulations.

scholarly journals Direct Synthesis of Oxynitride Nanowires through Atmospheric Pressure Chemical Vapor Deposition

Nanomaterials ◽  
2020 ◽  
Vol 10 (12) ◽  
pp. 2507
Author(s):  
Babak Adeli ◽  
Fariborz Taghipour
Keyword(s):  
Solid Solution ◽  
Vapor Deposition ◽  
Atmospheric Pressure ◽  
Wide Spectrum ◽  
Direct Synthesis ◽  
Chemical Vapor ◽  
Building Blocks ◽  
Operating Conditions ◽  
Wide Range ◽  
Pressure Chemical

Binary and ternary oxynitride solid alloys were studied extensively in the past decade due to their wide spectrum of applications, as well as their peculiar characteristics when compared to their bulk counterparts. Direct bottom-up synthesis of one-dimensional oxynitrides through solution-based routes cannot be realized because nitridation strategies are limited to high-temperature solid-state ammonolysis. Further, the facile fabrication of oxynitride thin films through vapor phase strategies has remained extremely challenging due to the low vapor pressure of gaseous building blocks at atmospheric pressure. Here, we present a direct and scalable catalytic vapor–liquid–solid epitaxy (VLSE) route for the fabrication of oxynitride solid solution nanowires from their oxide precursors through enhancing the local mass transfer flux of vapor deposition. For the model oxynitride material, we investigated the fabrication of gallium nitride and zinc oxide oxynitride solid solution (GaN:ZnO) thin film. GaN:ZnO nanowires were synthesized directly at atmospheric pressure, unlike the methods reported in the literature, which involved multiple-step processing and/or vacuum operating conditions. Moreover, the dimensions (i.e., diameters and length) of the synthesized nanowires were tailored within a wide range.

Development of a Semi-Implicit Solver for Detailed Chemistry in I.C. Engine Simulations

2005 ◽  
Author(s):  
Long Liang ◽  
Chulhwa Jung ◽  
Song-Charng Kong ◽  
Rolf D. Reitz
Keyword(s):  
Chemical Kinetic ◽  
Rate Of Change ◽  
Operating Conditions ◽  
Explicit Methods ◽  
Implicit Methods ◽  
Specific Internal Energy ◽  
Detailed Chemistry ◽  
Key Species ◽  
Wide Range ◽  
Implicit Solver

An efficient semi-implicit numerical method is developed for solving the detailed chemical kinetic source terms in I.C. engine simulations. The detailed chemistry system is a group of coupled extremely stiff O.D.E.s, which presents a very stringent timestep limitation when solved by standard explicit methods, and is computationally expensive when solved by iterative implicit methods. The present numerical solver uses a stiffly-stable noniterative semi-implicit method, in which the numerical solution to the stiff O.D.E.s never blows up for arbitrary large timestep. The formulation of numerical integration exploits the physical requirement that the species density and specific internal energy in the computational cells must be nonnegative, so that the Lipschitz timestep constraint is not present [1,2], and the computation timestep can be orders of magnitude larger than that possible in standard explicit methods and can be formulated to be of high formal order of accuracy. The solver exploits the characteristics of the stiffness of the O.D.E.s by using a sequential sort algorithm that ranks an approximation to the dominant eigenvalues of the system to achieve maximum accuracy. Subcycling within the chemistry solver routine is applied for each computational cell in engine simulations, where the subcycle timestep is dynamically determined by monitoring the rate of change of concentration of key species which have short characteristic time scales and are also important to the chemical heat release. The chemistry solver is applied in the KIVA-3V code to diesel engine simulations. Results are compared with those using the CHEMKIN package which uses the VODE implicit solver. Very good agreement was achieved for a wide range of engine operating conditions, and 40∼70% CPU time savings were achieved by the present solver compared to CHEMKIN.

Ethanol Mechanism Reduction Based on DRGEPSA Method at Various Operating Ranges

2020 ◽  
Author(s):  
Shrabanti Roy ◽  
Omid Askari
Keyword(s):  
Sensitivity Analysis ◽  
Error Propagation ◽  
Cfd Simulation ◽  
Reduction Process ◽  
Chemical Kinetic ◽  
Operating Conditions ◽  
Computational Time ◽  
Wide Range ◽  
Relation Graph ◽  
Future Work

Abstract Reducing the size of a detail chemical kinetic is necessary in the prospect of numerical computation. In this work a skeleton reduction is done on a detail mechanism of ethanol. The detailed ethanol mechanism used here is developed through reaction mechanism generator (RMG). The generated mechanism is validated at wide range of engine relevant operating conditions using laminar burning speed (LBS), ignition delay time (IDT) and species mole fraction calculation at different reactor conditions. This detail mechanism consists of 67 species and 1031 reactions. Though the mechanism is in a very good agreement at various operating ranges with experimental data, it is costly to use a detail mechanism for 3D computational fluid dynamics (CFD) analysis. To make the mechanism applicable for CFD simulation further reduction of species and reactions is essential. In this work a skeleton mechanism is generated using directed relation graph technique with error propagation and sensitivity analysis (DRGEPSA). The DRGEPSA method, works based on error calculation at user defined condition. This technique is a combination of two methods, directed relation graph with error propagation (DRGEP) and directed relation graph with sensitivity analysis (DRGASA). To ensure the wide range of applicability of the skeleton mechanism, IDT is calculated at temperature, pressure, and equivalence ratio ranges from 700–2000 K, 1–40 atm and 0.6–1.4 respectively. A 10% error estimation is considered during the process. Initially DRGEP is applied on the detail mechanism to eliminate unimportant species. Further, sensitivity analysis helps to identify and reduce more unimportant species from the mechanism. Reactions related to the deleted species are automatically removed from the mechanism in each step. The final skeleton mechanism has 42 species and 464 reactions. This skeleton mechanism is validated and compared with different IDT data for the conditions not used in reduction technique. Results of LBS and different species concentration from reactor conditions is considered for validation. The skeleton mechanism can reduce computational time by 35% for LBS and 25% for IDT calculation. For future work, this skeleton mechanism will be considered in optimum reduction process.

Comparative Analysis of Chemical Kinetic Models Using the Alternate Species Elimination Approach

2014 ◽  
Vol 137 (2) ◽  
Author(s):  
Nathan D. Peters ◽  
Ben Akih-Kumgeh ◽  
Jeffrey M. Bergthorson
Keyword(s):  
Kinetic Models ◽  
Chemical Species ◽  
Predictive Performance ◽  
Chemical Kinetic ◽  
Operating Conditions ◽  
Prediction Ability ◽  
Combustion Properties ◽  
Wide Range ◽  
Depth Analysis ◽  
Syngas Combustion

A major thrust in combustion research is the development of chemical kinetic models for computational analysis of various combustion processes. Significant deviations can be seen when comparing predictions of these models against experimentally determined combustion properties over a wide range of operating conditions and mixture strengths. However, these deviations vary from one model to another. It would be insightful in such circumstances to elucidate the species and subchemistry models which lead to the varying prediction ability in various models. In this work, we apply the alternate species elimination (ASE) method to selected mechanisms in order to analyze their predictive ability with respect to propane and syngas combustion. ASE is applied to a homogeneous reactor undergoing ignition. The ranked species of each model are compared based on their normalized changes. We further provide skeletal versions of the various models for propane and syngas combustion analysis. It is observed that this approach provides an easy way to determine the chemical species which are central to the predictive performance of a model in their order of importance. It also provides a direct way to compare the relative importance of chemical species in the models under consideration. Further development and in-depth analysis could provide more information and guidance for model improvement.

Comparative Analysis of Chemical Kinetic Models Using the Alternate Species Elimination (ASE) Approach

2014 ◽  
Author(s):  
Nathan D. Peters ◽  
Ben Akih-Kumgeh ◽  
Jeffrey M. Bergthorson
Keyword(s):  
Kinetic Models ◽  
Chemical Species ◽  
Predictive Performance ◽  
Chemical Kinetic ◽  
Operating Conditions ◽  
Prediction Ability ◽  
Combustion Properties ◽  
Wide Range ◽  
Depth Analysis ◽  
Syngas Combustion

A major thrust in combustion research is the development of chemical kinetic models for computational analysis of various combustion processes. Significant deviations can be seen when comparing predictions of these models against experimentally determined combustion properties over a wide range of operating conditions and mixture strengths. However, these deviations vary from one model to another. It would be insightful in such circumstances to elucidate the species and sub chemistry models which lead to the varying prediction ability in various models. In this work we apply the Alternate Species Elimination (ASE) method to selected mechanisms in order to analyze their predictive ability with respect to propane and syngas combustion. ASE is applied to a homogeneous reactor undergoing ignition. The ranked species of each model are compared based on their Normalized Change. We further provide skeletal versions of the various models for propane and syngas combustion analysis. It is observed that this approach provides an easy way to determine the chemical species which are central to predictive performance of a model in their order of importance. It also provides a direct way to compare the relative importance of chemical species in the models under consideration. Further development and in-depth analysis could provide more information and guidance for model improvement.

Control of Thin Film Growth in Chemical Vapor Deposition Manufacturing Systems: A Feasibility Study

2002 ◽  
Vol 124 (3) ◽  
pp. 715-724 ◽  
Author(s):  
Wilson K. S. Chiu ◽  
Yogesh Jaluria ◽  
Nick G. Glumac
Keyword(s):  
Thin Film ◽  
Chemical Vapor Deposition ◽  
Vapor Deposition ◽  
Design Space ◽  
Chemical Vapor ◽  
Film Deposition ◽  
Operating Conditions ◽  
Design And Optimization ◽  
Wide Range ◽  
Computer Aided

A study is carried out to design and optimize Chemical Vapor Deposition (CVD) systems for material fabrication. Design and optimization of the CVD process is necessary to satisfying strong global demand and ever increasing quality requirements for thin film production. Advantages of computer aided optimization include high design turnaround time, flexibility to explore a larger design space and the development and adaptation of automation techniques for design and optimization. A CVD reactor consisting of a vertical impinging jet at atmospheric pressure, for growing titanium nitride films, is studied for thin film deposition. Numerical modeling and simulation are used to determine the rate of deposition and film uniformity over a wide range of design variables and operating conditions. These results are used for system design and optimization. The optimization procedure employs an objective function characterizing film quality, productivity and operational costs based on reactor gas flow rate, susceptor temperature and precursor concentration. Parameter space mappings are used to determine the design space, while a minimization algorithm, such as the steepest descent method, is used to determine optimal operating conditions for the system. The main features of computer aided design and optimization, using these techniques, are discussed in detail.

Parameterization of Battery Electrothermal Models Coupled With Finite Element Flow Models for Cooling

2017 ◽  
Vol 139 (7) ◽  
Author(s):  
Nassim A. Samad ◽  
Boyun Wang ◽  
Jason B. Siegel ◽  
Anna G. Stefanopoulou
Keyword(s):  
Finite Element ◽  
Equivalent Circuit Model ◽  
Element Model ◽  
Operating Conditions ◽  
Complex Geometries ◽  
Flow Models ◽  
Cooling Channels ◽  
Temperature State ◽  
Wide Range ◽  
Battery Packs

Developing and parameterizing models that accurately predict the battery voltage and temperature in a vehicle battery pack are challenging due to the complex geometries of the airflow that influence the convective heat transfer. This paper addresses the difficulty in parameterizing low-order models which rely on coupling with finite element simulations. First, we propose a methodology to couple the parameterization of an equivalent circuit model (ECM) for both the electrical and thermal battery behavior with a finite element model (FEM) for the parameterization of the convective cooling of the airflow. In air-cooled battery packs with complex geometries and cooling channels, an FEM can provide the physics basis for the parameterization of the ECM that might have different convective coefficients between the cells depending on the airflow patterns. The second major contribution of this work includes validation of the ECM against the data collected from a three-cell fixture that emulates a segment of the pack with relevant cooling conditions for a hybrid vehicle. The validation is performed using an array of thin film temperature sensors covering the surface of the cell. Experiments with pulsing currents and drive cycles are used for validation over a wide range of operating conditions (ambient temperature, state of charge, current amplitude, and pulse width).

An Analytical Examination of the Partial Oxidation of Rich Mixtures of Methane and Oxygen

1992 ◽  
Vol 114 (2) ◽  
pp. 152-157 ◽  
Author(s):  
G. A. Karim ◽  
A. S. Hanafi
Keyword(s):  
Partial Oxidation ◽  
Equivalence Ratio ◽  
Kinetic Scheme ◽  
Reaction Rates ◽  
Chemical Kinetic ◽  
Operating Conditions ◽  
Wide Range ◽  
Rich Mixtures ◽  
Detailed Chemical

The uncatalyzed partial oxidation of rich mixtures of methane and oxygen is examined analytically, primarily with the view of hydrogen and/or synthesis gas (hydrogen plus carbon monoxide) production while employing a detailed chemical kinetic scheme of 108 simultaneous reactions and 28 species. The role of various operating conditions in establishing the yield of hydrogen and other products, the corresponding ignition delay periods and reaction rates is examined over a wide range of temperature, equivalence ratio and pressure. Correlations in terms of simple overall Arrhenius expressions are also provided.

Cathodoluminescence of Catalyst Crystallites

1982 ◽  
Vol 40 ◽  
pp. 664-665
Author(s):  
E.D. Boyes ◽  
P.L. Gai ◽  
D.B. Darby ◽  
C. Warwick
Keyword(s):  
Defect Density ◽  
Chemical Properties ◽  
Operating Conditions ◽  
Semiconductor Materials ◽  
Environmental Cell ◽  
High Resolution Structure ◽  
Commercially Important ◽  
Crystallographic Defects ◽  
Resolution Structure

The extended crystallographic defects introduced into some oxide catalysts under operating conditions may be a consequence and accommodation of the changes produced by the catalytic activity, rather than always being the origin of the reactivity. Operation without such defects has been established for the commercially important tellurium molybdate system. in addition it is clear that the point defect density and the electronic structure can both have a significant influence on the chemical properties and hence on the effectiveness (activity and selectivity) of the material as a catalyst. SEM/probe techniques more commonly applied to semiconductor materials, have been investigated to supplement the information obtained from in-situ environmental cell HVEM, ultra-high resolution structure imaging and more conventional AEM and EPMA chemical microanalysis.

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