An Evaluation of Simplified Models for Surface Kinetics in Movpe Processes

1988 ◽  
Vol 131 ◽  
Author(s):  
Max Tirtowidjojo ◽  
Richard Pollard
Keyword(s):  
Gas Flow ◽  
Equilibrium Constants ◽  
Operating Conditions ◽  
Surface Kinetics ◽  
Partial Pressures ◽  
Alternative Approach ◽  
Process Behavior ◽  
Parameter Values ◽  
Rate Limiting ◽  
Reactor Pressure

ABSTRACTA general MOVPE model has been used to assess the applicability of simplified representations for surface kinetics. With the general model, predictions for GaAs deposition on (111 )Ga using trimethylgallium and arsine show excellent agreement with observed growth rates. However, if Langmuir-Hinshelwood kinetics is assumed, the model only matches the deposition rates over a narrow range of operating conditions, even when several rate-limiting steps are included. This limitation arises because combinations of equilibrium constants and local partial pressures often do not give reasonable approximations for the surface concentrations of reactive intermediates. The form of the Langmuir-Hinshelwood relation(s) and the parameter values can be fitted empirically to experimental data, but this could lead to erroneous conclusions concerning process behavior and the model would have limited predictive capabilities. An alternative approach is to use surface reaction probabilities, but they can only be applied in an empirical fashion and their magnitudes depend on gas flow rate, inlet composition, and reactor pressure as well as surface temperature.

Modeling of a Fixed-Bed Reactor for the Production of Phthalic Anhydride

2011 ◽  
Vol 6 (1) ◽  
Author(s):  
Amir Rahimi ◽  
Sogand Hamidi
Keyword(s):  
Phthalic Anhydride ◽  
Fixed Bed ◽  
Tubular Reactor ◽  
Operating Conditions ◽  
Fixed Bed Reactor ◽  
Conversion Degree ◽  
Reactor Length ◽  
Reactor Temperature ◽  
Reported Data ◽  
Reactor Pressure

In this study, the performance of a fixed–bed tubular reactor for the production of phthalic anhydride is mathematically analyzed. The conversion degree and reactor temperature values are compared with the measured one in a tubular reactor applied in Farabi petrochemical unit in Iran as well as reported data in the literature for a pilot plate. The comparisons are satisfactory. The effects of some operating parameters including reactor length, feed temperature, reactor pressure, and existence of an inert in the catalytic bed are investigated. The optimum value of each parameter is determined on the basis of the corresponding operating conditions.

Break-Up of Threads From Laminar Open Channel Flow Influenced by Cross-Wind Gas Flow

2014 ◽  
Author(s):  
Jens Kamplade ◽  
Tobias Mack ◽  
Andre Küsters ◽  
Peter Walzel
Keyword(s):  
Size Distribution ◽  
Channel Flow ◽  
Gas Flow ◽  
Drop Size ◽  
Open Channel ◽  
Open Channel Flow ◽  
Drop Size Distribution ◽  
Operating Conditions ◽  
Breakup Process ◽  
Breakup Length

The breakup process of threads from laminar operating rotary atomizer (LamRot) is in the scope of this investigation. A similarity trail is used to investigate the influence of the thread deformation within a cross-wind flow on the thread breakup process. The threads emerge from laminar open channel flow while the liquid viscosity, the flow rate, the pipe inclination towards the gravity as well as the cross-wind velocity is varied. The breakup length and drop size distribution are analyzed by a back-light photography setup. The results thus obtained are compared with results of previous examination by Schröder [1] and Mescher [2]. It is found that the breakup length decreases and that the drop size grows with rising cross-wind intensity, while the width of the drop size distribution increases. At the same operating conditions, the breakup length for laminar open channel flow is smaller compared to completely filled capillaries. In contrast to this observation, the drop size distribution remains nearly unchanged. The critical velocity for the transition from axisymmetric to wind-induced thread breakup was found to be smaller than for completely filled capillaries.

scholarly journals Growth of GaN from elemental Gallium and Ammonia via Modified Sandwich Growth Technique

2004 ◽  
Vol 831 ◽  
Author(s):  
E. Berkman ◽  
R. Collazo ◽  
R. Schlesser ◽  
Z. Sitar
Keyword(s):  
Growth Rate ◽  
Gas Flow ◽  
Transport Model ◽  
Theoretical Calculations ◽  
Substrate Surface ◽  
Maximum Growth ◽  
Direct Reaction ◽  
Pure Nitrogen ◽  
Flow Rates ◽  
Reactor Pressure

ABSTRACTGallium nitride (GaN) films were grown on (0001) sapphire substrates at 1050°C by controlled evaporation of gallium (Ga) metal and reaction with ammonia (NH3) at a total reactor pressure of 800 Torr. Pure nitrogen (N2) was flowed directly above the molten Ga source to prevented direct reaction between the molten Ga and ammonia, which causes Ga spattering and GaN crust formation. At the same time, this substantially enhanced the Ga transport to the substrate. A simple mass-transport model based on total reactor pressure, gas flow rates and source temperature was developed and verified. The theoretical calculations and growth rate measurements at different ammonia flow rates and reactor pressures showed that the maximum growth rate was controlled by transport of both Ga species and reactive ammonia to the substrate surface.

Experimental Inverstigations On the Pressure Fluctuations in the Sealing Gap of Dry Gas Seals with Embedded Pressure Sensors

2021 ◽  
Author(s):  
Jingjing Luo ◽  
Dieter Brillert
Keyword(s):  
High Speed ◽  
Gas Flow ◽  
Static Pressure ◽  
Pressure Sensors ◽  
Operating Conditions ◽  
Test Facility ◽  
Experimental Investigations ◽  
Mechanical Seals ◽  
Process Gas ◽  
Sealing Gap

Abstract Dry gas lubricated non-contacting mechanical seals (DGS), most commonly found in centrifugal compressors, prevent the process gas flow into the atmosphere. Especially when high speed is combined with high pressure, DGS is the preferred choice over other sealing alternatives. In order to investigate the flow field in the sealing gap and to facilitate the numerical prediction of the seal performance, a dedicated test facility is developed to carry out the measurement of key parameters in the gas film. Gas in the sealing film varies according to the seal inlet pressure, and the thickness of gas film depends on this fluctuated pressure. In this paper, the test facility, measurement methods and the first results of static pressure measurements in the sealing gap of the DGS obtained in the described test facility are presented. An industry DGS with three-dimensional grooves on the surface of the rotating ring, where experimental investigations take place, is used. The static pressure in the gas film is measured, up to 20 bar and 8,100 rpm, by several high frequency ultraminiature pressure transducers embedded into the stationary ring. The experimental results are discussed and compared with the numerical model programmed in MATLAB, the characteristic and magnitude of which have a good agreement with the numerical simulations. It suggests the feasibility of measuring pressure profiles of the standard industry DGS under pressurized dynamic operating conditions without altering the key components of the seal and thereby affecting the seal performance.

Researches of technological mode of operation of gas wells with a single-lift elevator at a critical speed of upper flow

2021 ◽  
pp. 97-103
Author(s):  
R.A. Gasumov ◽  
◽  
E.R. Gasumov ◽  
Keyword(s):  
Gas Flow ◽  
Operating Conditions ◽  
Physical Parameters ◽  
Gas Wells ◽  
Gas Well ◽  
Field Development ◽  
Mode Of Operation ◽  
Water Drops ◽  
Liquid Flows ◽  
Technological Mode

The article discusses the modes of movement of gas-liquid flows in relation to the operating conditions of waterlogged gas wells at a late stage of field development. Algorithms have been developed for calculating gas well operation modes based on experimental work under conditions that reproduce the actual operating conditions of flooded wells of Cenomanian gas deposits. The concept of calculating the technological mode of operation of gas wells with a single-row elevator according to the critical velocity of the upward flow is considered based on the study of the equilibrium conditions of two oppositely directed forces: the gravity of water drops directed downward and the lifting force moving water drops with a gas flow directed upward. A calculation was made according to the method of the averaged physical parameters of formation water and natural gas in the conditions of flooded Cenomanian gas wells in Western Siberia. The results of a study of the dependence of the critical flow rate of Cenomanian wells on bottomhole pressure and diameter of elevator pipes are presented.

Influence of the Variation of Plasma Torch Parameters on Particle Melting and Solidification

1997 ◽  
Author(s):  
M. Vardelle ◽  
P. Fauchais ◽  
A. Vardelle ◽  
A.C. Léger
Keyword(s):  
Flow Rate ◽  
High Speed ◽  
Gas Flow ◽  
Operating Conditions ◽  
Characteristic Parameters ◽  
Powder Mass ◽  
Arc Current ◽  
Plasma Sprayed ◽  
Carrier Gas Flow ◽  
Melting And Solidification

Abstract A study of the flattening and cooling of particles plasma-sprayed on a substrate is presented. The characteristic parameters of the splats are linked to the parameters of the impacting particles by using an experimental device consisting of a phase Doppler particle analyzer and a high-speed pyrometer. However, during the long experiments required to get reliable correlations, it was observed that variations in plasma spray operating conditions may alter the particles behavior in the plasma jet. Therefore, a simple and easy-to-use system was developed to control in real time the spray jet. In this paper, the effect of carrier gas flow rate, arc current and powder mass flow rate is investigated. The results on zirconia and alumina powders show the capability of the technique to sense the particle spray position and width.

Mass Transfer Enhancement for CO2 Absorption in Structured Packed Absorption Column

2019 ◽  
Vol 41 (5) ◽  
pp. 820-820
Author(s):  
Pongayi Ponnusamy Selvi and Rajoo Baskar Pongayi Ponnusamy Selvi and Rajoo Baskar
Keyword(s):  
Mass Transfer ◽  
Transfer Coefficient ◽  
Mass Transfer Coefficient ◽  
Gas Flow ◽  
Aqueous Ammonia ◽  
Volume Flow Rate ◽  
Packed Column ◽  
Operating Conditions ◽  
Co2 Absorption ◽  
Absorption Column

The acidic gas, Carbon dioxide (CO2) absorption in aqueous ammonia solvent was carried as an example for industrial gaseous treatment. The packed column was provided with a novel structured BX-DX packing material. The overall mass transfer coefficient was calculated from the absorption efficiency of the various runs. Due to the high solubility of CO2, mass transfer was shown to be mainly controlled by gas side transfer rates. The effects of different operating parameters on KGav including CO2 partial pressure, total gas flow rates, volume flow rate of aqueous ammonia solution, aqueous ammonia concentration, and reaction temperature were investigated. For a particular system and operating conditions structured packing provides higher mass transfer coefficient than that of commercial random packing.

Investigation of the Flow Phenomenon Inside Gas Ejectors With Moist Gas Entrainment

2016 ◽  
Vol 9 (1) ◽  
Author(s):  
Yuping Wang ◽  
Mark Pellerin ◽  
Pravansu Mohanty ◽  
Subrata Sengupta
Keyword(s):  
Water Vapor ◽  
Phase Change ◽  
Gas Flow ◽  
Phase Distribution ◽  
Light Attenuation ◽  
Three Dimensional ◽  
Operating Conditions ◽  
Second Phase ◽  
Symmetric Model ◽  
Design And Optimization

This paper focuses on the gas flow study of an ejector used in applications where moist gases are being entrained. Two parts of work are presented. In the first part, characteristics of gas flow inside an ejector, as well as the ejector's performance under various operating and geometric configurations, were studied with a three-dimensional computational model. Measurements were also performed for validation of the model. In the second part, focus was given to the potential condensation or desublimation phenomena that may occur inside an ejector when water vapor is included in the entrained stream. Experiments using light-attenuation method were performed to verify the presence of a second phase; then, the onset of phase change and the phase distribution were obtained numerically. A two-dimensional axis-symmetric model was developed based on the model used in the first part. User-defined functions were used to implement the phase-change criteria and particle prediction. A series of simulations were performed with various amounts of water vapor added into the entrained flow. It was found that both frost particles and water condensate could form inside the mixing tube depending on the operating conditions and water vapor concentrations. When the concentration exceeds 3% by mass, water vapor could condense throughout the mixing tube. Some preliminary results of the second phase particles formed, e.g., critical sizes and distributions, were also obtained to assist with the design and optimization of gas ejectors used in similar applications.

Process Maps for Plasma Spray Part I: Plasma-Particle Interactions

2000 ◽  
Author(s):  
D.L. Gilmore ◽  
R.A. Neiser ◽  
Y. Wan ◽  
S. Sampath
Keyword(s):  
Plasma Spray ◽  
Gas Flow ◽  
Operating Conditions ◽  
Injection Velocity ◽  
Microstructural Development ◽  
Spray Parameters ◽  
Particle Interactions ◽  
Plasma Particle ◽  
Particle Injection ◽  
Process Maps

Abstract This is the first paper of a two part series based on an integrated study carried out at Sandia National Laboratories and the State University of New York at Stony Brook. The aim of the study is to develop a more fundamental understanding of plasma-particle interactions, droplet-substrate interactions, deposit formation dynamics and microstructural development as well as final deposit properties. The purpose is to create models that can be used to link processing to performance. Process maps have been developed for air plasma spray of molybdenum. Experimental work was done to investigate the importance of such spray parameters as gun current, auxiliary gas flow, and powder carrier gas flow. In-flight particle diameters, temperatures, and velocities were measured in various areas of the spray plume. Samples were produced for analysis of microstructures and properties. An empirical model was developed, relating the input parameters to the in-flight particle characteristics. Multi-dimensional numerical simulations of the plasma gas flow field and in-flight particles under different operating conditions were also performed. In addition to the parameters which were experimentally investigated, the effect of particle injection velocity was also considered. The simulation results were found to be in good general agreement with the experimental data.

scholarly journals Potential of Ceria-Zirconia-Based Materials in Carbon Soot Oxidation for Gasoline Particulate Filters

Catalysts ◽  
2020 ◽  
Vol 10 (7) ◽  
pp. 768
Author(s):  
Eleonora Aneggi ◽  
Alessandro Trovarelli
Keyword(s):  
Oxygen Vacancies ◽  
Mixed Oxides ◽  
Direct Injection ◽  
Soot Oxidation ◽  
Operating Conditions ◽  
Gasoline Direct Injection ◽  
Low Oxygen ◽  
Engine Exhaust ◽  
Partial Pressures ◽  
Carbon Soot

ZrO2 and Ce0.8Zr0.2O2 mixed oxides were prepared and tested in the oxidation of carbon soot at different oxygen partial pressures and degrees of catalyst/soot contact to investigate their activity under typical gasoline direct injection (GDI) operating conditions. Under reductive atmospheres, generation of oxygen vacancies occurs in Ce0.8Zr0.2O2, while no reduction is observed on ZrO2. Both materials can oxidize carbon under high oxygen partial pressures; however, at low oxygen partial pressures, the presence of carbon can contribute to the reduction of the catalyst and formation of oxygen vacancies, which can then be used for soot oxidation, increasing the overall performance. This mechanism is more efficient in Ce0.8Zr0.2O2 than ZrO2, and depends heavily on the interaction and the degree of contact between soot and catalyst. Thus, the ability to form oxygen vacancies at lower temperatures is particularly helpful to oxidize soot at low oxygen partial pressures, and with higher CO2 selectivity under conditions typically found in GDI engine exhaust gases.

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