Optimal Design of Stagnation-Flow MOVPE Reactors with Axisymmetric Multi-Aperture Inlets

1997 ◽  
Vol 490 ◽  
Author(s):  
V. Gupta ◽  
C. Theodoropoulos ◽  
J. D. Peck ◽  
T. J. Mountziaris
Keyword(s):  
Optimal Design ◽  
Film Thickness ◽  
Contact Time ◽  
Transport Model ◽  
Arrival Rate ◽  
Operating Conditions ◽  
Stagnation Flow ◽  
Time Operation ◽  
Reactor Height ◽  
Selection Of

ABSTRACTAn approach for optimal design of vertical stagnation flow Metalorganic Vapor Phase Epitaxy (MOVPE) reactors that minimizes parasitic pre-reactions between the film precursors is presented. The use of axisymmetric multi-aperture inlets (e.g. tube-in-tube or concentric-ring inlets) enables the separation of incompatible precursors, while preserving the axial symmetry of the reactor. A careful selection of the inlet velocity of each stream and the distance between the inlet and the susceptor (reactor height) can lead to complete mixing just above the substrate, while keeping the contact time between the precursors in the gas phase low enough to suppress pre-reactions. This idea has been used by our group for growing high quality ZnSe films on GaAs substrates from (CH3)2Zn:N(C2H5)3 and H2Se diluted in H2 in a stagnation flow MOVPE reactor with an axisymmetric split inlet. A transport model describing the MOVPE of ZnSe, for conditions at which the growth rate is limited by the precursors' arrival rate at the surface, has been developed. A parametric study was performed aiming at identifying operating conditions in industrial-scale reactors that maximize film thickness uniformity while minimizing precursor contact time. Operation atGr/Re2<100 eliminated flow recirculations in the region above the substrate. Such recirculations may lead to formation of particulates by trapping reactants. Optimal conditions correspond to equal velocities of the inlet streams, satisfying the above criterion, and to the minimum possible reactor height leading to uniform film thickness across the substrate.

Optimal Design of Reactors for Metalorganic Vapor Phase Epitaxy of Group III Nitrides

2000 ◽  
Vol 616 ◽  
Author(s):  
R. P. Pawlowski ◽  
C. Theodoropoulos ◽  
T.J. Mountziaris ◽  
H.K. Moffat ◽  
J. Han ◽  
...  
Keyword(s):  
Optimal Design ◽  
Vapor Phase ◽  
Rotating Disk ◽  
Group Iii Nitrides ◽  
Metalorganic Vapor Phase Epitaxy ◽  
Vapor Phase Epitaxy ◽  
Operating Conditions ◽  
Industrial Scale ◽  
Stagnation Flow ◽  
Group Iii

AbstractMetalorganic Vapor Phase Epitaxy (MOVPE) has emerged as the technique of choice for growing thin films and structures of group III-nitrides. The objective of this work is to address the optimal design of vertical rotating disk and stagnation flow MOVPE reactors in order to achieve film thickness uniformity over large area substrates. Gas inlets that preserve the axial symmetry and enable alternating feeding of the precursors through coaxial rings were studied. The growth of GaN films from trimethyl-gallium and ammonia was used as a typical example. A fundamental reaction-transport model of the MOVPE process including gas-phase reactions and gas-surface interactions has been developed. The model was validated through comparison with growth rate data obtained from both research-scale and industrial-scale reactors. Performance diagrams for industrial-scale stagnation flow and rotating disk reactors were developed by varying the reactor geometry and operating conditions to identify regions of uniform film growth.

Selection-Integrated Optimization (SIO) Methodology for Optimal Design of Adaptive Systems

2006 ◽  
Author(s):  
Ritesh A. Khire ◽  
Achille Messac
Keyword(s):  
Optimal Design ◽  
Adaptive Systems ◽  
Adaptive System ◽  
System Optimization ◽  
Building Envelope ◽  
Operating Conditions ◽  
Integrated Optimization ◽  
Design Variables ◽  
Fixed Design ◽  
Selection Of

Many engineering systems are required to operate under changing operating conditions. A special class of systems called adaptive systems have been proposed in the literature to achieve high performance under changing environments. Adaptive systems acquire this powerful feature by allowing their design configuration to change with operating conditions. In the optimization of the adaptive systems, designers are often required to select (i) adaptive and (ii) non-adaptive (or fixed) design variables of the design configuration. Generally, the selection of these variables, and the optimization of adaptive systems are performed sequentially, thus leaving a likelihood of a sub-optimal design. In this paper, we propose the Selection-Integrated Optimization (SIO) methodology that integrates the two key processes: (1) the selection of the adaptive and fixed design variables, and (2) the optimization of the adaptive system, thereby leading to an optimum design. A major challenge to integrating these two key processes is the selection of the number of fixed and adaptive design variables, which is discrete in nature. We propose the Variable-Segregating Mapping-Function (VSMF) that overcomes this roadblock by progressively approximating the discreteness in the design variable selection process. This simple yet effective approach allows the SIO methodology to integrate the selection and optimization processes, and help avoid one significant source of sub-optimality from typical optimization formulations. The SIO methodology finds its applications in a variety of other engineering fields as well, such as product family optimization. However, in this paper, we limit the scope of our discussion to adaptive system optimization. The effectiveness of the SIO methodology is demonstrated by optimally designing a new air-conditioning system called Active Building Envelope (ABE) System.

Second-Law Analysis in a Steam Power Plant for Minimization of Avoidable Exergy Destruction

2010 ◽  
Author(s):  
Tapan K. Ray ◽  
Pankaj Ekbote ◽  
Ranjan Ganguly ◽  
Amitava Gupta
Keyword(s):  
Work Performance ◽  
Operating Conditions ◽  
Performance Criteria ◽  
Second Law ◽  
Feed Water ◽  
Exergy Destruction ◽  
Actual Performance ◽  
Time Operation ◽  
Major Equipment ◽  
Cycle Efficiency

Performance analysis of a 500 MWe steam turbine cycle is performed combining the thermodynamic first and second-law constraints to identify the potential avenues for significant enhancement in efficiency. The efficiency of certain plant components, e.g. condenser, feed water heaters etc., is not readily defined in the gamut of the first law, since their output do not involve any thermodynamic work. Performance criteria for such components are defined in a way which can easily be translated to the overall influence of the cycle input and output, and can be used to assess performances under different operating conditions. A performance calculation software has been developed that computes the energy and exergy flows using thermodynamic property values with the real time operation parameters at the terminal points of each system/equipment and evaluates the relevant rational performance parameters for them. Exergy-based analysis of the turbine cycle under different strategic conditions with different degrees of superheat and reheat sprays exhibit the extent of performance deterioration of the major equipment and its impact to the overall cycle efficiency. For example, during a unit operation with attemperation flow, a traditional energy analysis alone would wrongly indicate an improved thermal performance of HP heater 5, since the feed water temperature rise across it increases. However, the actual performance degradation is reflected as an exergy analysis indicates an increased exergy destruction within the HP heater 5 under reheat spray. These results corroborate to the deterioration of overall cycle efficiency and rightly assist operational optimization. The exergy-based analysis is found to offer a more direct tool for evaluating the commercial implication of the off-design operation of an individual component of a turbine cycle. The exergy destruction is also translated in terms of its environmental impact, since the irretrievable loss of useful work eventually leads to thermal pollution. The technique can be effectively used by practicing engineers in order to improve efficiency by reducing the avoidable exergy destruction, directly assisting the saving of energy resources and decreasing environmental pollution.

An Accurate Solution of the Gas Lubricated, Flat Sector Thrust Bearing

1977 ◽  
Vol 99 (1) ◽  
pp. 82-88 ◽  
Author(s):  
I. Etsion ◽  
D. P. Fleming
Keyword(s):  
Film Thickness ◽  
Thrust Bearing ◽  
Load Capacity ◽  
Thickness Distribution ◽  
Maximum Load ◽  
Accurate Solution ◽  
Operating Conditions ◽  
Thrust Bearings ◽  
Practical Design ◽  
Minimum Film Thickness

A flat sector shaped pad geometry for gas lubricated thrust bearings is analyzed considering both pitch and roll angles of the pad and the true film thickness distribution. Maximum load capacity is achieved when the pad is tilted so as to create a uniform minimum film thickness along the pad trailing edge. Performance characteristics for various geometries and operating conditions of gas thrust bearings are presented in the form of design curves. A comparison is made with the rectangular slider approximation. It is found that this approximation is unsafe for practical design, since it always overestimates load capacity.

Measurement of Liquid Film Thickness for Annular Two-Phase HFC134a Gas-Liquid Ethanol Flow in the Vertical Tube

2021 ◽  
Author(s):  
Huacheng Zhang ◽  
Tutomo Hisano ◽  
Shoji Mori ◽  
Hiroyuki Yoshida
Keyword(s):  
Film Thickness ◽  
Liquid Film ◽  
Thin Liquid Film ◽  
Atmospheric Condition ◽  
Heating Surface ◽  
Operating Conditions ◽  
Liquid Film Thickness ◽  
Two Phase ◽  
Disturbance Waves ◽  
Analytical Approaches

Abstract Annular gas-liquid two-phase flows, such as the flows attached to the fuel rods of boiling water reactors (BWR), are a prevalent occurrence in industrial processes. At the gas-liquid interface of such flows, disturbance waves with diverse velocity and amplitude commonly arise. Since the thin liquid film between two successive disturbance waves leads to the dryout on the heating surface and limits the performance of the BWRs, complete knowledge of the disturbance waves is of great importance for the characterized properties of disturbance waves. The properties of disturbance waves have been studied by numerous researchers through extensive experimental and analytical approaches. However, most of the experimental data and analyses available in the literature are limited to the near atmospheric condition. In consideration of the properties of liquids and gases under atmospheric pressure which are distinct from those under BWR operating conditions (7 MPa, 285 °C), we employed the HFC134a gas and liquid ethanol whose properties at relatively low pressure and temperature (0.7 MPa, 40 °C) are similar to those of steam and water under BWR operating conditions as working fluids in a tubular test section having an inside diameter 5.0mm. Meanwhile, the liquid film thickness is measured by conductance probes. In this study, we report the liquid film thickness characteristics in a two-phase HFC134a gas-liquid ethanol flow. A simple model of the height of a disturbance wave was also proposed.

Selection of the Optimal Structural Design of a Spar Composite Wing

2021 ◽  
pp. 90-99
Author(s):  
O.V. Tatarnikov ◽  
W.A. Phyo ◽  
Lin Aung Naing
Keyword(s):  
Optimal Design ◽  
Element Analysis ◽  
Minimal Weight ◽  
Wing Structures ◽  
Optimization Parameters ◽  
Nonlinear Static ◽  
Wing Structure ◽  
Pareto Method ◽  
Selection Of ◽  
Composite Wing

This paper describes a method for optimizing the design of a spar-type composite aircraft wing structure based on multi-criterion approach. Two types of composite wing structures such as two-spar and three-spar ones were considered. The optimal design of a wing frame was determined by the Pareto method basing on three criteria: minimal weight, minimal wing deflection, maximal safety factor and minimal weight. Positions of wing frame parts, i.e. spars and ribs, were considered as optimization parameters. As a result, an optimal design of a composite spar-type wing was proposed. All the calculations necessary to select the optimal structural and design of the spar composite wing were performed using nonlinear static finite element analysis in the FEMAP with NX Nastran software package.

Adaptation Application to Engine Modelling

2007 ◽  
Author(s):  
Jude Iyinbor
Keyword(s):  
Measurement Data ◽  
Engine Performance ◽  
Performance Model ◽  
Operating Conditions ◽  
Adaptation Process ◽  
Design Point ◽  
Component Map ◽  
Important Measurement ◽  
Unknown Component ◽  
Selection Of

The optimisation of engine performance by predictive means can help save cost and reduce environmental pollution. This can be achieved by developing a performance model which depicts the operating conditions of a given engine. Such models can also be used for diagnostic and prognostic purposes. Creating such models requires a method that can cope with the lack of component parameters and some important measurement data. This kind of method is said to be adaptive since it predicts unknown component parameters that match available target measurement data. In this paper an industrial aeroderivative gas turbine has been modelled at design and off-design points using an adaptation approach. At design point, a sensitivity analysis has been used to evaluate the relationships between the available target performance parameters and the unknown component parameters. This ensured the proper selection of parameters for the adaptation process which led to a minimisation of the adaptation error and a comprehensive prediction of the unknown component and available target parameters. At off-design point, the adaptation process predicted component map scaling factors necessary to match available off-design point performance data.

Studying Systems of Stabilization of Supports in Hydrostatic Machine Tool

2012 ◽  
Vol 622-623 ◽  
pp. 489-493
Author(s):  
Iskander Beisembetov ◽  
Sabyi Ussupov ◽  
Bakhyt Absadykov ◽  
Beken Arymbekov ◽  
Birzhan Bektibay
Keyword(s):  
Film Thickness ◽  
Machine Tools ◽  
Operating Conditions ◽  
Coefficient Of Performance ◽  
Operational Parameters ◽  
Automatic Stabilization ◽  
Design Elements ◽  
Oil Film ◽  
Hydrostatic Bearing ◽  
Automatic Control Systems

Development relevance to improve the operational parameters of the support units of machine tools in their design elements is introduced that increase the rigidity of the components, their carrying capacity, damp occurring vibrations in the process, the coefficient of performance (COP), smoothness of motion, positioning accuracy, reducing the wear of their working surfaces and maintain the original accuracy. A number of engineering development [1], [2], aimed at improving the above characteristics of the machine by changing and improving design of reference nodes used in these rails rolling bearings, aerostatic and hydrostatic guides, as well as the use of automatic control systems of its basic parameters, determine its quality. However, in some operating conditions in which errors occur, mainly due to the instability of oil-film thickness (gap) between the mobile and immobile elements of the hydrostatic bearing. For high accuracy requirements it will negatively affect the quality of machined parts and equipment performance. On this basis, it becomes apparent urgency of the problem of automatic stabilization of oil-film thickness (gap) in the IR. To ensure high precision equipment to improve power system hydrostatic bearing units of machine tools. This, in turn, creates the prerequisite for the development of stabilization systems of the gap in the hydrostatic bearing, with the help of which the thickness of oil layer in them would be kept constant even with significant dynamic load on the support.

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