Experimental Investigation of Microscale Effects in Perforated Plate Aerodynamics

2013 ◽  
Vol 135 (12) ◽  
Author(s):  
Ryszard Szwaba ◽  
Tomasz Ochrymiuk ◽  
Tomasz Lewandowski ◽  
Justyna Czerwinska
Keyword(s):  
Experimental Investigation ◽  
Compressible Flows ◽  
Large Scale ◽  
Gas Flow ◽  
Perforated Plate ◽  
Quadratic Function ◽  
Accommodation Coefficient ◽  
Turbulence Transition ◽  
Wide Range ◽  
Strong Relation

This paper contains an extensive analysis of the flow in microholes based on an experimental investigation. Experiments of the gas flow past a perforated plate with microholes (110μm) were carried out. A wide range of pressure differences between the inlet and the outlet were investigated for that purpose. Two distinguishable flow regimes were obtained: the laminar flow with the slip effects and the turbulence transition regime for a very low Reynolds number. The results are in good agreement with the theory, simulations, experiments for large scale perforated plates, and compressible flows in microtubes. The relation between the mass flow rate and the Knudsen, Reynolds, and Mach numbers for the laminar and transitional regime was obtained. It is a quadratic function of the Reynolds and Knudsen numbers (ReKn) based on the hole's diameter. The value of the first order tangential momentum accommodation coefficient was estimated. It shows a strong relation to the inlet Knudsen number.

scholarly journals A rarefied gas flow around a rotating sphere: diverging profiles of gradients of macroscopic quantities

2019 ◽  
Vol 862 ◽  
pp. 5-33 ◽  
Author(s):  
Satoshi Taguchi ◽  
Kazuyuki Saito ◽  
Shigeru Takata
Keyword(s):  
Gas Flow ◽  
Rarefied Gas ◽  
Velocity Distribution Function ◽  
Normal Derivative ◽  
Accommodation Coefficient ◽  
Jump Discontinuity ◽  
Rotating Sphere ◽  
Wide Range ◽  
Normal Distance ◽  
The Moment

The steady behaviour of a rarefied gas around a rotating sphere is studied numerically on the basis of the linearised ellipsoidal statistical model of the Boltzmann equation, also known as the ES model, and the Maxwell diffuse–specular boundary condition. It is demonstrated numerically that the normal derivative of the circumferential component of the flow velocity and that of the heat flux diverge on the boundary with a rate $s^{-1/2}$, where $s$ is the normal distance from the boundary. Further, it is demonstrated that the diverging term is proportional to the magnitude of the jump discontinuity of the velocity distribution function on the boundary, which originates from the mismatch of the incoming and outgoing data on the boundary. The moment of force exerted on the sphere is also obtained for a wide range of the Knudsen number and for various values of the accommodation coefficient.

scholarly journals Turbulence in Large-Scale Two-Dimensional Balanced Hard Sphere Gas Flow

Atmosphere ◽  
2021 ◽  
Vol 12 (11) ◽  
pp. 1520
Author(s):  
Rafail V. Abramov
Keyword(s):  
Turbulent Flows ◽  
Hard Sphere ◽  
Large Scale ◽  
Gas Flow ◽  
Spatial Scales ◽  
Mean Field ◽  
Current Work ◽  
Two Dimensional ◽  
Dynamical Mechanism ◽  
Wide Range

In recent works, we developed a model of balanced gas flow, where the momentum equation possesses an additional mean field forcing term, which originates from the hard sphere interaction potential between the gas particles. We demonstrated that, in our model, a turbulent gas flow with a Kolmogorov kinetic energy spectrum develops from an otherwise laminar initial jet. In the current work, we investigate the possibility of a similar turbulent flow developing in a large-scale two-dimensional setting, where a strong external acceleration compresses the gas into a relatively thin slab along the third dimension. The main motivation behind the current work is the following. According to observations, horizontal turbulent motions in the Earth atmosphere manifest in a wide range of spatial scales, from hundreds of meters to thousands of kilometers. However, the air density rapidly decays with altitude, roughly by an order of magnitude each 15–20 km. This naturally raises the question as to whether or not there exists a dynamical mechanism which can produce large-scale turbulence within a purely two-dimensional gas flow. To our surprise, we discover that our model indeed produces turbulent flows and the corresponding Kolmogorov energy spectra in such a two-dimensional setting.

Incompressible Criterion and Pressure Drop for Gaseous Slip Flow in Circular and Noncircular Microchannels

2011 ◽  
Vol 133 (7) ◽  
Author(s):  
Zhipeng Duan
Keyword(s):  
Mach Number ◽  
Simple Model ◽  
Pressure Drop ◽  
Compressible Flows ◽  
Gas Flow ◽  
Slip Flow ◽  
Accommodation Coefficient ◽  
Gaseous Slip Flow ◽  
Practical Engineering ◽  
Poiseuille Number

Slip flow in various noncircular microchannels has been further examined, and a simple model for a normalized Poiseuille number is proposed. As for slip flow, no solutions or graphical and tabulated data exist for most geometries; the developed simple model fills this void and can be used to predict the Poiseuille number, mass flow rate, tangential momentum accommodation coefficient, pressure distribution, and pressure drop of slip flow in noncircular microchannels by the research community for the practical engineering design of microchannels. The incompressible flow criterion for gas flow in microchannels is given. A Mach number less than 0.3 is not sufficient to ensure that the flow is incompressible. Compressibility depends on the product of two dimensionless parameters: L/L(DRe)(DRe) and Ma (Arkilic et al., 1997, “Gaseous Slip Flow in Long Microchannels,” J. Microelectromech. Syst., 6(2), pp. 167–178). Some flows where Ma < 0.3 are low speed compressible flows. A fresh general pressure drop model for isothermal low Mach number compressible flow in microchannels is proposed. If the pressure drop is less than 10% of the outlet pressure, the flow can be considered as incompressible for practical engineering applications. This paper improves and extends previous studies on slip flow in noncircular microchannels.

Large Scale Production of Nanoparticles by Laser Pyrolysis

2007 ◽  
Vol 534-536 ◽  
pp. 85-88 ◽  
Author(s):  
Adrien Reau ◽  
Benoit Guizard ◽  
Cyrille Mengeot ◽  
Loic Boulanger ◽  
François Ténégal
Keyword(s):  
Large Scale ◽  
Gas Flow ◽  
Laser Intensity ◽  
Scale Up ◽  
Pilot Scale ◽  
Scale Production ◽  
Laser Pyrolysis ◽  
Quenching Effect ◽  
Wide Range ◽  
The Mean

Laser pyrolysis is a very suitable gas-phase process for the synthesis of a wide range of nanoparticles at laboratory scale. The principle of the method is based on the decomposition of gaseous or liquid reactants by a high power CO2 laser followed by a quenching effect. The literature reports the possibility to produce carbides, nitrides, oxides, metals and composites nanoparticles by this process. This paper reports a study of the effect of the laser intensity (using an innovative optical system) and of the gas flow rates on the characteristics (size and structure) of silicon carbide (SiC) nanoparticles produced at pilot scale (up to 1.13 kg/h) by using a mixture of silane (SiH4) and acetylene (C2H2). It has been shown that the decrease of the gas flow rate favors the increase of the mean grain size of the particles and that the increase of the laser intensity seems to provoke an increase of the mean crystal size and/or crystal number.

Experimental Investigation of Vortex Flow in a Two-Chamber Solar Thermochemical Reactor

2013 ◽  
Vol 135 (11) ◽  
Author(s):  
Erik E. Koepf ◽  
Matthew D. Lindemer ◽  
Suresh G. Advani ◽  
Ajay K. Prasad
Keyword(s):  
High Temperature ◽  
Flow Visualization ◽  
Large Scale ◽  
Gas Flow ◽  
Vortex Flow ◽  
Solar Reactor ◽  
Concentrated Solar Energy ◽  
Wide Range ◽  
Reactor Geometry ◽  
Solar Thermochemical

Recent advances in the field of large-scale solar thermochemical processing have given rise to substantial research efforts and demonstration projects. Many applications of high-temperature solar-thermal technology employ an enclosed cavity environment, thus requiring a transparent window through which concentrated solar energy can enter. One configuration employed is a two-cavity reactor connected by a narrow aperture, where solar flux entering through the window is focused at the aperture plane before diverging into the lower chamber, where the chemical reaction occurs. For the Zn/ZnO thermochemical cycle where Zn is solar-thermally reduced from ZnO in a high-temperature cavity environment, effective removal of the product gas stream containing zinc vapor is of paramount importance to prevent fouling by condensation on the reactor window. Two argon-jet configurations, tangential and radial, located around the circumference of the upper chamber are used to control the gas flow within the reactor cavity. First, the tangential jets drive a vortex flow, and second, the radial wall jet travels across the window before converging at the reactor center line and turning downward to create a downward jet. The tangential jet-induced flow creates a rotating vortex, contributing to overall flow stability, and the radial jet-induced downward flow counters the updraft created by the vortex while actively cooling and sweeping clear the inner surface of the window. Flow visualization in a full-scale transparent model of the reactor using smoke and laser illumination is employed to characterize the effectiveness of aerodynamic window clearing and to characterize the processes by which a vortex flow develops and breaks down in a two-chamber solar reactor geometry. Based on a large dataset of flow visualization images, a metric is developed to define vortex stability over a wide range of flow conditions and identify an ideal operating range for which a vortex formation path is established that maintains stable flow patterns and removes product gases while minimizing the use of argon gas. The predominant influence of vortex instability and breakdown is identified and examined for the case of a beam-down, two-chamber solar reactor geometry.

Electron microscopy study of reactively sputter-deposited Ti/N films on silicon

1992 ◽  
Vol 50 (2) ◽  
pp. 1362-1363
Author(s):  
V. C. Kannan ◽  
A. K. Singh ◽  
R. B. Irwin ◽  
S. Chittipeddi ◽  
F. D. Nkansah ◽  
...  
Keyword(s):  
Integrated Circuits ◽  
Large Scale ◽  
Hexagonal Phase ◽  
Microscopy Study ◽  
Electron Microscopy Study ◽  
Process Conditions ◽  
Tin Films ◽  
Wide Range ◽  
Fcc Phase ◽  
Circuits Vlsi

Titanium nitride (TiN) films have historically been used as diffusion barrier between silicon and aluminum, as an adhesion layer for tungsten deposition and as an interconnect material etc. Recently, the role of TiN films as contact barriers in very large scale silicon integrated circuits (VLSI) has been extensively studied. TiN films have resistivities on the order of 20μ Ω-cm which is much lower than that of titanium (nearly 66μ Ω-cm). Deposited TiN films show resistivities which vary from 20 to 100μ Ω-cm depending upon the type of deposition and process conditions. TiNx is known to have a NaCl type crystal structure for a wide range of compositions. Change in color from metallic luster to gold reflects the stabilization of the TiNx (FCC) phase over the close packed Ti(N) hexagonal phase. It was found that TiN (1:1) ideal composition with the FCC (NaCl-type) structure gives the best electrical property.

THE SOME QUESTIONS OF AUTONOMOUS MOTION AND MANAGEMENT OF LAND-MOBILE ROBOTIC COMPLEXES FOR UKRAINIAN GROUND FORCESE

2019 ◽  
pp. 53-58
Author(s):  
О. Кravchuk ◽  
V. Symonenkov ◽  
I. Symonenkova ◽  
O. Hryhorev
Keyword(s):  
Large Scale ◽  
Armed Forces ◽  
Distributed Information ◽  
Wide Range ◽  
Highly Effective ◽  
Information Management Systems ◽  
Robotic Devices ◽  
Principles And Standards ◽  
And Control ◽  
The Eu

Today, more than forty countries of the world are engaged in the development of military-purpose robots. A number of unique mobile robots with a wide range of capabilities are already being used by combat and intelligence units of the Armed forces of the developed world countries to conduct battlefield intelligence and support tactical groups. At present, the issue of using the latest information technology in the field of military robotics is thoroughly investigated, and the creation of highly effective information management systems in the land-mobile robotic complexes has acquired a new phase associated with the use of distributed information and sensory systems and consists in the transition from application of separate sensors and devices to the construction of modular information subsystems, which provide the availability of various data sources and complex methods of information processing. The purpose of the article is to investigate the ways to increase the autonomy of the land-mobile robotic complexes using in a non-deterministic conditions of modern combat. Relevance of researches is connected with the necessity of creation of highly effective information and control systems in the perspective robotic means for the needs of Land Forces of Ukraine. The development of the Armed Forces of Ukraine management system based on the criteria adopted by the EU and NATO member states is one of the main directions of increasing the effectiveness of the use of forces (forces), which involves achieving the principles and standards necessary for Ukraine to become a member of the EU and NATO. The inherent features of achieving these criteria will be the transition to a reduction of tasks of the combined-arms units and the large-scale use of high-precision weapons and land remote-controlled robotic devices. According to the views of the leading specialists in the field of robotics, the automation of information subsystems and components of the land-mobile robotic complexes can increase safety, reliability, error-tolerance and the effectiveness of the use of robotic means by standardizing the necessary actions with minimal human intervention, that is, a significant increase in the autonomy of the land-mobile robotic complexes for the needs of Land Forces of Ukraine.

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