Application of the shock tube unsteady expansion wave technique to the study of chemical reactions

1978 ◽  
Vol 11 (9) ◽  
pp. 1249-1262 ◽  
Author(s):  
W H Beck ◽  
J C Mackie
Keyword(s):  
Shock Tube ◽  
Chemical Reactions ◽  
Expansion Wave ◽  
Wave Technique

scholarly journals Dust Eruptions

2021 ◽  
Author(s):  
◽  
Harpreet Singh
Keyword(s):  
Shock Tube ◽  
Pressure Difference ◽  
Momentum Conservation ◽  
Expansion Wave ◽  
Wall Friction ◽  
Good Match ◽  
New Model ◽  
Bead Diameter ◽  
Pressure Changes

<p>We present a new model for the fragmentation of dust beds in laboratory shock tube experiments. The model successfully explains the formation of layers in the bed using mass and momentum conservation. Our model includes the effect of wall friction, inherent cohesion, and gravitational overburden. We find that the pressure changes caused by the expansion wave take time to penetrate into the bed, while simultaneously increasing in magnitude. By the time the pressure difference is large enough to overcome wall friction, the overburden and the intrinsic cohesion of the bed, it has penetrated ~8-15 bead diameters into the bed, thus causing a layer of dust to be lifted off. We have found the dependence of layer size upon bead diameter and found a good match to experiment. We have also predicted the dependence of layer size and fragmentation time on bead density.</p>

scholarly journals Dust Eruptions

2021 ◽  
Author(s):  
◽  
Harpreet Singh
Keyword(s):  
Shock Tube ◽  
Pressure Difference ◽  
Momentum Conservation ◽  
Expansion Wave ◽  
Wall Friction ◽  
Good Match ◽  
New Model ◽  
Bead Diameter ◽  
Pressure Changes

<p>We present a new model for the fragmentation of dust beds in laboratory shock tube experiments. The model successfully explains the formation of layers in the bed using mass and momentum conservation. Our model includes the effect of wall friction, inherent cohesion, and gravitational overburden. We find that the pressure changes caused by the expansion wave take time to penetrate into the bed, while simultaneously increasing in magnitude. By the time the pressure difference is large enough to overcome wall friction, the overburden and the intrinsic cohesion of the bed, it has penetrated ~8-15 bead diameters into the bed, thus causing a layer of dust to be lifted off. We have found the dependence of layer size upon bead diameter and found a good match to experiment. We have also predicted the dependence of layer size and fragmentation time on bead density.</p>

Expansion wave diffraction over a 90 degree corner

2014 ◽  
Vol 757 ◽  
pp. 649-664 ◽  
Author(s):  
Irshaad Mahomed ◽  
Beric W. Skews
Keyword(s):  
Shock Wave ◽  
Shock Tube ◽  
Shear Layer ◽  
Wave Diffraction ◽  
Compression Wave ◽  
Large Scale ◽  
Separation Bubble ◽  
Pressure Ratio ◽  
Expansion Wave ◽  
Turbulent Structures

AbstractThe diffraction of an initially one-dimensional plane expansion wave over a 90° corner was explored using experiment and numerical simulation. Unlike studies of shock diffraction, expansion wave diffraction has hardly been documented previously. The planar expansion wave was produced in a shock tube by bursting a diaphragm. Two independent parameters were identified for study: (i) the initial diaphragm shock tube pressure ratio, which determines the strength (pressure ratio) of the expansion, and (ii) the position of the diaphragm from the apex of the 90° corner, which determines the width of the wave. The experimentation only considered variation in the shock tube pressure ratio whereas the simulation varied both parameters. A Navier–Stokes solver with Menter’s shear stress transport $\def \xmlpi #1{}\def \mathsfbi #1{\boldsymbol {\mathsf {#1}}}\let \le =\leqslant \let \leq =\leqslant \let \ge =\geqslant \let \geq =\geqslant \def \Pr {\mathit {Pr}}\def \Fr {\mathit {Fr}}\def \Rey {\mathit {Re}}k\mbox{--}\omega $ turbulence model was found to adequately model the overall flow field. A number of major flow features were identified occurring in the vicinity of the corner. These were: a shear layer that originated by flow separation at the apex of the corner; a vortex within a separation bubble that remained attached to the wall, in sharp contrast to what happens in the shock wave diffraction case, where the vortex convects downstream; and a reflected compression wave arising from perturbation signals generated by the diffraction. For a narrow-width expansion wave existing prior to diffraction, the reflected compression wave steepens into an outwardly propagating, weak cylindrical shock wave. Regions of supersonic flow are identified surrounding the bubble and can extend downstream depending on the pressure ratio. Another major flow feature identified in some cases was an oblique shock located near the separation bubble. A large wake region is evident immediately downstream of the bubble and appears to consist of two distinct layers. The experimental results showed large-scale turbulent structures within the separation bubble, and shear layer instability and vortex shedding from the separation bubble were also evident.

The interaction region in the boundary layer of a shock tube

1969 ◽  
Vol 38 (1) ◽  
pp. 109-125 ◽  
Author(s):  
S. D. Ban ◽  
G. Kuerti
Keyword(s):  
Boundary Layer ◽  
Shock Tube ◽  
Elliptic Equations ◽  
Weak Shock ◽  
Flow Fields ◽  
Interaction Region ◽  
Expansion Wave ◽  
Expansion Waves ◽  
Consistent Linearization ◽  
Singular Parabolic Equations

Velocity and temperature boundary layers developed on a plane wall by ideal shock-tube flow are considered for weak shock and expansion waves. Analytically, the boundary layer consists of three regions, bounded by (1) expansion-wave head, (2) diaphragm location, (3) contact discontinuity, (4) shock. The flow fields (1, 2) and (3, 4) are, essentially, known. In the interaction region (2, 3), these flow fields merge, the governing equations are ‘singular parabolic’ and admit boundary conditions usually associated with elliptic equations. It is convenient to replace the weak expansion wave in the main flow by a line discontinuity. A consistent linearization scheme can now be devised to obtain the solution in the three regions. In (2, 3), the resulting linear singular parabolic equations for the first-order solutions are solved successfully by an iterative finite difference method, normally applied to elliptic equations.

Human-hair analysis

1992 ◽  
Vol 50 (1) ◽  
pp. 886-887
Author(s):  
Brenda E. Lambert ◽  
Ernest C. Hammond
Keyword(s):  
Human Hair ◽  
Hair Analysis ◽  
Hair Shaft ◽  
White Female ◽  
Chemical Processing ◽  
X Ray ◽  
Hair Samples ◽  
Wave Technique ◽  
Permanent Wave ◽  
Scanning Electron

The purpose of this study was to examine the external structure of four human hair shaft samples with the scanning Electron Microscope (SEM) and to obtain information regarding the chemical composition of hair by using the attached x ray microanalysis unit.The hair samples were obtained from two female subjects. Sample A was taken from a black female and had not undergone any type of chemical processing. Sample B, C, D were taken from a white female, and were natural, processed, and unpigmented, i.e. “gray”, respectively. Sample C had been bleached, tinted, and chemically altered using a permanent wave technique.

Surface reactions observed by photoemission electron microscopy (PEEM)

1992 ◽  
Vol 50 (1) ◽  
pp. 286-287
Author(s):  
H.H. Rotermund
Keyword(s):  
Electron Microscopy ◽  
Electron Microscope ◽  
Work Function ◽  
Chemical Reactions ◽  
Reaction Diffusion ◽  
Dynamic Processes ◽  
Clean Surface ◽  
Crystal Surfaces ◽  
Single Crystal Surfaces ◽  
Photoemission Electron

Chemical reactions at a surface will in most cases show a measurable influence on the work function of the clean surface. This change of the work function δφ can be used to image the local distributions of the investigated reaction,.if one of the reacting partners is adsorbed at the surface in form of islands of sufficient size (Δ>0.2μm). These can than be visualized via a photoemission electron microscope (PEEM). Changes of φ as low as 2 meV give already a change in the total intensity of a PEEM picture. To achieve reasonable contrast for an image several 10 meV of δφ are needed. Dynamic processes as surface diffusion of CO or O on single crystal surfaces as well as reaction / diffusion fronts have been observed in real time and space.

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