scholarly journals Mechanochemical mechanism for reaction of aluminium nano- and micrometre-scale particles

2013 ◽  
Vol 371 (2003) ◽  
pp. 20120215 ◽  
Author(s):  
Valery I. Levitas
Keyword(s):  
Diffusion Mechanism ◽  
Quantitative Agreement ◽  
Oxide Shell ◽  
Fast Reaction ◽  
Fast Heating ◽  
Current Trends ◽  
Dispersion Mechanism ◽  
Unloading Wave ◽  
Theoretical Predictions ◽  
Hoop Stresses

A recently suggested melt-dispersion mechanism (MDM) for fast reaction of aluminium (Al) nano- and a few micrometre-scale particles during fast heating is reviewed. Volume expansion of 6% during Al melting produces pressure of several GPa in a core and tensile hoop stresses of 10 GPa in an oxide shell. Such stresses cause dynamic fracture and spallation of the shell. After spallation, an unloading wave propagates to the centre of the particle and creates a tensile pressure of 3–8 GPa. Such a tensile pressure exceeds the cavitation strength of liquid Al and disperses the melt into small, bare clusters (fragments) that fly at a high velocity. Reaction of the clusters is not limited by diffusion through a pre-existing oxide shell. Some theoretical and experimental results related to the MDM are presented. Various theoretical predictions based on the MDM are in good qualitative and quantitative agreement with experiments, which resolves some basic puzzles in combustion of Al particles. Methods to control and improve reactivity of Al particles are formulated, which are exactly opposite to the current trends based on diffusion mechanism. Some of these suggestions have experimental confirmation.

The propagation of gravity currents in a V-shaped triangular cross-section channel: experiments and theory

2014 ◽  
Vol 754 ◽  
pp. 232-249 ◽  
Author(s):  
Marius Ungarish ◽  
Catherine A. Mériaux ◽  
Cathy B. Kurz-Besson
Keyword(s):  
Reynolds Number ◽  
Cross Section ◽  
Viscosity Coefficient ◽  
Gravity Currents ◽  
Quantitative Agreement ◽  
Flat Bottom ◽  
Special Configuration ◽  
Theoretical Predictions ◽  
Speed Of Propagation ◽  
High Reynolds

AbstractWe investigate the motion of high-Reynolds-number gravity currents (GCs) in a horizontal channel of V-shaped cross-section combining lock-exchange experiments and a theoretical model. While all previously published experiments in V-shaped channels were performed with the special configuration of the full-depth lock, we present the first part-depth experiment results. A fixed volume of saline, that was initially of length $\def \xmlpi #1{}\def \mathsfbi #1{\boldsymbol {\mathsf {#1}}}\let \le =\leqslant \let \leq =\leqslant \let \ge =\geqslant \let \geq =\geqslant \def \Pr {\mathit {Pr}}\def \Fr {\mathit {Fr}}\def \Rey {\mathit {Re}}x_0$ and height $h_0$ in a lock and embedded in water of height $H_0$ in a long tank, was released from rest and the propagation was recorded over a distance of typically $ 30 x_0$. In all of the tested cases the current displays a slumping stage of constant speed $u_N$ over a significant distance $x_S$, followed by a self-similar stage up to the distance $x_V$, where transition to the viscous regime occurs. The new data and insights of this study elucidate the influence of the height ratio $H = H_0/h_0$ and of the initial Reynolds number ${\mathit{Re}}_0 = (g^{\prime }h_0)^{{{1/2}}} h_0/ \nu $, on the motion of the triangular GC; $g^{\prime }$ and $\nu $ are the reduced gravity and kinematic viscosity coefficient, respectively. We demonstrate that the speed of propagation $u_N$ scaled with $(g^{\prime } h_0)^{{{1/2}}}$ increases with $H$, while $x_S$ decreases with $H$, and $x_V \sim [{\mathit{Re}}_0(h_0/x_0)]^{{4/9}}$. The initial propagation in the triangle is 50 % more rapid than in a standard flat-bottom channel under similar conditions. Comparisons with theoretical predictions show good qualitative agreements and fair quantitative agreement; the major discrepancy is an overpredicted $u_N$, similar to that observed in the standard flat bottom case.

The liquid blister test

2008 ◽  
Vol 464 (2099) ◽  
pp. 2887-2906 ◽  
Author(s):  
Julien Chopin ◽  
Dominic Vella ◽  
Arezki Boudaoud
Keyword(s):  
Surface Tension ◽  
Surface Energy ◽  
Vertical Displacement ◽  
Quantitative Agreement ◽  
Elastic Plates ◽  
Blister Test ◽  
Thin Liquid Layer ◽  
Theoretical Predictions ◽  
Thin Elastic Plates ◽  
Adhesive Forces

We consider a thin elastic sheet adhering to a stiff substrate by means of the surface tension of a thin liquid layer. Debonding is initiated by imposing a vertical displacement at the centre of the sheet and leads to the formation of a delaminated region or ‘blister’. This experiment reveals that the perimeter of the blister takes one of three different forms depending on the vertical displacement imposed. As this displacement is increased, we observe first circular, then undulating and finally triangular blisters. We obtain theoretical predictions for the observed features of each of these three families of blisters. The theory is built upon the Föppl–von Kármán equations for thin elastic plates and accounts for the surface energy of the liquid. We find good quantitative agreement between our theoretical predictions and experimental results, demonstrating that all three families are governed by different balances between elastic and capillary forces. Our results may bear on micrometric tapered devices and other systems, where elastic and adhesive forces are in competition.

Inflation and Compression of Rubber Tubes between Parallel Plates

1971 ◽  
Vol 44 (5) ◽  
pp. 1380-1390
Author(s):  
J. M. Charrier ◽  
A. N. Gent
Keyword(s):  
Internal Pressure ◽  
Pressure Rise ◽  
Compressive Force ◽  
Quantitative Agreement ◽  
Elastic Behavior ◽  
Rubber Tube ◽  
Parallel Plates ◽  
Compression Stiffness ◽  
Theoretical Predictions ◽  
Different Dimensions

Abstract When a thin-walled rubber tube containing an incompressible fluid is compressed between two parallel plates the internal pressure rise depends on the restraints in the contact regions. When there is no friction in the contact zone the pressure rise is lower than when slip is prevented, so that the tube, regarded as a spring, has a compression stiffness which depends on the frictional conditions. The same considerations apply to the inflation of a tube between fixed parallel plates. In this case unstable inflation sets in at a critical pressure when the interfaces are frictionless; the tube develops a pronounced bulge when this pressure is approached. Simple theoretical relations are derived for the internal pressure and compressive force for both these deformations, and for both boundary conditions, assuming that the rubber is neo-Hookean in elastic behavior. Experimental measurements on tubes of different dimensions are shown to be in reasonably good quantitative agreement with these theoretical predictions in all cases.

Interfacial wave theory for oscillatory finger formation in a Hele–Shaw cell: a comparison with experiments

1996 ◽  
Vol 7 (2) ◽  
pp. 169-199 ◽  
Author(s):  
Jian-Jun Xu
Keyword(s):  
Wave Theory ◽  
Quantitative Agreement ◽  
Instability Mechanism ◽  
Interfacial Wave ◽  
Wave Instability ◽  
Viscous Fingers ◽  
Theoretical Predictions ◽  
Finger Tip ◽  
Hele Shaw Cell ◽  
Comparison With Experiments

This paper is devoted to an analysis of the formation of oscillatory viscous fingers in a Hele-Shaw cell on the basis of the interfacial wave theory, previously established for the pattern formation dynamics in dendrite growth, as well as in the classic Saffman–Taylor flow. In particular, we study the problem of selection and persistence of oscillatory fingers with a tiny bubble at the finger tip. We obtain uniformly valid asymptotic solutions for this problem, and derive the linear, global wave instability mechanism for this more complicated system. The global, neutrally stable modes are computed in a large region of parameters, which select the form of oscillatory fingers in the later stage of evolution. We have compared the theoretical predictions with the experimental data by Couder et al. (1986) and by Kopf-Sill & Homsy (1987), and found excellent quantitative agreement.

scholarly journals Asymptotic temperature of a lossy condensate

2020 ◽  
Vol 8 (4) ◽  
Author(s):  
Isabelle Bouchoule ◽  
Max Schemmer
Keyword(s):  
Sound Velocity ◽  
Loss Rate ◽  
Theoretical Calculations ◽  
Quantitative Agreement ◽  
Energy Scale ◽  
Atomic Mass ◽  
Collective Modes ◽  
Asymptotic Value ◽  
One Dimensional ◽  
Theoretical Predictions

We monitor the time evolution of the temperature of phononic collective modes in a one-dimensional quasicondensate submitted to losses. At long times the ratio between the temperature and the energy scale mc^2mc2, where mm is the atomic mass and cc the sound velocity takes, within a precision of 20%, an asymptotic value. This asymptotic value is observed while mc^2mc2 decreases in time by a factor as large as 2.5. Moreover this ratio is shown to be independent on the loss rate and on the strength of interactions. These results confirm theoretical predictions and the measured stationary ratio is in quantitative agreement with the theoretical calculations.

scholarly journals Morphometric properties of alternate bars and water discharge: a laboratory investigation

2020 ◽  
Author(s):  
Marco Redolfi ◽  
Matilde Welber ◽  
Mattia Carlin ◽  
Marco Tubino ◽  
Walter Bertoldi
Keyword(s):  
Water Discharge ◽  
Hydrological Regime ◽  
Theoretical Models ◽  
Quantitative Information ◽  
Quantitative Agreement ◽  
Critical Threshold ◽  
Morphological Variations ◽  
Theoretical Predictions ◽  
Alternate Bars ◽  
Harmonic Composition

Abstract. The formation of alternate bars in straightened river reaches represents a fundamental process of river morphodynamics that has received great attention in the last decades. It is well-established that migrating alternate bars arise from an autogenic, instability mechanism occurring when the channel width-to-depth ratio is sufficiently large. While several empirical and theoretical relations for predicting how bar height and length depend on the key dimensionless parameters are available, there is a lack of direct, quantitative information about the dependence of bar properties on flow discharge. We performed a series of experiments in a long, mobile-bed flume with fixed and straight banks, at different discharges. The self-formed bed topography was surveyed, different metrics were analysed to obtain quantitative information about bar height and shape, and results were interpreted in the light of existing theoretical models. The analysis reveals that the shape of alternate bars highly depends on their formative discharge, with remarkable variations in the harmonic composition and a strong decreasing trend of the skewness of the bed elevation. Similarly, the height of alternate bars clearly decreases with the water discharge, in quantitative agreement with theoretical predictions. However, the disappearance of bars when discharge exceeds a critical threshold is not as sharp as expected, due to the formation of so-called diagonal bars. This work provides basic information for modelling and interpreting short-term morphological variations during individual flood events and long-term trajectories due to alterations of the hydrological regime.

The rise and fall of turbulent fountains: a new model for improved quantitative predictions

2010 ◽  
Vol 657 ◽  
pp. 265-284 ◽  
Author(s):  
G. CARAZZO ◽  
E. KAMINSKI ◽  
S. TAIT
Keyword(s):  
Steady State ◽  
Froude Number ◽  
Turbulent Flows ◽  
Scaling Laws ◽  
Quantitative Agreement ◽  
Industrial Applications ◽  
Clear Understanding ◽  
New Model ◽  
Major Interest ◽  
Theoretical Predictions

Turbulent fountains are of major interest for many natural phenomena and industrial applications, and can be considered as one of the canonical examples of turbulent flows. They have been the object of extensive experimental and theoretical studies that yielded scaling laws describing the behaviour of the fountains as a function of source conditions (namely their Reynolds and Froude numbers). However, although such scaling laws provide a clear understanding of the basic dynamics of the turbulent fountains, they usually rely on more or lessad hocdimensionless proportionality constants that are scarcely tested against theoretical predictions. In this paper, we use a systematic comparison between the initial and steady-state heights of a turbulent fountain predicted by classical top-hat models and those obtained in experiments. This shows scaling agreement between predictions and observations, but systematic discrepancies regarding the proportionality constant. For the initial rise of turbulent fountains, we show that quantitative agreement between top-hat models and experiments can be achieved by taking into account two factors: (i) the reduction of entrainment by negative buoyancy (as quantified by the Froude number), and (ii) the fact that turbulence is not fully developed at the source at intermediate Reynolds number. For the steady-state rise of turbulent fountains, a new model (‘confined top-hat’) is developed to take into account the coupling between the up-flow and the down-flow in the steady-state fountain. The model introduces three parameters, calculated from integrals of experimental profiles, that highlight the dynamics of turbulent entrainment between the up-flow and the down-flow, as well as the change of buoyancy flux with height in the up-flow. The confined top-hat model for turbulent fountains achieves good agreement between theoretical predictions and experimental results. In particular, it predicts a systematic increase of the ratio between the initial and steady-state heights of turbulent fountains as a function of their source Froude number, an observation that was not handled properly in previous models.

MONTE CARLO STUDY OF THE VACANCY MECHANISM IN DILUTE FCC BINARY ALLOYS

2000 ◽  
Vol 11 (07) ◽  
pp. 1417-1423
Author(s):  
A. HASNAOUI
Keyword(s):  
Monte Carlo ◽  
Solute Atom ◽  
Gaussian Function ◽  
Monte Carlo Study ◽  
Periodic Boundary Conditions ◽  
Solute Concentration ◽  
Quantitative Agreement ◽  
Vacancy Mechanism ◽  
Theoretical Predictions ◽  
Fcc Binary Alloys

The vacancy mechanism is simulated by means of Monte Carlo (MC) method. In this model, the impurity diffusion occurs by migration of substitutional atoms B via the exchange with vacancies whose frequencies near a solute atom differ from a free vacancy. Whenever a defect leaves the lattice, periodic boundary conditions are made to bring it into the lattice. The solute concentration profiles are given using a technique developed by Murch which has been shown to be equivalent to a finite source. The fit of these profiles allows the comparison between our results and analytical solutions. The parameters extracted from a Gaussian function fit which agrees well with numerical profiles are in very good quantitative agreement with theoretical predictions.

An experimental study of the explosion generated by a pressurized sphere

1960 ◽  
Vol 9 (3) ◽  
pp. 401-429 ◽  
Author(s):  
D. W. Boyer
Keyword(s):  
Numerical Solutions ◽  
Quantitative Agreement ◽  
External Pressure ◽  
Glass Spheres ◽  
Theoretical Predictions ◽  
Physical Limitations ◽  
Initial Shock ◽  
Spherical Shock ◽  
Wave Phenomena ◽  
High Internal Pressure

An experimental investigation of the explosions of 2 in. diameter glass spheres under high internal pressure has been made. The spheres were initially filled with air or helium at 400 and 326 p.s.i., respectively, and were exploded in air at atmospheric pressure. Experiments on the simulation of high-altitude explosions are also described. Schlieren and spark shadowgraph records of explosion phenomena, and pressure records of the reflexion of the spherical shock wave at various radii, are presented.An account of some initial experiments on the implosion of 5 in. diameter glass spheres is given. The results were not very satisfactory because of the failure of the spheres to shatter in a desirable manner while under an external pressure of 65 p.s.i.Numerical solutions to the air and helium sphere explosions are described and the experimental wave phenomena are shown to be in good quantitative agreement with the theoretical predictions, in that they exhibit all the main features that were predicted and are modified only by the physical limitations of the glass diaphragm. A formation process is associated with the spherical shock waves in practice, resulting in initial shock velocities which are lower than the theoretical values.

Experiments on vertical slender flexible cylinders clamped at both ends and subjected to axial flow

2007 ◽  
Vol 366 (1868) ◽  
pp. 1275-1296 ◽  
Author(s):  
Y Modarres-Sadeghi ◽  
M.P Païdoussis ◽  
C Semler ◽  
E Grinevich
Keyword(s):  
Axial Flow ◽  
Quantitative Agreement ◽  
Dynamical Behaviour ◽  
High Flow ◽  
The Third ◽  
Theoretical Predictions ◽  
Series Of Experiments ◽  
Linear And Nonlinear ◽  
Theory And Experiment ◽  
Flow Velocities

Three series of experiments were conducted on vertical clamped–clamped cylinders in order to observe experimentally the dynamical behaviour of the system, and the results are compared with theoretical predictions. In the first series of experiments, the downstream end of the clamped–clamped cylinder was free to slide axially, while in the second, the downstream end was fixed; the influence of externally applied axial compression was also studied in this series of experiments. The third series of experiments was similar to the second, except that a considerably more slender, hollow cylinder was used. In these experiments, the cylinder lost stability by divergence at a sufficiently high flow velocity and the amplitude of buckling increased thereafter. At higher flow velocities, the cylinder lost stability by flutter (attainable only in the third series of experiments), confirming experimentally the existence of a post-divergence oscillatory instability, which was previously predicted by both linear and nonlinear theory. Good quantitative agreement is obtained between theory and experiment for the amplitude of buckling, and for the critical flow velocities.

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