Chaotic mixing in a steady flow in a microchannel

We report experiments on mixing of a passively advected fluorescent dye in a low Reynolds number flow in a microscopic channel. The channel is a chain of repeating segments with a custom designed profile that generates a steady three-dimensional flow with stretching and folding, and chaotic mixing. A few statistical characteristics of mixing in the flow are studied and are all found to agree with theoretical and experimental results for the flows in the Batchelor regime of mixing that are chaotic in time. The proposed microchannel provides fast and efficient mixing and is simple to fabricate.     

Detonation in a Three-Dimensional Elbowed Channel

The results of simulation of detonation in a curved three-dimensional channel with a circular cross section of constant width blown through by a supersonic flow of a stoichiometric propane?air mixture are presented. In the bending zone, the channel wall was toroidal. The study was carried out within the framework of the one-stage combustion kinetics by the numerical method based on Godunov’s scheme in the original software package developed for multiparameter calculations and visualization of flows. The initiation of detonation occurs as a result of the formation of the shockwave configurations associated with the flow turn in the channel. Unsteady flow patterns are obtained, and their dependence on the parameters of the problem is investigated. The flow regime without detonation, the mode with the detonation wave emerging from the channel through the input cross section, and the mode with steady detonation are obtained.     

Rectification effect in a quantum contact

The rectification of current has been observed in a quasi-one-dimensional ballistic quantum channel. The effect is explained by the asymmetry of the potential profile in the channel. The dependence of the rectified current on the height of the potential barrier in the channel exhibits sharp maxima, which are associated with conductance quantization steps. A model of the rectification is proposed.     

Sound propagation in a planar channel in the presence of a two-layer flow

Expressions describing the field of a point source in a planar channel with admittance walls enclosing a two-layer nonuniform flow are obtained. The dispersion equation that determines the eigenvalues in a wide range of flow velocities in the layers (including supersonic velocities) is studied. The effect of the admittance of the channel walls on the growth rate of unstable disturbances is considered for different frequencies. It is established that the effect of the admittance of the channel walls on the growth rate of the instability waves decreases with increasing frequency and essentially depends on the type of admittance. It is shown that, in the presence of the admittance, new unstable disturbances are formed with a growth rate that can exceed that of the Kelvin—Helmholtz instability wave.     

Edge flames stabilized in a non-premixed microcombustor

The dynamics of an edge flame confined in a non-premixed microcombustor model is studied numerically within the context of a diffusive-thermal model. Fuel and oxidizer, separated upstream by a thin plate, flow through a channel with a prescribed velocity. At the tip of the plate, the fuel and oxidizer mix and, when ignited, an edge flame is sustained at some distance from the plate. The objective in this work is to consider the effects of confinement, differential diffusion, and heat loss on the dynamics of an edge flame in a narrow channel. We consider a wide range of channel widths and allow for changing Lewis numbers, and both adiabatic conditions and heat losses along the channel walls. The results illustrate how the flame shape and standoff distance are affected by the channel width, by mixture composition through variations in Lewis numbers and by heat losses. Conditions for flame stabilization, flame oscillations and flame extinction or blowoff are predicted.     

Flow separation behind a rib in a channel with laminar flow

Visualization data and results of combined measurements of flow quantities in flow with separation past a rib at nominally laminar regime of channel flow are reported. In the separation region, the flow is found to be essentially three-dimensional and unsteady, exhibiting a distinct cellular structure and flow zones with transverse motion. It is shown that the rib-induced flow separation gives rise to low-frequency fluctuations of flow velocity and initiates the turbulence transition in the channel flow. The critical Reynolds number at which flow instability starts developing in the channel is estimated. It is shown that at Reynolds numbers higher than the critical Reynolds number the linear integral scale of flow velocity fluctuations in the channel is defined by the duct size.     

Constrained Brownian Motion of a Single Ellipsoid in a Narrow Channel

We study the Brownian motion of a single ellipsoidal particle diffusing in a narrow channel by video-microscopy measurement. The experiments allow us to obtain the trajectories of ellipsoids and measure the diffusion coefficients. It is found that the channel constraints lead to suppression of the particle motion, especially the perpendicular motion to the channel, and the long axis of the particle tends to be parallel to the channel. A stable stratification phenomenon is observed, which is rarely discussed in studies of spherical particles. We also derive an approximate solution of theoretical prediction with the method of reflections, and obtain numerical simulation results using finite element software. They are proven to be effective by comparing them with the experimental results. All of these indicate that the aspect ratio and size of ellipsoid, the width of channel, and the transverse position distinctly affect the Brownian motion of ellipsoids.     

Modeling of methane steam reforming in a microchannel with a heat flow distributed in length

Numerical modeling of a flow of a high-temperature mixture of methane with water vapors in a two-dimensional plane microchannel with activation of chemical conversions on the channel wall has been performed. The modeling was performed within the framework of Navier-Stokes equations for a laminar flow of a multicomponent compressible gas. The influence of the external heat flux supplied to the gas mixture and its distribution along the channel length on the properties of the methane steam reforming have been investigated. It has been shown that not only the amount of heat supplied to the reaction zone but also the method of heat supply along the channel length are important. All the reactions with the residence time of the mixture on the order of tens of milliseconds terminate several centimeters downstream from the channel inlet, which makes it possible to optimize a compact reactor for obtaining a synthesis gas.     

Interactions of glide dislocations in a channel of a persistent slip band

Two unlike dislocations gliding in parallel slip planes in a channel of a persistent slip band are considered. Initially they are kept apart in straight screw positions. As the dislocations are pushed by the applied stress between two walls in the opposite directions, they bow out and attract one another forming a dipole. With the increasing stress the dislocations become more and more curved, until they separate. The walls of the channel are represented by elastic fields of rigid edge dipoles. The dislocations are modelled as planar curves approximated by moving polygons. The objective of the simulations is to determine the stress in the channel needed for the dislocations to escape one another. The stress and strain controlled regimes considered provide upper and lower estimates of the escape stress. The results are compared with the studies by Mughrabi and Pschenitzka, and Brown and the recent dislocation dynamics estimates. Problems encountered in the dislocation dynamics evaluation of the escape stress are analyzed.     

Motion of a helium atom through a comparable-diameter channel in the Frenkel-Kontorova model

The motion of a helium atom through a channel with a diameter comparable to the diameter of this atom is investigated. Such channels are observed in materials of the quartz type. The inclusion of the local law of momentum conservation in the analysis of the interaction between the He atom and the atoms forming the channel wall makes it possible to reduce the problem to one-dimensional motion similar to the motion of a dislocation in the Frenkel-Kontorova model. In the model proposed here, the activation energy of the complex formed by the He atom and the displacements of atoms of the channel wall is calculated. The obtained energy is expressed in terms of the shear modulus of the material forming the channel and the helium atom polarizability, which depends on the state of the helium atom.     

Calculation of force exerted by the Ohmic plasma channel on a relativistic electron beam propagating in a dense gas-plasma medium

The problem on the interaction of an Ohmic plasma channel displaced in the transverse direction with a paraxial azimuthally symmetric relativistic electron beam propagating in a dense gas-plasma medium is considered. The formula for determining the force of the beam-plasma interaction is derived using the “hard” model of the beam and the channel in the case of an arbitrary displacement of the symmetry axis of the plasma channel relative to the corresponding axis of the beam. The forces are calculated in the Bennett and Gauss approximations for the radial profiles of the beam and the channel.     

X-ray emission from betatron motion in a plasma wiggler

The successful utilization of an ion channel in a plasma to wiggle a 28.5-GeV electron beam to obtain broadband x-ray radiation is reported. The ion channel is induced by the electron bunch as it propagates through an underdense 1.4-meter-long lithium plasma. The quadratic density dependence of the spontaneously emitted betatron x-ray radiation and the divergence angle of approximately (1-3)x10(-4) radian of the forward-emitted x-rays as a consequence of betatron motion in the ion channel are in good agreement with theory. The absolute photon yield and the peak spectral brightness at 14.2-keV photon energy are estimated.     

Bifurcation of a Newtonian-fluid flow in a planar channel with sudden contraction and expansion

The features of a Newtonian-fluid flow in a two-dimensional channel with sudden contraction and expansion are investigated by numerical modeling. The kinetics of the bifurcation transition from the symmetric mode to steady-state asymmetric flow on the outlet from the zone of contraction of the channel is analyzed. The linear dependence of the degree of asymmetry of flow on the Reynolds number is established.     

Heat transfer at a laminar free convection and separated flow past a rib in a vertical channel with isothermal walls

The results of numerical computations of a free laminar convection and heat transfer between two parallel isothermal plates in the presence of a single rib on the channel surface are presented. The investigations have been conducted for a channel with the aspect ratio AR = L/w = 10, where L is the channel height, and w is the distance between the plates. An infinitely thin adiabatic rib was located on one of the channel walls in the middle of its height. The relative rib height l/w was varied in the range 0÷0.8. The wall temperature was higher than the ambient temperature, and the Rayleigh number was varied in the range Ra = 10²÷10⁵. The main attention has been paid to the study of the influence of the rib height and the Rayleigh number on local and integral heat transfer and the Reynolds number in the channel (the convective thrust). A fundamental difference in the heat transfer over the channel height has been shown on the ribbed wall and on a smooth surface. The computational results have been compared with the case of a symmetric distribution of the ribs on the both walls with the integral height equal to a single rib.     

Distribution of a modulated squeezed state over a lossy channel

The distribution of a modulated squeezed state over a quantum channel is the basis for quantum key distribution(QKD) with a squeezed state. In this Letter, a modulated squeezed state is distributed over a lossy channel. The Wigner function of the distributed state is measured to observe the evolution of the quantum state over a lossy channel, which shows that the squeezing level and the displacement amplitude of the quantum state are decreased along with the increase of the channel loss. We also measure the squeezing level in the frequency domain by the frequency shift technique. The squeezing of the modulated squeezed state at the modulation frequency is observed in this way. The presented results supply a reference for a QKD with a squeezed state.     

Mathematical simulation of the pulsed current amplification mode in a channel of a microchannel plate

The boundary-value problem is solved for electric field in a channel of a microchannel plate under pulsed modulation of the output current. Analytic equations are determined for the field and current in the channel, as well as for the current at the channel exit and for the gain in the time domain. The effect of modulation parameters on the shape of the output current pulses is analyzed.     

Intense laser beam propagating in a plasma channel with flat-bottom leaky density profile

The propagation characteristics of an intense laser beam in a preformed plasma channel with the flat-bottom leaky density profile are investigated in detail. The evolution equation of the laser spot size is derived by employing variational technique. Seven propagation modes of the laser spot size are identified and some numerical results are presented. By comparison, we find that the results in this Letter may be more realistic since the flat-bottom leaky plasma channel comes closer to the practical plasma channel.     

The electromagnetic mechanism of plasmon decay to a neutrino pair in a strongly magnetized electron gas

An expression for the neutrino luminosity of a degenerate electron gas in a strong magnetic field via plasmon decay to a neutrino pair due to electromagnetic neutrino moments is derived. The neutrino luminosity of the medium in an electromagnetic reaction channel is shown to be comparable with the luminosity in a weak channel. The relative upper bounds for the effective magnetic neutrino moment are obtained.     

Conductivity of a steadily glowing shock-compressed channel in a film metal-insulator-metal structure

The action of particles accelerated in an electrostatic accelerator on film metal-insulator-metal structures is described. The effect of steady glow of a shock-compressed conducting channel is studied. The temperature of the shock-compressed channel, the through conductivity of the metal-insulator-metal structure, and the related ion mass spectra are found. The applications of the results in various fields of technology are shown.     

Mathematical model of the direct current amplification mode in a channel of a microchannel plate

The boundary-value problem is solved for electric field in a channel of a microchannel plate for a preset value of current at the channel entrance. Analytic equations are determined for the distributions of field, potential, and current along the channel, as well as for the current gain and the current in the circuit of the source of constant voltage as a function of the input current.