Showing papers on "Rarefaction published in 2005"

Application of Ultrasound

Abstract: Publisher Summary Major mechanical effects of ultrasound are provided when the power is sufficiently high to cause cavitation. Like any sound wave, ultrasound is propagated via a series of compression and rarefaction waves induced in the molecules of the medium through which it passes. At sufficiently high power, the rarefaction cycle may exceed the attractive forces of the molecules of the liquid and cavitation bubbles will form. Such bubbles grow by a process known as rectified diffusion, that is, small amounts of vapor (or gas) from the medium enters the bubble during its expansion phase and is not fully expelled during compression. The effectiveness of ultrasound as a food processing tool has been proven in the laboratory and there are a number of examples of scale-up. In most cases, commercially available frequency is used, that is 20 or 40 kHz, and this has proved quite satisfactory. In such cases, the variable parameters are temperature, treatment time, and acoustic power. Little attention has been paid to the use of different frequencies except in a few cases. One such is the use of ultrasound in food preservation using the bactericidal action of sonication combined with other techniques such as heat, ultraviolet light, and the use of a biocide.

The driven cavity flow over the whole range of the Knudsen number

Abstract: The flow of a rarefied gas in a rectangular enclosure due to the motion of the upper wall is solved over the whole range of the Knudsen number. The formulation is based on the two–dimensional linearized Bhatnagar-Gross-Krook (BGK) kinetic equation with Maxwell diffuse-specular boundary conditions. The integro-differential equations are solved numerically implementing the discrete velocity method. The discontinuity at the boundaries between stationary and moving walls is treated accordingly. A detailed investigation of the rarefaction effects on the flow pattern and quantities is presented over the whole range of the Knudsen number and various aspect (height/width) ratios. Numerical results of flow characteristics, including the streamlines, the velocity profiles, the pressure and temperature contours, and the drag force of the moving wall, are presented for different aspect ratios and various degrees of gas rarefaction from the free molecular through the transition up to the continuum limit. On several occasions, depending upon the flow parameters, in addition to the main vortex, corner eddies are created. As the depth of the cavity is increased, these eddies grow and merge into additional vortices under the top one. The mesoscale kinetic-type approach proves to be efficient and suitable for problems that incorporate multiscale physics, such as the present nonequilibrium flow.

Simulation of gas flow in microchannels with a sudden expansion or contraction

Abstract: Two-dimensional simulations based on the isothermal lattice-Boltzmann method have been undertaken on microchannels with a sudden expansion or contraction. The study provides insight into the analysis of flows in complicated microdevices. The flow is pressure driven, and computations are performed for several Knudsen numbers, and area and pressure ratios, allowing the effects of compressibility and rarefaction to be assessed. The pressure drop for both the converging and diverging channels shows a discontinuity in slope at the junction, and is accompanied by a jump in velocity. The pressure drop in each section can be predicted well by the theory for straight channels. The mass flow ratio between converging and diverging channels is close to unity, and the streamlines are attached in both cases. It is deduced that compressibility and rarefaction have opposite effects on the flow. These results suggest that complex channels of the type considered here can be understood in terms of their primary units, and they experience only small secondary losses.

Ion acceleration in short-laser-pulse interaction with solid foils

Abstract: We discuss the physical processes, which take place in a multi-component plasma set in expansion by a minority of energetic electrons. The expansion is in the form of a collisionless rarefaction wave associated with three types of electrostatic shocks. Each shock manifests itself in a potential jump and in the spatial separation of plasma species. The shock front associated with the proton–electron separation sets the maximum proton velocity. Two other shocks are due to the hot–cold electron separation and the light–heavy ion separation. They result in the light ion acceleration and their accumulation in the phase space. These structures open possibilities for control of the number and the energy spectrum of accelerated ions. Simple analytical models are confirmed in numerical simulations where the ions are described kinetically, and the electrons assume the Boltzmann distribution.

A criterion for experimental validation of slip-flow models for incompressible rarefied gases through microchannels

Abstract: This paper is devoted to analysing the friction factor for incompressible rarefied gas flow through microchannels. A theoretical investigation is conducted in order to underline the conditions for experimentally evidencing rarefaction effects on the pressure drop. It is demonstrated that for a fixed geometry of the microchannel cross-section, it is possible to calculate the minimum value of the Knudsen number for which the rarefaction effects can be observed experimentally, taking into account the uncertainties related to evaluation of the friction factor.

Global entropy solutions to the relativistic Euler equations for a class of large initial data

Abstract: We are concerned with global entropy solutions to the relativistic Euler equations for a class of large initial data which involve the interaction of shock waves and rarefaction waves. We first carefully analyze the global behavior of the shock curves, the rarefaction wave curves, and their corresponding inverse curves in the phase plane. Based on these analyses, we use the Glimm scheme to construct global entropy solutions to the relativistic Euler equations for the class of large discontinuous initial data.

The structural basis of hypertension: vascular remodelling, rarefaction and angiogenesis/arteriogenesis.

Abstract: The established phase of human essential hypertension is characterized by a normal cardiac output and an elevation in peripheral resistance. A considerable part of this increase in vascular resistance is determined by the structure of the microvasculature, in particular the small arteries and precapillary arterioles, where increases in the wall thickness : lumen ratios are frequently observed [1]. In addition, other abnormalities in the microvasculature are also known to occur, such as a reduction in microvessels. Rarefaction of capillaries and arterioles has been reported in many animal models of hypertension [2,3], and may also be involved in increasing peripheral resistance in essential hypertension [4]. Rarefaction of capillaries is caused by an absence of capillaries or a functional rarefaction, in which the capillaries are present but not perfused. Capillary rarefaction has not only been reported in established essential hypertension [4], but also in borderline essential hypertension [5] and young adults with a predisposition to high blood pressure [6]. This latter observation suggests that defective angiogenesis/ arteriogenesis may be an etiological component in the inheritance of high blood pressure, and raises the possibility that genetic factors may be responsible for at least a component of microvascular rarefaction.

Solitary wave complexes in two-component condensates.

Abstract: Axisymmetric three-dimensional solitary waves in uniform two-component mixture Bose-Einstein condensates are obtained as solutions of the coupled Gross-Pitaevskii equations with equal intracomponent but varying intercomponent interaction strengths. Several families of solitary wave complexes are found: (1) vortex rings of various radii in each of the components; (2) a vortex ring in one component coupled to a rarefaction solitary wave of the other component; (3) two coupled rarefaction waves; (4) either a vortex ring or a rarefaction pulse coupled to a localized disturbance of a very low momentum. The continuous families of such waves are shown in the momentum-energy plane for various values of the interaction strengths and the relative differences between the chemical potentials of two components. Solitary wave formation, their stability, and solitary wave complexes in two dimensions are discussed.

Low-density anomalies and sub-Alfvénic solar wind

Abstract: [1] During 10–12 May 1999, the solar wind density dropped to an anomalously low value of ∼0.1 cm−3. The density depletion occurred in the midst of relatively slow wind flow, in between faster flows, and was apparently associated with neither a coronal mass ejection nor a fast corotating stream. While the magnetic field intensity did not show any notable variation across the density depletion, plasma analyzers on the ACE and Wind spacecraft revealed an abnormally strong nonradial flow component with an azimuthal speed that peaked at ∼100 km s−1. Usmanov et al. [2000b] suggested that the density anomaly was, in fact, a rarefaction at the trailing edge of relatively fast flow that formed as a result of suppression of coronal outflow from a region that earlier provided fast wind flow. The suppression in turn may have resulted from a rapid restructuring of solar magnetic fields during the polar field reversal. Here we show results from a two-dimensional time-dependent MHD simulation applied to the helioequatorial plane. The initially longitude-independent Parker solar wind and Archimedean spiral magnetic field are disturbed by a low-velocity/high-density jump on an inner computational boundary at 20 R⊙. We follow the development and propagation of the rarefaction to Earth orbit and compare pseudo-time series with near-Earth spacecraft measurements. We show that a strong rarefaction can develop behind the fast flow and that simulation results and spacecraft observations are generally in agreement. The simulated radial magnetic field shows a relatively small variation across the density anomaly compared with that of the density. The stream interaction generates strong azimuthal velocities in the slow flow region, as observed. The simulation shows a sub-Alfvenic flow region embedded within the low-density region that does not extend all the way back to the Sun but which has become disconnected as the depletion propagates to Earth orbit. We discuss also the correlation between low-density and sub-Alfvenic events in the solar wind as inferred from spacecraft observations using the OMNI 2 data set from 1963 to 2003.

Solitary waves in self-gravitating molecular clouds

Abstract: Molecular clouds are self-gravitating fluids that support different waves and contain highly nonlinear clumps and filaments, for which explanations have been sought in terms of solitons. The present paper explores the possibility that several (neutral) species with different thermal speeds coexist, as in a molecular cloud consisting of gas and dust, or of a mixture of normal matter and dark matter. It is shown that this model can support soliton formation, both with humps or dips in the self-gravitational potential. The existence domain has been given in terms of the hot species Mach number and fractional mass density, in a gas-dynamic description which emphasizes the constraints coming from the sonic and neutral points, and from the limits due to infinite compression or total rarefaction. One species is compressed while the other is rarefied, allowing the system to reach a mass neutral point outside equilibrium. In this way, solitons are possible without invoking interaction with a weakly ionized cloud component or involving envelope solitons that are not really stationary structures.

Stability conditions for strong rarefaction waves

Abstract: In this paper we study a number of algebraic conditions connected with the stability of strictly hyperbolic $n\times n$ systems of conservation laws in one space dimension: ut + f(u)x = 0 Such conditions yield existence and continuity of the flow of solutions in the vicinity of the reference solution Our main concern is a single rarefaction wave having arbitrarily large strength

DSMC simulation of low-speed gas flow and heat transfer in 2D rectangular micro-channel

Abstract: Effective boundary condition is one of the most critical problems in the computation of micro-channel flows with direct simulation Monte-Carlo (DSMC) method. In the present work, the implementation of DSMC with specified pressure boundary condition (PBC) was discussed in detail. The variations of gaseous local pressure, temperature and number density of the particles caused by the temperature difference between channel walls and gas were presented. It was found that with the increase of both gaseous compressibility and rarefaction, the pressure distribution along micro-channel became more nonlinear. Heat transfer occurred almost only at channel inlet and outlet, and the average wall heat flux increased almost linearly to the inlet-to-outlet pressure ratio. The computational results also showed that PBC was more suitable for the simulation of micro-channel flow problems than the conventional velocity boundary condition (VBC).

Appearance of Nucleation Shocks in a Boiling Liquid

Abstract: Depressurization of high-pressure vessels filled with a liquid coming to the boil with a decrease in pressure is investigated. After depressurization, which takes less than 1 ms, a rarefaction wave propagates into the vessel. Experiments [1–5] demonstrated that the pressure behind the wave goes over to a constant value, which is independent of the vessel diameter and lies between the saturation point and atmospheric pressure. The correspondence between the experiments and different bubble formation theories (bubble formation on the vessel walls, due to rupture of the bonds between the water molecules or boiling on foreign particles) is analyzed. A “ mechanical nucleation” theory is proposed, in which it is assumed that the liquid comes to the boil on a limited number of foreign particles, and the bubbles formed on the nucleation centers undergo multiple fragmentation due to the instability developing under the action of centrifugal accelerations of the bubble surface in the course of bubble growth. The calculations demonstrated that, after depressurization, bubble fragmentation occurs at the vessel outlet. Due to the growth of the phase interface in the course of fragmentation, the boiling intensity increases, the pressure grows, and a shock wave propagates into the vessel, following the rarefaction wave. Multiple fragmentation of the bubbles occurs on the shock front. This wave is followed by a series of waves with smaller amplitudes. The pressure in the vessel attains a stable level, without any shocks. This level is characterized by the metastability or superheating of the liquid, i.e. the difference between the liquid temperature and the saturation point. It is demonstrated that the resultant pressure in the vessel is independent of the number of initial boiling centers or the initial pressure in the vessel and is determined only by the initial temperature. For water, the dependence of the superheating of the liquid on the initial temperature is found and compared with experimental data.

Luminescence induced by spherically focused acoustic pulses in liquids

Abstract: The determination of the phase of the bubble oscillation at the instant of light emission, which is a key issue for understanding the origin of cavitation luminescence of liquids, is discussed. The observation of luminescence in the course of the nucleation and growth of a bubble up to its collapse is performed in a bipolar wave consisting of a compression phase followed by a rarefaction phase in the regime of a two-fraction bubble cluster formation. The space-time distributions of the luminescence intensity and pressure and the dynamics of the cluster in water and a glycerin solution are investigated at the early stage of cavitation. A correlation between the maximal density of light flashes and the positive pressure pulses in the field of superposition of the initial and secondary cavitation compression waves is revealed. It is shown that the spherical focusing of acoustic pulses both away from the boundaries of the liquid and near its free surface makes it possible to compare the luminescence intensities for different rates of the pressure decrease.

Zero Dissipation Limit to Rarefaction Waves for the p –System

Abstract: We study the zero–dissipation problem for a one–dimensional model system for the isentropic flow of a compressible viscous gas, the so–called p–system with viscosity. When the solution of the inviscid problem is a rarefaction wave with finite strength, there exists unique solution to the viscous problem with the same initial data which converges to the given inviscid solution as ∈ goes to zero. The proof consists of a scaling argument and elementary energy analysis, based on the underlying wave structure.

Experimental study on interference effect of rarefaction wave on laminar propagating flame

Abstract: In order to study the interference effect of rarefaction wave on the laminar flame propagating structure and pressure characteristics of methane-air mixture, a small scale combustion chamber has been built. The techniques of high speed Schlieren photograph, pressure measurement and so on, are used to study the influence of rarefaction wave on the laminar flame propagating through methane-air mixture. The results show that, after the rarefaction wave acts on the propagation laminar flame, the laminar combustion is fully transformed into turbulent combustion just during several milliseconds, which leads to a sharp increase in the burning surface area and the pressure rise rate.

Direct Statistical Simulation of a Supersonic Flow of a Binary Mixture of Rarefied Gases around a Transversely Positioned Cylinder

Abstract: A supersonic flow of a binary mixture of gases in a wide range of rarefaction (from a flow with a Knudsen number Kn = 0.1 to a free-molecular flow) around a cylinder is studied by means of direct statistical Monte Carlo simulations (DSMC method). The influence of a small fraction of heavy particles in a light gas flow on the region of significant nonequilibrium near the cylinder and on the heat flux is considered.

Dynamic fatigue

Abstract: Dynamic fatigue differs from quasi-static fatigue in the spall damage nature. A consequence of the spall nature is the alternate appearance of longitudinal cracks, each of which becomes the source of rarefaction. The focusing or interference of rarefaction waves specifies the sites of nucleation and growth of channel and ring cracks; therefore, initially existing surface defects are not operative. Another consequence of the spall damage nature is the determining effect of the orientation of the lateral faces of flyer plates having finite dimensions, since these faces specify the intensity of the appearing lateral rarefaction wave.

Head-disk interface modeling with the lattice Boltzmann method

Abstract: Molecular rarefaction within gaseous lubricating films is critical to the analysis of the head-disk interface (HDI) as the spacing between the slider and the disk becomes extremely small in order to achieve higher areal recording density. The molecular rarefaction was incorporated via the Boltzmann transport equation (BTE), by Fukui & Kaneko (1987) and Kang et al. (1999), to describe a slip flow using the Knudsen number (Kn) and surface accommodation factor and was implemented to accurately simulate slider attitude. Since the trailing edge fly height is only a few times greater than the lubricant thickness, it is desirable to invent an innovative rarefied gas dynamics model by incorporating molecular information of the lubricant layer.

Evaluating Anisotropy and Thermodynamic Non‐Equilibrium in Hypersonic Transitional Regime

Abstract: This paper is the logical continuation of a former paper by Zuppardi and Paterna where the limits, in terms of rarefaction, of the proper working of a Navier‐Stokes (NS) and a Direct Simulation Monte Carlo (DSMC) code were fixed. That analysis relied on the comparison of the aerodynamic coefficients, from the two codes, of a typical capsule along a probable re‐entry path to Earth from an interplanetary mission. As the basic principle of the DSMC method is valid at each rarefaction level, the limitation in using a DSMC code with decreasing rarefaction was verified to be due just to the computer capabilities. On the contrary with increasing rarefaction, the proper use of a NS code is affected by intrinsic limitations like: i) failure of the classical phenomenological equations, ii) difference of the components of the translational temperature, of the pressure tensor and of the diffusion velocity of chemical species (anisotropy) and difference of the traslational, vibrational and rotational temperatures (the...

Experimental study on interference effect of rarefaction wave on laminar propagating flame

Abstract: In order to study the interference effect of rarefaction wave on the laminar flame propagating structure and pressure characteristics of methane-air mixture, a small scale combustion chamber has been built. The techniques of high speed Schlieren photograph, pressure measurement and so on, are used to study the influence of rarefaction wave on the laminar flame propagating through methane-air mixture. The results show that, after the rarefaction wave acts on the propagation laminar flame, the laminar combustion is fully transformed into turbulent combustion just during several milliseconds, which leads to a sharp increase in the burning surface area and the pressure rise rate.

Compaction and rarefaction affect photolithography system lifetimes

Abstract: Stringent performance requirements limit the number of optical materials that can be used to make the 193-nm lens systems used in semiconductor-manufacturing equipment.

Asymptotic stability of rarefaction wave for generalized burgers equation

Abstract: This paper is concerned with the stability of the rarefaction wave for the Burgers equation{ ut+f(u)x=μtαuxx, μ＞0, x∈R, t＞0, (Ⅰ)u|t=o = u0(x) →u± , x →∞ ,where 0 ≤α＜ 1/4q (q is determined by (2.2)). Roughly speaking, under the assumption that u- ＜ u+, the authors prove the existence of the global smooth solution to the Cauchy problem (Ⅰ), also find the solution u(x, t) to the Cauchy problem (Ⅰ) satisfying sup |u(x, t)-x∈RuR(x/t)| → 0 as t →∞, where uR(x/t) is the rarefaction wave of the non-viscous Burgers equation ut + f(u)x = 0 with Riemann initial data u(x, 0) ={u_,x＜0, u+, x＞0.

Similarity of Microscale and Rarefied Gas Flows

Abstract: The similarity between micro gas flow and rarefied gas flow was numerically investigated using a DSMC method. With compressibility and rarefaction effects, the similarity parameters are the Mach number and the Knudsen number, since the Reynolds number is dependent on the Mach number and the Knudsen number for an ideal gas. Comparisons of numerical results for various scales show that the normalized fields for the macroscopic quantities are quite similar, which shows that the microscale flow is similar to rarefied flow of an ideal gas. Therefore, existing rarefied flow results can be applied to microscale flows. However, for dense gas flows, the three dimensionless parameters are independent, so the similarity breaks down for dense gas flows. Simulation results for an ideal gas using nitrogen as an example show that the similarity holds for densities less than 7–8 times the density at standard conditions.Copyright © 2005 by ASME

Mach disk destruction by interference of rarefaction and compression waves

Abstract: New method of stagnation wave destruction that leads to diminishing of total pressure losses in the non-stationary post-shock flows was proposed. It was proved by pressure measurements of the effect of such flow on the flat plate located in front of the exit of shock tube. The results showed the essential pressure increase on the obstacle. To explain the nature of this phenomenon the schlieren flow visualization was made. Numerical modelling enabled the description of flow parameters distribution on the obstacle.

Asymptotic stability of rarefaction wave of the Cauchy problem for viscous conservation laws

Abstract: This paper is concerned with the asymptotic stability of rarefaction waves for the two-dimensional steady isentropic irrotational flow with artificial viscosity. We prove that if the initial value is close to a constant state and the corresponding inviscid hyperbolic system admits a weak rarefaction wave, then the solution tends to this rarefaction wave as t → ∞ .

Numerical simulation on pulse detonation propulsion

Abstract: In this study, wave processes in pulse detonation facility are numerically simulated to gain basic understanding on the PDEs working mechanism. A detailed aspect of wave motion in one PDE cycle is obtained and can be used as the basis of PDE timing system. It is also understand that reflected rarefaction fans are strong enough to decrease the reaction product pressure at the closed end to a low level, but the temperature is still so high that auto-ignition of fresh gas mixture may be induced, therefore, a pure air purge must be employed to separate the fresh gas mixture from the high temperature products.