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1.
A mathematical model of two-phase (gas-solid particle) flow which takes into account particle-particle collisions and the feedback effect of the admixture on the gas parameters is proposed. The dispersed phase is described by a kinetic equation of the Boltzmann type and the carrier gas by modified Navier-Stokes equations. Using this model, a supersonic uniform dusty-gas flow past a cylinder is calculated. The fields of the macroparameters of the admixture and the carrier medium are obtained. The dependence of the heat transfer at the stagnation point on the relative particle size and the free-stream admixture concentration is studied in detail. The ranges of these parameters on which particle collisions and the feedback effect of the admixture on the carrier-gas flow are important are found. 相似文献
2.
The problem of hydrodynamic interaction between a laminar flow of a viscous fluid and a partially permeable spherical particle
is formulated and solved analytically. The filtration flow inside the particle is assumed to obey the Darcy law. Expressions
for the filtration flow velocity, drag, sedimentation velocity, and stream functions are obtained. The effect of the permeability
of the particle on the flow characteristics is studied. Stream functions of the flow are constructed.
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Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 50, No. 4, pp. 48–53, July–August, 2009. 相似文献
3.
Yu. A. Sergeev 《Fluid Dynamics》1987,22(3):410-413
The effect of particle size (Archimedes number) on the propagation of a kinematic particle concentration wave in a fluidized bed is investigated. The dependence of the characteristic wave velocity on the porosity of the bed (particle concentration) and the Archimedes number (or the Reynolds number for flow past individual particles of the dispersed phase) is determined. The evolution of a nonlinear perturbation of the bed porosity is investigated and the formation of discontinuities in the concentration of the dispersed phase is studied in relation to the particle size (Archimedes number). It is shown, in particular, that, as distinct from a bed of small particles, in a bed of large particles with quadratic interphase interaction only compression discontinuities can be formed. The results obtained can be used to analyze the formation of inhomogeneities (slugs and bubbles) in a fluidized bed in relation to the particle size.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 3, pp. 96–100, May–June, 1987. 相似文献
4.
A problem of regular (symmetric and asymmetric) interaction of plane shock waves in a steady-state dusty-gas flow is considered.
The possibility of the formation of wave structures is revealed, in which either all or some of the incident or reflected
waves degenerate into fully dispersed waves, i.e. zones in which the parameters of both phases vary continuously. Using the
Rankine-Hugoniot relations for a one-velocity “effective-gas” model, the ranges of nondimensional governing parameters (the
Mach number, the angles between the incident waves and the free stream, the phase specific-heat ratio, and the particle mass
concentration) are found, which correspond to different wave configurations. In the framework of a two-fluid dusty-gas model,
the flow structure in the region of symmetric interaction of the shocks is calculated numerically for typical configurations
containing fully dispersed waves. The flow in the region of a normal fully dispersed wave is also calculated. Good agreement
between the calculated wave structure and the data known in the literature is obtained. A range of governing parameters in
which the carrier-phase temperature has a local maximum inside the wave structure is found. 相似文献
5.
The turbulent fluid and particle interaction in the turbulent boundary layer for cross flow over a cylinder has been experimentally
studied. A phase-Doppler anemometer was used to measure the mean and fluctuating velocities of both phases. Two size ranges
of particles (30μm–60μm and 80μm–150μm) at certain concentrations were used for considering the effects of particle sizes
on the mean velocity profiles and on the turbulent intensity levels. The measurements clearly demonstrated that the larger
particles damped fluid turbulence. For the smaller particles, this damping effect was less noticeable. The measurements further
showed a delay in the separation point for two phase turbulent cross flow over a cylinder.
The project supported by the National Natural Science Foundation of China 相似文献
6.
During the flow of an emulsion, droplets of the dispersed phase can deform, break up, coalesce or migrate to other regions
within the flow field. Understanding these different processes is relevant to morphology development in immiscible polymer
blends. Here, emulsions of castor oil in silicone oil were employed to study shear-induced coalescence alone; the conditions
chosen were such that drop breakup and drop migration did not occur. A cone-and-plate device and tubes of varying length were
used to examine the influence of the average shear rate, the time of shearing, concentration of the dispersed phase, and temperature
on the average droplet size. It was found that the extent of “demixing” was not influenced by the spatially non-homogeneous
nature of flow in a tube; results correlated very well with the average shear rate. On the other hand, coalescence was significant
even when the concentration of the dispersed phase was as low as 0.5%, and it became more important as the concentration was
increased. Other results were that the extent of coalescence could be promoted by lowering the shear rate. In quantitative
terms, it was found that available coalescence theory gave the correct order of magnitude for the average steady-state droplet
size as a function of the imposed shear rate, but the actual variation of drop size with shear rate was gentler than that
predicted by theory. An unusual observation was that, under some circumstances, the droplets did not coalesce but simply stuck
to each other and maintained their separate identity.
Received: 25 March 1999/Accepted: 22 July 1999 相似文献
7.
The parameters of an axisymmetric turbulent two-phase swirling flow of a viscous heat-conducting gas containing a liquid dispersed phase in the presence of water vapor condensation on the particles are calculated. For the dispersed phase, a model taking into account the variation of the vapor concentration and the particle size due to condensation or evaporation is proposed. The distributions of the parameters of the basic unperturbed flow obtained numerically are used in the numerical solution of the linear problem of hydrodynamic stability within the time-dependent formulation. The parameters of small-amplitude harmonic perturbations propagating along the vortex axis are investigated in the linear formulation. A significant effect of heat release in the gas due to water vapor condensation on the parameters of the neutral perturbations and the neutral-stability curves is detected. 相似文献
8.
K. N. Volkov 《Journal of Applied Mechanics and Technical Physics》2008,49(3):425-436
The motion and heat and mass transfer of particles of a disperse admixture in nonisothermal jets of a gas and a low-temperature
plasma are simulated with allowance for the migration mechanism of particle motion actuated by the turbophoresis force and
the influence of turbulent fluctuations of the jet flow velocity on heat and mass transfer of the particle. The temperature
distribution inside the particle at each time step is found by solving the equation of unsteady heat conduction. The laws
of scattering of the admixture and the laws of melting and evaporation of an individual particle are studied, depending on
the injection velocity and on the method of particle insertion into the jet flow. The calculated results are compared with
data obtained with ignored influence of turbulent fluctuations on the motion and heat and mass transfer of the disperse phase.
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Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 49, No. 3, pp. 95–108, May–June, 2008. 相似文献
9.
In this study the effect of the volume percentage dispersed phase on the flow structure in an immiscible liquid–liquid system is investigated. A model system, consisting of two refraction index matched liquids, is presented along with velocity measurements of the continuous phase utilising the particle image velocimetry technique. Velocity fields at three locations have been measured inside a baffled cylindrical tank, stirred with a six-bladed Rushton turbine. The experiments show that this technique is applicable for volume fractions of up to 10% of dispersed phase. The magnitudes of velocity and turbulence are clearly affected by the level of the dispersed volume fraction. 相似文献
10.
The interaction between a particle and a shock wave leads to unsteady forces that can be an order of magnitude larger than
the quasi-steady force in the flow field behind the shock wave. Simple models for the unsteady force have so far not been
proposed because of the complicated flow field during the interaction. Here, a simple model is presented based on the work
of Parmar et al. (Phil Trans R Soc A 366:2161–2175, 2008). Comparisons with experimental and computational data for both stationary
spheres and spheres set in motion by shock waves show good agreement in terms of the magnitude of the peak and the duration
of the unsteady force.
相似文献
11.
In dense two-phase flows, it is well known that phase Doppler anemometry is not well suited for the measurement of concentration
and mass flux. Laser diagnostics based on fluorescence can provide the dispersed phase concentration but without discrimination
between size classes. We present a new method of coupling the two techniques, in order to extract the local value of concentration
and flux per size class. The method is applied to an axisymmetric turbulent jet, laden with polydispersed droplets 1–90 μm.
Droplet concentration profiles are obtained in the development zone (x/d
0 < 20) of the dense jet and are used to study droplet dispersion. The results are then introduced into the momentum transport
equations to analyze the influence of droplets on the carrier phase. We show that the local decrease of the rate of variation
of mean momentum with mass loading is due both to an increase in interfacial transfer rate and to a decrease in turbulent
diffusion effects.
Received: 20 November 2000 / Accepted: 3 April 2001 相似文献
12.
In this work we examine first the flow field of a confined jet produced by a turbulent flow in a long cylindrical pipe issuing
in an abrupt angle diffuser. Second, we examine the dispersion of inertial micro-particles entrained by the turbulent flow.
Specifically, we examine how the particle dispersion field evolves in the multiscale flow generated by the interactions between
the large-scale structures, which are geometry dependent, with the smaller turbulent scales issued by the pipe which are advected
downstream. We use Large-Eddy-Simulation (LES) for the flow field and Lagrangian tracking for particle dispersion. The complex
shape of the domain is modelled using the immersed-boundaries method. Fully developed turbulence inlet conditions are derived
from an independent LES of a spatially periodic cylindrical pipe flow. The flow field is analyzed in terms of local velocity
signals to determine spatial coherence and decay rate of the coherent K–H vortices and to make quantitative comparisons with
experimental data on free jets. Particle dispersion is analyzed in terms of statistical quantities and also with reference
to the dynamics of the coherent structures. Results show that the particle dynamics is initially dominated by the Kelvin–Helmholtz
(K–H) rolls which form at the expansion and only eventually by the advected smaller turbulence scales. 相似文献
13.
Effect of the boundary layer on the base pressure in a two-dimensional flow with a Mach number M = 5
M. G. Ktalkherman V. M. Malkov 《Journal of Applied Mechanics and Technical Physics》2005,46(3):324-328
New data on the base pressure in a two-dimensional ow with a Mach number M = 5 are obtained for a wide range of variation of the normalized boundary-layer thickness in the flow-separation cross section.
The test results are compared with Tanner’s theory, and a conclusion is made that this numerical model has to be corrected.
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Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 46, No. 3, pp. 23–28, May–June, 2005. 相似文献
14.
D. V. Sadin 《Journal of Applied Mechanics and Technical Physics》1999,40(1):130-135
The unsteady axisymmetric jet produced by discharge of a mixture of a pressurized gas and dispersed particles from a circular
duct into the atmosphere is studied within the framework of two-velocity, two-temperature gas dynamics. An attempt is undertaken
to allow for the effective pressure due to random particle motion. The collision mechanism is found to be essential to radial
expansion of the flow. Experimental data that support the results obtained are reported.
Mozhaiskii Military Spacecraft Engineering Academy, St. Petersburg 197082. Translated from Prikladnaya Mekhanika i Tekhnicheskaya
Fizika, Vol. 40, No. 1, pp. 151–157, January–February, 1999. 相似文献
15.
S. A. Boronin 《Fluid Dynamics》2012,47(3):351-363
The classical stability theory for multiphase flows, based on an analysis of one (most unstable) mode, is generalized. A method
for studying an algebraic (non-modal) instability of a disperse medium, which consists in examining the energy of linear combinations
of three-dimensional modes with given wave vectors, is proposed. An algebraic instability of a dusty-gas flow in a plane channel
with a nonuniform particle distribution in the form of two layers arranged symmetrically with respect to the flow axis is
investigated. For all possible values of governing parameters, the optimal disturbances of the disperse flow have zero wavenumber
in the flow direction, which indicates their banded structure (“streaks”). The presence of dispersed particles in the flow
increases the algebraic instability, since the energy of optimal disturbances in the disperse medium exceeds that for the
pure-fluid flow. It is found that for a homogeneous particle distribution the increase in the energy of optimal perturbations
is proportional to the square of the sum of unity and the particle mass concentration and is almost independent of particle
inertia. For a non-uniform distribution of the dispersed phase, the largest increase in the initial energy of disturbances
is achieved in the case when the dust layers are located in the middle between the center line of the flow and the walls. 相似文献
16.
The present paper studies numerical modelling of near-wall two-phase flows induced by a normal shock wave moving at a constant speed, over a micron-sized particles bed. In this two-fluid model, the possibility of particle trajectory intersection is considered and a full Lagrangian formulation of the dispersed phase is introduced. The finiteness of the Reynolds and Mach numbers of the flow around a particle as well as the fineness of the particle sizes are taken into account in describing the interactions between the carrier- and dispersed-phases. For the small mass-loading ratio case, the numerical simulation of flow structure of the two phases is implemented and the profiles of the particle number density are obtained under the constant-flux condition on the wall. The effects of the shock Mach number and the particle size and material density on particle entrainment motion are discussed in detail. The obtained results indicate that interphase non-equilibrium in the velocity and temperature is a common feature for this type of flows and a local particle accumulation zone may form near the envelope of the particle trajectory family. 相似文献
17.
Bert Vreman Bernard J. Geurts N. G. Deen J. A. M. Kuipers J. G. M. Kuerten 《Flow, Turbulence and Combustion》2009,82(1):47-71
Large-eddy simulations (LES) of a vertical turbulent channel flow laden with a very large number of solid particles are performed.
The motivation for this research is to get insight into fundamental aspects of co-current turbulent gas-particle flows, as
encountered in riser reactors. The particle volume fraction equals about 1.3%, which is relatively high in the context of
modern LES of two-phase flows. The channel flow simulations are based on large-eddy approximations of the compressible Navier–Stokes
equations in a porous medium. The Euler–Lagrangian method is adopted, which means that for each individual particle an equation
of motion is solved. The method incorporates four-way coupling, i.e., both the particle-fluid and particle–particle interactions
are taken into account. The results are compared to single-phase channel flow in order to investigate the effect of the particles
on turbulent statistics. The present results show that due to particle–fluid interactions the mean fluid profile is flattened
and the boundary layer is thinner. Compared to single-phase turbulent flow, the streamwise turbulence intensity of the gas
phase is increased, while the normal and spanwise turbulence intensities are reduced. This finding is generally consistent
with existing experimental data. The four-way coupled simulations are also compared with two-way coupled simulations, in which
the inelastic collisions between particles are neglected. The latter comparison clearly demonstrates that the collisions have
a large influence on the main statistics of both phases. In addition, the four-way coupled simulations contain stronger coherent
particle structures. It is thus essential to include the particle–particle interactions in numerical simulations of two-phase
flow with volume fractions around one percent. 相似文献
18.
Results of experimental investigation of the problem of active control of the charge acquired by a body (sphere) in flow with
an electrically charged component (ions) and electrically charged dispersed phase (water drops) are obtained and analyzed.
This situation is not uncommon during aircraft flight in a cloud front. Previous experimental studies have mainly considered
flows without a dispersed phase. The required flow was created by introducing in a turbulent air-steam jet a corona discharge
on whose ions “electric” condensation developed and on the growing drops that arose a charge was accumulated due to diffusion
processes and directional ion motion in the electric field. On the sphere which was introduced in the charged jet a discharger
(active compensator) with an autonomous high-voltage power source creating a potential difference between the discharger corona
needle insulated from the body and the body surface was mounted. Measurements of the size and concentration of the drops ahead
of the critical point of the sphere were performed. The electric currents to elements of the experimental electric system
and the floating potential of the body were measured for various corona charge parameters and various voltages on the active
compensator. An active control of the sphere charge, its complete removal and the recharge of the sphere, is realized. 相似文献
19.
An experimental investigation on the convective heat transfer and friction factor characteristics in the plain and dimpled
tube under laminar flow with constant heat flux is carried out with distilled water and CuO/water nanofluids. For this, CuO
nanoparticles with an average size of 15.3 nm were synthesized by sol–gel method. The nanoparticles are then dispersed in
distilled water to form stable suspension of CuO/water nanofluid containing 0.1, 0.2 and 0.3% volume concentration of nanoparticles.
It is found that the experimental Nusselt numbers for 0.1, 0.2 and 0.3% volume concentration of CuO nanoparticles are about
6, 9.9 and 12.6%, respectively higher than those obtained with distilled water in plain tube. However, the experimental Nusselt
numbers for 0.1, 0.2 and 0.3% volume concentration of CuO nanoparticles are about 3.4, 6.8 and 12%, respectively higher than
those obtained with distilled water in dimpled tube. The friction factor of CuO/water nanofluid is also increased due to the
inclusion of nanoparticles and found to increase with nanoparticle volume concentration. The experimental results show that
there exists a difference in the enhancement levels of Nusselt numbers obtained with nanofluids in plain tube and dimpled
tube. Hence it is proposed that the mechanism of heat transfer enhancement obtained with nanofluids is due to particle migration
from the core of fluid flow to tube wall. 相似文献