The Hydrodynamics and Heat and Mass Transfer of Particles under Conditions of Turbulent Flow of Gas Suspension in a Pipe and in an Axisymmetric Jet

A mathematical model for the calculation of the hydrodynamic and thermal parameters of dispersed impurity in a round pipe and in a jet is given in Eulerian variables. The model is based on a unified set of equations describing the turbulent characteristics of particles in nonisothermal flow and of boundary conditions representing the interaction of the particles with the rough channel surface and the boundary of submerged jet. The effect of the anisotropy of turbulent fluctuations of the particle velocity and of the correlation between the thermal properties of the particle material and carrier gas on the intensity of momentum, heat, and mass transfer in the dispersed phase is investigated. The calculation results are compared with the experimental data.     

Modeling nonlocal mass transfer of a dispersed impurity in turbulent flows of a gas suspension

The effect of nonlocal phenomena occurring with the motion of inertial particles on the rate of mass transfer of the dispersed phase is studied on the basis of a closed expression constructed for the probability density function determining the transport of these particles in a turbulent nonuniform flow.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 59, No. 3, pp. 454–466, September, 1990.     

Numerical modeling of the aerodynamics, heat exchange, and combustion of a polydisperse ensemble of coke-ash particles in ascending axisymmetric two-phase flow

A two-dimensional stationary model of motion, heat and mass exchange, and chemical reaction of polydisperse coke and ash particles in ascending gas-suspension flow has been constructed with allowance for the turbulent and pseudoturbulent mechanisms of transfer in the dispersed phase. The system of equations that describes motion and heat transfer in the solid phase has been closed at the level of the equations for the second moments of velocity and temperature pulsations, whereas the momentum equations of the carrying medium have been closed using the equation for turbulent gas energy, which allows for the influence of the particles and heterogeneous reactions.     

Analysis of statistical model of heat transfer of particles in isotropic turbulence with constant temperature gradient

Comparison with the data of direct numerical calculations in isotropic turbulence with constant temperature gradient is used for verifying the statistical model of heat transfer in gas-dispersed turbulent flows. Analysis is made of the effect of thermal inertia of particles on the correlations between turbulent heat fluxes and intensities of temperature fluctuations in the dispersed and continuous phases.     

Calculation of a turbulent monodisperse flow in an axisymmetric channel

A stationary isothermal model of the aerodynamics of a two-phase flow in an axisymmetric channel has been constructed with allowance for the turbulent and pseudoturbulent mechanisms underlying the transfer of the solid phase momentum. The equations of dispersed phase motion are closed at the level of the equations for the second moments of the pulsation velocities of particles, whereas the equation of momentum transfer of the carrier is closed on the basis of a one-parameter model of turbulence extended to the case of two-phase turbulent flows. The results of calculations are compared with experimental data. __________ Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 81, No. 5, pp. 844–855, September–October, 2008.     

Numerical model of the scattering of a gaseous and dispersed impurity in the atmosphere

A numerical model of the transfer of a gaseous and dispersed impurity in the atmosphere is described. The model is based on the semi-empirical stationary equation of turbulent diffusion in the boundary layer of the atmosphere with account for the gravitational deposition of particles. The altitude profiles of the coefficient of turbulent diffusion and of the wind velocity are approximated according to the Monin-Obukhov theory and the data obtained by Byzova with her coworkers. The atmosphere stratification is determined on the basis of standard meteorological data. The model is compared with experimental data and with well-known techniques used to calculate the propagation of impurity in the atmosphere. __________ Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 81, No. 5, pp. 907-911, September–October, 2008.     

Simulation of Second Moments of Fluctuations of the Velocity and Temperature of Particles in Equilibrium Turbulent Flows

An analysis is performed of equilibrium solutions of equations for the second moments of fluctuations of the velocity and temperature of particles in a homogeneous shear flow, in a homogeneous flow subjected to tensile or compressive strain, and in a wall layer. The stability of equilibrium solutions to small perturbations is investigated. Algebraic models are given for turbulent stresses in the dispersed phase.     

Diffusion-migration description of finely dispersed impurity propagation in a turbulent jet

Computations of the scattering of a finely dispersed impurity in a submerged jet are performed on the basis of a model taking account of turbulent diffusion and turbulent migration together.Translated from Inzhenerno-fizicheskii Zhurnal, Vol. 59, No. 4, pp. 609–614, October, 1990.     

Clustering of charged particles in isotropic turbulence

A statistical model is given of the formation of ordered structures (clusters) in a homogeneous isotropic turbulent field. The suggested model is based on the kinetic equation for the probability density function of relative velocity of a pair of particles. The solution of the problem is treated for a steady-state rarefied system of dispersed particles in view of pair interaction.Translated from Teplofizika Vysokikh Temperatur, Vol. 42, No. 6, 2004, pp. 908–916.Original Russian Text Copyright © 2004 by V. M. Alipchenkov, L. I. Zaichik, and O. F. Petrov.     

Influence of particle density and size on turbulence, friction, and heat exchange characteristics

Numerical simulation of turbulent flows of a gas suspension in the vicinity of the critical point and in a channel with permeable walls has been carried out. The influence of the concentration of the dispersed phase and the size of its particles on the distribution of mean and pulsation characteristics of the flow, as well as on the friction and heat transfer coefficients, is discussed.     

Use of equations for transfer of particle pulsation characteristics for calculating two-phase flows in the stabilized section of a tube

A stationary isothermal system of equations defining the behavior of a two-phase rising flow in the region of steady motion of a gas suspension in an axially symmetric channel has been developed. The equation of motion of the carrying medium is closed using a one-parameter model of turbulence, and the equation of momentum transfer in the dispersed phase is closed with the use of the equations for the second, third, and fourth moments of the pulsation velocities of the particles. The main mechanisms of two-phase turbulent flows were numerically investigated. __________ Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 80, No. 4, pp. 99–109, July–August, 2007.     

Electrode self-cleaning in a barrier ozonizer operating in a turbulent gas flow regime

The effect of self-cleaning of the discharge gaps in electric barrier ozonizers featuring a turbulent gas flow is related to the fact that the hydrodynamic forces (separating foreign solid and liquid particles from the electrode surface) predominate over electric forcers (attracting such particles to the electrodes). In this respect, ozonizers operating in a turbulent gas flow regime are advantageous over devices operating with a laminar flow.     

Direct numerical simulation of turbulent heat transfer modulation in micro-dispersed channel flow

Summary The objective of this paper is to study the influence of dispersed micrometer size particles on turbulent heat transfer mechanisms in wall-bounded flows. The strategic target of the current research is to set up a methodology to size and design new-concept heat transfer fluids with properties given by those of the base fluid modulated by the presence of dynamically-interacting, suitably-chosen, discrete micro- and nano-particles. We ran direct numerical simulations for hydrodynamically fully developed, thermally developing turbulent channel flow at shear Reynolds number Re _τ = 150 and Prandtl number Pr = 3, and we tracked two large swarms of particles, characterized by different inertia and thermal inertia. Preliminary results on velocity and temperature statistics for both phases show that, with respect to single-phase flow, heat transfer fluxes at the walls increase by roughly 2% when the flow is laden with the smaller particles, which exhibit a rather persistent stability against non-homogeneous distribution and near-wall concentration. An opposite trend (slight heat transfer flux decrease) is observed when the larger particles are dispersed into the flow. These results are consistent with previous experimental findings and are discussed in the frame of the current research activities in the field. Future developments are also outlined. Dedicated to Professor Franz Ziegler on the occasion of his 70th birthday It is our great pleasure to take part in this Festschrift Issue dedicated to the celebration of the 70th birthday of Professor Franz Ziegler. To honour his activity and his scientific achievements, we prepared this paper, crafted with friendship and respect. We wish Franz many more productive, enjoyable and happy years and a solid and long collaboration as Editors of Acta Mechanica.     

Electrodeposition of Zirconia Particles in a Copper Matrix

Electrochemical codeposition is one of the most important methods of providing composites with metallic or nonmetallic compounds as a second phase, in a metallic matrix or nonmetallic matrix. Composite coatings can be prepared by electrodeposition from an electrolytic solution containing a suspension of insoluble ZrO₂ particles. Interesting applications have been developed for wear resistance, dry lubrication, anticorrosion, dispersion hardening, and electrocatalysis. The aim of the present study is to obtain a better understanding of the effects of the dispersed particles on the mechanism of copper electrocrystallization and on the incorporation rate of dispersed phase in the deposit. Cathodic polarization curves in electrolytes with and without dispersed particles were plotted to identify their influence in the process of metal electrodeposition. The effect of the operating parameters (current density, concentration of the dispersed phase in the electrolyte) on the concentration of the dispersed phase in the composite layer is described by means of simple mathematical equations.     

Analysis of triboelectric charging of particles due to aerodynamic dispersion by a pulse of pressurised air jet

Triboelectric charging of powders causes nuisance and electrostatic discharge hazards. It is highly desirable to develop a simple method for assessing the triboelectric charging tendency of powders using a very small quantity. We explore the use of aerodynamic dispersion by a pulse of pressurised air using the disperser of Morphologi G3 as a novel application. In this device particles are dispersed by injection of a pulse of pressurised air, the dispersed particles are then analysed for size and shape analysis. The high transient air velocity inside the disperser causes collisions of sample particles with the walls, resulting in dispersion, but at the same time it could cause triboelectric charging of the particles. In this study, we analyse this process by evaluating the influence of the transient turbulent pulsed-air flow on particle impact on the walls and the resulting charge transfer. Computational Fluid Dynamics is used to calculate particle trajectory and impact velocity as a function of the inlet air pressure and particle size. Particle tracking is done using the Lagrangian approach and transient conditions. The charge transfer to particles is predicted as a function of impact velocity and number of collisions based on a charge transfer model established previously for several model particle materials. Particles experience around ten collisions at different velocities as they are dispersed and thereby acquire charges, the value of which approaches the equilibrium charge level. The number of collisions is found to be rather insensitive to particle size and pressure pulse, except for fine particles, smaller than about 30 µm. As the particle size is increased, the impact velocity decreases, but the average charge transfer per particle increases, both very rapidly. Aerodynamic dispersion by a gas pressure pulse provides an easy and quick assessment of triboelectric charging tendency of powders.     

Modeling of ascending polydisperse flow with allowance for heterogeneous combustion,particle rotation,and turbulent and pseudoturbulent effects

A closed system of equations that describes motion and physicochemical processes in ascending polydisperse flow with allowance for the rotation of the dispersed phase, the aerodynamic-drag, gravity, and Magnus forces, and the interaction of particles with each other and with the reactor wall is constructed. The equations of motion and heat transfer of the solid phase are closed at the level of equations for the second moments of pulsations of the linear and angular velocities of particles and their temperature. The pulsation characteristics of the carrying medium are computed using the equation for the turbulent gas energy.     

Experimental study of fluctuations of particle velocity in a turbulent flow of air in a pipe

The distribution of longitudinal and normal components of the fluctuation velocity of particles in their motion in a downward turbulent airflow in a pipe is obtained. The effect of the concentration of particles on the intensity of fluctuations of their velocity is studied. A high rise of the longitudinal fluctuation of the velocity of particles in the pipe wall region with an increase in their concentration is revealed.     

Velocity Fluctuations in a Particle-Laden Turbulent Flow over a Backward-Facing Step

Dilute gas-particle turbulent flow over a backward-facing step is numerically simulated. Large Eddy Simulation (LES) is used for the continuous phase and a Lagrangian trajectory method is adopted for the particle phase. Four typical locations in the flow field are chosen to investigate the two-phase velocity fluctuations. Time-series velocities of the gas phase with particles of different sizes are obtained. Velocity of the small particles is found to be similar to that of the gas phase, while high frequency noise exists in the velocity of the large particles. While the mean and rms velocities of the gas phase and small particles are correlated, the rms velocities of large particles have no correlation with the gas phase. The frequency spectrum of the velocity of the gas phase and the small particle phase show the -5/3 decay for higher wave number, as expected in a turbulent flow. However, there is a "rising tail' in the high frequency end of the spectrum for larger particles. It is shown that large particles behave differently in the flow field, while small particles behave similarly and dominated by the local gas phase flow.     

The effect of interphase interaction on the development of perturbations in a turbulent swirl flow in multicomponent cocurrent supersonic stream

The parameters are calculated of flow in the viscous core of an axisymmetric multicomponent turbulent vortex in a cocurrent supersonic stream containing liquid particles and water vapor condensing on these particles. The effect of interphase transfer of momentum and energy on the flow parameters in the vortex core is taken into account. The results of analysis of harmonic disturbances of infinitely small amplitude propagating along the vortex axis are used to determine the effect of turbulent swirl flow on the behavior of neutral disturbances associated with the processes of evaporation and condensation of water vapor on liquid particles in the axisymmetric vortex.