Simulation of fine-dispersed turbulent flow in a pipe on the basis of the nonlinear model of turbulent viscosity

A nonlinear model of turbulent viscosity (the explicit algebraic Reynolds stress model) for gas-dispersed flow with small heavy particles has been presented. The calculations have been checked by comparison with the experimental data on the effect of the fine-dispersed admixture on turbulent flow of air in a pipe.     

The Theory of Equilibrium Fluctuations of Thermodynamic Quantities in Open Systems with a Small Number of Particles

Fluctuations in open subsystems with a small number of particles and fixed volume immersed in an equilibrium system (thermostat) are treated. Within the framework of classical thermodynamics, the distribution functions of fluctuations of the number of particles, momentum, and energy in these subsystems are derived. These results are compared with the corresponding data obtained for hard spheres using the method of molecular dynamics. Their satisfactory agreement is observed. It is demonstrated that the distribution functions of fluctuations of the number of particles and energy are significantly different from both the Gauss and Poisson distribution. The distribution function of fluctuations of momentum of a small subsystem is Gaussian and independent of the density of the thermostat.     

Distinctive features of phase transitions in the formation of nanosized aerosol particles

The influence of a foreign gas on the formation of nanosized particles is investigated theoretically. The influence of heating the particles on the concentration of admixture molecules that are trapped in the process of condensation growth of the particles is considered. __________ Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 81, No. 2, pp. 264–270, March–April, 2008.     

Oscillatory-like relaxation behavior of light transmitted through ferrofluids

An oscillatory-like relaxation process in which there are two valleys in the T-t curve is observed when light is transmitted through binary ferrofluids composed of both ferrimagnetic CoFe(2)O(4) nanoparticles and paramagnetic p-MgFe(2)O(4) nanoparticles in the presence of a high magnetic field and through pure (single) CoFe(2)O(4) ferrofluids in a low magnetic field. This relaxation behavior is explained using a model of a bidispersed system based on both chained and unchained particles. In such a bidispersed system, the variation of the transmitted light results mainly from the motion of the chains, with the polarized unchained particles' gas producing the modulation effect. The oscillatory-like relaxation phenomenon depends on the features of both the chained and unchained particle systems. If either the particle volume fraction of chained particles or of unchained particles is very low, or the degree of polarization of the unchained particles gas is very weak, a simple nonlinear relaxation process, giving only a valley in the T-t curve, will appear for the transmitted light. For pure CoFe(2)O(4) ferrofluids, the number of chained and unchained particles does not remain constant under different values of the magnetic field. According to the analysis of the relaxation behavior of transmitted light, it is known that binary ferrofluids based on strong magnetic CoFe(2)O(4) particles and weak magnetic p-MgFe(2)O(4) particles can be much closer to the theoretical bidispersed system than single ferrofluids containing only strong magnetic particles.     

Influence of Surface Phenomena on the Growth of Aerosol Particles in a Buffer (Admixture) Gas

The influence of a buffer (admixture) gas on the deposition of molecules of a vapor on particles of an aerosol system is investigated.     

Radiation and dynamics of a nanoparticle in equilibrium background radiation upon translational–rotational motion

We have obtained general expressions for the intensity of radiation and tangential force of a small polarizable particle in the process of translational–rotational motion in equilibrium radiation background (thermalized photon gas) of a certain temperature at an arbitrary relative orientation of the linear and angular velocity vectors. It is shown that, in a cold vacuum background, the translational velocity of particle is independent of time and the intensity of its spontaneous emission is determined by the angular velocity and imaginary part of the particle polarizability.     

Gas-particle turbulent flow of foursquare tangential jets in a simplified pulverized-coal firing boiler

An experimental cold-model of a simplified tangential firing boiler was established to investigate the mesoscale turbulent flow behaviors, including gas vortex structures, particle motions and interactions between two phases. A modified PIV technology, employing two pairs of lasers and cameras, was applied to measure the velocity and velocity gradient of turbulent flow in foursquare tangential jets alternatively. At a given initial gas velocity and particle mass loading, the interaction between gas and particles was studied at three different particle sizes. It was found that two main coherent vortex structures, circular eddy and hairpin eddy, distributed mainly in low speed area and heavy impingement area, respectively. The characteristics of particle motion in foursquare tangential jets correlated with gas turbulence dissipation, particle size, particle concentration and particle density. Small particles were easily entrained by gas vortex, so that they consumed more turbulence energy and attenuated the gas turbulence intensity. On the contrary, large particles had more inertia and led to heavier impingement in the chamber center, resulting in particle random distribution and complex momentum transfer between gas and particles. Moreover, large particles stretched the coherent vortex to be narrow and long, while small particles pulled down the vortices rotation intensity.     

Vibrational Relaxation in Several Derivatives of Benzene

Acoustical spectroscopy at frequencies up to 10 GHz gives the possibility of the investigation of liquid substances, where the relaxation process observed is caused by energy transfer between translational and vibrational degrees of freedom. The compounds presented in this article belong to this group of liquids. The acoustic investigations in the group of benzene derivatives, particularly research of the dependencies of acoustic parameters and the structure of organic liquids, demonstrated some interesting regularities in the group of these compounds in gas and liquid states. In this article, the results of research on five cyclic liquids: bromo-, chloro-, fluoro-, iodo-, and nitrobenzene as well as toluene and aniline are discussed and compared to benzene. The acoustic relaxation observed in all these compounds was found to result from Kneser’s processes (vibrational relaxation). Based on investigations reported in this article, as well as by other authors, and taking into account experimental and literature data concerning a great number of compounds, one can draw a conclusion that almost all acoustic relaxation (Kneser-type) processes in liquids can be described using a single relaxation time. It also seems that all vibrational degrees of freedom of the molecule take part in this process. It is known that the appearance of differences in transition probabilities could be caused by additional attraction in interactions of molecules having dipole moments. Halogen derivatives have higher values of dipole moments than benzene. This difference could be responsible for the difference of transition probabilities and changes in the relaxation times. However, benzene derivatives with amino, nitro, and methyl groups and halides show the other type of relaxation.     

便携式渗透法湿度发生器的研制

介绍了一种便携式渗透法湿度发生器的工作原理及研制过程。详细阐述了该湿度发生器的恒温体设计、渗透管选择、气路的优化设计等。该便携式温度发生器可产生-30,-40,-50,-60℃四路定点样气,其发生的低露点标准气体最大误差值在±0.4℃内且总重量仅有10kg左右。试验证明该装置性能稳定可靠,适合开展工业露点仪的现场校准工作。     

Simulation of interphase exchange in heterogeneous media to develop highly efficient technologies

Continuous-medium flows containing suspended particles have drawn the attention of research workers for several decades now. Experiments have shown that even a small amount of admixture in the form of solid particles may exert a substantial influence on the hydrodynamics and convective heat exchange of a stream. Insight into the physics of the interaction of particles with the carrier phase and bodies immersed in the stream makes it possible to control the stream for the purpose of creating fundamentally new technologies for the synthesis and treatment of materials. This is due primarily to the fact that the presence of a disperse admixture in a continuous-medium flow considerably intensifies the processes of transfer and exchange of momentum and heat. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 71, No. 1, pp. 19–29, January–February, 1998.     

Thermal relaxation time of particles in a fluidized bed

Results are given of an experimental investigation of the thermal relaxation time of particles in a fluidized bed. Values of the coefficient of heat transfer from particles to gas are determined.     

Absorptive Bistability of Carbon Monoxide Initiated by Resonance Radiation

Abstract

The kinetics of the absorption of resonance radiation in carbon monoxide is analysed. It is found that when the radiation acts on high-lying vibrational energy levels of the CO molecule, absorptive bistability may arise. If the radiation flux is lower than a certain critical value, the gas is essentially transparent to radiation and the degree of vibrational non-equilibrium of the system is small. When the radiation flux exceeds a different critical value, we have another type of stable state. This state is characterized by a strong vibrational non-equilibrium, the radiation being effectively absorbed by the gas. Within the interval between these two critical values there are both lower and higher stable states of the system which are separated by an unstable state. A jump-like transition from one stable state to another, so called ‘absorptive instability’ is possible at certain values of the radiation flux and vibrational energy stored in the system. The development of absorptive instability is analysed in both isothermal and non-isothermal cases. A short-term decrease in the translational temperature is revealed at the initial stage of radiation absorption. It is found that the development of absorptive instability in a gas contained in a closed resonator is limited by the process of stimulated radiation which leads to a dissipation of the vibrational energy of the system. The fraction of the absorbed energy spent on this relaxation channel may approach unity.     

Ductilization and embrittlement during the crystallization of Ni-Ti-B glasses

The fracture responses of three Ni-Ti-B glasses have been studied during the very early stages of crystallization. Comparison of alloys leads to a separation of relaxation and crystallization effects. The tendency toward reductilization in the presence of a small quantity of crystalline particles is directly related to the fine distribution and very small size of these particles which tends to interrupt concentrated shear without causing significant localized failure. Such particles thereby tend to distribute the plastic deformation homogeneously and to compensate the simultaneous relaxation embrittlement.     

Investigation of the influence of thermostat configurations on the mechanical properties of carbon nanotubes in molecular dynamics simulations

The effect of thermostat configurations on the mechanical behavior of empty and butane (n-C4H10) filled (10, 10) carbon nanotubes (CNTs) is examined using classical, atomistic, molecular dynamics (MD) simulations. In particular, the influence of different types of thermostats, relative numbers of thermostat atoms, and rates of deformation are considered. The compressive forces on the atoms are calculated using the second generation reactive empirical bond-order potential. The results indicate that use of a Langevin thermostat leads to a substantial dependency of the results of CNT compression on the number of thermostat atoms and the rate of deformation. On the other hand, the Nosé-Hoover and the velocity rescaling thermostats exhibit consistent mechanical responses during CNT compression regardless of the relative number of thermostat atoms. However, the Nosé-Hoover thermostat fails to maintain the system temperature at a constant value during the compression process. Thus, this study indicates that the Langevin and velocity rescaling thermostats are more appropriate for use in classical MD simulations of CNT systems than the Nosé-Hoover thermostat, and reveals the conditions under which these thermostats should be used for optimal consistency.     

Mass Action Law in Two-Temperature Reacting Systems

Within the framework of linear nonequilibrium thermodynamics, a generalization of the mass action law to the case of two-temperature reacting gases is performed. Concrete calculations are performed for the dissociation of diatomic molecules and ionization of atoms under conditions when the translational temperature of heavy particles differs from the vibrational temperature of molecules and from the temperature of electrons.     

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.     

Characteristics of heavy metals on particles with different sizes from municipal solid waste incineration

Information on the concentration and size distribution of particles in the flue gas streams is essential for selecting and designing particle removal systems. Two municipal solid waste incinerators (MWIs) were selected for conducting flue gas sampling to determine the particulate distribution and heavy metals concentration on particles with different sizes by US EPA Method 5 sampling train and a cascade impactor. In addition, the characteristics of heavy metals contained on particles were investigated via isokinetic sampling of flue gas stream of air pollution control devices (APCDs). The experimental results indicated that average particulate matter (PM) concentrations at APCDs inlet were 2288.2+/-825.9 and 3069.2+/-810. 0mg/Nm(3), while the concentrations of PM at stack were 1.51+/-0.20 and 14.81+/-4.52mg/Nm(3) in MWI-A and MWI-B, respectively. The differential mass size distribution of PM and differential elemental size distribution of Zn, Pb, and Cu in front of APCDs were of bimodal forms. Results indicate that Zn>Pb>Cu in order of mass concentration in each stage. The fine particles represent approximately 70% and the coarse particles account for the rest 30% of total particulate matters collected on eight stages for both incinerators. Zn, Pb and Cu on fine particles account for approximately 80% and those on the coarse particles are less than 20% of the total heavy metals collected on eight stages of the cascade impactor for both incinerators.     

Modeling the dynamics of several particles behind a propagating shock wave

The interaction of a shock wave in a gas phase with a system of particles moving in this gas has been numerically simulated. The wave pattern of the nonstationary interaction of the propagating shock wave with these particles is described in detail. The mathematical model and computational technology employed is compared with experimental data on the dynamics of particles behind the shock wave. It is established that the approximate model of separate particles used to calculate relaxation of their velocities unsatisfactorily operates in the presence of a mutual influence of particles, whereby one particle can occur in the aerodynamic shadow of an adjacent particle.     

Measurements of the Nuclear Spin Relaxation Times for Small Grains of Solid Hydrogen Suspended in Liquid Helium

Measurements of the nuclear spin-lattice relaxation times (T ₁) and the nuclear spin-spin relaxation times (T ₂) are reported for suspensions of small grains of solid hydrogen in liquid helium. The measurements have been carried out for temperatures 1.8>T>4.9 K and for a nuclear Larmor frequency of 4.0 MHz. The samples were prepared by rapid condensation of hydrogen and helium gas in a precooled cell. The hydrogen pressure was maintained below the triple point to prepare a “slush” of hydrogen particles in liquid helium. The characteristic relaxation times are much shorter, typically by an order of magnitude for T ₂, than those observed and reported previously for bulk samples of solid hydrogen for the same ortho-hydrogen concentrations and applied magnetic fields. Possible origins for this difference between the relaxation in bulk and micro-geometries are discussed.     

Random pulsations in a coarsely disperse fluidized bed

A simple model of a uniform isotropic bed of large particles fluidized by a gas is offered which allows one to estimate the intensity of the chaotic translational and rotational motion of the particles. The influence of the pulsations on the observed macroscopic properties of the bed is discussed.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 35, No. 6, pp. 1089–1097, December, 1978.