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A method is suggested for the simulation of the evolution of the size distribution of droplets as a result of simultaneous processes of nucleation (spontaneous condensation), heterogeneous condensation/evaporation, and coagulation. The results of analysis of the effect of initial moisture on spontaneous condensation of steam in transonic nozzles are given.

The problem on the thermal interaction between a hot thermal particle and ambient water is treated. The stability of a growing vapor film to small perturbations of its spherical shape is investigated.

Collisions of aerosol particles caused by their involvement in Brownian and turbulent motion are treated. Analysis is performed of the ratio between the collision and coagulation nuclei depending on the particle size.

The objective of the paper is to present a statistical model for predicting transport and deposition of high-inertia colliding particles in two-phase turbulent flows. This model is based on a kinetic equation for the probability density function (PDF) of the particle velocity distribution in a turbulent flow field. The model developed is applied to the simulation of fluctuating particle motion and deposition in vertical pipe flow.

The paper deals with the problem on thermal explosion in a two-phase polydisperse combustible mixture. Analysis is performed of the effect of the size distribution of fuel droplets and of radiation heat transfer on the conditions of ignition. The inclusion of the polydispersity of droplets and semitransparency of diesel fuel made possible a serious revision of the known estimates of the importance of thermal radiation.

The results of a competition for the development and verification of a more accurate domestic integrated computer code for simulating processes occurring in the containment shell of a nuclear power plant with a VVER reactor are examined. The basic requirements for the competing codes, the results of the calculations performed on the basis of the standard safety problem, a comparative analysis of the codes presented, and the steps in the development and verification of the KUPOL-M code are presented.

The paper deals with the boundary conditions for continuous equations of conservation of mass, momentum, and turbulent stresses of the disperse phase in a two-phase flow. The boundary conditions and some assumptions made in deriving them are verified by comparison with the results of numerical solution of the kinetic equation for the probability density function (PDF) of the particle velocity.

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.

The limiting laws of turbulent transfer of momentum and heat at high values of the Reynolds number are used to derive wall functions (“wall laws”) under conditions of a flow of gas with variable physical properties along a permeable surface.

High-Rayleigh-number natural-convection heat transfer on inclined surfaces is treated. The analysis of the effect of thermogravitational forces on turbulent transfer of momentum and heat in the wall region is based on the balance equations for the second moments of pulsations of velocity and temperature. Analytical dependences are derived for the coefficient of turbulent thermal conductivity and for the Nusselt number in a wide range of values of the Prandtl number.

The problem on the thermal interaction of a hot spherical particle with ambient water heated to the boiling point is solved. The level of physical parameters is treated that corresponds to the interaction between molten core droplets and cooling water in the case of severe accident in a nuclear reactor. In calculating the heat transfer via the vapor shell, the thermal radiation of the particle is included. An analytical solution in isobaric approximation is derived for the initial stage of interaction. As demonstrated by the results of comparison with a complete numerical solution, the oscillations of vapor pressure and vapor shell thickness do not affect the mean parameters of heat transfer from particle to water. Results are obtained that illustrate the damping effect of thermal radiation of the particle on the oscillation of the particle vapor shell. The possible destruction of a melt droplet under the effect of oscillation of pressure in the vapor shell is estimated, and the value of the droplet size is obtained at which its further destruction is unlikely.

A mathematical model is given for the calculation of binary condensation of H2O/H2SO4 in plumes of jet engines in the presence of chemical transformations, which includes the coagulation of particles along with the processes of nucleation and condensation growth of droplets. The model enables one to derive information about the evolution of the size and composition distribution function of aerosols

A computational analysis is performed of the use of zirconium dioxide ceramic in melt containment systems with relatively thin heat-conducting structures. The results of an investigation of the physicochemical processes for the interaction of melt with zirconium dioxide ceramic are presented. It is shown that the use of zirconium dioxide ceramic together with a passive water source gives the required melt cooling parameters for 3 to 24 h depending on the cooling regime. 4 figures, 9 references.

Hence, analysis shows that the model described adequately represents the features of the change in the boron concentration in the water during the time the main circulating pumps start up. It is particularly useful when carrying out multivariant calculations. Apart from the impossibility of describing the spatial nonuniformity of the boron concentration, its drawbacks include uncertainty of the integral parameters. These parameters effectively represent the mixing process and the spatial structure of the flow and must be determined from experimental data or by carrying out three-dimensional calculations, which we plan to do.

This paper is aimed at the application of a model for simulating the dispersed turbulent flows. The presented model proceeds from a kinetic equation for the probability density function of the particle velocity distribution in turbulent flow. This approach is called the diffusion-inertia model (DIM). Applications of the model to droplet and bubble flows are presented. In the case of vaporized liquid, the interphase heat and mass transfer is introduced by adding the corresponding governing equations. This extended version of the DIM was applied to simulating the boiling water flow in a heated pipe.

The paper is aimed at the application of a model for simulating the dispersed turbulent flows. The model presented proceeds from a kinetic equation for the probability density function of the particle velocity distribution in turbulent flow. This approach is called the diffusion-inertia model (DIM). Applications of the model to droplet and bubble flows are presented. In the case of vaporized liquid, the interphase heat and mass transfer is introduced by adding the corresponding governing equations. This extended version of the DIM was applied to simulating the boiling water flow in a heated pipe.

The purpose of the paper is to introduce the formalism of the joint fluid-particle PDF approach for polydisperse gas-particle flow and to focus on the derivation of the collision terms. The originality of this work is that our model takes into account the correlation between colliding particles and also the effect of a large drift. A discussion is performed on the model.Copyright © 2006 by ASME

The numerical simulation of turbulent gas-solid particle flow in vertical round pipe is performed & analyzed by three different approaches: RANS 2D modeling, PDF approach (Zaichik’s model 2001) & by two-phase TBL (turbulent boundary layer approach). The given performances include all relevant force factors imposed on the motion of solid phase (two-fluid model is considered): particle-turbulence, particle-particle, particle-wall interactions, two-lift the Magnus & Saffman forces and buoyancy (gravitational) force. The dispersed phase is considered as a polydispersed phase composed of finite number of particle fractions and the mass & momentum equations are closed with the help of implementation of original “collision” model (Kartushinsky & Michaelides, 2004). The two/four-way coupling model of Gillandt & Crowe (1998) is accounted for turbulence modulation. The numerical results show that retaining of second diffusion terms in both directions (in streamwise & transverse directions) aligns the average x-velocity components of gas and dispersed phases as well as the particle mass concentration and k-profiles across the flow in case of both PDF and RANS 2D approaches that versus the distributions of parameters obtained by two-phase TBL approach. This is reasonable due to additional effect of fluxes diffusion of the carrier fluid & solid phase in the main direction derived from turbulence fluctuation and inter-particle collision which smoothes the profile shapes.

The objective of the paper is to present a new statistical model for predicting collision rates of inertial particles immersed in turbulent flow. This model is valid over the entire range of particle inertia (from the zero-inertia to the high-inertia limit) and accounts for two mechanisms influencing the collision rate, namely, the particle relative motion induced by turbulence and the accumulation effect that leads to an additional enhancement to the collision rate. The model is applicable to near-homogeneous two-phase turbulent flows with colliding or coalescing particles.

The purpose of the study is to present an explicit algebraic Reynolds stress (nonlinear turbulent viscosity) model combined with modified k – e turbulence model taking into account particles effect on turbulence for calculating the main turbulent characteristics of two-phase flows. For calculating particles distribution in space we used diffusion-inertia model (DIM). The turbulence attenuating in the presence of particles is clearly observed, investigated and compared with the experimental data. The developed model adequately described turbulence anisotropy and the influence of particles inertia and concentration on the turbulence intensity.

The purpose of this paper is twofold: (i) to advance and extend the statistical two-point models of pair dispersion and particle clustering in isotropic turbulence that were previously proposed by Zaichik and Alipchenkov (2003 Phys. Fluids15 1776?87; 2007 Phys. Fluids?19, 113308) and (ii) to present some applications of these models. The models developed are based on a kinetic equation for the two-point probability density function of the relative velocity distribution of two particles. These models predict the pair relative velocity statistics and the preferential accumulation of heavy particles in stationary and decaying homogeneous isotropic turbulent flows. Moreover, the models are applied to predict the effect of particle clustering on turbulent collisions, sedimentation and intensity of microwave radiation as well as to calculate the mean filtered subgrid stress of the particulate phase. Model predictions are compared with direct numerical simulations and experimental measurements.

The objective of this paper is to advance an Eulerian continuum approach for modeling the transport of inertial particles in the framework of large eddy simulation. This approach is based on a kinetic equation for the filtered probability density function of particle velocity in turbulent flow. Some models developed for the subgrid-scale turbulent stresses of the particulate phase are presented. The effect of filter width on the averaged subgrid particle kinetic energy is explored. It is revealed that, in the limit of zero filter width, the subgrid kinetic stress and energy of inertial particles can have nonzero values.

The purposes of the paper are threefold: (i) to refine the statistical model of preferential particle concentration in isotropic turbulence that was previously proposed by Zaichik and Alipchenkov [Phys. Fluids 15, 1776 (2003)], (ii) to investigate the effect of clustering of low-inertia particles using the refined model, and (iii) to advance a simple model for predicting the collision rate of aerosol particles. The model developed is based on a kinetic equation for the two-point probability density function of the relative velocity distribution of particle pairs. Improvements in predicting the preferential concentration of low-inertia particles are attained due to refining the description of the turbulent velocity field of the carrier fluid by including a difference between the time scales of the of strain and rotation rate correlations. The refined model results in a better agreement with direct numerical simulations for aerosol particles.

This paper presents two statistical models for predicting collision rates of bidisperse heavy particles suspended in homogeneous isotropic turbulence. One of the models is based on the assumption that the joint fluid-particle velocity distribution function is Gaussian. The other model stems from a kinetic equation for the two-point probability density function of the velocity distributions of two particles. The validity of these models is tested against DNS data by Zhou, Wexler, and Wang [J. Fluid Mech. 433, 77 (2001)]. Comparisons between the model predictions and DNS results demonstrate encouraging agreement.