Particle Dynamics and Turbulence

The general equation of motion is based on treatments of particle dynamics by Basset, Boussinesq, and Oseen and is essentially an application of Newton s second law (Soo, 1967)  

The lettered terms can each be given a physical interpretation  

A = mass X acceleration of the particle, which is present only in unsteady flow situations representing the force necessary to accelerate the particle B = drag force containing a drag coefficient that is a function of the Reynolds number 

C = force from the pressure gradient in the fluid surrounding the particle D = force due to acceleration of the apparent mass of the particle relative to the fluid 

E = Basset force, which is the force due to the deviation of the flow pattern around the particle from steady-state conditions this depends on the previous motion of the particle and the fluid F = external force 

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Because of a vivid interest in spray combustion, quite a few papers deal with the effect of finely dispersed particles or droplets on the turbulence characteristics of jets and sprays. The interaction of particle dynamics and turbulence in these flows has prompted very fundamental stochastic approaches involving filtering and averaging techniques, probability density functions, and quadrature-based moment methods (Fevrier et al, 2005 Fox, 2012 Labourasse et al, 2007) which are beyond the scope of this chapter. Riber et al (2009) and Senoner et al (2009) obtained LES results for recirculating and evaporating two-phase flows, respectively, by both Euler-Lagrange and Euler—Euler methods and compared them mutually and with experimental data. 

An important aspect of Clark s technology was that the oil being cracked, which flowed through the tubes and in a near vapor state, was maintained in a continually dynamic or turbulent condition. This meant that the coke particles which formed were prevented from... 

CFD might provide a way of elucidating all these spatial variations in flow conditions, in species concentrations, in bubble drop and particle sizes, and in chemical reaction rates, provided that such computational simulations are already capable of reliably reproducing the details of turbulent flows and their dynamic effects on the processes of interest. This Chapter reviews the state of the art in simulating the details of turbulent flows and turbulent mixing processes, mainly in stirred vessels. To this end, the topics of turbulence and CFD both need a separate introduction. 

Ten Cate, A., Turbulence and particle dynamics in dense crystal slurries—a numerical study by means of lattice-Boltzmann simulations , Ph.D. Thesis, Delft University of Technology, Delft, Netherlands (2002). 

As with the flow regimes in fluid dynamic theory, that is, the stagnation, laminar flow and turbulent flow, it is obvious that a solid phase can exhibit the corresponding flow pattern regimes, which herein are referred to as fixed, moving and mixed, respectively. The terms fixed, moving and mixed are defined as the relative motion of the particle phase with respect to a fixed coordinate system (see Figure 26). Examples of commercial PBC systems with different fuel-bed movement are found in section B.3.4. A comparison between theoretical and practical conversion systems. 

The aim of the present investigation is to create adequate semi-empirical physical and mathematical models that describe dynamics of turbulent combustion in heterogeneous mixtures of gas with polydispersed suspended particles. 

Physical and numerical models are created describing the dynamics of turbulent combustion in heterogeneous mixtures of gas with polydispersed particles. The models take into account the thermal destruction of particles, chemistry in the gas phase, and heterogeneous oxidation on the surface influenced by both diffusive and kinetic factors. The models are validated against independent experiments and enable the determination of peculiarities of turbulent combustion of polydispersed mixtures. 

Micro-cuboids in three-dimensional turbulent flow have been examined using Fraunhofer diffraction [86]. Both dynamic and static three dimensional particle shape features could be obtained and served as a basis for particle shape analysis by pattern recognition. 

Priedlander SK (2000) Smoke, Dust, and Haze Fundamentals of Aerosol Dynamics, Second Edition, Oxford University Press, New York Guido Lavalle G, Carrica PM, Clausse A, Qazi MK (1994) A bubble number density constitutive equation. Nucl Engng Des 152 213-224 Hagesaether L, Jakobsen HA, Svendsen HF (1999) Theoretical Analysis of Fluid Particle Collisions in Turbulent Flow. Chem Eng Sci 54(21) 4749-4755 Hagesaether L, Jakobsen HA, Hjarbo K, Svendsen HF (2000) A Coalescence and Breakup Module for Implementation in CFD-codes. Computer-Aided Chemical Engineering 8 367-372... 

Numerical simulation of the eddy diffusion of particles in the turbulent core of a pipe flow indicates that for particles smaller than about 170 rm, particle and gas eddy diffusion coefficients are about the same (Uijltewaal, 1995). The studies were made for three Reynolds numbers 5500,18,3(X), and 42,000 with particles of about unit density and a pipe diameter of 5 cm. Hence for the usual ranges of interest in aero.sol dynamics, particle and gas eddy diffusion coefficients can be a.ssumed equal in the turbulent core. However, the viscou.s sublayer near the wall of a turbulent pipe flow alters the situation as discussed in the next section. 

Revised and expanded, this second edition features new chapters on the kinetics of agglomeration of noncoale.seing particles and the fundamentals of aerosol reactor design. It covers the effecLs of turbulence on coagulation and gas-to-particle conversion and also di.scusses the formation of primary particles by the coltision-coale.scence niechani.sm. The chapter on the atmo.spheric aerosol has been completely rewritten within the aero.sol dynamics framework. Its basic approach and topicality make Smoke, Dust, and Haze Fundamentals of Aerosol Dynamics, 2le, an essential guide for both studenfs and researchers. 

Meng, H., and Hussain, F., Holographic particle velocimetry a 3D measurement technique for vortex interactions, coherent structures and turbulence, Fluid Dynamics Research, , 33-52 (1991). 

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