Particles In Turbulent Pipe Flow Research Articles

Deposition of submicron charged particles in turbulent pipe flow with an application to the trachea

The paper presents a study of the deposition of submicron charged spherical particles caused by convection, Brownian and turbulent diffusion in a pipe with a smooth wall and with a cartilaginous ring wall structure. The model is supposed to describe deposition of charged particles in generation 0 (trachea) of the human respiratory airways. The flow is modeled with a SST-turbulence model combined with a convective-diffusion equation including electric field migration for the particles, and Poisson’s equation for the determination of the electrostatic potential in terms of the space-charge density of the particles. An approximate analytical solution is derived for the case of a smooth pipe which is used to verify the numerical solutions obtained from using the commercial software Comsol Multiphysics. Numerical results of deposition rates are also provided for the case of a pipe with a cartilaginous ring wall structure.

Penetration efficiency and distribution of aerosol particles in turbulent pipe flow undergoing coagulation and breakage

When transporting aerosol particles through pipes, the penetration efficiencies are directly related to the particle distribution in the cross-section and deposition to the walls. In the present study, the moment equations for nano-sized aerosol particles are solved with the Taylor-series expansion moment method by considering the combined effect of Brownian diffusion, turbulent diffusion, particle coagulation and breakage. The distributions of particle number concentration, particle diameter and polydispersity over a range of particle diameters from 50 to 450nm in the cross-section at the outlet of the pipe are given. The results show that the particle number concentration is distributed non-uniformly along the radial direction, and the particles in the near wall region are diffused to the region near the pipe center and the wall. Particle diameter increases from an initial value at the inlet to the different values depending on the radial position at the outlet. The largest particles are found in the near wall region from which the particle diameters decrease gradually to the pipe center. Smaller particles become more polydisperse at the outlet. Then the penetration efficiencies over a range of Reynolds numbers from 4426 to 8500 and ratios of pipe length to diameter from 375 to 625 are calculated, and some corresponding experiments are carried out. The results show that 65–95% particles flow through the pipe. The penetration efficiencies increase with increasing particle size, while decrease as Reynolds number increases. The longer the residence time of particles in the pipe is, the larger the probability that particles deposit on the wall is, hence the smaller the penetration efficiency is. Finally, the relationship of penetration efficiency and related synthetic parameters is built up, and the expression for the difference in mean particle diameter between the outlet and inlet of the pipe as function of related parameters is derived, based on the numerical and experimental data.

Deposition of particles in turbulent pipe flow

The deposition of particles in turbulent pipe flow was investigated in terms of two mechanisms, turbulent and thermophoretic. A general equation incorporating these two mechanisms was formulated to calculate the deposition efficiency of aerosol particles in turbulent pipe flow together with thermophoretic deposition. The validity of the equation was confirmed by good agreement between calculated and measured results.

Numerical study of the near-wall behaviour of particles in turbulent pipe flows

The near-wall behaviour of particles is important in terms of predicting both the particle-deposition and the near-wall particle-concentration. In this paper, we study the near-wall behaviour of elastic-bouncing small heavy spheric particles in fully developed turbulent pipe flows without gravity, using direct numerical simulations (DNS) with a one-way point-particle approach. The particle-concentration is assumed to be small enough such that the influence of the particles on the fluid and interparticle interactions can be neglected. The focus of the paper is on: (i) the understanding of the differences between elastic-bouncing and absorbing walls, and (ii) the evaluation of simple “local-equilibrium” models. Our results show that the near-wall behaviour of elastic-bouncing walls is very different from absorbing walls. The absence of a mean radial particle-velocity leads to a much higher particle-concentration near the wall than in the case of absorbing walls. This can be explained by the absence of a “mean drag force”: the “turbophoretic effect”, due to the gradient in the particle-velocity fluctuation in the radial direction, is balanced only by the “drift-velocity”, due to a gradient in the particle-concentration. Our results indicate that, from a pragmatic perspective, simple “local-equilibrium” models for the “turbophoretic effect”, assuming a proportionality between the particle and fluid “Reynolds-stresses”, are adequate, except very close to the wall, where the reduction in the radial fluid-velocity fluctuation is not accompanied by an equivalent reduction in the radial particle-velocity fluctuation.

Deposition of particles in turbulent pipe flows

Deposition of particles in turbulent pipe flows

Dispersion and deposition of particles in a turbulent pipe flow with sudden expansion

Numerical simulations of dispersion and deposition of particles in an axisymmetric turbulent pipe flow with sudden expansion are performed. The cases that particles of different sizes are released from point sources and/or are uniformly distributed are studied. The effects of turbulence diffusion, Brownian dispersion, lift force, and gravity are included in the computational model. A thermodynamically consistent, rate-dependent algebraic stress model is used to simulate the mean velocity and turbulent intensity fields. The instantaneous fluctuating velocity is simulated as a continuous Gaussian random vector field. The Brownian force is modeled as a Gaussian white noise random process. Ensembles of several thousand particle trajectories are evaluated and are statistically analyzed. The effects of particle source location, particle size, and gravity on dispersion and deposition are studied. The particle capture efficiency for an initially uniform distribution is also evaluated. The predicted particle and fluid velocities are compared with the available experimental data and reasonable agreement is observed.

Dispersion and deposition of particles in a turbulent pipe flow with sudden expansion

Numerical simulations of dispersion and deposition of particles in an axisymmetric turbulent pipe flow with sudden expansion are performed. The cases that particles of different sizes are released from point sources and/or are uniformly distributed are studied. The effects of turbulence diffusion, Brownian dispersion, lift force, and gravity are included in the computational model. A thermodynamically consistent, rate-dependent algebraic stress model is used to simulate the mean velocity and turbulent intensity fields. The instantaneous fluctuating velocity is simulated as a continuous Gaussian random vector field. The Brownian force is modeled as a Gaussian white noise random process. Ensembles of several thousand particle trajectories are evaluated and are statistically analyzed. The effects of particle source location, particle size, and gravity on dispersion and deposition are studied. The particle capture efficiency for an initially uniform distribution is also evaluated. The predicted particle and fluid velocities are compared with the available experimental data and reasonable agreement is observed.

Deposition of particles in turbulent pipe flows

Deposition rates of aerosol particles onto pipe walls under turbulent flow conditions were measured. Dioctyl phthalate (DOP) aerosols of six different sizes ranging from 0.035 to 1.3 μm were used in air flows whose Reynolds numbers were controlled at selected values between 1800 and 15,600. The turbulent inertial impaction, transition, and turbulent diffusion regimes were covered. The measured results show that the theory by Wells and Chamberlain (1967, Brit. J. appl. Phys. 19, 1793) predicts deposition by diffusion in turbulent flows reasonably well, while the theory of Friedlander and Johnstone (1957, Ind. Engr. Chem. 49, 1151) is suitable for correlating the data for deposition by inertial impaction. However, these theories alone were not satisfactory for estimating deposition rates in the neighborhood of the minimum aerosol deposition regime where both Brownian diffusional and inertial deposition mechanisms operate simultaneously.

Deposition of glass fiber particles from turbulent air flow in a pipe

A novel experimental technique is developed and used for measuring the deposition velocities of nonspherical particles from turbulent air flow in a horizontal pipe. The deposition velocities of glass fiber cylindrical particles of diameters 0.6–2.5 μm and lengths of up to 50 μm are measured in wide ranges of the flow Reynolds number and particles' aspect ratio for upward, downward and sideward orientations of the deposition surface. It is found that the deposition velocity of particles, characterized by intermediate values of the effective relaxation time, is significantly affected by the nonspherical particles' shape via the interception mechanism. Known correlations proposed for the deposition velocity of spherical particles are shown to significantly underestimate the experimental data for glass fibers, if these correlations are employed using the fibers' aerodynamically equivalent diameters. The latter diameter is, thus, shown to be inappropriate for predicting deposition velocities of nonspherical particles. A turbulent-interception model for deposition of nonspherical particles is proposed to correlate the experimental data obtained for glass fibers. Several formulas for the deposition velocity of cylindrical particles in turbulent pipe flows are proposed.

Deposition of Aerosol Particles in Turbulent Pipe Flow — The Deposition in a Horizontal Pipe —

Deposition of Aerosol Particles in Turbulent Pipe Flow — The Deposition in a Horizontal Pipe —

Lateral diffusion of large particles in turbulent pipe flow

A closed flow circuit, comprising a smooth horizontal plastic pipe transporting a dilute suspension of plastic particles in water, was modified to produce a satisfactory environment for the detection of mean particle location across a fixed plane normal to the mean turbulent flow direction. It was established that mean concentration in the vicinity of the vertical diameter was a function of the vertical co-ordinate only, and this result enabled the particle diffusivity to be evaluated for a core region of the cross-section. For a particle relative density in the range 1.035 to 1.126 and a variety of flows, a suitable expression for the dimensionless particle diffusivity is A (1 - BW/u) SN, where u is the friction velocity, W the fall velocity for a particle in still water, S the relative density of the suspended material, and A, B and N are constants.