Particle dispersion in a vertical round sudden-expansion flow

1992 ◽  
Vol 341 (1662) ◽  
pp. 411-442 ◽  
Keyword(s):  
Recirculation Zone ◽  
Probability Distributions ◽  
Mean Transit Time ◽  
Fluid Velocity ◽  
Particle Dispersion ◽  
Sudden Expansion ◽  
Stream Line ◽  
Phase Doppler Anemometry ◽  
Flow Through ◽  
Time Required

The dispersion of glass beads in an air flow through sudden step expansions in the direction of gravity has been investigated with phase-Doppler anemometry, which provided measurements of the velocity, flux and concentration characteristics. The purpose was to quantify the effect of increasing the air velocity over a factor of 5 for bead diameters of 40 µm and 80 µm and two expansion diameter ratios, 3.33 and 5, and at mass loadings of beads up to 90% of the air mass flow-rate. The results showed that the beads dispersed into the recirculation zone in the lee of the step by interaction with eddies characterized by length and velocity scales of the order of the expansion step height and the downstream area-averaged velocity. Particle dispersion into the recirculation zone was reduced when the bead mean transit time across the recirculation zone was shorter than the bead relaxation time, defined as the time required for a motionless bead suddenly exposed to a constant velocity fluid stream to reach 63% of its surrounding fluid velocity. Also the centrifuging effect, caused by the mean stream line curvature of the recirculation zone, could reduce particle dispersion into the recirculation zone, when its characteristic dimensionless group was less than unity. Beads, because of their mass, left the recirculation zone by sliding down the wall and past the air reattachment point or near the step, giving rise to bimodal probability distributions of velocity.

Biphasic co-flow through a sudden expansion or contraction of a Hele-Shaw channel

2021 ◽  
Vol 6 (7) ◽  
Author(s):  
Boris Y. Rubinstein ◽  
Dana Zusmanovich ◽  
Zhenzhen Li ◽  
Alexander M. Leshansky
Keyword(s):  
Sudden Expansion ◽  
Flow Through

Bifurcation analysis of two-dimensional laminar flow through sudden expansion channel

2022 ◽  
Vol 13 (1) ◽  
pp. 0-0
Keyword(s):  
Laminar Flow ◽  
Expansion Ratio ◽  
Sudden Expansion ◽  
Two Dimensional ◽  
Governing Equations ◽  
Bifurcation Phenomena ◽  
Different Types ◽  
Fluent Software ◽  
Flow Through ◽  
Volume Method

In this work, bifurcation characteristics of unsteady, viscous, Newtonian laminar flow in two-dimensional sudden expansion and sudden contraction-expansion channels have been studied for different values of expansion ratio. The governing equations have been solved using finite volume method and FLUENT software has been employed to visualize the simulation results. Three different mesh studies have been performed to calculate critical Reynolds number (Recr) for different types of bifurcation phenomena. It is found that Recr decreases with the increase in expansion ratio (ER).

Numerical Simulation of Heavy Particle Dispersion—Scale Ratio and Flow Decay Considerations

1994 ◽  
Vol 116 (1) ◽  
pp. 154-163 ◽  
Author(s):  
Lian-Ping Wang ◽  
David E. Stock
Keyword(s):  
Numerical Simulation ◽  
Time Scale ◽  
Dispersion Coefficient ◽  
Fluid Velocity ◽  
Heavy Particle ◽  
Particle Dispersion ◽  
Heavy Particles ◽  
Velocity Scale ◽  
Scale Ratio ◽  
Diffusivity Ratio

Lagrangian statistical quantities related to the dispersion of heavy particles were studied numerically by following particle trajectories in a random flow generated by Fourier modes. An experimental fluid velocity correlation was incorporated into the flow. Numerical simulation was performed with the use of nonlinear drag. The simulation results for glass beads in a nondecaying turbulent air showed a difference between the horizontal dispersion coefficient and vertical dispersion coefficient. This difference was related to the differences of both the velocity scale and the time scale between the two direction. It was shown that for relatively small particle sizes the particle time scale ratio dominates the value of the diffusivity ratio. For large particles, the velocity scale ratio reaches a value of 1/2 and thus fully determines the diffusivity ratio. Qualitative explanation was provided to support the numerical findings. The dispersion data for heavy particles in grid-generated turbulences were successfully predicted by the simulation when flow decay was considered. As a result of the reduction in effective inertia and the increase in effective drift caused by the flow decay, the particle dispersion coefficient in decaying flow decreases with downstream location. The particle rms fluctuation velocity has a slower decay rate than the fluid rms velocity if the drift parameter is large. It was also found that the drift may substantially reduce the particle rms velocity.

Dispersion resulting from flow through spatially periodic porous media

1980 ◽  
Vol 297 (1430) ◽  
pp. 81-133 ◽  
Keyword(s):  
Porous Media ◽  
Velocity Vector ◽  
Tracer Particle ◽  
Fluid Velocity ◽  
Complex Structure ◽  
Molecular Diffusivity ◽  
Spatially Periodic ◽  
Flow Through ◽  
Limiting Case ◽  
Interstitial Velocity

A rigorous theory of dispersion in both granular and sintered spatially-periodic porous media is presented, utilizing concepts originating from Brownian motion theory. A precise prescription is derived for calculating both the Darcy-scale interstitial velocity vector v* and dispersivity dyadic D* of a tracer particle. These are expressed in terms of the local fluid velocity vector field v at each point within the interstices of a unit cell of the spatially periodic array and, for the dispersivity, the molecular diffusivity of the tracer particle through the fluid. Though the theory is complete, numerical results are not yet available owing to the complex structure of the local interstitial velocity field v. However, as an illustrative exercise, the theory is shown to correctly reduce in an appropriate limiting case to the well-known Taylor-Aris results for dispersion in circular capillaries.

scholarly journals ANALYTICAL AND CFD INVESTIGATION OF TURBULENT DIFFUSION MODEL FOR PARTICLE DISPERSION AND DEPOSITION

1970 ◽  
Vol 40 (1) ◽  
pp. 39-53
Author(s):  
Alamgir Hossain ◽  
Jamal Naser
Keyword(s):  
Diffusion Model ◽  
Turbulent Diffusion ◽  
Particle Deposition ◽  
Fluid Velocity ◽  
Particle Diameter ◽  
Particle Dispersion ◽  
Homogeneous Distribution ◽  
Lower Velocity ◽  
Different Depths ◽  
Diffusion Particle

A 2D analytical turbulent diffusion model for particle dispersion and deposition at different heights across the pipe flow and circumferential deposition has been developed. This liquid-solid turbulent diffusion model presented in this paper has emanated from an existing gas-liquid turbulent diffusion model. Simultaneously a comprehensive 3D numerical investigation has been carried out to study the above making of multiphase mixture model available in Fluent 6.1. In both studies different particles sizes and densities were used. The deposition was studied as a function of particle diameter, density and fluid velocity. The deposition of particles, along the periphery of the wall and at different depths, was also investigated. Both studies showed that the deposition of heavier particles at the bottom of the pipe wall was found to be higher at lower velocities and lower at higher velocities. The lighter particles were found mostly suspended with homogeneous distribution. Smaller particles were also suspended with marginal higher concentration near the bottom of the wall. This marginal higher concentration of the smaller particles was found to be slightly pronounced for lower velocity. The larger particles clearly showed deposition near the bottom of the wall. These analogies of particles are well discussed with the ratio between free flight velocity and the gravitational settling velocity. Key Words: Multiphase flow, turbulence diffusion, particle deposition, horizontal flow.   doi: 10.3329/jme.v40i1.3472 Journal of Mechanical Engineering, Vol. ME40, No. 1, June 2009 39-53

Sign in / Sign up

Export Citation Format

Share Document