Group Title: 7th International Conference on Multiphase Flow - ICMF 2010 Proceedings
Title: 16.5.1 - An Analysis of High Concentration Gas-Solid Flows with a Direct Numerical Simulation Approach
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 Material Information
Title: 16.5.1 - An Analysis of High Concentration Gas-Solid Flows with a Direct Numerical Simulation Approach Environmental and Geophysical Flows
Series Title: 7th International Conference on Multiphase Flow - ICMF 2010 Proceedings
Physical Description: Conference Papers
Creator: Ahmadi, G.
Nasr, H.
McLaughlin, J.B.
Publisher: International Conference on Multiphase Flow (ICMF)
Publication Date: June 4, 2010
 Subjects
Subject: DNS
inter-particle collisions
two-way coupling
particle deposition velocity
DNS
 Notes
Abstract: This study was concerned with the effect of particle-particle collisions and two-way coupling on the particle deposition velocity in a turbulent channel flow. The time history of the instantaneous turbulent velocity vector was generated by the two-way coupled direct numerical simulation (DNS) of the Navier-Stokes equation via a pseudospectral method. The particle equation of motion included the Stokes drag, the Saffman lift, and the gravitational forces. The effect of particles on the flow was included in the analysis via a feedback force that acted on the fluid on the computational grid points. Several simulations for different particle relaxation times and particle mass loading were performed, and the effects of the inter-particle collisions and two-way coupling on the particle deposition velocity, fluid and particle fluctuating velocities, particle normal mean velocity, and particle concentration were determined. It was found that when particle-particle collisions were included in the computation, the particle deposition velocity increased. When the particle collision was neglected but the particle-fluid two-way coupling was accounted for, the particle deposition velocity decreased slightly. For the four-way coupling case, when both inter-particle collisions and two-way coupling effects were taken into account, the particle deposition velocity increased. Comparisons of the present simulation results with the available experimental data and earlier numerical results are also presented.
General Note: The International Conference on Multiphase Flow (ICMF) first was held in Tsukuba, Japan in 1991 and the second ICMF took place in Kyoto, Japan in 1995. During this conference, it was decided to establish an International Governing Board which oversees the major aspects of the conference and makes decisions about future conference locations. Due to the great importance of the field, it was furthermore decided to hold the conference every three years successively in Asia including Australia, Europe including Africa, Russia and the Near East and America. Hence, ICMF 1998 was held in Lyon, France, ICMF 2001 in New Orleans, USA, ICMF 2004 in Yokohama, Japan, and ICMF 2007 in Leipzig, Germany. ICMF-2010 is devoted to all aspects of Multiphase Flow. Researchers from all over the world gathered in order to introduce their recent advances in the field and thereby promote the exchange of new ideas, results and techniques. The conference is a key event in Multiphase Flow and supports the advancement of science in this very important field. The major research topics relevant for the conference are as follows: Bio-Fluid Dynamics; Boiling; Bubbly Flows; Cavitation; Colloidal and Suspension Dynamics; Collision, Agglomeration and Breakup; Computational Techniques for Multiphase Flows; Droplet Flows; Environmental and Geophysical Flows; Experimental Methods for Multiphase Flows; Fluidized and Circulating Fluidized Beds; Fluid Structure Interactions; Granular Media; Industrial Applications; Instabilities; Interfacial Flows; Micro and Nano-Scale Multiphase Flows; Microgravity in Two-Phase Flow; Multiphase Flows with Heat and Mass Transfer; Non-Newtonian Multiphase Flows; Particle-Laden Flows; Particle, Bubble and Drop Dynamics; Reactive Multiphase Flows
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7th International Conference on Multiphase Flow
ICMF 2010, Tampa, FL USA, May 30-June 4, 2010


An Analysis of High Concentration Gas-Solid Flows with a Direct Numerical Simulation
Approach

Goodarz Ahmadi,1 Hojjat Nasr,1 and John B. McLaughlin2

1 Department of Mechanical Engineering and Aeronautical, Clarkson University, Potsdam, NY 13699, USA
2Department of Chemical and Biomolecular Engineering, Clarkson University, Potsdam, NY 13699, USA
ahmadi@tclarkson.edu
Keywords: DNS, Inter-particle collisions, Two-way coupling, Particle deposition velocity, Direct numerical simulation


Abstract

This study was concerned with the effect of particle-particle collisions and two-way coupling on the particle deposition
velocity in a turbulent channel flow. The time history of the instantaneous turbulent velocity vector was generated by the
two-way coupled direct numerical simulation (DNS) of the Navier-Stokes equation via a pseudospectral method. The particle
equation of motion included the Stokes drag, the Saffman lift, and the gravitational forces. The effect of particles on the flow
was included in the analysis via a feedback force that acted on the fluid on the computational grid points. Several simulations
for different particle relaxation times and particle mass loading were performed, and the effects of the inter-particle collisions
and two-way coupling on the particle deposition velocity, fluid and particle fluctuating velocities, particle normal mean
velocity, and particle concentration were determined. It was found that when particle-particle collisions were included in the
computation, the particle deposition velocity increased. When the particle collision was neglected but the particle-fluid
two-way coupling was accounted for, the particle deposition velocity decreased slightly. For the four-way coupling case,
when both inter-particle collisions and two-way coupling effects were taken into account, the particle deposition velocity
increased. Comparisons of the present simulation results with the available experimental data and earlier numerical results are
also presented.


Introduction

Study of transport and deposition of aerosols in
particle-laden flows is of considerable interest due to its
importance in numerous industrial and environmental
applications. Despite numerous experimental and
computational studies, the interactions of particles with
turbulent eddies is not fully understood due to its
complexity.
Caporaloni et al. (1975) discovered the existence of
turbophoresis. They showed that due to spatial
inhomogeneity of the turbulent intensities, there is a mean
flux of particles towards the wall. The earliest model for
turbulent deposition was reported by Friedlander and
Johnstone (1957). They proposed the so-called free-flight
theory, which implies that particles reaching the stopping
distance from the wall will deposit on the wall. While this
model gives relatively reasonable results for the eddy
impaction regime, some of the assumptions of free flight
model are difficult to justify. McLaughlin (1989) found that
the Saffman lift force had a significant effect on aerosol
deposition although the assumptions of Saffman's theory
were not satisfied by many of the aerosols as they
approached the wall. The simulation results of Wang and
Stock (1993) showed the importance of nonlinear drag for
particles with high settling velocities. Direct numerical
simulations of particle deposition in wall-bounded turbulent
flows were performed by McLaughlin (1989). Zhang and
Ahmadi (2000) used DNS to study aerosol particle transport


and deposition in vertical and horizontal turbulent duct
flows. They showed that the wall coherent structure plays an
important role in the particle deposition process. Squires
and Eaton (1991a) simulated a homogeneous isotropic
non-decaying turbulent flow field by imposing an excitation
at low wave numbers, and studied the effects of inertia on
particle dispersion. They also used DNS to study the
preferential micro-concentration structure of particles as a
function of Stokes number in turbulent near-wall flows
(Squires and Eaton 1991b). Brooke et al. (1992) employed
DNS to study particle deposition in a channel flow with the
view of evaluating the free flight theory of Friedlander and
Johnstone (1957). Yamamoto et al. (2001) studied the
interaction between turbulence and solid particles in a fully
developed channel flow using large eddy simulation; they
also considered inter-particle collisions as an important
mechanism in high mass loading of the particles. They
showed that the shape and scale of particle concentration
calculated considering inter-particle collision are in good
agreement with experimental observations of Fessler et al.
(1994). Li et al. (2001) showed that particle-particle
collisions greatly reduce the tendency of particles to
accumulate near the wall.
In this study, the effects of inter-particle collisions and
two-way coupling on dispersed and carrier phase
fluctuations were studied using the direct numerical
simulation of the Navier-Stokes equation via a
pseudospectral method. The particle deposition velocity,
particle fluctuating velocities, particle normal velocity, and






7th International Conference on Multiphase Flow
ICMF 2010, Tampa, FL USA, May 30-June 4, 2010


particle concentration profiles were evaluated under
different conditions. The cases of one-way coupling,
two-way coupling, four-way coupling, and inter-particle
collisions without two-way coupling were analyzed. The
effects of particle-particle collisions as well as two-way
coupling on the simulation results are discussed.


Nomenclature
CD
d
Fd
F,
H
J
M.L.
N,
Nd
nx x ny x nz

P
Re
S
S P

t
U

U
Ud
u',V', W'









P
z
Greek letters
V
P
7-
,w


Drag coefficient
Particle diameter (m)
Drag force (N)

Saffman lift force (N)

Channel width (m)
Particle mass flux
Particle mass loading
Total number of particles
Number of deposited particles
Number of grid points in x-, y- and z-
direction
Pressure (Nm 2)
Reynolds number
Density ratio
Particle feedback force (N)

Time (s)
velocity (ms-1)
Friction velocity (ms-1)
Particle deposition velocity (ms-1)
Streamwise, normal, and spanwise
fluctuating velocities (ms-1)
Particle normal velocity (ms-1)
Stramwise Coordinate
Distance from the wall (m)
Spanwise Coordinate

Kinematic viscosity ((m2 s-')
Density (Kg m-3)
Particle relaxation time (s)
Wall shear stress (Nm 2)


'x, Periodic segment in x- and z- directions

01 Volume fraction
Supersripts
P particle
f fluid
+ Wall unit


Governing equations

Particle phase
The Lagrangian equation of motion of spherical particles
moving in a wall-bounded channel flow including the
wall-corrected nonlinear drag and lift forces in wall units is
given as


d ?
=i CDFd + F
dt+

and


-=+p
dU
dt+

where

*2
x+ + tu
V V


-+ U
U =-
U


Here, u + is the non-dimensional particle velocity,, CD

is the nonlinear drag correction factor, Fd is the drag

force after including the wall drag corrections, and F1 is
the wall induced and shear induced lift force. In equation
(3), u is the flow shear velocity.
The details of the lift force including the near wall effects
were described in the work of Chen and McLaughlin
(1995) and Zhang and Ahmadi (2000) and therefore are not
repeated here. (Note that only the y-component of lift force
is considered in this study.)
Based on a synthesis of available experimental results,
Clift et al. (1978) and Beard et al. (1971) recommended the
following nonlinear drag correction factors:


1.0 +0.1875Rep

CD

1.0 +0.1315Re 82002171n(Re


Rep, 0.01'




0.01< Rep <20


Here, Rep =d+ u+f -+p is the particle Reynolds
number. Additional details of the drag and lift forces
were described in detail by Chen and McLaughlin (1995)
and Ounis et al. (1991).
The non-dimensional particle relaxation time is defined
as
d2
r+ =S (5)
18
here d+ =du*/v is the non-dimensional particle
diameter and S is the particle-to-fluid density ratio.
For evaluating the forces acting on the particles, the fluid
velocities at the locations of particles must be evaluated
using an interpolation technique. An accurate evaluation
of particle velocities is also essential for analysis of
inter-particle collisions that depend on the often small
relative particle velocities. In this study, partial Hermite
interpolation method was used for evaluating the fluid
velocities at the locations of particles and for the inverse
action of particle drag on the fluid. To evaluate the particle
deposition velocity, it is assumed that when a particle
reaches to distance of one radius from the wall, it deposits
with no rebound. In order to keep a uniform particle
concentration inside the channel, when a particle is
deposited on the wall, another particle is randomly









introduced in the computational domain.
The hard sphere particle-particle collision model with a
coefficient of restitution equal to 0.95 was used in the
analysis. The procedure for the numerical implementation
of the particle-particle collisions as described by Li et al.
(2001) was implemented in the present analysis. In this
study, the collisions were assumed to be binary since
multiple collisions are extremely rare at the particle
concentrations that were considered.

Gas phase
The instantaneous fluid velocity field in the channel is
evaluated by DNS of the Navier-Stokes equation using an
additional source term due to the presence of particles. It is
assumed that the flow is incompressible, and a constant
mean pressure gradient in x-direction is imposed. The
corresponding governing equations of motion are:
Continuity Equation: In this study the volume fraction of
particles is very small, ,< <10 3; therefore, the continuity
equation may be expressed as:
V .+f =0 (6)

Momentum Equation: The effect of particles is added to
the Navier-Stokes equations by an additional source term
using the point force model:
Du +f 1
V+p -- i + V +S/VP+ (7)
Dt+ H
where Ef+ =(uf+,vf+,wf+ ) is the fluid velocity vector
in wall units, and p+ is the pressure in wall units. The
coupling between fluid and dispersed phases incorporated
into the momentum equation via a feedback force per unit
mass, which is the negative of the drag and lift forces
acting on the particles exerted by the fluid in a certain
computational cell; the particle feedback force per unit
mass is given by
dNP NP
Si = -- (CD Fd +F+ ) (8)
n=l dt n=l
No-slip boundary conditions are assumed on the channel
walls and periodic boundary conditions are imposed in the
x- and z-directions as follows:


if+ = 0,


y = +H


f+ (x+ +ml+ ,y+ ,z+ +nA+ ,t+)=if+ (x+ ,y ,z ,t )
(9)
where m and n are integers.
In the present simulations a channel that has half-width
H+ inwall units, and a x,+x ,+ periodic segment inx-
and z- directions is used. A schematic of the flow domain
and the periodic cell are shown in Figure 1. A
nx x ny x nz computational grid in the x-, y- and
z-directions is employed. The grid spacing in the x- and z-
directions are constant, while the variation of grid points in
the y-direction is determined by the collocation points of
the C hlib shei series. The distance of the ith grid point in
the y-direction from the centerline is given as:
+ H+
Y, =-- cos(7ri/AM), O 2


7th International Conference on Multiphase Flow
ICMF 2010, Tampa, FL USA, May 30-June 4, 2010

where M =nz-1.
The channel flow code used in this study is the one
developed by McLaughlin (1989). The code used a
pseudo-spectral method for computing the fluid velocity
field. That is, the fluid velocity is expanded in a
three-dimensional Fourier-C hlib s',IK series. The fluid
velocity field is expanded in Fourier series in the x- and z-
direction, while in the y-direction aC (hbi IsheI series is
used. The code uses an Adams-Bashforth-Crank-Nickolson
(ABCN) scheme to compute the nonlinear and viscous
terms in the Navier-Stokes equation and performs three
fractional time steps to advance the fluid velocity from
time step (n) to time step (n+l). The details of the
numerical techniques were described by McLaughlin
(1989).


Figure 1: Schematics of the channel flow and
computational periodic cell used

Results and discussion

In this section, simulation results for different particle
parameters such as particle fluctuation velocities, particle
streamwise and normal velocities, and particle deposition
velocity are presented. All simulations are performed for
four approaches: 1) one-way coupling, 2) two-way
coupling, 3) four-way coupling, and 4) only inter-particle
collisions. The results are compared to show the effect of
the particle feedback force and inter-particle collisions on
the aforementioned particle parameters. All variables are
nondimensionalized by the fluid viscosity, v, and the
friction velocity, u* = That is

x= t =- u = (11)
V V ,
A temperature of 288 K, v = 1.5 x 105 N.s/m2,
and pf = 1.2kg /m3 for air are used. The friction velocity,
u is assumed to be 0.3 m/s. The channel half width is
H+ = 125 and the streamwise and spanwise periods are
chosen to be A +=630 and A +=630, respectively. The
numbers of grid points in the x-, y- and z-directions are nx
= 32, ny = 65 and nz = 64. In this case, the Reynolds
number based on the friction velocity, u*, and the half
channel width is 125, while the flow Reynolds number
based on the Hydraulic diameter and the centerline
velocity is about 8000. This condition corresponds to a






7th International Conference on Multiphase Flow
ICMF 2010, Tampa, FL USA, May 30-June 4, 2010


channel half width of H = 12.5 mm, the streamwise and
spanwise periods of 31.5 mm. The value for the density
ratio, S = pP /pf, was taken to be 1000. Each simulation
was performed for 2500 time steps, and the
nondimentional time step was chosen to be 0.25.
Simulations were performed for four particle
diameters, d = 20, 25, 30, and 40 um ; this can be
expressed in terms of non-dimensional particle relaxation
time, r+ = 9, 14, 20, and 35. Simulations were performed
at two particle mass loadings, M.L.=20% and 40%. It is
important to mention that for particles with + = 8.9 and
at M.L.=40%, approximately 1 200 000 particles were
tracked which required an expensive computation. All
results have been averaged over the simulation time, and
over the streamwise and spanwise directions. Particles
were uniformly distributed in the channel, and the initial
velocity of each particle was set equal to the local fluid
velocity evaluated at the center of the particle. It is
assumed that when a particle hits the wall, it sticks to the
wall and no rebound occurs. When a particle deposits on
the wall, another particle is randomly distributed inside the
computational domain in order to keep the total number of
particles constant.
Figure 2 shows a sample instantaneous velocity
vector plot in the x-y plane at t =100 in the case of
one-way coupling. The random deviations from the
expected mean velocity are clearly seen from this figure.
Figures 3-5 show the velocity field in the y-z plane at
t+ =500 in the case of one-way and four-way coupling at
mass loadings of M.L.=20% and M.L.=40%. The near
wall coherent eddies and flow streams toward and away
from the wall can be observed in these figures. Comparing
the results for the one-way coupling in Figure 3 with the
four-way coupling in Figures 4 and 5, it appears that the
presence of solid particles damps the turbulence
fluctuations and also decreases the number of eddies. The
simulated root-mean square (RMS) fluctuation fluid
velocities in the case of one way and four-way coupling at
M.L.=20% and 40% are shown in Figure 6. It is seen that,
the addition of particles with r+ = 20 attenuates the
intensity of the fluctuations, and as particle mass loading
increases, the level of attenuation increases. This trend is in
agreement with earlier experimental data and numerical
results. As was noted before, it has been widely shown
that particles with diameter less than the Kolomogorov
length scale attenuate the turbulence while particles with
diameters larger than the Kolmogorov length scale
augment it.

ioo0h k_%hhhhhh WhSl


0 100 200 300 400 500 600

X
Figure 2: Sample velocity vector plot in x-y plane.


-100
0 200 400 600
Z+

Figure 3: Velocity vector plot in y-z plane in presence of
T+ = 20.0 particles, one-way coupling


-100 1 bii
0 200 400 600
z
Z+

Figure 4: Velocity vector plot in y-z plane in presence of
T+ = 20.0 particles four-way coupling at M.L.=20%


200 400 600


Figure 5: Velocity vector plot in y-z plane in presence of
T+ = 20.0 particles four-way coupling at M.L.=40%


- - 20% Fowr-wmy cooling
---- 40% Faou-w cup tin


2 2



1-




10o 10' 10'

y

Figure 6: Effects of r =20.0 particles on the flow
fluctuating velocities

Figure 7 depicts the number of deposited particles versus









time for r = 20.0 for different approaches. Since in each
case the number of tracked particles is different, the
number of deposited particles in this figure is
nondimensionalized by the total number of particles. It is
observed that in the case of two-way coupling, the number
of deposited particles decreases, and as particle mass
loading increases, fewer particles deposit. When the
particle feedback force is eliminated and inter-particle
collisions are taken into account, the number of deposited
particles increases; increasing particle mass loading,
enhances the number of deposited particles.


100 200


Figure 7: Normalized number of deposited particles
versus non-dimensional time for particles with -+ =20.0

When the particle feedback force and inter-particle
collisions are considered (four-way coupling), the number
of deposited particles increases comparing with one-way
coupling approach and decreases comparing with the case
in which inter-particle collisions are only taken into the
calculations. In the case of four-way coupling, as particle
mass loading increases, more particles deposit. It can be
concluded that two-way coupling causes a decrease in the
number of deposited particles, while the inter-particle
collisions lead to an increase in the number of deposited
particles. The increase in the number of deposited particles
due to four-way coupling shows that the power of
inter-particle collisions in increasing the number of
deposited particles is more than the power of two-way
coupling in decreasing it.

Particle deposition velocity

The dimensionless deposition velocity for particles
released with a uniform concentration CO is defined as

Ud+ =JICOU* (12)
where J is the particle mass flux to the wall per unit time.
In the computer simulation, the particle deposition velocity
may be estimated as

S- (Nd /2)/t (13)
(N /2)/(H /2)
where No is the total number of the particles in the


7th International Conference on Multiphase Flow
ICMF 2010, Tampa, FL USA, May 30-June 4, 2010

channel, and Nd is the number of deposited particles in
the time interval td+ on the channel walls. Figure 8
shows the non-dimensional particle deposition velocity,
ud versus the non-dimensional particle relaxation time,
+ To verify the present simulation results, the
experimental data of Papavergos and Headly (1982), and
the numerical results of Li and Ahmadi (1992) and He and
Ahmadi (1999) are shown in this figure. The present
simulation results in the case of one-way coupling
approach are in favorable agreement with the experimental
data and other simulation results. It is observed that as the
particle relaxation time increases, the particle deposition
velocity increases. In the case of four way coupling, the
particle deposition velocity increases, and as mass loading
increases, this value increases.


Figure 8: Non-dimensional particle deposition velocity
versus non-dimensional particle relaxation time

For particle deposition, the normal component of particle
fluctuating velocity plays a crucial role. Figure 9 shows the
normal fluctuating velocity of the flow and particles with
z+ = 20 for different approaches. Several features are
noteworthy to mention. The normal fluctuating velocity of
particles in the case of one-way coupling is less than the
fluid one in the region where y+ > 10.0 and greater in the
wall region (y+ <10.0). The decrease of the normal
fluctuating velocity of the particles in the region where
y+ > 10.0 can be explained by the fact that inertial
particles are not fully responsive to all turbulent eddies,
and they fluctuate less than the flow. The increase of the
normal fluctuating velocity of the particles in the wall
region ( y+ < 10.0) is because the maximum particle
normal velocity occurs at y+ = 20 and it goes to zero at
the wall; therefore, a wide range of particle normal
velocities is found in the wall region, causing an increase
in the normal particle fluctuating velocity. In the case of
two-way coupling, the particle normal fluctuating velocity
decreases in the entire channel comparing with one-way









coupling approach, and as particle mass loading increases,
the particle normal fluctuating velocity decreases. This can
be explained in terms of turbulence attenuation due to the
presence of the particle feedback force as shown in Figure
6.
When the particle feedback force is eliminated and
inter-particle collisions are considered, the particle normal
fluctuating velocity increases in the entire channel
comparing with one-way coupling approach, and as
particle mass loading increases, the level of augmentation
in particle normal fluctuating velocity increases.
In the case of four-way coupling, the particle normal
fluctuating velocity decreases in the region where
y+ > 10.0 and increases in the wall region (y+<10.0)
comparing with one-way coupling approach. It can be
concluded that two-way coupling decreases the particle
normal fluctuating velocity, while inter-particle collisions
increase it.


101 102


y
Figure 9: Normal fluctuating velocity versus the distance
from the wall for particles with -+ =20.0


The particle normal velocity versus the distance from the
wall for r+ = 20.0 particles with and without inter-particle
collisions is respectively shown in Figure 10. Despite the
zero-mean normal velocity, it is observed that there is a
particle flux toward the wall with a maximum value at
y+ = 20. In the case of four-way coupling and as mass
loading increases, the particle normal velocity decreases.
When two-way coupling is eliminated (only inter-particle
collisions), the particle normal velocity increases, but it is
still less than its value in the case of one-way coupling.

Summary and Conclusions

The goal of this paper was to study the effect of
particle-particle collisions and two-way coupling on
particle deposition velocity, fluid and particle fluctuating
velocities, particle normal velocity, and particle
concentration profile in a turbulent channel flow. The time
history of the instantaneous turbulent velocity vector was
generated by the two-way coupled direct numerical


7th International Conference on Multiphase Flow
ICMF 2010, Tampa, FL USA, May 30-June 4, 2010

simulation (DNS) of the Navier- Stokes equation via a
pseudo spectral method. The particle equation of motion
included the Stokes drag, the Saffman lift, and the
gravitational forces. The effect of particles on the flow is
included in the analysis via a feedback force on the grid
points. The key ideas proposed in this paper may be
summarized as follows:

0
One-way
---- 20% colsbons only
--- 40% coMnlons only
........... 20% two-way ,
-0.03 1 .. ... 4 two-way
.. - - 20% four-way .'
\1 ------- 44% four-way ,
P+ e






-0.12 ' '
10 10' 102

y

Figure 10: Normal particle velocity versus distance from
the wall for particles with r+ =20.0


1) The addition of particles attenuates the intensity of the
fluid fluctuations in x-, y-, and z- directions, and as particle
mass loading increases, the level of attenuation increases.
2) Inter-particle collisions increase the particle normal
fluctuating velocity, while two-way coupling decreases it.
In the case of four-way coupling, the particle normal
fluctuating velocity decreases in the region where
y+ > 10.0 and increases in the wall region (y+<10.0);
increasing particle mass loading magnifies this change.
3) Since inter-particle collisions and increasing particle
mass loading increase the particle normal fluctuating
velocity in the wall region, it is observed that the particle
deposition velocity increases.

4) In the case of four-way coupling and as mass loading
increases, the particle normal velocity decreases. When
two-way coupling is eliminated, the particle normal
velocity increases, but it is still less than its value in the
case of one-way coupling.

Acknowledgements

The financial support of the Environmental Protection
Agency (EPA) and the NYSTAR Center of Excellence is
gratefully acknowledged.


References

Brooke, J. W., Kontomaris, K., Hanratty, T J. &
McLaughlin, J. B., "Turbulent deposition and trapping of
aerosols at a wall," Phys. Fluids A 4, 825-834, (1992).






7th International Conference on Multiphase Flow
ICMF 2010, Tampa, FL USA, May 30-June 4, 2010

Caporaloni, M., Tampieri, F., Trombetti, F. & Vittori, O., in a vertical channel: effect of considering inter-particle
"Transfer of Particles in Nonisotropic Air Turbulence," J. collisions," J. Fluid Mech., 442, 303-334, (2001).
Atmos. Sci., 32, 565-568, (1975).

Chen, M., Y, McLaughlin, J. B., "A New Correlation for
the Aerosol Deposition Rate in Vertical. J. Colloid
Interface Sci., 169, 437, (1995).

Clift, R., Grace, J.R., & Weber, M.E., "Bubbles, Drops and
Particles," Academic Press, New York (1978).


Fessler, JR & Eaton, J. K., "Turbulence Modification by
Particles in a Backward Facing Step," J. Fluid Mech., 394,
97-117, (1994).

Friedlander, S.K. & Johnstone H.F., "Deposition of
Suspended Particles from turbulent gas streams," Ind. Eng.
Chem., 49, 1151-1156, (1957).

Haifeng, Z. & Ahmadi, G, "Aerosol particle transport and
deposition in vertical and horizontal turbulent duct flows,"
J. Fluid Mech., 406, 55-80, (2000).

He, C. & Ahmadi, G, "Particle deposition in a nearly
developed turbulent duct flow with electrophoresis," J.
Aerosol Sci. 30, 739 (1999).

Li, A. & Ahmadi, G, "Computer simulation of deposition
of aerosols in a turbulent channel flow with rough wall,"
Aerosol Sci. Techno. 16, 209 (1992).

Li, Y, McLaughlin, J. B., Kontomaris, K., & Portela, L.,
Numerical Simulation of Particle-Laden Turbulent
Channel Flow. Phys. Fluids., 13 (10): 2957-2967, (2001)

McLaughlin, J. B., "Aerosol Particle Deposition in
Numerically Simulated Turbulent Channel Flow," Phys.
Fluids, Al, 1211-1224, (1989).

Ounis, H., G Ahmadi, & J. B. McLaughlin, "Dispersion
and deposition of Brownian particles from point sources
in a simulated turbulent channel flow. J. Colloid Interface
Sci., 147, 233 (1991).


Reeks, M. W., "The transport of discrete particles in
inhomogeneous turbulence," J. Aerosol Sci. 14, 729-739,
(1983).

Squires, K. D. & Eaton, J. K., "Measurements of particle
dispersion obtained from direct numerical simulations of
isotropic turbulence," J. Fluid Mech. 226, 1-35, (1991a).

Squires, K. D. & Eaton J. K., "Preferential concentration of
particles by turbulence," Phys. of Fluids A 3, 1169-1178,
(1991b).

Wang L.P & Stock D.E., "Dispersion of Heavy Particles
by Turbulent Motion," J. Atm. Sci., 50, 1897-1913, (1993).

Yamamoto, Y, Potthoff, M., Tanaka, T, Kajishima, T, &
Tsuji, Y, Large eddy simulation of turbulent gas-solid flow




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