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JOURNAL OF APPLIED ENGINEERING SCIENCES VOL. 4(17), ISSUE 2/20 14

ISSN: 2247-3769 / e-ISSN: 2284-7197 ART.NO. 157, pp. 19-26

19

STUDY ON MECHANICAL SEPARATION OF DUST USING

LOUVER TYPE INERTIAL SEPARATOR

F. Domniţa a, *, C. Bacoţiu a, Anca Hoţupan a, T. Popovici a, P. Kapalo b

a Technical University of Cluj-Napoca, Romania – *e-mails: florin.domnita@insta.utcluj.ro,

ciprian.bacotiu@insta.utcluj.ro, anca.hotupan@insta.utcluj.ro, tudor.popovici@insta.utcluj.ro,

b Technical University of Kosice, Slovakia, e-mail: peter.kapalo@tuke.sk

Received: 05.09.2014 / Accepted: 15.09.2014

Revised: 13 .10.2014 / Available online: 15.12.2014

KEY WORDS: louver type separator, powder, dust, mechanical separation, inertial separator, purification, air movement

ABSTRACT:

Since louver type collector has reduced dimensions, it can be used as a pre-separator in addition to a filtering installation, in order to

increase the degree of mechanical separation of dust particles. The use of the louver type collector in a filtering installation requires a

description of the particle movement inside the device and also a method for determining the rate of particles separation.

* Corresponding author

1. INTRODUCTION

The separation of dust particles from gases has been a

concern for researchers since the development of

industrial processes. The necessity to approach such an

issue was imposed because the solid particles

circulation together with technological gases through

installations leads to high energy consumption and low

reliability of technological equipment. Equally, the

fight against dust from the industrial environment is of

special importance for health and social hygiene.

One of the areas where environmental quality can be

significantly improved is dealing with the removal of

dust particles in suspension in gas streams. This

favourable evolution is due to industrial processes

based on mechanical, electrical, hydraulic separation

techniques and also on porous layer hydraulic

separation (Lăzăroiu, 2006).

When a gas stream changes direction as it flows around

an object in its path, suspended particles tend to keep

moving in their original direction due to their inertia.

Particulate collector devices based on this principle

include cyclones, scrubbers, louver type separators and

filters.

The main elements required for choosing the method

and separation equipment are: particles concentration

in the gas stream, particles size analysis, required

degree of particles removal, physical and chemical

characteristics of dust particles, and also temperature,

pressure and flow rate of polluted air or gas.

This paper presents a new method of separation of solid

particles from gases using louver type inertial

separator.

Inertial separators are devices working on the principle

of inertia. If suddenly the movement direction of the

carrier gas is changed due to inertial forces, the

particles are separated from the deflected stream. Thus,

the gas comes out through device side openings, having

a much reduced concentration of particles. Due to this,

as the carrier gas passes through the device, the particle

concentration will increase, reaching its maximum at

the main exit from the device (Popovici et al., 2011).

The gas cleaned by the inertial separator has a much

lesser concentration of particles than the carrier gas

before the entrance to the collector. Therefore, these

devices can be used in industrial installations as pre-

separators. As a result, the required degree of particles

removal is much lower for the next steps of dust

collectors (located downstream the louver type inertial

separator), which represents a big advantage.

Design features associated with louver separators have

been evaluated by a number of researchers. They

investigated design features such as louver length,

JOURNAL OF APPLIED ENGINEERING SCIENCES VOL. 4(17), ISSUE 2/20 14

ISSN: 2247-3769 / e-ISSN: 2284-7197 ART.NO. 157, pp. 19-26

20

louver angle, louver spacing, louver overlap, scavenge

flow rate, and Reynolds number. Further studies

showed effects of these parameters on particle

separation and pressure losses.

Zverev (1946) has performed one of the earliest studies

of a louver separator. He experimentally measured

separation efficiency and found that increased

scavenge flow rate, increased Reynolds number and

decreased louver spacing led to an increased

efficiency.

Smith and Goglia (2006) found that particle separation

was highly dependent upon the location of the

particle’s impact on the louver. They found that

separation efficiency could be increased by modifying

the louver array to eliminate the louver overlap and to

include a louver anchor. Their findings, confirmed by

Gee and Cole (2009), concluded that for obtaining

good collection efficiency, equal flow rates through

each louver passage were necessary.

This paper studies the two-phase flow in inertial

separators by first solving for the flow field in the

separator, and then calculating particle trajectories by

solving a force balance on each particle. This method

assumes that the particle concentration in the fluid is

small enough that particle interactions are negligible.

This method also assumes that there is no effect of the

particles on the flow field (Jones et al., 2011)

(Ghenaiet and Tan, 2004).

2. MATERIALS AND METHODS

2.1. Principle of operation

Louver type inertial separators consist of a series of

truncated cone-shaped louvers, whose diameter

decreases in the direction of flow of the mixture of dust

and gas. Thereby, about 90% of carrier gas comes out

clean through the device side openings, and the

remaining 10% of the gas, together with all of the dust

particles, maintain their direction until reaching the exit

of the collector (Figure 1). The first fraction will be

called deflected clean gas and the second, undeflected

carrier gas.

Figure 1 presents the principle of operation of a louver

type inertial collector. The carrier gas enters along the

longitudinal axis of the separator and the cleaned gas

comes out on the sides (through the openings between

truncated cone-shaped louvers). The louvers have very

narrow spacing, which cause a very abrupt change in

direction for the carrier gas. The dust particles are

thrown against the flat surfaces; they agglomerate and

concentrate while approaching the exit of the collector

(Popovici et al., 2011).

After passing through the last louver of the device, the

undeflected carrier gas, enriched with dust particles,

enters a duct leading to a cyclone collector, in which

concentrated particles are removed with high efficiency

(Bancea, 2009). The cleaned air comes out of the

separator and is discharged outside, together with the

cleaned air from the cyclone.

Figure 1. Louver type inertial separator

Louver type inertial separators may operate in good

condition in any position because the influence of

gravity is negligible compared to the separation inertial

forces of particles from the gas stream.

Because these devices have relatively small

dimensions, they can be used to improve a classic

cyclone mechanical separation installation, when the

available space is limited and the required degree of

particles removal is high.

2.2. Forces acting on the particles

The particle removal into an inertial separator is

influenced mostly by the trajectories that particles

follow under the action of the separation forces (Fs)

and resistance forces (Fr). The percentage of particles

that follow the stream of undeflected carrier gas is

calculated based on theoretically determined

trajectories of the particles (Jones et al., 2011)

(Ghenaiet and Tan, 2004). Thus, the degree of

fractional separation of inertial collector is theoretically

estimated.

Resistance force:

For determining trajectories that particles take, it is

necessary to know the magnitude of the resistance

force Fr opposed by the carrier gas due to deformation

and friction, caused by the relative movement of the

particles.

The resistance force is calculated with the Newton

relationship:

JOURNAL OF APPLIED ENGINEERING SCIENCES VOL. 4(17), ISSUE 2/20 14

ISSN: 2247-3769 / e-ISSN: 2284-7197 ART.NO. 157, pp. 19-26

21

2

2

rel

v

A

aR

C

r

F⋅⋅⋅=

ρ

(1)

where: CR – resistance coefficient of particle

movement, relative to carrier gas

(calculated with relationships summarized

in Table 1);

ρa – carrier gas density;

A – projection area of the particle in carrier gas

movement direction;

vrel – relative velocity of the particle with respect to

carrier gas.

Mathematical relationships presented in Table 1 are

valid under the following assumptions:

• the particles have a spherical shape;

• bounding walls influence on the flow is absent;

• particle diameter is sufficiently large compared to

the free path of the carrier gas molecules;

• particles do not influence the trajectory and the

velocity field of the carrier gas;

• particles do not gather or crumble along the

stream.

Taking into account these simplifying hypotheses, the

resistance coefficient of particle movement relative to

carrier gas depends only on Reynolds:

ν

p

d

rel

v

Re ⋅

= (2)

where: dp – particle diameter;

ν – kinematic viscosity of the carrier gas.

No. Relationship Validity domain Maximum deviation Relationship

no.

1 Re

24

R

C= Re≤0.2 - (3)

2 2

Re

24

R

C+= Re<1

Re<10

<2%

±4% (4)

3 28,0

Re

6

Re

21

R

C++= 0.1≤Re≤4000 ±4% (5)

4 4,0

R

C= 2000≤Re≤104 ±4% (6)

5 44,0

R

C= 2000≤Re≤105 +10%;-12% (7)

6 4,0

Re

4

Re

21

R

C++= Re≤2·105 ±6% (8)

Table 1.Calculation relationships of particle movement resistance coefficient relative to carrier gas CR

(Smith and Goglia, 2004)

Resistance forces always oppose separating forces of

the particles. When the separation forces are equal to

the resistance forces, the relative velocity between

particle and carrier gas remains constant and will be

equal to:

• Sedimentation velocity vs, when only the separation

force due to gravity Gp and the resistance force Fr act

on the particle;

• Floating velocity vp, when more separation forces Fs

and resistance forces Fr act on the particle.

Separation forces:

Separation forces may have a value that exceeds

several times the weight of the particle GP. Thus, there

is the possibility that through the action of separation

forces Fs, the gravity force will increase by a factor n.

With the help of the multiplication factor n, the

separation force can be calculated:

p

Gn

s

F⋅= (9)

For n=1, particle velocity is equal to the sedimentation

velocity. The value of sedimentation velocity results

from the condition: r

F

s

F=. Substituting the

expressions of the two forces based on relationships

(1), (2), (3), (9) and taking into consideration that

Gp=m·g, gives:

⎪

⎪

⎭

⎪

⎪

⎬

⎫

⋅

⋅⋅−

=⇒

⋅=⋅⋅⋅⋅⋅

μ

ρρ

ρνπ

18

2

p

dg)

ap

(

s

v

gm

s

v

p

d

a

3

(10)

JOURNAL OF APPLIED ENGINEERING SCIENCES VOL. 4(17), ISSUE 1/2014

ISSN: 2247-3769 / e-I SSN: 2284-7197 GUIDE FOR AUTHORS

22

Gas streams having velocities that exceed the

sedimentation velocity vs will cause the particles to

float in the gas.

Figure 2 presents the variation of floating velocity vp

with respect to particle diameter dp and multiplication

factor n.

Figure 2. Variation of floating velocity vp with respect to

particle diameter dp and multiplication factor n

Inertial forces:

The inertial force occurs in accelerated or delayed

movement of a particle:

a

p

m

i

F

r

r

⋅= (11)

When the particle movement is flat and is related to a

rectangular coordinate system, the acceleration is given

by:

y

a

x

aa

r

r

r

+= (12)

Acceleration components ax and ay result from the

variation of velocity components vx and vy, according

to a rectangular 0xy coordinate system:

2

dt

x

2

d

x

a=

r and 2

dt

y

2

d

y

a=

r (13)

Reporting the flat particle movement to a polar

coordinate system gives:

t

a

r

aa

r

r

r

+= (14)

where: ar – radial acceleration along the pole radius r;

at – tangential acceleration.

Each of these two accelerations has also two

components, a linear one and a centrifugal one (Kurten

et al., 1996):

• Linear acceleration component is 2

dt

2

dr along the pole

radius direction, respectively 2

dt

2

d

rϕ along the tangent

direction (they result from the variation of radial and

tangential velocities);

• Centrifugal acceleration component is

r

2

t

v

r

2

2

dt

d

r=⋅ω=

⎟

⎠

⎞

⎜

⎝

⎛ϕ along the pole radius direction,

respectively the Coriolis acceleration

dt

dr

2

dt

dr

dt

d2 ⋅ω⋅=⋅

ϕ along the tangent direction (they

result from the change in direction of particle motion).

Scalar values of these accelerations are given by the

relations:

r

2

2

dt

r

2

d

r

a⋅−=

ω

(15)

dt

dr

2

2

dt

2

dr

t

a

ω

ϕ

⋅+

⋅

= (16)

The inertial force may be determined using Newton's

law, according to which the inertial force is equal to

the sum of all forces acting on the particle:

r

F

s

F

i

F

r

r

r

+= (17)

2.1. Particles motion equations in inertial

separators

Particles motion equations in carrier gas of an inertial

separator were determined according to the

relationship (17). This vectorial relationship expresses

the equilibrium between external forces acting on the

particle and the inertial forces.

In the case of inertial separators, only resistance and

inertial forces are acting on the particles.

r

F

dt

vd

p

m

p

a

p

m

i

F

r

r

r

r

=⋅=⋅= (18)

JOURNAL OF APPLIED ENGINEERING SCIENCES VOL. 4(17), ISSUE 1/2014

ISSN: 2247-3769 / e-I SSN: 2284-7197 GUIDE FOR AUTHORS

23

Between relative velocity vrel, carrier gas velocity va

and particle velocity vp exists the following

relationship:

p

v

a

v

rel

v

r

r

r

−= (19)

Taking into account the Fr formula and relationship

(19), we obtain:

(

)

(

)

2

p

v

a

v

p

v

a

v

A

aR

C

p

a

p

m

r

rrr

r−−

⋅⋅=⋅

ρ

(20)

For relatively low velocities of small spherical particles

(Re≤0,2), based on the relationship (3), we have:

(

)

p

v

a

v

p

d3

p

a

p

m

r

r

r

−⋅⋅⋅⋅=⋅

μ

π

(21)

Replacing the particle mass mp and considering

relationships (10), (4) and (16), we obtain:

()

()

()

⎪

⎪

⎪

⎭

⎪

⎪

⎪

⎬

⎫

−⋅=

−⋅

−

⋅

==

p

v

a

v

s

v

g

p

a

p

v

a

v

ap

2

p

d

18

dt

vd

p

a

rrr

rr

r

r

ρρ

μ

(22)

Forces acting on the particle are situated in the same

plane; therefore particle motion in inertial separators

will be planar. As a result, the flat trajectory of the

particle can be bounded to a rectangular or polar

coordinate system.

In rectangular coordinates, the differential equation

(22) is expressed by the relationships:

()

px

v

ax

v

s

v

g

dt

px

dv

px

a−⋅== (23)

()

py

v

ay

v

s

v

g

dt

py

dv

py

a−⋅== (24)

Using polar coordinates and considering the

relationships (15) and (16), the differential equation

(22) becomes:

()

⎪

⎪

⎪

⎭

⎪

⎪

⎪

⎬

⎫

−⋅=

−=⋅−=

pr

v

ar

v

s

v

g

r

a

r

2

pt

v

dt

pr

dv

r

2

2

dt

r

2

d

r

a

ω

(25)

()

⎪

⎪

⎪

⎭

⎪

⎪

⎪

⎬

⎫

−⋅=

+=+=

pt

v

at

v

s

v

g

t

a

pr

v

r

pt

v

2

dt

pt

dv

dt

dr

2

2

dt

2

rd

t

a

ω

ϕ

(26)

Differential equations of particle motion (23), (24),

(25) and (26) can be integrated only in specific cases,

namely when the carrier gas velocity components vax,

vay, var and vat are constant, or the variation laws of

these components are known.

The paper presents the integration of the particle

motion equations, when the size and direction of

velocity va are constant.

2.4. Integration of the particle motion equations,

when the size and direction of velocity va are

constant

In order to facilitate the integration, the relationship

(19) was considered, and because the size and the

direction of carrier gas velocity are constant, the

following equation was obtained (by derivation relative

to time):

dt

rel

dv

dt

dv −= (27)

Taking into account that CR=CR(Re), the differential

equation (18) becomes:

2

2

rel

v

A

a

(Re)

R

C

r

F

dt

rel

dv

p

m⋅⋅⋅==⋅−

ρ

(28)

Considering the particle shape as a sphere, 4

2

p

d

A⋅π

=

and

()

ap

6

3

p

d

p

mρ−ρ

⋅π

=. Because the value of ρa is

much smaller that ρp, ρa is not taken into consideration.

Finally, the equation becomes:

2

rel

v(Re)

R

C

p

d

p

4

a

3

dt

rel

dv ⋅⋅

⋅⋅

⋅

=−

ρ

ρ

(29)

Considering Re given by relationship (2), equation (29)

becomes:

dt

2

p

d

p

4

a

3

2

Re(Re)

R

C

Red

⋅⋅

⋅⋅

=

⋅

−

ρ

νρ

(30)

JOURNAL OF APPLIED ENGINEERING SCIENCES VOL. 4(17), ISSUE 1/2014

ISSN: 2247-3769 / e-I SSN: 2284-7197 GUIDE FOR AUTHORS

24

It is important to emphasize that both terms of the

equation are dimensionless.

By integrating the right side of equation (30) between

the boundaries t=0 and t=t1, the corresponding

boundary values for Reynolds numbers to the left side

of the equation will be Re0 and Re1:

1

t

2

p

d

p

4

a

3

1

Re

0

Re 2

Re(Re)

R

C

Red ⋅

⋅⋅

⋅⋅

=

∫⋅

−

ρ

νρ

(31)

This integral was determined by Lapple and Shepherd

(1940), but in the end it has not been used for the

determination of particle trajectories under the action

of the carrier gas flow. For these purposes, it was used

another relationship, that gives the elementary time dt,

depending on the elementary relative distance dsrel:

rel

v

rel

ds

dtdt

rel

v

rel

ds ==>= (32)

By introducing this value in equation (30), we obtain:

rel

ds

p

d

p

4

a

3

Re(Re)

R

C

Red

⋅⋅

⋅

=

⋅

−

ρ

ρ

(33)

By integrating between boundaries Re = Re0, for srel =

0 and Re = Re1 for srel = srel1, we have:

1rel

s

p

d

p

4

a

3

1

Re

0

Re Re(Re)

R

C

Red ⋅

⋅⋅

⋅

=

∫⋅

−

ρ

ρ

(34)

In order to determine the relative distance srel within

the validity limits of the Stokes's law, relationship (3)

was used. Together with equation (33) gives:

)

1

Re

0

(Re

a

18

p

d

p

rel

s−⋅

⋅

⋅

=

ρ

ρ

(35)

If movement takes place in a field in which the

Reynolds number of the particle is between 0.1 and

4000, by taking into consideration the equation (5), the

relationship (34) becomes:

∫++

=

0

Re

1

Re Re28,0Re621

Red

a

3

p

d

p

4

1rel

s

ρ

ρ

(36)

2.5. Determination of separation degrees of

particles from the gas stream

There are two separation degrees of particles from

gases, carried out by inertial separators:

• fractional separation degree, ηf;

• total separation degree, ηt.

The fractional separation degree is the ratio between

the number of particles of a certain diameter dp

collected in the separator and the number of particles

of the same diameter entered in the separator per unit

of time.

The total separation degree is determined by reporting

the weight of all separated particles, regardless of their

diameter, to the total weight of all the particles existing

in carrier gas at separator inlet.

The total separation degree can be also determined if

one knows the granulometric structure of powder at

separator inlet and the fractional separation degree

accomplished by the separator.

The fractional separation degree can be determined in

several ways:

• theoretically, by the means of the mathematical

relationships determined on the basis of the differential

equations of the particles;

• by tracing the appropriate trajectories, both for each

particle diameter dp (from powder granulometry at the

entrance in separator), and for the position held by

each particle (at the beginning of the movement);

• by laboratory tests carried out by the means of

pattern/template separators.

The paper only presents the determination of fractional

separation degree through the theoretic method.

When the particles are uniformly spread in the carrier

gas (Musgrove et al., 2009), the separation degree is

determined by the relationship:

i

r

a

r

0

r

a

r

'fs −

−

=

η

(37)

where: ra - radius of the duct outer wall or of the outer

gas stream;

ri – radius of the duct inner wall or of the inner

gas stream;

ro – radius corresponding to the position held by

the particle at the beginning of the movement.

Relation (37) was established on the assumption that

all particles that reach during their movement the

outside of the pipe wall are separated (r≥ra for ϕ=π/2).

Consequently, particles whose polar radius r<ra, for

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25

ϕ=π/2, are not separated, being taken further away

along the deflected carrier gas stream.

In order to determine the separation degree η′fs, it is

necessary to provide the polar radius of the particle

trajectory, based on the polar angle ϕ, r=f(ϕ). Schetz

and Fuhs (1996) determined the mathematical

relationship of the separation degree in the following

hypotheses:

• deflected carrier gas streams are circular, symmetric;

• tangential velocities of the carrier gas and tangential

velocities of the particles are equal and have constant

values vat=vpt=ct. within the whole area of the gas

flow;

• radial velocity of the deflected carrier gas var=0

(consequently, a relative movement between the

particle and gaseous environment exists only in the

radial direction);

• in the separation zone, particle concentration in the

carrier gas is homogeneous;

• particles movement takes place within the validity

limits of the Stokes's law (Re≤0.2).

Starting from the trajectory equation in polar

coordinates:

0

r

18

at

v

2

p

d)

ap

(

)(fr −

⋅

⋅⋅⋅−

==

μ

ϕρρ

ϕ

(38)

It results:

)

i

r

a

r(18

at

v

2

p

d)

ap

(

'fs −⋅⋅

⋅⋅⋅−

=

μ

ϕρρ

η

(39)

Which is valid to apply for ηfs<1.

The above relationship indicates the possibility to

improve the separation degree η′fs by increasing the

deflected carrier gas velocity vat or by decreasing the

separation section width, S=ra-ri

Figure 3. Fractional separation degree variation curves

depending on dp and vat

Figure 3 presents the variation curves of fractional

separation degree '

fs

ηdepending on particle diameter

dp and radial velocity of the deflected carrier gas vat for

an inertial separator, calculated with relationship (39).

In the same hypotheses, the fractional separation

degree can be calculated using the equation:

S

S

'fs

Δ

η

= (40)

S is the distance covered by a particle in the radial

direction under the inertial forces action.

3. CONCLUSIONS

Tests and experiments performed during the operation

showed, that under certain conditions, cyclones can be

replaced by inertial separators in a dust extraction

installation. In case of cyclones, the particles removal

is selective because only especially heavy and large

granulated particles are retained with high efficiency.

Introducing a louver type inertial collector as pre-

separator in a cyclone de-dusting system leads to

increased efficiency of the separation process for the

whole spectrum of particles. Also, this solution has the

advantage of reducing investment costs and required

installation space.

In order to use an inertial collector as pre-separator, it

is necessary to know:

• the movement of gas inside the collector;

• the type and size of the forces acting on the particles;

• the particles movement equations;

• the values of separation degrees.

These aspects are needed for determining the

characteristic parameters of the gas at the outlet of the

inertial separator and the inlet of the cyclone. These

parameters are required as initial data for dimensioning

the cyclone, in the second stage of particle separation.

4. REFERENCES

Bancea, O., 2009. Sisteme de ventilare industrială (Industrial

ventilation systems). Timişoara, Ed. Politehnica, ISBN 978-

973-625-800-8, Chapter 8, pp. 90-122, (in Romanian).

Gee, D.E., Cole, B.N., 2009. A Study of the Performance of

Inertia Air Filters, Inst. Mech. Engineers - Symposium on

Fluid Mechanics and Measurements in Two-Phase Systems,

University of Leeds, pp. 167-176.

JOURNAL OF APPLIED ENGINEERING SCIENCES VOL. 4(17), ISSUE 1/2014

ISSN: 2247-3769 / e-I SSN: 2284-7197 GUIDE FOR AUTHORS

26

Ghenaiet, A., Tan, S.C., 2004. “Numerical Study of an Inlet

Particle Separator,” GT2004-54168.

Jones, G.J., Mobbs, F.R., Cole, B.N., 2011. “Development of

a Theoretical Model for an Inertial Filter,” Pneumotransport

1 – 1st Int’l. Conf. on Pneumatic Transport of Solids in

Pipes, Paper B1.

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