Environmental Engineering Reference
In-Depth Information
17.5   METHOD OF CALCULATION OF PARTICLE DEPOSITION 
EFFICIENCY IN REAL FILTERING MATERIALS
It was assumed at the development of the method to calculate eficiency in real ilters that a fan
model ilter is a reference standard of an ideal homogeneous ibrous ilter. That enables introducing
a quantity characteristic of inhomogeneity grade of a real ilter structure presented as a relation of
nondimensional force F f acting on a unit of iber in a fan model to the value F in a real ilter at equal
values of α and a .
It was established as the result of numerous experiments with fan-type model and real ibrous
ilters that structure inhomogeneity of real ilters equally affects both their resistance and particle
deposition:
f
f
F
F
= η
η
(17.25)
Although no complete theoretical proof of this empiric correlation has been found until now, it is
of fundamental signiicance for calculation of ilter eficiency as it enables to calculate their efi-
ciency from hydrodynamic resistance using equations for particle deposition in a fan model ilter.
Penetration of particles with the radius r p at velocity U (at Re < 1) through a ilter with known resis-
tance Δ p may be evaluated in the following way [25]:
f
N
N
2
a
η
μ
Δ
p
=
exp
(17.26)
f
U F
0
where
f
η
=
η
+
η
+
η
(17.27)
R
D
DR
{
}
2 3
/
1 3
/
1 3
/
(17.28)
η D
=
2 7
.
Pe
1 0 55
+
.
(
k
)
Pe Kn
1
{
}
1
1
1
(17.29)
η R
=
(
2
k
)
(
1
+
R
)
− +
(
1
R
)
+
2 1
(
+
R
) ln(
1
+
R
)
+
2 86
.
Kn
(
2
+
R R
)
(
1
+
R
)
1
1 2
/
1 2
/
2 3
/
(17.30)
η DR
=
1 24 1
.
(
k
)
Pe
R
(
)
−1
2
2
a
a
a
0 64
1
.
a
1
1
+
a
k
= −
0 5
.
ln
0 52
.
+
+
1 43
.
Kn
, σ
=
1
2
(
1
+
σ
)
(
+
σ
)
(
σ
)
a
A possibility to calculate the eficiency of real HEPA-ilters consisting of polydisperse ultrathin
ibers was demonstrated on the example of national and international ibrous ilters intended for
ine gas puriication. Compliance of the theory with experiments is acquired for different ilters
with particles of different size, including that in the area of maximal penetration. The model fan
ilter was an analogue to FP ilters made of monodisperse ibers, in which there is no effect of ibers
sticking together due to the presence of static charge on ibers [89,90]. Results of extensive studies
of highly eficient ilters are given in Refs [91,92,140].
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