Environmental Engineering Reference
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6
5
4
η
1
3
2
2
0.02
0.04
0.06
0.08
0.1
r p
FIGURE 17.8  Capture coeficient versus particle radius r p , μm: U = 3 cm/s (1, 1′), 10 cm/s (2, 2′). Curves 1, 2,
air; 1′, 2′, helium; a = 0.04 μm; α = 1/36. (From Kirsh, V.A., Colloid J ., 66(3), 311, 2004.)
0.35
0.3
0.25
1
3
2
0.2
0.15
0.1
0.2
r p (MKM)
0.3
0.4
FIGURE 17.9  Diffusive capture coeficient versus particle radius: (1, 2) considering the particle inite size
and van der Waals attraction η DRW ; (3) η DR without considering van der Waals attraction. Fiber radius a = 1 μm,
low velocity before the ilter U = 1 cm/s, constant of the retarded van der Waals attraction A 7 = 10 −18 erg cm
(1), A 7 = 10 −19 erg cm (2), packing density of the ilter α = 1/16. (From Kirsh, V.A., Colloid J ., 66(4), 444, 2004.)
penetration. In Ref. [70], capture coeficients were calculated both for nondiffusing particles inter-
ception and point particles diffusion at medium Knudsen numbers in the model ilter with parallel
ibers. Diffusive particle deposition in the range Kn = 0.1−10 considering interception was studied in
Ref. [71]. The problem is solved in the approximation to the diffusion boundary layer δ. The calcu-
lated capture coeficients η( R /δ) ( R —interception parameter) can be approximated to straight lines
up to R /δ = 2 at Kn > 1 and at different values of δ. It is shown that at low Knudsen numbers and on
condition that the Knudsen layer thickness is smaller than the diffusion boundary layer thickness
the capture coeficient η is higher than the sum of η R and η D , which conforms with the calculations
performed in Refs [5,25] at Kn = 0.
At Ре >> 1 and Kn > 1 the value η is clearly less than the sum of η R and η D . At medium Pe num-
bers and Kn > 1 the overall capture coeficient practically equals this sum. This result is important
 
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