Page 423 - Air pollution and greenhouse gases from basic concepts to engineering applications for air emission control

13.4 Separation of Nanoaerosol from the Air 403

air. It may work effective for small quantity of air, however, it becomes costly for
large air flow rates.
Filtration of nanoaerosol particles from its carrier gas is important to nanoaerosol
sampling and characterization as well as air cleaning. The filtration efficiency for
nanoaerosol is also described using Eq. (13.8)
g nano ¼ g g ð13:8Þ
ts ad

13.4.1 Nanoparticle Transport Efficiency

Same as microparticles, nanoparticle transport efficiency (η ts ) is calculated based on
the single fiber efficiency (η sf ) as described in Sect. 6.5:

4ag L
sf
g ¼ 1 exp ð13:9Þ
ts
ð 1 aÞpd f
where d f is the diameter of the fiber, L is the thickness of the bulk filter, and α is the
solidity of the filter. The single fiber filtration efficiency can still be determined
using Eq. (6.8)

g ¼ 1 1 gð it Þ 1 g ip ð 1 g Þ 1 gð E Þ ð13:10Þ
D
sf
However, the dominating mechanisms for removing neutral airborne nanopar-
ticles using fibrous filters are Brownian diffusion and interception.

g ¼ 1 1 gð it Þ 1 g Þ ð13:11Þ
ð
D
sf
There have been several models developed for these mechanisms, and the state
of the art is summarized in the paper by Givehchi and Tan [16]. We choose the
latest one for each of these two mechanisms. The single fiber efficiency for neutral
particles in a slip flow for a Brownian diffusion (η D ) considering slipping effect is
described using the following equation [62].

g ¼ 0:84Pe 0:43 ð13:12Þ
D
where Pe is Peclet number is defined using Eq. (13.13)

U 0 d f
Pe ¼ ð13:13Þ
D p