Geoscience Reference
In-Depth Information
The result demonstrates that the flow regime is laminar. Now use Equation 17.9 to determine the
settling velocity:
(
)
×
=
()
=
2
2
−
4
gp
dC
pp
980
×
0 899
.
×
45
×
10
1
f
v
=
538
.
m/sec
(
)
18
µ
−
4
18
×
1
.82
×
10
■
EXAMPLE 17.2
Problem:
Three differently sized fly ash particles settle through air. Calculate the particle terminal set-
tling velocity (assume the particles are spherical) and determine how far each will fall in 30 seconds.
Given:
Fly ash particle diameters = 0.4, 40, and 400 µm
Air temperature and pressure = 238°F, 1 atm
Specific gravity of fly ash = 2.31
Because the Cunningham correction factor is usually applied to particles equal to or smaller than 1
micron, check how it affects the terminal settling velocity for the 0.4-µm particle.
Solution
: Determine the value for
K
for each fly ash particle size settling in air by first calculating
the particle density using the specific gravity given:
144.14 lb/ft
3
p
p
=
Specificgravity of flyash
×
Density of water
=×=
2.31
62.4
Calculate the air density and air viscosity:
PM
RT
129
×
×+
=
lb/ft
3
p
=
=
0 0569
.
0 7302
.
(
238
460
)
−
5
µ 0 021
=
.
p
=× ⋅
1.41
10
lb/fts
Determine the flow regime (
K
):
033
.
Kd
gp p
pa
=
p
µ
2
For
d
p
= 0.4 µm:
033
.
04
25 000
.
32 2
.
×
144 14
.
×
0 0569
.
K
=
×
=
0 0144
.
(
)
2
,
×
12
−
5
141
.
×
10
where
1 ft = 25,400 × 12 µm = 304,800 µm
For
d
p
= 40 µm:
033
.
40
25 000
32 2
.
×
144 14
.
×
0 0569
.
K
=
×
=
144
.
(
)
2
,
×
12
−
5
141
.
×
10
Search WWH ::
Custom Search