Inclined settling device can give a much higher sedimentation rate ...

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22 Φεβ 2014 (πριν από 3 χρόνια και 7 μήνες)

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Unit Operation(II)

First Exam. 9
2
,
3/29


Prob.1 (
40
%)

(1)

簡述
(a)cake filtration, (b)deep bed filtration

(c)cross flow filtration
等三種過濾操
方式及其個別適用之對象。
(10%)

(2)

對於含膠體粒子之懸浮液,若欲分離該膠體粒子,可採用的處理單元有哪些?請
簡述之!

(3)

試說明
free settling


hindered settling
兩者之差異。

(4)

簡述
cyclone
的構造及操作原理。

(5)

濾餅內之孔隙度分布與一般粒子填充床者常有很大的差異,試說明其原因。

(6)

在離心沉降操作設計中,對某一特定之離心機與懸浮液而言,若在進料體積流率

Q
1
時所得之
cut point diameter

D
pc,1
,則當體積流率提高至
2Q
1

cut point
diameter
值應為何?



Prob. 2 (2
5
%)

The particle size distribution of a powder with
cubical
particles
(
立方型顆粒
) measure
d by
sieving analysis
is reported as :





f(D
p
)


mass (1/mm)


frequency




D
p
(
m
m)

(a)

Calculate the cumulative mass fraction for D
p
= 4 mm of the powder,

(b)

Calculate the cumulative number fraction fo
r D
p
= 4 mm of the powder,

(c)

Calculate the specific surface area per unit volume of the powder in m
2
/m
3
.




Prob.3 (
20
%)

A concentrated slurry consisting of particles of density 2800 kg/m
3

and size 200
μ
m in
water

=1000 kg/m
3
,

=1.0cp)

is designed to be thickened by gravity sedimentation. If the
particles are spherical and the mass fraction of particles in the slurry is 0.15, estimate the
settling velocity of the slurry by the empirical re
lation as v
t
=v
ts
ε
4.65
, where
ε
is the
volumetric fraction of liquid in the slurry.




Prob.4 (15%)

The filtration equation for a slurry

filtered under
constant pressure

drop

,
Δ
P,
is reported as



V
t
K
1
Δ
P


0.5
V+

K
2
Δ
P


1.0

where

t is in s

,

V in m
3

,
Δ
P in N/m
2
, and K
1

and K
2

are constants. If now a filter of surface
A is used for the slurry and designed to operate at a constant rate, v, where v is in m/s,
estimate the running time t for reaching the maximum pressure drop,
Δ
P
max
, permissib
le for
the filter (
可允許之最大壓降
).



Given Eqs.:

cake filtration:
PA
Δ
R
μ
V
pA
Δ
C
μα
dV
dt
m
2
av



Stoke’s law

(for N
Re,P
<1.0)
for a spherical sphere settling by gravity:


μ
18
gD
v
2
p
t
p





For N
Re,p

in the range from 1 to 10
4
, the drag coefficient for sphe
re is

34
.
0
3
24
Re,
Re,



p
p
D
N
N
C