filtration questions)
TRANSCRIPT
FILTRATION 1. Water is filtered through a sand bed 150 mm thick. The depth
of water on top of the bed is 120 mm. the porosity is 0.4
and the mean particle diameter is 0.25 mm. The dynamic
viscosity is 0.89 cP and the density is 998 kg/m3. Calculate
the flow rate per square meter of area.
a. 2.72 x 10-2 m3/s
b. 0.543 x 10-3 m3/s
c. 15.50 m/s
d. 0.543 x 10-3 m/s
2. (29.7) The following relation between α and ∆ p for
superlight CaCO3 has been determined to be
∝=8.8 x1010¿Where ∆ p is in pounds for per square foot. This relation is
followed over a pressure range from 0 to 1,000 lb/in2. A
slurry of this material giving 3.0 lb of cake solid per
cubic foot of filtrate is to be filtered at a constant
pressure drop of 70 lbf/in2 and a temperature of 70°F.
Experiments on this sludge and the filter cloth to be used
gave a value of Rm= 1.2 x 1010 ft-1. A pressure filter of the
tank type is to be used. How many square feet of filter
surface are needed to give 1,400 gal of filtrate in a 1-h
filtration? The viscosity is that of water at 70°F.
a. 71.71 ft2
b. 71.44 ft2
c. 71.44 ft2
d. 71.44 ft2
3. (29.8) The filter of Prob. 29.7 is washed at 70°F and 70
lbf/in2 with a volume of wash water equal to one-third that
of the filtrate. The washing rate is 85 percent of the
theoretical value. How long should it take to wash the cake?
a. 2812.40 s or 0.781 hr
b. 2808.73 s or 0.780 hr
c. 2791.12 s or 0.775 hr
d. 2798.21 s or 0.777 hr
4. (29.10) A continuous pressure filter is to yield 1,400 gal/h
of filtrate from the slurry described in Prob. 29.7. The
pressure drop is limited to a maximum of 50 lbf/in2. How
much filter area must be provded if the cycle time is 3 min
and the drum submergence is 50 percent?
a. 483 ft2
b. 34.09 ft2
c. 27.34 ft2
d. 26.73 ft2
5. (29.17) A microfiltration unit is used to concentrate a
suspension of 0.8 micrometer spherical particles has a
permeate flux of 150 L/m2-h at 30°C and a pressure drop of
2.1 atm. Under the same conditions, the pure water flux was
280 L/m2-h. How thick a layer of particles would be needed
to account for the gel-layer resistance if ε = 0.40?
a. 2.23 x10−3m∨2.24mm
b. 2.18 x10−3m∨2.28mm
c. 2.25 x10−3m∨2.25mm
d. 2.08 x10−3m∨2.08mm6. In constant pressure filtration, the rate of filtration
follows the relation (v – filtrate volume, t- time, k and c
– constants)
a. dVdt
=kV +C
b. dVdt
= 1kV +C
c. dVdt
=kV
d. dVdt
=k V 2
7. A filtration is conducted at constant pressure to recover
solids from the dilute slurry. To reduce the time of
filtration, the solids concentration in the feed slurry is
increased by evaporating half the solvent. If the
resistance of the filter medium is negligible, the
filtration time will be reduced by a factor of:
a. 1
b. 2
c. 4
d. 8
8. In constant pressure filtration,
a. resistance decreases with time
b. resistance increases with time
c. rate of filtration increases with time
d. rate of filtration decreases with time
9. At the beginning of filtration, the cake resistance is :
a. maximum
b. optimum
c. minimum and greater the zero
d. zero
10. The filter medium resistance of an old, used filter is:
a. much smaller than that of a new filter
b. much larger than that of a new filter
c. equal to that of new filter
d. infinitely large
11. A filtration is carried out for 10 min at a constant
rate in a leaf filter and thereafter it is continued at
constant pressure which is attained at the end of the
constant rate period. If one quarter of the total value of
the filtrate is collected during the constant rate period,
what is the total filtration time? Assume that the cake is
incompressible and the filter medium resistance is
negligible.
a. 55 minutes
b. 60 minutes
c. 50 minutes
d. 57 minutes
12. A vacuum leaf filter gives a total value of 10 m3 of
filtrate of 30 minutes. If the resistance of the filter
cloth is negligible, the time taken for the collection of 20
m3 of filter is __________ minutes and for the collection of
30 m3 is _______ minutes.
a. 60 minutes, 90 minutes, respectively(V2/V1 is used)
b. 600 minutes, 300 minutes, respectively (V1 used is 1
cubicmeter)
c. 15 minutes, 10 minutes, respectively ((V1/V2) squared is
used)
d. 120 minutes, 270 minutes, respectively (proper use of
solution)
13. A constant pressure filtration test gave data that can
fit an expression:dt/dv = 9.3V + 8.5 (V = liters,t=seconds)
If the resistance of the filter medium is assumed unaffected
with pressure drop and the compressibility coefficient of
the filter cake is 0.3, what will be the time taken for the
collection of 3.5 L of filtrates at a filtration pressure
twice that is used in the test?
a. 55 s
b. 58 s
c. 50 s
d. 53 s
14. The basic filtration equation is given as dtdV
=−∝CVA
+Rm
. Where V is the filtrate, A is the filtration area; α is
specific cake resistance, μ is viscosity of the filtrate,
and C is the concentration of solids in the feed slurry.
In a 20 min. Constant rate filtration, 5m3 of filtrate was
obtained. If this is followed by a constant pressure
filtration, how much more time in minutes will it take for
another 5m3 of filtrate to be produced? Neglect filter
medium resistance, Rmi assume incompressible cake.
a. 10
b. 20
c. 25
d. 30
15. A centrifugal filtration unit at a rotational speed of
ω has inner surface of the liquid (density ρL) located at a
radial distance R from the axis of rotation. The thickness
of the liquid film is δand no cake s formed. The initial
pressure drop during filtration is__________.
a. 12ω2R2 ρL
b. 12ω2δ 2ρL
c. 12ω2δ ρL (2R+δ)
d. 12ω2R ρL (2R+2δ)
16. For laminar flow conditions, the relationship between
the pressure (∆Pc) across an incompressible filter cake and
the specific surface area (So) of the particles being
filtered in given by ONE of the following:
a. (∆Pc)is proportional to (So)
b. (∆Pc)is proportional to 1/(So)
c. (∆Pc)is proportional to (So)2
d. (∆Pc)is proportional to 1/(So)2
17. Filter aids are added to the slurry prior to filtration
in order to form ________________.
a. compact cakes of low porosity
b. cakes of increased
c. crystalline cakes
d. none of the above
18. In a filter bed, the liquid fl;ow
a. is laminar
b. is turbulent
c. is between laminar and turbulent
d. cannot be predicted, information on process conditions
and filter medium is necessary
19. Which of the following statement is true about vacuum
filtration is incorrect?
a. the solids in the slurry are very fine
b. the liquid has a high vapour pressure
c. the liquid has a low viscosity
d. the liquid is a saturated solutions which will
crystallize on cooling
20. In order to achieve rapid filtration of viscous liquids
or slurries containing fine solids, which filter do you
recommend?
a. Discontinuous pressure filter
b. Continuous vacuum filter
c. Discontinuous vacuum filter
d. none of the above
21. The filter medium resistance usually is important
a. only during the early stages of filtration
b. only during the final stages of filtration
c. all through the filtration process
d. none of these.
22. The rate of filtration in a rotary-drum filter
a. increases with an increase in drum speed
b. decreases with an increase in drum speed
c. is independent of the drum speed
d. increases with an increase in drum speed up to a
certain critical value and thereafter, filtration rate no
longer increases with drum speed
23. The flow of filtrate through cake deposited on septum
is usually which equation will use to calculate pressure
drop for this situation?
a. Leva’s equation
b. Kozeny-Carman equation
c. Blake-Plummer equation
d. Bernoulli’s equation
24. A rotary drum filter is –
a. Continuous Vacuum filter
b. A Discontinuous Vacuum Filter
c. A Continuous Pressure Filter
d. None of the above
25. The speed of rotation of an industry rotary – drum
filter is
a. 0.1 to 2 RPM
b. 25 to 50 RPM
c. 50 to 100 RPM
d. 100 to 200 RPM