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Particle Technology > Centrifugation > Flashcards

Centrifugation Flashcards

1
Q

In suspended centrifuges the filter media are canvas or other fabric or woven metal cloth. In automatic machines fine metal screens are used; in conveyor centrifuges the filter medium is usually the slotted wall of the basket itself.

A

Both statements are true

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2
Q

The chief quantities of interest are the flow rate through the filter and the pressure drop
across the unit. As time passes during filtration, either the flow rate diminishes or the
pressure drop rises.

A

Both statements are true

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3
Q

Most cakes encountered industrially are made up of individual rigid particles. The usual slurry is a mixture of agglomerates, or flocs, consisting of loose assemblies of very large particles.

A

Both statements are false

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4
Q

The effects of gravity and of changes in potential energy of the liquid are neglected.
The pressure drop from centrifugal action equals the drag of the liquid flowing through the cake.

A

Only second statement is true

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5
Q

The rate of flow of the wash liquid and the volume of liquid needed to reduce the solute
content of the cake to the desired degree are important quantities for the design and
operation of a filter.

A

Both statements are true

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6
Q

Displacement wash could remove all the solvent with a minimum volume of wash
liquid if the bed had uniform size pores and ideal plug flow with no axial dispersion.
The effluent concentration would remain constant until all the solution was displaced
and then drop abruptly to zero.

A

Only second statement is true

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7
Q

Clarifying filters remove small amounts of solids or liquid droplets from either liquids
or gasses. The particles are trapped inside the filter medium or on its surfaces

A

Both statements are true

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8
Q

The ideal membrane for crossflow filtration would have a high porosity and a less
narrow pore size distribution, with the largest pores slightly larger than the particles or
molecules to be retained.

A

Both statements are false

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9
Q

For large-scale commercial applications, continuous operation is recommended with several feed-and-bleed units in series. Each UF module operates with a large recycle
rate to maintain high velocity, and a small bleed stream of the retentate is sent to the
next unit

A

Both statements are true

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10
Q

Sometimes a final ultrafiltration step is needed to obtain a more concentrated protein solution. For small batches, diafiltration can be carried out by intermittent addition of
water to the feed tank, though this is less efficient than continuous addition.

A

Both statements are true

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11
Q

A given particle in a given fluid settles under gravitational force at a fixed maximum
rate. To increase the settling rate, the force of gravity acting on the particle may be
replaced by a much stronger centrifugal force.

A

Both statements are true

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12
Q

Immiscible liquids are separated industrially in centrifugal decanters. The main types of centrifugal decanters are tubular centrifuges and disk centrifuges.

A

Only second statement is true

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13
Q

In a sedimenting centrifuge a particle of given size is removed from the liquid if
sufficient time is available for the particle to reach the wall of the separator bowl. If it
is assumed that the particle is at all times moving radially at its terminal velocity, the
diameter of the smallest particle that should just be removed can be calculated.

A

Both statements are true

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14
Q

In a helical flow conveyor centrifuge, the scroll is cut away in the feed and
sedimentation sections to form a rectangular conveyor operating near the bowl wall,
leaving the liquid surface undisturbed. The liquid layer can then flow in an axial
direction from the feed point to the solid discharge.

A

Both statements are false

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15
Q

During the passage of the liquid through a centrifuge bowl, the heavier, larger solid
particles are thrown out of the liquid. Finer, lighter particles may not settle in the time
available and may be carried out with the liquid effluent.

A

Both statements are true

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16
Q

What does this symbol “ω” mean?

A

angular velocity

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17
Q

What is the separating force used in centrifugation?

A
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18
Q

In a centrifuge, which component moves outward due to inertia?

A
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19
Q

What is an example of separating solids from liquids using centrifugation?

A
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20
Q

Which type of centrifugation relies solely on density difference?

A
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21
Q

What is the shape of the bowl in a tubular bowl centrifuge?

A
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22
Q

In a disc stack centrifuge, where does the mixture enter the stack?

A
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23
Q

What is used as a filter medium in filtration centrifugation?

A
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24
Q

What component is retained inside the basket of a basket centrifuge?

A
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25
Q

Which centrifuge type has a perforated inner wall and a concentric nozzle?

A
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26
Q

Centrifugation is mainly used for separating ______________

A
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27
Q

In a sedimenting centrifuge, a particle will be removed from the liquid if:
a. It is small enough to be carried by the liquid flow.
b. It has enough time to reach the centrifuge wall.

A

Both a and b

28
Q

The terminal velocity of a settling particle in a centrifuge depends on:
a. The particle’s diameter.
b. The liquid’s viscosity.
c. The distance from the rotation axis.
d. All of the above

A

All of the above

29
Q

In the simplified case of a thin liquid layer, the settling velocity is assumed to be:

A

Constant and independent of the radius.

30
Q

Sigma (Σ) in the equation (29.83) represents:

A

The centrifuge’s capacity for separation.

31
Q

A high sigma value indicates:

A

A larger cut point diameter.

32
Q

The actual capacity of a centrifuge may be less than predicted by the sigma value
because of:

A

The complex flow patterns in the bowl.

33
Q

The cut point diameter (Dpc) refers to the diameter of a particle that reaches what
distance in the bowl?

A

Exactly halfway between the bowl wall and the axis of rotation

34
Q

The residence time (tT) in a centrifuge is equal to what?

A

V divided by q (V/q)

35
Q

The cut point refers to the diameter of a particle that:

A

Reaches halfway between the inner and outer radius

36
Q

A high sigma value indicates what about a centrifuge?

A

It can handle larger particles

37
Q

Disk Centrifuge is a short, wide bowl 100 to 300 mm (8 to 20 in.) in diameter turns on
a vertical axis. The bowl has a flat bottom and a comical top.

A

Only the second statement is true.

38
Q

In Disc stack Centrifuge, the bowl has a flat bottom and a conical top. Feed enters the
bowl and is forced outwards by the centrifugal force, separating the denser and less
dense components.

A

Only the first statement is true.

39
Q

Two liquid layers are formed as in a nozzle-discharge centrifuge. They flow over
adjustable dams into separate discharge spouts

A

Only the second statement is true.

40
Q

During the passage of the liquid through a centrifuge bowl, the heavier, larger solid
particles are thrown out of the liquid. Finer, lighter particles may not settle in the time
available and may be carried out with the liquid effluent.

A

Both statements are true.

41
Q

In Disc stack Centrifuge, the bowl has a flat bottom and a conical top. Feed enters the
bowl and is forced outwards by the centrifugal force, separating the denser and less
dense components.

A

Only the first statement is true.

42
Q

This type of centrifuge is made with maximum bowl diameters from 100 - 1,400 mm
(4 to 54 in.).

A

Helical-conveyor Centrifuge

43
Q

In a ________ a particle of given size is removed from the liquid if sufficient time is
available for the particle to reach the wall of the separator bowl.

A

Sedimenting Centrifuge

44
Q

In a ________ the solids leave the bowl from below the liquid surface and therefore
carry with them considerable quantities of liquid.

A

Nozzle-discharge Centrifuge

45
Q

It is a short, wide bowl 200 to 500 mm (8 to 20 in.) in diameter turns on a vertical axis.

A

Disk Centrifuge

46
Q

The bowl is tall and narrow, 100 to 150 mm (4 to 6 in.) in diameter, and turns in a
stationary casing at about 15,000 r/min.

A

Tubular Centrifuge

47
Q

In batch filters the precoat layer is usually thin. In a continuous precoat filter, the layer of precoat is thick.

A

Both statements are true

48
Q

In suspended centrifuges the filter media are canvas or other fabric or woven metal
cloth. In automatic machines fine metal screens are used in conveyor centrifuges, the
filter medium is usually the slotted wall of the basket itself.

A

Both statements are true

49
Q

Top suspended centrifuges are used extensively in sugar refining where they operate on
short cycles of _____ to _____ min per load and produce up to ______ ton/h of crystals
per machine.

A

2 to 3 min per load; 5 ton/h

50
Q

A short-cycle automatic batch centrifuge, in this machine the basket rotates at constant
speed about a __________ axis.

A

Horizontal

51
Q

In a nozzle discharge centrifuge the solids leave the bowl from above the liquid surface.
For separating a feed slurry into a clear liquid fraction and a heavy “dry” sludge.

A

Only second statement is true

52
Q

A given fluid settles under gravitational force at a fixed minimum rate. In increasing
the settling rate, the force or gravity acting on the particle may be replaced by a much
weaker centrifugal force.

A

Both statements are false

52
Q

Tubular centrifuge’s bowl measures 100 to 500 mm. The Disc centrifuge’s bowl
measures 200 to 500 mm

A

Both statements are true

53
Q

Heavier liquid is thrown upward, displacing the lighter liquid toward the center of the
bowl. Light liquid similarly flows inward and upward over the upper surfaces of the
disks.

A

Both statements are true

54
Q

__________ are also used for separating solids from liquids, sometimes as thickeners
but much more commonly as classifiers.

A

Cyclones

54
Q

Most of the liquid goes back upward in an inner vortex and leaves through the central
discharge pipe, which is known as a ___________.

A

Vortex Finder

55
Q

Tubular centrifuge’s bowl is tall and narrow. Disk centrifuge’s bowl is wide and short.

A

Both statements are true.

56
Q

Tubular centrifuge’s bowl measures 8 to 20 inches in diameter. Disk centrifuge’s bowl has a flat bottom and a conical top.

A

Only the second statement is true.

57
Q

Helical-conveyor centrifuges are made with maximum bowl diameters from 4 to 54
inches. Disk centrifuge’s bowl measures 4 to 6 inches in diameter.

A

Only the first statement is true.

58
Q

Tubular and disk centrifuges are used to remove traces of solids from lubricating oil,
process liquids, ink, and beverages that must be perfectly clean. Tubular and disk centrifuges may throw down solids while simultaneously separating two liquid phases.

A

Both statements are true.

59
Q

Tubular centrifuge’s bowl turns in a stationary case at about 20,000 r/min. For some
liquid-liquid separations, the disk-type centrifuge is highly effective.

A

Only the second statement is true.

60
Q

The pressure drop in a hydroclone varies with a feed rate raised to a power between 4.0 and 6.3. Hydroclones range in diameter from 10 mm to 1.2 m.

A

Only the second statement is true

61
Q

Tubular and disk centrifuges can take out gelatinous or slimy solids that would quickly
plug a filter. Tubular and disk centrifuges clarify a single liquid in a bowl provided with
but a single liquid overflow.

A

Both statements are true.

62
Q

In a disk centrifuge, lighter liquid is thrown outward, displacing heavier liquid toward the center of the bowl. In a disk centrifuge, heavy liquid similarly flows inward and upward over the upper surfaces of the disks.

A

Both statements are false.

63
Q

In a tubular centrifuge, heavy liquid flows over another weir into a separate cover and
a discharge spout. The weir over which the liquid flows is removable and may be
replaced with another having an opening of a different size

A

Both statements are true.

64
Q

Tubular and disk centrifuge are the main types of centrifugal decanters. Immiscible
liquids are separated industrially in centrifugal decanters.

A

Particle Technology (9 decks)

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