centrifugation

Question 1

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. First statement is true
b. Only second statement is true
c. Both statements are true
d. Both statements are false

Answer 1

c. Both statements are true

Question 2

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. First statement is true
b. Only second statement is true
c. Both statements are true
d. Both statements are false

Answer 2

c. Both statements are true

Question 3

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. First statement is true
b. Only second statement is true
c. Both statements are true
d. Both statements are false

Answer 3

d. Both statements are false

Question 4

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. First statement is true
b. Only second statement is true
c. Both statements are true
d. Both statements are false

Answer 4

b. Only second statement is true

Question 5

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. First statement is true
b. Only second statement is true
c. Both statements are true
d. Both statements are false

Answer 5

c. Both statements are true

Question 6

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. First statement is true
b. Only second statement is true
c. Both statements are true
d. Both statements are false

Answer 6

b. Only second statement is true

Question 7

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. First statement is true
b. Only second statement is true
c. Both statements are true
d. Both statements are false

Answer 7

c. Both statements are true

Question 8

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. First statement is true
b. Only second statement is true
c. Both statements are true
d. Both statements are false

Answer 8

d. Both statements are false

Question 9

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. First statement is true
b. Only second statement is true
c. Both statements are true
d. Both statements are false

Answer 9

c. Both statements are true

Question 10

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. First statement is true
b. Only second statement is true
c. Both statements are true
d. Both statements are false

Answer 10

c. Both statements are true

Question 11

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. First statement is true
b. Only second statement is true
c. Both statements are true
d. Both statements are false

Answer 11

c. Both statements are true

Question 12

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

a. First statement is true
b. Only second statement is true
c. Both statements are true
d. Both statements are false

Answer 12

c. Both statements are true

Question 13

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. First statement is true
b. Only second statement is true
c. Both statements are true
d. Both statements are false

Answer 13

c. Both statements are true

Question 14

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. First statement is true
b. Only second statement is true
c. Both statements are true
d. Both statements are false

Answer 14

d. Both statements are false

Question 15

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. First statement is true
b. Only second statement is true
c. Both statements are true
d. Both statements are false

Answer 15

c. Both statements are true

Question 16

Label the centrifuge working principle.

Answer 16

Orbit
Axis
Centrifugal Force
Velocity

Question 17

What is the separating force used in centrifugation?

a. Gravity
b. Centrifugal force
c. Magnetic force
d. Electrical force

Answer 17

b. Centrifugal force

Question 18

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

a. Denser component
b. Less dense component
c. Both components move equally
d. Neither components moves

Answer 18

a. Denser component

Question 19

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

a. Separating oil and water
b. Separating micelles from cell lysate
c. Separating crystals from a solution
d. Separating blood plasma from red blood cells

Answer 19

c. Separating crystals from a solution

Question 20

Which type of centrifugation relies solely on density difference?

a. Filtration centrifugation
b. Sedimentation centrifugation
c. Both centrifugation types relies solely on density difference
d. Neither centrifugation type uses density difference

Answer 20

b. Sedimentation centrifugation

Question 21

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

a. Spherical
b. Cylindrical
c. Conical
d. Rectangular

Answer 21

b. Cylindrical

Question 22

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

a. Top
b. Bottom
c. Center
d. Sides

Answer 22

c. Center

Question 23

What is used as a filter medium in filtration centrifugation?

a. A solid barrier
b. A screen or cloth
c. A chemical solution
d. A heating element

Answer 23

d. A heating element

Question 24

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

a. Liquid
b. Solid
c. Gas
d. All components are retained

Answer 24

a. Liquid

Question 25

Which centrifuge type has a perforated inner wall and a concentric nozzle? a. Basket centrifuge b. Nozzle bowl centrifuge c. Tubular bowl centrifuge d. Disc stack centrifuge

Answer 25

b. Nozzle bowl centrifuge

Question 26

Centrifugation is mainly used for separating ______________. a. Chemical elements b. Different colored liquids c. Mixtures with similar densities d. Mixtures based on size and density differences

Answer 26

a. Chemical elements

Question 27

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. c. Both a and b d. Neither a nor b

Answer 27

a. It is small enough to be carried by the liquid flow.

Question 28

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

Answer 28

b. The liquid's viscosity.

Question 29

In the simplified case of a thin liquid layer, the settling velocity is assumed to be: a. Constant and independent of the radius. b. Proportional to the square of the particle diameter. c. Dependent on the residence time of the liquid. d. Affected by the flow rate of the liquid.

Answer 29

c. Dependent on the residence time of the liquid.

Question 30

Sigma (Σ) in the equation (29.83) represents: a. The particle’s density. b. The centrifuge's capacity for separation. c. The liquid's viscosity. d. The gravitational acceleration.

Answer 30

b. The centrifuge's capacity for separation.

Question 31

A high sigma value indicates: a. A larger cut point diameter. b. A smaller centrifuge bowl. c. A more efficient separation process. d. A higher liquid flow rate.

Answer 31

b. A smaller centrifuge bowl.

Question 32

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. b. The high rotational speed. c. The presence of a feed point. d. The use of a specific liquid.

Answer 32

d. The use of a specific liquid.

Question 33

The cut point diameter (Dpc) refers to the diameter of a particle that reaches what distance in the bowl? a. The bottom of the bowl b. Exactly halfway between the bowl wall and the axis of rotation c. The top of the liquid layer d. Any distance within the liquid layer

Answer 33

c. The top of the liquid layer

Question 34

The residence time (tT) in a centrifuge is equal to what? a. The volume of liquid in the bowl (V) b. The volumetric flow rate (q) c. V divided by q (V/q) d. q divided by V (q/V)

Answer 34

d. q divided by V (q/V)

Question 35

The cut point refers to the diameter of a particle that: a. Reaches the exact center of the bowl b. Reaches halfway between the inner and outer radius c. Leaves the bowl with the liquid d. Deposits on the bowl wall

Answer 35

a. Both statements are true.

Question 36

A high sigma value indicates what about a centrifuge? a. It has a lower separation capacity b. It can handle larger particles c. It has a simpler design d. It operates at a slower speed

Answer 36

a. Both statements are true.

Question 37

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. Both statements are true. b. Both statements are false. c. Only the first statement is true. d. Only the second statement is true.

Answer 37

c. Only the first statement is true.

Question 38

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. Both statements are true. b. Both statements are false. c. Only the first statement is true. d. Only the second statement is true.

Answer 38

d. Only the second statement is true

Question 39

Two liquid layers are formed as in a nozzle-discharge centrifuge. They flow over adjustable dams into separate discharge spouts. a. Both statements are true. b. Both statements are false. c. Only the first statement is true. d. Only the second statement is true.

Answer 39

b. Both statements are false.

Question 40

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. b. Both statements are false. c. Only the first statement is true. d. Only the second statement is true.

Answer 40

d. Only the second statement is true.

Question 41

It is a type of centrifugal decanter where the feed enters from a stationary nozzle inserted through an opening in the bottom of the bowl. a. Tubular Centrifuge c. Nozzle-discharge Centrifuge c. Sedimenting Centrifuge d. Disc Centrifuge

Question 42

This type of centrifuge is made with maximum bowl diameters from 100 - 1,400 mm (4 to 54 in.). a. Disk Centrifuge b. Nozzle-discharge Centrifuge c. Helical-conveyor Centrifuge d. Sedimenting Centrifuge

Question 43

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. Disk Centrifuge b. Nozzle-discharge Centrifuge c. Helical-conveyor Centrifuge d. Sedimenting Centrifuge

Question 44

In a ________ the solids leave the bowl from below the liquid surface and therefore carry with them considerable quantities of liquid. a. Tubular Centrifuge c. Nozzle-discharge Centrifuge c. Sedimenting Centrifuge d. Disk Centrifuge

Question 45

It is a short, wide bowl 200 to 500 mm (8 to 20 in.) in diameter turns on a vertical axis. a. Tubular Centrifuge c. Nozzle-discharge Centrifuge c. Sedimenting Centrifuge d. Disk Centrifuge

Question 46

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 c. Nozzle-discharge Centrifuge c. Sedimenting Centrifuge d. Disk Centrifuge

Answer 46

a. Tubular Centrifuge

Question 47

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 b. Both statements are false c. Only the first statement is true d. Only the second statement is true

Answer 47

a. Both statements are true

Question 48

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 b. Both statements are false c. Only the first statement is true d. Only the second statement is true

Answer 48

a. Both statements are true

Question 49

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. 4 to 6 min per load; 3 ton/h b. 30 to 50 min per load; 12 ton/h c. 2 to 3 min per load; 5 ton/h d. 5 to 9 min per load; 1 ton/h

Answer 49

c. 2 to 3 min per load; 5 ton/h

Question 50

A short-cycle automatic batch centrifuge, in this machine the basket rotates at constant speed about a __________ axis. a. Vertical b. Parallel c. Horizontal d. Diagonal

Answer 50

c. Horizontal

Question 51

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. Both statements are true b. Both statements are false c. Only first statement is true d. Only second statement is true

Answer 51

d. Only second statement is true

Question 52

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 true b. Both statements are false c. Only first statement is true d. Only second statement is true

Answer 52

b. Both statements are false

Question 53

Tubular centrifuge’s bowl measures 100 to 500 mm. The Disc centrifuge’s bowl measures 200 to 500 mm. a. Both statements are true b. Both statements are false c. Only first statement is true d. Only second statement is true

Answer 53

a. Both statements are true

Question 54

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 b. Both statements are false c. Only first statement is true d. Only second statement is true

Answer 54

a. Both statements are true

Question 55

Most of the liquid goes back upward in an inner vortex and leaves through the central discharge pipe, which is known as a ___________. a. Hydroclones b. Centrifugal Decanters c. Sludge Separators d. Vortex Finder

Answer 55

d. Vortex Finder

Question 56

The purpose of a funnel to a Continuous Filtering Centrifuges is to _________ the feed slurry gently and smoothly. a. Increase b. Rotate c. Decrease d. Accelerate

Answer 56

d. Accelerate

Question 57

Tubular centrifuge’s bowl is tall and narrow. Disk centrifuge’s bowl is wide and short. a. Both statements are true. b. Both statements are false. c. Only the first statement is true. d. Only the second statement is true.

Answer 57

a. Both statements are true.

Question 58

Tubular centrifuge’s bowl measures 8 to 20 inches in diameter. Disk centrifuge’s bowl has a flat bottom and a conical top. a. Both statements are true. b. Both statements are false. c. Only the first statement is true. d. Only the second statement is true.

Answer 58

d. Only the second statement is true.

Question 59

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. Both statements are true. b. Both statements are false. c. Only the first statement is true. d. Only the second statement is true.

Answer 59

c. Only the first statement is true.

Question 60

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. b. Both statements are false. c. Only the first statement is true. d. Only the second statement is true.

Answer 60

a. Both statements are true.

Question 61

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. Both statements are true. b. Both statements are false. c. Only the first statement is true. d. Only the second statement is true.

Answer 61

d. Only the second statement is true.

Question 62

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. Both statements are true. b. Both statements are false. c. Only the first statement is true. d. Only the second statement is true.

Answer 62

d. Only the second statement is true.

Question 63

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. b. Both statements are false. c. Only the first statement is true. d. Only the second statement is true.

Answer 63

a. Both statements are true.

Question 64

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 true. b. Both statements are false. c. Only the first statement is true. d. Only the second statement is true.

Answer 64

b. Both statements are false.

Question 65

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. b. Both statements are false. c. Only the first statement is true. d. Only the second statement is true.

Answer 65

a. Both statements are true.

Question 66

Tubular and disk centrifuge are the main types of centrifugal decanters. Immiscible liquids are separated industrially in centrifugal decanters. a. Both statements are true. b. Both statements are false. c. Only the first statement is true. d. Only the second statement is true.

Answer 66

a. Both statements are true.