Mass Transfer (Set 3)

Question 1

Solvent extraction is the terminology applied to the liquid-liquid extraction, which is preferred for the separation of the components of liquids, when

Answer 1

one of the liquid components has very high affinity towards the solvent.

Question 2

Inside the distillation column, the
a. driving force for the vapour flow is the pressure drop.
b. liquids are not always at their bubble points.
c. pressure increases gradually from bottom to the top of the column.
d. none of these

Answer 2

driving force for the vapour flow is the pressure drop.

Question 3

Diffusivity in concentrated solutions differs from that in dilute solutions, because of the changes in

Answer 3

both (a) and (b).

viscosity with concentration. & degree of ideality of the solution.

Question 4

Occurrence of ‘case hardening’ during drying of a high moisture solid cake ____ the drying rate.

Answer 4

decreases

Question 5

Which of the following is not a continuous drier?

Answer 5

Tray drier

Question 6

Humidification involves mass transfer between a pure liquid phase and a fixed gas, which is

Answer 6

insoluble in the liquid

Question 7

____ is the temperature at which a gas-vapor mixture becomes saturated, when cooled at constant total pressure out of contact with a liquid.

Answer 7

Dew point

Question 8

Rate of leaching increases with increasing

Answer 8

temperature

Question 9

An azeotropic mixture is a ____ mixture.

Answer 9

constant boiling point

Question 10

Pick out the wrong statement.

Answer 10

For Laminar flow over a plate of length L, the local mass transfer co-efficient at a distance L from the leading edge is 1.5 x 10-2m/s. Then the average mass transfer co-efficient for the plate is 2 x 10-2m/s.

Question 11

Molecular seives are regenerated by heating to ____ °C.

Answer 11

200-330

Question 12

In continuous distillation, the internal reflux ratio (Ri) and the external reflux ratio (Re) are related as

Answer 12

Ri = Re/1+Re

Question 13

In a counter-current extractor, as the axial mixing increases, the extraction efficiency

Answer 13

decreases

Question 14

Heat sensitive materials like certain pharmaceuticals and food stuffs can be dried in a/an ____ dryer.

Answer 14

freeze

Question 15

In extractive distillation, solvent is

Answer 15

added to alter the relative volatility of the mixture.

Question 16

Radioactive nuclear waste is treated in

Answer 16

pulsed column extractor

Question 17

Large scale drying of sugar is done in a ____ dryer.

Answer 17

rotary

Question 18

____ temperature is the steady state temperature attained by a small amount of liquid evaporating into a large quantity of unsaturated gas-vapor mixture.

Answer 18

Wet bulb

Question 19

The drying time between fixed moisture contents within the ‘constant rate period’ is proportional to (assuming that drying occurs from all surfaces of the solid) (where, T = thickness of the solid)

Answer 19

T

Question 20

____ equation applies to diffusivities in liquids.

Answer 20

Gilliland

Question 21

A packed tower compared to a plate tower for a particular mass transfer operation

Answer 21

incurs smaller pressure drop.

Question 22

Which of the following is the most commonly used leaching solvent in vegetable oil industry?

Answer 22

Hexane

Question 23

In an absorber, HETP does not vary with the

Answer 23

none of these

Question 24

Large quantity of silica gel is normally dried in a ____ dryer.

Answer 24

through circulation

Question 25

For the same system, if the same liquid used in an absorber is decreased, the tower height will

Answer 25

increase

Question 26

Hydrogenation of oil is carried out in a/an ____ in Vanaspati manufacturing plant.

Answer 26

agitated vessel

Question 27

Sides of equilateral-triangular co-ordinates (on which ternary liquid system is plotted) represent

Answer 27

a binary mixture.

Question 28

In distillation column design, the McCabe-Thiele procedure is inadequate and a Ponchan-Savarit procedure is needed, when

Answer 28

a total condenser is used.

Question 29

In an interphase mass transfer process, the lesser the solubility of a given solute in a liquid, the higher are the chances that the transfer process will be

Answer 29

gas phase resistance controlled.

Question 30

As the reflux ratio decreases, the

Answer 30

number of plates increases.

Question 31

Which of the following equipments is not used for gas dispersion?

Answer 31

Spray towers

Question 32

One mole feed of a binary mixture of a given composition is flash vaporised at a fixed P and T. If Raoult's law is obeyed, then changing the feed composition would effect

Answer 32

the fraction vaporised but not the product composition.

Question 33

The equation, https://www.indiabix.com/_files/images/chemical-engineering/mass-transfer/315-483-1.png is for (see attached picture)

Answer 33

steady state equimolar counter diffusion

Question 34

With increase in the liquid flow rate at a fixed gas velocity in a randomly packed counter current gas-liquid absorption column, the gas pressure drop

Answer 34

increases

Question 35

The equation, https://www.indiabix.com/_files/images/chemical-engineering/mass-transfer/314-467-1.png is for (see attached ppicture)

Answer 35

stready state diffusion for stagnant case.

Question 36

Which of these columns incurs the lowest pressure drop?

Answer 36

Packed column (with stacked packing)

Question 37

In the desorption of highly soluble gas from the liquid, the main resistance will be in the ____ phase.

Answer 37

liquid

Question 38

If G = insoluble gas in gas stream and L = non-volatile solvent in liquid stream, then the slope of the operating line for the absorber is

Answer 38

L/G

Question 39

Which of the following remains constant during evaporative cooling process with recirculated water supply?

Answer 39

Wet bulb temperature

Question 40

For stripping of a gas in a counter current stripper, the operating line

Answer 40

can lie above or below the equilibrium curve.

Question 41

Which of the following same diameter columns gives lowest pressure drop per unit height?

Answer 41

Packed column (stacked)

Question 42

Diffusion in concentrated solutins differs from that in dilute solutions, because of the change in the ____ with the concentration of the solution.

Answer 42

both 'a '& 'b'

Question 43

Stage efficiency in a leaching process depends on the

Answer 43

both (a) and (b)

Question 44

Operating velocity in a packed tower is usually ____ the flooding velocity.

Answer 44

half

Question 45

The Knudsen diffusivity is dependent on the

Answer 45

molecular velocity and por radius of the catalyst.

Question 46

Minimum possible diameter of a packed coloumn is decided mainly by the

Answer 46

flooding

Question 47

Solvent used in extractive distillation

Answer 47

forms a low boiling azeotrope.

Question 48

Capacity of a rotary dryer depends on its

Answer 48

both (a) and (b)

Question 49

The cooling effect in a cooling tower can be speeded up by

Answer 49

all (a), (b) and (c).

Question 50

The following plot gives the saturated humidity (He) versus temperature (T).Line joining (H1, T1) and (H2, T2) is the constant enthalpy line. Choose the correct one from among the alternatives A, B, C and D. The following plot gives the saturated humidity (He) versus temperature (T).Line joining (H1, T1) and (H2, T2) is the constant enthalpy line. Choose the correct one from among the alternatives A, B, C and D. https://www.indiabix.com/_files/images/chemical-engineering/mass-transfer/335-677-1.png

Answer 50

T1-Dry bulb temp; T2-Wet bulb temp; T3-Dew point temp.

Question 51

When both the fluids flow concurrently in an absorber, the slope of the operating line is

Answer 51

(-) ve

Question 52

The percentage humidity is less than the relative humidity only at ____ percent humidity.

Answer 52

both zero and hundred

Question 53

Back-trapping in a distillation column

Answer 53

decreases tray efficiency.

Question 54

Flooding in a vapor-liquid contacting equipment occurs in a tray, when the pressure drop through a tray is ____ the liquid head available in the downcomer.

Answer 54

more than

Question 55

Milk is dried usually in a ____ dryer.

Answer 55

spray

Question 56

At a given equilibrium pressure, with increase in temperature, the concentration of adsorbed gas on solid adsorbant

Answer 56

decreases

Question 57

Which of the following adsorbent is used to decolourise yellow glycerine?

Answer 57

Activated carbon

Question 58

Which of the following liquid temperature (T) Vs. vapor-gas mixture enthalpy (H) diagram is valid for humidification operation?

Answer 58

https://www.indiabix.com/_files/images/chemical-engineering/mass-transfer/317-499-2.png

Question 59

In a distillation column, with increase in the reflux ratio, the heat removed in the cooler

Answer 59

increases.

Question 60

Pick out the wrong statement.

Answer 60

Relative volatility of a binary mixture changes appreciably with the minor change in temperature.

Question 61

Which of the following is not a unit of mass transfer co-efficient?

Answer 61

None of these

Question 62

The falling rate period in the drying of a solid is characterised by

Answer 62

increasing temperatures both on the surface and within the solid.

Question 63

In which of the following unit operations, the selectivity is an important parameter?

Answer 63

Solvent extraction

Question 64

Which of the following is an undesirable characteristic for the solvent used in gas absorption?

Answer 64

None of these

Question 65

Which of the following equipments is not used for liquid dispersion?

Answer 65

Agitated vessels

Question 66

Diameter of raschig rings used in packed tower in industry is normally around ____ inches.

Answer 66

2

Question 67

The diffusion co-efficient in m2 /s. of acetic acid in benzene (liquid in liquid) is

Answer 67

2.09 x 10-9

Question 68

Pick out the wrong statement.

Answer 68

According to film theory for equimolar counter diffusion, the mass transfer coefficient is given by sqrt(DAB)(b)P - 3, Q - 2

Question 69

In case of non-ideal gases and liquids, the molal diffusivity

Answer 69

is independent of pressure.

Question 70

Condensation of a vapour-gas mixture just begins, when (where, p = partial pressure of the vapour P = vapour pressure of the liquid)

Answer 70

p = P

Question 71

____ number indicates the ratio of the rates of the heat and mass transfer incase of a cooling tower.

Answer 71

Lewis

Question 72

The expression, y(1 - x)/x(1 - y) is for

Answer 72

relative volatility

Question 73

In physical terms, Schmidt number means

Answer 73

momentum diffusivity/mass diffusivity.

Question 74

In case of liquids, the binary diffusivity is proportional to (where, T = temperature)

Answer 74

T

Question 75

The diffusivity, DAB (for component A diffusing in B) is equal to the diffusivity DBA (for component B diffusing in A) for a binary mixture of

Answer 75

ideal gases

Question 76

Mass transfer co-efficient is directly proportional to DAB0.5, according to ____ theory.

Answer 76

penetration

Question 77

Sand is dried in foundaries in a___drier.

Answer 77

fluidised bed

Question 78

Which of the following employs an accessory known as 'drift eliminator'?

Answer 78

Mechanical draft cooling tower.

Question 79

Pick out the correct statement.

Answer 79

For a non-reacting binary mixture of ideal gases, the partial pressure distribution of both components is linear in the case of steady state equimolal counter-diffusion.

Question 80

Pick out the correct statement.

Answer 80

all (a), (b) and (c).

Question 81

Humid volume is the total volume in m3 of 1 kg of

Answer 81

gas plus its accompanying vapour at 1 atm. and gas temperature.

Question 82

Diameter to height ratio for a rashig ring is

Answer 82

1

Question 83

The equipment used in the extraction of highly corrosive radio active liquids is

Answer 83

pulse column

Question 84

Advantage of continuous drying over batch drying is that the

Answer 84

all 'a', 'b' & 'c'

Question 85

With increase in temperature, the rate of extraction in leaching (solid-liquid extraction system)

Answer 85

increases

Question 86

In a packed bed absorption column, the channelling will be noted by the

Answer 86

sharp drop in pressure drop.

Question 87

Gaseous diffusivity at atmospheric pressure is of the order of ____ cm2/second.

Answer 87

1

Question 88

In liquid-liquid extraction, the number of phases at plait point is

Answer 88

1

Question 89

In a liquid-liquid extraction, 10 kg of a solution containing 2 kg of solute C and 8 kg of solvent A is brought into contact with 10 kg of solvent B. Solvent A and B are completely immiscible in each other whereas solute C is soluble in both the solvents. The extraction process attains equilibrium. The equilibrium relationship between the two phases is Y* = 0.9X, where Y* is the kg of C/kg of B and X is kg of C/kg of A. Choose the correct answer.

Answer 89

The entire amount of C is transferred to solvent B.

Question 90

The surface renewal frequency in Danckwerts' model of mass transfer is given by (KL: mass transfer co-efficient)

Answer 90

sqrt(KL2.DA)

Question 91

If Rm is the minimum reflux ratio, the optimum reflux ratio may be around ____ Rm.

Answer 91

1.2 to 1.5

Question 92

During dehumidification of unsaturated air wet bulb temperature & partial pressure of vapor are not constant. However, during evaporative cooling process with recirculated water supply, the ____ remains constant.

Answer 92

wet bulb temperature

Question 93

In case of absorption, both the operating and equilibrium lines will be straight for

Answer 93

dilute solutions and isothermal operation.

Question 94

Mass transfer co-efficient varies as DAB0.5, according to the ____ theory.

Answer 94

surface renewal

Question 95

For an absorber, both equilibrium and operating line will be straight for

Answer 95

dilute solution and isothermal operation.

Question 96

A distillation column separates 10000 kg/hr of a benzene-toluene mixture as shown in the figure below: https://www.indiabix.com/_files/images/chemical-engineering/mass-transfer/335-680-1.png In the figure xF, xD and xW represent the weight fraction of benzene in the feed, distillate and residue respectively. The reflux ratio is

Answer 96

0.6

Question 97

Unsaturated air (with dry bulb and wet bulb temperatures being 45°C and 25°C respectively) is passed through a water spray chamber maintained at 23°C. The air will be cooled and

Answer 97

humidified with wet bulb temperature decreasing.

Question 98

Humid volume, at a given temperature is a/an ____ function of humidity.

Answer 98

linear

Question 99

The Schmidt number which is defined as, μ/ρ D, is the ratio of the

Answer 99

momentum diffusivity to the mass diffusivity.

Question 100

If f is defined as above, then which of the following applies to a feed at dew point ?

Answer 100

f = 1