Mass Transfer (Set 6)

Question 1

In a binary system, separation is very efficient, when the relative volatility is

Answer 1

> 1

Question 2

Fenske-Underwood equation used for calculating the minimum number of theoretical plates in distillation column is valid for

Answer 2

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

Question 3

The binary diffusivity in gases does not depend upon the

Answer 3

none of these

Not pressure, temperature, and nature of components

Question 4

Berl saddle made of carbon cannot be used for

Answer 4

oxidising atmosphere

Question 5

1 kg of a saturated aqueous solution of a highly soluble component A at 60°C is cooled to 25°C. The solubility limits of A are (0.6 kgA/kg water) at 60°C and (0.2 kgA/kg water) at 25°C. The amount in kg of the crystals formed is

Answer 5

0.2

Question 6

During drying of a solid, the critical moisture content increases with
a. decreased drying rate
b. increased thickness of the solid
c. increased drying rate
d. both (b) and (c).

Answer 6

both (b) and (c).

Question 7

Priming in a distillation column

Answer 7

is characterised by the presence of foam throughout the space between trays.

Question 8

The commonly used solvent in supercritical extraction is

Answer 8

carbon dioxide.

Question 9

When the liquid over a plate is of uniform concentration, then

Answer 9

Murphree efficiency = point efficiency.

Question 10

In saturated gas, the

Answer 10

vapour is in equilibrium with the liquid at the gas temperature.

Question 11

As per Gilliland’s equation, the diffusivity is

Answer 11

all ‘a’, ‘b’ & ‘c’.

Question 12

Pick out the wrong statement.

Answer 12

The operating line lies above the equilibrium curve in case of a gas desorber.

Question 13

A mixture of 10% C6H6 vapour in air at 25°C and 750 mm Hg has a dew point of 20°C. Its dew point at 30°C and 700 mm Hg will be around ____ °C.

Answer 13

18.7

Question 14

Which of the following is not fixed by the process requirements, in the design of absorbers?

Answer 14

None of these.

Question 15

If the amount of the steam used in steam distillation is increased, the temperature of distillation

Answer 15

decreases

Question 16

Moisture in a solid exerting an equilibrium vapour pressure equal to that of the pure liquid at the same temperature is called the ____ moisture.

Answer 16

unbound

Question 17

Inside the distillation columns, the

Answer 17

driving force for the liquid flow is its weight.

Question 18

When the psychometric ratio is ____ then the adiabatic saturation temperature and wet bulb temperature becomes equal.

Answer 18

1

Question 19

Desirable value of absorption factor in an absorber is

Answer 19

> 1

Question 20

Refractory bricks are usually dried in a ____ dryer.

Answer 20

tunnel

Question 21

For ____ drying, the effects of velocity, temperature and humidity of the gas and the thickness of the solid are the same.

Answer 21

both (a) and (b)

Question 22

What is the degree of freedom of an absorption process in which only one component is transferred between phases?

Answer 22

3

Question 23

Sticky material can be dried in a ____ dryer.

Answer 23

tray

Question 24

Langmuir equation is associated with

Answer 24

adsorption

Question 25

During the constant rate period of drying of a solid,

Answer 25

surface evaporation of unbound moisture occurs.

Question 26

At a fixed total pressure, humidity depends only on the

Answer 26

partial pressure of vapour in the mixture.

Question 27

If moisture content of solid on dry basis is X, then the same on wet basis is

Answer 27

X/X+1

Question 28

Flash distillation is

Answer 28

used for multicomponent systems like crude refining.

Question 29

____ developed the film theory.

Answer 29

Higbie

Question 30

For absorbers, high pressure drop results in

Answer 30

high operating cost.

Question 31

Which of the following parameters remains almost constant during adiabatic saturation of unsaturated air?

Answer 31

Wet bulb temperature

Question 32

Coffee is prepared from coffee beans by leaching with

Answer 32

hot water

Question 33

Gaseous diffusion co-efficient increases with increase in the

Answer 33

temperature

Question 34

With increase in absolute humidity, the dew point of an unsaturated mixture of air and water vapor (at constant pressure and temperature)

Answer 34

increases

Question 35

If xD = overhead product molal composition and RD = reflux ratio, then slope and intercept of the operating line for rectifying section are respectively

Answer 35

https://www.indiabix.com/_files/images/chemical-engineering/mass-transfer/287-102-2.png

Question 36

Pick out the wrong statement. Raoult's law does not apply, when the

Answer 36

component molecules are nonpolar.

Question 37

Water-ethyl alcohal solution can be concentrated (in respect of alcohal concentration) by ____ distillation.

Answer 37

vacuum

Question 38

L/mG is the expression for

Answer 38

absorption factor

Question 39

Extraction of pencillin employs a ____ extraction coloumn.

Answer 39

centrifugal

Question 40

In case of gases, the binary diffusivity is proportional to (where, P = pressure)

Answer 40

1/P

Question 41

When the gas to be dissolved in liquid is a/an ____ then normally co-current adsorber are used.

Answer 41

pure gas

Question 42

Corresponding to Prandtl number in heat transfer, the dimensionless group in mass transfer is the ____ number.

Answer 42

Schmidt

Question 43

If a two phase system is in physical equilibrium; then it means that, the

Answer 43

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

Question 44

McCabe-Thiele method of binary distillation does not assume that the

Answer 44

none of these

Question 45

(NSh/NRe.NSc) is termed in mass transfer operation as the

Answer 45

Stanton number

Question 46

The Hatta number is important in

Answer 46

gas absorption with chemical reaction.

Question 47

When a multistage tray tower uses a minimum reflux ratio, it implies

Answer 47

infinite trays and minimum reboiler heat load.

Question 48

CO2 can be absorbed by

Answer 48

heated charcoal

Question 49

For the same process conditions, the reflux ratio of an unlagged distillation column

Answer 49

increases in winter

Question 50

An ideal tower packing should not

Answer 50

hold up large amount of liquid in the packing.

Question 51

Which of the following is a suitable absorbent for removal of H2S from natural gas?

Answer 51

Monoethanol amine (MEA)

Question 52

Acetone is to be removed from air in an isothermal dilute absorber using pure water as solvent. The incoming air contains 5 mole% of acetone (yin = 0.05). The design equation to be used for obtaining the number of trays (N) of the absorber is, N+2 = 6 log (yin/yout).For 98% recovery of acetone, the number of trays required is/are

Answer 52

9

Question 53

Schimdt number and Lewis number for pure air at atmospheric conditions are respectively

Answer 53

< 1 and ≈ 1

Question 54

Below is given an equilibrium moisture curve of a substance. State which regions represent free moisture and unbound moisture respectively. https://www.indiabix.com/_files/images/chemical-engineering/mass-transfer/292-170-1.png

Answer 54

II, III

Question 55

Molecular diffusion is caused by the

Answer 55

thermal energy of the molecules.

Question 56

At ____ reflux, theoretical number of plates in a distillation coloumn is calculated using Fenske-Underwood equation.

Answer 56

total

Question 57

Separation of a mixture of two gases by absorption in the liquid solvent depends upon the difference in their

Answer 57

solubility

Question 58

Components, having widely different boiling point in a binary mixture, can be separated using ____ distillation.

Answer 58

simple

Question 59

Which of the following equipments is not used in liquid-liquid extraction?

Answer 59

Pachuka tank

Question 60

Pick out the wrong statement.

Answer 60

Diameter of randomly packed tower is normally more than 1.2 metres.

Question 61

Equilibrium-moisture curves of different solids

Answer 61

are different

Question 62

Azeotropism for ethyl alcohol-water system disappears by

Answer 62

decreasing pressure

Question 63

Degree of freedom for leaching and solvent extraction process is

Answer 63

3

Question 64

Diffusion co-efficient generally depends upon the temperature, pressure & the nature of the components of the system. Its dimension is not the same as that of the

Answer 64

mass transfer co-efficient.

Question 65

Equilibrium moisture of a solid is equal to the total moisture minus free moisture. Which of the following substances will have maxi-mum equilibrium moisture?

Answer 65

Bamboo

Question 66

In the absorption of ammonia in water, the main resistance to absorption is by the ____ phase.

Answer 66

gas

Question 67

Drying of refractory is normally carried out in a ____ dryer.

Answer 67

truck/tunnel.

Question 68

The expression, ln(F/W) = https://www.indiabix.com/_files/images/chemical-engineering/mass-transfer/314-454-1.png is

Answer 68

differential distillation equation

Question 69

Heat sensitive materials with very high latent heat of vaporisation may be economically separated using

Answer 69

liquid extraction

Question 70

When the solvent dissolves very little of solute, then

Answer 70

large quantity of solvent is required to extract the solute.

Question 71

An alkaline solution is used to reduce the concentration of carbon dioxide in a stream from 10% to 0.1% by absorption with irreversible chemical reaction. The overall number of transfer units based on gas phase is

Answer 71

4.605

Question 72

HETP is numerically equal to HTU, only when the operating line

Answer 72

and equilibrium lines are parallel.

Question 73

In a distillation operation, what is the effect of the temperature of the reflux stream (given below) on the condenser and reboiler loads ? Reflux conditions: (i) Reflux stream is completely liquid and is at its bubble point. (ii) Reflux stream is below its bubble point.

Answer 73

Both condensor and reboiler loads are higher in case (ii) as compared to case (i).

Question 74

Steady state equimolal counter diffusion occurs in case of

Answer 74

binary phase distillation

Question 75

JD factor for mass transfer is a function of Reynolds number. Mass transfer by molecular diffusion from a single drop to surrounding still air is given by

Answer 75

Nsh = 2

Question 76

The relative saturation of an unsaturated mixture of gas and vapor is independent of the

Answer 76

none of these.

Question 77

The adiabatic saturation curve for a vapour-gas mixture is

Answer 77

slightly concave upward.

Question 78

Pick out the wrong statement.

Answer 78

Zirconia probe is used for the humidity measurement.

Question 79

The value of NA/(NA + NB), for steady state equimolal counter diffusion of two gases 'A' and 'B' is

Answer 79

∞

Question 80

Drift in a cooling tower is

Answer 80

the water entrained by the circulating air.

Question 81

With increase in the concentration of the adsorbate, the integral heat of adsorption

Answer 81

decreases.

Question 82

Small dia distillation column can be a

Answer 82

packed column

Question 83

If mass diffusivity in a mixture is equal to the thermal diffusivity, then the Lewis number is

Answer 83

1

Question 84

An air-water vapour mixture has a dry bulb temperature of 60°C and a dew point temperature of 40°C. The total pressure is 101.3 kPa and the vapour pressure of water at 40°C and 60°C are 7.30 kPa and 19.91 kPa respectively.The humidity of air sample expressed as kg of water vapour/kg of dry air is

Answer 84

0.152

Question 85

____ column is used in gas absorption process.

Answer 85

Packed

Question 86

Nitrobenzene (boiling point = 210.6°C) is steam distilled at 1 atm pressure.Nitrobenzene will distill off ____ °C.

Answer 86

at < 100

Question 87

Pick out the wrong statement.

Answer 87

Vanderwall adsorption is also called chemisorption.

Question 88

At what value of reflux ratio, number of theoretical plates in a distillation column is minimum?

Answer 88

∞

Question 89

Batch tray dryers suffers from the disadvantage of

Answer 89

high labour cost & low heat economy.

Question 90

In a moderately sized packed absorption tower, channeling (which is most severe with stacked packings) can be minimised by taking the ratio of tower diameter to packing diameter

Answer 90

> 8:1

Question 91

____ column is preferred to be used, when a high liquid hold up is required in a reactor for gas-liquid reaction.

Answer 91

Bubble

Question 92

The 'shanks system' of leaching (i.e., counter-current multiple contact leaching) is used for

Answer 92

both (a) and (b).

Question 93

Penetration model (theory) for mass transfer was enunciated by

Answer 93

Higbie

Question 94

Surface renewal model of mass transfer was enunciated by

Answer 94

Danckwerts

Question 95

When the ____ the relative humidity of air decreases, despite an increase in the absolute humidity.

Answer 95

temperature rises

Question 96

For turbulent mass transfer in pipes, the Sherwood number depends on the Reynolds number as

Answer 96

Re^0.83

Question 97

The relative humidity of air decreases in-spite of an increase in the absolute humidity, when the

Answer 97

temperature rises.

Question 98

Unit of molal diffusivity is

Answer 98

gm moles/cm. sec

Question 99

The term "approach" in a cooling tower refers to the difference in the temperature of the

Answer 99

cold water leaving the tower and the wet bulb temperature of the surrounding air.

Question 100

Binary distillation involves the mass transfer by ____ at the gas-liquid interface.

Answer 100

a counter diffusion at an almost equal molar rate