Mass Transfer

Question 1

Mass transfer rate between two fluid phases does not necessarily depend on the __________ of the two phases.

Answer 1

chemical properties

Question 2

In a solution containing 0.30 kg mole of solute and 600 kg of solvent, the molality is

Answer 2

0.50

Question 3

Fenske equation determines the

Answer 3

minimum number of theoretical plates

Question 4

The term “co” in a cooling tower refers to the difference in the temperature of

Answer 4

hot water entering the tower and the cooled water leaving the tower

Question 5

Which of the following is the most suitable for extraction in a system having very low density difference?

Answer 5

Centrifugal extractor

Question 6

Total reflux in a distillation operation requires minimum

Answer 6

number of plates

Question 7

The difference of wet bulb temperature and adiabatic saturation temperature of unsaturated mixture of any system is

Answer 7

+ve

Question 8

Fenske’s equation for determining the minimum number of theoretical stages in distillation column holds good, when the

Answer 8

relative volatility is reasonably constant.

Question 9

When the temperature and humidity of air is low, we usually use __________ draft cooling tower.

Answer 9

natural

Question 10

Pick out the correct statement.
a. In case of liquid-liquid extraction, no separation is possible, if the selectivity of the solvent used is unity.
b. With increase in temperature, the selectivity of the solvent used in solvent extraction decreases.
c. The selectivity of solvent used in solvent extraction is unity at the plait point.
d. all (a), (b) and (c).

Answer 10

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

Question 11

__________ columns are used for liquid dispersion in a continuous gas phase.

Answer 11

Packed

Question 12

Overall efficiency of the distillation column is

Answer 12

the ratio of number of ideal plates to actual plates.

Question 13

Which is the controlling factor for a drum drier?

Answer 13

Heat transfer

Question 14

Drying operation under vacuum is carried out to

Answer 14

reduce drying temperature.

Question 15

Air initially at 101. 3 kPa and 40°C and with a relative humidity of 50%, is cooled at constant pressure to 30°C. The cooled air has a

Answer 15

higher relative humidity

Question 16

Separation of two or more components of a liquid solution can not be achieved by

Answer 16

absorption

Question 17

At minimum reflux ratio for a given separation

Answer 17

number of plates is infinity.

Question 18

Relative humidity is the ratio of the

Answer 18

partial pressure of the vapour to the vapour pressure of the liquid at gas temperature.

Question 19

In batch distillation with constant reflux, overhead product composition __________ with time.

Answer 19

decreases

Question 20

Psychrometry deals with the properties of gas-vapor mixture. Humidity can be determined by the measurement of the __________ of a fibre.

Answer 20

electrical resistance

Question 21

Heat in BTU necessary to increase the temperature of 1 lb of gas and its accompanying vapour by 1°F is called the

Answer 21

specific heat

Question 22

To increase the absorption factor, (where, G = gas flow rate, S = solvent flow rate)

Answer 22

increase ‘S’ and decrease ‘G’.

Question 23

The mass diffusivity, the thermal diffusivity and the eddy momentum diffusivity are same for, NPr = NSc = __________

Answer 23

1

Question 24

Dew point of a gas-vapour mixture

Answer 24

decreases with decrease in pressure.

Question 25

Which of the following plays an important role in problems of simultaneous heat and mass transfer ?

Answer 25

Lewis number

Question 26

In case of an absorber, the operating

Answer 26

line always lies above the equilibrium curve

Question 27

As the reflux ratio in a distillation coloumn is increased from the minimum, the

Answer 27

total cost first decreases and then increases.

Question 28

Absorption factor is defined as (where, S1 = slope of the operating line S2 = slope of the equilibrium curve)

Answer 28

S1/S2

Question 29

A plait point is the point on the solubility curve, where the tie line reduces to a point. What is the number of plait point for a ternery system containing twopairs of partially miscible liquids?

Answer 29

0

Question 30

Make up water is required in a cooling tower to replace the water lost by
a. evaporation
b. drift
c. blowdown and leakage
d. all (a), (b), and (c)

Answer 30

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

Question 31

Which of the following quantities need not be fixed before starting the design of a co-current absorber?

Answer 31

Flow rate of entering liquid

Question 32

Mass transfer co-efficient of liquid is

Answer 32

affected more by temperature than that for gases.

Question 33

Absorption accompanied with chemical reaction is exemplified by the absorption of

Answer 33

SO2 in alkaline solution.

Question 34

Which of the following unit operations makes use of Thiele-Geddes equation ?

Answer 34

Multicomponent distillation.

Question 35

Which of the following liquid-vapor contacting devices provides maximum contact surface area for a particular duty?

Answer 35

Wetted wall column

Question 36

The equipment frequently used for adiabatic humidification-cooling operation with recirculating liquid is

Answer 36

spray chamber

Question 37

Chemisorption (chemical adsorption) is

Answer 37

an irreversible phenomenon.

Question 38

The rate of solid-liquid extraction is limited by the a. phase change of the solute as it dissolves in the solvent.
b. diffusion of the solute through the solvent in the pores to the outside of the particle.
c. diffusion of the solute from the solution in contact with the particle to the main bulk of the solution.
d. all ‘a’, ‘b’ & ‘c’.

Answer 38

d. all ‘a’, ‘b’ & ‘c’.

Question 39

Raoult’s law applies to the

Answer 39

solvents

Question 40

In distillation columns, the number of bubble caps per tray primarily depends upon the

Answer 40

allowable gas and liquid velocities.

Question 41

In distillation, overhead product contains

Answer 41

any number of components

Question 42

With increase in pressure, the relative volatility for a binary system

Answer 42

decreases

Question 43

Mass transfer co-efficient (K) and diffusivity (D) are related according to film theory as

Answer 43

K ∝ D

Question 44

The McCabe Δ L law states that the

Answer 44

linear crystal growth rate does not depend on the crystal size.

Question 45

Bollman extractor

Answer 45

is used for extraction of oil from oilseed.

Question 46

The relation, Sc = Pr = 1, is valid, when the mechanism of __________ transfer is same.

Answer 46

heat and mass

Question 47

For the same feed, feed quality and separation (in a distillation column), with the increase of total pressure, the number of ideal plates will

Answer 47

increase

Question 48

Pick out the correct statement.
a. Ponchan-Savarit method is more accurate than McCabe-Thiele method to determine the number of theoretical stages required for the separation of non-ideal binary system by distillation.
b. A sharp decrease in pressure drop is an indication of flooding in a distillation coloumn.
c. Solvent used in extractive distillation should be of high volatility.
d. Flash distillation is suitable for separating components which have very close boiling temperature.

Answer 48

Ponchan-Savarit method is more accurate than McCabe-Thiele method to determine the number of theoretical stages required for the separation of non-ideal binary system by distillation.

Question 49

When the liquid phase and vapour phase of a binary system obeys Raoult’s and Dalton’s law respectively, the relative volatility is the ratio of

Answer 49

vapour pressure of component A to that of component B.

Question 50

The operation involved when the soluble material is largely on the surface of an insoluble solid and is merely washed off by the solvent is called

Answer 50

elutriation or elution

Question 51

The operation involved when the soluble material is largely on the surface of an insoluble solid and is merely washed off by the solvent is called

Answer 51

elutriation or elution

Question 52

In the constant rate period of the rate of drying curve for batch drying,

Answer 52

surface evaporation of unbound moisture occurs.

Question 53

It takes 6 hours to dry a wet solid from 50% moisture content to the critical moisture content of 15%. How much longer it will take to dry the solid to 10% moisture content, under the same drying conditions? (The equilibrium moisture content of the solid is 5%).

Answer 53

71 min

Question 54

__________ diffusion is used for separating the isotopes of methane.

Answer 54

Thermal

Question 55

Ordinary diffusion process is also called __________ diffusion

Answer 55

concentration

Question 56

Pick out the wrong statement.
a. Different solids have different equilibrium moisture curves.
b. Total condenser or reboiler is considered equivalent to one theoretical plate in McCabe-Thiele method of theoretical plate calculation for distillation column.
c. Heat removal load on cooler remains constant, even with increase of the reflux ratio in a distillation column.
d. Even a forced draft cooling tower can not cool water below the wet bulb temperature.

Answer 56

c. Heat removal load on cooler remains constant, even with increase of the reflux ratio in a distillation column.

Question 57

Pick out the wrong statement pertaining to the rotary dryer.
a. Flights (located in the inside shell of rotary dryer) lift the material being dried and shower it down through the current of hot air/gases. It extends from the wall to a distance which is about 812% of the inside diameter of shell.
b. Hold up of a rotary drier is defined as the fraction of the dryer volume occupied by the solid at any instant. The best performance for rotary drier is obtained, when the hold up is in the range of 0.05 to 0.15.
c. Rotary dryer is suitable for drying sticky material. d. Recommended peripherial speed of a rotary drier is in the range of 10 to 30 metres/minute.

Answer 57

c. Rotary dryer is suitable for drying sticky material.

Question 58

The reason for preferring packed towers over plate towers in distillation practice is that the packed tower operation gives

Answer 58

low pressure drop and low hold up.

Question 59

If the path of liquid across the plate is very long as in case of large diameter tower, Murphree efficiency can be __________ percent.

Answer 59

> 100

Question 60

Compound A is extracted from a solution of A + B into a pure solvent S. A Co-current unit is used for the liquid-liquid extraction. The inlet rate of the solution containing A is 200 moles of B/hr.m2 and the solvent flow, rate is 400 moles of S/m2. hr. The equilibrium data is represented by Y = 3X2 , where Y is in moles of a A/moles of B and X is in moles A/moles of S. The maximum percentage extraction achieved in the unit is

Answer 60

50%

Question 61

Raoult’s law is applicable to the

Answer 61

ideal solutions

Question 62

Weeping in a distillation column

Answer 62

results due to very low gas velocity.

Question 63

In case of binary distillation, increasing the reflux ratio above optimum does not result in the increase of

Answer 63

area between operating line and 45° diagonal x-y diagram.

Question 64

Wetted wall tower experiment determines the

Answer 64

mass transfer co-efficient.

Question 65

In McCabe-Thiele method, at infinite reflux ratio

Answer 65

the overhead product is minimum.

Question 66

With decrease in the throughput (compared with the design capacity) for a bubble cap distillation column, its efficiency

Answer 66

increases

Question 67

Plate towers are preferred to packed towers, when large temperature changes are involved, because of the reason that the

Answer 67

packing may be crushed due to thermal expansion/contraction of the components of the equipments.

Question 68

The equilibrium liquid composition compared to the vapor composition in case of azeotropic mixture is

Answer 68

same

Question 69

Out of the following gas-liquid contacting devices, for a given set of operating conditions, gas pressure drop is the least in __________ tower.

Answer 69

wetted wall

Question 70

Pick out the system with minimum boiling azeotrope at 1 atm.

Answer 70

ethyl alcohol-water

Question 71

Free flowing granular materials can be best dried in a __________ drier.

Answer 71

rotary

Question 72

In case of an ideal solution, the total vapor pressure varies __________ with the composition expressed as mole fraction,

Answer 72

linearly

Question 73

In case of an ideal solution, the total vapor pressure varies __________ with the composition expressed as mole fraction,

Answer 73

linearly

Question 74

Corresponding to Nusselt number in heat transfer, the dimensionless group in mass transfer is the __________

Answer 74

Sherwood

Question 75

If the specific heats of a gas and a vapor are 0.2KJ/Kg.°K and 1.5 KJ/Kg.°K respectively, and the humidity is 0.01; the humid heat in KJ/°Kg. is

Answer 75

0.215

Question 76

Liquid diffusivity is of the order of __________ cm2 /second.

Answer 76

10^-5 to 10^-6

Question 77

The solvent used in liquid extraction should not have high latent heat of vaporisation, because

Answer 77

its recovery cost by distillation may be prohibitatively high.

Question 78

At the same gas flow rate, the pressure drop in a packed tower being irrigated with liquid __________ that in dry packed tower.

Answer 78

is greater than

Question 79

Molarity is defined as the number of gm moles of solute per __________ of solvent.

Answer 79

litre

Question 80

The value of Lewis number (Le = Sc/Pr) for air-water vapour system is around

Answer 80

1

Question 81

An aqueous solution of methanol is to be distilled in a tray column. High pressure steam is available as a source of heat. For a given reflux ratio and overhead composition, two options are being explored; (i) a reboiler is used and (ii) no reboiler is used but steam is fed directly to the bottom of the column. As compared to option (i), in option (ii)

Answer 81

less number of trays are required.

Question 82

The partial pressure distribution of an ideal gas diffusing through another stagnant ideal gas at steady state follows a/an __________ law.

Answer 82

exponential

Question 83

Which of the following binary systems is an example of a maximum boiling azeotrope ?

Answer 83

Water-hydrochloric acid.

Question 84

(NRe . NSc) is termed in mass transfer operation as the __________ number.

Answer 84

Peclet

Question 85

The binary diffusivity in gases and liquids vary respectively as

Answer 85

T3/2 and T

Question 86

Pick out the correct statement.
a. The slope of the stripping line is always less than unity.
b. For a given separation in a binary distillation column, with increase in reflux ratio (above the minimum reflux ratio), the fixed cost of the distillation column first increases and then decreases.
c. In Ponchon-Savarit method of no. of theoretical plate determination, the stripping and rectifying operating lines are vertical at total reflux.
d. Kremsor-Brown-Souder’s equation is used to calculate the efficiency of a plate tower

Answer 86

In Ponchon-Savarit method of no. of theoretical plate determination, the stripping and rectifying operating lines are vertical at total reflux.

Question 87

Pick out the correct statement.
a. Dialysis process is used for the production of fresh water from brine.
b. Electrodylsis is used in the manufacture of NaOH.
c. Electrodylsis is used for the refin-ning/purification of petrol.
d. both (b) and (c).

Answer 87

Electrodylsis is used in the manufacture of NaOH.

Question 88

Pick out the correct statement.
a. Bound moisture is removed during constant rate drying period.
b. Free moisture is removed during falling rate drying period.
c. The sum of free moisture and equilibrium moisture in a solid is called the critical moisture.
d. The driving force for mass transfer in a wet solid is its free moisture content.

Answer 88

The driving force for mass transfer in a wet solid is its free moisture content.

Question 89

Very tall packed towers are divided into series of beds to

Answer 89

avoid channelling

Question 90

Moisture contained by a substance in excess of the equilibrium moisture is called the __________ moisture.

Answer 90

free

Question 91

With increase in temperature, the solubility of gases in liquids, at fixed pressure

Answer 91

decreases

Question 92

In most of the vacuum crystalliser, vacuum is generally produced by means of a

Answer 92

steam jet ejector with a barometric condenser

Question 93

On moving the feed line (q-line) from saturated liquid feed (vertical position) to saturated vapor feed (horizontal feed), if the slope of both the operating lines are to be increased, then it will result in

Answer 93

increased reflux ratio

Question 94

__________ column is the most suitable for achieving the best performance for mass transfer operations involving liquid with dispersed solids.

Answer 94

Plate

Question 95

Deairation (removal of O2) of water is done by

Answer 95

ion-exchange

Question 96

Pick out the wrong statement.
a. The mole fraction of solute is directly proportional to the molality of a ‘dilute’ solution.
b. For a non-reacting binary mixture of ideal gases, the partial pressure distribution of both components is nonlinear in the case of steady state unimolal unidirectional diffusion.
c. Azeotropes obey Raoult’s law at all temperature.
d. The relative volatility of a binary mixture at the azeotropic composition is 1.

Answer 96

c. Azeotropes obey Raoult’s law at all temperature.

Question 97

A minimum boiling azeotrope is exemplified by

Answer 97

acetone-carbon disulphide

Question 98

Which of the following solutions will follow Raoult’s law most closely ?

Answer 98

A solution of benzene, toluene and oxylene.

Question 99

Use of raschig rings in place of crushed stones as packing in packed beds (other things being same)

Answer 99

decreases pressure drop, increases surface area.

Question 100

The assumption made in Elis method in distillation is that enthalpy concentration lines of vapor and liquid are

Answer 100

both parallel and straight

Question 101

As complete saturation of an adsorbent is approached, the differential heat of adsrop-tion approaches

Answer 101

that of normal condensation

Question 102

Absorption with chemical reaction’ is involved in the removal of

Answer 102

carbon dioxide from gaseous stream using alkaline solution.

Question 103

The-relative volatility for separation of a non-ideal binary mixture by distillation should be

Answer 103

> 1

Question 104

Pick out the wrong statement:
a. Reboiler is not used in open steam distillation.
b. The separation of solutes of different molecular sizes in a liquid solution by use of a suitable membrane is called dialysis.
c. Freeze drying is used for the drying of fish.
d. Fenske-Underwood equation is used for calculating theoretical number of plates in a distillation column at normal operating reflux condition.

Answer 104

Fenske-Underwood equation is used for calculating theoretical number of plates in a distillation column at normal operating reflux condition.

Question 105

In paper industry, paper is dried in a __________ dryer.

Answer 105

heated cylinder

Question 106

Pick out the wrong statement.
a. Critical moisture content is not a property of the material itself.
b. A sharp increase in pressure drop gives an indication of the flooding in a distillation column.
c. Separation of components is not possible in liquid extraction, if selectivity is unity.
d. Dehydration of ethyl alcohol is most economically done by molecular distillation at very high vacuum.

Answer 106

Dehydration of ethyl alcohol is most economically done by molecular distillation at very high vacuum.

Question 107

Only small amount of evaporation of water produces large cooling effects because of its

Answer 107

large latent heat

Question 108

The most common packing used in industrial operations is __________ rings.

Answer 108

raschig

Question 109

When the feed to a distillation column is a saturated liquid, slope of the feed line is

Answer 109

infinity

Question 110

When the feed to a distillation column is a saturated liquid, slope of the feed line is

Answer 110

infinity

Question 111

When the feed to a distillation column is a saturated liquid, slope of the feed line is

Answer 111

infinity

Question 112

Leaching of sugar from sugar beets is done by

Answer 112

hot water

Question 113

Absorption factor method is used to calculate the number of ideal stages, when

Answer 113

both operating and equilibrium lines are parallel.

Question 114

Flights in a rotary dryer are provided to

Answer 114

lift and shower the solids thus exposing it thoroughly to the drying action of the gas.

Question 115

If the solubilities of different components (in a liquid-liquid extraction system) increase with rise in temperature, then the temperature above which they dissolve completely is known as the critical solution temperature (CST or consolute temperature). If solubilities increase with decrease in temperature, then CST is the temperature below which they dissolve completely. If a binary system has no critical solution temperature, it implies that

Answer 115

on heating, a vapor phase will appear ; while on cooling, a solid phase will appear.

Question 116

The rate of mass transfer is not dependent upon the
a. degree of dispersion of one fluid in the other.
b. interfacial surface exposed between the phases.
c. both (a) & (b).
d. none of these.

Answer 116

none of these

Question 117

At equilibrium the concentration of water in vapour phase (C)in kg/m3 of air space and the amount of water (m) adsorbed per kg of dry silica gel are related by, C = 0.0667m. To maintain dry conditions in a room of air space 100m3 containing 2.2 kg of water vapour initially, 10 kg of dry silica gel is kept in the room. The fraction of initial water remaining in the air space after a long time (during which the temperature is maintained constant) is

Answer 117

0.4

Question 118

At equilibrium the concentration of water in vapour phase (C)in kg/m3 of air space and the amount of water (m) adsorbed per kg of dry silica gel are related by, C = 0.0667m. To maintain dry conditions in a room of air space 100m3 containing 2.2 kg of water vapour initially, 10 kg of dry silica gel is kept in the room. The fraction of initial water remaining in the air space after a long time (during which the temperature is maintained constant) is

Answer 118

0.4

Question 119

For the case of flow of air past a wet bulb thermometer (air water vapour system), the approximate value of h2/ky.Cz is around

Answer 119

1

Question 120

The reciprocal of stripping factor is termed as

Answer 120

absorption factor

Question 121

Ponchan-Savarit method analyses the fractional equipment based on

Answer 121

both enthalpy and material balances

Question 122

The binary diffusivity in gases at atmospheric conditions is about

Answer 122

10^-1 cm2/sec

Question 123

Percentage saturation is __________ the relative saturation.

Answer 123

always smaller than

Question 124

In case of a desorber (stripper), the

Answer 124

operating line always lies below the equilibrium curve.

Question 125

What is the reflux ratio at total reflux?

Answer 125

Infinity

Question 126

Under conditions of flooding in packed tower, the gas pressure drop

Answer 126

is maximum

Question 127

For achieving rapid drying rate in a spray dryer, the diameter of the particles in the feed should be in the range of __________ microns (1 mm = 1000 microns).

Answer 127

10-60

Question 128

For absorbing a sparingly soluble gas in a liquid

Answer 128

liquid side mass transfer co-efficient should be increased.

Question 129

The change in enthalpy per unit weight of adsorbed gas when adsorbed on gas free or “outgassed” adsorbent to from a definite concentration of adsorbate is called its

Answer 129

integral heat of adsorption.

Question 130

The minimum number of theoretical plates is required for achieving a given separation in distillation column with

Answer 130

total reflux

Question 131

A good solvent used for absorption should not have very high
a. viscosity
b. vapor pressure
c. freezing point
d. all (a), (b) & (c)

Answer 131

d. all (a), (b) & (c)

Question 132

In a counter-current liquid extractor

Answer 132

only one of the liquids may be pumped at any desired rate.

Question 133

In a counter-current liquid extractor

Answer 133

only one of the liquids may be pumped at any desired rate.

Question 134

Which of the following is an undesirable property for an absorbing solvent ?
a. Low vapour pressure
b. Low velocity
c. Low freezing point
d. None of these

Answer 134

d. none of these

Question 135

The wetted wall tower is used to determine

Answer 135

individual mass transfer co-efficient (M.T.C.) in gaseous system.

Question 136

Weight of 1 m3 of humid air as compared to 1 m3 of dry air, under the same conditions, is

Answer 136

less

Question 137

Positive deviation from Raoult’s law means a mixture whose total pressure is

Answer 137

greater than that computed for ideality.

Question 138

With increase in gas rate, the number of transfer units, NtoG, for a fixed degree of absorption by a fixed amount of solvent

Answer 138

increases

Question 139

Prandtl number for water at 20°C is about

Answer 139

7

Question 140

Boiling point diagram is

Answer 140

affected by pressure

Question 141

When acetone is added in a two layer mixture of methyl isobutyl ketone and water at 30°C, the acetone distributes between the two layers and the composition of the layer follows two solubility curves. For this system,
a. as the acetone concentration increases, the solubility curves approach each other.
b. both the phases become identical at a particular common point on both the solubility curves called the plait point.
c. the distribution curve which is a plot between x (acetone concentration in one phase) and y (acetone concentration in other phase) is analogous to x-y curve used in distillation and absorption terminates on the x = y diagonal at the concentration of the plait point.
d. all (a), (b) and (c)

Answer 141

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

Question 142

Steam distillation is used to

Answer 142

avoid thermal decomposition of a component.

Question 143

Freundlich equation applies to the adsorption of solute from

Answer 143

dilute solutions, over a small concentration range.

Question 144

For ethanol-water system, the lowering of distillate quality from 95% to 92% will cause __________ plate requirement.

Answer 144

marginal decrease in the number of

Question 145

The apex of an equilateral-triangular coordinate (in ternary liquid system) represents a/an

Answer 145

pure component

Question 146

A slurry is to be dried to produce flaky solid. Which dryer would you recommend ?

Answer 146

Spray dryer

Question 147

Which of the following psychrometric processes is followed by water vapour laden unsaturated air, when it is passed through solid or liquid adsorbent ?

Answer 147

Heating and dehumidification at almost constant wet bulb temperature.

Question 148

In gas-liquid contact operation, the number of ideal stages, . This is true when the stripping factor ‘S’ is

Answer 148

S > 1

Question 149

The cooling effect in a cooling tower can not be increased by
a. increasing the air velocity over the wet surfaces. b. reducing the humidity of entering air.
c. lowering the barometric pressure.
d. none of these.

Answer 149

d. none of these

Question 150

The value of NA/(NA + NB) for steady state molecular diffusion of gas ‘A’ through non-diffusing gas ‘B’ is

Answer 150

1

Question 151

Pick out the wrong statement
a. Co-current absorbers are usually used, when the gas to be dissolved in the liquid is a pure substance. b. In case of gas absorption, HETP is equal to HTU, when both the operating line & the equilibrium lines are parallel.
c. Hatta number is important in case of gas absorption with chemical reaction.
d. In actual practice, absorption is an en-dothermic process, while stripping is an exothermic process.

Answer 151

d. In actual practice, absorption is an en-dothermic process, while stripping is an exothermic process.

Question 152

When the mixture to be distilled has a very high boiling point and the product material is heat sensitive, the separation technique to be used is __________ distillation.

Answer 152

steam

Question 153

Large scale drying of wheat is done in a __________ dryer.

Answer 153

spouted bed

Question 154

Azeotropic distillation is employed to separate

Answer 154

constant boiling mixture.

Question 155

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

Answer 155

T^2

Question 156

At the boiling point of the liquid at the prevailing pressure, the saturated absolute humidity becomes

Answer 156

∞

Question 157

Pressure drop through plate tower as compared to that through packed tower, for the same duty will be

Answer 157

more

Question 158

Dimension of mass diffusivity is the same as that of

Answer 158

kinematic viscosity

Question 159

Dorr thickener is an equipment used for

Answer 159

sedimentation

Question 160

Steam distillation is used to separate

Answer 160

high boiling substances from nonvolatile impurities.

Question 161

In distillation where q is defined as the moles of liquid flow in the stripping section per mole of feed introduced, for saturated liquid feed

Answer 161

q=1

Question 162

Which of the following is an undesirable property in a tower packing ?

Answer 162

Large weight of liquid retained.

Question 163

Water entrained by circulating air in cooling towers is termed as

Answer 163

drift

Question 164

A 25 cm x 25 cm x 1 cm flat sheet weighing 1.2 kg initially was dried from both sides under constant drying rate conditions. It took 1500 seconds for the weight of the sheet to reduce to 1.05 kg. Another 1m x 1m x 1cm flat sheet of the same material is to be dried from one side only.Under the same constant drying rate conditions, the time required for drying (in seconds) from its initial weight of 19.2 kg to 17.6 kg is

Answer 164

1000

Question 165

With increase in temperature, the rate of leaching increases, because the

Answer 165

diffusivity of solute increases.

Question 166

Humidity chart is useful for the solution of problems concerning condensation, vaporisation and air conditioning. At a given dry bulb temperature, value of humidity obtained from the humidity chart directly, is in terms of __________ humidity.

Answer 166

molal

Question 167

The Kundsen diffusivity is proportional to (where, T = absolute temperature)

Answer 167

T^1/2

Question 168

In an absorption coloumn, the flooding velocity for random packing is __________ that for stacked/regular packing.

Answer 168

smaller than

Question 169

The relation among various mass transfer co-efficients (M.T.C) for ideal gases is given by (where, Kc & Km are M.T.C. for equimolar counter diffusion with concentration & mole fraction respectively as the driving force. and, Kp = M.T.C. for diffusion of a gas through a stagnant inert gas with pressure as driving force.)

Answer 169

Kc = Kp . RT = Km . RT/p

Question 170

Leaching of uranium ore and gold ore is done in

Answer 170

Pachuka tanks

Question 171

Blowdown in a cooling tower

Answer 171

means discarding a small fraction of circulating water to prevent and limit the concentration of salt and impurities.

Question 172

Blowdown in a cooling tower

Answer 172

means discarding a small fraction of circulating water to prevent and limit the concentration of salt and impurities.

Question 173

Antibiotics are best handled in a

Answer 173

Podbielniak extractor.

Question 174

The fixed cost of a distillation column at minimum reflux ratio is

Answer 174

infinite

Question 175

_________ extractor uses centrifugal force for separating the two phases.

Answer 175

Podbielniak

Question 176

Pick out the wrong statement.
a. Mechanical agitation is required, if the system has low interfacial tension.
b. Seive tray towers are generally used for systems having low interfacial tension.
c. When Henry’s law constant is very small, then the mass transfer rate is controlled by the gas film resistance.
d. Taylor-Prandtl analogy for heat and mass transfer considers the transfer through both laminar and turbulent layers.

Answer 176

a. Mechanical agitation is required, if the system has low interfacial tension.

Question 177

Acetic acid will be most economically separated from a dilute solution of acetic acid in water by

Answer 177

solvent extraction

Question 178

Design calculation for multiple component distillation is done by

Answer 178

tray to tray calculations.

Question 179

To get high tray efficiency

Answer 179

interfacial surface between liquid and gas phase should be large.

Question 180

The mass transfer co-efficient for a solid sphere of radius ‘a’ dissolving in a large volume of quiescent liquid, in which D is the diffusivity of solute, is

Answer 180

dependent on the Reynolds number

Question 181

Pick out the wrong statement. Generally for physical adsorption, a gas of
a. higher molecular weight is adsorbed in preference to a gas of low molecular weight.
b. high critical temperature is adsorbed in preference to a gas of low critical temperature.
c. low volatility is adsorbed in preference to a gas of high volatility.
d. none of these.

Answer 181

d. none of these.

Question 182

In most of the mechanically agitated liquid-liquid extractors, baffles or horizontal compartmental plates are provided, which helps in
a. reducing the axial mixing.
b. increasing the rate of extraction.
c. maintaining the concentration difference between the two phases.
d. all ‘a’, ‘b’ & ‘c’.

Answer 182

d. all ‘a’, ‘b’ & ‘c’.

Question 183

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

Answer 183

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

Question 184

Inside the distillation column, the

Answer 184

driving force for the vapour flow is the pressure drop.

Question 185

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

Answer 185

decreases

Question 186

Which of the following is not a continuous drier ?

Answer 186

Tray drier

Question 187

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

Answer 187

insoluble in the liquid

Question 188

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

Answer 188

Dew point

Question 189

Rate of leaching increases with increasing

Answer 189

temperature

Question 190

An azeotropic mixture is a __________ mixture.

Answer 190

constant boiling point

Question 191

Pick out the wrong statement.
a. In the McCabe-Thiele diagram for binary distillation, vertical feed line represents saturated liquid feed and horizontal feed line represents saturated vapour feed.
b. In small columns, local efficiency is larger than Murphree efficiency; in large columns local efficiency is smaller than Murphree efficiency.
c. 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 102m/s.
d. The concentration and hydrodynamic boundary layers over a flat plate are of equal thickness, if Schmidt number is equal to unity.

Answer 191

c. 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 102m/s.

Question 192

Molecular seives are regenerated by heating to __________ °C.

Answer 192

200-330

Question 193

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

Answer 193

decreases

Question 194

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

Answer 194

freeze

Question 195

In extractive distillation, solvent is

Answer 195

added to alter the relative volatility of the mixture.

Question 196

Radioactive nuclear waste is treated in

Answer 196

pulsed column extractor

Question 197

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

Answer 197

rotary

Question 198

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

Answer 198

wet bulb

Question 199

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 199

T

Question 200

__________ equation applies to diffusivities in liquids.

Answer 200

Gilliland

Question 201

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

Answer 201

incurs smaller pressure drop.

Question 202

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

Answer 202

Hexane

Question 203

In an absorber, HETP does not vary with the
a. flow rate of liquid
b. flow rate of gas
c. type and size of packing
d. none of these

Answer 203

d. none of these

Question 204

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

Answer 204

through circulation

Question 205

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

Answer 205

increase

Question 206

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

Answer 206

agitated vessel

Question 207

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

Answer 207

a binary mixture.

Question 208

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

Answer 208

a total condenser is used.

Question 209

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 209

gas phase resistance controlled.

Question 210

As the reflux ratio decreases, the

Answer 210

number of plates increases.

Question 211

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

Answer 211

Spray towers

Question 212

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 212

the fraction vaporised but not the product composition.

Question 213

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 213

increases

Question 214

Which of these columns incurs the lowest pressure drop ?

Answer 214

Packed column (with stacked packing)

Question 215

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

Answer 215

liquid

Question 216

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 216

L/G

Question 217

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

Answer 217

Wet bulb temperature

Question 218

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

Answer 218

can lie above or below the equilibrium curve.

Question 219

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

Answer 219

Packed column (stacked)

Question 220

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

Answer 220

half

Question 221

The Knudsen diffusivity is dependent on the

Answer 221

molecular velocity and por radius of the catalyst.

Question 222

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

Answer 222

flooding

Question 223

Solvent used in extractive distillation

Answer 223

forms a low boiling azeotrope.

Question 224

The cooling effect in a cooling tower can be speeded up by
a. increasing the air velocity and area of exposed wet surface.
b. reducing the barometric pressure.
c. reducing the humidity of the air.
d. all (a), (b) and (c).

Answer 224

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

Question 225

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.

Answer 225

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

Question 226

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

Answer 226

• ve

Question 227

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

Answer 227

both zero and hundred

Question 228

Back-trapping in a distillation column

Answer 228

decreases tray efficiency.

Question 229

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 229

more than

Question 230

Milk is dried usually in a __________ dryer.

Answer 230

spray

Question 231

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

Answer 231

decreases

Question 232

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

Answer 232

Activated carbon

Question 233

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

Answer 233

increases

Question 234

Pick out the wrong statement.
a. Constant pressure distillation can not separate an azeotropic mixture.
b. Relative volatility of a binary mixture changes appreciably with the minor change in temperature. c. The relative volatility of a binary mixture at azeotropic composition is unity.
d. Flash distillation is practised on wide spread scale in petroleum refinery.

Answer 234

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

Question 235

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

Answer 235

increasing temperatures both on the surface and within the solid.

Question 236

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

Answer 236

Solvent extraction

Question 237

Which of the following is an undesirable characteristic for the solvent used in gas absorption ?
a. Low vapor pressure
b. Low viscosity
c. High gas solubility
d. None of these

Answer 237

d. None of these

Question 238

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

Answer 238

Agitated vessels

Question 239

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

Answer 239

2

Question 240

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

Answer 240

2.09 x 10-9

Question 241

Pick out the wrong statement.
a. The Reynolds analogy for mass transfer is given by Lewis relation and is applicable, when Schmidt number is one.
b. Sherwood number for flow in pipes can be expressed as the ratio of the concentration gradient at wall to the overall concentration difference.
c. According to film theory for equimolar counter diffusion, the mass transfer coefficient is given by DAB(b)P - 3, Q - 2
d. The z-component of the total mass flux of a component A in binary mixture of A and B is given by - Dab’.dCA/dz.

Answer 241

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

Question 242

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

Answer 242

is independent of pressure.

Question 243

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

Answer 243

p = P

Question 244

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

Answer 244

Lewis

Question 245

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

Answer 245

relative volatility

Question 246

In physical terms, Schmidt number means

Answer 246

momentum diffusivity/mass diffusivity.

Question 247

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

Answer 247

T

Question 248

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 248

ideal gases

Question 249

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

Answer 249

penetration

Question 250

Sand is dried in foundaries in a___drier.

Answer 250

fluidisedbed

Question 251

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

Answer 251

Mechanical draft cooling tower.

Question 252

Pick out the correct statement.
a. Higher hold up of the solid in the rotary dryer results in better exposure of the solids to the gas. b. The ‘Hatta number’ is important in problems involving gas absorption without chemical reaction. c. 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.
d. Total reflux in case of distillation operation requires infinite number of plates for a binary system separation.

Answer 252

c. 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 253

Pick out the correct statement.
a. For identical gas flow rates, less pressure drop occurs through a plate tower than through a packed tower.
b. Plate column can handle greater liquid loads without flooding than packed column, but the liquid hold up is more in the case of plate column.
c. For the same duty, plate columns weigh less than packed columns.
d. all (a), (b) and (c).

Answer 253

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

Question 254

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

Answer 254

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

Question 255

Diameter to height ratio for a rashig ring is

Answer 255

1

Question 256

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

Answer 256

pulse column

Question 257

Advantage of continuous drying over batch drying is that the
a. drying cost per unit weight of dried product is less.
b. product with more uniform moisture content is produced.
c. equipment size required is smaller.
d. all ‘a’, ‘b’ & ‘c’

Answer 257

d. all ‘a’, ‘b’ & ‘c’

Question 258

With increase in temperature, the rate of extraction in leaching (solidliquid extraction system)

Answer 258

increases

Question 259

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

Answer 259

sharp drop in pressure drop.

Question 260

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

Answer 260

1

Question 261

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

Answer 261

1

Question 262

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 262

The entire amount of C is transferred to solvent B.

Question 263

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

Answer 263

(KL^2.DA)^1/2

Question 264

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

Answer 264

1.2 to 1.5

Question 265

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 265

wet bulb temperature

Question 266

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

Answer 266

dilute solutions and isothermal operation.

Question 267

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

Answer 267

surface renewal

Question 268

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

Answer 268

dilute solution and isothermal operation.

Question 269

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 269

humidified with wet bulb temperature decreasing.

Question 270

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

Answer 270

linear

Question 271

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

Answer 271

momentum diffusivity to the mass dif-fusivity.

Question 272

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

Answer 272

f = 1

Question 273

Perforated plate towers are unique for solvent extraction because, they provide

Answer 273

repeated coalescence & redispersion of the drop phase.

Question 274

In case of absorption & stripping, the interface of the liquid & gas phases are present in equilibrium, when the diffusional resistance of __________ is zero.

Answer 274

interface

Question 275

Pick out the wrong statement pertaining to the analogy between equations of heat and mass transfer operations.
a. Sherwood number in mass transfer is analogous to Nusselt number in heat transfer.
b. Prandtl number in heat transfer is analogous to Schmidt number in mass transfer.
c. Reynolds number in mass transfer is analogous to Grashoff number in heat transfer.
d. Reynolds number remains the same in both heat and mass transfer.

Answer 275

c. Reynolds number in mass transfer is analogous to Grashoff number in heat transfer.

Question 276

The slope of the operating line for a single component co-current absorber when plotted in terms of mole ratio units is

Answer 276

-ve

Question 277

The individual mass transfer co-efficients (moles/m2 . s) for absorption of a solute from a gas mixture into a liquid solvent are, KL = 4.5 and KG = 1.5. The slope of the equilibrium line is 3. Which of the following resistance (s) is (are) controlling ?

Answer 277

gas side

Question 278

Pore size of the molecular seive 5A is __________ mm.

Answer 278

0.5

Question 279

Swenson-Walker crystalliser is a __________ unit

Answer 279

continuous

Question 280

According to the Fenske equation, what will be the minimum number of plates required in a distillation column to separate an equimolar binary mixture of components A and B into an overhead fraction containing 99 mol% A and a bottom fraction containing 98 mol% B ? Assume that relative volatility (αAB = 2) does not change appreciably in the coloumn.

Answer 280

12

Question 281

Absorption (liquid-gas system) with evolution of heat as compared to isothermal absorption results in
a. decreased solute solubility.
b. large minimum liquid to gas (L/G) ratio.
c. large number of trays.
d. all (a), (b) and (c).

Answer 281

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

Question 282

With increase in temperature, the mutual solubility of two liquids

Answer 282

increases

Question 283

Pick out the wrong statement.
a. In solvent extraction, the distribution co-efficient should be as large as possible for solvent economy. b. With increase in pressure, the solubility of gases in solvent increases at a fixed temperature. c. Decrease in Murphree plate efficiency is an indication of entrainment in distillation coloumn.
d. The capacity of a distillation coloumn is maximum at total reflux.

Answer 283

d. The capacity of a distillation coloumn is maximum at total reflux.

Question 284

The relative volatility of a binary mixture at the azeotropic composition is

Answer 284

1

Question 285

Relative volatility varies with the concentration of component for an ideal solution. The relative volatity of a binary mixture may be defined as the ratio of vapor pressure of component ‘A’ to that of component ‘B’, when

Answer 285

Vapor phase obeys Dalton’s law and liquid phase obeys Raoult’s law.

Question 286

Bound moisture is that liquid which exerts an equilibrium vapor pressure __________ that of the pure liquid at the given temperature.

Answer 286

less than

Question 287

Lewis number (Le) is

Answer 287

Sc / Pr

Question 288

Which of the following is not a continuous leaching equipment ?

Answer 288

Pachuka tank

Question 289

__________ extractor is used for the concentration of radioactive nuclear waste.

Answer 289

Pulsed column

Question 290

Moisture content of a substance when at equilibrium with a given partial pressure of the vapour is called the __________ moisture.

Answer 290

equilibrium

Question 291

All moisture in a non-hygroscopic material is the __________ moisture.

Answer 291

unbound

Question 292

Pick out the correct relationship. (where, Ri = internal reflux ratio Ro = external reflux ratio. )

Answer 292

(1 + Ro) = Ro/Ri

Question 293

Separation of __________ employs gaseous diffusion process.

Answer 293

isotopes of uranium

Question 294

For water-ethanol system, the minimum reflux ratio

Answer 294

is computed from the slope of the upper operating line that is tangent to the equilibrium curve.

Question 295

The interfacial area per unit volume of dispersion, in a gas-liquid contactor, for fractional hold up of gas = 0.1 and gas bubble diameter = 0.5 mm is given by (in m2/m3)

Answer 295

500

Question 296

Though, theoretically the adsorption & desorption isotherms is expected to coincide but sometimes at least a part of the isotherms does not coincide and this phenomenon is known as adsorption hysterisis. In such cases, the desorption equilibrium pressure is __________ that obtained for adsorption.

Answer 296

lower than

Question 297

Experimental determination of __________ is done by wetted wall column method.

Answer 297

mass transfer co-efficient

Question 298

Pick out the wrong statement:
a. Absorption factor is constant, when the equilibrium and operating lines are straight.
b. In case of a stripper, the equilibrium curve is always below the operating line.
c. In case of an absorber, the operating line is always above the equilibrium curve.
d. In the absorption of low solubility gases, the liquid film is the controlling resistance.

Answer 298

b. In case of a stripper, the equilibrium curve is always below the operating line.

Question 299

In liquid extraction, if the selectivity is unity, then

Answer 299

no separation will occur.

Question 300

Paper industry employs __________ driers.

Answer 300

cylinder

Question 301

Pick out the wrong statement pertaining to the cooling towers.

Answer 301

Effectiveness of a mechanical draft cooling tower is reduced with increase in air wet-bulb temperature.

Question 302

Experiments were conducted to determine the flux of a species A in a stagnant medium across a gas-liquid interface. The overall mass transfer coefficient based on the liquid side for dilute systems for the above was estimated to be 4 x 10-3 kg mole/m2.s. The equilibrium data for the system is given as y = 2x. The flux across the interface (in kg mole/m2 .s) for bulk concentrations of A in gas phase and liquid phase as y = 0.4 and x = 0.01 respectively is

Answer 302

8.5 x 10-4

Question 303

Leaching of coarse solid lumps is also termed as

Answer 303

percolation

Question 304

The main reason for dividing a tall packed tower into series of small towers is to

Answer 304

avoid channeling

Question 305

Co-current absorbers are usually used when the gas to be dissolved in the liquid is

Answer 305

a pure substance

Question 306

At what percentage (by volume) of alcohol composition, it forms an azeotrope with water ?

Answer 306

95

Question 307

Measurement of the interfacial area of mass transfer is achieved easily & accurately in case of a __________ coloumn.

Answer 307

wetted wall

Question 308

With the lowering of equiliDrium pressure, at a given temperature, the amount of ad-sorbate on the adsorbent

Answer 308

decreases

Question 309

Mass transfer co-efficient is defined as

Answer 309

Co-efficient = Flux/concentration difference.

Question 310

When an unsaturated air-water mixture is heated at constant pressure, then

Answer 310

The relative humidity decreases.

Question 311

At a fixed pressure, the humidity depends upon the partial pressure of vapor in the mixture. Humidity of a vapour free gas is __________ percent.

Answer 311

0

Question 312

In case of physical adsorption, the difference between heat of adsorption and heat of normal condensation is

Answer 312

equal to the heat of wetting.

Question 313

Pick out the wrong statement:
a. Change in barometric pressure does not affect the relative humidity.
b. In case of a packed tower, the operating velocity is about half of the flooding velocity, generally.
c. ‘Elution’ means the desorption of the adsorbed solute by a solvent.
d. The equilibrium moisture content of the solid can be reduced by increasing the absolute humidity.

Answer 313

d. The equilibrium moisture content of the solid can be reduced by increasing the absolute humidity.

Question 314

The value of L/mG ratio for economical absorption operation ranges from

Answer 314

1.25 to 2.0

Question 315

Large scale usage of flash distillation is practised in

Answer 315

petroleum refining

Question 316

High pressure at the bottom of a distillation tower handling heat sensitive materials results in

Answer 316

thermal decomposition of bottoms.

Question 317

Alcohol is dehydrated using __________ distillation.

Answer 317

azeotropic

Question 318

Separation of two volatile liquids by distillation makes use of their

Answer 318

relative volatility

Question 319

Dried finished product sampled from various parts of a __________ dryer exhibits non-uniformity in the moisture content.

Answer 319

tray

Question 320

__________ is used as an ‘entrainer’ for the separation of acetic acid-water mixture by distillation.

Answer 320

Butyl acetate

Question 321

Rotary dryers cannot handle __________ materials.

Answer 321

sticky

Question 322

Pick out the correct statement.
a. Diffusivity decreases with increase in temperature.
b. Diffusivity increases with increase in molecular weight.
c. Diffusivity increases with the size of the individual molecule.
d. none of these.

Answer 322

d. none of these.

Question 323

An example of elutioh is

Answer 323

separation of uranium oxide from its ore by H2SO4 in a Pachuca tank.

Question 324

The operating line for an absorber is curved, when plotted in terms of

Answer 324

partial pressure

Question 325

Relative volatility does not change appreciably with the change in

Answer 325

temperature

Question 326

The dew point of a saturated gas phase equals the __________ temperature.

Answer 326

gas

Question 327

A solid material shows case hardening properties while drying. Which of the following should be controlled to control the drying process ?

Answer 327

Temperature of the solid

Question 328

In case of liquid-liquid binary diffusion, diffusivity of one constituent into another is not dependent on the
a. temperature and pressure
b. concentration
c. nature of the constituents
d. none of these

Answer 328

d. none of these

Question 329

For continuous drying of grannular or crystalline material, the dryer used is the __________ dryer.

Answer 329

rotary

Question 330

When adsorption hysteresis is observed, the desorption equilibrium pressure is __________ that obtained by adsorption.

Answer 330

always lower than

Question 331

Moisture in a substance exerting an equilibrium vapour pressure less than that of pure liquid at the same temperature is called the __________ moisture.

Answer 331

bound

Question 332

For a binary mixture with low relative volatility, continuous rectification to get pure products will require

Answer 332

high reflux ratio

Question 333

For a binary mixture with low relative volatility, continuous rectification to get pure products will require

Answer 333

high reflux ratio

Question 334

Detergent solution is dried to a powder in a

Answer 334

spray dryer

Question 335

Which of the following mixtures does not form an azeotrope at atmosheric pressure?
a. Water-alcohol
b. Methyl alcohol-acetone
c. Butyl acetate-water
d. None of these

Answer 335

d. None of these

Question 336

During bottling of cold drinks (e.g. Pepsi), the main resistance to mass transfer for the absorption of carbon dioxide in water lies in the

Answer 336

liquid film

Question 337

The overall mass transfer co-efficient for the absorption of SO2 in air with dilute NaOH solution can be increased substantially by

Answer 337

increasing the gas film co-efficient.

Question 338

Flooding results in

Answer 338

low tray efficiency

Question 339

For the air water system under ambient conditions, the adiabatic saturation temperature and the wet bulb temperature are nearly equal, because

Answer 339

water has a high latent heat of evaporation.

Question 340

In an operating distillation column, the

Answer 340

driving force for the vapor flow is the pressure drop, as the pressure decreases gradually from the bottom to the top of the column.

Question 341

The diffusivity (D) in a binary gas mixture is related to the temperature (T) as

Answer 341

D ∝ T1.5

Question 342

For which of the following unit operations, Lewis number is of significance ?

Answer 342

Humidification

Question 343

Tray spacing in a distillation column of dia 10-12 ft. used in petroleum refinery may be around __________ inches.

Answer 343

30

Question 344

If a1 and a2 are the relative volatilities when the pressure in the distillation column is 1 and 2 atm respectively. Pick out the correct statement.
a. a1 = a2
b. a1 = 2a2
c. a1 = 0.5 a2
d. none of these

Answer 344

d. none of these

Question 345

The dimension of diffusivity is same as that of the

Answer 345

kinematic viscosity

Question 346

The temperature to which a vapour gas mixture must be cooled (at varying humidity) to become saturated is called the __________ temperature.
a. dew point
b. wet bulb
c. dry bulb
d. none of these

Answer 346

d. none of these

Question 347

Entrainer used in azeotropic distillation should

Answer 347

form a low boiling azeotrope with one of the constituents of the mixture.

Question 348

In case of steam distillation, the steam leaving the liquid is not completely saturated with distillate vapour, because

Answer 348

mixing of steam with the material being vaporised is not so intimate as to result in equilibrium condition.

Question 349

Pick out the wrong statement.
a. The operating line always lies above the equilibrium solubility curve in case of a single component absorber.
b. The operating line always lies below the equilibrium solubility curve in case of a single component stripper.
c. The operating pressure in solvent extraction system should be below vapor pressures of all components.
d. The solubility of a particular gas in ideal solution in any solvent is always the same.

Answer 349

c. The operating pressure in solvent extraction system should be below vapor pressures of all components.

Question 350

Leaching of coffee from coffee beans is done by

Answer 350

hot water

Question 351

For contacting a highly soluble gas with a liquid

Answer 351

bubble the gas through liquid.

Question 352

During drying operation, it is easier to remove the __________ moisture.

Answer 352

unbound

Question 353

Ion exchange process is similar to

Answer 353

adsorption

Question 354

A distillation column with N plates is being operated under normal conditions. At some point of time, the operation is shifted to total reflux condition (i.e., no product and residue are being withdrawn and feed to the column is stopped). At the new steady state,

Answer 354

the top and bottom compositions correspond to the maximum enrichment available.

Question 355

Dryer widely used in a textile industry is __________ dryer.

Answer 355

conveyor

Question 356

Solvent used in extractive distillation

Answer 356

changes the relative volatility of the original components.

Question 357

Air at a particular humidity is heated in a furnace. The new dew point

Answer 357

increases

Question 358

The vapour pressure exerted by the moisture contained in a wet solid depends upon the
a. nature of the moisture.
b. temperature
c. nature of the solid.
d. all (a), (b) and (c).

Answer 358

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

Question 359

Smoke is an example of

Answer 359

solid dispersed in gas

Question 360

Which of the following adsorbant is used in the refinning of sugar ?

Answer 360

Bone charcoal

Question 361

In McCabe-Thiele method of theoretical plate calculation for a distillation column, the operating lines of stripping and rectifying sections coincide with the diagonal at __________ reflux.

Answer 361

total

Question 362

Which of the following parameters remains constant during chemical dehumidifica-tion?

Answer 362

Dry bulb temperature

Question 363

Drying of a solid involves __________ transfer.

Answer 363

both heat and mass

Question 364

Mechanism of moisture removal in case of freeze drying of food stuff is by

Answer 364

sublimation

Question 365

The dew point of an unsaturated gas-vapor mixture does not depend upon the __________ of the mixture.

Answer 365

temperature

Question 366

Which is not concerned directly with mass transfer ?

Answer 366

Froude number

Question 367

Removal of __________ exemplifies an adsorption unit operation.

Answer 367

water from petrol

Question 368

Can the efficiency of a plate in the distillation tower be greater than 100% ?

Answer 368

Never

Question 369

With increase in the mass velocity of the gas, the rate of drying during the constant rate period __________ , if the conduction and radiation through the solid are negligible.

Answer 369

increases

Question 370

For gas absorption, low viscosity solvents are preferred, because of their
a. better flow characteristics.
b. low pumping pressure drop.
c. rapid absorption rates.
d. all (a), (b) and (c).

Answer 370

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

Question 371

To remove all the moisture from a wet solid it requires exposure to __________ air.

Answer 371

perfectly dry

Question 372

The operating cost of a distillation column at minimum reflux ratio is

Answer 372

minimum

Question 373

The reflux to a distillation column is 100 moles/hr, when the overhead product rate is 50 moles/hr. The reflux ratio is

Answer 373

2

Question 374

Molecular diffusivity of a liquid

Answer 374

increases with temperature.

Question 375

Henry’s law states that the

Answer 375

partial pressure of a component over a solution is proportional to its mole fraction in the liquid.

Question 376

Ammonia present in the coke oven gas is removed by washing with

Answer 376

dilute ammoniacal liquor

Question 377

Which of the following processes is not an example of adsorption applied to gaseous separations ?

Answer 377

Decolouration of yellow glycerene.

Question 378

The critical moisture content in case of drying indicates the __________ rate period.

Answer 378

beginning of falling

Question 379

Pick out the wrong statement
a. A horizontal line on the humidity chart indicates the temperature changes at constant molal humidity.
b. When water is cooled from 80 to 70°C by exposure to the air with a wet bulb temperature of 60°C, then both the approach & the range would be 10°C.
c. For unsaturated air-water vapor mixture at atmospheric conditions, the wet bulb temperature & adiabatic cooling lines are the same.
d. Relative saturation of unsaturated mixture of water vapor & air can not be increased by either reducing the mixture temperature or by increasing the total pressure.

Answer 379

d. Relative saturation of unsaturated mixture of water vapor & air can not be increased by either reducing the mixture temperature or by increasing the total pressure.

Question 380

According to Poiseuille’s law, the permeability for gas flow through a capillary is proportional to (where, μ = gas viscosity)

Answer 380

1/μ

Question 381

For a binary mixture distillation process, the degree of freedom is 2. However, if the pressure is fixed in this process, the number of independent variables in this process will be

Answer 381

1

Question 382

H2S is being absorbed in a gas absorber unit. The height of the transfer unit based on the overall mass transfer coefficient on the gas side is 0.4 m. The equilibrium data is given by, y = 1.5 x. The bulk concentration of H2S has to be reduced from 0.05 to 0.001 mole fraction in the gas side. The height of the tower (in metres) corresponding to an operating line given by, y = 5x + 0.001 is

Answer 382

2

Question 383

For the flow of gases through a capillary, with increase in temperature, the permeability __________ as per Knudsen law.

Answer 383

increases

Question 384

Which of the following is directly concerned with psychrometry ?

Answer 384

Lewis reltionship

Question 385

Plate efficiency in a distillation column is reduced due to the __________ of liquid.
a. entrainment
b. foaming
c. weeping & dumping
d. all (a), (b) & (c)

Answer 385

d. all (a), (b) & (c)

Question 386

The most efficient cooling tower out of the following is

Answer 386

induced draft

Question 387

Sodium bicarbonate is produced during soda ash manufacture using a __________ tower.

Answer 387

baffle

Question 388

Powdery materials can be guarded against caking tendency on storage by
a. providing irregular grain size.
b. providing minimum percentage of voids.
c. having maximum possible points of contact.
d. none of these.

Answer 388

d. none of these.

Question 389

In case of cooling towers, the ratio of the rates of heat and mass transfer is indicated by the __________ number.

Answer 389

Lewis

Question 390

Which one of the following devices is not used for both the absorption as well as the liquid-liquid extraction processes ?

Answer 390

Wetted wall columns

Question 391

The temperature of water cooled in cooling tower is always __________ temperature of entering air.

Answer 391

more than the wet bulb

Question 392

Which of the following processes is followed by unsaturated air (with dry bulb temperature 12°C and relative humidity 47%) passing through water spray washer (temperature of water being constant at 40°C?

Answer 392

Both heating and humidification

Question 393

Mass transfer co-efficient is directly proportional to DAB according to the __________ theory.

Answer 393

film

Question 394

Tower diameter may be decreased by

Answer 394

use of increased tray spacing.

Question 395

Rayleigh’s equation applies to __________ distillation.

Answer 395

differential

Question 396

Steady state equimolal counter diffusion is encountered in

Answer 396

separation of a binary mixture by distillation.

Question 397

Polar organic compounds are normally used as separating agents for the azeotropic and extractive distillation. Which of the following is the most important factor to be considered for the choice of the separating agent for extractive distillation ?

Answer 397

Selectivity

Question 398

As the reflux ratio increases, the slope of the operating line for rectifying section

Answer 398

increases

Question 399

Cox chart, which is useful in the design of distillation column particularly for petroleum hydrocarbons, is a plot of (where, P = vapor pressure, T = temperature)

Answer 399

log P vs . T

Question 400

The unit of volumetric diffusivity is

Answer 400

cm2/sec

Question 401

For a ternery mixture, in which equilateral triangular co-ordinate is used in leaching and extraction, a __________ of the equilateral triangular coordinates.

Answer 401

pure component is represented by the apex.

Question 402

Steady state temperature reached by a small amount of liquid evaporating into a large amount of unsaturated vapour-gas mixture is called the __________ temperature.

Answer 402

wet-bulb

Question 403

The Reynolds number of the liquid was increased 100 fold for a laminar falling film used for gas-liquid contacting. Assuming penetrating theory is applicable, the fold increase in the mass transfer co-efficient (Kc) for the same sytem is

Answer 403

10

Question 404

The slope of 9-line is determined by the

Answer 404

thermal condition of the feed

Question 405

In steam distillation, the

Answer 405

product must be immiscible with water.

Question 406

Which of the following can be calculated theoretically using steam table and Dalton’s law of partial pressure; if the relative humidity and dry bulb temperature of moist air is known ?

Answer 406

Wet bulb temperature

Question 407

The feed to fractionating column is changed from saturated vapour to saturated liquid. If the separation and reflux ratio remains unchanged, the number of ideal stages will

Answer 407

increase

Question 408

Rose oil is extracted from rose leaves using __________ distillation.

Answer 408

steam

Question 409

Hypersorption refers to a __________ process.

Answer 409

moving bed adsorption

Question 410

Extraction of coffee from its seed is done by

Answer 410

leaching

Question 411

In azeotropic mixture, the equilibrium vapour composition is

Answer 411

same as liquid composition.

Question 412

With lapse of time, the overhead composition of light component in case of batch distillation with constant reflux

Answer 412

decreases

Question 413

Lewis number, which is important in problems involving simultaneous heat and mass transfer, is the ratio of

Answer 413

thermal diffusivity to mass diffusivity.

Question 414

According to the film theory of mass transfer, the mass transfer coefficient is proportional to (where, D = molecular diffusivity)

Answer 414

D

Question 415

Dry bulb temperature of the gas is __________ the wet bulb temperature.

Answer 415

more than

Question 416

Decoction refers to the use of solvent

Answer 416

at its boiling point

Question 417

Flash distillation is suitable for separating the constituents of a binary system, which

Answer 417

have very wide boiling points.

Question 418

The ratio of Murphree plate efficiency to point efficiency is 1 in a __________ flow model.

Answer 418

perfectly mixed

Question 419

The rough value of diffusion co-efficient of water vapor into air at 25°C may be about __________ cm2/sec.

Answer 419

0.25

Question 420

Flooding in a column results due to

Answer 420

high pressure drop

Question 421

Which of the following gas-liquid contacting devices incurs the least pressure drop for a particular duty ?

Answer 421

Wetted wall tower

Question 422

A liquid mixture contains 30% o-xylene, 60% p-xylene and 10%. mxylene (all percentages in w/w). Which of the following statements would be true in respect of this mixture?

Answer 422

The mixture exhibits an azeotrope at 101.3 kPa.

Question 423

Unsaturated air (with dry bulb temperature and dew point being 35°C and 18°C respectively) is passed through a water spray chamber maintained at 15°C. The air will be cooled

Answer 423

and dehumidified with decrease in wet bulb temperature.

Question 424

The process employing desorption of the absorbed solute by a solvent is called

Answer 424

elution

Question 425

Which of the following operations does not involve leaching ?

Answer 425

Removing nicotine from its water solution by kerosene.

Question 426

The recovery of pencillin from the acidified fermentation broth is done by

Answer 426

liquid extraction

Question 427

Molecular seives are porous

Answer 427

synthetic zeolites crystals/metal alumino-silicates.

Question 428

Calcium ammonium nitrate (a fertiliser) is dried in a __________ dryer.

Answer 428

rotary

Question 429

A binary mixture of benzene and cyclohexane is separated by

Answer 429

extractive distillation

Question 430

Component A is diffusing in a medium B. The flux NA relative to a stationary point is equal to the flux due to molecular difusion, if

Answer 430

there is equimolar counter diffusion.

Question 431

Cox chart is useful in the design of

Answer 431

distillation column

Question 432

Dew point of an air-water vapor mixture
a. decreases with decrease in pressure.
b. at constant humidity & total pressure is fixed. c. corresponding to any point on the humidity chart is obtained by projecting a line through this point parallel to the temperature axis and to the saturation curve.
d. All ‘a’, ‘b’ & ‘c’.

Answer 432

d. All ‘a’, ‘b’ & ‘c’.

Question 433

Can a cooling tower cool water below the wet bulb temperature of inlet air ?

Answer 433

no

Question 434

The suitable evaporator for concentration of foaming liquids is a __________ evaporator.

Answer 434

long tube

Question 435

The ratio of Murphree plate efficiency to point efficiency is always > 1 in a __________ flow model.

Answer 435

plug

Question 436

Tea percolation employs

Answer 436

leaching

Question 437

Which of the following assumes constant molal vaporisation and overflow ?

Answer 437

McCabe-Thiele method

Question 438

Absorption factor, for a fixed degree of absorption from a fixed amount of gas should be

Answer 438

> 1

Question 439

Selectivity of the solvent used in solvent extraction should be

Answer 439

> 1

Question 440

Pick out the wrong statement pertaining to leaching. a. Fine solids can not be leached in a Pachuka tank. b. Door classifier can be used for leaching of coarse solids.
c. Vegetable seeds can be leached in either of Bollman extractor, Rotocel or Kennedy extractor. d. Very high temperature is not needed for the leaching of sugar beet.

Answer 440

a. Fine solids can not be leached in a Pachuka tank.

Question 441

Wet bulb and dry bulb temperatures becomes identical at __________ percent saturation curve.

Answer 441

100

Question 442

McCabe-Thiele method

Answer 442

uses molal units for material and energy balance.

Question 443

The film penetration model of mass transfer was enunciated by

Answer 443

Toor and Marchello

Question 444

The most economical range of absorption factor is

Answer 444

1.25 to 2

Question 445

Channelling is most severe

Answer 445

in towers packed with stacked packing.

Question 446

Out of two equilibrium curves, first one lies above the diagonal and the second lies below the diagonal in the x-y plot. It means that separation by distillation is

Answer 446

more readily done in the second case compared to first one.

Question 447

ADDUCTS’ and ‘CLATHRATES’ are used in case of

Answer 447

crystallisation

Question 448

Adsorption is an unit operation which generally involves __________ systems.

Answer 448

fluid-solid

Question 449

In case of __________ distillation, a solvent is added to alter the relative volatility of the mixture to be separated.

Answer 449

extractive

Question 450

Separation of the isotopes of helium for scientific investigations is done by

Answer 450

thermal diffusion

Question 451

Separation of the isotopes of helium for scientific investigations is done by

Answer 451

thermal diffusion

Question 452

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

Answer 452

> 1

Question 453

Fenske-Underwood equation used for calculating the minimum number of theoretical plates in distillation column is valid for
a. constant molal overflow
b. total reflux
c. constant relative volatility
d. all (a), (b) and (c)

Answer 453

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

Question 454

The binary diffusivity in gases does not depend upon the
a. pressure
b. temperature
c. nature of the components
d. none of these

Answer 454

d. none of these

Question 455

Berl saddle made of carbon cannot be used for

Answer 455

oxidising atmosphere

Question 456

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 456

0.2

Question 457

Priming in a distillation column

Answer 457

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

Question 458

The commonly used solvent in supercritical extraction is

Answer 458

carbon dioxide.

Question 459

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

Answer 459

Murphree efficiency = point efficiency.

Question 460

In saturated gas, the

Answer 460

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

Question 461

As per Gilliland’s equation, the diffusivity is a. directly proportional to ‘T1.5’.
b. inversely proportional to ‘P’.
c. dependent on the molecular volume & molecular weight of components.
d. all ‘a’, ‘b’ & ‘c’.

Answer 461

d. all ‘a’, ‘b’ & ‘c’.

Question 462

Pick out the wrong statement.
. When the concentration difference for the mass transfer becomes zero at the bottom of the gas absorption tower, then the upper end of the operating line touches the equilibrium curve.
b. The average distance between the operating line and equilibrium line is large, when the liquid-gas ratio is also large in case of a counter current gas absorption tower.
c. The operating line lies above the equilibrium curve in case of a gas desorber.
d. With decrease in the liquid flow rate for a fixed gas flow rate, the slope of the operating line decreases, in case of gas absorption process.

Answer 462

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

Question 463

Pick out the wrong statement.
. When the concentration difference for the mass transfer becomes zero at the bottom of the gas absorption tower, then the upper end of the operating line touches the equilibrium curve.
b. The average distance between the operating line and equilibrium line is large, when the liquid-gas ratio is also large in case of a counter current gas absorption tower.
c. The operating line lies above the equilibrium curve in case of a gas desorber.
d. With decrease in the liquid flow rate for a fixed gas flow rate, the slope of the operating line decreases, in case of gas absorption process.

Answer 463

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

Question 464

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 464

18.7

Question 465

Which of the following is not fixed by the process requirements, in the design of absorbers ?
a. Flow rate of the entering gas.
b. Composition of the entering liquid.
c. Terminal concentrations of gas stream.
d. None of these.

Answer 465

d. None of these.

Question 466

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

Answer 466

decreases

Question 467

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 467

unbound

Question 468

Inside the distillation columns, the

Answer 468

driving force for the liquid flow is its weight.

Question 469

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

Answer 469

1

Question 470

Desirable value of absorption factor in an absorber is

Answer 470

> 1

Question 471

Refractory bricks are usually dried in a __________ dryer.

Answer 471

tunnel

Question 472

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

Answer 472

3

Question 473

Sticky material can be dried in a __________ dryer

Answer 473

tray

Question 474

Sticky material can be dried in a __________ dryer

Answer 474

tray

Question 475

Langmuir equation is associated with

Answer 475

adsorption

Question 476

During the constant rate period of drying of a solid,

Answer 476

surface evaporation of unbound moisture occurs.

Question 477

At a fixed total pressure, humidity depends only on the

Answer 477

partial pressure of vapour in the mixture.

Question 478

Flash distillation is

Answer 478

used for multicomponent systems like crude refining.

Question 479

__________ developed the film theory.

Answer 479

Higbie

Question 480

For absorbers, high pressure drop results in

Answer 480

high operating cost.

Question 481

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

Answer 481

Wet bulb temperature

Question 482

Coffee is prepared from coffee beans by leaching with

Answer 482

hot water

Question 483

Gaseous diffusion co-efficient increases with increase in the

Answer 483

temperature

Question 484

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

Answer 484

increases

Question 485

Pick out the wrong statement. Raoult’s law does not apply, when the
a. size of component molecules are not equal.
b. attractive forces between like and unlike molecules in the solution are approximately equal.
c. component molecules are nonpolar.
d. chemical combination or molecular association between unlike molecules takes place in the formation of solution.

Answer 485

c. component molecules are nonpolar.

Question 486

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

Answer 486

vacuum

Question 487

L/mGis the expression for

Answer 487

absorption factor

Question 488

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

Answer 488

1/P

Question 489

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

Answer 489

1/P

Question 490

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

Answer 490

pure gas

Question 491

If a two phase system is in physical equilibrium; then it means that, the
a. escaping tendency of each component from the liquid phase to the vapor phase is exactly equal to that from vapor phase to liquid phase.
b. temperature of the liquid phase is equal to that of the vapor phase.
c. total pressure throughout the liquid phase is equal to that throughout the vapor phase.
d. all (a), (b) and (c).

Answer 491

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

Question 492

McCabe-Thiele method of binary distillation does not assume that the
a. sensible heat changes are negligible compared with latent heat changes.
b. molar latent heats of all components are equal.
c. heat of mixing is negligible.
d. none of these

Answer 492

d. none of these

Question 493

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

Answer 493

Stanton number

Question 494

The Hatta number is important in

Answer 494

gas absorption with chemical reaction.

Question 495

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

Answer 495

infinite trays and minimum reboiler heat load.

Question 496

CO2 can be absorbed by

Answer 496

heated charcoal

Question 497

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

Answer 497

increases in winter

Question 498

An ideal tower packing should not

Answer 498

hold up large amount of liquid in the packing.

Question 499

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

Answer 499

Monoethanol amine (MEA)

Question 500

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 500

9

Question 501

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

Answer 501

< 1 and ≈ 1

Question 502

Molecular diffusion is caused by the

Answer 502

thermal energy of the molecules.

Question 503

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

Answer 503

total

Question 504

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

Answer 504

solubility

Question 505

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

Answer 505

simple

Question 506

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

Answer 506

Pachuka tank

Question 507

Pick out the wrong statement.
a. Packed towers are preferred for vacuum operation, because the pressure drop through the packing is less and they (packings) also lessen the possibility of tower wall collapse.
b. Packed towers are preferred over plate towers for handling corrosive and foamy liquids.
c. Diameter of randomly packed tower is normally more than 1.2 metres.
d. Due to uneven supply and improper distribution of liquid, problem of channeling, loading & flooding is generally encountered in packed towers.

Answer 507

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

Question 508

Equilibrium-moisture curves of different solids

Answer 508

are different

Question 509

Azeotropism for ethyl alcohol-water system disappears by

Answer 509

decreasing pressure

Question 510

Degree of freedom for leaching and solvent extraction process is

Answer 510

3

Question 511

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 511

mass transfer co-efficient.

Question 512

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 512

Bamboo

Question 513

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

Answer 513

gas

Question 514

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

Answer 514

truck/tunnel.

Question 515

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

Answer 515

liquid extraction

Question 516

When the solvent dissolves very little of solute, then

Answer 516

large quantity of solvent is required to extract the solute.

Question 517

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 517

4.605

Question 518

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

Answer 518

and equilibrium lines are parallel.

Question 519

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 519

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

Question 520

Steady state equimolal counter diffusion occurs in case of

Answer 520

binary phase distillation

Question 521

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 521

Nsh = 2

Question 522

The relative saturation of an unsaturated mixture of gas and vapor is independent of the
a. nature of the vapor.
b. temperature of the mixture.
c. composition of the mixture.
d. none of these.

Answer 522

d. none of these.

Question 523

The adiabatic saturation curve for a vapour-gas mixture is

Answer 523

slightly concave upward.

Question 524

Pick out the wrong statement.
a. Cellulose acetate membranes are used in dialysis process.
b. Elutriation process refers to when the soluble material is largely concentrated on the surface of an insoluble solid and is simply washed off by the solvent.
c. ‘Cascade’ means a group of stages interconnected so that various streams flow from one to another.
d. Zirconia probe is used for the humidity measurement.

Answer 524

d. Zirconia probe is used for the humidity measurement.

Question 525

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

Answer 525

∞

Question 526

Drift in a cooling tower is

Answer 526

the water entrained by the circulating air.

Question 527

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

Answer 527

decreases

Question 528

Small dia distillation column can be a

Answer 528

packed column

Question 529

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

Answer 529

1

Question 530

_________ column is used in gas absorption process.

Answer 530

Packed

Question 531

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

Answer 531

at < 100

Question 532

Pick out the wrong statement.
a. With decrease in feed temperature, the number of plates required for binary distillation decreases for a given L/V ratio. b. The extraction per unit of total height for a short packed column is more effective than for a tall column, in case of liquid-liquid extraction.
c. Natural draft cooling towers are made of ferro-concrete and its cross-section is wider at the bottom.
d. Vanderwall adsorption is also called chemisorption.

Answer 532

Vanderwall adsorption is also called chemisorption.

Question 533

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

Answer 533

∞

Question 534

Batch tray dryers suffers from the disadvantage of

Answer 534

high labour cost & low heat economy.

Question 535

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 535

> 8:1

Question 536

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

Answer 536

Bubble

Question 537

Penetration model (theory) for mass transfer was enunciated by

Answer 537

Higbie

Question 538

Surface renewal model of mass transfer was enunciated by

Answer 538

Danckwerts

Question 539

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

Answer 539

temperature rises

Question 540

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

Answer 540

Re^0.83

Question 541

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

Answer 541

temperature rises.

Question 542

Unit of molal diffusivity is

Answer 542

gm moles/cm. sec

Question 543

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

Answer 543

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

Question 544

Binary distillation involves the mass transfer by __________ at the gasliquid interface.

Answer 544

a counter diffusion at an almost equal molar rate

Question 545

In a gas-liquid absorption coloumn, for obtaining the maximum absorption efficiency

Answer 545

both gas as well as liquid streams should be distributed uniformly.

Question 546

Reverse osmosis is also called

Answer 546

ultrafiltration

Question 547

Which of the following is not a batch drier?

Answer 547

Fluidised bed drier

Question 548

Steam distillation is not recommended to be used, if the

Answer 548

azeotropic mixture is to be separated and the final product is miscible with water.

Question 549

Rayleigh equation applies to __________ distillation.

Answer 549

differential

Question 550

Mass transfer co-efficient ‘K’ according to penetration theory varies with mass dif-fusivity as

Answer 550

D^0.5

Question 551

Most important factor to be considered in the selection of packings for absorbers is the __________ of packing.

Answer 551

porosity

Question 552

_________ is the separation technique used for desalination of sea water.

Answer 552

Reverse osmosis

Question 553

Danckwerts developed the __________ theory.

Answer 553

surface renewal

Question 554

Drying of a wet solid under constant drying conditions means the exposure of the wet solid to the air of constant
a. humidity
b. velocity
c. temperature
d. all (a), (b) & (c)

Answer 554

d. all (a), (b) & (c)

Question 555

Which of the following provides maximum contact surface for a liquidvapour system?

Answer 555

Packed tower

Question 556

For experimental determination of mass transfer co-efficient by wetted wall tower, the mass transfer area is

Answer 556

known

Question 557

In stripping section of continuous distillation column, the

Answer 557

liquid is enriched with high boiler.

Question 558

Molality is defined as the number of gm moles of solute per __________ of solvent.

Answer 558

Kg

Question 559

__________ is concerned with the adsorption equilibria.

Answer 559

Freundlich equation

Question 560

Fractional solvent extraction

Answer 560

employs two solvents

Question 561

In the layout plan for a vacuum distillation unit, operating at 60 mm Hg, supported by a barometric condenser, the appropriate place for the location of vacuum drum for collecting the distillate will be

Answer 561

at ground level.

Question 562

Raschig ring made of procelain cannot be used for treating concentrated

Answer 562

alkalis

Question 563

H2S present in naphtha reformed gas is removed by absorbing with

Answer 563

ethanolamine

Question 564

During constant rate drying period, vaporisation rate per unit drying surface area

Answer 564

does not change with time,

Question 565

Pick out the wrong statement.
a. Mass transfer co-efficient does not account for gase-liquid diffusion.
b. Diffusion co-efficient and mass transfer co-efficient are not same in any mass transfer operation.
c. Contacting cold vapor-gas mixture with hot liquid exemplifies humidification process.
d. Contacting cold liquid with warm vapor-gas mixture exemplifies dehumidification process.

Answer 565

a. Mass transfer co-efficient does not account for gase-liquid diffusion.

Question 566

In rectifying section of a continuous distillation column, the

Answer 566

vapour is enriched with high boilers.

Question 567

For a fixed number of ideal stages in a distillation column, as the reflux ratio is increased, the difference in composition between the top and bottom product streams

Answer 567

increases

Question 568

According to Chilton-Colburn analogy for mass transfer, NSt.NSc^2/3 is equal to

Answer 568

f/2

Question 569

A pure drug is administered as a sphere and as a cube. The amount of drug is the same in the two tablets. Assuming that the shape and size do not influence the mass transfer, the ratio of rate of dissolution in water at t = 0 for the cubic to spherical tablet is

Answer 569

1.24

Question 570

Minimum reflux ratio in a distillation column results in

Answer 570

maximum condenser size.

Question 571

Flooding in a distillation column is detected by a sharp

Answer 571

increase in pressure drop.

Question 572

In extraction, as the temperature increases, the area of hetrogeneity (area covered by binodal curve)

Answer 572

decreases

Question 573

Pick out the wrong statement.
a. The mass diffusivity, the thermal diffusivity and the eddy momentum diffusivity are the same for NSc = NPr = 1.
b. 1 Nm3 of dry air is lighter than 1Nm3 of humid air.
c. The Lewis number of a mixture is unity, when the thermal diffusivity is equal to the mass diffusivity.
d. An azeotropic mixture of two liquids has boiling point higher than either of them, when it shows negative deviation from Raoult’s Law.

Answer 573

b. 1 Nm3 of dry air is lighter than 1Nm3 of humid air.

Question 574

In case of an unsaturated mixture of gas and vapor, the percentage saturation is __________ its relative saturation.

Answer 574

lower than

Question 575

At constant pressure, with increase of temperature, the dew point will

Answer 575

increase

Question 576

For a single component absorber, the operating line is straight only when plotted in term of __________ units.

Answer 576

mole ratio

Question 577

For a binary mixture with low relative volatility,

Answer 577

an azeotrope may be formed during distillation.

Question 578

Plate efficiency

Answer 578

is a function of the mass transfer between liquid and vapour.

Question 579

Absorption accompanied by heat evolution results in

Answer 579

decrease in equilibrium solubility.

Question 580

Even though bubble cap towers are very effective for humidification operation, they are not used commonly in industries, because of the

Answer 580

high pressure drop of the gas.

Question 581

For a distillation column operating at minimum reflux, the

Answer 581

number of plates required will be maximum.

Question 582

A solid is being dried in the linear drying rate regime from moisture content Xo to XF. The drying rate is zero at X = 0 and the critical moisture content is the same as the initial moisture Xo. The drying time for M = (Ls/ARc) is (where, L = total mass of dry solid, A = total surface area for drying Rc = Constant maximum drying rate per unit area X = moisture content (in mass of water/mass of dry solids))

Answer 582

MXo ln(Xo/XF)

Question 583

Flash distillation is suitable for the separation of components

Answer 583

having very wide boiling points.

Question 584

In Mcabe-Thiele method, at infinite reflux ratio

Answer 584

both the operating lines coincide with the diagram.

Question 585

Leaching rate is independent of the
a. agitation
b. temperature
c. particle size
d. none of these

Answer 585

d. none of these

Question 586

Use of packed towers for distillation is generally limited to the

Answer 586

small sizes.

Question 587

Pick out the wrong statement.
a. The binary diffusivity in liquids is of the order of 10-5 cm2 /sec.
b. Molecular diffusion in solid is much faster than that in liquids. c. Particles movement from higher concentration to lower concentration takes place in diffusion process.
d. According to Poiseuille’s law, the permeability decreases with increase in temperature for flow of a gas through a given capillary.

Answer 587

b. Molecular diffusion in solid is much faster than that in liquids.

Question 588

Which of the following decreases during evaporative cooling process with recirculated water supply ?
a. Wet bulb temperature
b. Relative humidity
c. Partial pressure of vapour
d. None of these

Answer 588

d. None of these

Question 589

Laboratory determination of the dif-fusivity of vapor is done by __________ method.

Answer 589

Winkel mann’s

Question 590

The minimum liquid rate to be used in an absorber corresponds to an operating line

Answer 590

tangential to the equilibrium curve

Question 591

Unsaturated air (with dry and wet bulb temperatures being 35 and 25°C respectively) is passed through water spray chamber maintained at 35°C. The air will be

Answer 591

humidified

Question 592

For absorbing a sparingly soluble gas in a liquid, the

Answer 592

liquid side coefficient should be increased.

Question 593

A natural draft cooling tower is filled with wooden grids, which covers about __________ percent of the tower height.

Answer 593

10-15

Question 594

The boiling points of pure components of a binary system________with increase in total pressure of the system.

Answer 594

increases

Question 595

The change in enthalpy, when a unit quantity of gas is absorbed by relatively large quantity of adsorbent (on which a definite concentration of the adsorbed gas already exists) is termed as the

Answer 595

differential heat of adsorption.

Question 596

Penetration theory relates the average mass transfer co-efficient (K) with diffusivity (D) as

Answer 596

K ∝D^1/2

Question 597

Desulphurisation of petrol is done in a

Answer 597

rotating disc extractor

Question 598

Chemisorption compared to physical absorption has

Answer 598

increased utilisation of stagnant zones of the liquid phase.

Question 599

Rate of adsorption increases as the

Answer 599

temperature decreases.

Question 600

Pick out the system with maximum boiling azeotrope at 1 atm

Answer 600

acetone chloroform

Question 601

At 750°K and 1 atm, the approximate value of Schmidt number for air is

Answer 601

0.1

Question 602

Calculation of mass transfer co-efficient is mostly/normally done using __________ theory.

Answer 602

film

Question 603

The velocity, concentration and temperature boundary, for the boundary layer development on a flat plate during connective mass transfer will be same, if

Answer 603

NSc = NPr = NLe

Question 604

Which of the following is used for the concentration of rubber latex ?

Answer 604

Agitated film evaporator

Question 605

As the reflux ratio, in a continuous counter-current extraction is increased, the number of stages

Answer 605

decrease

Question 606

In triangular co-ordinates, the ternery composition point falls __________ of the triangle.

Answer 606

inside

Question 607

In a single stage extraction process, 10 kg of pure solvent S (containing no solute A) is mixed with 30 kg of feed F containing A at a mass fraction xf = 0.2. The mixture splits into an extract phase E and a raf-finate phase R containing A at xB = 0.5 and xR = 0.05 respectively. The total mass of the extract phase is (in Kg)

Answer 607

8.89

Question 608

Penetration theory states that the mass transfer co-coefficient is equal to (where, De is diffusivity and ‘t’ is time)

Answer 608

(4De/πt)^1/2

Question 609

Reboiler is considered as one theoretical plate, because

Answer 609

of the assumption that vapour and liquid leaving the reboiler are in equilibrium.

Question 610

Reboiler is considered as one theoretical plate, because

Answer 610

of the assumption that vapour and liquid leaving the reboiler are in equilibrium.