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

0.5

Question 3

Fenske equation determines the

Answer 3

minimum number of theoretical plates.

Question 4

The term “cooling range” 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 amount of steam required per unit quantity of distillate in case of steam distillation will be reduced by

Answer 7

raising the temperature, lowering the total pressure.

Question 8

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

Answer 8

(+)ve

Question 9

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

Answer 9

relative volatility is reasonably constant.

Question 10

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

Answer 10

natural

Question 11

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 11

all

Question 12

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

Answer 12

Packed

Question 13

Overall efficiency of the distillation column is

Answer 13

the ratio of number of ideal plates to actual plates.

Question 14

On addition of solute in the solvent, the __________ of the solution decreases.

Answer 14

freezing point, vapour pressure

Question 15

Which is the controlling factor for a drum drier?

Answer 15

Heat transfer

Question 16

Drying operation under vacuum is carried out to

Answer 16

reduce drying temperature.

Question 17

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 17

higher relative humidity

Question 18

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

Answer 18

absorption

Question 19

Stefan’s law describes the mass transfer by

Answer 19

both ‘a’ & ‘b’

Question 20

At minimum reflux ratio for a given separation

Answer 20

number of plates is infinity.

Question 21

Relative humidity is the ratio of the

Answer 21

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

Question 22

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

Answer 22

decreases

Question 23

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

Answer 23

electrical resistance

Question 24

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

Answer 24

specific heat

Question 25

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

Answer 25

increase 'S' and decrease 'G'.

Question 26

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

Answer 26

1

Question 27

Dew point of a gas-vapour mixture

Answer 27

decreases with decrease in pressure.

Question 28

In a packed absorption tower, if the equilibrium and operating lines are both straight lines, then the ratio, HETP/HTUOG __________ the absorption factor.

Answer 28

increases with increase in, is one at unity value of

Question 29

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

Answer 29

Lewis number

Question 30

In case of an absorber, the operating

Answer 30

line always lies above the equilibrium curve.

Question 31

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

Answer 31

total cost first decreases and then increases.

Question 32

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

Answer 32

S1/S2

Question 33

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 33

0

Question 34

Which of the following remains constant during sensible cooling process?

Answer 34

Specific humidity, Partial pressure of vapour

Question 35

Physical absorption is

Answer 35

a reversible phenomenon, accompanied by evolution of heat

Question 36

Make up water is required in a cooling tower to replace the water lost by

Answer 36

all

Question 37

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

Answer 37

Flow rate of entering liquid

Question 38

Mass transfer co-efficient of liquid is

Answer 38

affected more by temperature than that for gases.

Question 39

Absorption accompanied with chemical reaction is exemplified by the absorption of

Answer 39

SO2 in alkaline solution.

Question 40

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

Answer 40

Multicomponent distillation.

Question 41

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

Answer 41

Wetted wall column

Question 42

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

Answer 42

spray chamber

Question 43

Chemisorption (chemical adsorption) is

Answer 43

an irreversible phenomenon.

Question 44

The rate of solid-liquid extraction is limited by the

Answer 44

all

Question 45

Raoult's law applies to the

Answer 45

solvents.

Question 46

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

Answer 46

allowable gas and liquid velocities.

Question 47

In distillation, overhead product contains

Answer 47

any number of components

Question 48

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

Answer 48

decreases.

Question 49

Low viscosity absorbent is preferred for reasons of

Answer 49

all

Question 50

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

Answer 50

K ∝ D

Question 51

The McCabe Δ L law states that the

Answer 51

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

Question 52

Bollman extractor

Answer 52

is used for extraction of oil from oilseed.

Question 53

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

Answer 53

heat and mass

Question 54

A coalescer in a mixer-settler liquid-liquid extraction coloumn

Answer 54

all

Question 55

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 55

increase

Question 56

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 56

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 57

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 57

vapour pressure of component A to that of component B.

Question 58

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 58

elutriation or elution

Question 59

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

Answer 59

surface evaporation of unbound moisture occurs.

Question 60

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 60

71 min

Question 61

Agitator is provided in a crystalliser for

Answer 61

all

Question 62

__________ diffusion is used for separating the isotopes of methane.

Answer 62

Thermal

Question 63

Ordinary diffusion process is also called __________ diffusion.

Answer 63

concentration

Question 64

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 64

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

Question 65

Pick out the wrong statement pertaining to the rotary dryer.

Answer 65

Rotary dryer is suitable for drying sticky material.

Question 66

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

Answer 66

low pressure drop and low hold up.

Question 67

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

Answer 67

> 100

Question 68

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 68

0.5

Question 69

Raoult's law is applicable to the

Answer 69

ideal solutions

Question 70

Weeping in a distillation column

Answer 70

results due to very low gas velocity.

Question 71

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

Answer 71

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

Question 72

Wetted wall tower experiment determines the

Answer 72

mass transfer co-efficient.

Question 73

In McCabe-Thiele method, at infinite reflux ratio

Answer 73

the overhead product is minimum.

Question 74

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

Answer 74

increases

Question 75

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

Answer 75

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

Question 76

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

Answer 76

same

Question 77

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

Answer 77

wetted wall

Question 78

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

Answer 78

ethyl alcohol-water

Question 79

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

Answer 79

rotary

Question 80

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

Answer 80

linearly

Question 81

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

Answer 81

Sherwood

Question 82

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 82

0.215

Question 83

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

Answer 83

10-5 to 10-6

Question 84

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

Answer 84

its recovery cost by distillation may be prohibitatively high.

Question 85

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

Answer 85

is greater than

Question 86

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

Answer 86

liter

Question 87

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

Answer 87

1

Question 88

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 88

less number of trays are required.

Question 89

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

Answer 89

exponential

Question 90

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

Answer 90

Water-hydrochloric acid.

Question 91

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

Answer 91

Peclet

Question 92

The binary diffusivity in gases and liquids vary respectively as

Answer 92

T^3/2 and T

Question 93

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 93

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

Question 94

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 94

Electrodylsis is used in the manufacture of NaOH.

Question 95

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 95

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

Question 96

Very tall packed towers are divided into series of beds to

Answer 96

avoid channelling

Question 97

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

Answer 97

free

Question 98

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

Answer 98

decreases

Question 99

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

Answer 99

steam jet ejector with a barometric condenser

Question 100

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 100

increased reflux ratio

Question 101

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

Answer 101

Plate

Question 102

Deairation (removal of O2) of water is done by

Answer 102

ion-exchange

Question 103

Make up water is supplied during cooling tower operation to compensate for water losses due to

Answer 103

all

Question 104

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 104

Azeotropes obey Raoult's law at all temperature.

Question 105

A minimum boiling azeotrope is exemplified by

Answer 105

acetone-carbon disulphide

Question 106

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

Answer 106

A solution of benzene, toluene and oxylene.

Question 107

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

Answer 107

decreases pressure drop, increases surface area.

Question 108

Critical humidity of a solid salt means the humidity

Answer 108

above which it will always become damp, below which it will always stay dry

Question 109

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

Answer 109

both parallel and straight

Question 110

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

Answer 110

that of normal condensation.

Question 111

Absorption with chemical reaction' is involved in the removal of

Answer 111

carbon dioxide from gaseous stream using alkaline solution.

Question 112

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

Answer 112

> 1

Question 113

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 113

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

Question 114

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

Answer 114

heated cylinder

Question 115

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 115

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

Question 116

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

Answer 116

large latent heat

Question 117

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

Answer 117

raschig

Question 118

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

Answer 118

infinity

Question 119

Leaching of sugar from sugar beets is done by

Answer 119

hot water

Question 120

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

Answer 120

both operating and equilibrium lines are parallel.

Question 121

Flights in a rotary dryer are provided to

Answer 121

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

Question 122

If f = moles of vapour present per mole of feed, then the slope of feed line is (Mcabe-Thiele method)

Answer 122

-1/f

Question 123

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 123

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

Question 124

The rate of mass transfer is not dependent upon the

Answer 124

none of these.

Question 125

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 125

0.4

Question 126

Dry bulb temperature of unsaturated air is more than its __________ temperature.

Answer 126

dew point, wet bulb

Question 127

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 127

1

Question 128

The reciprocal of stripping factor is termed as

Answer 128

absorption factor

Question 129

Ponchan-Savarit method analyses the fractional equipment based on

Answer 129

both enthalpy and material balances.

Question 130

The binary diffusivity in gases at atmospheric conditions is about

Answer 130

10^-1 cm2/sec

Question 131

Percentage saturation is __________ the relative saturation.

Answer 131

always smaller than

Question 132

In case of a desorber (stripper), the

Answer 132

operating line always lies below the equilibrium curve.

Question 133

What is the reflux ratio at total reflux?

Answer 133

Infinity

Question 134

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

Answer 134

is maximum

Question 135

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 135

10-60

Question 136

For absorbing a sparingly soluble gas in a liquid

Answer 136

liquid side mass transfer co-efficient should be increased.

Question 137

Channelling in a packed tower results from the

Answer 137

maldistribution of liquid, non-uniformity of packing

Question 138

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 138

integral heat of adsorption.

Question 139

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

Answer 139

total reflux

Question 140

A good solvent used for absorption should not have very high

Answer 140

all

Question 141

In a counter-current liquid extractor

Answer 141

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

Question 142

Which of the following is an undesirable property for an absorbing solvent ?

Answer 142

None of these

Question 143

The wetted wall tower is used to determine

Answer 143

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

Question 144

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

Answer 144

less

Question 145

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

Answer 145

greater than that computed for ideality.

Question 146

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

Answer 146

increases

Question 147

Schmidt number is given by

Answer 147

μ/ρDAB

Question 148

The caking of crystals can be prevented by

Answer 148

maintaining high critical humidity, coating the product with inert material

Question 149

Prandtl number for water at 20°C is about

Answer 149

7

Question 150

Boiling point diagram is

Answer 150

affected by pressure.

Question 151

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,

Answer 151

all

Question 152

Steam distillation is used to

Answer 152

avoid thermal decomposition of a component.

Question 153

Freundlich equation applies to the adsorption of solute from

Answer 153

dilute solutions, over a small concentration range.

Question 154

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

Answer 154

marginal decrease in the number of

Question 155

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

Answer 155

pure component

Question 156

The diffusivity (D) in a binary gas mixture is related to the pressure (P) as

Answer 156

D ∝ 1/P

Question 157

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

Answer 157

Spray dryer

Question 158

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

Answer 158

Heating and dehumidification at almost constant wet bulb temperature.

Question 159

In gas-liquid contact operation, the number of ideal stages, https://www.indiabix.com/_files/images/chemical-engineering/mass-transfer/331-646-1.png . This is true when the stripping factor 'S' is (see picture)

Answer 159

S > 1

Question 160

The cooling effect in a cooling tower can not be increased by

Answer 160

none of these.

Question 161

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

Answer 161

1

Question 162

The humid volume may be increased by increasing the

Answer 162

temperature at constant humidity, humidity at constant temperature.

Question 163

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 163

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

Question 164

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 164

steam

Question 165

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

Answer 165

spouted bed

Question 166

Azeotropic distillation is employed to separate

Answer 166

constant boiling mixture.

Question 167

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 167

T^2

Question 168

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

Answer 168

∞

Question 169

Use of natural draft cooling tower is practised, when the air has low

Answer 169

humidity, temperature

Question 170

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

Answer 170

more

Question 171

Dimension of mass diffusivity is the same as that of

Answer 171

kinematic viscosity

Question 172

Dorr thickener is an equipment used for

Answer 172

sedimentation

Question 173

Steam distillation is used to separate

Answer 173

high boiling substances from nonvolatile impurities.

Question 174

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 174

q = 1

Question 175

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

Answer 175

Large weight of liquid retained.

Question 176

Water entrained by circulating air in cooling towers is termed as

Answer 176

drift

Question 177

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 177

1000

Question 178

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

Answer 178

diffusivity of solute increases.

Question 179

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. molal

Answer 179

molal

Question 180

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

Answer 180

sqrt(T)

Question 181

In case of constant underflow extraction operation, the __________ at all solute concentration.

Answer 181

solids are drained to the same extent, ratio of the insoluble to solution is constant

Question 182

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

Answer 182

smaller than

Question 183

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 183

Kc = Kp . RT = Km . RT/p

Question 184

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

Answer 184

increased diffusivity, decreased viscosity of liquid

Question 185

Leaching of uranium ore and gold ore is done in

Answer 185

Pachuka tanks

Question 186

Blowdown in a cooling tower

Answer 186

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

Question 187

During constant rate period, the rate of drying decreases with the

Answer 187

decrease in air temperature, increase in air humidity

Question 188

Antibiotics are best handled in a

Answer 188

Podbielniak extractor.

Question 189

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

Answer 189

infinite

Question 190

__________ extractor uses centrifugal force for separating the two phases.

Answer 190

Podbielniak

Question 191

In a binary distillation column, if the feed contains 40 mole % vapour, the q line will have a slope of

Answer 191

-1.5

Question 192

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 192

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

Question 193

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

Answer 193

solvent extraction

Question 194

Design calculation for multiple component distillation is done by

Answer 194

tray to tray calculations.

Question 195

To get high tray efficiency

Answer 195

interfacial surface between liquid and gas phase should be large.

Question 196

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 196

dependent on the Reynolds number

Question 197

Pick out the wrong statement. Generally for physical adsorption, a gas of

Answer 197

none of these.

Question 198

In most of the mechanically agitated liquid-liquid extractors, baffles or horizontal compartmental plates are provided, which helps in

Answer 198

all

Question 199

In a vapor-liquid contacting equipment, the overall gas phase mass transfer co-efficient (M.T.C), KG is related to individual co-efficients (KG and KL) as

Answer 199

1/KG = 1/KG + m/KL

Question 200

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

Answer 200

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

Question 201

Inside the distillation column, the

Answer 201

driving force for the vapour flow is the pressure drop.

Question 202

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

Answer 202

viscosity with concentration, degree of ideality of the solution

Question 203

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

Answer 203

decreases

Question 204

Which of the following is not a continuous drier?

Answer 204

Tray drier

Question 205

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

Answer 205

insoluble in the liquid

Question 206

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

Answer 206

Dew point

Question 207

Rate of leaching increases with increasing

Answer 207

temperature

Question 208

An azeotropic mixture is a __________ mixture.

Answer 208

constant boiling point

Question 209

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 10- 2m/s. d. The concentration and hydrodynamic boundary layers over a flat plate are of equal thickness, if Schmidt number is equal to unity

Answer 209

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

Question 210

Molecular seives are regenerated by heating to __________ °C.

Answer 210

200-330

Question 211

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

Answer 211

Ri = Re/1+Re

Question 212

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

Answer 212

decreases

Question 213

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

Answer 213

freeze

Question 214

In extractive distillation, solvent is

Answer 214

added to alter the relative volatility of the mixture.

Question 215

Radioactive nuclear waste is treated in

Answer 215

pulsed column extractor

Question 216

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

Answer 216

rotary

Question 217

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

Answer 217

Wet bulb

Question 218

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 218

T

Question 219

__________ equation applies to diffusivities in liquids.

Answer 219

Gilliland

Question 220

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

Answer 220

incurs smaller pressure drop.

Question 221

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

Answer 221

Hexane

Question 222

In an absorber, HETP does not vary with the

Answer 222

none of these

Question 223

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

Answer 223

through circulation

Question 224

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

Answer 224

increase

Question 225

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

Answer 225

agitated vessel

Question 226

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

Answer 226

a binary mixture.

Question 227

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

Answer 227

a total condenser is used.

Question 228

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 228

gas phase resistance controlled.

Question 229

As the reflux ratio decreases, the

Answer 229

number of plates increases.

Question 230

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

Answer 230

Spray towers

Question 231

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 231

the fraction vaporised but not the product composition.

Question 232

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

Answer 232

steady state equimolar counter diffusion

Question 233

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 233

increases

Question 234

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

Answer 234

stready state diffusion for stagnant case.

Question 235

Which of these columns incurs the lowest pressure drop?

Answer 235

Packed column (with stacked packing)

Question 236

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

Answer 236

liquid

Question 237

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 237

L/G

Question 238

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

Answer 238

Wet bulb temperature

Question 239

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

Answer 239

can lie above or below the equilibrium curve.

Question 240

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

Answer 240

Packed column (stacked)

Question 241

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

Answer 241

degree of ideality, viscosity

Question 242

Stage efficiency in a leaching process depends on the

Answer 242

time of contact between the solid and the solution, rate of diffusion of the solute through the solid and into the liquid

Question 243

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

Answer 243

half

Question 244

The Knudsen diffusivity is dependent on the

Answer 244

molecular velocity and por radius of the catalyst.

Question 245

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

Answer 245

flooding

Question 246

Solvent used in extractive distillation

Answer 246

forms a low boiling azeotrope.

Question 247

Capacity of a rotary dryer depends on its

Answer 247

r.p.m, inclination with ground surface

Question 248

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

Answer 248

all

Question 249

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

Answer 249

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

Question 250

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

Answer 250

- ve

Question 251

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

Answer 251

both zero and hundred

Question 252

Back-trapping in a distillation column

Answer 252

decreases tray efficiency.

Question 253

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 253

more than

Question 254

Milk is dried usually in a __________ dryer.

Answer 254

spray

Question 255

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

Answer 255

decreases

Question 256

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

Answer 256

Activated carbon

Question 257

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

Answer 257

increases.

Question 258

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 258

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

Question 259

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

Answer 259

None of these

Question 260

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

Answer 260

increasing temperatures both on the surface and within the solid.

Question 261

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

Answer 261

Solvent extraction

Question 262

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

Answer 262

None of these

Question 263

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

Answer 263

Agitated vessels

Question 264

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

Answer 264

2

Question 265

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

Answer 265

2.09 x 10-9

Question 266

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 266

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

Question 267

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

Answer 267

is independent of pressure.

Question 268

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

Answer 268

p = P

Question 269

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

Answer 269

Lewis

Question 270

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

Answer 270

relative volatility

Question 271

In physical terms, Schmidt number means

Answer 271

momentum diffusivity/mass diffusivity.

Question 272

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

Answer 272

T

Question 273

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 273

ideal gases

Question 274

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

Answer 274

penetration

Question 275

Sand is dried in foundaries in a___drier.

Answer 275

fluidised bed

Question 276

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

Answer 276

Mechanical draft cooling tower.

Question 277

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 277

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 278

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 278

all

Question 279

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

Answer 279

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

Question 280

Diameter to height ratio for a rashig ring is

Answer 280

1

Question 281

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

Answer 281

pulse column

Question 282

Advantage of continuous drying over batch drying is that the

Answer 282

all

Question 283

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

Answer 283

increases

Question 284

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

Answer 284

sharp drop in pressure drop.

Question 285

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

Answer 285

1

Question 286

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

Answer 286

1

Question 287

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 287

The entire amount of C is transferred to solvent B.

Question 288

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

Answer 288

sqrt(KL2.DA)

Question 289

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

Answer 289

1.2 to 1.5

Question 290

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 290

wet bulb temperature

Question 291

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

Answer 291

dilute solutions and isothermal operation.

Question 292

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

Answer 292

surface renewal

Question 293

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

Answer 293

dilute solution and isothermal operation.

Question 294

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

Answer 294

0.6

Question 295

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 295

humidified with wet bulb temperature decreasing.

Question 296

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

Answer 296

linear

Question 297

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

Answer 297

momentum diffusivity to the mass diffusivity.

Question 298

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

Answer 298

f = 1

Question 299

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

Answer 299

repeated coalescence & redispersion of the drop phase.

Question 300

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

Answer 300

interface

Question 301

Pick out the wrong statement pertaining to the analogy between equations of heat and mass transfer operations.

Answer 301

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

Question 302

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

Answer 302

(-) ve

Question 303

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 303

gas side

Question 304

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

Answer 304

0.5

Question 305

Swenson-Walker crystalliser is a __________ unit

Answer 305

continuous

Question 306

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 306

12

Question 307

Absorption (liquid-gas system) with evolution of heat as compared to isothermal absorption results in

Answer 307

all

Question 308

With increase in temperature, the mutual solubility of two liquids

Answer 308

increases

Question 309

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 309

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

Question 310

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

Answer 310

1

Question 311

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 311

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

Question 312

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

Answer 312

less than

Question 313

Lewis number (Le) is

Answer 313

Sc / Pr

Question 314

Which of the following is not a continuous leaching equipment?

Answer 314

Pachuka tank

Question 315

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

Answer 315

Pulsed column

Question 316

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

Answer 316

equilibrium

Question 317

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

Answer 317

unbound

Question 318

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

Answer 318

(1 + Ro) = Ro/Ri

Question 319

Separation of __________ employs gaseous diffusion process.

Answer 319

isotopes of uranium

Question 320

For water-ethanol system, the minimum reflux ratio

Answer 320

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

Question 321

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 321

500

Question 322

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 322

lower than

Question 323

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

Answer 323

mass transfer co-efficient

Question 324

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 324

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

Question 325

In liquid extraction, if the selectivity is unity, then

Answer 325

no separation will occur.

Question 326

Paper industry employs __________ driers.

Answer 326

cylinder

Question 327

Which of the following has the same dimension as mass diffusivity?

Answer 327

Kinematic viscosity, Thermal diffusivity

Question 328

Pick out the wrong statement pertaining to the cooling towers.

Answer 328

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

Question 329

Experiments were conducted to determine the flux of a species A in a stagnant medium across a gas-liquid interface. The overall mass transfer co-efficient 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 329

8.5 x 10-4

Question 330

Leaching of coarse solid lumps is also termed as

Answer 330

percolation

Question 331

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

Answer 331

avoid channeling.

Question 332

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

Answer 332

a pure substance

Question 333

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

Answer 333

95

Question 334

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

Answer 334

wetted wall

Question 335

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

Answer 335

decreases.

Question 336

Mass transfer co-efficient is defined as

Answer 336

Co-efficient = Flux/concentration difference.

Question 337

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

Answer 337

the relative humidity decreases.

Question 338

During sensible cooling process

Answer 338

relative humidity increases, wet bulb temperature decreases

Question 339

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 339

0

Question 340

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

Answer 340

equal to the heat of wetting.

Question 341

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 341

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

Question 342

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

Answer 342

1.25 to 2.0

Question 343

Large scale usage of flash distillation is practised in

Answer 343

petroleum refinning

Question 344

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

Answer 344

thermal decomposition of bottoms.

Question 345

Alcohol is dehydrated using __________ distillation.

Answer 345

azeotropic

Question 346

Separation of two volatile liquids by distillation makes use of their

Answer 346

relative volatility

Question 347

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

Answer 347

Relative humidity, Partial pressure of vapour

Question 348

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

Answer 348

tray

Question 349

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

Answer 349

Butyl acetate

Question 350

Rotary dryers cannot handle __________ materials.

Answer 350

sticky

Question 351

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 351

none of these.

Question 352

An example of elution is

Answer 352

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

Question 353

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

Answer 353

partial pressure

Question 354

Relative volatility does not change appreciably with the change in

Answer 354

temperature

Question 355

Boiling point diagram is not affected by the ambient

Answer 355

humidity, temperature

Question 356

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

Answer 356

gas

Question 357

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

Answer 357

Temperature of the solid

Question 358

In case of liquid-liquid binary diffusion, diffusivity of one constituent into another is not dependent on the

Answer 358

none of these

Question 359

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

Answer 359

rotary

Question 360

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

Answer 360

always lower than

Question 361

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

Answer 361

bound

Question 362

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

Answer 362

high reflux ratio

Question 363

The efficiency of a plate column will be maximum, when the flow is ideal __________ the plate.

Answer 363

across, above

Question 364

Heat load in a cooling tower

Answer 364

means the amount of heat thrown away (KCal/hr.) by the cooling tower, is equal to the number of kg, of water circulated times the cooling range.

Question 365

In case of absorption with exothermic reaction, for fluids having

Answer 365

Pr = Sc; percentage change in heat and mass transfer flux will be the same for a given change in the degree of turbulence, Pr = Sc = 1; total mass, momentum and thermal diffusivity will be the same

Question 366

Detergent solution is dried to a powder in a

Answer 366

spray dryer

Question 367

Which of the following mixtures does not form an azeotrope at atmosheric pressure?

Answer 367

None of these

Question 368

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 368

liquid film

Question 369

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

Answer 369

increasing the gas film co-efficient.

Question 370

Flooding results in

Answer 370

low tray efficiency

Question 371

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

Answer 371

water has a high latent heat of evaporation.

Question 372

In an operating distillation column, the

Answer 372

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 373

In a forced draft cooling tower, water is cooled from 95 to 80°F by exposure to air with a wet bulb temperature of 70°F. In this case, the

Answer 373

range is 15°F, approach is 10°F

Question 374

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

Answer 374

D ∝ T^1.5

Question 375

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

Answer 375

Humidification

Question 376

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

Answer 376

30

Question 377

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.

Answer 377

none of these

Question 378

The dimension of diffusivity is same as that of the

Answer 378

kinematic viscosity

Question 379

The temperature to which a vapour gas mixture must be cooled (at varying humidity) to become saturated is called the __________ temperature.

Answer 379

none of these

Question 380

Entrainer used in azeotropic distillation should

Answer 380

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

Question 381

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

Answer 381

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

Question 382

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 382

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

Question 383

Leaching of coffee from coffee beans is done by

Answer 383

hot water

Question 384

For contacting a highly soluble gas with a liquid

Answer 384

bubble the gas through liquid.

Question 385

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

Answer 385

unbound

Question 386

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

Answer 386

decreases

Question 387

Ion exchange process is similar to

Answer 387

adsorption

Question 388

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 388

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

Question 389

Dryer widely used in a textile industry is __________ dryer.

Answer 389

conveyor

Question 390

Solvent used in extractive distillation

Answer 390

changes the relative volatility of the original components.

Question 391

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

Answer 391

increases

Question 392

In a packed tower, the value of HETP equals HTUOG, when the equilibrium and the operating lines are (where, HETP = height equivalant to a theoretical plate HTUOG = overall gas phase height of a transfer unit)

Answer 392

straight, parallel

Question 393

The vapour pressure exerted by the moisture contained in a wet solid depends upon the

Answer 393

all

Question 394

The absorption factor is defined as (where, L = liquid flow rate, G = gas flow rate and, m = slope of the equilibrium line)

Answer 394

L/mG

Question 395

Smoke is an example of

Answer 395

solid dispersed in gas

Question 396

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

Answer 396

Bone charcoal

Question 397

Stacked packing compared to dumped packing

Answer 397

provides poorer contact between the fluids, gives lower pressure drop.

Question 398

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 398

total

Question 399

Which of the following parameters remains constant during chemical dehumidification?

Answer 399

Dry bulb temperature

Question 400

Drying of a solid involves __________ transfer.

Answer 400

both heat and mass

Question 401

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

Answer 401

sublimation

Question 402

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

Answer 402

temperature

Question 403

Which is not concerned directly with mass transfer?

Answer 403

Froude number

Question 404

Removal of __________ exemplifies an adsorption unit operation.

Answer 404

water from petrol

Question 405

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

Answer 405

Never

Question 406

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 406

increases

Question 407

For gas absorption, low viscosity solvents are preferred, because of their

Answer 407

all

Question 408

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

Answer 408

perfectly dry

Question 409

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

Answer 409

minimum

Question 410

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

Answer 410

2

Question 411

Molecular diffusivity of a liquid

Answer 411

increases with temperature.

Question 412

The wet and 'dry bulb temperature for a vapour-gas mixture are 25°C and 30°C respectively. If the mixture is heated to 45°C at constant pressure, the wet bulb temperature will be __________ °C.

Answer 412

> 25

Question 413

Henry's law states that the

Answer 413

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

Question 414

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

Answer 414

dilute ammoniacal liquor

Question 415

With increase in temperature, the leaching rate increases due to

Answer 415

decreased liquid viscosity, increased diffusivity

Question 416

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

Answer 416

Decolouration of yellow glycerene.

Question 417

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

Answer 417

beginning of falling

Question 418

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 418

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 419

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

Answer 419

1/μ

Question 420

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 420

1

Question 421

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 421

2

Question 422

Packed column distillation is limited to the column __________ metres.

Answer 422

height < 6, diameter < 0.6

Question 423

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

Answer 423

increases

Question 424

Which of the following is directly concerned with psychrometry?

Answer 424

Lewis relationship

Question 425

Plate efficiency in a distillation column is reduced due to the __________ of liquid.

Answer 425

all

Question 426

The most efficient cooling tower out of the following is

Answer 426

induced draft

Question 427

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

Answer 427

baffle

Question 428

Powdery materials can be guarded against caking tendency on storage by

Answer 428

none of these.

Question 429

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

Answer 429

Lewis

Question 430

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

Answer 430

Wetted wall columns

Question 431

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

Answer 431

more than the wet bulb

Question 432

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 432

Both heating and humidification

Question 433

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

Answer 433

film

Question 434

The relative volatility of a binary mixture at constant temperature __________ the total pressure.

Answer 434

decreases with increase in

Question 435

Tower diameter may be decreased by

Answer 435

use of increased tray spacing.

Question 436

Rayleigh's equation applies to __________ distillation.

Answer 436

differential

Question 437

Steady state equimolal counter diffusion is encountered in

Answer 437

separation of a binary mixture by distillation.

Question 438

Which of the following is considered equivalent to one theoretical stage in Mc-Cabe Thiele's method?

Answer 438

Total condenser, Reboiler

Question 439

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 439

Selectivity

Question 440

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

Answer 440

increases

Question 441

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 441

log P vs . T

Question 442

The unit of volumetric diffusivity is

Answer 442

cm2/sec

Question 443

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

Answer 443

pure component is represented by the apex.

Question 444

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 444

wet-bulb

Question 445

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 445

10

Question 446

The slope of 9-line is determined by the

Answer 446

thermal condition of the feed

Question 447

In steam distillation, the

Answer 447

product must be immiscible with water.

Question 448

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 448

Wet bulb temperature

Question 449

Steam distillation is used for separation of high boiling

Answer 449

substances from non-volatile impurities, volatile impurity from still higher boiling substances

Question 450

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 450

increase

Question 451

Rose oil is extracted from rose leaves using __________ distillation.

Answer 451

steam

Question 452

Hypersorption refers to a __________ process.

Answer 452

moving bed adsorption

Question 453

Extraction of coffee from its seed is done by

Answer 453

leaching.

Question 454

In azeotropic mixture, the equilibrium vapour composition is

Answer 454

same as liquid composition.

Question 455

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

Answer 455

decreases

Question 456

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

Answer 456

thermal diffusivity to mass diffusivity.

Question 457

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

Answer 457

D

Question 458

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

Answer 458

more than

Question 459

Decoction refers to the use of solvent

Answer 459

at its boiling point

Question 460

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

Answer 460

have very wide boiling points.

Question 461

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

Answer 461

perfectly mixed

Question 462

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

Answer 462

0.25

Question 463

Flooding in a column results due to

Answer 463

high pressure drop

Question 464

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

Answer 464

Wetted wall tower

Question 465

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

Answer 465

The mixture exhibits an azeotrope at 101.3 kPa.

Question 466

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 466

and dehumidified with decrease in wet bulb temperature.

Question 467

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

Answer 467

elution

Question 468

If the overall efficiency and Murphree plate efficiency are equal, then both the equilibrium and operating lines are

Answer 468

straight, parallel

Question 469

Which of the following operations does not involve leaching?

Answer 469

Removing nicotine from its water solution by kerosene.

Question 470

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

Answer 470

liquid extraction

Question 471

Unit operation involved in the prilling of urea is

Answer 471

drying. Crystallisation

Question 472

Molecular seives are porous

Answer 472

synthetic zeolites crystals/metal alumino-silicates.

Question 473

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

Answer 473

rotary

Question 474

A binary mixture of benzene and cyclohexane is separated by

Answer 474

extractive distillation

Question 475

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 475

there is equimolar counter diffusion.

Question 476

Cox chart is useful in the design of

Answer 476

distillation column

Question 477

Dew point of an air-water vapor mixture

Answer 477

all

Question 478

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

Answer 478

no

Question 479

The solvent used in liquid-liquid extraction should have __________ less than one.

Answer 479

neither

Question 480

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

Answer 480

long tube

Question 481

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

Answer 481

plug

Question 482

Tea percolation employs

Answer 482

leaching

Question 483

Which of the following assumes constant molal vaporisation and overflow?

Answer 483

McCabe-Thiele method

Question 484

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

Answer 484

> 1

Question 485

Selectivity of the solvent used in solvent extraction should be

Answer 485

> 1

Question 486

Pick out the wrong statement pertaining to leaching.

Answer 486

Fine solids can not be leached in a Pachuka tank.

Question 487

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

Answer 487

100

Question 488

NSc/NPr is called the

Answer 488

Lewis number

Question 489

McCabe-Thiele method

Answer 489

uses molal units for material and energy balance.

Question 490

The film penetration model of mass transfer was enunciated by

Answer 490

Toor and Marchello

Question 491

The most economical range of absorption factor is

Answer 491

1.25 to 2

Question 492

Channelling is most severe

Answer 492

in towers packed with stacked packing.

Question 493

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 493

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

Question 494

ADDUCTS' and 'CLATHRATES' are used in case of

Answer 494

crystallisation.

Question 495

Adsorption is an unit operation which generally involves __________ systems.

Answer 495

fluid-solid

Question 496

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

Answer 496

extractive

Question 497

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

Answer 497

thermal diffusion

Question 498

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

Answer 498

> 1

Question 499

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

Answer 499

all

Question 500

The binary diffusivity in gases does not depend upon the

Answer 500

none of these

Question 501

Berl saddle made of carbon cannot be used for

Answer 501

oxidising atmosphere

Question 502

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 502

0.2

Question 503

During drying of a solid, the critical moisture content increases with

Answer 503

increased thickness of the solid, increased drying rate

Question 504

Priming in a distillation column

Answer 504

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

Question 505

The commonly used solvent in supercritical extraction is

Answer 505

carbon dioxide.

Question 506

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

Answer 506

Murphree efficiency = point efficiency.

Question 507

In saturated gas, the

Answer 507

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

Question 508

As per Gilliland's equation, the diffusivity is

Answer 508

all

Question 509

Pick out the wrong statement. a. 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 509

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

Question 510

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 510

18.7

Question 511

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

Answer 511

None of these.

Question 512

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

Answer 512

decreases

Question 513

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 513

unbound

Question 514

Inside the distillation columns, the

Answer 514

driving force for the liquid flow is its weight.

Question 515

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

Answer 515

1

Question 516

Desirable value of absorption factor in an absorber is

Answer 516

> 1

Question 517

Refractory bricks are usually dried in a __________ dryer.

Answer 517

tunnel

Question 518

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

Answer 518

unsaturated surface, constant rate

Question 519

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

Answer 519

3

Question 520

Sticky material can be dried in a __________ dryer.

Answer 520

tray

Question 521

Langmuir equation is associated with

Answer 521

adsorption

Question 522

During the constant rate period of drying of a solid,

Answer 522

surface evaporation of unbound moisture occurs.

Question 523

At a fixed total pressure, humidity depends only on the

Answer 523

partial pressure of vapour in the mixture.

Question 524

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

Answer 524

X/X+1

Question 525

Flash distillation is

Answer 525

used for multicomponent systems like crude refining.

Question 526

__________ developed the film theory.

Answer 526

Higbie

Question 527

For absorbers, high pressure drop results in

Answer 527

high operating cost.

Question 528

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

Answer 528

Wet bulb temperature

Question 529

Coffee is prepared from coffee beans by leaching with

Answer 529

hot water

Question 530

Gaseous diffusion co-efficient increases with increase in the

Answer 530

temperature

Question 531

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

Answer 531

increases

Question 532

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

Answer 532

component molecules are nonpolar.

Question 533

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

Answer 533

vacuum

Question 534

L/mG is the expression for

Answer 534

absorption factor

Question 535

Extraction of pencillin employs a __________ extraction coloumn.

Answer 535

centrifugal

Question 536

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

Answer 536

1/P

Question 537

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

Answer 537

pure gas

Question 538

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

Answer 538

Schmidt

Question 539

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

Answer 539

all

Question 540

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

Answer 540

none of these

Question 541

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

Answer 541

Stanton number

Question 542

The Hatta number is important in

Answer 542

gas absorption with chemical reaction.

Question 543

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

Answer 543

infinite trays and minimum reboiler heat load.

Question 544

CO2 can be absorbed by

Answer 544

heated charcoal

Question 545

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

Answer 545

increases in winter

Question 546

An ideal tower packing should not

Answer 546

hold up large amount of liquid in the packing.

Question 547

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

Answer 547

Monoethanol amine (MEA)

Question 548

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 548

9

Question 549

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

Answer 549

< 1 and ≈ 1

Question 550

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

Answer 550

II, III

Question 551

Molecular diffusion is caused by the

Answer 551

thermal energy of the molecules.

Question 552

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

Answer 552

total

Question 553

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

Answer 553

solubility

Question 554

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

Answer 554

simple

Question 555

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

Answer 555

Pachuka tank

Question 556

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 556

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

Question 557

Equilibrium-moisture curves of different solids

Answer 557

are different

Question 558

Azeotropism for ethyl alcohol-water system disappears by

Answer 558

decreasing pressure

Question 559

Degree of freedom for leaching and solvent extraction process is

Answer 559

3

Question 560

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 560

mass transfer co-efficient.

Question 561

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 561

Bamboo

Question 562

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

Answer 562

gas

Question 563

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

Answer 563

truck/tunnel.

Question 564

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

Answer 564

differential distillation equation

Question 565

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

Answer 565

liquid extraction

Question 566

When the solvent dissolves very little of solute, then

Answer 566

large quantity of solvent is required to extract the solute.

Question 567

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 567

4.605

Question 568

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

Answer 568

and equilibrium lines are parallel.

Question 569

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 569

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

Question 570

Steady state equimolal counter diffusion occurs in case of

Answer 570

binary phase distillation

Question 571

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 571

Nsh = 2

Question 572

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

Answer 572

none of these.

Question 573

The adiabatic saturation curve for a vapour-gas mixture is

Answer 573

slightly concave upward.

Question 574

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 574

Zirconia probe is used for the humidity measurement.

Question 575

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

Answer 575

∞

Question 576

Drift in a cooling tower is

Answer 576

the water entrained by the circulating air.

Question 577

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

Answer 577

decreases.

Question 578

Small dia distillation column can be a

Answer 578

packed column

Question 579

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

Answer 579

1

Question 580

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

Answer 580

0.152

Question 581

__________ column is used in gas absorption process.

Answer 581

Packed

Question 582

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

Answer 582

at < 100

Question 583

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 583

Vanderwall adsorption is also called chemisorption.

Question 584

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

Answer 584

∞

Question 585

Batch tray dryers suffers from the disadvantage of

Answer 585

high labour cost & low heat economy.

Question 586

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 586

> 8:1

Question 587

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

Answer 587

Bubble

Question 588

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

Answer 588

recovery of tannis from the tree barks and woods, leaching sodium nitrate from Chilean nitrate bearing rock.

Question 589

Penetration model (theory) for mass transfer was enunciated by

Answer 589

Higbie

Question 590

Surface renewal model of mass transfer was enunciated by

Answer 590

Danckwerts

Question 591

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

Answer 591

temperature rises

Question 592

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

Answer 592

Re^0.83

Question 593

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

Answer 593

temperature rises.

Question 594

Unit of molal diffusivity is

Answer 594

gm moles/cm. sec

Question 595

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

Answer 595

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

Question 596

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

Answer 596

a counter diffusion at an almost equal molar rate

Question 597

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

Answer 597

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

Question 598

Reverse osmosis is also called

Answer 598

ultrafiltration.

Question 599

Which of the following is not a batch drier?

Answer 599

Fluidised bed drier

Question 600

Steam distillation is not recommended to be used, if the

Answer 600

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

Question 601

Rayleigh equation applies to __________ distillation.

Answer 601

differential

Question 602

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

Answer 602

D^0.5

Question 603

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

Answer 603

porosity

Question 604

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

Answer 604

Reverse osmosis

Question 605

The relative saturation of a partially saturated mixture of vapour and gas can be increased by __________ of the mixture.

Answer 605

increasing the total pressure, reducing the temperature

Question 606

Danckwerts developed the __________ theory.

Answer 606

surface renewal

Question 607

Molecular distillation is

Answer 607

for heat-sensitive materials, very low pressure distillation

Question 608

Drying of a wet solid under constant drying conditions means the exposure of the wet solid to the air of constant

Answer 608

all

Question 609

Which of the following provides maximum contact surface for a liquid-vapour system?

Answer 609

Packed tower

Question 610

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

Answer 610

known

Question 611

In stripping section of continuous distillation column, the

Answer 611

liquid is enriched with high boiler.

Question 612

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

Answer 612

Kg

Question 613

__________ is concerned with the adsorption equilibria.

Answer 613

Freundlich equation

Question 614

Fractional solvent extraction

Answer 614

employs two solvents

Question 615

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 615

at ground level.

Question 616

Raschig ring made of procelain cannot be used for treating concentrated

Answer 616

alkalis

Question 617

H2S present in naphtha reformed gas is removed by absorbing with

Answer 617

ethanolamine

Question 618

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

Answer 618

does not change with time,

Question 619

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 619

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

Question 620

In rectifying section of a continuous distillation column, the

Answer 620

vapour is enriched with high boilers.

Question 621

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 621

increases

Question 622

According to Chilton-Colburn analogy for mass transfer, NSt.NSc2/3 is equal to

Answer 622

f/2

Question 623

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 623

1.24

Question 624

Minimum reflux ratio in a distillation column results in

Answer 624

maximum condenser size.

Question 625

Flooding in a distillation column is detected by a sharp

Answer 625

increase in pressure drop.

Question 626

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

Answer 626

decreases

Question 627

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 627

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

Question 628

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

Answer 628

lower than

Question 629

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

Answer 629

increase

Question 630

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

Answer 630

mole ratio

Question 631

In case of unsaturated air

Answer 631

dew point < wet bulb temperature, wet bulb temperature < dry bulb temperature

Question 632

For a binary mixture with low relative volatility,

Answer 632

an azeotrope may be formed during distillation.

Question 633

Plate efficiency

Answer 633

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

Question 634

Absorption accompanied by heat evolution results in

Answer 634

decrease in equilibrium solubility.

Question 635

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

Answer 635

high pressure drop of the gas.

Question 636

For a distillation column operating at minimum reflux, the

Answer 636

number of plates required will be maximum.

Question 637

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 637

MXo ln(Xo/XF)

Question 638

Flash distillation is suitable for the separation of components

Answer 638

having very wide boiling points.

Question 639

In Mcabe-Thiele method, at infinite reflux ratio

Answer 639

both the operating lines coincide with the diagram.

Question 640

Leaching rate is independent of the

Answer 640

none of these

Question 641

Use of packed towers for distillation is generally limited to the

Answer 641

small sizes.

Question 642

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 642

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

Question 643

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

Answer 643

None of these

Question 644

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

Answer 644

Winkel mann's

Question 645

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

Answer 645

tangential to the equilibrium curve

Question 646

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 646

humidified

Question 647

For absorbing a sparingly soluble gas in a liquid, the

Answer 647

liquid side coefficient should be increased.

Question 648

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

Answer 648

45580

Question 649

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

Answer 649

increases

Question 650

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 650

differential heat of adsorption.

Question 651

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

Answer 651

K ∝sqrt(D)

Question 652

Desulphurisation of petrol is done in a

Answer 652

rotating disc extractor

Question 653

Chemisorption compared to physical absorption has

Answer 653

increased utilisation of stagnant zones of the liquid phase.

Question 654

Rate of adsorption increases as the

Answer 654

temperature decreases.

Question 655

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

Answer 655

acetone chloroform

Question 656

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

Answer 656

0.1

Question 657

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

Answer 657

film

Question 658

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

Answer 658

NSc = NPr = NLe

Question 659

For the gas absorption, the height of a transfer unit, based on the gas phase is given by (G: superficial molar gas velocity, L: superficial molar liquid velocity, FG:mass transfer co-efficient, mols/m2 , a: in-terfacial area per unit volume of tower)

Answer 659

G/FG.a

Question 660

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

Answer 660

Agitated film evaporator

Question 661

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

Answer 661

decrease

Question 662

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

Answer 662

inside

Question 663

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 663

8.89

Question 664

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

Answer 664

(4De/πt)^1/2

Question 665

Reboiler is considered as one theoretical plate, because

Answer 665

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