Mass Transfer Quiz 8

1 / 50

Paper industry employs ________ driers?

Cylinder

Spray

Rotary

Fluidised bed

2 / 50

Overall efficiency of the distillation column is _______?

Same as the Murphree efficiency

The ratio of number of ideal plates to actual plates

The ratio of number of actual plates to ideal plates

Always more than the point efficiency

3 / 50

Pick out the correct statement ?

Dialysis process is used for the production of fresh water from brine

Electrodialysis is used in the manufacture of NaOH

Electrodialysis is used for the refining/purification of petrol

Both B. and C.

4 / 50

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__________?

More readily done in the second case compared to first one

None of these

Not possible in the second case unless vacuum is applied

Not possible in the second case unless high pressure is applied

5 / 50

Pick out the wrong statement ?

Decrease in Murphree plate efficiency is an indication of entrainment in distillation column

The capacity of a distillation column is maximum at total reflux

With increase in pressure, the solubility of gases in solvent increases at a fixed temperature

In solvent extraction, the distribution co-efficient should be as large as possible for solvent economy

6 / 50

Pick out the wrong statement?

?Elution? means the desorption of the adsorbed solute by a solvent

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

In case of a packed tower, the operating velocity is about half of the flooding velocity, generally

Change in barometric pressure does not affect the relative humidity

7 / 50

Pick out the wrong statement ?

When Henry?s law constant is very small, then the mass transfer rate is controlled by the gas film resistance

Sieve tray towers are generally used for systems having low interfacial tension

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

Taylor-Prandtl analogy for heat and mass transfer considers the transfer through both laminar and turbulent layers

8 / 50

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

Low volatility is adsorbed in preference to a gas of high volatility

Higher molecular weight is adsorbed in preference to a gas of low molecular weight

High critical temperature is adsorbed in preference to a gas of low critical temperature

None of these

9 / 50

Paper industry employs ______ driers ?

Spray

Cylinder

Rotary

Fluidised bed

10 / 50

Penetration theory states that the mass transfer co-coefficient is equal to (where, De is diffusivity and ?t? is time) ?

(De/t)1/2

(De.t)1/2

(4De/?t)1/2

(4De/t)

11 / 50

Pick out the correct statement?

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

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

Kremser-Brown-Souder?s equation is used to calculate the efficiency of a plate tower

The slope of the stripping line is always less than unity

12 / 50

Pick out the correct statement ?

Higher hold up of the solid in the rotary dryer results in better exposure of the solids to the gas

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

Total reflux in case of distillation operation requires infinite number of plates for a binary system separation

The ?Hatta number? is important in problems involving gas absorption without chemical reaction

13 / 50

Pick out the wrong statement ?

?Cascade? means a group of stages interconnected so that various streams flow from one to another

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

Cellulose acetate membranes are used in dialysis process

Zirconia probe is used for the humidity measurement

14 / 50

Pick out the wrong statement ?

Even a forced draft cooling tower cannot cool water below the wet bulb temperature

Total condenser or reboiler is considered equivalent to one theoretical plate in McCabe-Thiele method of theoretical plate calculation for distillation column

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

Different solids have different equilibrium moisture curves

15 / 50

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

K ??D

K ?D2

K ?D1.5

K ?D

16 / 50

Percentage saturation is ________ the relative saturation?

None of these

Always smaller than

Always greater than

Not related to

17 / 50

Pick out the wrong statement pertaining to leaching ?

Door classifier can be used for leaching of coarse solids

Very high temperature is not needed for the leaching of sugar beet

Vegetable seeds can be leached in either of Bollman extractor, Rotocel or Kennedy extractor

Fine solids cannot be leached in a Pachuca tank

18 / 50

Physical absorption is___________?

An irreversible phenomenon

Both B. and C.

Accompanied by evolution of heat

A reversible phenomenon

19 / 50

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

(1 ? Ri) = Ro/Ri

(1 ? Ro) = Ro/Ri

(1 + Ri) = Ro/Ri

(1 + Ro) = Ro/Ri

20 / 50

Pick out the wrong statement ?

With decrease in feed temperature, the number of plates required for binary distillation decreases for a given ?L/V? ratio

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

Vander wall adsorption is also called chemisorption

Natural draft cooling towers are made of ferroconcrete and its cross-section is wider at the bottom

21 / 50

Pick out the wrong statement?

An Azeotropic mixture of two liquids has boiling point higher than either of them, when it shows negative deviation from Raoult?s Law

The Lewis number of a mixture is unity, when the thermal diffusivity is equal to the mass diffusivity

The mass diffusivity, the thermal diffusivity and the eddy momentum diffusivity are the same for NSc = NPr= 1

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

22 / 50

Pick out the wrong statement ?

Change in barometric pressure does not affect the relative humidity

In case of a packed tower, the operating velocity is about half of the flooding velocity, generally

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

?Elution? means the desorption of the adsorbed solute by a solvent

23 / 50

Pick out the wrong statement?

Packed towers are preferred over plate towers for handling corrosive and foamy liquids

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

Diameter of randomly packed tower is normally more than 1.2 metres

Due to uneven supply and improper distribution of liquid, problem of channelling, loading & flooding is generally encountered in packed towers

24 / 50

Pick out the wrong statement?

Separation of components is not possible in liquid extraction, if selectivity is unity

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

A sharp increase in pressure drop gives an indication of the flooding in a distillation column

Critical moisture content is not a property of the material itself

25 / 50

Pick out the correct statement?

Bound moisture is removed during constant rate drying period

Free moisture is removed during falling rate drying period

The sum of free moisture and equilibrium moisture in a solid is called the critical moisture

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

26 / 50

Pick out the correct statement ?

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

For identical gas flow rates, less pressure drop occurs through a plate tower than through a packed tower

For the same duty, plate columns weigh less than packed columns

All A., B. and C.

27 / 50

Pick out the wrong statement?

Mass transfer co-efficient does not account for gas-liquid diffusion

Diffusion co-efficient and mass transfer co-efficient are not same in any mass transfer operation

Contacting cold liquid with warm vapor-gas mixture exemplifies dehumidification process

Contacting cold vapor-gas mixture with hot liquid exemplifies humidification process

28 / 50

Pick out the wrong statement ?

Freeze drying is used for the drying of fish

Reboiler is not used in open steam distillation

The separation of solutes of different molecular sizes in a liquid solution by use of a suitable membrane is called dialysis

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

29 / 50

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

Component molecules are non-polar

Size of component molecules are not equal

Attractive forces between like and unlike molecules in the solution are approximately equal

Chemical combination or molecular association between unlike molecules takes place in the formation of solution

30 / 50

Pick out the wrong statement ?

The mole fraction of solute is directly proportional to the molality of a ?dilute? solution

The relative volatility of a binary mixture at the Azeotropic composition is 1

Azeotropes obey Raoult?s law at all temperature

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

31 / 50

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

Perforated tray

Packed

Bubble cap

Wetted wall

32 / 50

Pick out the wrong statement ?

In the absorption of low solubility gases, the liquid film is the controlling resistance

Absorption factor is constant, when the equilibrium and operating lines are straight

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

In case of an absorber, the operating line is always above the equilibrium curve

33 / 50

Pick out the correct statement?

Diffusivity increases with the size of the individual molecule

None of these

Diffusivity increases with increase in molecular weight

Diffusivity decreases with increase in temperature

34 / 50

Pick out the wrong statement pertaining to the rotary dryer ?

Hold up of a rotary drier is defined as the fraction of the dryer volume occupied by the solid at any instant. The best performance for rotary drier is obtained, when the hold up is in the range of 0.05 to 0.15

Recommended peripheral speed of a rotary drier is in the range of 10 to 30 metres/minute

Flights (located in the inside shell of rotary dryer) lift the material being dried and shower it down through the current of hot air/gases. It extends from the wall to a distance which is about 8-12% of the inside diameter of shell

Rotary dryer is suitable for drying sticky material

35 / 50

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

Hydrochloric acid-water

All A., B. and C.

Benzene-toluene

Ethyl alcohol-water

36 / 50

Pick out the correct statement ?

Flash distillation is suitable for separating components which have very close boiling temperature

Solvent used in extractive distillation should be of high volatility

A sharp decrease in pressure drop is an indication of flooding in a distillation coloumn

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

37 / 50

Pick out the wrong statement ?

The relative volatility of a binary mixture at Azeotropic composition is unity

Constant pressure distillation cannot separate an Azeotropic mixture

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

Flash distillation is practised on wide spread scale in petroleum refinery

38 / 50

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

Sherwood number in mass transfer is analogous to Nusselt number in heat transfer

Reynolds number remains the same in both heat and mass transfer

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

Prandtl number in heat transfer is analogous to Schmidt number in mass transfer

39 / 50

Pick out the wrong statement pertaining to the cooling towers ?

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

In case of induced draft cooling tower, the fan is placed at the top of the tower

Effectiveness of forced draft cooling tower is reduced by the recirculation of the humid and hot discharged air

A natural draft cooling tower is recommended to be used, when the air humidity is low and air temperature is also low

40 / 50

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

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

Prandtl number in heat transfer is analogous to Schmidt number in mass transfer

Reynolds number remains the same in both heat and mass transfer

Sherwood number in mass transfer is analogous to Nusselt number in heat transfer

41 / 50

Penetration model (theory) for mass transfer was enunciated by _______?

Kissinevskii

Toor and Marcello

Danckwerts

Higbie

42 / 50

Pick out the correct statement ?

With increase in temperature, the selectivity of the solvent used in solvent extraction decreases

In case of liquid-liquid extraction, no separation is possible, if the selectivity of the solvent used is unity

All A., B. and C.

The selectivity of solvent used in solvent extraction is unity at the plait point

43 / 50

Pick out the wrong statement?

Particles movement from higher concentration to lower concentration takes place in diffusion process

The binary diffusivity in liquids is of the order of 10-5 cm2/sec

According to Poiseuille?s law, the permeability decreases with increase in temperature for flow of a gas through a given capillary

Molecular diffusion in solid is much faster than that in liquids

44 / 50

Pick out the wrong statement ?

A horizontal line on the humidity chart indicates the temperature changes at constant molal humidity

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

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

For unsaturated air-water vapor mixture at atmospheric conditions, the wet bulb temperature & adiabatic cooling lines are the same

45 / 50

Pick out the wrong statement?

In small columns, local efficiency is larger than Murphree efficiency; in large columns local efficiency is smaller than Murphree efficiency

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 ? 10-2m/s. Then the average mass transfer co-efficient for the plate is 2 ? 10-2m/s

In the McCabe-Thiele diagram for binary distillation, vertical feed line represents saturated liquid feed and horizontal feed line represents saturated vapour feed

The concentration and hydrodynamic boundary layers over a flat plate are of equal thickness, if Schmidt number is equal to unity

46 / 50

Pick out the wrong statement ?

In case of gas absorption, HETP is equal to HTU, when both the operating line & the equilibrium lines are parallel

Hatta number is important in case of gas absorption with chemical reaction

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

In actual practice, absorption is an endothermic process, while stripping is an exothermic process

47 / 50

Pick out the wrong statement?

The binary diffusivity in liquids is of the order of 10-5 cm2/sec

Molecular diffusion in solid is much faster than that in liquids

Particles movement from higher concentration to lower concentration takes place in diffusion process

According to Poiseuille?s law, the permeability decreases with increase in temperature for flow of a gas through a given capillary

48 / 50

Pick out the wrong statement pertaining to the cooling towers ?

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

In case of induced draft cooling tower, the fan is placed at the top of the tower

A natural draft cooling tower is recommended to be used, when the air humidity is low and air temperature is also low

Effectiveness of forced draft cooling tower is reduced by the recirculation of the humid and hot discharged air

49 / 50

Packed column distillation is limited to the column ______ metres?

Both A. & B.

Diameter < 0.6

Neither A. nor B.

Height < 6

50 / 50

Perforated plate towers are unique for solvent extraction because, they provide_______?

None of these

Better contact of the phase

Higher contact area

Repeated coalescence & redispersion of the drop phase

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