Mass Transfer Flashcards by . .

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

chemical properties

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

0.50

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Fenske equation determines the

minimum number of theoretical plates

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

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

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

Centrifugal extractor

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Total reflux in a distillation operation requires minimum

number of plates

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

+ve

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

relative volatility is reasonably constant.

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

natural

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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).

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

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

Packed

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Overall efficiency of the distillation column is

the ratio of number of ideal plates to actual plates.

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Which is the controlling factor for a drum drier?

Heat transfer

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Drying operation under vacuum is carried out to

reduce drying temperature.

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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

higher relative humidity

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

absorption

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At minimum reflux ratio for a given separation

number of plates is infinity.

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Relative humidity is the ratio of the

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

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

decreases

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

electrical resistance

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

specific heat

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

increase ‘S’ and decrease ‘G’.

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

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Dew point of a gas-vapour mixture

decreases with decrease in pressure.

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Which of the following plays an important role in problems of simultaneous heat and mass transfer ? a. Lewis number b. Schmidt number c. Prandtl number d. Sherwood number

Lewis number

In case of an absorber, the operating

line always lies above the equilibrium curve

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

total cost first decreases and then increases.

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

S1/S2

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?

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

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

Which of the following quantities need not be fixed before starting the design of a co-current absorber? a. Heat gain or loss b. Flow rate of entering liquid c. Flow rate of gas d. None of these

Flow rate of entering liquid

Mass transfer co-efficient of liquid is

affected more by temperature than that for gases.

Absorption accompanied with chemical reaction is exemplified by the absorption of

SO2 in alkaline solution.

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

Multicomponent distillation.

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

Wetted wall column

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

spray chamber

Chemisorption (chemical adsorption) is

an irreversible phenomenon.

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

d. all 'a', 'b' & 'c'.

Raoult's law applies to the

solvents

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

allowable gas and liquid velocities.

In distillation, overhead product contains

any number of components

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

decreases

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

K ∝ D

The McCabe Δ L law states that the

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

Bollman extractor

is used for extraction of oil from oilseed.

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

heat and mass

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

increase

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.

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.

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

vapour pressure of component A to that of component B.

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

elutriation or elution

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

elutriation or elution

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

surface evaporation of unbound moisture occurs.

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%).

71 min

__________ diffusion is used for separating the isotopes of methane.

Thermal

Ordinary diffusion process is also called __________ diffusion

concentration

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.

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

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

c. Rotary dryer is suitable for drying sticky material.

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

low pressure drop and low hold up.

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

>100

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

50%

Raoult's law is applicable to the

ideal solutions

Weeping in a distillation column

results due to very low gas velocity.

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

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

Wetted wall tower experiment determines the

mass transfer co-efficient.

In McCabe-Thiele method, at infinite reflux ratio

the overhead product is minimum.

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

increases

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

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

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

same

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

wetted wall

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

ethyl alcohol-water

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

rotary

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

linearly

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

linearly

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

Sherwood

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

0.215

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

10^-5 to 10^-6

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

its recovery cost by distillation may be prohibitatively high.

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

is greater than

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

litre

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

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)

less number of trays are required.

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

exponential

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

Water-hydrochloric acid.

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

Peclet

The binary diffusivity in gases and liquids vary respectively as

T3/2 and T

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

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

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).

Electrodylsis is used in the manufacture of NaOH.

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.

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

Very tall packed towers are divided into series of beds to

avoid channelling

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

free

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

decreases

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

steam jet ejector with a barometric condenser

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

increased reflux ratio

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

Plate

Deairation (removal of O2) of water is done by

ion-exchange

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.

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

A minimum boiling azeotrope is exemplified by

acetone-carbon disulphide

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

A solution of benzene, toluene and oxylene.

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

decreases pressure drop, increases surface area.

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

both parallel and straight

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

that of normal condensation

Absorption with chemical reaction' is involved in the removal of

carbon dioxide from gaseous stream using alkaline solution.

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

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.

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

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

heated cylinder

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.

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

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

large latent heat

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

raschig

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

infinity

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

infinity

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

infinity

Leaching of sugar from sugar beets is done by

hot water

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

both operating and equilibrium lines are parallel.

Flights in a rotary dryer are provided to

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

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

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

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

none of these

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

0.4

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

The reciprocal of stripping factor is termed as

absorption factor

Ponchan-Savarit method analyses the fractional equipment based on

both enthalpy and material balances

The binary diffusivity in gases at atmospheric conditions is about

10^-1 cm2/sec

Percentage saturation is __________ the relative saturation.

always smaller than

In case of a desorber (stripper), the

operating line always lies below the equilibrium curve.

What is the reflux ratio at total reflux?

Infinity

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

is maximum

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).

10-60

For absorbing a sparingly soluble gas in a liquid

liquid side mass transfer co-efficient should be increased.

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

integral heat of adsorption.

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

total reflux

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

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

In a counter-current liquid extractor

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

In a counter-current liquid extractor

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

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

d. none of these

The wetted wall tower is used to determine

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

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

less

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

greater than that computed for ideality.

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

increases

Prandtl number for water at 20°C is about

Boiling point diagram is

affected by pressure

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

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

Steam distillation is used to

avoid thermal decomposition of a component.

Freundlich equation applies to the adsorption of solute from

dilute solutions, over a small concentration range.

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

marginal decrease in the number of

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

pure component

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

Spray dryer

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

Heating and dehumidification at almost constant wet bulb temperature.

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

S > 1

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

d. none of these

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

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.

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

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.

steam

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

spouted bed

Azeotropic distillation is employed to separate

constant boiling mixture.

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 )

T^2

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

∞

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

Dimension of mass diffusivity is the same as that of

kinematic viscosity

Dorr thickener is an equipment used for

sedimentation

Steam distillation is used to separate

high boiling substances from nonvolatile impurities.

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

q=1

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

Large weight of liquid retained.

Water entrained by circulating air in cooling towers is termed as

drift

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

1000

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

diffusivity of solute increases.

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

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

T^1/2

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

smaller than

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.)

Kc = Kp . RT = Km . RT/p

Leaching of uranium ore and gold ore is done in

Pachuka tanks

Blowdown in a cooling tower

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

Blowdown in a cooling tower

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

Antibiotics are best handled in a

Podbielniak extractor.

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

infinite

_________ extractor uses centrifugal force for separating the two phases.

Podbielniak

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.

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

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

solvent extraction

Design calculation for multiple component distillation is done by

tray to tray calculations.

To get high tray efficiency

interfacial surface between liquid and gas phase should be large.

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

dependent on the Reynolds number

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

d. none of these.

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

d. all 'a', 'b' & 'c'.

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

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

Inside the distillation column, the

driving force for the vapour flow is the pressure drop.

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

decreases

Which of the following is not a continuous drier ?

Tray drier

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

insoluble in the liquid

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

Dew point

Rate of leaching increases with increasing

temperature

An azeotropic mixture is a __________ mixture.

constant boiling point

Pick out the wrong statement. a. In the McCabe-Thiele diagram for binary distillation, vertical feed line represents saturated liquid feed and horizontal feed line represents saturated vapour feed. b. In small columns, local efficiency is larger than Murphree efficiency; in large columns local efficiency is smaller than Murphree efficiency. c. For Laminar flow over a plate of length L, the local mass transfer co-efficient at a distance L from the leading edge is 1.5 x 10-2m/s. Then the average mass transfer co-efficient for the plate is 2 x 102m/s. d. The concentration and hydrodynamic boundary layers over a flat plate are of equal thickness, if Schmidt number is equal to unity.

c. For Laminar flow over a plate of length L, the local mass transfer co-efficient at a distance L from the leading edge is 1.5 x 10-2m/s. Then the average mass transfer co-efficient for the plate is 2 x 102m/s.

Molecular seives are regenerated by heating to __________ °C.

200-330

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

decreases

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

freeze

In extractive distillation, solvent is

added to alter the relative volatility of the mixture.

Radioactive nuclear waste is treated in

pulsed column extractor

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

rotary

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

wet bulb

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 )

__________ equation applies to diffusivities in liquids.

Gilliland

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

incurs smaller pressure drop.

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

Hexane

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

d. none of these

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

through circulation

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

increase

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

agitated vessel

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

a binary mixture.

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

a total condenser is used.

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

gas phase resistance controlled.

As the reflux ratio decreases, the

number of plates increases.

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

Spray towers

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

the fraction vaporised but not the product composition.

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

increases

Which of these columns incurs the lowest pressure drop ?

Packed column (with stacked packing)

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

liquid

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

L/G

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

Wet bulb temperature

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

can lie above or below the equilibrium curve.

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

Packed column (stacked)

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

half

The Knudsen diffusivity is dependent on the

molecular velocity and por radius of the catalyst.

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

flooding

Solvent used in extractive distillation

forms a low boiling azeotrope.

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

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

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.

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

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

- ve

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

both zero and hundred

Back-trapping in a distillation column

decreases tray efficiency.

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.

more than

Milk is dried usually in a __________ dryer.

spray

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

decreases

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

Activated carbon

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

increases

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.

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

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

increasing temperatures both on the surface and within the solid.

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

Solvent extraction

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

d. None of these

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

Agitated vessels

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

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

2.09 x 10-9

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.

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

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

is independent of pressure.

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

p = P

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

Lewis

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

relative volatility

In physical terms, Schmidt number means

momentum diffusivity/mass diffusivity.

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

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

ideal gases

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

penetration

Sand is dried in foundaries in a___drier.

fluidisedbed

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

Mechanical draft cooling tower.

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.

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.

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).

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

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

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

Diameter to height ratio for a rashig ring is

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

pulse column

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

d. all 'a', 'b' & 'c'

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

increases

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

sharp drop in pressure drop.

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

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

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.

The entire amount of C is transferred to solvent B.

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

(KL^2.DA)^1/2

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

1.2 to 1.5

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.

wet bulb temperature

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

dilute solutions and isothermal operation.

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

surface renewal

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

dilute solution and isothermal operation.

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

humidified with wet bulb temperature decreasing.

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

linear

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

momentum diffusivity to the mass dif-fusivity.

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

f = 1

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

repeated coalescence & redispersion of the drop phase.

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

interface

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

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

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

-ve

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 ?

gas side

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

0.5

Swenson-Walker crystalliser is a __________ unit

continuous

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.

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

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

With increase in temperature, the mutual solubility of two liquids

increases

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.

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

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

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

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

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

less than

Lewis number (Le) is

Sc / Pr

Which of the following is not a continuous leaching equipment ?

Pachuka tank

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

Pulsed column

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

equilibrium

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

unbound

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

(1 + Ro) = Ro/Ri

Separation of __________ employs gaseous diffusion process.

isotopes of uranium

For water-ethanol system, the minimum reflux ratio

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

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)

500

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.

lower than

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

mass transfer co-efficient

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.

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

In liquid extraction, if the selectivity is unity, then

no separation will occur.

Paper industry employs __________ driers.

cylinder

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.

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

8.5 x 10-4

Leaching of coarse solid lumps is also termed as

percolation

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

avoid channeling

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

a pure substance

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

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

wetted wall

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

decreases

Mass transfer co-efficient is defined as

Co-efficient = Flux/concentration difference.

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

The relative humidity decreases.

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

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

equal to the heat of wetting.

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.

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

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

1.25 to 2.0

Large scale usage of flash distillation is practised in

petroleum refining

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

thermal decomposition of bottoms.

Alcohol is dehydrated using __________ distillation.

azeotropic

Separation of two volatile liquids by distillation makes use of their

relative volatility

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

tray

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

Butyl acetate

Rotary dryers cannot handle __________ materials.

sticky

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.

d. none of these.

An example of elutioh is

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

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

partial pressure

Relative volatility does not change appreciably with the change in

temperature

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

gas

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

Temperature of the solid

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

d. none of these

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

rotary

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

always lower than

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

bound

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

high reflux ratio

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

high reflux ratio

Detergent solution is dried to a powder in a

spray dryer

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

d. None of these

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

liquid film

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

increasing the gas film co-efficient.

Flooding results in

low tray efficiency

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

water has a high latent heat of evaporation.

In an operating distillation column, the

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

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

D ∝ T1.5

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

Humidification

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

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

d. none of these

The dimension of diffusivity is same as that of the

kinematic viscosity

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

d. none of these

Entrainer used in azeotropic distillation should

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

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

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

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.

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

Leaching of coffee from coffee beans is done by

hot water

For contacting a highly soluble gas with a liquid

bubble the gas through liquid.

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

unbound

Ion exchange process is similar to

adsorption

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,

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

Dryer widely used in a textile industry is __________ dryer.

conveyor

Solvent used in extractive distillation

changes the relative volatility of the original components.

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

increases

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

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

Smoke is an example of

solid dispersed in gas

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

Bone charcoal

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.

total

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

Dry bulb temperature

Drying of a solid involves __________ transfer.

both heat and mass

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

sublimation

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

temperature

Which is not concerned directly with mass transfer ?

Froude number

Removal of __________ exemplifies an adsorption unit operation.

water from petrol

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

Never

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.

increases

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

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

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

perfectly dry

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

minimum

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

Molecular diffusivity of a liquid

increases with temperature.

Henry's law states that the

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

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

dilute ammoniacal liquor

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

Decolouration of yellow glycerene.

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

beginning of falling

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.

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.

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

1/μ

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

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

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

increases

Which of the following is directly concerned with psychrometry ?

Lewis reltionship

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

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

The most efficient cooling tower out of the following is

induced draft

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

baffle

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

d. none of these.

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

Lewis

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

Wetted wall columns

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

more than the wet bulb

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?

Both heating and humidification

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

film

Tower diameter may be decreased by

use of increased tray spacing.

Rayleigh's equation applies to __________ distillation.

differential

Steady state equimolal counter diffusion is encountered in

separation of a binary mixture by distillation.

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 ?

Selectivity

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

increases

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)

log P vs . T

The unit of volumetric diffusivity is

cm2/sec

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

pure component is represented by the apex.

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

wet-bulb

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

The slope of 9-line is determined by the

thermal condition of the feed

In steam distillation, the

product must be immiscible with water.

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 ?

Wet bulb temperature

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

increase

Rose oil is extracted from rose leaves using __________ distillation.

steam

Hypersorption refers to a __________ process.

moving bed adsorption

Extraction of coffee from its seed is done by

leaching

In azeotropic mixture, the equilibrium vapour composition is

same as liquid composition.

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

decreases

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

thermal diffusivity to mass diffusivity.

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

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

more than

Decoction refers to the use of solvent

at its boiling point

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

have very wide boiling points.

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

perfectly mixed

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

0.25

Flooding in a column results due to

high pressure drop

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

Wetted wall tower

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

The mixture exhibits an azeotrope at 101.3 kPa.

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

and dehumidified with decrease in wet bulb temperature.

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

elution

Which of the following operations does not involve leaching ?

Removing nicotine from its water solution by kerosene.

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

liquid extraction

Molecular seives are porous

synthetic zeolites crystals/metal alumino-silicates.

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

rotary

A binary mixture of benzene and cyclohexane is separated by

extractive distillation

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

there is equimolar counter diffusion.

Cox chart is useful in the design of

distillation column

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

d. All ‘a’, ‘b’ & ‘c’.

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

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

long tube

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

plug

Tea percolation employs

leaching

Which of the following assumes constant molal vaporisation and overflow ?

McCabe-Thiele method

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

Selectivity of the solvent used in solvent extraction should be

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

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

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

100

McCabe-Thiele method

uses molal units for material and energy balance.

The film penetration model of mass transfer was enunciated by

Toor and Marchello

The most economical range of absorption factor is

1.25 to 2

Channelling is most severe

in towers packed with stacked packing.

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.

ADDUCTS' and 'CLATHRATES' are used in case of

crystallisation

Adsorption is an unit operation which generally involves __________ systems.

fluid-solid

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

extractive

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

thermal diffusion

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

thermal diffusion

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

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

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

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

d. none of these

Berl saddle made of carbon cannot be used for

oxidising atmosphere

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

0.2

Priming in a distillation column

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

The commonly used solvent in supercritical extraction is

carbon dioxide.

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

Murphree efficiency = point efficiency.

In saturated gas, the

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

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

d. all 'a', 'b' & 'c'.

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

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

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.

18.7

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

d. None of these.

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

decreases

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

unbound

Inside the distillation columns, the

driving force for the liquid flow is its weight.

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

Desirable value of absorption factor in an absorber is

Refractory bricks are usually dried in a __________ dryer.

tunnel

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

Sticky material can be dried in a __________ dryer

tray

Sticky material can be dried in a __________ dryer

tray

Langmuir equation is associated with

adsorption

During the constant rate period of drying of a solid,

surface evaporation of unbound moisture occurs.

At a fixed total pressure, humidity depends only on the

partial pressure of vapour in the mixture.

Flash distillation is

used for multicomponent systems like crude refining.

__________ developed the film theory.

Higbie

For absorbers, high pressure drop results in

high operating cost.

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

Wet bulb temperature

Coffee is prepared from coffee beans by leaching with

hot water

Gaseous diffusion co-efficient increases with increase in the

temperature

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

increases

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

c. component molecules are nonpolar.

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

vacuum

L/mGis the expression for

absorption factor

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

1/P

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

1/P

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

pure gas

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

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

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

d. none of these

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

Stanton number

The Hatta number is important in

gas absorption with chemical reaction.

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

infinite trays and minimum reboiler heat load.

CO2 can be absorbed by

heated charcoal

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

increases in winter

An ideal tower packing should not

hold up large amount of liquid in the packing.

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

Monoethanol amine (MEA)

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

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

< 1 and ≈ 1

Molecular diffusion is caused by the

thermal energy of the molecules.

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

total

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

solubility

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

simple

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

Pachuka tank

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.

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

Equilibrium-moisture curves of different solids

are different

Azeotropism for ethyl alcohol-water system disappears by

decreasing pressure

Degree of freedom for leaching and solvent extraction process is

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

mass transfer co-efficient.

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 ?

Bamboo

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

gas

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

truck/tunnel.

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

liquid extraction

When the solvent dissolves very little of solute, then

large quantity of solvent is required to extract the solute.

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

4.605

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

and equilibrium lines are parallel.

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.

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

Steady state equimolal counter diffusion occurs in case of

binary phase distillation

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

Nsh = 2

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

d. none of these.

The adiabatic saturation curve for a vapour-gas mixture is

slightly concave upward.

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.

d. Zirconia probe is used for the humidity measurement.

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

∞

Drift in a cooling tower is

the water entrained by the circulating air.

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

decreases

Small dia distillation column can be a

packed column

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

_________ column is used in gas absorption process.

Packed

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

at < 100

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.

Vanderwall adsorption is also called chemisorption.

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

∞

Batch tray dryers suffers from the disadvantage of

high labour cost & low heat economy.

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

>8:1

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

Bubble

Penetration model (theory) for mass transfer was enunciated by

Higbie

Surface renewal model of mass transfer was enunciated by

Danckwerts

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

temperature rises

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

Re^0.83

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

temperature rises.

Unit of molal diffusivity is

gm moles/cm. sec

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

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

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

a counter diffusion at an almost equal molar rate

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

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

Reverse osmosis is also called

ultrafiltration

Which of the following is not a batch drier?

Fluidised bed drier

Steam distillation is not recommended to be used, if the

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

Rayleigh equation applies to __________ distillation.

differential

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

D^0.5

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

porosity

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

Reverse osmosis

Danckwerts developed the __________ theory.

surface renewal

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

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

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

Packed tower

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

known

In stripping section of continuous distillation column, the

liquid is enriched with high boiler.

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

__________ is concerned with the adsorption equilibria.

Freundlich equation

Fractional solvent extraction

employs two solvents

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

at ground level.

Raschig ring made of procelain cannot be used for treating concentrated

alkalis

H2S present in naphtha reformed gas is removed by absorbing with

ethanolamine

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

does not change with time,

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.

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

In rectifying section of a continuous distillation column, the

vapour is enriched with high boilers.

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

increases

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

f/2

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

1.24

Minimum reflux ratio in a distillation column results in

maximum condenser size.

Flooding in a distillation column is detected by a sharp

increase in pressure drop.

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

decreases

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.

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

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

lower than

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

increase

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

mole ratio

For a binary mixture with low relative volatility,

an azeotrope may be formed during distillation.

Plate efficiency

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

Absorption accompanied by heat evolution results in

decrease in equilibrium solubility.

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

high pressure drop of the gas.

For a distillation column operating at minimum reflux, the

number of plates required will be maximum.

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))

MXo ln(Xo/XF)

Flash distillation is suitable for the separation of components

having very wide boiling points.

In Mcabe-Thiele method, at infinite reflux ratio

both the operating lines coincide with the diagram.

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

d. none of these

Use of packed towers for distillation is generally limited to the

small sizes.

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.

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

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

d. None of these

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

Winkel mann's

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

tangential to the equilibrium curve

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

humidified

For absorbing a sparingly soluble gas in a liquid, the

liquid side coefficient should be increased.

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

10-15

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

increases

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

differential heat of adsorption.

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

K ∝D^1/2

Desulphurisation of petrol is done in a

rotating disc extractor

Chemisorption compared to physical absorption has

increased utilisation of stagnant zones of the liquid phase.

Rate of adsorption increases as the

temperature decreases.

Pick out the system with maximum boiling azeotrope at 1 atm

acetone chloroform

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

0.1

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

film

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

NSc = NPr = NLe

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

Agitated film evaporator

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

decrease

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

inside

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)

8.89

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

(4De/πt)^1/2

Reboiler is considered as one theoretical plate, because

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

Reboiler is considered as one theoretical plate, because

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