IndiaBIX Chemical Engineering: Mass Transfer Section 5

incurs smaller pressure drop.

A packed tower compared to a plate tower for a particular mass transfer operation incurs smaller pressure drop. allows installation of cooling coils. is less costly when built in large sizes/diameters. is more suitable, if suspended solids are present in fluid streams.

constant boiling point

An azeotropic mixture is a __________ mixture. binary ternary constant boiling point none of these

number of plates increases.

As the reflux ratio decreases, the separation becomes more efficient. number of plates increases. column diameter increases. none of these.

both (a) and (b)

Capacity of a rotary dryer depends on its r.p.m inclination with ground surface both (a) and (b) neither (a) nor (b)

both 'a '& 'b'

Diffusion in concentrated solutins differs from that in dilute solutions, because of the change in the __________ with the concentration of the solution. degree of ideality viscosity both 'a '& 'b' neither 'a' nor 'b'

both (a) and (b).

Diffusivity in concentrated solutions differs from that in dilute solutions, because of the changes in viscosity with concentration. degree of ideality of the solution. both (a) and (b). neither (a) nor (b).

can lie above or below the equilibrium curve.

For stripping of a gas in a counter current stripper, the operating line lies above the equilibrium curve. lies below the equilibrium curve. can lie above or below the equilibrium curve. is always parallel to the equilibrium curve.

increase

For the same system, if the same liquid used in an absorber is decreased, the tower height will increase decrease remain unaffected decrease or increase ; depends on the type of liquid

freeze

Heat sensitive materials like certain pharmaceuticals and food stuffs can be dried in a/an __________ dryer. indirect tray spray freeze none of these

insoluble in the liquid

Humidification involves mass transfer between a pure liquid phase and a fixed gas, which is insoluble in the liquid soluble in the liquid non-ideal in nature at a fixed temperature

agitated vessel

Hydrogenation of oil is carried out in a/an __________ in Vanaspati manufacturing plant. agitated vessel sieve tray column bubble cap column packed tower

L/G

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 G/L always < 1 none of these

decreases

In a counter-current extractor, as the axial mixing increases, the extraction efficiency increases decreases remains unchanged depends on the pressure of the system

none of these

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

gas phase resistance controlled.

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 liquid phase resistance-controlled. gas phase resistance controlled. impossible. driven by a non-linear driving force.

Ri = Re/(1+Re)

In continuous distillation, the internal reflux ratio (Ri) and the external reflux ratio (Re) are related as Ri = Re/(1-Re) Ri = (1-Re)/Re Ri = Re Ri = Re/(1+Re)

a total condenser is used.

In distillation column design, the McCabe-Thiele procedure is inadequate and a Ponchan-Savarit procedure is needed, when saturated feed is not used. an azeotrope forms. the latent heat of vaporisation of the more and less volatile components are greatly different. a total condenser is used.

added to alter the relative volatility of the mixture.

In extractive distillation, solvent is added to alter the relative volatility of the mixture. of high volatility. present in overhead stream. of high viscosity to give high tray efficiency.

liquid

In the desorption of highly soluble gas from the liquid, the main resistance will be in the __________ phase. gas liquid both (a) & (b) neither (a) nor (b)

driving force for the vapour flow is the pressure drop.

Inside the distillation column, the driving force for the vapour flow is the pressure drop. liquids are not always at their bubble points. pressure increases gradually from bottom to the top of the column. none of these

through circulation

Large quantity of silica gel is normally dried in a __________ dryer. freeze through circulation rotary vacuum tray

rotary

Large scale drying of sugar is done in a __________ dryer. spouted bed tray rotary truck

flooding

Minimum possible diameter of a packed coloumn is decided mainly by the flooding gas viscosity liquid density liquid hold up

200-330

Molecular seives are regenerated by heating to __________ °C. < 150 200-330 > 500 > 1000

decreases

Occurrence of 'case hardening' during drying of a high moisture solid cake __________ the drying rate. increases decreases does not affect exponentially increases

the fraction vaporised but not the product composition.

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 product composition but not the fraction vaporised. the product composition as well as the fraction vaporised. the fraction vaporised but not the product composition. neither the product composition nor the fraction vaporised.

half

Operating velocity in a packed tower is usually __________ the flooding velocity. half twice equal to more than

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

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

pulsed column extractor

Radioactive nuclear waste is treated in mixer-settler extractor rotating-disc contactor pulsed column extractor Bollman extractor

temperature

Rate of leaching increases with increasing temperature viscosity of solvent pressure size of the solid

a binary mixture.

Sides of equilateral-triangular co-ordinates (on which ternary liquid system is plotted) represent a pure component. a binary mixture. a ternary mixture. partially miscible ternary system.

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

Solvent extraction is the terminology applied to the liquid-liquid extraction, which is preferred for the separation of the components of liquids, when extracting solvent is cheaply & abundantly available. one of the liquid components is heat sensitive. viscosity of liquid components is very high. one of the liquid components has very high affinity towards the solvent.

forms a low boiling azeotrope.

Solvent used in extractive distillation is of low volatility. forms a low boiling azeotrope. forms a high boiling azeotrope. does not alter the relative volatility of the original components.

both (a) and (b)

Stage efficiency in a leaching process depends on the time of contact between the solid and the solution rate of diffusion of the solute through the solid and into the liquid both (a) and (b) vapour pressure of the solution

molecular velocity and por radius of the catalyst.

The Knudsen diffusivity is dependent on the molecular velocity only. pore radius of the catalyst only. molecular mean free path only. molecular velocity and por radius of the catalyst.

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

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

T

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 ) sqrt(T) T T^1.5 T^3

stready state diffusion for stagnant case.

The equation, NA = (DAB * Pt / R * T *Z * PBM) * (PA1 - PA2) is for Fick's second law of diffusion. stready state diffusion for stagnant case. liquid M.T.C. by Higbie penetration theory. none of these.

steady state equimolar counter diffusion

The equation, NA = (DAB * Pt / R * T *Z) * (y1 - y2) is for steady state equimolar counter diffusion Fick's first law of diffusion steady state diffusion for stagnant case liquid M.T.C. by penetration theory.

Spray towers

Which of the following equipments is not used for gas dispersion ? Agitated vessels Bubble cap tray towers Perforated sieve tray towers Spray towers

Tray drier

Which of the following is not a continuous drier ? Drum drier Spray drier Tunnel drier Tray drier

Hexane

Which of the following is the most commonly used leaching solvent in vegetable oil industry ? Phenol Hexane Furfurol Liquid SO2

Wet bulb temperature

Which of the following remains constant during evaporative cooling process with recirculated water supply ? Relative humidity Partial pressure of vapour Wet bulb temperature None of these

Packed column (stacked)

Which of the following same diameter columns gives lowest pressure drop per unit height ? Bubble-cap column Sieve-plate column Packed column (stacked) Randomly packed column

Packed column (with stacked packing)

Which of these columns incurs the lowest pressure drop ? Packed column (with stacked packing) Packed column (with dumped packing) Bubble plate column Pulse column

increases

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 decreases remains unchanged increases decreases exponentially

Gilliland

__________ equation applies to diffusivities in liquids. Gilliland Hirschfelder Wilke and Chang none of these

Dew point

__________ 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 Bubble point Dry bulb temperature Wet bulb temperature

Wet bulb

__________ temperature is the steady state temperature attained by a small amount of liquid evaporating into a large quantity of unsaturated gas-vapor mixture. Dry bulb Wet bulb Dew point none of these

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

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