GATE CH topic:mass-transfer PYQs & Answers — Page 3

Questions 21–30 of 77. Imported answers require independent review unless marked reviewed.

Which one of the given statements is correct with reference to gas-liquid contactors for mass transfer applications?

Your answerChoose one option.

A tray tower is more suitable for foaming systems than a packed tower.

Tray towers are preferred over packed towers for systems requiring frequent cleaning.

For a given liquid flow rate, the gas flow rate in the loading region is greater than that in the flooding region.

Flooding can never occur for counter-current contact.

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A gas stream containing 95 mol% CO

and 5 mol% ethanol is to be scrubbed with pure water in a counter-current, isothermal absorption column to remove ethanol. The desired composition of ethanol in the exit gas stream is 0.5 mol%. The equilibrium mole fraction of ethanol in the gas phase,

, is related to that in the liquid phase,

, as

. Assume CO

is insoluble in water and neglect evaporation of water. If the water flow rate is twice the minimum, the mole fraction of ethanol in the spent water is

Your answerChoose one option.

0.0225

0.0126

0.0428

0.0316

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Sulfur dioxide (SO

) gas diffuses through a stagnant air-film of thickness 2 mm at 1 bar and 30 °C. The diffusion coefficient of SO

in air is

. The SO

partial pressures at the opposite sides of the film are 0.15 bar and 0.05 bar. The universal gas constant is 8.314 J mol

. Assume ideal gas behavior, the steady-state flux of SO

in mol m

through the air-film is

Your answerChoose one option.

0.077

0.022

0.085

0.057

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A simple distillation column separates a binary mixture of

and

. The relative volatility of

with respect to

is 2. The steady-state composition of

in the vapour leaving the 1

, 2

and 3

trays in the rectifying section are 94, 90 and 85 mol%, respectively. For ideal trays and constant molar overflow, the reflux-to-distillate ratio is

Your answerChoose one option.

1.9

2.7

1.2

1.1

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Alumina particles with an initial moisture content of 5 kg per kg dry solid are dried in a batch dryer. For the first two hours, the measured drying rate is constant at 2 kg m

. Thereafter, in the falling-rate period, the rate decreases linearly with the moisture content. The equilibrium moisture content is 0.05 kg per kg dry solid and the drying area of the particles is 0.5 m

per kg dry solid. The total drying time, in h, to reduce the moisture content to half its initial value is

Your answerChoose one option.

4.13

2.55

3.22

5.13

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Consider a tray-column of diameter 120 cm. Each downcomer has a cross-sectional area of 75 cm². For a tray, the percentage column cross-sectional area not available for vapour flow due to the downcomers, rounded off to 1 decimal place, is __________

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Spray dryers have many advantages. Which one of the following is NOT an advantage of a typical spray dryer?

Your answerChoose one option.

Has short drying time

Produces hollow spherical particles

Has high heat efficiency

Is suitable for heat sensitive materials

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A packed distillation column, with vapor having an average molecular weight of 45 kg·mol⁻¹, density of 2 kg·m⁻³ and a molar flow rate of 0.1 kmol·s⁻¹, has a flooding velocity of 0.15 m·s⁻¹. The column is designed to operate at 60 % of the flooding velocity. Which one of the following is the CORRECT value for the column diameter (in m)?

Your answerChoose one option.

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A liquid

containing a dissolved gas

is stripped in a countercurrent operation using a pure carrier gas

. The liquid phase inlet and outlet mole fractions of

are 0.1 and 0.01, respectively. The equilibrium distribution of

between

and

is governed by

, where

and

are the mole fractions of

and

, respectively. The molar feed rate of the carrier gas stream is twice that of the liquid stream. Under dilute solution conditions, the minimum number of ideal stages required is __________ (in integer).

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In a binary gas-liquid system,

is the molar flux of a gas A for equimolar counter diffusion with a liquid B.

is the molar flux of A for steady one component diffusion through stagnant B. Using the mole fraction of A in the bulk of the gas phase as 0.2 and that at the gas-liquid interface as 0.1 for both the modes of diffusion, the ratio of

is equal to _____ (rounded off to two decimal places).

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GATE CH topic:mass-transfer PYQs

Question 24

Question 40

Question 41

Question 42

Question 43

Question 65

Question 23

Question 26

Question 34

Question 35