Mass Transfer

Question: Back-trapping in a distillation column
[A].

increases tray efficiency.

[B].

decreases tray efficiency.

[C].

reduces pressure drop.

[D].

is desirable, as it provides improved vapour-liquid contact.

Answer: Option B

Explanation:

No answer description available for this question.

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

100

[B].

> 100

[C].

< 100

[D].

none of these

Answer: Option B

Explanation:

No answer description available for this question.

Question: Overall efficiency of the distillation column is
[A].

the ratio of number of ideal plates to actual plates.

[B].

the ratio of number of actual plates to ideal plates.

[C].

same as the Murphree efficiency.

[D].

always more than the point efficiency.

Answer: Option A

Explanation:

No answer description available for this question.

Question: Absorption factor method is used to calculate the number of ideal stages, when
[A].

operating line lies above the equilibrium line.

[B].

operating line lies below the equilibrium line.

[C].

both operating and equilibrium lines are parallel.

[D].

pressure drop in the column is very high.

Answer: Option C

Explanation:

No answer description available for this question.

Question: 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
[A].

0.0

[B].

0.2

[C].

0.4

[D].

1.0

Answer: Option C

Explanation:

No answer description available for this question.

Question: As the reflux ratio decreases, the
[A].

separation becomes more efficient.

[B].

number of plates increases.

[C].

column diameter increases.

[D].

none of these.

Answer: Option B

Explanation:

No answer description available for this question.

Question: 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
[A].

1000

[B].

1500

[C].

2000

[D].

2500

Answer: Option A

Explanation:

No answer description available for this question.

Question: 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)
[A].

less number of trays are required.

[B].

composition of the residue remains unchanged.

[C].

more number of trays are required but the residue composition remains unchanged.

[D].

more number of trays are required and the residue composition is more dilute in methanol.

Answer: Option A

Explanation:

No answer description available for this question.

Question: For water-ethanol system, the minimum reflux ratio
[A].

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

[B].

is computed from the intercept of the operating line.

[C].

cannot be computed.

[D].

is the optimum reflux ratio.

Answer: Option A

Explanation:

No answer description available for this question.

Question: 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,
[A].

composition of vapors and that of liquid do not vary throughout the column.

[B].

reboiler load and condenser load are minimum.

[C].

the top and bottom compositions are unchanged with and without total reflux.

[D].

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

Answer: Option D

Explanation:

No answer description available for this question.