Mass Transfer MCQs

167. Relative humidity is the ratio of the

Partial pressure of the vapour to the vapour pressure of the liquid at room temperature
Partial pressure of the vapour to the vapour pressure of the liquid at gas temperature
Actual humidity to saturation humidity
None of these
✅ The correct answer is option B.

169. 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 At some point of time, the operation is shifted to total reflux condition (i.e., no product and residue are being withdrawn and feed to the column is stopped).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,

Composition of vapors and that of liquid do not vary throughout the column
Reboiler load and condenser load are minimum
The top and bottom compositions are unchanged with and without total reflux
The top and bottom compositions correspond to the maximum enrichment available
✅ The correct answer is option D.

170. In an operating distillation column, the

Vapors and liquids are at their dew point and bubble point respectively
Driving force for the liquid flow is its specific weight
Driving force for the vapor flow is the pressure drop, as the pressure decreases gradually from the bottom to the top of the column
Highest temperature is encountered at the top of the column
✅ The correct answer is option C.
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