Free Mass Transfer Operations MCQs with Answers

• A. Composition of vapors and that of liquid do not vary throughout the column
• B. The top and bottom compositions correspond to the maximum enrichment available
• C. The top and bottom compositions are unchanged with and without total reflux
• D. Reboiler load and condenser load are minimum

Explanation: At total reflux, all condensed overhead liquid is returned and no products are withdrawn, giving the maximum theoretical enrichment for…

• A. Free flowing
• B. Dry
• C. Granular
• D. Sticky

Explanation: Sticky materials adhere to the dryer surfaces and flights, causing agglomeration, poor mixing and blockage.

• A. Bound
• B. Unbound
• C. Critical
• D. None of these

Explanation: Bound moisture is held within the solid or associated with it, so its equilibrium vapour pressure is lower than that of the pure liquid at…

• A. Drum drier
• B. Tray drier
• C. Tunnel drier
• D. Spray drier

Explanation: Tray dryers generally operate as batch units because material is loaded onto trays, dried, and then removed.

• A. Vapors and liquids are at their dew point and bubble point respectively
• B. Driving force for the liquid flow is its specific weight
• C. Driving force for the vapor flow is the pressure drop, as the pressure decreases gradually from
• D. the bottom to the top of the column
• E. Highest temperature is encountered at the top of the column

Explanation: Vapour rises through a distillation column because the pressure is slightly higher at the bottom and decreases toward the top, providing…

• 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.

Explanation: Gilliland's diffusivity correlation gives diffusivity proportional to T^1.5 and inversely proportional to pressure, while also including…

• A. Acetone-carbon disulphide
• B. Toluene-benzene
• C. Water-isobutyl alcohol
• D. None of these

Explanation: Acetone and carbon disulphide form a minimum-boiling azeotrope because their mixture shows positive deviation from Raoult's law, giving a…

• A. Sieve tray
• B. Packed column
• C. Bubble cap
• D. Any of these

Explanation: Small-diameter distillation columns are commonly packed because packing is easier to install and gives lower cost and pressure drop at…

• A. The overall M.T.C. of the system
• B. M.T.C. of individual components in a liquid-liquid system
• C. M.T.C. of liquid in liquid-gas system
• D. Individual mass transfer co-efficient (M.T.C.) in gaseous system

Explanation: A wetted-wall tower provides a known interfacial area and is used to measure individual gas-side or liquid-side mass-transfer…

• A. Rapid absorption rates and good heat transfer characteristics
• B. Improved flooding characteristics
• C. Low pressure drop on pumping
• D. All A., B. and C.

Explanation: Low viscosity improves liquid circulation, absorption rate, heat transfer and pumping, and generally permits better hydraulic operation…

• A. Liquid side mass transfer co-efficient should be increased
• B. Gas side mass transfer co-efficient should be increased
• C. Liquid side mass transfer co-efficient should be decreased
• D. Mass transfer co-efficient must be kept constant

Explanation: For a sparingly soluble gas, the dominant resistance is usually in the liquid film because the dissolved gas must diffuse through the…

• A. Allowable liquid velocity
• B. Allowable gas and liquid velocities
• C. Allowable gas velocity
• D. Feed composition

Explanation: Bubble-cap capacity is limited by both vapour passage through the caps and liquid flow across the tray, so the design depends on allowable…

• A. Selectivity index
• B. Relative volatility
• C. Absorption factor
• D. Murphree efficiency

Explanation: The stripping factor is the ratio of the stripping tendency to the liquid-flow effect, so its reciprocal is the absorption factor.

• A. None of these
• B. Affected much less by temperature than that for gases
• C. Not affected by the temperature
• D. Affected more by temperature than that for gases

Explanation: Liquid-phase diffusivity and mass-transfer coefficients are strongly influenced by temperature because temperature changes liquid…

• A. Schmidt number
• B. Lewis number
• C. Prandtl number
• D. Sherwood number

Explanation: The Lewis number compares thermal diffusivity with mass diffusivity and is central when heat and mass transfer occur together.

• A. Tunnel
• B. Conveyor
• C. Heated cylinder
• D. Festoon

Explanation: Paper webs are commonly passed over a series of steam-heated cylinders, whose hot surfaces evaporate the moisture continuously.

• A. Partial pressure of the vapour to the vapour pressure of the liquid at room temperature
• B. None of these
• C. Actual humidity to saturation humidity
• D. Partial pressure of the vapour to the vapour pressure of the liquid at gas temperature

Explanation: Relative humidity is the ratio of the actual vapour partial pressure to the saturation vapour pressure at the same gas temperature.

• A. That of normal condensation
• B. Integral heat of adsorption
• C. Zero
• D. None of these

Explanation: Near complete surface coverage, the additional molecules occupy sites with adsorption energies approaching those of ordinary condensation.

• A. Physical properties
• B. Chemical properties
• C. Degree of turbulence
• D. Interfacial area

Explanation: Interphase mass transfer is governed mainly by physical properties, turbulence, and interfacial area; chemical properties alone do not…

• A. Greater degree of separation with a fixed number of trays
• B. Increased reboiler load
• C. Increased reflux ratio
• D. None of these

Explanation: The rectifying-line slope increases when the reflux ratio increases, and the stripping-line slope also rises because the internal liquid…