Free Mass Transfer Operations MCQs with Answers

• A. Having very close boiling points
• B. Which form maximum boiling azeotrope
• C. Having very wide boiling points
• D. Which form minimum boiling azeotrope

Explanation: Flash distillation gives only limited separation in a single equilibrium stage, so it is most useful when the components have widely…

• A. f
• B. 1/f
• C. 2f
• D. f/2

Explanation: The Chilton-Colburn analogy equates the mass-transfer j-factor, St_m Sc^(2/3), to half the Fanning friction factor, f/2.

• A. Exponential
• B. Parabolic
• C. Linear
• D. Cubic

Explanation: For diffusion of one ideal gas through a stagnant second gas, integration of the flux equation gives a logarithmic relation in distance…

• A. Thermal diffusion
• B. Adsorption
• C. Reverse osmosis
• D. Absorption

Explanation: Reverse osmosis forces seawater through a semipermeable membrane at pressure greater than its osmotic pressure, allowing water to pass…

• A. Employs only one solvent
• B. None of these
• C. Results in low interfacial tension
• D. Employs two solvents

Explanation: Fractional solvent extraction uses two immiscible solvents and exploits the different distribution of solutes between them.

• A. Plug
• B. Perfectly mixed
• C. Both A. & B.
• D. Neither A. nor B.

Explanation: For plug flow across a plate, the driving force varies along the flow path, and the resulting Murphree efficiency is greater than the…

• A. Increase in flow rate
• B. Sharp drop in pressure drop
• C. Sharp rise in pressure drop
• D. None of these

Explanation: Channelling causes the fluid to bypass much of the packing, reducing the effective wetted area and flow resistance.

• A. 1/D
• B. D
• C. D0.5
• D. D1.5

Explanation: Penetration theory gives a mass-transfer coefficient proportional to the square root of diffusivity, typically expressed as k proportional…

• A. Flash vaporisation
• B. Ordinary distillation
• C. Solvent extraction
• D. Extractive distillation

Explanation: Benzene and cyclohexane have nearly identical boiling points, making ordinary distillation difficult because their relative volatility is…

• A. Pressure drop in the equipment will be very high
• B. equipments
• C. Packing may be crushed due to thermal expansion/contraction of the components of the
• D. Viscosity variation of the fluids may cause channelling/flooding
• E. None of these

Explanation: Large temperature changes can cause packing to expand, contract, or become damaged, disturbing the packed bed and liquid distribution.

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

Explanation: Relative volatility is the ratio of vapour-to-liquid composition ratios, giving α = [y/(1−y)]/[x/(1−x)] = y(1−x)/[x(1−y)].

• A. Number of plates is maximum
• B. Overhead product is maximum
• C. Both the operating lines coincide with the diagram
• D. None of these

Explanation: At infinite reflux, no products are withdrawn, so both rectifying and stripping operating lines approach the diagonal y = x.

• A. Increases tray efficiency
• B. Provides large interfacial surface for mass transfer
• C. Results due to very high gas velocity
• D. Results due to very low gas velocity

Explanation: Weeping occurs when vapour velocity is too low to support the liquid on a tray, allowing liquid to leak through the tray openings.

• A. Perfectly mixed
• B. Plug
• C. Both A. & B.
• D. Neither A. nor B.

Explanation: In a perfectly mixed flow model, the composition is uniform across the tray, so the local point efficiency equals the overall Murphree…

• A. Osmosis
• B. Elution
• C. Reverse osmosis
• D. Sublimation

Explanation: Elution is the removal or desorption of an absorbed solute by passing a solvent through the absorbent.

• A. Increases due to liquid entrainment
• B. Increases due to foaming
• C. Is a function of the mass transfer between liquid and vapour
• D. Increases due to weeping and dumping of liquid

Explanation: Plate efficiency depends on the rates of mass transfer between the liquid and vapour phases, as well as tray hydraulics.

• A. 2
• B. 8
• C. 12
• D. 18

Explanation: Raschig rings used in industrial packed towers commonly have sizes near 2 inches, although several sizes are selected according to the…

• A. Low pressure drop and low hold up
• B. High pressure drop and low hold up
• C. Low pressure drop and high hold up
• D. High pressure drop and high hold up

Explanation: Packed towers are preferred in many applications because packing provides gas-liquid contact with low pressure drop and relatively low…

• A. More than liquid composition
• B. Less than liquid composition
• C. Same as liquid composition
• D. Independent of pressure

Explanation: At an azeotropic composition, the vapour and liquid have the same composition, so ordinary distillation cannot further separate them.

• A. Momentum flux
• B. Kinematic viscosity
• C. Thermal diffusivity
• D. Both B. and C.

Explanation: Mass diffusivity has dimensions of length squared per time, the same as both kinematic viscosity and thermal diffusivity.