Free Mass Transfer Operations MCQs with Answers

• A. Wetted wall
• B. Packed
• C. Plate
• D. Spray

Explanation: Plate columns are generally preferred when the liquid contains suspended solids because trays are less prone to plugging than packed beds.

• A. Agitated vessels
• B. Bubble cap tray towers
• C. Spray towers
• D. Perforated sieve tray towers

Explanation: Spray towers disperse the liquid as droplets into a continuous gas phase, rather than dispersing gas bubbles into liquid.

• A. Minimum number of theoretical plates
• B. Height of the distillation column
• C. Maximum number of ideal plates
• D. Optimum reflux ratio

Explanation: The Fenske equation calculates the minimum number of theoretical stages at total reflux for a specified separation.

• A. Re × Pe
• B. μ/ρDAB
• C. Sh × Pe
• D. Re/Pe

Explanation: The Schmidt number is the ratio of momentum diffusivity to mass diffusivity: Sc = ν/D_AB = μ/(ρD_AB).

• A. Provides poorer contact between the fluids
• B. Gives lower pressure drop
• C. Both A. and B.
• D. Gives higher pressure drop

Explanation: Stacked packing usually gives poorer fluid contact because it can form preferential channels, but it offers a lower pressure drop than…

• A. Is more suitable, if suspended solids are present in fluid streams
• B. Allows installation of cooling coils
• C. Is less costly when built in large sizes/diameters
• D. Incurs smaller pressure drop

Explanation: Packed towers generally have a smaller pressure drop because they provide a relatively open continuous passage for the gas.

• A. None of these
• B. Low velocity
• C. Low freezing point
• D. Low vapour pressure

Explanation: Low vapour pressure and low freezing point are desirable because they reduce solvent loss and prevent solidification.

• A. Leaching
• B. Adsorption
• C. Steam distillation
• D. Multi-component absorption

Explanation: The Langmuir equation describes monolayer adsorption on a surface, assuming a finite number of identical adsorption sites.

• A. Mixer-settler extractor
• B. Rotating-disc contactor
• C. Pulsed column extractor
• D. Bollman extractor

Explanation: Pulsed columns are used for liquid-liquid solvent extraction, including the treatment and separation of radioactive materials.

• A. Line always lies above the equilibrium curve
• B. Line always lies below the equilibrium curve
• C. Line can be either above or below the equilibrium curve
• D. Velocity is more than the loading velocity

Explanation: For absorption, the operating line normally lies above the equilibrium curve on a y-x diagram, providing a positive concentration driving…

• A. Tunnel
• B. Rotary
• C. Tray
• D. None of these

Explanation: A rotary dryer provides continuous movement and contact of granular or crystalline solids with hot gas.

• A. Furfural
• B. Benzol
• C. Butyl acetate
• D. Hexane

Explanation: Butyl acetate is used as an entrainer in azeotropic distillation to facilitate separation of acetic acid and water by altering the…

• A. Leaching
• B. Absorption
• C. Liquid-liquid extraction
• D. Binary phase distillation

Explanation: Binary phase distillation is commonly analysed using steady-state equimolal counterdiffusion, where the molar flow of one component upward…

• A. Total
• B. Minimum
• C. Operating
• D. Maximum permissible

Explanation: At total reflux, no feed or products are withdrawn, so both operating lines reduce to the diagonal y = x.

• A. Are same
• B. Are different
• C. Depend on the humidity of the gas
• D. None of these

Explanation: Equilibrium moisture content depends on the nature of the solid, including its pore structure, composition, and binding of moisture.

• A. Nature of the moisture
• B. Temperature
• C. Nature of the solid
• D. All A., B. and C.

Explanation: Equilibrium vapour pressure over a wet solid is affected by temperature, the moisture or liquid itself, and how that moisture interacts…

• A. Re0.83
• B. Re0.53
• C. Re0.33
• D. Re

Explanation: For turbulent flow in a pipe, common mass-transfer correlations have the form Sh proportional to Re^0.83 Sc^n.

• A. Decreases
• B. Increases
• C. Decreases linearly
• D. Remain unaffected

Explanation: A higher solvent rate provides a larger liquid-side capacity and usually increases the absorption driving force throughout the column.

• A. 0
• B. ∞
• C. 1
• D. < 1

Explanation: At total reflux, the entire overhead product is returned to the column, producing the maximum enriching effect per stage.

• A. Straight line
• B. Slightly concave downward
• C. Slightly concave upward
• D. None of these

Explanation: Because saturation humidity varies nonlinearly with temperature, an adiabatic saturation locus is not exactly straight.