Free Mass Transfer Operations MCQs with Answers
669 Mass Transfer Operations MCQs from Chemical Engineering, each with the correct answer and a written explanation of why it is correct. Free and unlimited, with no account needed.
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669 questions · page 7 of 34
- A. 5
- B. 15
- C. 7.5
- D. 50
Explanation: For large industrial distillation columns of about 3 to 6 m diameter, round bubble caps are commonly sized near 15 cm.
Correct answer: 15- A. 2-3
- B. 20-25
- C. 10-15
- D. 5-8
Explanation: Liquid redistributors in packed towers are commonly installed after about 5 to 8 column diameters, with 6 m used as the maximum spacing…
Correct answer: 5-8- A. 0.1 to 0.3
- B. 0.6 to 0.7
- C. 0.85 to 0.95
- D. 1.5 to 2
Explanation: Distillation columns normally operate below flooding, commonly at about 60 to 70% of the flooding vapor velocity for non-foaming systems.
Correct answer: 0.6 to 0.7- A. Plate spacing
- B. Depth of liquid above the bubble cap slots
- C. All A., B. and C.
- D. Vapour velocity in the volume between the plates
Explanation: Entrainment depends on tray geometry and operating conditions: plate spacing and liquid depth affect droplet carryover, while vapour…
Correct answer: All A., B. and C.- A. Number of theoretical plates
- B. Static submergence
- C. Length of straight rectangular weir on cross-flow tray
- D. Allowable vapour velocity
Explanation: Column diameter is governed by the vapour-handling capacity of the tower, so the allowable vapour velocity is used to determine its…
Correct answer: Allowable vapour velocity- A. < 7
- B. < 30
- C. > 7 20 < 50
Explanation: Liquid distribution becomes difficult when the tower diameter is less than about seven times the packing diameter, because too few packing…
Correct answer: < 7- A. 1 to 2
- B. 4 to 10
- C. 10 to 20
- D. 20 to 30
Explanation: Rotary dryers are generally long, slowly rotating cylinders, with length-to-diameter ratios commonly around 4 to 10.
Correct answer: 4 to 10128. "A claming section" before the liquid flows into the downcomer is provided to__________________?
- A. Ensure better vapour-liquid contact
- B. Reduce the discharge fluctuation
- C. Permit release of entrained vapour in the liquid
- D. Cool the liquid before it flows down
Explanation: A calming section gives entrained vapour bubbles time and space to disengage from the liquid before the liquid enters the downcomer.
Correct answer: Permit release of entrained vapour in the liquid- A. 0.5 to 1.5
- B. 10 to 15
- C. 5 to 10
- D. 2.5 to 4.0
Explanation: Sieve-tray hole pitch is typically about 2.5 to 4 times the hole diameter, giving adequate open area without making the perforations so…
Correct answer: 2.5 to 4.0- A. Raschig rings
- B. Cross-partition rings
- C. Raschig rings
- D. All give the same value
Explanation: Cross-partition rings provide greater wetted surface area and improved gas-liquid contact than ordinary Raschig rings, giving higher…
Correct answer: Cross-partition rings- A. Size, shape, orientation and surface of the packing particles
- B. Density and viscosity of fluids
- C. All A., B. and C.
- D. Fluid flow rates
Explanation: Packed-tower pressure drop depends on packing geometry and surface, fluid density and viscosity, and gas-liquid flow rates.
Correct answer: All A., B. and C.- A. -q
- B. -q/(1-q)
- C. -q/(q-1)
- D. None of these
Explanation: The q-line equation has slope q/(q-1), which is equal to -q/(1-q). Thus option b represents the usual negative-slope form when q is…
Correct answer: -q/(1-q)- A. Resistance offered to flow of liquids by caps & risers and the flow of gas
- B. Low gas velocity
- C. Large plate spacing
- D. Large reflux ratio
Explanation: Liquid gradient develops as liquid flows across the tray and loses head because of resistance from caps, risers, and the opposing gas…
Correct answer: Resistance offered to flow of liquids by caps & risers and the flow of gas- A. Flow rates of each fluid
- B. All A, B. & C.
- C. Concentration of each fluid
- D. Type and size of packing
Explanation: HETP is an experimental packing-performance measure affected by fluid flow rates, packing type and size, and the fluid concentrations or…
Correct answer: All A, B. & C.135. The most common standard size of bubble caps used in industrial operation is___________________?
- A. 1″ dia cap with 0.5″ dia riser
- B. 8″ dia cap with 1″ dia riser
- C. 6″ dia cap with 4″ dia riser
- D. 4″ dia cap with 8″ dia riser
Explanation: A standard industrial bubble cap is commonly about 6 inches in diameter with a 4-inch riser.
Correct answer: 6″ dia cap with 4″ dia riser- A. CO2
- B. SO2
- C. None of these
- D. NH3
Explanation: Ammonia is highly soluble in water, so the liquid-side resistance is small and the gas-film resistance controls the overall absorption…
Correct answer: NH3- A. 0
- B. ∞
- C. 1
- D. Minimum
Explanation: The rectifying-line slope is R/(R+1), where R is the reflux ratio. This approaches unity only as R becomes infinite, corresponding to…
Correct answer: ∞- A. 4-8
- B. 17-34
- C. 52-68
- D. 88-105
Explanation: Commercial packed scrubbers are commonly designed for a pressure drop of about 17 to 34 mm water per metre of packing.
Correct answer: 17-34- A. 10
- B. 50
- C. 100
- D. 200
Explanation: Bubble caps for large distillation columns commonly have diameters of about 100 mm.
Correct answer: 100140. Optimum reflux ratio in a continuous distillation column is determined by the__________________?
- A. Maximum permissible vapour velocity
- B. Flooding limit of the column
- C. None of these
- D. Total cost consideration (fixed cost of the column plus the cooling water & steam cost)
Explanation: The economic optimum reflux is where annual fixed cost and operating costs are balanced.
Correct answer: Total cost consideration (fixed cost of the column plus the cooling water & steam cost)