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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- A. Rate of adsorption is controlled by the resistance to surface reaction
- B. Quantity adsorbed per unit mass is higher
- C. Activation energy is very high
- D. Heat of adsorption is very large
Explanation: Physical adsorption involves weak intermolecular forces, commonly permits multilayer adsorption, and has a relatively low heat of…
Correct answer: Quantity adsorbed per unit mass is higher42. Saturated molal absolute humidity of the vapor-gas mixture depends upon the______________________?
- A. Vapor pressure at dry bulb temperature
- B. Both A. and B.
- C. Total pressure
- D. Neither A. nor B.
Explanation: For a saturated vapor-gas mixture, humidity depends on the saturation vapor pressure of the vapor at the dry-bulb temperature and on total…
Correct answer: Both A. and B.- A. Mixing
- B. Wetting
- C. Adsorption
- D. None of these
Explanation: An Othmer chart correlates adsorption data and is used to estimate the heat of adsorption.
Correct answer: Adsorption- A. Maintenance cost for valve and sieve trays are comparatively more than bubble cap tray due to their relatively complicated construction features
- B. Murphree efficiency of all the three trays are nearly equal, however the peak efficiency is generally higher for sieve and valve trays than the bubble cap
- C. Bubble cap trays though most expensive are the best in situations, where low vapour rates is to be handled and a positive liquid seal is essential at all flow rates
- D. Valve trays have the highest turn down ratio (i.e. the ratio of the highest to the lowest vapour flow rates) and thus provide the maximum flexible operating range
Explanation: Bubble-cap trays are the most mechanically complicated and therefore usually have higher construction and maintenance costs than sieve or…
Correct answer: Maintenance cost for valve and sieve trays are comparatively more than bubble cap tray due to their relatively complicated construction features- A. An increased weir height improves the tray efficiency at the cost of high plate pressure drop; optimum wear height being 40-90 mm for column pressure above atmospheric and 6-12 mm for vacuum columns
- B. For segmental downcomers, the chord length is 60-80% of the column diameter. An initial value of downcomer area of 12% is taken in the design
- C. Width of the calming section provided at the inlet and outlet sides of the plate is 75 mm for column diameter below 1.5 metres and 100 mm for larger diameter columns
- D. Minimum recommended downcomer residence time for the disengagement of entrained vapour is the same for both foaming and non-foaming liquids, which is about 20 seconds
Explanation: Downcomer residence time cannot be the same for foaming and non-foaming liquids because foaming systems require additional disengagement…
Correct answer: Minimum recommended downcomer residence time for the disengagement of entrained vapour is the same for both foaming and non-foaming liquids, which is about 20 seconds- A. Distillation under vacuum is a substitute for steam distillation
- B. In differential (simple) distillation, the vapour is removed as soon as it is formed without appreciable condensation
- C. Flash distillation, differential distillation & steam distillation are all continuous distillation processes
- D. In flash (equilibrium) distillation, a definite fraction of liquid is vaporised in such a way that the evolved vapour & residual liquids are in equilibrium with each other
Explanation: Differential distillation is normally a batch operation, while flash distillation may be continuous and steam distillation may be operated…
Correct answer: Flash distillation, differential distillation & steam distillation are all continuous distillation processes- A. None of these
- B. Mildly endothermic
- C. Highly endothermic
- D. Exothermic
Explanation: Crystallisation releases the heat of crystallisation when dissolved solute forms an ordered solid lattice, so it is generally exothermic.
Correct answer: Exothermic- A. Viscosity
- B. Density
- C. Thermal conductivity
- D. Corrosive nature
Explanation: Viscosity strongly affects the ease of liquid circulation: highly viscous liquors offer greater resistance and commonly require forced…
Correct answer: Viscosity- A. Feed is introduced in the first effect
- B. Feed flows from low pressure to high pressure
- C. No pumps are required between successive effects
- D. None of these
Explanation: In backward feeding, fresh feed enters the last, low-pressure effect and moves toward the first, high-pressure effect.
Correct answer: Feed flows from low pressure to high pressure- A. Fuel is cheaply available
- B. Corrosive liquids are to be concentrated
- C. Large scale evaporation of liquor is needed
- D. Evaporation on small scale is to be done
Explanation: Multiple-effect evaporation reuses the vapor from one effect as the heating medium for the next, saving steam in large-capacity operation.
Correct answer: Large scale evaporation of liquor is needed- A. Partial condenser
- B. Vacuum evaporator
- C. Total condenser
- D. Double pipe heat exchanger
Explanation: A dephlegmator is a partial condenser that condenses part of an ascending vapor and returns the condensate as reflux.
Correct answer: Partial condenser- A. Same velocity profile or equal eddy diffusivities
- B. Both B. and C.
- C. Viscous heating or chemical reaction
- D. Thermal or pressure mass diffusion
Explanation: Heat and mass-transfer analogies require comparable transport mechanisms and no additional effects such as thermal or pressure diffusion…
Correct answer: Both B. and C.- A. 4000
- B. 9000
- C. 4600
- D. 3000
Explanation: Let the unchanged solids mass be S. Initial water is 9S and final water is 1.5S because the final solution contains 40% solids, so 9S −…
Correct answer: 4000- A. Rate of heat transfer
- B. Degree of turbulence
- C. Degree of super-saturation
- D. All A., B. and C
Explanation: Crystal size is governed by the supersaturation available for crystal growth, while heat-transfer rate can generate that supersaturation…
Correct answer: All A., B. and C- A. Multiple effect evaporator
- B. Single effect evaporator followed by a crystalliser
- C. Single effect evaporator
- D. Multiple effect evaporators followed by a crystalliser
Explanation: Black liquor is normally concentrated economically in multiple-effect evaporators, where vapour from one effect heats the next.
Correct answer: Multiple effect evaporator- A. Decreased economy
- B. Increased economy
- C. Lower capacity
- D. No effect on economy
Explanation: In backward feeding, the concentrated, viscous liquor enters the hottest effect, where the high temperature lowers its viscosity and…
Correct answer: Increased economy57. In a multiple effect evaporator, the effect of boiling point elevation is to______________________?
- A. None of these
- B. Reduce the economy
- C. Increase the economy
- D. Reduce the capacity
Explanation: Boiling-point elevation makes the liquor boil at a higher temperature, reducing the available temperature difference across the effects…
Correct answer: Reduce the capacity- A. Saturated
- B. All A., B. and C.
- C. Under-saturated
- D. Supersaturated
Explanation: A supersaturated solution has more dissolved solute than equilibrium permits, providing the driving force for nucleation and crystal…
Correct answer: Supersaturated- A. Viscous
- B. Foaming
- C. Very thin
- D. Corrosive
Explanation: Agitation continuously renews the liquid film and prevents excessive residence time, making an agitated film evaporator particularly…
Correct answer: Viscous- A. Economy
- B. Capacity
- C. Steam load
- D. None of these
Explanation: Evaporator capacity is the mass of liquid evaporated per unit time, commonly reported in kg/h.
Correct answer: Capacity