Mass Transfer Set 5

Mechanical Engineering

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This set of Mass Transfer Multiple Choice Questions & Answers (MCQs) focuses on Mass Transfer Set 5

Q1 | The wet and 'dry bulb temperature for a vapour-gas mixture are 25°C and 30°C respectively. If the mixture is heated to 45°C at constant pressure, the wet bulb temperature will be __________ °C.
  • 25
  • > 25
  • < 25
  • -25
Answer: > 25
Q2 | Water entrained by circulating air in cooling towers is termed as
  • Drift
  • Blow down
  • Vapor load
  • None of these
Answer: Drift
Q3 | Pick out the wrong statement. Raoult's law does not apply, when the
  • Size of component molecules are not equal
  • Attractive forces between like and unlike molecules in the solution are approximately equal
  • Component molecules are non-polar
  • Chemical combination or molecular association between unlike molecules takes place in the formation of solution
Answer: Component molecules are non-polar
Q4 | Pick out the wrong statement pertaining to the analogy between equations of heat and mass transfer operations.
  • Sherwood number in mass transfer is analogous to Nusselt number in heat transfer
  • Prandtl number in heat transfer is analogous to Schmidt number in mass transfer
  • Reynolds number in mass transfer is analogous to Grashoff number in heat transfer
  • Reynolds number remains the same in both heat and mass transfer
Answer: Reynolds number in mass transfer is analogous to Grashoff number in heat transfer
Q5 | Plate efficiency in a distillation column is reduced due to the __________ of liquid.
  • Entrainment
  • Foaming
  • Weeping & dumping
  • All (A), (B) & (C)
Answer: All (A), (B) & (C)
Q6 | Pick out the wrong statement.
  • Mass transfer co-efficient does not account for gas-liquid diffusion
  • Diffusion co-efficient and mass transfer co-efficient are not same in any mass transfer operation
  • Contacting cold vapor-gas mixture with hot liquid exemplifies humidification process
  • Contacting cold liquid with warm vapor-gas mixture exemplifies dehumidification process
Answer: Mass transfer co-efficient does not account for gas-liquid diffusion
Q7 | Blowdown in a cooling tower
  • Means discarding a small fraction of circulating water to prevent and limit the concentration of salt and impurities
  • Increases the scale forming tendencies of water
  • Is undesirable
  • All (A), (B) & (C)
Answer: Means discarding a small fraction of circulating water to prevent and limit the concentration of salt and impurities
Q8 | Pick out the wrong statement.
  • In solvent extraction, the distribution co-efficient should be as large as possible for solvent economy
  • With increase in pressure, the solubility of gases in solvent increases at a fixed temperature
  • Decrease in Murphree plate efficiency is an indication of entrainment in distillation column
  • The capacity of a distillation column is maximum at total reflux
Answer: The capacity of a distillation column is maximum at total reflux
Q9 | Rayleigh's equation applies to __________ distillation.
  • Continuous
  • Steam
  • Differential
  • Flash
Answer: Differential
Q10 | In extraction, as the temperature increases, the area of heterogeneity (area covered by binodal curve)
  • Decreases
  • Increases
  • Remains unchanged
  • None of these
Answer: Decreases
Q11 | In most of the mechanically agitated liquid-liquid extractors, baffles or horizontal compartmental plates are provided, which helps in
  • Reducing the axial mixing
  • Increasing the rate of extraction
  • Maintaining the concentration difference between the two phases
  • All 'a', 'b' & 'c'
Answer: All 'a', 'b' & 'c'
Q12 | The interfacial area per unit volume of dispersion, in a gas-liquid contactor, for fractional hold up of gas = 0.1 and gas bubble diameter = 0.5 mm is given by (in m2 /m3 )
  • 500
  • 1200
  • 900
  • 800
Answer: 500
Q13 | The slope of 9-line is determined by the
  • Reflux ratio
  • Plate efficiency to be achieved
  • Thermal condition of the feed
  • Relative volatility
Answer: Thermal condition of the feed
Q14 | For a binary mixture with low relative volatility,
  • Use steam distillation
  • Use molecular distillation
  • Use high pressure distillation
  • An azeotrope may be formed during distillation
Answer: An azeotrope may be formed during distillation
Q15 | Freundlich equation applies to the adsorption of solute from
  • Dilute solutions, over a small concentration range
  • Gaseous solutions at high pressure
  • Concentrated solutions
  • None of these
Answer: Dilute solutions, over a small concentration range
Q16 | Pick out the wrong statement pertaining to the cooling towers.
  • In case of induced draft cooling tower, the fan is placed at the top of the tower
  • Effectiveness of forced draft cooling tower is reduced by the recirculation of the humid and hot discharged air
  • A natural draft cooling tower is recommended to be used, when the air humidity is low and air temperature is also low
  • Effectiveness of a mechanical draft cooling tower is reduced with increase in air wet-bulb temperature
Answer: Effectiveness of a mechanical draft cooling tower is reduced with increase in air wet-bulb temperature
Q17 | The Hatta number is important in
  • Multi-component distillation
  • Binary distillation
  • Gas absorption without chemical reaction
  • Gas absorption with chemical reaction
Answer: Gas absorption with chemical reaction
Q18 | The dew point of an unsaturated gas-vapor mixture does not depend upon the __________ of the mixture.
  • Composition
  • Temperature
  • Total pressure
  • All (A), (B) and (C)
Answer: Temperature
Q19 | A solid is being dried in the linear drying rate regime from moisture content Xo to XF. The drying rate is zero at X = 0 and the critical moisture content is the same as the initial moisture Xo. The drying time for M = (Ls /ARc) is (where, L = total mass of dry solid, A = total surface area for drying Rc = Constant maximum drying rate per unit area X = moisture content (in mass of water/mass of dry solids))
  • M(Xo - XF)
  • M(Xo/XF)
  • M ln(Xo/XF)
  • MXo ln(Xo/XF)
Answer: MXo ln(Xo/XF)
Q20 | In case of physical adsorption, the difference between heat of adsorption and heat of normal condensation is
  • Equal to the heat of formation of surface compound
  • Equal to the heat of wetting
  • Zero
  • Called integral heat of adsorption
Answer: Equal to the heat of wetting
Q21 | The critical moisture content in case of drying indicates the __________ rate period.
  • Beginning of falling
  • Beginning of constant
  • End of falling
  • None of these
Answer: Beginning of falling
Q22 | Pick out the wrong statement.
  • The binary diffusivity in liquids is of the order of 10-5 cm2 /sec
  • Molecular diffusion in solid is much faster than that in liquids
  • Particles movement from higher concentration to lower concentration takes place in diffusion process
  • According to Poiseuille's law, the permeability decreases with increase in temperature for flow of a gas through a given capillary
Answer: Molecular diffusion in solid is much faster than that in liquids
Q23 | Humidity chart is useful for the solution of problems concerning condensation, vaporisation and air conditioning. At a given dry bulb temperature, value of humidity obtained from the humidity chart directly, is in terms of __________ humidity.
  • Molal
  • Relative
  • Percentage
  • None of these
Answer: Molal
Q24 | Separation of two volatile liquids by distillation makes use of their
  • Selectivity
  • Relative volatility
  • Solubility
  • Density difference
Answer: Relative volatility
Q25 | Powdery materials can be guarded against caking tendency on storage by
  • Providing irregular grain size
  • Providing minimum percentage of voids
  • Having maximum possible points of contact
  • None of these
Answer: None of these
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