McqMate
These multiple-choice questions (MCQs) are designed to enhance your knowledge and understanding in the following areas: Mechanical Engineering .
| 1. |
According to the Fenske equation, what will be the minimum number of plates required in a distillation column to separate an equimolar binary mixture of components A and B into an overhead fraction containing 99 mol% A and a bottom fraction containing 98 mol% B ? Assume that relative volatility (αAB = 2) does not change appreciably in the column. |
| A. | 5 |
| B. | 9 |
| C. | 12 |
| D. | 28 |
| Answer» C. 12 | |
| 2. |
With increase in the mass velocity of the gas, the rate of drying during the constant rate period __________, if the conduction and radiation through the solid are negligible. |
| A. | Increases |
| B. | Decreases |
| C. | Remain same |
| D. | Increases linearly |
| Answer» A. Increases | |
| 3. |
During the constant rate period of drying of a solid, |
| A. | Increased air humidity decreases the rate of drying |
| B. | Increasing the air temperature decreases the drying rate |
| C. | Surface evaporation of unbound moisture occurs |
| D. | None of these |
| Answer» C. Surface evaporation of unbound moisture occurs | |
| 4. |
Large scale drying of wheat is done in a __________ dryer. |
| A. | Fluidised bed |
| B. | Spouted bed |
| C. | Tray |
| D. | Vacuum rotary |
| Answer» B. Spouted bed | |
| 5. |
Humidification involves mass transfer between a pure liquid phase and a fixed gas, which is |
| A. | Insoluble in the liquid |
| B. | Soluble in the liquid |
| C. | Non-ideal in nature |
| D. | At a fixed temperature |
| Answer» A. Insoluble in the liquid | |
| 6. |
With increase in temperature, the leaching rate increases due to |
| A. | Decreased liquid viscosity |
| B. | Increased diffusivity |
| C. | Both (A) and (B) |
| D. | Neither (A) nor (B) |
| Answer» C. Both (A) and (B) | |
| 7. |
As the reflux ratio, in a continuous counter-current extraction is increased, the number of stages |
| A. | Increase |
| B. | Decrease |
| C. | Remain unchanged |
| D. | Can either increase or decrease, depends on the system |
| Answer» B. Decrease | |
| 8. |
In distillation where q is defined as the moles of liquid flow in the stripping section per mole of feed introduced, for saturated liquid feed |
| A. | q > 1 |
| B. | q < 1 |
| C. | q = 1 |
| D. | q = 0 |
| Answer» C. q = 1 | |
| 9. |
Large scale drying of sugar is done in a __________ dryer. |
| A. | Spouted bed |
| B. | Tray |
| C. | Rotary |
| D. | Truck |
| Answer» C. Rotary | |
| 10. |
Though, theoretically the adsorption & desorption isotherms is expected to coincide but sometimes at least a part of the isotherms does not coincide and this phenomenon is known as adsorption hysteresis. In such cases, the desorption equilibrium pressure is __________ that obtained for adsorption. |
| A. | Lower than |
| B. | Higher than |
| C. | Same as |
| D. | Either same or higher than |
| Answer» A. Lower than | |
| 11. |
H2S is being absorbed in a gas absorber unit. The height of the transfer unit based on the overall mass transfer coefficient on the gas side is 0.4 m. The equilibrium data is given by, y = 1.5 x. The bulk concentration of H2S has to be reduced from 0.05 to 0.001 mole fraction in the gas side. The height of the tower (in metres) corresponding to an operating line given by, y = 5x + 0.001 is |
| A. | 2.0 |
| B. | 1.56 |
| C. | 1.0 |
| D. | 0.56 |
| Answer» A. 2.0 | |
| 12. |
Reboiler is considered as one theoretical plate, because |
| A. | Of the assumption that vapour and liquid leaving the reboiler are in equilibrium |
| B. | Vapour is recycled to the column |
| C. | Reboiler itself contains one plate |
| D. | None of these |
| Answer» A. Of the assumption that vapour and liquid leaving the reboiler are in equilibrium | |
| 13. |
In an absorption column, the flooding velocity for random packing is __________ that for stacked/regular packing. |
| A. | Greater than |
| B. | Smaller than |
| C. | Equal to |
| D. | Either (A), or (B); depends on the type of packing |
| Answer» B. Smaller than | |
| 14. |
Experiments were conducted to determine the flux of a species A in a stagnant medium across a gas-liquid interface. The overall mass transfer co-efficient based on the liquid side for dilute systems for the above was estimated to be 4 × 10-3 kg mole/m2 .s. The equilibrium data for the system is given as y = 2x. The flux across the interface (in kg mole/m2 .s) for bulk concentrations of A in gas phase and liquid phase as y = 0.4 and x = 0.01 respectively is: |
| A. | 5.6 × 10-4 |
| B. | 8.5 × 10-4 |
| C. | 5.6 × 10-3 |
| D. | 8.5 × 10-3 |
| Answer» B. 8.5 × 10-4 | |
| 15. |
In case of cooling towers, the ratio of the rates of heat and mass transfer is indicated by the __________ number. |
| A. | Lewis |
| B. | Grashoff |
| C. | Sherwood |
| D. | None of these |
| Answer» A. Lewis | |
| 16. |
When the gas to be dissolved in liquid is a/an __________ then normally co-current adsorber are used. |
| A. | Mixture of two gases |
| B. | Pure gas |
| C. | Ideal gas |
| D. | Sparingly soluble gas |
| Answer» B. Pure gas | |
| 17. |
Unsaturated air (with dry and wet bulb temperatures being 35 and 25°C respectively) is passed through water spray chamber maintained at 35°C. The air will be |
| A. | Cooled |
| B. | Humidified |
| C. | Both (A) & (B) |
| D. | Dehumidified |
| Answer» B. Humidified | |
| 18. |
__________ equation applies to diffusivities in liquids. |
| A. | Gilliland |
| B. | Hirschfelder |
| C. | Wilke and Chang |
| D. | None of these |
| Answer» A. Gilliland | |
| 19. |
Mass transfer co-efficient is defined as |
| A. | Flux = Co-efficient/concentration difference |
| B. | Co-efficient = Flux/concentration difference |
| C. | Flux=concentration difference/coefficient |
| D. | None of these |
| Answer» B. Co-efficient = Flux/concentration difference | |
| 20. |
The relative volatility of a binary mixture at constant temperature __________ the total pressure. |
| A. | Decreases with increase in |
| B. | Increases with increase in |
| C. | Is independent of |
| D. | None of these |
| Answer» A. Decreases with increase in | |
| 21. |
Large quantity of silica gel is normally dried in a __________ dryer. |
| A. | Freeze |
| B. | Through circulation |
| C. | Rotary vacuum |
| D. | Tray |
| Answer» B. Through circulation | |
| 22. |
The mass transfer co-efficient for a solid sphere of radius 'a' dissolving in a large volume of quiescent liquid, in which „D’ is the diffusivity of solute, is |
| A. | D/a |
| B. | D/2a |
| C. | Proportional to √D |
| D. | Dependent on the Reynolds number |
| Answer» D. Dependent on the Reynolds number | |
| 23. |
The value of „L/mG’ ratio for economical absorption operation ranges from |
| A. | 0.5 to 0.8 |
| B. | 0.8 to 1.2 |
| C. | 1.25 to 2.0 |
| D. | 2.5 to 3.5 |
| Answer» C. 1.25 to 2.0 | |
| 24. |
Cox chart, which is useful in the design of distillation column particularly for petroleum hydrocarbons, is a plot of (where, P = vapor pressure, T = temperature). |
| A. | log P vs. T |
| B. | log P vs. log T |
| C. | T vs. P |
| D. | P vs. log T |
| Answer» A. log P vs. T | |
| 25. |
In a single stage extraction process, 10 kg of pure solvent S (containing no solute A) is mixed with 30 kg of feed F containing A at a mass fraction xf = 0.2. The mixture splits into an extract phase E and a raffinate phase R containing A at xB = 0.5 and xR = 0.05 respectively. The total mass of the extract phase is (in Kg) |
| A. | 6.89 |
| B. | 8.89 |
| C. | 10 |
| D. | 8.25 |
| Answer» B. 8.89 | |
| 26. |
The commonly used solvent in supercritical extraction is |
| A. | Methyl ethyl ketone |
| B. | Water |
| C. | Carbon tetrachloride |
| D. | Carbon dioxide |
| Answer» D. Carbon dioxide | |
| 27. |
Dried finished product sampled from various parts of a __________ dryer exhibits nonuniformity in the moisture content. |
| A. | Rotary |
| B. | Tray |
| C. | Freeze |
| D. | None of these |
| Answer» B. Tray | |
| 28. |
For the same system, if the same liquid used in an absorber is decreased, the tower height will |
| A. | Increase |
| B. | Decrease |
| C. | Remain unaffected |
| D. | Decrease or increase; depends on the type of liquid |
| Answer» A. Increase | |
| 29. |
In steam distillation, the |
| A. | Temperature is 100°C |
| B. | Temperature is more than 100° C |
| C. | Product must be immiscible with water |
| D. | Temperature is higher than the boiling point of either component |
| Answer» C. Product must be immiscible with water | |
| 30. |
The equation, NA = (DAB . Pt /RTZ . PBM) (PA1 - PA2) is for |
| A. | Fick's second law of diffusion |
| B. | Steady state diffusion for stagnant case |
| C. | Liquid M.T.C. by Higbie penetration theory |
| D. | None of these |
| Answer» B. Steady state diffusion for stagnant case | |
| 31. |
A slurry is to be dried to produce flaky solid. Which dryer would you recommend? |
| A. | Spray dryer |
| B. | Drum dryer |
| C. | Rotary dryer |
| D. | Dielectric dryer |
| Answer» A. Spray dryer | |
| 32. |
Perforated plate towers are unique for solvent extraction because, they provide |
| A. | Higher contact area |
| B. | Better contact of the phase |
| C. | Repeated coalescence & redispersion of the drop phase |
| D. | None of these |
| Answer» C. Repeated coalescence & redispersion of the drop phase | |
| 33. |
Which of the following parameters remains constant during chemical dehumidification? |
| A. | Dry bulb temperature |
| B. | Partial pressure of vapour |
| C. | Wet bulb temperature |
| D. | None of these |
| Answer» A. Dry bulb temperature | |
| 34. |
For the gas absorption, the height of a transfer unit, based on the gas phase is given by (G: superficial molar gas velocity, L: superficial molar liquid velocity, FG: mass transfer co-efficient, moles/m2, a: interfacial area per unit volume of tower) |
| A. | G/(FG . a) |
| B. | FG/(G . a) |
| C. | (G . a)/FG |
| D. | L/(FG . G) |
| Answer» A. G/(FG . a) | |
| 35. |
Coffee is prepared from coffee beans by leaching with |
| A. | Cold water |
| B. | Hot water |
| C. | Dilute hot caustic solution |
| D. | Naphtha |
| Answer» B. Hot water | |
| 36. |
Pore size of the molecular sieve 5A is __________ mm. |
| A. | 5 |
| B. | 0.5 |
| C. | 0.05 |
| D. | 50 |
| Answer» B. 0.5 | |
| 37. |
The equation, NA = (DAB . Pt /RTZ) (y1 - y2) is for |
| A. | Steady state equimolar counter diffusion |
| B. | Fick's first law of diffusion |
| C. | Steady state diffusion for stagnant case |
| D. | Liquid M.T.C. by penetration theory |
| Answer» A. Steady state equimolar counter diffusion | |
| 38. |
To remove all the moisture from a wet solid it requires exposure to __________ air. |
| A. | Perfectly dry |
| B. | Highly humid |
| C. | High temperature |
| D. | None of these |
| Answer» A. Perfectly dry | |
| 39. |
Penetration theory states that the mass transfer co-coefficient is equal to (where, De is diffusivity and 't' is time) |
| A. | (De.t)1/2 |
| B. | (De/t)1/2 |
| C. | (4De/πt)1/2 |
| D. | (4De/t) |
| Answer» C. (4De/πt)1/2 | |
| 40. |
The cooling effect in a cooling tower can be speeded up by |
| A. | Increasing the air velocity and area of exposed wet surface |
| B. | Reducing the barometric pressure |
| C. | Reducing the humidity of the air |
| D. | All (A), (B) and (C) |
| Answer» D. All (A), (B) and (C) | |
| 41. |
The relative volatility of a binary mixture at the Azeotropic composition is |
| A. | 1 |
| B. | > 1 |
| C. | 0 |
| D. | ∞ |
| Answer» A. 1 | |
| 42. |
Which of the following processes is not an example of adsorption applied to gaseous separations? |
| A. | Recovery of valuable solvent vapors from dilute mixture with air and other gases |
| B. | Dehumidification of air and gas |
| C. | Removal of objectionable odour and impurities from industrial gases |
| D. | Decolouration of yellow glycerine |
| Answer» D. Decolouration of yellow glycerine | |
| 43. |
For absorbing a sparingly soluble gas in a liquid, the |
| A. | Gas side co-efficient should be increased |
| B. | Liquid side coefficient should be increased |
| C. | Gas side co-efficient should be decreased |
| D. | Liquid side co-efficient should be decreased |
| Answer» B. Liquid side coefficient should be increased | |
| 44. |
The Knudsen diffusivity is proportional to (where, T = absolute temperature) |
| A. | √T |
| B. | T2 |
| C. | T |
| D. | T4 |
| Answer» A. √T | |
| 45. |
Moisture content of a substance when at equilibrium with a given partial pressure of the vapour is called the __________ moisture. |
| A. | Free |
| B. | Unbound |
| C. | Equilibrium |
| D. | Bound |
| Answer» C. Equilibrium | |
| 46. |
For the flow of gases through a capillary, with increase in temperature, the permeability __________ as per Knudsen law. |
| A. | Increases |
| B. | Decreases |
| C. | Remain same |
| D. | Either (A) or (B); depends on the gas |
| Answer» A. Increases | |
| 47. |
A natural draft cooling tower is filled with wooden grids, which covers about __________ percent of the tower height. |
| A. | 10-15 |
| B. | 30-40 |
| C. | 70-80 |
| D. | 90-100 |
| Answer» A. 10-15 | |
| 48. |
With increase in the liquid flow rate at a fixed gas velocity in a randomly packed counter current gas-liquid absorption column, the gas pressure drop |
| A. | Decreases |
| B. | Remains unchanged |
| C. | Increases |
| D. | Decreases exponentially |
| Answer» C. Increases | |
| 49. |
Which of the following is not fixed by the process requirements, in the design of absorbers? |
| A. | Flow rate of the entering gas |
| B. | Composition of the entering liquid |
| C. | Terminal concentrations of gas stream |
| D. | None of these |
| Answer» D. None of these | |
| 50. |
Pick out the wrong statement: |
| A. | Absorption factor is constant, when the equilibrium and operating lines are straight |
| B. | In case of a stripper, the equilibrium curve is always below the operating line |
| C. | In case of an absorber, the operating line is always above the equilibrium curve |
| D. | In the absorption of low solubility gases, the liquid film is the controlling resistance |
| Answer» B. In case of a stripper, the equilibrium curve is always below the operating line | |
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