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## Machine Design MCQ Set 1

1. Find the operation where diffusion of solids not occurs
b) Leaching
c) Drying
d) Distillation

Answer: d [Reason:] Distillation is the liquid-liquid operation where no diffusion on solid is possible.

2. Find the diffusivity through slab if N flux of A 4 mol/sq.m sec, concentration difference is 2mol/cu.m and distance is 3 m.
a) 2 sq.m/s
b) 4 sq.m/s
c) 6 sq.m/s
d) 8 sq.m/s

Answer: c [Reason:] N flux of A= D(AB)/z * concentration difference D(AB) = 6 sq.m/sec.

3. Find the activated diffusivity of carbon if energy of activation is 6 kJ; the value of constant diffusivity is 2.5 sq.m/sec. (Hint: the value of exponential of (-6/RT) is 2.55)
a) 6.375 sq.m/s
b) 1.02 sq.m/s
c) 15.3 sq.m/s
d) 16.25 sq.m/s

Answer: a [Reason:] Activated diffusivity= constant diffusivity * exponential value = 2.5 * 2.55 = 6.375.

4. The term activated means _____________
a) Pressure dependency
b) Temperature dependency
c) Volume dependency
d) None of the mentioned

Answer: b [Reason:] Activated represents the activation energy which depends on temperature.

5. If the two gases are separated by a polymer membrane, the extent of diffusion depends on _______ law.
a) Hendy
b) Raoult
c) Newton
d) None of the mentioned

Answer: a [Reason:] Concentration is directly proportional to pressure so Hendry law is applicable.

6.For permanent gases diffusivity the order is _________ sq.m/s
a) 10-7
b) 10-8
c) 10-9
d) 10-10

Answer: d [Reason:] The gas can become permeable to certain substance if it is in an order of 10-10.

7. The solute movement of fluid on solids are __________
a) Hygrodynamic
b) Hydrodynamic
c) Fluid dynamic
d) None of the mentioned

Answer: b [Reason:] Solute movement is due to pressure difference which is hydrodynamic.

8. If the pore of the solid is inaccessible to external fluids then it is known as dead end.
a) True
b) False

Answer: b [Reason:] If the pore of the solid is inaccessible to external fluids then it is known as isolate.

9. Macroporic surrounding of microscopic pellets powders of different magnitude in size is _______
a) Disperse
b) Bi-disperse
c) Tri-disperse
d) None of the mentioned

Answer: b [Reason:] The double surrounding of these pellets is known as bi-disperse.

10. Find the permeability if diffusivity is 2 units and solubility coefficient is 5 units assume all are in SI units.
a) 10 units
b) 2.5 units
c) 0.4 units
d) None of the mentioned

Answer: a [Reason:] Permeability = solubility co-efficient * diffusivity = 2 * 5 =10 units.

## Machine Design MCQ Set 2

1. A mixture undergoing multicomponent diffusion is analyzed through the Maxwell-Stefan approach. With regard to this approach which among the following statements are incorrect? The difference in the partial pressure of the Component A over a small distance ∆z (AB)is proportional to
a) The molar concentration at the two points.
b) Length of the diffusion path.
c) Velocity at the point A.
d) Difference in the velocities at point A and B.

2. If all the components except 1 of the multicomponent diffusing mixture are inert, then what will be the expression for Diffusivity of the component 1 in the mixture?
a) D1m=(N1-Y1∑Nj)/(∑(YjN1-Y1Nj)/Dij)
b) D1m=(Y1∑Nj)/(∑(YjN1-Y1Nj)/Dij)
c) D1m=N1/(∑[(YjN1-Y1Nj)/Dij])
d) D1m=(1-Y1)/(∑[Yj/Dij])

Answer: d [Reason:] For an inert component Nj=0.

Paragraph for question numbers (3-5)

A mixture of 60% hydrogen and 40% oxygen is blowing over a pan of water at 1atm pressure. The bulk gas temperature is 30°c and the water temperature is 20°C. The vapor pressure of water at this temperature is 17.53mm Hg. The concentration of moisture in the bulk gas is negligible and the diffusivity values are DO2-H2O=0.357cm2/s,DH2-H2O=0.972cm2/s at 34°C and DH2-O2=0.891cm2/s at 43°C.

3. Which of the following statements are correct?
a) Water vapor diffuses through non-diffusing hydrogen and oxygen.
b) Hydrogen and Oxygen is diffusing through water vapor.
c) Hydrogen is diffusing through water vapor and oxygen.
d) None of Hydrogen, Oxygen and water vapor is diffusing.

Answer: a [Reason:] Water vapor has a source (pan) as well as a sink (bulk gas) whereas hydrogen and oxygen has no sink.

4. What will be the values of the diffusivities (in cm2/s) at the mean gas-film temperature?
a) 0.923,0.267
b) 0.483,1.351
c) 0.294,0.368
d) 1.381,0.364

Answer a [Reason:] Use the relation D∝T1.75 Mean gas-film temperature= (30+20)/2=25°C.

5. What is the value of the flux (kmol/m3.s) of water vapor through a stagnant film of estimated thickness 1.5mm on the water surface?
a) 1.36*10-5
b) 1.96*10-5
c) 1.96*10-1
d) 1.96*10-7

Answer: b [Reason:] Calculate D1m from the equation, D1m=(1-Y1)/(∑〖Yj/Dij〗) D1m=0.465cm2/s Use the equation, N1=(D1mC/l)*ln⁡〖(1-Yil)/(1-Y10)〗, where Yil=0(dry air) and Y10=0.023 (17.53/760).

6. For a steady state equimolar counter diffusion of A and B. The N flux of A is ________
a) – N flux of A
b) N flux of A
c) – N flux of B
d) N flux of B

Answer: c [Reason:] For equimolar counter diffusion N Flux of A is opposite to N flux of B.

7. The value of ratio of N flux of A to the total N flux for a steady state equimolar counter diffusion is
a) 0
b) Infinity
c) 1
d) None of the mentioned

Answer: b [Reason:] As the total flux becomes zero, the value of the ratio becomes infinity.

8. In sulphuric acid plants dry air is used for burning of sulphur. Air is dried in contact with concentrated Sulphuric acid. Moisture diffuses through a layer of air, reaches the surface and gets absorbed in it. Here air is said to be non-diffusing were as moisture is diffusing. Which of the following statements are correct?
a) Moisture has a source and a sink whereas dry air has a source but no sink.
b) Moisture as well as dry air have a sink.
c) Moisture has a source but no sink whereas dry air has source as well as sink.
d) Moisture as well as dry sir have no sink.

Answer: a [Reason:] A component is said to be diffusing if it has both source as well as sink.

## Machine Design MCQ Set 3

1. Fractionator(s) required for separating binary azeotropic mixture is
a) 1
b) 2
c) 3
d) 4

Answer: b [Reason:] Azeotropes has the same boiling point so for effective separation of two mixture we need additional fractionator since the vapour.

2. Process mainly involved in Azeotropic separation is
a) Condensation
b) Decantation
c) Agitation
d) All the mentioned

Answer: b [Reason:] Decantation is the process of separating the two solutions by precipitation or other. The decanted products are sent to the other fractionator.

3. The second fractionator tower is applicable for stripping process alone.
a) True
b) False

Answer: a [Reason:] Yes. On the second fractionator the more volatile components gets transferred from condensed liquid to the reboiler vapour.

4. Condenser required for rectifying binary Azeotropic mixture is
a) 1
b) 2
c) 3
d) 4

Answer: a [Reason:] Since the distillate vapour from the fractionator are sent to the same condenser used for the first for minimizing the fixed cost.

5. If the distillate has composition of azeotrope and the residue has rich phase of one component. Then the azeotropic mixture is a
a) Maximum-boiling mixture
b) Minimum boiling mixture
c) Constant boiling mixture
d) Differential boiling mixture

Answer: b [Reason:] Minimum boiling mixture is the mixture where the high volatile component goes to the distillate and other comes to residue.

6. Distillate from the first fractionator should be ______ bubble point.
a) Below
b) More than
c) Equals to
d) None of the mentioned

Answer: a [Reason:] If the distillate is above bubble point then the vapour gets loss from the decanter.

7. The method applicable for Azeotropic rectification is
a) McCabe method
b) Ponchon method
c) Extraction method
d) Other method

Answer: b [Reason:] Rectification of azeotropes is based on enthalpy data so Ponchon Savorit method is preferred.

8. For the azeotropic rectification which, of the following is applicable?
a) Distillate should be above bubble point
b) To have the excessive vapour loss
c) To decrease the internal reflux ratio
d) None of the mentioned

Answer: c [Reason:] Since if the internal reflux ratio is increased the vapours will get loss. The vapour loss will affect the separation.

9. For the maximum boiling mixture the residue has the azeotropic mixture.
a) True
b) False

Answer: b [Reason:] Since the maximum boiling mixture is for low volatile component it will comes to the residue and separated by adding other component.

10. To prevent the composition change the vapour should not gets loss from the decanter.
a) True
b) False

Answer: a [Reason:] If the vapour gets loss it will affect the compositions of the residue.

## Machine Design MCQ Set 4

1. What is the value of Schmidt number for ammonia?
a) 0.78
b) 0.79
c) 0.81
d) 0.82

Answer: a [Reason:] Ammonia also known as Azane is a colorless gas with a characteristics pungent smell. It is also used in many commercial cleaning products.

2. What is the value of Schmidt number for carbon-dioxide?
a) 0.92
b) 0.93
c) 0.94
d) 0.95

Answer: c [Reason:] It is a colorless, odorless gas vital to life on earth. This naturally occurring chemical compound is composed of a carbon atom covalently double bonded to two oxygen atoms.

3. What is the dimension of Schmidt number?
a) Newton
b) Meter
c) Celsius
d) It is a dimensional quantity

Answer: d [Reason:] Schmidt number = v/D and it has no dimensions.

4. Which one of the following is having lowest value of Schmidt number?
a) Oxygen
b) Water
c) Benzene
d) Ethyl alcohol

Answer: b [Reason:] Schmidt number of water is 0.60 while that of oxygen, ethyl alcohol and benzene are 0.75, 1.76 and 1.30 respectively.

5. What is the value of Schmidt number for water?
a) 0.62
b) 0.61
c) 0.60
d) 0.59

Answer: c [Reason:] Water is a transparent fluid and its molecules are connected by covalent bonds. It is tasteless and odorless.

6. Schmidt number is given by the formula
a) 2 D/v
b) v/D
c) D/v
d) 2 v/D

Answer: b [Reason:] Schmidt number is defined as the ratio of viscosity and mass diffusivity and is used to characterize fluid flows in which there are simultaneous momentum and mass diffusion convection processes.

7. Which one of the following is having highest value of Schmidt number?
a) Benzene
b) Carbon dioxide
c) Acetic acid
d) Ammonia

Answer: a [Reason:] Schmidt number of benzene is 1.78 while that of carbon dioxide, acetic acid and ammonia are 0.78, 1.16 and 0.78 respectively.

8. What is the value of Schmidt number for acetic acid?
a) 4.16
b) 3.16
c) 2.16
d) 1.16

Answer: d [Reason:] It is a colorless liquid and weak acid. It is an important chemical reagent.

9. What is the value of Schmidt number for benzene?
a) 1.96
b) 1.86
c) 1.76
d) 1.66

Answer: c [Reason:] Its molecule is composed of six carbon atoms joined in a ring with one hydrogen atom attached to each carbon atom.

10. Schmidt number is given by
a) German engineer
b) British engineer
c) French engineer
d) American engineer

Answer: a [Reason:] It was named after the German engineer Ernst Heinrich Wilhelm Schmidt.

## Machine Design MCQ Set 5

1. The extraction compositions in equilibrium are represented by equilateral triangle whose co-ordinates are known as
a) Isobar
b) Isotrope
c) Isotherm
d) None of the mentioned

Answer: c [Reason:] The co-ordinates of the equilateral triangle are constant temperatures so it is an isotherm.

2. Find LPM in the below one pair partially miscible ternary diagram.

Where, A,B,C are the pure components
a) Temperature curve
b) Solubility Curve
c) Solution curve
d) Pressure curve

Answer: b [Reason:] Solubility curve represent the components solubility on other component.

3.The change of solubility by adding other component gives rise to binodal solubility curve.
a) True
b) False

Answer: a [Reason:] Binodal curve is the solubility curve of the ternary diagram.

4. Justify that X represents heterogeneity of the solution.

a) True
b) False

Answer: a [Reason:] Here LPM represents the binodal solubility curve which represents the three component mixture.

5. The system becomes solutropic if the tie line inside the binodal solubility curves becomes_________
a) Vertical
b) Horizontal
c) Straight
d) None of the mentioned

Answer: b [Reason:] If the tie line becomes horizontal the mixture solubility on each other remains same which represents solutropic system.

6. The point where A and B rich solubility curve merge is known as _________

a) Pinch point
b) Plait point
c) Key point
d) None of the mentioned

Answer: b [Reason:] Upon addition of B, the solubility of A and B rich phases meets is known as plait point where the separation is not possible.

7. Consider a solutropic system; the plait point will be at the maximum addition of? Find from the figure.

a) A
b) B
c) C
d) M

Answer: b [Reason:] Upon addition of B the tie line will be horizontal for solutropic system and will be maximum at B.

8. Separation is not possible at plait point.
a) True
b) False

Answer: a [Reason:] At plait point, the separation factor becomes 1.

9. The plait point is the ____ tie line of the binodal curve.
a) Last
b) First
c) Middle
d) None of the mentioned

Answer: a [Reason:] At plait point, the separation factor becomes 1 and both solubility curves merges.

10. Find the Distribution coefficient if equilibrium solute concentration in extract is 0.75 and the solute concentration in Raffinate is 0.6.
a) 1.25
b) 0.8
c) 1
d) 0