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Machine Design MCQ Set 1

1. What is the value of emissivity for polished aluminum?
a) 0.01
b) 0.02
c) 0.03
d) 0.04

View Answer

Answer: c [Reason:] The emissivity of the surface of a material is its effectiveness in emitting energy as thermal radiation.

2. Which one is having highest emissivity?
a) Tarnished copper
b) Polished aluminum
c) Aluminum foil
d) Polished copper

View Answer

Answer: a [Reason:] Emissivity of tarnished copper is 0.75 while that of polished aluminum, aluminum foil and polished copper are 0.03, 0.05 and 0.03 respectively.

3. What is the value of emissivity for polished copper?
a) 0.02
b) 0.03
c) 0.04
d) 0.05

View Answer

Answer: b [Reason:] This is the total hemispherical emissivity from the surfaces. It describes thermal radiation emitted near specific wavelength and at specific angles to surface.

4. What is the value of emissivity for tarnished copper?
a) 0.78
b) 0.77
c) 0.76
d) 0.75

View Answer

Answer: d [Reason:] This is optically thick material. The absorptivity at the wavelengths doesn’t depend on the thickness of the material.

5. Which one is having lowest emissivity?
a) Polished stainless steel
b) White marble
c) Snow
d) Asphalt

View Answer

Answer: a [Reason:] Emissivity of polished stainless steel is 0.60 while that of white marble, snow and asphalt are 0.95, 0.97 and 0.90 respectively.

6. What is the value of emissivity for dull stainless steel?
a) 0.24
b) 0.23
c) 0.22
d) 0.21

View Answer

Answer: d [Reason:] It is transparent with low emissivity coatings. It emits less thermal radiation than ordinary window.

7. What is the value of emissivity for white marble?
a) 0.96
b) 0.95
c) 0.94
d) 0.93

View Answer

Answer: b [Reason:] It is based on evacuated glass tube collectors. Sunlight is absorbed by a selective surface.

8. Which one is having highest emissivity?
a) Red brick
b) Concrete
c) Black paint
d) Dull stainless steel

View Answer

Answer: c [Reason:] Emissivity of black paint is 0.97 while that of red brick, concrete and dull stainless steel are 0.93, 0.88 and 0.21 respectively.

9. What is the value of emissivity for asphalt?
a) 0.90
b) 0.80
c) 0.70
d) 0.60

View Answer

Answer: a [Reason:] It is an ordinary black surface that absorbs sunlight efficiently but emit thermal radiation copiously.

10. Which one is having lowest emissivity?
a) Snow
b) White marble
c) Concrete
d) Polished stainless steel

View Answer

Answer: d [Reason:] Emissivity of polished stainless steel is 0.60 while that of snow, white marble and concrete are 0.97, 0.95 and 0.88 respectively.

Machine Design MCQ Set 2

1. Partial pressure equals vapour pressure if it is___________
a) Saturated
b) Unsaturated
c) Isothermal
d) None of the mentioned

View Answer

Answer: a [Reason:] At saturation, the vapour-gas mixture will be at equilibrium so the vapour pressure equals partial pressure.

2. Say True or False
I) Vapour- at superheated temperature
II) Gas – at condensation temperature
a) True
b) False

View Answer

Answer: b [Reason:] Since vapour has liquid portion we cannot say superheated. Superheated means free from other component like unique gas.

3. Guess the saturated molar absolute humidity of the gas(A.- Vapour(B. mixture at 100 degree Celsius. Vapour pressure of A is 300 mmHg and the total pressure is 760 mmHg.
a) 0.39
b) 0.65
c) 0.60
d) Cannot determine

View Answer

Answer: b [Reason:] Saturated molar humidity= Vapour pressure of A/ Vapour pressure of B = 300/(760-300) =0.65.

4. The system is unsaturated if partial pressure _________ equilibrium vapour pressure.
a) Less than
b) Greater than
c) Equals to
d) All the mentioned

View Answer

Answer: a [Reason:] If saturated, the vapour pressure equals partial pressure. If unsaturated, the pressure will be less than vapour pressure.

5. Consider a saturated gas(A.-vapour(B. mixture , if the absolute molal humidity is 0.265 and the total pressure= 760 mmHg. Find the vapour pressure of B.
a) 149.21 mmHg
b) 159.21 mmHg
c) 169.21 mmHg
d) 600.8 mmHg

View Answer

Answer: d [Reason:] First, we have to find the vapour pressure of A. 0.265= pA/760-pA pA= 159.21 pB=760-159.21= 600.8.

6. The vapour pressure of the nitrogen gas is 400mmHg and the partial pressure is 300mmHg. Find the relative saturation.
a) 75
b) 133
c) 100
d) 50

View Answer

Answer: a [Reason:] Relative saturation or relative humidity = (partial pressure/vapour pressure. x100 =75.

7. Thermometer measurement temperature is
a) Dry bulb temperature
b) Wet bulb temperature
c) Dew point temperature
d) Room temperature

View Answer

Answer: a [Reason:] Dry bulb temperature is the actual measuring temperature of the thermometer.

8. Find the dew point
mass-transfer-questions-answers-experienced-q8
a) X
b) Y
c) Z
d) None of the mentioned

View Answer

Answer: a [Reason:] The point at 100% saturation is known as dew point. Below the point, the vapour starts to condense.

9. Temperature at which the partial pressure of the gas-vapour mixture equals vapour pressure _______
a) Dry bulb temperature
b) Wet bulb temperature
c) Dew point temperature
d) None of the mentioned

View Answer

Answer: c [Reason:] At saturation, the vapour pressure equals partial pressure. At dew point, saturation attains.

10. Check whether we get approximately 80% saturation if the total pressure and the partial pressure of the gas mixture is 760 mmHg and 260 mmHg. Also the vapour pressure is 300 mmHg.
a) True
b) False

View Answer

Answer: a [Reason:] Percentage saturation is the ratio of absolute molal humidity to the saturated molal humidity. Absolute molal humidity= 260/(760-260. =0.52. Saturated molal humidity= 300/(760-300 =0.652. %saturation= 0.52/0.652= 79.8(Approximately 80.

Machine Design MCQ Set 3

1. __________ is the single stage device in extractor types.
a) Mixer settler
b) Sieve trays
c) Agitator vessel
d) Packed column

View Answer

Answer: a [Reason:] Mixer-settler is a single stage device used for extraction operation.

2. Settler in the mixer settler is applicable for rapid agitation.
a) True
b) False

View Answer

Answer: a [Reason:] Settler is used for settling.

3. The substance to get mixed enters into the mixer through.
a) Orifice
b) Nozzle
c) Orifice or nozzle
d) None of the mentioned

View Answer

Answer: c [Reason:] Orifice or nozzle both are used for allowing the substance into the mixer.

4. Line mixers are ________
a) Small
b) Large
c) Very high
d) None of the mentioned

View Answer

Answer: a [Reason:] Line mixers or flow mixers are use d inside pipes so it must be small.

5. The two liquids while mixing gets dispersed inside the mixer.
a) True
b) False

View Answer

Answer: a [Reason:] Due to loss of energy by pressure drop the liquids gets dispersed inside the mixer.

6. If the holding time is more in a mixer then _______ will be poor.
a) Mass transfer
b) Heat transfer
c) Momentum transfer
d) Both mass and momentum transfer

View Answer

Answer: a [Reason:] If the holding of liquids inside the mixer is poor then the rate of mass transfer gets decrease.

7. More than three stages of mixer settler attached to get _____________
a) Multi-component cascade
b) Mixer settler cascade
c) Extraction multi-stages
d) None of the mentioned

View Answer

Answer: b [Reason:] Generally two or more stages inter connected to form cascades so it is an mixer settler cascades.

8. The extractor preferred for getting immediate dispersion after piping is ___________________
a) Don extractor
b) Box extractor
c) Boltzmann extractor
d) Immediate dispersion is not possible

View Answer

Answer: b [Reason:] The box arrangement of alternate stages produces immediate dispersion.

9. If a system has low interfacial tension _________ extractor is preferred.
a) Packed column
b) Pulse column
c) Sieve plates
d) Agitator column

View Answer

Answer: c [Reason:] For system with low interfacial tension need not need mechanical agitation so sieve plates are preferred.

10. _____________ mixing is applicable for differential contractors.
a) Axial
b) Radial
c) Both axial and radial
d) Not the above mentioned

View Answer

Answer: a [Reason:] Due to the reduction of concentration difference between the phases axial mixing is preferred.

11. Packed tower with ________ packing preferable for liquid extraction.
a) Uniform
b) Random
c) Complete
d) None of the mentioned

View Answer

Answer: b [Reason:] To reduce axial mixing random packing are preferred in packed column.

12. Motivational force in differential contractor is
a) Centrifugal force
b) Gravitational force
c) Electromagnetic forces
d) All the mentioned

View Answer

Answer: b [Reason:] In extractor the light liquid enters the bottom and also the extractor is vertical so gravitational force is a motivational force.

13. The high density difference among the liquid in the extractor cause ________
a) Flooding
b) Loading
c) Agitation
d) None of the mentioned

View Answer

Answer: a [Reason:] Generally, the density difference leads to separation from each other which results in flooding.

14. Differential contractors are continuous extractor.
a) True
b) False

View Answer

Answer: a [Reason:] Differential contractor was named because of continuous contact of entering and leaving streams.

15. Find the process.
mass-transfer-questions-answers-extraction-equipments-q15
a) Batch process
b) Continuous process
c) Batch+ continuous process
d) None of the mentioned

View Answer

Answer: c [Reason:] Mixer is a batch process and settler is a continuous process.

Machine Design MCQ Set 4

1. Fick’s law is given by the formula
a) N b = – D b c d C b/d x
b) N b = – 2 D b c d C b/d x
c) N b = – 3 D b c d C b/d x
d) N b = – 4 D b c d C b/d x

View Answer

Answer: a [Reason:] Experimental evidences shows that molecular diffusion is goverened by the empirical relation suggested by Fick.

2. Figure shows equimolal diffusion between species B and C. Identify the correct molar diffusion rate
mass-transfer-questions-answers-ficks-law-q2
a) N b = m c/M b
b) N b = m b/M b
c) N c = m b/M b
d) N c = m b/M c

View Answer

Answer: b [Reason:] Equimolal diffusion between species B and C of a binary gas system implies that each molecule of component B is replaced by each molecule of constituent C.

3. What is the unit of diffusion coefficient?
a) m2
b) s
c) m2 s
d) m2/s

View Answer

Answer: d [Reason:] D = – N/ (d C/ d x).

4. What is the molecular weight of ammonia?
a) 31
b) 53
c) 29
d) 39

View Answer

Answer: c [Reason:] Formula of ammonia is NH3.

5. What is the molecular volume of air at normal boiling point?
a) 29.89 cm3/gm mole
b) 39.89 cm3/gm mole
c) 49.89 cm3/gm mole
d) 59.89 cm3/gm mole

View Answer

Answer: a [Reason:] Air contains some dust particles due to which its molecular volume decreases by a small factor.

6. What is the value of Schmidt number for hydrogen?
a) 0.23
b) 0.22
c) 0.21
d) 0.21

View Answer

Answer: b [Reason:] Schmidt number = v/D.

7. Estimate the diffusion coefficient for ammonia in air t 25 degree Celsius temperature and one atmospheric pressure.
For ammonia,
Molecular weight = 17
Molecular volume = 25.81 cm3/gm mole
For air,
Molecular weight = 29
a) 0.4880 cm2/s
b) 0.3880 cm2/s
c) 0.2880 cm2/s
d) 0.1880 cm2/s

View Answer

Answer: d [Reason:] D = 0.0043 T 3/2/p t (V b1/3 + V c1/3) 2 [1/M b + M c] ½.

8. Estimate the diffusion coefficient of carbon monoxide through air in which the mole fractions of each constituents are
O 2 = 0.18
N 2 = 0.72
CO = 0.10
The gas mixture is at 300 K and 2 atmosphere total pressure. The diffusivity values are
D CO = 18.5 * 10 -6 m2/s at 273 K, 1 atm
D CN = 19.2 * 10 -6 m2/s at 288 K, 1 atm
The subscripts C is carbon monoxide, O is oxygen and N is nitrogen
a) 10.29 * 10 -6 m2/s
b) 18.5 * 10 -6 m2/s
c) 17.5 * 10 -6 m2/s
d) 13.5 * 10 -6 m2/s

View Answer

Answer: a [Reason:] (T 1/T 2) 3/2 (p 2/p 1) = D 1/D 2.

9. What is the molecular weight of Sulphur-dioxide?
a) 84
b) 74
c) 64
d) 54

View Answer

Answer: c [Reason:] Formula of Sulphur-dioxide is SO 2.

10. The dimension of diffusion coefficient is given by
a) M L T -2
b) L 2 T -1
c) L T -1
d) M L -2 T

View Answer

Answer: b [Reason:] Unit is m2/s.

Machine Design MCQ Set 5

1. For what kind of mixtures DAB=DBA holds?
a) Ideal
b) Real
c) For both real and ideal
d) This relation is never true.

View Answer

Answer: a [Reason:] None.

2. In the expression for molar flux NA=(NA+NB)CA/C – DABdCA/dz, the terms representing bulk flow and molecular diffusion are, respectively
a) (NA+NB)CA/C, DABdCA/dz
b) (NA+NB)CA/C, DABdCA/dz
c) (NA+NB)CA/C, (NA+NB)CA/C
d) (DABdCA/dz, DABdCA/dz)

View Answer

Answer:a [Reason:] None.

3. Consider loss of ethanol vapor by diffusion from a half-filled open test tube. At what point in the diffusion path will the contribution of the bulk flow term to the molar flux be maximum?
a) At the liquid-gas interface
b) In the bulk liquid
c) In the bulk gas
d) None of the mentioned

View Answer

Answer: a [Reason:] At the liquid-gas interface concentration will be maximum. Bulk liquid is not a part of the diffusion path.

4. A reaction 3A+2B+C=1.5D+E occurs in a reactor at steady state. What will be the value of the flux ratio NA/ND
(a)-2
(b)-0.5
(c) 2
(d)-0.5

View Answer

Answer: a [Reason:] NA/ND= (rate of disappearance of A)/(rate of appearance of D) = -3/1.5 = -2.

5. For a component A of a mixture, concentration as a function of x is given:
CA=5e-10x (x is in cm and CA in mol/liter)
Calculate the value of diffusion velocity (m/s)of the component A at the point x=0, if diffusivity of A in the mixture is 2.567*10-5m2/s.
a) 0.2567
b) 2.567
c) 0.0025
d) 3.541

View Answer

Answer: a [Reason:] By Fick’s law, JA=(-)DAB*dC/dx CA(uA-U)= (-)DABdC/dx…………1 Diffusion velocity= (uA-U)=(-DABdC/dx)/CA dC/dx = -50e-10x CA= 5 mol/lit Put all the values in equation 1.

6. A sheet of Fe 1.0 mm thick is exposed to a oxidizing gas on one side and a deoxidizing gas on the other at 725°C. After reaching steady state, the Fe membrane is exposed to room temperature, and the C concentrations at each side of the membrane are 0.012 and 0.075 wt%. Calculate the diffusion coefficient (m2/sec) if the diffusion flux is 1.4×10-8kg/m2-sec.
a) 9.87*10-12
b) 9.87*10-13
c) 9.87*10-11
d) 9.87*10-10

View Answer

Answer: a [Reason:] Convert from wt% to kg/m3 . Concentration in kg/m3=[C1/(C11+C2/ρ2)]*1000 0.012% and 0.075% in kg/m3 are 0.270 and 1.688 respectively. Putting all the values in the equation JA=(-)DABdC/dx.

7. At which condition molar flux with respect to a stationary observer and with respect to a observer moving with molar average velocity?
a) In a very dilute solution
b) In a highly concentrated solution
c) At moderate concentration
d) Never

View Answer

Answer: a [Reason:] In a very dilute solution, the contribution of the bulk flow term becomes negligible. NA= (NA+NB)CA/C – DABdCA/dz (general equation) (NA+NB)CA/C =0 (in dilute solution) NA= -DABdCA/dz = JA.

8. Which among the following is the statement of the ‘Fick’s Law’?
a) The molar flux of species relative to an observer moving with the molar average velocity is proportional to the concentration gradient of the species.
b) The mass flux of species relative to an observer moving with the molar average velocity is proportional to the concentration gradient of the species.
c) The molar flux of species relative to an observer moving with the mass average velocity is proportional to the concentration gradient of the species.
d) The molar flux of species relative to a stationary observer is proportional to the concentration gradient of the species.

View Answer

Answer: a [Reason:] None.

9. The gas A diffuses through non-diffusing B from point 1 to point 2. The total pressure is 2atm and yA1=0.1 and yA2=0.Then the ratio (dPA/dz)1/(dPA/dz)2 is
a) 10
b) 1.11
c) 0.9
d) 2.3

View Answer

Answer: c [Reason:] None.

10. In industries titanium is hardened through diffusion of carbon. The concentration of carbon at 1mm into the surface of the titanium slab is 0.25kg/m3 and at 3mm the concentration is 0.68kg/m3. The rate at which the carbon is entering into its surface is 1.27*10-9kg/m2.s. calculate the value of diffusion coefficient of carbon.
a) 5.91*10-12
b) 5.91*10-10
c) 5.91*10-11
d) 5.91*10-13

View Answer

Answer: a [Reason:] J=-D(∂C/∂x) ∂C/∂x= Δc/Δx=(0.25-0.68)/(0.003-0.001)=-215kg/m4 1.27*10-19kg/m2.s= -D*(-215kg/m4) D=5.91*10-12m2/s.