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Machine Design MCQ Set 1

1. Which of the following reboiler is considering as an additional tray?
a) Jacketed kettle
b) Internal reboiler
c) Kettle-reboiler
d) None of the mentioned

View Answer

Answer: c [Reason:] Kettle boiler is the external boiler considered as an additional tray.

2. The internal reboilers are preferred for maintaining economy of an industry.
a) True
b) False

View Answer

Answer: b [Reason:] The internal reboilers need shutting down of distillation column for cleaning.

3. The vertical-syphon reboilers are not preferred because of
a) Fouling
b) Overheat
c) Large tubes
d) None of the mentioned

View Answer

Answer: a [Reason:] Vertical-syphon has inside tubes fouls frequently.

4. Jacketed kettle are preferred for kettle type reboiler.
a) True
b) False

View Answer

Answer: b [Reason:] Jacketed kettle needs fractionator shut down and has low heat transfer area.

5. The reboiler which is most preferred is
a) External
b) Internal
c) Middle
d) All the mentioned

View Answer

Answer: a [Reason:] External reboiler can easily replace and no need for shutting down of fractionator.

6. Find the condenser location.
mass-transfer-questions-aptitude-test-q6
a) X
b) Y
c) Z
d) No condenser

View Answer

Answer: a [Reason:] Condenser is used to condense the high volatile vapour gas to liquid so it must present at the top.

7. Condenser or reboiler is consider as a trays or stage in a fractionator.
a) True
b) False

View Answer

Answer: a [Reason:] Some separated units are present in condenser or reboiler so it also included in number of trays.

8. The fuel fired furnace is preferred for high boiling point.
a) True
b) False

View Answer

Answer: a [Reason:] The low volatile (high boiling point) components need more heat. So fuel fired furnace is preferred.

9. Will this arrangement is possible and effective.
mass-transfer-questions-aptitude-test-q9
a) True
b) False

View Answer

Answer: b [Reason:] NO distillate forms. NO separation occurs. Since the more volatile component and low volatile component remains similar to feed condition.

10. Most reboilers are
a) Heat regulators
b) Heat exchangers
c) Heat analyser
d) Heat rectifiers

View Answer

Answer: b [Reason:] Stream is the economical for heat production so heat exchangers are preferred. Heat exchangers are easy to handle and replace.

Machine Design MCQ Set 2

1. Most economical cost is
a) Minimum cost
b) Optimum cost
c) Balanced cost
d) Fixed cost

View Answer

Answer: b [Reason:] Optimum cost will be efficient at any conditions.

2. Consider an operating line touches the equilibrium line, and then the fixed cost becomes
a) Minimum
b) Infinite
c) No fixed cost
d) None of the mentioned

View Answer

Answer: b [Reason:] If the operating line touches the equilibrium line, obviously the number of trays becomes infinite leads to infinite fixed cost.

3. If the operating cost is low, then the fixed cost is more.
a) True
b) False

View Answer

Answer: a [Reason:] The operating cost will be low if the numbers of trays are more; simultaneously if the number of trays increases.

4. If the reflux ratio increases _________ increases.
a) Fixed cost
b) Operating cost
c) Optimum
d) All of the mentioned

View Answer

Answer: b [Reason:] If the reflux ratio increases, the load of condenser has to increase which leads to increase of operating cost.

5. If the reflux increases ________ increases in the fractionator.
a) Diameter
b) Length
c) Volume
d) None of the mentioned

View Answer

Answer: a [Reason:] If the reflux ratio is more, reflux increases. For the more condensed liquid, the column diameter should be more.

6. Total cost is
a) Operating + optimum cost
b) Fixed + optimum cost
c) Fixed + operating cost
d) None of the mentioned

View Answer

Answer: c [Reason:] The total cost is estimated by the sum of cost of trays and other devices like condenser, reboiler which is equals to sum of operating and fixed cost.

7. At optimum reflux ratio,
a) Operating and optimum cost are equal
b) Operating and fixed cost are equal
c) Fixed and optimum cost are equal
d) Total and optimum cost are equal

View Answer

Answer: b [Reason:] To get the optimum cost the cost used for the trays and other devices should be same.

8. Total cost will be minimum at
a) Minimum reflux ratio
b) Maximum reflux ratio
c) Optimum reflux ratio
d) None of the mentioned

View Answer

Answer: c [Reason:] At optimum reflux ratio, the fixed cost and the operating cost will be equal so the total cost will be minimum.

9. A designer gave us a report on distillation column and said he was perfect.
mass-transfer-questions-campus-interviews-q9
a) True
b) False

View Answer

Answer: b [Reason:] We can get the minimum operational cost only at minimum reflux ratio.

10. Estimate the fixed cost if the operational cost is 7 lakhs and the total cost is 15 lakhs.
a) 21 lakhs
b) 8 lakhs
c) 7 lakhs
d) None of the mentioned

View Answer

Answer: b [Reason:] Total cost= fixed cost + operational cost.

11. Estimate the operational cost if the fixed cost is 15 lakhs.
(Hint: reflux ratio= optimum)
a) 15 lakhs
b) 30 lakhs
c) 0
d) None of the mentioned

View Answer

Answer: a [Reason:] At optimum reflux ratio, the fixed cost = operational cost= 15 lakhs.

Machine Design MCQ Set 3

1. In respect to free convection over a vertical flat plate, the Nusselt number for laminar and turbulent flows varies respectively with Grashoff number G r as
a) G r and G r1/4
b) G r1/2 and G r1/3
c) G r1/4 and G r1/3
d) G r1/3 and G r1/4

View Answer

Answer: c [Reason:] It varies as G r1/4 and G r1/3.

2. Experimental results indicate that the local heat transfer coefficient h g for flow over a flat plate with an extremely rough surface is approximated by the relation
h x = a x -0.12
Where a is a constant coefficient and x is distance from the leading edge of the plate. What is the relation between this local heat transfer coefficient and the average heat transfer coefficient for a plate of length x?
a) 1.136 h x
b) 2.136 h x
c) 3.136 h x
d) 4.136 h x

View Answer

Answer: a [Reason:] h = 1.136 a x -0.12 = 1.136 h x.

3. For the free convection circumstances, the following dimensionless numbers apply
(i) Grashof number
(ii) Prandtl number
(iii) Nusselt number
Identify the correct answer
a) 2 and 3
b) 2 only
c) 1 and 2
d) 1, 2 and 3

View Answer

Answer: d [Reason:] All these numbers are useful in free convection.

4. Two horizontal steam mains with diameters 5 cm and 15 cm are to be laid in a boiler house that any mutual heat effect is precluded. The mains are at the same surface temperature of 500 degree Celsius whilst the ambient air is at 50 degree Celsius. Workout the ratios of the heat transfer coefficients
a) 0.136
b) 1.316
c) 2.136
d) 3.136

View Answer

Answer: b [Reason:] h 1/h 2 = (d 2/d 1) 0.25 = 1.136.

5. Consider the above problem, workout the heat losses from one meter length of the mains
a) 0.458
b) 0.448
c) 0.438
d) 0.428

View Answer

Answer: c [Reason:] Q 1/Q 2 = h 1 d 1 l/h 2 d 2 l = 0.438.

6. A spherical heater of 20 cm diameter and at 60 degree Celsius is immersed in a tank of water at 20 degree Celsius. Determine the value of convective heat transfer coefficient
a) 458.32 W/m2 K
b) 558.32 W/m2 K
c) 658.32 W/m2 K
d) 758.32 W/m2 K

View Answer

Answer: a [Reason:] h = Nusselt number (k/d) = 458.32 W/m2 K.

7. A steam pipe 50 mm diameter and 2.5 m long has been placed horizontally and exposed to still air at 25 degree Celsius. If the pipe wall temperature is 295 degree Celsius, determine the rate of heat loss. At the mean temperature difference of 160 degree Celsius, the thermo-physical properties of air are
k =3.64 * 10 -2 W/m K
v =30.09 * 10 -6 m2/s
P r =0.682
Β =1/160 + 273 = 2.31 * 10 -3 per K
a) 1156.5 W
b) 1146.5 W
c) 1136.5 W
d) 1126.5 W

View Answer

Answer: d [Reason:] Q = h A d t, where h = 14.60 k/D.

8. Consider the above problem, find out the Grashof number
a) 0.8447 * 10 5
b) 0.8447 * 10 6
c) 0.8447 * 10 7
d) 0.8447 * 10 8

View Answer

Answer: b [Reason:] Grashoff number = D 3 P 2 (β g d t)/µ 2.

9. Estimate the heat transfer from a 40 W incandescent bulb at 125 degree Celsius to 25 degree Celsius in quiescent air. Approximate the bulb as a 50 mm diameter sphere. The approximate correlation for the convection coefficient is
Nu = 0.60 (Gr Pr) 0.25
Where the different parameters are evaluated at the mean film temperature, and characteristics length is the diameter of the sphere
a) 4.71 W
b) 5.71 W
c) 6.71 W
d) 7.71 W

View Answer

Answer: d [Reason:] Q = h A d t = 7.71 W.

10. Consider the above problem, find what percent of power is lost by free convection?
a) 19.478%
b) 19.378%
c) 19.278%
d) 19.178%

View Answer

Answer: c [Reason:] Percentage of power lost by free convection = 7.71 * 100/40 = 19.278%.

Machine Design MCQ Set 4

1. Find the moisture to be evaporated per kg of dried product if initial and final moisture content per kg of dry solid is 85% and 15%.
a) 0.5
b) 0.6
c) 0.7
d) 0.8

View Answer

Answer: c [Reason:] Moisture to dry = Initial moisture – final moisture content = 0.85 – 0.15 =0.7 per kg of dry solid.

2. Convert 80% of moisture in wet basis to dry basis ( kg water/kg dry solid)
a) 4
b) 8
c) 12
d) 16

View Answer

Answer: a [Reason:] 0.8/1-0.8 = 4 kg water/kg dry solid.

3. If the equilibrium vapour pressure is lower than pure liquid pressure then the moisture content is ___________
a) Bound moisture
b) Unbound moisture
c) Equilibrium moisture
d) None of the mentioned

View Answer

Answer: a [Reason:] Bound moisture is the inside moisture present inside the compound which can be removed only by unsaturated surface drying.

4. The substance moisture exerts equilibrium vapour pressure equals to vapour pressure of liquid is ________
a) Bound moisture
b) Unbound moisture
c) Equilibrium moisture
d) None of the mentioned

View Answer

Answer: b [Reason:] The saturated surface moisture is un bound moisture which equals the equilibrium vapour pressure.

5. The moisture which can be evaporated is bound moisture.
a) True
b) False

View Answer

Answer: b [Reason:] The moisture which can be evaporated is known as free moisture which is the moisture excess to equilibrium moisture.

6. The method of drying by conduction through materials are done by _________
a) Direct driers
b) Indirect driers
c) Tray driers
d) None of the mentioned

View Answer

Answer: b [Reason:] Conduction through metals is heating indirectly so here indirect driers are used.

7. The substance like food stuff, pharma products are dried by _______ drying.
a) Direct
b) Indirect
c) Freeze
d) None of the mentioned

View Answer

Answer: c [Reason:] The compounds have to be preserved carefully so for drying these products we need sublimation drying known as freeze drying.

8. The representation AB is known as
tough-mass-transfer-questions-answers-q8
a) Bound moisture
b) Unbound moisture
c) Equilibrium moisture
d) None of the mentioned

View Answer

Answer: b [Reason:] The saturated region is the unbound moisture region.

9.The name of the curve between relative humidity and moisture content is equilibrium moisture curve.
a) True
b) False

View Answer

Answer: a [Reason:] The equilibrium moisture curve gives us the relation between relative saturation and moisture content.

10. Convert 5 kg of moisture /kg of dry solid to wet basis.
a) 3/6
b) 4/6
c) 5/6
d) 1

View Answer

Answer: c [Reason:] In wet basis, 5/(5+1) (kg of moisture/kg of wet solid) = 5/6.

Machine Design MCQ Set 5

1. Find the time taken to dry 50% to 40% of moisture (dry basis) if critical moisture content is 30%. If the weight of the wet solid is 5 kg and the product of area and constant rate is 0.5 kg/min.
a) 20 sec
b) 40 sec
c) 60 sec
d) 80 sec

View Answer

Answer: c [Reason:] Time for drying = ( wet solid weight * change in moisture )/ Area * constant rate = (5 * 0.1/0.5) min = 1 min = 60 sec.

2. Find the period if the initial and the final moisture content are 60% and 40%. Also the critical moisture content is 30%.
a) Constant rate period
b) Falling rate period
c) Unsaturated period
d) None of the mentioned

View Answer

Answer: a [Reason:] Here the final moisture content is greater than critical moisture content so it must be a constant rate period.

3. Find the period if the initial and the final moisture content are 50% and 20%. Also the critical moisture content is 30%.
a) Constant rate period
b) Falling rate period
c) saturated period
d) None of the mentioned
.

View Answer

Answer: b [Reason:] Here the final moisture content is less than critical moisture content so it must be a falling rate period or unsaturated drying.

4. At the constant drying period of a batch process, the rate of drying varies accordingly.
a) True
b) False

View Answer

Answer: b [Reason:] For the constant drying period the rate of drying remains constant by analysing drying curve.

5. Find the change in moisture content from the given data
Given data:
Time for drying= 6 sec
Area * Constant rate = 8 kg per sec
Weight of wet solid = 100 kg
a) 0.21
b) 0.12
c) 0.48
d) 0.84

View Answer

Answer: c [Reason:] Difference in moisture = (time *area* rate )/Weight of the solid = 0.48.

6. Find the initial moisture content for the batch process if the final moisture content is 25% (dry basis) and the constant moisture content is 40%. (Includes constant and falling rate period)
a) 35
b) 30
c) 60
d) None of the mentioned

View Answer

Answer: c [Reason:] Here the initial moisture content must be greater than critical moisture content.

7. Find the final moisture content for the batch process if the initial moisture content is 75% (dry basis) and the constant moisture content is 40%. (Includes constant and falling rate period)
a) 45
b) 50
c) 60
d) None of the mentioned

View Answer

Answer: d [Reason:] Here the final moisture content must be less than critical moisture content.

8. Falling rate period of a batch process starts at
a) Saturated drying surface
b) Unsaturated drying surface
c) Both unsaturated and saturated region
d) None of the mentioned

View Answer

Answer: b [Reason:] The bound moistures gets evaporated only at unsaturated surface which is a falling rate period.

9. If the time taken for the moisture removal is obtained from the formula
Time = Ss(Xc – Xe)/ Nc * A ln ((X1-Xe)/(X2-Xe)) then the falling curve will be curves symmetrically
Where, Ss= Wet solid weight
Xc,Xe- constant & equilibrium moisture content
X1,X2 – initial and final moisture content
a) True
b) False

View Answer

Answer: b [Reason:] This relation gives the linear relation so the falling rate curve will be linear.

10. There will be a change in rate of drying of a batch process after the constant drying process.
a) True
b) False

View Answer

Answer: a [Reason:] After the constant drying curve, the unsaturated drying starts then the rate of drying decreases due to moisture removal.

11. Find the Constant rate representation
tricky-mass-transfer-questions-answers-q11
a) X
b) Y
c) Z
d) A

View Answer

Answer: a [Reason:] Constant drying period has constant rate.

12. Find the representation of critical moisture content value
tricky-mass-transfer-questions-answers-q11
a) A
b) B
c) Z
d) Y

View Answer

Answer: c [Reason:] At the end of constant rate period we get critical moisture content value.

13. Find the equilibrium content value
tricky-mass-transfer-questions-answers-q13
a) A
b) B
c) C
d) Y

View Answer

Answer: c [Reason:] After the rate has stopped, the remaining moisture is known as equilibrium moisture content.

14. Falling rate period of the batch drying curve = _______ + ___________
a) Internal movement, unsaturated surface drying
b) Internal movement, saturated surface drying
c) External movement, unsaturated surface drying
d) External movement, saturated surface drying

View Answer

Answer: a [Reason:] From the drying curve we know the falling rate period represents the bound moisture removal so it includes internal movement and unsaturated surface drying.

15. Find the region if the final and the initial moisture content are 40% and 30% (Dry basis) and the critical moisture content is 45%.
a) Constant rate
b) Falling rate
c) Internal movement
d) None of the mentioned

View Answer

Answer: b [Reason:] Here both initial and final moisture content are less than critical moisture content so the rate is falling rate period.