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Multiple choice question for engineering

Set 1

1. Pick the odd one out
a) Open feed water heaters
b) Jet condensers
c) De-super heaters
d) Surface condensers

View Answer

Answer: d [Reason:] In surface condenser, the heat transfer occurs between the fluid streams without mixing or physical contact with each other.

2. The lubricating oil for a large industrial gas turbine engine is cooled in a counter flow, concentric tube heat exchanger. The cooling water flows through the inner tube ( diameter = 25 mm) with inlet temperature 25 degree celsius and mass flow rate 0.2 kg/s. The oil flows through the annulus (diameter = 50 mm) with mass flow rate 0.125 kg/s and its temperature at entry and exit are 90 degree Celsius and 60 degree Celsius. Find outlet temperature of cooling water
heat-transfer-questions-puzzles-q2
a) 14.58 degree celsius
b) 24.58 degree celsius
c) 34.58 degree celsius
d) 44.58 degree celsius

View Answer

Answer: c [Reason:] m h c c (t h1 – t h2) = m c c c(t c2 – t c1).

3. A cross flow type air heater has an area of 50 cm2. The overall heat transfer coefficient is 100 W/m2 K and heat capacity of both hot and cold stream is 1000 W/m K. The value of NTU is
a) 1000
b) 500
c) 5
d) 0.2

View Answer

Answer: b [Reason:] NTU = A U/C MIN = 5.

4. In a balanced counter flow heat exchanger with m h c h = m c c c, the NTU is equal to unity. What is the effectiveness of heat exchanger?
a) 0.5
b) 1.5
c) 0.33
d) 0.2

View Answer

Answer: a [Reason:] Effectiveness = NTU/NTU – 1 = 0.5.

5. After expansion from a gas turbine, the hot exhaust gases are used to heat the compressed air from a compressor with the help of a cross flow heat exchanger of 0.8 effectiveness. What is the number of transfer units of the heat exchanger?
a) 2
b) 4
c) 8
d) 16

View Answer

Answer: b [Reason:] Effectiveness = NTU/NTU – 1 = 0.5.

6. E – NTU method is particularly useful in thermal design of heat exchangers when
a) Inlet temperature of the fluid streams are not known as a priori
b) The outlet temperatures of the hot fluid streams is known but that of cold fluid stream is not known as a priori
c) The outlet temperatures of the fluid streams is known as a priori
d) The outlet temperatures of the fluid streams are not known as a priori

View Answer

Answer: d [Reason:] It is useful when outlet temperatures of the fluid streams are not known as a priori.

7. The engine oil at 150 degree Celsius is cooled to 80 degree Celsius in a parallel flow heat exchanger by water entering at 25 degree Celsius and leaving at 60 degree Celsius. Estimate the number of transfer units
a) 1.221
b) 2.221
c) 3.221
d) 4.221

View Answer

Answer: a [Reason:] Effectiveness = 1 – exponential [- NTU (1 – C)]/1 + C.

8. In a surface condenser, the water flowing through a series of tubes at the rate of 200 kg/hr is heated from 15 degree Celsius to 75 degree Celsius. The steam condenses on the outside surface of tubes at atmospheric pressure and the overall heat transfer coefficient is estimated at 860 k J/m2 hr degree. Find the number of transfer units of the heat exchanger. At the condensing pressure, stream has saturation temperature 0f 100 degree Celsius and the latent heat of vaporization is 2160 k J/kg. Further, the steam is initially just saturated and the condensate leaves the exchanger without sub-cooling i.e. only latent heat of condensing steam is transferred to water. Take specific heat of water as 4 k J/kg K
a) 3.224
b) 2.224
c) 1.224
d) 0.224

View Answer

Answer: c [Reason:] Effectiveness = 1 – exponential [- NTU].

9. Consider the above problem, find the steam condensation rate
a) 52.22 kg/hr
b) 42.22 kg/hr
c) 32.22 kg/hr
d) 22.22 kg/hr

View Answer

Answer: d [Reason:] m h f g = m c c c (t c 2 – t c 1).

10. NTU is a number of transfer units, dimensionless parameter defined as
a) U A/C MIN
b) 2 U A/C MIN
c) 3 U A/C MIN
d) 4 U A/C MIN

View Answer

Answer: a [Reason:] The number of transfer units is a measure of the size of the heat exchanger, it provides some indication of the size of the heat exchanger.

Set 2

1. The hydrodynamic friction is associated with the phenomena when a complete film of lubricant exists between the two bearing surfaces.
a) True
b) False

View Answer

Answer: a

2. In hydrodynamic friction, the friction force does not depends on the lubricant viscosity.
a) True
b) False

View Answer

Answer: b [Reason:] In fact, in hydrodynamic friction, the friction force entirely depends on the lubricant viscosity.

3. During normal engine operation there is almost no metallic contact except between the compression piston ring and cylinder walls.
a) True
b) False

View Answer

Answer: a

4. During starting of the engine, the journal bearings operate in ____________ friction.
a) rolling
b) hydrodynamic friction
c) partial-film
d) none of the mentioned

View Answer

Answer: c

5. The ____________ friction is due to rolling motion between the two surfaces.
a) rolling
b) hydrodynamic friction
c) partial-film
d) none of the mentioned

View Answer

Answer: a

6. Ball and roller bearings and tappet rollers are subjected to rolling friction.
a) True
b) False

View Answer

Answer: a

7. Rolling friction coefficient is ____________ than journal bearing friction coefficient during starting and initial running of engine.
a) higher
b) lower
c) faster
d) none of the mentioned

View Answer

Answer: b

8. A circular cylindrical shaft called journal rotates against a cylindrical surface called the bearing.
a) True
b) False

View Answer

Answer: a

9. Total friction is negligible compared to rolling friction.
a) True
b) False

View Answer

Answer: b [Reason:] No, but rolling friction is negligible compared to total friction.

10. The mechanical friction ___________ with increase in speed.
a) increases
b) reduces
c) unpredictable
d) none of the mentioned

View Answer

Answer: a [Reason:] Mechanical friction is directly proportional to engine speed, so the mechanical friction increases with increase in speed.

Set 3

1. In SI engine, to obtain required firing order
a) battery is installed
b) distributor is installed
c) carburettor is installed
d) ignition coil is installed

View Answer

Answer: b [Reason:] In SI engine, to obtain required firing order distributor is installed and not battery or ignition coil.

2. In a four cylinder petrol engine the standard firing order is
a) 1-2-3-4
b) 1-4-3-2
c) 1-3-2-4
d) 1-3-4-2

View Answer

Answer: d

3. Firing order is the order in which various cylinders of a multi cylinder engine fire.
a) True
b) False

View Answer

Answer: a

4. The firing order is arranged to have power impulses equally spaced, and from the point of view of balancing.
a) True
b) False

View Answer

Answer: a

5. The main function of a ___________ is to conduct the high potential from the ignition system into the combustion chamber.
a) spark plug
b) magneto ignition
c) battery
d) none of the mentioned

View Answer

Answer: a [Reason:] The main function of a spark plug is to conduct the high potential from the ignition system into the combustion chamber while magneto ignition ignites with magnetic effect and battery provides electricity.

6. The spark plug must withstand pressures up to at least __________ bar.
a) 40
b) 50
c) 55
d) 60

View Answer

Answer: c

7. A cold plug has a large heat transfer path and a large area exposed to the combustion gases, or compared to hot plug.
a) True
b) False

View Answer

Answer: b [Reason:] In fact, a cold plug has a short heat transfer path and a small area exposed to the combustion gases, or compared to hot plug.

8. In CDI system a capacitor is used to store the energy.
a) True
b) False

View Answer

Answer: a [Reason:] In CDI system a capacitor is used to store the energy, induction coil is not used.

9. In CDI system, the output voltage is relatively dependent of engine speed.
a) True
b) False

View Answer

Answer: b [Reason:] Actually, in CDI system, the output voltage is relatively independent of engine speed.

10. Ignition timing is the correct instant for the introduction of spark near the end of compression stroke in the combustion chamber.
a) True
b) False

View Answer

Answer: a

Set 4

1. Mist lubrication system is used for ____________ stroke cycle engines.
a) four
b) two
c) unpredictable
d) none of the mentioned

View Answer

Answer: b

2. In drip system oil is fed to machine parts drop by drop, from an oil cup.
a) True
b) False

View Answer

Answer: a

3. The ball and roller bearings are lubricated to reduce friction and wear between the sliding parts of the bearing.
a) True
b) False

View Answer

Answer: a

4. The ball and roller bearings are lubricated to prevent rusting or corrosion of bearing surfaces.
a) True
b) False

View Answer

Answer: a

5. All the lubricating oil from the oil sump, must pass through an oil filter before it is supplied to the engine bearings.
a) True
b) False

View Answer

Answer: b [Reason:] All the lubricating oil from the oil sump, must pass through an oil filter before it is supplied to the engine bearings.

6. Bearings maintain very close tolerances and are likely to be damaged by an foreign abrasive material entering the lubrication line.
a) True
b) False

View Answer

Answer: a

7. In by pass type filter arrangement, only a small portion of the lubricating oil is passed through the filter and the remaining lubricating oil is directly supplied to the bearings by the oil pump at pre-set pressure.
a) True
b) False

View Answer

Answer: a

8. In full flow type filter arrangement, whole of the oil is filtered before it is supplied to various bearings.
a) True
b) False

View Answer

Answer: b [Reason:] In full flow type filter arrangement, whole of the oil is filtered before it is supplied to various bearings.

9. All the lubricating oil, in normal course, should be filtered approximately every minute.
a) True
b) False

View Answer

Answer: b [Reason:] But in fact, all the lubricating oil, in normal course, should be filtered approximately every half minute.

10. In closed system, the fresh air supply is taken to the crankcase from the carburettor.
a) True
b) False

View Answer

Answer: a

Set 5

1. If the engine is operating with richer mixtures the optimum spark timing must be
a) constant
b) increased
c) retarded
d) none of the mentioned

View Answer

Answer: c [Reason:] If the engine is operating with richer mixtures the optimum spark timing must be retarded as if the mixture is rich it has its low self ignition temperature.

2. Part load operation of a spark ignition engine is not affected by throttling the incoming charge.
a) True
b) False

View Answer

Answer: b [Reason:] In fact, part load operation of a spark ignition engine is affected by throttling the incoming charge.

3. Due to throttling a smaller amount of charge enters the cylinder and the dilution due to residual gases is also greater.
a) True
b) False

View Answer

Answer: a

4. Ignition delay does not depend upon the type of the fuel used in the engine.
a) True
b) False

View Answer

Answer: b [Reason:] Actually, ignition delay will depend upon the type of the fuel used in the engine.

5. For maximum power and economy a slow burning fuel needs a higher spark advance than a fast burning fuel.
a) True
b) False

View Answer

Answer: a

6. The ignition timing is fixed to obtain minimum power from the engine.
a) True
b) False

View Answer

Answer: b [Reason:] In fact, the ignition timing is fixed to obtain maximum power from the engine.

7. The ignition timing is affected by
a) compression ratio
b) engine speed
c) mixture strength
d) all of the mentioned

View Answer

Answer: d [Reason:] The ignition timing is affected by i) compression ratio ii) engine speed iii) mixture strength iv) combustion chamber design v) throttle opening vi) engine temperature vii) type of fuel.

8. The ignition timing is affected by
a) combustion chamber design
b) throttle opening
c) engine temperature
d) all of the mentioned

View Answer

Answer: d [Reason:] The ignition timing is affected by i) compression ratio ii) engine speed iii) mixture strength iv) combustion chamber design v) throttle opening vi) engine temperature vii) type of fuel.