Quiz: Mechanical Engineering 17th June

Quiz: Mechanical Engineering
Exam: AE/JE
Topic: Miscellaneous

Each question carries 2 mark
Negative marking: 1/3 mark
Time: 10 Minutes

Q1. The lowest temperature at which the oil ceases to flow cooled is known as __.
(a) Flash point
(b) Fire point
(c) Cloud point
(d) Pour point

Q2. For diesel engine, the method of governing employed is
(a) Quality governing
(b) Quantity governing
(c) Hit and miss governing
(d) None of the above

Q3. The output of a diesel engine can be increased without increasing the engine revolution or size in following way
(a) by feeding more fuel
(b) by increasing flywheel size
(c) by heating incoming air
(d) by supercharging

Q4. A refrigeration cycle operates between condenser temperature of +27°C and evaporator temperature of -23°C. the Carnot coefficient of performance of cycle will be __.
(a) 0.2
(b) 1.2
(c) 5
(d) 6

Q5. The door of a running refrigerator inside a room was left open. Which of the following statement is correct?
(a) The room will be cooled to the temperature inside the refrigerator
(b) the room will be cooled slightly
(c) the roam will be gradually warmed up
(d) the temperature of the air in the room will remain unaffected.

Q6. Why is multi-staging in centrifugal pump used?
(a) For high flow rate
(b) For high head
(c) For high speed
(d) For high efficiency

Q7. The water level in a dam is 10 m. the total force acting on vertical wall per metre length is
(a) 49.05 kN
(b) 490.5 kN
(c) 981 kN
(d) 490.5 N

Q8. Consider the following statements:
A surge tank provided on the penstock connected to a water turbine

  1. Helps in reducing the water hammer.
  2. Stores extra water when not needed.
  3. Provides increased demand of water.
    Which of these statements are correct?
    (a) 1 and 3
    (b) 2 and 3
    (c) 1 and 2
    (d) 1, 2 and 3

Q9. A draft tube is used in a reaction turbine
(a) To guide water downstream without splashing
(b) To convert residual pressure energy into kinetic energy
(c) To convert residual kinetic energy into pressure energy
(d) To streamline the flow in the tail race

Q10. Heat is transferred by conduction, convection and radiation in____.
(a) Boiler furnaces
(b) Melting of ice
(c) condensation of steam in condenser
(d) None of these

Solutions
S1. Ans.(c)
Sol.
Cloud point It is the temperature below which wax in diesel forms a cloudy appearance. This wax thickens the oil and clogs fuel filters and injectors in engine.
Pour point : It is the minimum temperature at which a lubricant turns into semi solid and almost losses its flow characteristics.
Flash point : For a flammable liquid, it is the minimum temperature at which there are enough vapors of the liquid to ignite when a heat source is brought near it.
Fire point : For a fuel, it is the lowest temperature at which the vapor of that fuel will continue to burn for at least 5 seconds after ignition source removed.

S2. Ans.(a)
Sol. For diesel engine, the method of governing employed is quality governing. Governing means the action of varying the fuel supply in accordance with the load demands so that the engine runs at practically constant speed. Some important methods of governing of IC engines.

  1. Hit and miss governing: This method is suitable for small gas engines. In this system of governing, whenever the engine starts running at higher speed (due to decreased load), some explosions are omitted or missed. This is done with the help of a centrifugal governor.
  2. Qualitative governing: In this system of governing, a control valve is fitted in the fuel delivery pipe which controls the quantity of fuel to be mixed in the charge. The movement of control valve is regulated by the centrifugal governor through rack and pinion arrangement.
  3. Quantitative governing: In this system of governing, the quality of charge (i.e. air-fuel ratio of the mixture) is kept constant, but the quantity of mixture supplied to the engine cylinder is varied by means of a throttle valve which is regulated by the centrifugal governor through rack and pinion arrangement.

S3. Ans.(d)
Sol. A supercharger is an air compressor that increases the pressure or density of air supplied to an internal combustion engine. This gives each intake cycle of the engine more oxygen, letting it burn more fuel and do more work, thus increasing power.

S4. Ans.(c)
Sol.
T_H=27°C=300K
T_L= -23°C=250 K
(COP)_ref=T_L/(T_H-T_L )=250/(300-250)=5

S5. Ans.(c)
Sol. The door of a running refrigerator inside a room was left open than the roam will be gradually warmed up.

S6. Ans (b)
Sol. For high head multi-staging centrifugal pump is used.

S7. Ans (b)
Sol.
Exerted force (F) = ρgAx ̅
F = 1000×9.81×10×1×5
F = 490.5 KN

S8. Ans (d)
Sol. A surge tank provided on the penstock connected to a water turbine

  1. Helps in reducing the water hammer.
  2. Stores extra water when not needed.
  3. Provides increased demand of water.

S9. Ans (c)
Sol. A draft tube is used in a reaction turbine to convert residual kinetic energy into pressure energy.

S10. Ans.(a)
Sol. Heat is transferred by conduction, convection and radiation in Boiler furnaces.

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