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Wednesday 17 September 2014

100 MECHANICAL ENGINEERING INTERVIEW QUESTION AND ANSWER

 100 Mechanical Engineering Interview Question and Answers http://upseexam.blogspot.com/

1. What is the difference between scavenging and
supercharging?

Ans: Scavenging is process of flushing out burnt gases
from engine cylinder by introducing fresh air in the
cylinder before exhaust stroke ends. Supercharging is
the process of supplying higher mass of air by
compressing  the  atmospheric  air.

2. What are the names given to constant temperature,
constant pressure, constant volume, constant internal
energy, constant enthalpy, and constant entropy
processes?

2. Ans: Isothermal, isochoric, isobaric, free expression,
throttling  and  adiabatic  processes  respectively.

3. In a Rankine cycle if maximum steam pressure is
increased keeping steam temperature and condenser
pressure same, what will happen to dryness fraction of
steam after expansion ?Ans: It will decrease.

4. Why entropy change for a reversible adiabatic process
is  zero?

Ans: Because there is no heat transfer in this process.

5. What are two essential conditions of perfect gas?
Ans: It satisfies equation of state and its specific heats
are  constant.

6. Enthalpy and entropy are functions of one single
parameter.  Which  is  that?

Ans:  Temperature.

100 Mechanical Engineering Interview Question and Answers http://upseexam.blogspot.com/
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100 Mechanical Engineering Interview Question and Answers http://upseexam.blogspot.com/

7. Why rate of condensation is higher on a polished
surface  compared  to  rusty  surface?

Ans: Polished surface promotes drop wise condensation
and  does  not  wet  the  surface.

8. How much resistance is offered to heat flow by drop
wise  condensation?

Ans:  Nil

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9. What is the relationship between COP of heating and
cooling?

Ans: COP of heating is one (unity) more than COP of
cooling.

10. How much is the work done in isochoric process?

Ans:  Zero.

11. When maximum discharge is obtained in nozzle?
Ans:  At  the  critical  pressure  ratio.

1. Under what condition the work done in reciprocating
compressor  will  be  least?

Ans: It is least when compression process approaches
isothermal. For this purpose, attempts are made to cool
the  air  during  compression.

13. What is the difference between stalling and surging

100 Mechanical Engineering Interview Question and Answers http://upseexam.blogspot.com/
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100 Mechanical Engineering Interview Question and Answers http://upseexam.blogspot.com/

in  rotary  compressions?

Ans: Stalling is a local phenomenon and it occurs when
How breaks away from the blades. Surging causes
complete breakdown of flow and as such it affects the
whole  machine.

14. Why the electric motor of a fan with backward
curved blades is never got overloaded under any
condition?

Ans: The maximum power is consumed at about 70%
of maximum flow in case ‘of fan with backward blades.
For higher flow, power consumption gets lower.

15. Why the work per kg of air flow in axial flow
compressor is less compared to centrifugal compressor
for  same  pressure  ratio?

Ans: Isentropic efficiency of axial flow compressor is
higher.

16. What is the name given to portion of thermal energy
to  be  necessarily  rejected  to  environment?

Ans:  Energy.

17.  What  is  pitting?  How  it  is  caused?

Ans: Non uniform corrosion over the entire metal
surface, but occurring only in small pits is called pitting.
It is caused by lack of uniformity in metal.

18.  What  is  caustic  embrittlement?

Ans: It is the actual physical change in metal that makes
it extremely brittle and filled with minute cracks. It
occurs particularly in the seams of riveted joints and
around  the  rivet  holes.

19. Which impurities form hard scale and which
impurities  soft  scale?

Ans: Sulphates and chlorides of lime and magnesium
form hard scale, and carbonates of lime and magnesium
form  soft  scale.

20. What is the difference between hard water and soft
water?

Ans: Hard water contains excess of scale forming
impurities and soft water contains very little or no scale
forming  substances.

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50 Mechanical Engineering Interview Question and Answer

Mechanical engineering interview question and answer http://upseexam.blogspot.in/

1. What is the difference between Critical Speed and Whirling Speed?
Ans. In Solid mechanics, in the field of rotor dynamics, the critical speed is the theoretical angular velocity which excites the natural frequency of a rotating object, such as a shaft, propeller or gear. As the speed of rotation approaches the objects natural frequency, the object begins to resonate which dramatically increases system vibration. The resulting resonance occurs regardless of orientation. Whirling Speed is due to the unbalanced forces acting on a rotating shaft.

2. How a Diesel Engine Works as Generator?
Ans. Diesel engine is a prime mover, for a generator, pump, and for vehicles etc. generator is connected to engine by shaft. Mostly in thermal power plat, there is an engine is used to drive generator to generate power.

3. Explain Second Law of Thermodynamics?
Ans. The entropy of the universe increases over time and moves towards a maximum value.

4. Compare Brayton Cycle and Otto Cycle?
Ans. The heat addition and rejection processes in Otto cycle are of constant volume, whereas in Brayton cycle, they are of constant pressure. Otto  cycle  is  the  ideal  cycle  for  spark  ignition  engines. Brayton cycle is the ideal cycle for gas power turbines.

5. What is the purpose of Scrapper Ring?
Ans. Scrap the excess lube oil from the cylinder walls. There by preventing oil from entering combustion zone.


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50 Mechanical Engineering Interview Question and Answer

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