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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