Mechanical Engineering Interview Questions Part 2
This is the second part of the mechanical engineering viva questions.
This part mainly discusses the common questions of refrigeration, air
conditioning systems and some thermodynamics If You haven’t read the first part
then go through link.
Qn. What is
Refrigeration? What is the unit of refrigeration?
Ans. Refrigeration is the process where heat is transferred from low
temperature to high-temperature medium with the help of external work. Its unit
is ton of refrigeration.
Qn. What is COP?
Answer: COP = Coefficient of Performance. It is used to measure the
performance of a refrigeration system. It is generally expressed by the ratio
of evaporation work or refrigeration effect to the compressor work or network.
Qn. What is a
ton of refrigeration?
Answer: 1 ton of refrigeration means heat absorbed while melting 1 ton
(2000 lb) of ice at zero degree Celsius at 24 hours.
Qn. What is BTU?
answer: BTU = British Thermal Unit; 1 BTU is the amount of heat required
to raise the temperature of one lb water by one degree Fahrenheit.
Qn. What is
sub-cooling and superheating in refrigeration system ? Why these are used?
Answer: Sub-cooling or under cooling is done before throttling or
expanding the refrigerant and it ensures that no vapor enters the expansion
valve.
Super-heating is done before compression and it ensures that no liquid
enters the compressor.
Qn. Which
thermodynamic cycle is implied in the refrigeration system?
answer: Reversed Carnot or Reversed Rankin Cycle.
Qn. Draw the T-S
diagram and schematic arrangement of reversed Carnot Cycle and Reversed Rankin
Cycle in a basic vapor compression refrigeration system.
Qn. Draw the
T-S, P-h diagram of refrigeration system with sub-cooling and super-heating in
vapor compression refrigeration system.
answer: T-S and P-h diagram with subcooling and superheating.
Qn. What is the
most commonly used refrigerant?
answer: R134a
Qn. What is
Vapor compression and Vapor Absorption Refrigeration system ? (Difference between)
/ What are the advantages of Vapor absorption systems over Vapor compression?
answer: Please follow this link for the answer – Vapor Compression Vs
Vapor Absorption Refrigeration System
Detect absorbers and refrigerant in these systems – Li-Br and NH3 – H2O.
answer: In Li-Br – Water is the refrigerant and Li-Br is the absorbent.
In NH3 – H2O: NH3 is the
refrigerant and water is absorber.
Qn. What is the
LMTD method?
answer: LMTD refers to Logarithmic Mean Temperature Difference. It is
used to measure the temperature difference in double pipe heat exchangers. The
more the LMTD the more heat will be transferred.
Qn. What is the
difference between a cooler and an air conditioner?
answer: For a cooler to become air conditioner it must meet the
following requirements :
It must control the 1. temperature 2. Humidity 3. the motion of air 4.
purity of air.
Qn. What is the
difference between cooling tower and condenser?
answer: Condenser is a heat exchanger which converts saturated vapor
into liquid. For doing so the condenser temperature must be below than the
saturation temp.
A cooling tower is a device in which recirculating condenser water is
cooled by the evaporative method with direct contact to the atmosphere.
Qn. What is a
chiller?
answer: Chiller is a device/machine
for cooling something. (I will be writing some articles about chillers very
soon)
Thanks for visit my blog.
Best of luck for your job.
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