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Mechanical engineering interview questions – Refrigeration

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  • Q:What is Refrigeration ? What is the unit of refrigeration ?
Refrigeration is the process where heat is transferred from low temperature to high temperature medium with the help of external work. It’s unit is ton of refrigeration.
  • Q:What is COP ?
answer: COP = Co-efficient 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 net work .
  • Q:What is 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 .
  • Q: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.
  • Q:What is sub-cooling and super heating 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.
  • Q:Which thermodynamic cycle is implied in refrigeration system ?
answer: Reversed Carnot or Reversed Rankin Cycle.
  • Draw the T-S diagram and schematic arrangement of reversed Carnot Cycle and Reversed Rankin Cycle in a basic vapor compression refrigeration system.
  • Draw the T-S, P-h  diagram of refrigeration system with sub-cooling and super-heating in vapor compression refrigeration system .
  • Q:What is the most commonly used refrigerant ?
answer: R134a
  • 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.
  • 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.
  • Q:What is 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 transfered.
answer : For a cooler to become air conditioner it must meet the following requirements :
It must control the 1. temperature 2. Humidity 3 . motion of air 4. purity of air.
  • Q: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.
Cooling tower is the device in which recirculating condenser water is cooled by the evaporative method with direct contact to the atmosphere.
  • Q:What is a chiller ?
answer:  Chiller is a device / machine for cooling something.
Mechanical engineers !  The third part is coming up very soon. So stay with basic mechanical engineering.  Thanks  ! Enjoy !! Cheers !!!
Q:Which law must be satisfied to build a refrigeration system ?
answer: Second Law of Thermodynamics (Clausius Statement) .

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