Mechanical Interview Question on Refrigeration

  • 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.

  • What is COP ?

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 .

  • What is ton of refrigeration ?

1 ton of refrigeration means heat absorbed while melting 1 ton (2000 lb) of ice at zero degree Celsius at 24 hours .

  • What is BTU ?

BTU = British Thermal Unit ; 1 BTU is the amount of heat required to raise the temperature of one lb water by one degree Fahrenheit.

  • What is sub-cooling and super heating in refrigeration system ? Why these are used ?

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.

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  • Which thermodynamic cycle is implied in refrigeration system ?

Reversed Carnot or Reversed Rankin Cycle

  • What is the most commonly used refrigerant ?

R134a

  • Detect absorbers and refrigerant in these systems – Li-Br and NH3 – H2O .

In Li-Br – Water is the refrigerant and Li-Br is the absorbent.

In  NH3 – H2O : NH3 is the refrigerant and water is absorber.

  • What is LMTD method ?

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.

  • What is the difference between a cooler and an air conditioner ?

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.

  • What is the difference between cooling tower and condenser ?

Condenser is a heat exchanger which converts saturated vapor into liquid. For doing so the condenser temperature must be below than the saturation temp.

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Cooling tower is the device in which recirculating condenser water is cooled by the evaporative method with direct contact to the atmosphere.

  • What is a chiller ?

Chiller is a device / machine for cooling something.

 

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