Question Set 119

• What is the difference between Impulse Turbine and Reaction Turbine?

• What is NPSH?

Net Positive Suction Head (NPSH)

It is defined as the absolute pressure head at the inlet to the pump minus (-) the vapor pressure head corresponding to the temperature of the liquid pumped plus (+) the velocity head.

• 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 (one) 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.

• Which thermodynamic cycle is implied in refrigeration system ?

Reversed Carnot or Reversed Rankine Cycle.

• What is the most commonly used refrigerant ?

R134a

• 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 transferred.

• 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.

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