How To Learn Refrigeration Evaporators

The evaporator is the component of the refrigeration system in which the heat is removed from the air, water, or any other body by the evaporating refrigerant.

It is a device in which the refrigerant is evaporated by absorbing the heat from a surrounding medium.

CLASSIFICATION OF EVAPORATORS

Based on the circulation

1. Natural circulation evaporators
2. Forced circulation evaporators

Based on the method of liquid (refrigerant) feed

1. Dry expansion (DX) evaporators
   1. DX cooling coils- used for cooling air.
   2. DX chilers- used for cooling water or other liquids.

2. Flooded evaporators

A. Full-flooded evaporators

B. Liquid overfeed evaporators

NATURAL CIRCULATION- FLOODED EVAPORATORS

• A full- flooded evaporator is operated completely filled with liquid refrigerant, which covers the entrie tube surface and provides the highest possible heat transfer rate.
• A liquid over feed evaporator is one in which the amount of liquid refrigerant circulated through the evaporator is considerably in excess of that which can be vapourised.
• The flow of the liquid refrigerant in flooded evaporator is outside the tubes whereas in the dry expansion type the flow is inside the tubes.
• The evaporator coil is kept inside the shell through which the fluid to be chilled is recirculated again and again to get the required cooling.
• Natural convection current is set up between the refrigerant and the fluid to be chilled, due to the temperature difference between them.
• The liquid refrigerant enters the shell through a float valve and due to the heat transfer the liquid refrigerant gets vapourised which cools the fluid to be chilled.
• The vapour refrigerant in the top of the shell is drawn by the compressor through the suction line and liquid refrigerant remains in the evaporator.

FORCED CIRCULATION- DRY EXPANSION (DX) EVAPORATOR

• In the dry expansion type, the refrigerant flows through tubing, and there is no liquid storage of refrigerant in the evaporator.
• The amount of liquid refrigerant fed into the evaporator is limited in such a way that at the end of the evaporator, the refrigerant is completely vapourised and only vapour refrigerant enters the suction line.
• The refrigerant flow control employed with method is usually either a thermostatic expansion valve or a capilary tube.
• A dry type direct- expansion (DX) evaporator with thermostatic expansion valve and fins on the air side which is commonly used in air- conditioing systems.
• The name direct- expansion is derived from the fact that the medium is cooled directly by the refrigerant evaporation.
• DX- evaporators are used in small capacity refrigeration and air conditioning plants.
• This type of evaporator is used when it is to be installed near the compressor to avoid leakage of refrigerant and to avoid pressure drop.