BASIC REFRIGERATION - Vapour compression, Vapour absorption

Definition: -

Refrigeration is defined as a process in which the temperature of the space or its content is reduced below its surrounding temperature.

Purpose of refrigeration on ships:

• To prolong the life of perishable food stuffs.
• Liquefaction of boil off on LNG carrier.
• To maintain sub zero temperature for certain chemicals.
• Removal of moisture from control air.
• Air conditioning for the comfort of personnel and prolonging life of electronic components.
• For cooling the drinking water.
• For making ice on passenger ships.
• For making interference fit of small components such as exhaust valve seat and valve guide etc.

Classification of refrigeration system:

Classification based on the uses

• Vapour compression
• Vapour absorption
• Steam ejection method
• Air refrigeration method
• Unconventional method

Classification as per the size of the plant

• Primary system
• Primary/secondary system

Classification based on the refrigerant 

• Freon-22
• R-134a
• R-404
• R-507
• Ammmonia

Different refrigeration system:

• Ice refrigeration.
• Vapour compression refrigeration system.
• Vapour absorption refrigeration system.
• Air refrigeration 
• Steam jet refrigeration system
• Spray refrigeration system
• Dry ice refrigeration
• Thermo-electric refrigeration

Vapour Compression Refrigeration system: -

Pic: Vapour compression refrigeration system

Components of vapour compression system:

• Evaporator
• Compressor
• Condenser
• Expansion valve

Operation: -

• In vapour compression system, the phase will change from liquid to vapour in evaporator and vapour to liquid in condenser.
• The refrigerant absorbs the latent heat from evaporator and reduces the temperature of the space from its surrounding thus change its phase from liquid to vapour.
• This high temperature refrigerant is then compressed in a compressor to make the pressure equal to the condensing pressure.
• In condenser, the refrigerant is cooled thus leaving the latent heat. The phase of refrigerant changes from vapour to liquid.
• This high pressure low temperature refrigerant is then passed through the expansion valve where its pressure is reduced and made equal to evaporating pressure.
• This refrigerant is thus again used for the refrigerant purpose.