REFRIGERATION SYSTEM COMPONENTS_PART A

COMPRESSORS

To reclaim the refrigerant vapor leaving the evaporator, it must be compressed to the pressure corresponding to a saturation temperature higher than the temperature of the naturally available air or water. A compressor is used for this purpose. The compressor also circulates the refrigerant through the system and its capacity determines the capacity of the refrigerating system as a whole.

Types of refrigeration compressors used are;

a) reciprocating
reciprocating compressors are available in sizes ranging from 1/8hp (approximately 9W input ) in small domestic units up to 250 tons or more in large industrial installations.

b) rotary
the displacement and compression of the refrigerant vapor is achieved in a rotary compressor by its circular or rotary motion, instead of a reciprocating motion.

c) screw
is a positive-displacement compressor. It consists of two meshing multi-start helically grooved rotors with very close tolerance clearances within a housing. Suction and discharge ports are provided at the either ends of the housing. The rotor whose shaft is connected to the motor is called the male rotor, and the other is the female rotor. When the male rotor rotates, the female rotor rotates in the opposite direction.

d) centrifugal
sometimes called ‘turbo-compressors’, are members of a family of turbo-machines that includes fans, propellers and turbines. These machines continuously exchange angular momentum between a rotating mechanical element and a steadily flowing fluid. For effective momentum exchange, their rotative speeds must be higher, but little vibration or wear results because of the steadiness of the motion and the absence of contacting parts. Centrifugal compressors are used in a variety of refrigeration and air-conditioning installations. Suction flow rates of compressors range between 60cfm and 30,000cfm, with rotational speeds between 1800rpm and 90,000rpm. As many as ten stages can be installed in a single casing. Side loads can be introduced between stages so that one compressor performs several functions at several temperature levels.