Compressor
The compressor is mechanically the most complex and is often the most expensive single item in the system. A more complete discussion of compressors can be found in the ashram handbook, HVAC system and equipment volume.
Compressors may be of two basic types: positive displacement and dynamic.positive displacement compressors increase the pressure of the refrigerant vapor by reducing the volume. Examples are the Reciprocating, rotary,(rolling piston, rotary vane, single screw, and twin screw),scroll, and trochoidal . Dynamic compressors increase the pressure of refrigerant vapor by a continuous transfer of angular momentum to the vapor from the rotating member followed by a conversation of this momentum into a pressure rise. The centrifugal compressor is of this type.
Reciprocating compressors.
Most Reciprocating compressors are single -acting , using pistons driven directly through a pin and connecting rod from the crankshaft.double-acting compressors are not extensively used.
Above image shows the schematic indicator diagram for Reciprocating compressors.The pressure at the cylinder is assumed constant during the exhaust process and during intake process, however the pressure loss in the valves must be considered.The gas remaining in the clearance volume expand in a polytropic process from state d to state a in above image. State b is generally different from that at a because if the mixing of expanded clearance volume vapour and the intake vapour.The vapour is compressed from state b to state c in a polytropic process. Heat transfer may occur during exhaust process c-d.Below image is a pressure-specific volume diagram for the compressor.
Rotary Compressor
Rotary Compressor are characterised by their circular or rotary motion as opposed to Reciprocating motion. Their positive displacement process is a non-reversing and either continuous or cyclical, depending in tha mechanism employed. Most are the direct drive machines.
Above are the two common types of rotary Compressor, the rolling piston type and rotating vane type.
The rotary Compressor are characterised by the high volumetric efficiency become of its small clearance volume and correspondingly low re-expansion loss. Rotary-vane Compressor have a low weight-to-displacement ratio which in combination with their small size , makes them suited to transport application.
Single Screw Compressor
The single screw Compressor consist of a single cylindrical main rotary that works pairs of gate rotors.The rotors may vary considerably in geometry.These are most often used in the liquid ejection mode,where sufficient liquid cools and seals the compressor.
Double helical Rotary (twin-screw) Compressor
The double helical Rotary or twin-screw Compressor,like the single screw Compressor,belongs to the broad class of positive displacement compressors. It was first introduced to the refrigeration industry in the late 1950s.
The machine essentially consist of two mating helically grooved rotors, a male (lobes) and a female(gullies), in a stationary housing with a suitable inlet and outlet gas ports.The flow of gas in the rotors is both radial and axial.
Compression in this machine is obtained by direct volume reduction with pure rotary motion.
The four basic continuous phases of working Cycle are Suction, transfer, Compression, Discharge.
Centrifugal compressor
Centrifugal compressor or turbocompressors, the the members of the turbo machines that includes fans, propeller, and turbines. Such machines are characterised by a continuous exchange of angular momentum between a rotating mechanical elements and a steadily flowing fluid.Becouse their flows are continuous, turbomachines have a greater volumetric capacities, size for size, than do positive displacement devices.For effective momentum exchange, their rotating speed must be higher.
Centrifugal compressor are used in vide variety of refrigeration and air conditioning application.
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