Rotary Screw Compressor Selection

Executive Summary About Screw Compressor By Scot Desiderio

The rotary screw belongs to the positive displacement compressor family. The Rotary screw compressor is composed of two intermeshing helical rotors contained in a housing. In the case of an oil injected machine, the female rotor is driven by the male rotor through a thin film of oil. As the rotor diameter increases, so does the air pumps capacity; As the length of the rotor increases, so does the pumps final pressure.

When the male rotor enters the interlobe space it begins to convey and compress the gas towards the discharge port. Continued rotation causes the gas volume to reduce to the stated design pressure.

Some rotary screw compressor designs employ a variable discharge valve that continuously seek maximum efficiency by opening and closing depending on system pressure conditions. The interlobe volume is a function of rotor profile, length and diameter. Where:
Qr = Displacement/Revolution
d = rotor diameter
C = typical profile constant

Where:
Qd = discharge volume
N = compressor speed
Qi = Qd x Ev

Where
Qi = actual inlet volume
Ev = volumetric efficiency

To find the final discharge temperature, add the inlet temperature to the temperature rise.

Where:
rp = pressure ratio
na = adiabatic efficiency
nt = temperature rise efficiency

Screw Compressors – A Look at Its Processes, Types and Applications

Executive Summary About Screw Compressor By Richard C. Milton

Female screws are those with concave inlets while male screws have convex ones.

Screw compressors operate in opposite directions. It is the female screw that receives the driving power. Processes

While the screws start rotating, the admission process takes place. There is one type known as the rotary screw compressor. It uses a mechanism through a single screw or a double counter helical screw. This type of screw compressor is applied in general industries like those trailer units powered by diesel as seen in construction sites.

Oil-free screw compressors are also examples of this industrial machinery.

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