Introduction The machine which takes in air or any other gas at low pressure and compresses it to high pressure are called as the compressors. The compressor is power consuming machine in which mechanical work is converted into the pressure energy of fluid. They are also considered as reversed heat engine.
Mechanical Energy Pressure Energy (Shaft Power) Generally, the compressors are driven by electric motors, I.C. engine, or gas turbines. A compressor used for increasing the pressure of air are called as air compressors. Compressor
Rotary Compressors A reciprocating compressor is employed for compressing a small volume of air or gas to a relatively high pressure ratio. But there are presence of reciprocating parts lower its mechanical efficiency, creates balancing problems and increases maintenance expenses. Therefore,whenever the large amount of air is required to delivered up to a pressure of 10 bar with continuous flow, the rotary compressor is used.
Types Of Rotary Compressors Roots blowers Vane type blower Screw compressor Scroll compressor Radial flow compressor Axial flow compressor
Screw compressors The rotary screw compressor is a positive displacement type compressor. It consists of two mating helically grooved rotors suitably housed in a cylinder equipped with appropriate suction and discharge ports. The rotors are driven through a set of synchronized gears. One rotor has three or four lobes, while other rotor has four or six recesses.
Working Cycle suction As the lobes of driving rotor begin to unmesh from recess of driven motor, a void is created on both male side and female side, gas enters suction port. As the rotors continue to turn, inter-lobe space increases in space, and gas flows continuously into space. Just prior tote point at which the inter-lobe space is leaves suction port, the entire length of the inter- lobe space is completely filled with gas.
Transportation A further rotation of rotor, the inter-lobe space which filled with gas is transported around the outer periphery without change of pressure until the male lobe begins to mesh with the considered space. Compression Further rotation starts the meshing of another male lobe with another female inter-lobe space on suction end progressively compressed the gas in the direction of the discharge port. Thus the occupied volume of the trapped gas within the inter-lobe space is decreased and the gas pressure consequently increased.
Advantages It is positive displacement machine, hence it produces high pressure of gas. It is also high speed rotary compressor, the large volume of gas can be handled by it. Therefore it is extremely suitable for large capacities such as food refrigeration and industrial refrigeration. No need of lubrication oil since there is no metal contact in the cylinder. It is for this reason that is not only used in food industry but also in chemical industry and transportation of loose materials.
The simplicity of screw compressor is its asset and it has the advantage of both the turbo - machine and reciprocating compressor without their short comings. Disadvantage The main disadvantage of screw compressor is the noise due to discontinuous suction and discharge of gas.