Whenever large quantities of air or gas are required at relatively low pressure, rotary compressors are used.
They are classified as
1. Positive displacement compressors.
2. Non - Positive Displacement Compressors.
POSITIVE DISPLACEMENT COMPRESSORS :
The Rotary Positive Displacement Compressors Are smaller than the reciprocating compressor at a given flow rate. The air is compressed adiabatically but uncooled. In Positive Displacement rotary type compressor, air is entrapped between two sets of engaging surfaces. The pressure rise is either by back flow of air ( as in Roots Blower) or both By variation in the volume and Back flow ( As in Vane Blower) .
Examples - 1. Roots Blower 2. Vane Blower.
NON POSITIVE DISPLACEMENT COMPRESSORS :
In Dynamic compressors, the air is not trapped in specific Boundaries but in flows continuously and steadily through the machine. The energy from the impeller is transferred to the air as the air flows through the machine the pressure rise is primarily due to the dynamic effects.
Examples - 1. Centrifugal Compressor 2. Axial Flow compressor .
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