Which compressor is NOT a positive displacement compressor?

The centrifugal compressor is classified as a dynamic compressor, which differentiates it from positive displacement compressors. In a positive displacement compressor, the action involves trapping a specific volume of gas and then reducing that volume to increase its pressure. This can be seen in compressors like rotary vane, rotary screw, and reciprocating types, where the movement of elements like vanes, screws, or pistons physically compresses the gas.

Centrifugal compressors operate on the principle of converting kinetic energy into pressure. They use a rotating impeller to impart velocity to the gas, which is then diffused into pressure as it moves through the compressor. This process does not involve trapping and reducing a fixed volume, making it distinct from positive displacement mechanisms. Thus, centrifugal compressors stand apart in the way they function, clearly categorizing them as non-positive displacement types.