Which type of compressor is classified as a non-positive displacement compressor?

Centrifugal compressors are classified as non-positive displacement compressors because they operate on the principle of converting kinetic energy into pressure energy through the acceleration of air. In these compressors, air enters the impeller at a low velocity and exits at a higher velocity, which increases its pressure as it moves through the compressor. This type of compressor is characterized by continuous flow, where the air is not trapped in a chamber and forced out, as seen in positive displacement compressors like reciprocating and rotary types.

In contrast, positive displacement compressors trap a fixed volume of air and compress it before releasing it, creating a pressure increase through a reduction in volume. This fundamental operational difference is what distinguishes centrifugal compressors as non-positive displacement types. Understanding this distinction is crucial for tasks involving air compression systems, as it influences selection based on the required flow rate and pressure characteristics.

The other choices represent positive displacement mechanisms. Rotary compressors compress air within a contained volume, and reciprocating compressors use pistons to achieve the same result. Screw compressors also work by positive displacement through rotating helical lobes that trap air and compress it. Thus, recognizing the centrifugal compressor's unique method of operation provides clarity in its classification.