Fans. Compressors - Fundamental concepts. Sizing

The purpose of fans, blowers and compressors designed to convey compressible fluids is to transfer mechanical energy to the fluids passing through them, in order to increase their pressure.

The engineer who enters the field of rotating machines that produce or consume energy is first struck by the great analogy that exists between the geometric shapes of equipment as diverse as :

• pumps handling incompressible fluids;

• compressible fluid fans, blowers and compressors;

• hydraulic turbines and motors producing energy from incompressible fluids;

• compressible fluid turbines and motors.

Within these various categories, we can already distinguish two large families:

• volumetric machines ;

• rotodynamic machines.

Historically, volumetric machines were the first to appear. The genius of mechanical engineers made this type of equipment a success. But the flow limitations of this type of machine and, above all, advances in fluid mechanics have led to a different way of mechanically exchanging energy with a fluid.

It's hard to find a generic term for this other type of machine, and in the literature we come across expressions such as centrifugal machines, turbomachines or rotodynamic machines.

Over the years, the term "centrifugal machines" has become a misnomer. Historically, it reflects the fact that the first non-volumetric machines built around 1900 were centrifugal; not because this type of compressor, invented by Professor Rateau, was so much earlier than the axial compressor studied in Great Britain by Parsons between 1901 and 1906, but because the centrifugal machine reached technical maturity much more quickly.

The term "turbomachine" is the most commonly used; "rotodynamic machine" is the most explicit: it means that, by using a system of blades driven in rotation around an axis, mechanical energy is transformed into momentum on the fluid. Then, by means of appropriate devices built into the machine, the energy contained in the form of velocity is recovered in the form of pressure.

This article is an update of the previous text Fans. Blowers. Compressors written by Messrs.Jean FRIBERG andJean-Marie MÉRIGOUX.