Ultra-thin low noise axial flow fan for office automation machines

In a small axial flow fan having a driving motor, a central hub section driven by the driving motor, and a plurality of blades, each of the blades having a root portion, which is closest to the central hub portion, and a tip portion, which is furthest from the central hub portion, and each blade having two sides, wherein the improvement comprising:

• (a) each blade being constructed in such a manner that the center line along each blade from the root portion to the tip portion of the blade having the shape of a circular arc, which is perpendicular to a circle defining the hub section at the root portion of the blade, said center line being defined as an arc connecting all middle points between corresponding end points at the two sides of the blades
• (b) each blade having a blade angle which is, measured from the root portion to the tip portion of the blade, at first directly proportional to the radius of the blade and then inversely proportional to the radius of the blade;
• and
• (c) each blade having a chord/pitch ratio which is inversely proportional to a radius of the blade from the root portion to the tip portion of the blade, thereby allowing said fan to provide high air flow, high pressure, low noise, and can be placed inside an ultra-thin outer casing.