Importance

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Abstract

A counter-rotating fan includes first and second fans that are coaxially arranged. The first ribs of the first fan and the second ribs of the second fan are arranged on an air-outlet side and an air-inlet side of the first impeller of the first fan, respectively. The first impeller includes first blades. When seen in an axial direction from the second fan side, while the first rib side edge of each first blade is at least partly located above one first rib, the second rib side edge of that first blade is not located below any second rib but is entirely located between two second ribs. Thus, interference of air taken in by the first blades with the second ribs and interference of air sent out by the first blades with the first ribs cannot occur simultaneously, resulting in improvement of the sound characteristics of the counter-rotating fan.

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First Claim