Patent ID: 8882455

Claim:
An axial fan comprising: an impeller arranged to rotate about a central axis and including a plurality of blades centered on the central axis, the plurality of blades being arranged to be spaced apart in a circumferential direction and to project radially outward; a housing including a side wall arranged to surround an outer circumference of the impeller; and a substantially square or substantially rectangular flange arranged on an axial end of the side wall on an inlet side or an outlet side; wherein the side wall includes a slit group including a plurality of slits arranged to be spaced apart in a circumferential direction of an inner circumferential surface of the side wall, and arranged to extend in the same direction perpendicular or substantially perpendicular to one side of the flange through the side wall from the inner circumferential surface to an outer circumferential surface thereof; and within the slit group, a total number of slits that are positioned forward, with respect to a rotation direction of the impeller, of a point at which a straight line extending from the central axis to one side of the flange and perpendicular to the side wall crosses the slit group is greater than a total number of slits that are positioned rearward of the point with respect to a circumferential rotation direction of the impeller.