Patent ID: 7217087

Claim:
A centrifugal fan, comprising: an impeller having an approximately cylindrical outline, the impeller designed for a minimum rotational operation speed of 10,000 rpm, by being configured with a plurality of blades arranged on a circumference of radius r, in which the length h in the impeller axial direction satisfies 2≦h/r≦20 and r is not more than 25 mm, and a connection portion for fixing the ends of the blades at a first axial end thereof; a motor that is connected to the impeller in the connection portion and rotates the impeller along one circumferential direction around a center axis the motor having an rpm rating of not less than 10,000; a housing for housing the impeller; an intake that is formed in the housing and opens opposite a second axial end of the impeller; an air blowing port that is formed in the housing and opens opposite a longitudinal side of the impeller; and a gap enlarged portion, in which the distance between the outer circumference of the impeller and the inner face of the housing starts to increase at a point where the distance between the outer circumferential of the impeller and the surface of a nose portion is smallest therein, the nose portion being a region of the vicinity of an edge portion of the air blowing port, the edge portion being the closest side to the outer circumference of the impeller, such that the gap of the gap enlarged portion is expanding gradually along the other circumferential direction; wherein the normal operating speed of the centrifugal fan is at least 10,000 rpm.