Patent ID: 7597541

Claim:
A centrifugal fan assembly comprising: a housing; a centrifugal fan positioned in the housing for rotation about a central axis, the centrifugal fan including a plurality of main blades arranged about the central axis, each main blade including a suction surface; a pressure surface opposite the suction surface; a leading edge; and a trailing edge; a plurality of secondary blades arranged about the central axis, each secondary blade including a suction surface; a pressure surface opposite the suction surface; a leading edge; and a trailing edge; wherein each main blade defines a main blade mean line between the suction surface and the pressure surface of the main blade; a main blade nose-tail line intersecting the main blade mean line at the leading edge and the trailing edge of the main blade; wherein each secondary blade defines a secondary blade mean line between the suction surface and the pressure surface of the secondary blade; wherein at least a portion of the secondary blade mean line adjacent the leading edge of the secondard blade is substantially parallel to the main blade mean Line when the secondary blade mean line is rotated about the central axis to superimpose at least a portion of the secondary blade mean line on the main blade mean line; and wherein when the secondary blade mean line is superimposed on the main blade mean line, at least a portion of the secondary blade mean line adjacent the trailing edge of the secondary blade deviates from the main blade mean line in a direction toward the main blade nose-tail line.