Patent ID: 7284952

Claim:
A centrifugal fan, suitable for a portable electrical apparatus, comprising: a casing comprising: a bottom plate; and a volute sidewall disposed on the bottom plate to define a cavity and an outlet, wherein a tongue shape is formed from the volute sidewall on at least one side of the outlet; and blades disposed vertically with a rotational axis on the bottom plate of the cavity, wherein the casing has a curved surface and a divergent duct with a variable section at the outlet to broaden the outlet, so that an inner surface of the volute sidewall at the tongue shape is non-parallel to the rotational axis of the blades, and an angle of the inner surface relative to the bottom plate is more than 90 and less than 180 degrees; and wherein the volute sidewall at the tongue shape has a variable thickness, so that a thickness at a base thereof is different from a thickness at a top thereof.