Patent ID: 8534998

Claim:
A centrifugal fan, comprising: a casing and an impeller received in the casing, an air channel defined in the casing between a sidewall of the casing and outermost free ends of blades of the impeller, the casing defining an air outlet at one side thereof adjacent to the sidewall, an air guide plate formed in the casing and extending from the air outlet to an inner region of the air channel, the air guide plate thereby dividing part of the air channel into two branch channels; the sidewall comprising a first curved section adjoining a second curved section, the first curved section located at a more upstream portion of the sidewall than the second curved section along a rotation direction of the impeller, the first curved section extending along a part of an Archimedes spiral or a part of a logarithmic spiral, and the second curved section located farther away from the impeller than an imaginary extension line of the first curved section along the Archimedes spiral or the logarithmic spiral; wherein the casing comprises a bottom plate from which the air guide plate extends, and the air guide plate is spaced from the sidewall; wherein the midway point of the air channel is diametrically opposite from the air outlet across a middle of the impeller, the air guide plate comprises a curved inner section adjoining a linear outer section, the outer section extends from the air outlet to a first position in the air channel, and the inner section extends from the first position to the midway point of the air channel; and wherein the inner section of the air guide plate coincides with the imaginary extension line of the first curved section of the sidewall along the Archimedes spiral or the logarithmic spiral.