US Patent 7306429 Axial-flow heat-dissipating fan

An axial-flow heat-dissipating fan includes an impeller and a casing. The impeller includes a hub and a plurality of blades formed on the hub. The casing includes an air inlet, an air outlet, a base in the air outlet, and guiding ribs mounted between the casing and the base. Each guiding rib includes an airflow-encountering line adjacent to a trailing edge of one of the blades that is closest to the guiding rib. Two of the blades adjacent to each other overlap with each other as viewed from the longitudinal direction such that each blade has a first overlapped area and a second overlapped area, thereby increasing an air inlet amount and reducing blowing noise in the air inlet. An angle between the trailing edge of the blade and the airflow-encountering line of the guiding rib is 10°-70°, thereby reducing blowing noise in the air outlet.