Patent ID: 8342799

Claim:
A centrifugal fan, comprising: a fan frame comprising a bottom base, an opposite top cover and a side wall interconnecting the bottom base and the top cover, a first air inlet defined in the top cover of the fan frame and a second air inlet defined in the bottom base of the fan frame; a stator received in the fan frame; a rotor driven by the stator to be rotatable in the fan frame, the rotor comprising a hub and a plurality of blades extending from an outer periphery of the hub, an air flow channel being formed between an outer periphery of the blades and the side wall of the fan frame; and at least one cylindrical wall formed around one of the first air inlet and the second air inlet and extending into the fan frame, the at least one cylindrical wall guiding airflow from one of the first and second air inlets into the air flow channel of the fan frame and blocking the airflow in the air flow channel from flowing back towards one of the first and second air inlets; wherein the at least one cylindrical wall extends from an inner periphery of the second air inlet of the bottom base, and the rotor further comprises a blade ring arranged on top faces of the blades and received in the first air inlet of the top cover, the blade ring comprising an annular, planar connecting wall, a cylindrical sidewall extending downwardly from an outer periphery of the connecting wall and located near an inner periphery of the first air inlet, and a flange extending outwardly from a bottom of the sidewall and located under the top cover, the connecting wall of the blade ring is received in the first air inlet of the top cover, a top surface of the connecting wall of the blade ring being coplanar with a top surface of the top cover, wherein the sidewall blocks the airflow in the air flow channel from flowing back towards the first air inlet.