Patent ID: 8251642

Claim:
A centrifugal fan, comprising: a top cover plate; a bottom plate opposite to the top cover plate, the top cover plate and the bottom plate each being defined with an air inlet; a sidewall between the bottom plate and the top cover plate, the sidewall being defined with an air outlet, the air outlet being perpendicular to the air inlets of the top cover plate and the bottom plate; and an impeller being rotatably received in a receiving space cooperatively defined by the top cover plate, the bottom plate and the sidewall, the impeller comprising a hub and a plurality of blades extending radially outwardly from the hub, an air passage channel being defined between outmost free ends of the blades and an inner surface of the sidewall, a tongue being provided near the air outlet and protruding laterally and inwardly from the inner surface of the sidewall towards the outmost free ends of the blades, the tongue having an outer surface facing the outmost free ends of the blades, a plurality of grooves being defined in the outer surface along a lengthwise direction of the tongue; wherein the tongue has a bulge at a middle portion thereof, and the bulge is located closer to the outmost free ends of the blades than other portions of the tongue; wherein the outer surface of the tongue is curved and a thickness of the tongue with respect to the sidewall decreases gradually from the bulge towards the inner and the outer ends of the tongue along the lengthwise direction of the tongue, and decreases gradually from the bottom plate towards the top cover plate along the height direction of the tongue; and wherein a distance between the outer surface of the tongue and the outmost free ends of the blades increases gradually from the bulge towards the inner and the outer ends of the tongue along the lengthwise direction of the tongue, and increases gradually from the bottom plate towards the top cover plate along the height direction of the tongue.