Abstract: An exemplary centrifugal fan includes a casing defining an air outlet, and an impeller in the casing. An air channel is defined in the casing between a sidewall of the casing and outermost free ends of the impeller. The sidewall includes a first curved section adjoining a second curved section. The first curved section is 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 extends along a part of an Archimedes spiral or a part of a logarithmic spiral. The second curved section is located farther away from the impeller than an imaginary extension line of the first curved section along the Archimedes spiral or the logarithmic spiral. An air guide plate is formed in the casing and extends from the air outlet to an inner region of the air channel.

Abstract: An exemplary centrifugal fan includes a casing defining an air outlet, and an impeller in the casing. An air channel is defined in the casing between a sidewall of the casing and outermost free ends of the impeller. The sidewall includes a first curved section adjoining a second curved section. The first curved section is 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 extends along a part of an Archimedes spiral or a part of a logarithmic spiral. The second curved section is located farther away from the impeller than an imaginary extension line of the first curved section along the Archimedes spiral or the logarithmic spiral. An air guide plate is formed in the casing and extends from the air outlet to an inner region of the air channel.

Abstract: A centrifugal fan includes a housing defining an inner space therein and an impeller rotatably received in the inner space of the housing. The impeller includes a hub, a blade ring surrounding the hub, a plurality of first blades extending from the hub to the blade ring, and a plurality of second blades extending from the blade ring. Each first blade includes an inner portion between the hub and the blade ring, and an outer portion extending from the blade ring. The second blades and the outer portions of the first blades are arranged in alternating fashion along a circumferential direction of the blade ring. In each pair of an outer portion and an adjacent second blade, the outer portion and the second blade are curved outwards away from each other toward substantially opposite directions.

Abstract: A heat dissipation device includes a heat sink, an axial fan and a fan cover. The heat sink includes a plurality of fins defining a plurality of longitudinal airflow channels therebetween. The axial fan is mounted on a top side of the heat sink. The axial fan defines an air inlet located adjacent to and communicating with the airflow channels of the heat sink. The fan cover is between the heat sink and the axial fan. The fan cover includes a side plate surrounding a top end of the heat sink to make the axial fan just draw cooling air into the heat sink from a position around a bottom end of the heat sink. The cooling air flows upwardly through the heat sink to the air inlet of the axial fan to thereby take heat away from the heat sink.