Abstract: A centrifugal fan includes a fan frame, a stator assembly and an impeller. The fan frame has a base plate portion, a cover plate portion and a lateral wall portion. The cover plate portion includes first and second faces. The cover plate portion includes an air inlet, and the lateral wall portion includes an air outlet. The impeller has a radial rotational range. The cover plate portion includes an air-guiding section and an enlarged guiding section. The air-guiding section is aligned with the radial rotational range, and the enlarged guiding section is aligned with an area outside the radial rotational range. A part of the second face is spaced from a bottom of the base plate portion by a first minimal axial distance, and another part of the second face is spaced from the bottom by a second minimal axial distance smaller than the first minimal axial distance.

Abstract: An advection fan includes a fan frame, an impeller and a cover plate. The fan frame has a bottom plate and a lateral wall. A shaft seat is arranged on the bottom plate. The lateral wall surrounds the shaft seat and has an inner peripheral face. The lateral wall includes first and second air-guiding portions. An air inlet and an air outlet are formed between the first and second air-guiding portions. The first air-guiding portion includes a first guiding face intersecting the inner peripheral face by a first included angle, which is smaller than 180 degrees. The second air-guiding portion includes a second guiding face. A distance between the first and second guiding faces is gradually reduced from the air inlet towards the center of the fan frame. The impeller is rotatably coupled with the shaft seat. The cover plate is coupled with the lateral wall.