Diagonal fan

A diagonal fan, comprising:

• a frame comprising an inlet, an outlet, an accommodation space and a guiding wall, wherein the inlet and the outlet are disposed at two opposite sides of the frame, respectively, and in fluid communication with each other through the accommodation space;
• and
• an impeller accommodated within the accommodation space of the frame and comprising a hub, a cylindrical part, a conical section shell and a plurality of blades, wherein the cylindrical part is configured to accommodate a rotor,
• wherein the cylindrical part comprises a plurality of protrusion portions and a plurality of indentation portions disposed on an inner surface thereof, and the plurality of protrusion portions are abutted against an outer surface of a magnetic shell of the rotor;
• wherein a gap having a spacing distance is substantially maintained between an inner wall surface of the frame, and an outer wall and an upper end of the conical section shell to form a backflow channel, and the backflow channel comprises an intake section, a horizontal section and an exhaust section;
• and
• wherein the conical section shell comprises a plurality of balance holes disposed around the lower end of the conical section shell, the horizontal section is spatially corresponding to the plurality of balance holes, and the backflow channel further comprises a second horizontal section spatially corresponding to the upper end of the conical section shell.