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, wherein the guiding wall is connected to an inner wall surface of the frame, and the guiding wall is extended from a periphery of the inlet along an axial direction into the accommodation space;
• and
• an impeller accommodated within the accommodation space of the frame, wherein when the impeller is rotated, an airflow flowing from the inlet to the outlet is generated, wherein the impeller comprises a conical section shell, and a gap having a spacing distance is substantially maintained between the inner wall surface of the frame, and an outer wall and an upper end of the conical section shell to form a backflow channel, wherein the impeller comprises a hub, and the outer diameter of the hub of the impeller is expended gradually in a direction from the inlet toward the outlet so that the flowing direction of the airflow is expended gradually around a periphery of the impeller,
• wherein the backflow channel comprises an intake section, a horizontal section and an exhaust section, the intake section is located adjacent to a lower end of the conical section shell and in fluid communication with the exhaust section through the horizontal section, and the upper end of the conical section shell is at least partially shielded by the guiding wall to form the exhaust section, wherein when the airflow flows from the inlet to the outlet, a backflow is transported from the intake section, flows through the horizontal section, is exhausted out through the exhaust section, and is converged with the airflow, 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,
• 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.