Centrifugal fan

A centrifugal fan, comprising:

• an impeller including a rotatable disk, and a plurality of blades extending vertically from the rotatable disk and arranged radially about an axis of rotation of the rotatable disk toward a rim of the rotatable disk;
• a casing accommodating the impeller, the casing including a base plate at a first end face thereof nearer the rotatable disk, a lid plate at a second end face thereof opposite to the base plate, and a peripheral wall surrounding an outer periphery of the impeller;
• and
• a motor mounted on the base plate of the casing externally, the motor including a shaft fixed at a center of the rotatable disk, the motor being configured to rotate the impeller,
• wherein the casing has an inlet port that is open in the lid plate at a position inward from the plurality of blades, and an air blowing channel extending from the peripheral wall,
• the motor is driven to rotate the impeller to cause a gas to be drawn through the inlet port and to be fed to an apparatus connectable to the air blowing channel, and
• the rotatable disk has a plurality of reflux holes at positions between inner rims and outer rims of the plurality of blades in a radial direction of the rotatable disk, and the plurality of reflux holes allow the gas to reflux from between the rotating disk and the base plate inside the impeller as the impeller rotates.