Centrifugal fans are more effective than axial fans if an application requires the air flow to be deflected by 90 degrees, or if there are components, filters etc. impeding free air flow, for example.
With a centrifugal fan, the air is drawn in axially, i.e. in parallel with the drive axis of the centrifugal fan, deflected through 90° by the rotation of the centrifugal impeller, and discharged radially. In other words, the entire air flow exits the impeller at the outer diameter. The higher kinetic energy of the air molecules this permits generates a higher pressure than an axial blower, the peripheral speed of which is limited at the hub.