Equipment, such as rack-level telecommunications equipment and computer room blade servers require cooling. Axial fans and centrifugal impeller based blowers are commonly mounted on top of the equipment and used to move air through such equipment for cooling purposes. The air is usually inducted at a front portion of the equipment, circulated past a bank of one or more vertical blades, electronic boards, or circuit packs, and finally exhausted at the back of the equipment, away from personnel. This commonly requires a ninety degree change in the direction of airflow.
In addition to the direction change, and partly because of it, the pressure drop across servers and telecom rack equipment can become quite high due to several factors. Packaging densities including small board pitch and/or dense component layout, air filtration requirements, and changes in direction of airflow can all contribute to the pressure drop. Impellers typically develop higher static pressures compared to axial fans, and are well suited to these types of high pressure applications where an axial fan may not be powerful enough to overcome the back pressure at a required cooling air flow rate.
One drawback of current centrifugal blowers is that they require either scrolling (forward-blade impellers) or breathing room on the sides (backward-blade impellers) because of the circumferential discharge. This makes it difficult to pack the blowers tightly in a tray to provide good airflow distribution among the circuit packs. Further, centrifugal blowers may have a smaller intake area as compared to the overall diameter of the impellers. This can make it more difficult to obtain even airflow distribution over the circuit packs, especially when plenum space is limited.