Helically conforming axial fan check valve

Details Helically conforming axial fan check valve Helically conforming axial fan check valve

1999-09-07

2001-01-16

Joyce, Harold (Department: 3449)

Ventilation

Electronic cabinet

C361S695000

Reexamination Certificate

active

06174232

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Technical Field
This invention relates in general to cooling systems for electrical component enclosures, and in particular to an improved valve for an electrical component enclosure cooling fan.
2. Background Art
Electronic cooling systems designed for high availability or continuous operation often employ redundant fans that are arranged in parallel. This arrangement is used to guard against catastrophic loss of cooling flow in the event of a single fan device failure. One problem with this type of parallel fan configuration is that when one fan fails, the pressure difference across the surviving fan pushes air backwards through the failed fan. This reduces the delivered flow rate that would otherwise be available from the surviving fan by almost half
To prevent back flow, the normal practice is to add a flap-type device on the exhaust side of the fans. Common flapper designs include swinging door flaps and multiple slat vanes. However, prior art designs neglect the inherent helical or swirling discharge pattern of tube axial exhaust fans, thereby inadvertently producing large pressure drops during normal operation of the fan before failure. It is well known tube axial fans have a discharge angle that is a direct function of the static pressure operating point on its pressure-flow curve. There is always some angle or spiral to the axial discharge direction. Indeed, the development of pressure in tube axial fans is dependent on the change in momentum brought about by changing the direction of the air. The spiral is never absent, even at free-air delivery, as velocity pressure must still be produced. The spiral always rotates in the same direction as the fan blade and appears as a helical vortex in flow visualizations. In addition, prior art designs tend to take up significant amounts of space in the axial direction that make parallel fan configurations difficult to implement in compact packages. Thus, an efficient, axially compact design for high availability exhaust fans is needed.
SUMMARY OF THE INVENTION
A fan check valve is formed from plastic film having an outer edge and a central region. The valve also has a number of slits that define flaps in the film. The flaps are symmetrically arrayed in a spiral-like pattern between the central region and the outer edge. The valve mounts to the outer surface of a tube axial fan. Under normal operating conditions, the fan moves a helical flow of air in a generally axial direction toward through the valve. The flaps are blown open and align with the oncoming flow at low angles of attack to minimize dynamic losses. The flaps are in the closed position and lie flush on the outer surface of the exhaust plate mounted on the fan at all other times to prevent airflow back through the fan in the opposite direction once the fan has failed.


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Ibm Technical Disclosure Bulletin/“Plastic Film Fan Valve For Backflow Preventtion in Multi-Fan Plenum Cooling Systems”/vol. 38, No. 6, Jun. 1995.

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