Classifying – separating – and assorting solids – Electrostatic
Reexamination Certificate
2002-07-16
2003-12-16
Walsh, Donald P. (Department: 3653)
Classifying, separating, and assorting solids
Electrostatic
C209S128000, C096S048000, C096S070000, C055S523000, C055SDIG003
Reexamination Certificate
active
06664492
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to systems and methods for removing conductive airborne contaminants, and more particularly, to eliminating electrically-conductive particles from an airstream.
BACKGROUND OF THE INVENTION
Airborne conductive contaminants can cause failure or malfunction of electrical and computer equipment, such as to short-circuit or cause other undesired circuit perturbation. Equipment, such as power supplies, that utilize forced air cooling and have high densities of electrical circuits with high voltages across small node gaps are particularly susceptible to malfunction associated with the presence of conductive contaminants.
Electrically-conductive airborne contamination may include metallic particulates, whiskers and shards, fragments of wires, and fibers used in anti-static floor coverings. For example, these electrically-conductive contaminants may have a diameter of about 1-2 microns and a length of about 0.5-5 mm, resulting in a particulate which is easily airborne. These particulates often become entrained in the airflow used to cool the electrical equipment. Metal whiskers are particularly hazardous to electrical equipment because the whiskers are extremely light and are therefore readily entrained in and transported by cooling air flows. These whiskers can grow on surfaces found in computer room environments, e.g. electroplated zinc surfaces, such as are present on the undersides of raised floor tiles, inside air-conditioning ducts and on the equipment chassis.
The electrically-conductive airborne contaminants, such as zinc whiskers or particles, often grow on metal stringers or off the bottom and sides of the floor tiles that have a zinc electroplated-passivation coating on the sheet-metal pan. These whiskers can grow to a length of well over 2000 microns (2 mm) if left undisturbed for several years, and may be dislodged when the tiles are removed to gain access to the under-floor area. For example, as floor tiles are moved or disturbed thousands of whiskers from the under side of the tile may be stripped off, and the normal airflow in the data center causes the contamination to quickly spread throughout the center. Also, movement of cables and equipment under the floor can dislodge the whiskers. Power supply fans, cooling blowers, and the like in the computer equipment then draw the whiskers into the internal logic cages and power supplies of the equipment. Once inside the computer equipment, the whiskers lodge themselves in the electronic components of logic cards and power supplies causing either a voltage or signal perturbation.
A whisker can be considered a low-capacity fuse with Direct Current (DC) resistance of 10 ohms to 40 ohms, depending on the whisker geometry, with a DC fusing current of 10 mA to 30 mA. When sensitive electronic equipment becomes contaminated with zinc whiskers, equipment failures and system resets can occur. In most cases, the same short circuit caused by the whisker either vaporizes the contaminating whisker by the current flow creating an arc path across adjacent etchings on the circuit board. Alternatively, the whisker may become dislodged when the circuit board or card is removed, thereby leaving definite fault analysis virtually impossible.
A typical long-term remediation or abatement process requires replacing the affected floor panels. Although, the panels can be cleaned, the whiskers typically grow back. Therefore, without proper equipment, personnel and procedures, the likelihood of sustained success is low. Generally, the remediation and abatement process involves the redirection and reduction of airflow, removal of contaminated floor tiles (individually bagged), cleaning of the air plenum (such as by using High Efficiency Particle Arresting vacuums), cleaning and sealing unmovable tiles, and installing new tiles. However, sealing or painting the bottoms of the panels may be ineffective since the whiskers can grow through most coatings.
Another method of removing airborne contaminants from the airstream is to utilize filters. Such filters are generally designed with an assembly of very small obstacles such as fibers or spheres, integrally bound together or a loosely-bound aggregate through which the dirty or contaminated air flows. However, the filters significantly increase air impedance, thereby restricting airflow. Additionally, the filter needs to be replaced or cleaned periodically to remove captured or collected contaminated airborne particles to prevent further restriction of the airflow.
BRIEF SUMMARY OF THE INVENTION
Preferred embodiments of the present invention provide systems and methods for removing electrically-conductive contaminants entrained in an airstream by redirecting the airstream to separate the electrically-conductive contaminants from the airstream and oxidizing the separated electrically-conductive contaminants.
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“Shaving Zinc Whiskers From Your Data Center” [online] [Retrieved On: Jul. 15, 2002] Retrieved From: http://www.dataclean.com
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Babb Samuel Martin
Dean Ronald Paul
Weaver Jeffrey S.
Hewlett-Packard Development Company
Miller Jonathan R.
Walsh Donald P.
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