Gas separation: processes – Liquid contacting – And deflection
Reexamination Certificate
1999-03-12
2001-04-17
Simmons, David A. (Department: 1724)
Gas separation: processes
Liquid contacting
And deflection
C095S219000, C095S220000, C095S222000, C095S227000, C096S286000, C096S316000, C096S327000, C096S366000, C055S339000, C055S465000, C073S863220
Reexamination Certificate
active
06217636
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
This invention relates generally to aerosol collection, and more particularly, to a transpirated wall aerosol collection system and method.
BACKGROUND OF THE INVENTION
Aerosol collection devices are used to transfer particulate matter contained in a gas flow onto a solid or liquid surface. One example use of a collection device is in the sampling of biological aerosols, or bioaerosols, where the aerosol collection system is based on jet impaction of aerosols onto a collection plate. The impactor may fractionate the aerosol and deposit size-segregated aerosol particles onto separate agar-filled petri dishes. For example, Graseby Anderson Inc., located in Smyrna, Ga., manufactures a multi-stage impactor that operates at a flow rate of twenty-eight liters per minute and fractionates the aerosol into six size fractions.
Another example of an aerosol collection system used for bioaerosols is a cyclone. A cyclone has been used to collect bioaerosol material from a high flow rate of air, such as approximately 500 liters per minute, into a small flow rate of liquid, generally a few milliliters per minute. Cyclones generally employ an upstream spray of liquid to form a mist. The mist is collected by the cyclone and washes particulate matter collected by the cyclone to a collection location.
SUMMARY OF THE INVENTION
Known systems present certain drawbacks. For example, jet impaction processes generally must be done on a batch basis because the particulate matter is generally not easily removable from the collection surfaces. Further, for example, liquid flow patterns in cyclones often break into rivulets, which reduce the area of the collection surface that is continuously washed. Additionally, cyclones may not be practical in cold weather applications because the liquid mist may freeze and be rendered incapable of continuously wetting the cyclone wall.
Accordingly, a need has arisen for an improved aerosol collection system and method. The present invention provides a transpirated wall aerosol collection system and method that addresses shortcomings of prior systems and methods.
According to one embodiment of the present invention, a transpirated wall aerosol collection system includes a collector operable to receive a gas flow containing particulate matter. The system also includes a porous wall having a first surface and a second surface. The porous wall is for transpiring a liquid from the first surface to the second surface. The liquid on the second surface receives particulate matter contained in the gas flow.
According to another embodiment of the present invention, a method for collecting aerosol includes receiving a gas flow containing particulate matter. The method also includes transpiring a liquid from a first surface to a second surface of a porous wall. The method further includes collecting the particulate matter in the liquid on the second surface of the porous wall using a collector.
The present invention provides several technical advantages. According to an aspect of the invention, liquid may be transpirated through a porous wall to wet a collection surface in a nearly uniform manner, thereby substantially preventing the formation of rivulets. The liquid containing the particulate matter may be removed and analyzed with near-real-time detectors for biological material. The liquid containing the particulate matter may also be stored for subsequent analysis using instrumental means or classical biological analysis techniques, such as culturing the collected biological particles in a nutrient medium. For example, near-real-time analyzers such as flow cytometers and immunoassay devices may be used to process low flow rate liquid samples. The liquid and/or the walls of the collector may be heated, thereby substantially precluding ice formation. Heating the liquid and/or the walls of the collector may also obviate a requirement to heat the gas flow, thereby reducing the energy required to operate the system.
According to another aspect of the present invention, a virtual impactor may be used to concentrate the particulate matter in the gas flow delivered to the transpirated wall particulate collections system. The particulate matter may be collected on a flowing liquid film transpirated through a porous wall. Therefore, the present invention provides greater sensitivity than prior systems by producing a higher concentration of particulate matter in the collected liquid.
According to another aspect of the invention, a jet impactor may be used for collecting the particulate matter. The jet impactor may be used to provide a continuous liquid sample to an analyzer such as an atomic absorption spectrometer.
The present invention may also be used in commercial or industrial applications. For example, a product may initially be in an aerosol state. The product may be collected using the present invention and delivered in hydrosol state for packaging or further processing. Therefore, the present invention provides greater flexibility than prior systems.
According to another aspect of the present invention, a slit impaction system may be used with the present invention. The slit impaction system may include one or more slits through which the gas flow may be accelerated. A transpirated porous wall may be disposed in close proximity to the discharge side of the slits. Particulate matter having sufficient inertia may be deposited in the liquid and be collected for near-real-time analysis or storage. Thus, the present invention provides greater flexibility than prior systems.
Other aspects and technical advantages will be readily apparent to one skilled in the art from the following figures, descriptions, and claims.
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patent: 5928405 (1999-07-01), Ranade et al.
patent: 6051257 (2000-04-01), Kodas et al.
Baker & Botts L.L.P.
Hopkins Robert A.
Simmons David A.
The Texas A&M University System
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