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US 4,301,002 AGranted
High efficiency virtual impactor
AssigneeThe United States of America as represented by the United States Department of Energy
InventorBilly W. Loo
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AssigneeThe United States of America as represented by the United States Department of Energy
InventorBilly W. Loo
Estimating the term…
Environmental monitoring of atmospheric air is facilitated by a single stage virtual impactor (11) for separating an inlet flow (Q.sub.O) having particulate contaminants into a coarse particle flow (Q.sub.1) and a fine particle flow (Q.sub.2) to enable collection of such particles on different filters (19a, 19b) for separate analysis. An inlet particle acceleration nozzle (28) and coarse particle collection probe member (37) having a virtual impaction opening (41) are aligned along a single axis (13) and spaced apart to define a flow separation region (14) at which the fine particle flow (Q.sub.2) is drawn radially outward into a chamber (21) while the coarse particle flow (Q.sub.1) enters the virtual impaction opening (41). Symmetrical outlet means (47) for the chamber (21) provide flow symmetry at the separation region (14) to assure precise separation of particles about a cutpoint size and to minimize losses by wall impaction and gravitational settling. Impulse defocusing means (42) in the probe member (37) provides uniform coarse particle deposition on the filter (19a) to aid analysis. Particle losses of less than 1% for particles in the 0 to 20 micron range may be realized.
A virtual impactor for dividing a particle containing gas flow into a coarse particle flow component carrying particles larger than a predetermined cutpoint size and a fine particle flow component carrying particles of less than said cutpoint size, said virtual impactor having an annular inlet flow tubulation, an annular coarse particle collection probe spaced from said inlet flow tubulation to define a flow separation region therebetween, a housing enclosing said separation region and defining an annular fine particle flow chamber therearound, said inlet flow tubulation and said collection probe and flow chamber being coaxial and aligned along a single linear axis, a coarse particle collector disposed within said probe in symmetrical relationship to said axis, a fine particle collector disposed outside of said flow chamber and at a position offset from said axis, first flow producing means for drawing said coarse particle flow component from said separation region into said collection probe and to said coarse particle collector therein, flow passage means for receiving said fine particle flow from said flow chamber and for transmitting said fine particle flow outwardly away from said axis to said fine particle collector, and second flow producing means for drawing said fine particle flow component outwardly from said separation region into said flow chamber and then to said fine particle collector through said flow passage means, wherein the improvement comprises:
A virtual impactor for dividing a particle containing gas flow into a coarse particle flow component carrying particles larger than a predetermined cutpoint size and a fine particle flow component carrying particles of less than said cutpoint size, said virtual impactor having an annular inlet flow tubulation, an annular coarse particle collection probe spaced from said inlet flow tubulation to define a flow separation region therebetween, a housing enclosing said separation region and defining an annular fine particle flow chamber therearound, said inlet fow tubulation and said collection probe and flow chamber being coaxial and aligned along a single linear axis, first flow producing means for withdrawing said coarse particle flow component from said separation region through said collection probe, and second flow producing means for drawing said fine particle flow component outwardly from said separation region and into said flow chamber, wherein the improvement comprises:
A virtual impactor comprising:
A virtual impactor comprising:
In a virtual impactor for separating particulate matter carried in a gas into a coarse particle flow component and a fine particle flow component, the virtual impactor having a coarse particle collecting filter, a coarse particle flow tubulation means for directing said coarse particle flow towards said filter along a flow path having a linear centerline and which is bounded by an aannular inner wall surface of said tubulation means, inlet means for directing said gas towards said tubulation means and which is spaced therefrom to define a flow separation region therebetween, flow producing means for drawing said coarse particle flow component into said tubulation means from said separation region while drawing said fine particle flow component outwardly from said separation region, wherein the improvement comprises:
In a virtual impactor for separating particulate matter carried in a gas into a coarse particle flow component and a fine particle flow component, the virtual impactor having a coarse particle collecting filter, a coarse particle flow tubulation means for directing said coarse particle flow towards said filter along a flow path having a linear centerline, inlet means for directing said gas towards said tubulation means and which is spaced therefrom to define a flow separation region therebetween, flow producing means for drawing said coarse particle flow component into said tubulation means from said separation region while drawing said fine particle flow component outwardly from said separation region, wherein the improvement comprises:
Dependencies are inferred from the claim text.
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No related US applications are recorded in the indexed filing history.
Involving separation of sample components during sampling: with impactors
Selective separation of solid materials carried by, or dispersed in, gas currents
Involving separation of sample components during sampling: with filters
General constructional details of gas analysers, e.g. portable test equipment: sample conditioning
Term ended 27 Mar 2000 (estimated)
USPTO file history isn’t available for this patent, so only indexed dates are shown.
This invention relates to apparatus for receiving and analyzing particulate matter contained in air or other gases. More particularly the invention relates to virtual impactors for dividing a gas flow into one flow component containing particles larger than a predetermined cutpoint size and another flow component carrying particles of less than the cutpoint size.
Airborne particulate matter variously includes natural aerosals such as soil dust, pollens and sea spray and a large number of other pollutants, such as hydrocarbons, sulphates and nitrates originating from human activities. Particles having aerodynamic sizes below about 15 microns are inhalable by humans and may produce adverse physiological effects. Monitoring of the particulate contaminants of atmospheric air, particularly in urban and industrialized areas, is therefore desirable in order to determine the nature, origin and severity of these effects and to assist in the development of countermeasures and controls.
The inhalable particles present in urban aerosals exhibit a bimodal size distribution having a minimum particle concentration at about 2.5 microns. The fine particle component, having sizes smaller than that value, tends to have a maximum concentration at a size of about 0.3 micron and is primarily derived from combustion products through condensation and coagulation. The coarse particles, having sizes larger than 2.5 microns are primarily of natural origin or are mechanically produced and are typically found in their greatest concentration at sizes around 10 microns.
The accompanying drawings, which are incorporated in and form a part of the specification, illustrate a preferred embodiment of the invention and, together with the description, serve to explain the principles of the invention. In the drawings:
FIG. 1 is a elevation section view of a virtual impactor embodying the invention, associated components for generating an air flow through the impactor being depicted in schematic form.
FIG. 2 is an enlarged diagrammatic elevation section view of the internal flow regions of the virtual impactor of FIG. 1 with significant configurational parameters being identified in the figure by letter designations to facilitate an understanding of the following description of a preferred embodiment.
Reference wil now be made in detail to the present preferred embodiment of the invention, an example of which is illustrated in the accompanying drawings.
Referring initially to FIG. 1, the virtual impactor 11 of this example includes inlet flow tubulation 12 which functions as flow acceleration and focusing means for converging an inlet gas flow Q.sub.0 towards a predetermined linear axis 13 defined by the centerline of the tubulation and for directing the converged gas flow along the axis to a flow separation region 14. The virtual impactor 11 further includes coarse particle flow tubulation or receiving means 16 which functions as a collection probe for receiving the portion Q.sub.1 of the inlet gas flow Q.sub.0 that travels across the separation region 14 without diverging from the axis 13 by more than a predetermined degree. A housing 17 defines a second or fine particle flow component receiving chamber means for receiving the portion Q.sub.2 of the inlet gas flow Q.sub.0 that diverges from the axis 13 by more than the predetermined degree during travel through the flow separation region 14. First and second flow producing means, 18a and 18b respectively, are provided for drawing the gas flow Q.sub.0, such as atmospheric air containing particulate matter, into the inlet flow tubulation 12 and for drawing the first or coarse particle flow component Q.sub.1 into coarse particle flow tubulation 16 while also drawing the second or fine particle flow component Q.sub.2 outwardly at separation region 14 and into the second flow component receiving means 17. The flow producing means 18a, and 18b draw flow component Q.sub.1 through a coarse particle collection filter 19a while drawing flow component Q.sub.2 from fine particle flow chamber 21 through a separate fine particle collection filter 19b.
Considering a suitable structure for the virtual impactor 11 in more detail, an upright cylindrical fine particle flow component receiving tube 22 having an internal flow passage 23 is secured to a base platform, 24, the centerline of the tube being coincident with axis 13. A cylindrical coarse particle flow receiving tube 25 extends upwardly through an opening 26 in base platform 24 and along axis 13 within the fine particle flow receiving tube 22. Thus tubes 25 and 22 are coaxial and share a single centerline defined by axis 13.