초록 ▼

Environmental monitoring of atmospheric air is facilitated by a single stage virtual impactor (11) for separating an inlet flow (QO) having particulate contaminants into a coarse particle flow (Q1) and a fine particle flow (Q2) to enable collection of such particles on different filters (19a, 19b) f

Environmental monitoring of atmospheric air is facilitated by a single stage virtual impactor (11) for separating an inlet flow (QO) having particulate contaminants into a coarse particle flow (Q1) and a fine particle flow (Q2) 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 (Q2) is drawn radially outward into a chamber (21) while the coarse particle flow (Q1) 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.

대표청구항 ▼

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

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 flow chamber endwall disposed between said flow chamber and said flow passage means in coaxial relationship to said inlet flow tubulation and said probe, said endwall having aperture means for transmitting said fine particle flow component out of said flow chamber and into said flow passage means in a flow pattern which is symmetrical with respect to said axis, said aperture means being sized to impede flow from said chamber into said flow passage means to an extent sufficient to prevent flow pattern asymmetry in said flow passage means from causing a flow pattern asymmetry at said separation region.