US3681973A

US3681973A - Centrifugal rotating particle sizing apparatus

Info

Publication number: US3681973A
Application number: US116582A
Authority: US
Inventors: Gary R Ludwig
Original assignee: Calspan Corp
Current assignee: Calspan Corp
Priority date: 1971-02-18
Filing date: 1971-02-18
Publication date: 1972-08-08
Anticipated expiration: 1989-08-08

Abstract

A particle sizing apparatus comprising a sampler mounted for rotation in a plane perpendicular to the wind direction having an entrance slot communicating with a hollow aerodynamically shaped chamber, the outer surface of which has a collection paper for collecting the particles along the length thereof as they impinge thereagainst at various points determined by the trajectories the particles follow once they are within the chamber.

Description

United States Patent Ludwig [451 Aug. 8, 1972 [s41 CENTRIFUGAL ROTATING PARTICLE I 2,973,642 3/1961 Grinnell et al ..73/28 x SIZING APPARATUS 3,395,516 8/1968 Schecter et a1. ..73/28 X Y [72] Inventor: R. Ludwig, East Amheist, Primary Examiner mchard Queisser Assistant Examiner-C. E. Snee, Ill [73] Assignee: Cornell Aeronautical Laboratory, Att rney-Allen J. J ff Inc., Buffalo, NY. 7 22 Filed: Feb. 18, 1971 [57] ABSTRACT A particle sizing apparatus comprising a sampler [21] Appl' 116582 mounted for rotation in a plane perpendicular to the 7 wind direction having an entrance slot communicating [52] US. Cl. ..73/28, 73/421.5 R, 73/170 R with a hollow aerodynamically shaped chamber, the [51] Int. Cl. ..G0ln 1/22 outer surface of which has acoflep ig 1 39*? Ot L58l field of Search .73/23, 28, 170, 188, 189, lecting the particles along file length H'Tereof as they 421.5 R, 73/42l.5 A,- 432 PS; 55/270, 400 impinge thereagainst at various points determined by 5 1 I aa- Cit d Ww the trajectories the particles follow once they are H V 7' TS Within the chamber.

2,645,941 7/ 1953 Reid 73/ I 7Q R 10 Claim, 3 Drawing Figures PATNTEUAus a|a12 3.681. 973

sum 1 0r 2 GARY ROY LUDWIG INVENTOR PATENTED A119 8 I972 SHEET 2 BF 2 I 9 M ..i A, LII 1 J v V N- m fi GARY ROY LUDWIG INVENTOR ATTORNEY CENTRIFUGAL ROTATING PARTICLE SIZING APPARATUS BACKGROUND OF THE INVENTION The present invention relates to particle sizing apparatus and, more particularly, to a centrifugal rotating aerosol particle sampling and sizing apparatus.

Numerous prior art devices are known which sample and size aerosol particles, most of which exhibit serious shortcomings. For example, the electro-optical devices are expensive and rather delicate. The aspirator devices exhibit a problem in matching the suction rate with the relative wind velocity such that the volume of air sampled is unknown; to overcome this shortcoming delicate and expensive velocity sensors and feedback controls are required.

SUMMARY OF THE INVENTION The above mentioned, as well as other, disadvantages of prior devices are overcome according to the principles of the present invention which provides a particle sampling and sizing apparatus which is inexpensive, rugged and can deliver data by simple and standard laboratory procedures.

Basically, the present invention provides a sampler rotating in a plane perpendicular to the wind vector and having a hollow interior in communication with an entrance opening for collecting the aerosol particles, the interior has aerodynamically shaped surfaces upon which the collected particles impinge. The interior surface may be lined with a suitable collecting paper for investigating the particles collected after the tests are completed.

The particles that enter the sampler follow trajecto- I ries therein which are determined by the action of inertial and centrifugal forces, which are functions of particle size. Thus, the particles are separated according to size in the sampler.

BRIEF DESCRIPTION OF THE DRAWINGS For a fuller understanding of the present invention, reference should now be had to the following detailed description of the same taken in conjunction with the accompanying drawings wherein;

FIG. 1 is a schematic pictorial representation of the apparatus according to the present invention;

FIG. 2 is a longitudinal sectional view of the sampler of the present invention; and

FIG. 3 is a chart of typical particle trajectories upon which the sampler in section is superimposed.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the drawings and more particularly to FIGS. 1 and 2, the particle sampling apparatus is generally depicted by the numeral and comprises essentially a sampler 12 mounted for rotation in the direction of arrow A by arm 14 about shaft 16 which is driven by motor means 18.

The end of shaft 16 remote from sampler 12 may contain a fin or wind vane 20 to align the sampler 12 such that it rotates in a plane perpendicular to the local wind vector W. The assembly is pivotatly mounted on a suitable support shaft 22, as illustrated.

Details of the sampler 12 are illustrated in FIG. 2 in which the sampler is shown in section. The sampler comprises an outer curved element which is generally streamlined and a inner surface 122. As illustrated the

surfaces

120 and 122 provide generally an airfoil shape and define an interior, hollow collection chamber 124. An opening 126 which may be a slot provides communication with the interior chamber 124.-

The inner surface of element 120 may removably contain means, 128, for collecting the aerosol particles. Any suitable collecting surface may be utilized, such-as an adhesive paper or the like. The collecting element extends substantially the entire inner surface of element 120.

The exact interior shape of chamber 124 is not critical, but should be consistent with the streamlined exterior shape which is necessary to minimize interference with the airstream which carries the particles to be collected. It is however important that the inner surface of element 120 immediately downstream of entrance opening 126 diverge outwardly as illustrated at to insure separation of the smaller particles.

In operation, the sampler 12 is rotated by motor 18 in a plane substantially perpendicular to the wind direction depicted by arrow W. Vane 20 functions to properly line up the sampler with respect to the wind vector. The speed of the motor is chosen such that the rotational speed of the sampler is approximately three times that of the local wind velocity to alleviate the necessity of determining the volume of air sampled.

During its rotation opening 126 faces along the circular path, traced by arrow A so that'particles enter the sampler essentially along a tangent to said path. Once a particle enters the sampler, the motion of the particle is subject only to aerodynamic drag, centrifugal and buoyancy forces inside the sampler in chamber 124. The trajectories that the particles take upon entering chamber 124 are determined by these forces, and since these forces are a function particle size, the particles are separated according to size and deposited onto collecting element 128. As illustrated in FIG. 3 the trajectories are indicated by T T T ...T,,.

The trajectories T T T ...T, can be calculated analytically. These trajectories depend only on the function, 0', which is defined by the equation:

where,

1 is the viscosity of air;

1 is the angular velocity of the sampler;

p is the density of the particle;

r is the radius of the particle;

The location of the particles impacting against surface 128 can be measured and a value of 0- can be determined from the analytical trajectory, calculations or from experimental calibrating curves. Then since the only unknown in the above equation is the particle radius, r, this is easily calculated.

Although not illustrated, the sampler would have means, such as a side door, to facilitate the removal and replacement of the collecting paper 128.

Although a preferred embodiment has been described, changes will obviously occur to those skilled in the art. It is therefore intended that the scope of the present invention is to be measured only by the scope of the appended claims.

I claim:

1. Aerosol sampling apparatus, comprising:

a. a substantially it aerodynamically shaped member having a hollow interior chamber,

b. entrance opening means communicating with said hollow interior chamber for collecting aerosol particles, and

c. means for rotating said sampler in a plane substantially perpendicular to the direction of local wind speed.

2. The apparatus according to claim 1, further comprising, v

d. means on an outer surface of said interior chamber for collecting particles along the extent thereof.

3. The apparatus according to claim 2, wherein;

e. said outer surface is curved and diverges away from said entrance opening means whereby the particles upon entering said chamber separate and follow trajectories according to the sizes thereof.

4. The apparatus according to claim 3, wherein;

f. said means on an outer surface of said chamber isremovable therefrom. 5. The apparatus according to claim 4, further comprising;

g. motor means for rotating said sampler. 6. The apparatus according to claim 5, further comprising;

b. means for aligning said sampler in a plane perpen dicular to the local wind vector. 7. The apparatus according to claim 6, wherein; i. said means for aligning comprises a vane.

8. The apparatus according to claim 1, further comprising;

d. adhesive means on an outer surface of said chamber for collecting particles along the extent thereof, and wherein;

9. The apparatus according to claim 1, wherein;

d. said entrance opening means comprises a slit.

10. The apparatus according to claim 8, further comprising;

e. removable means on said outer surface of said in terior chamber for collecting particles along the extent thereof.

Claims

1. Aerosol sampling apparatus, comprising: a. a substantially aerodynamically shaped member having a hollow interior chamber, b. entrance opening means communicating with said hollow interior chamber for collecting aerosol particles, and c. means for rotating said sampler in a plane substantially perpendicular to the direction of local wind speed.

2. The apparatus according to claim 1, further comprising, d. means on an outer surface of said interior chamber for collecting particles along the extent thereof.

3. The apparatus according to claim 2, wherein; e. said outer surface is curved and diverges away from said entrance opening means whereby the particles upon entering said chamber separate and follow trajectories according to the sizes thereof.

4. The apparatus according to claim 3, wherein; f. said means on an outer surface of said chamber is removable therefrom.

5. The apparatus according to claim 4, further comprising; g. motor means for rotating said sampler.

6. The apparatus according to claim 5, further comprising; h. means for aligning said sampler in a plane perpendicular to the local wind vector.

7. The apparatus according to claim 6, wherein; i. said means for aligning comprises a vane.

8. The apparatus according to claim 1, further comprising; d. adhesive means on an outer surface of said chamber for collecting particles along the extent thereof, and wherein; e. said outer surface is curved and diverges away from said entrance opening means whereby the particles upon entering said chamber separate and follow trajectories according to the sizes thereof.

9. The apparatus according to claim 1, wherein; d. said entrance opening means comprises a slit.

10. The apparatus according to claim 8, further comprising; e. removable means on said outer surface of said interior chamber for collecting particles along the extent thereof.