FR2969289A1 - Selector for use on sampler for sampling respirable fraction of aerosol of atmosphere, has plate assembled on body by spacer, where spacer with shape of sector of disk is turned toward axial well - Google Patents

Abstract

The selector (10) has a selector body (12) carrying a plate (15) in communication with an axial well (17) and another plate (13) delimiting with the former plate. An annular gap (19) for selection of suspended particles opens into the axial well. The latter plate is assembled on the selector body by a spacer (18) laid out between the plates, where the spacer with a shape of a sector of disk with vertex is turned toward the axial well. The spacer covers an angle ranging between 60 degrees and 120 degrees. The selector body and the plates are made of plastic.

Description

B10-3445EN 1 SELF-DIRECTION SINK PARTICULATOR SAMPLE AND PARTICULAR SAMPLING DEVICE PROVIDED WITH SUCH A SELECTOR The technical field of the invention is the sampling of atmospheric pollutants. The sampling of atmospheric pollutants consists in taking from the atmosphere solid or liquid particles present in aerosol form, and retaining these particles for later analysis. Documents FR2851656 and FR 2 851 657 are already known, portable individual sensors for carrying out such sampling. Sensors of this type comprise a sampling cup driven in rotation and in which are trapped the polluting particles and a selector, fixed relative to the cup, for the selection of particles to be retained in the cup. The selector assuming the selection of particles comprises an annular slot formed between two circular trays held together by pins.

However, the lugs described in documents FR2851656 and FR 2 851 657, allowing the trays to be held together, disturb the flow towards the cup and the acceleration of the aerosol, which must be kept constant. A consequence is then an uncontrolled change in the flow velocity in the vicinity of the lugs and the creation of turbulence. Another consequence is an aerodynamic deposition of the particles on the trays, thus creating a loss of the sucked material likely to distort the results of the analyzes. There is therefore a need for a tray assembly solution that avoids such drawbacks. The invention thus proposes a particle selector for a device for sampling particles suspended in an atmosphere, for sampling the inhalable aerosol fraction of the atmosphere, comprising a selector body carrying a first plate in communication with an axial well and a second plate delimiting therewith an annular slot for selecting the particles opening into the axial well.

The second plate is mounted on the selector body by means of a spacer disposed between the second plate and the first plate, the spacer having a form of disk sector whose apex is turned towards the axial well. The disturbances in the flow are thus considerably eliminated. The spacer can cover an angle of between 60 ° and 120 °. More particularly, the spacer may cover an angle substantially close to 90 °. The spacer has a thickness equal to the expected height of the annular slot. The second plate and the first plate may comprise plane and parallel facing surfaces which extend perpendicular to the general axis of the axial well. The plane and parallel facing surfaces of the second plate and the first plate can be sharpened on their circumference towards the outside of the annular slot. This ensures a suction efficiency comparable to that of a device with thin walls, without bounce of particles on the thickness of the second plate and the first plate.

The selector body, the first plate and the second plate can be made of non-electrostatic plastic or polished metal, especially polished stainless steel. The selector body and the first plate may be made of a first material, the second plate may be made of a second material different from the first material, the first material and the second material may be chosen from non-electrostatic plastics or metals. polished, especially polished stainless steel.

It is also proposed a portable device for sampling particles suspended in an atmosphere, comprising a diffuser, a cassette holder, a cassette, an end flange and a suspended particle selector mounted on the diffuser and in communication with the cassette, characterized in that the particle selector is constituted by a particle selector as defined above. The portable device may include a holder attached to the cassette holder for attaching the apparatus to an operator, said carrier extending over the particle selector. Other objects, features and advantages will appear on reading the following description given solely as a non-limitative example and with reference to the appended drawings in which: FIG. 1 illustrates a portable sampling device according to the invention ; and FIG. 2 illustrates, on a larger scale, the particle selector of the device of FIG. 1. FIG. 1 shows a perspective view of a sampling device according to the invention, indicated by the reference This device is intended to sample the inhalable fraction of an aerosol, that is to say a suspension of particles in the air, including microorganisms such as bacteria, spores, etc. .. and their fragments, and pollens and their fragments. As is known, the inhalable fraction of an aerosol is defined by a curve, generally accepted at the international level, which indicates the probability for a particle of this aerosol to penetrate and possibly to be retained by the part of the respiratory system concerned, depending on the size of this particle, and thus create a disorder. The purpose of the sampling device 1 is therefore to select and collect the offending particles and return them for later analysis, including quantitative.

FIG. 1 illustrates a first exemplary embodiment of a sampling device based on the use of a filter arranged in a cassette and in which a pump is used to suck the ambient air and deposit the particles to be sampled on the filtered.

The device 1 visible in FIG. 1 thus comprises a selector 10 mounted on a sampler 2. This sampler is intended to collect the inhalable fraction of an aerosol on a filter which can subsequently be used in the context of physico-chemical analyzes. I1 comprises a diffuser 9, integral with a cassette holder 6 in which is housed a cassette 6a filter holder, and an end plate 6b. A connector 6c allows the connection of a suction pump (not shown). The diffuser 9 is of flared shape, preferably frustoconical, having a small diameter adapted to cooperate with the selector, and a large diameter adapted to cooperate with the cassette holder 6. It ensures a slowing down of the speed of the suction flow from selector to homogenize the deposit on the filter. The cassette 6a is made in two parts and comprises a first lower ring on which is positioned a filter holder and a second upper ring to cap the first ring. The filter rests on the filter holder. The filter holder can be made from any suitable material, for example porous cardboard or in the form of a grid. The cassette holder 6 comprises a hollow body in which the cassette 6a is housed in position relative to the end flange 6b and to the diffuser 9. For this purpose, the cassette 6a rests on a flat gasket deposited between the flange of end 6b and the free surface of the lower ring. The cassette 6a is also held in place by another flat gasket located between the diffuser 9 and the free portion of the upper ring. The combination of the seals and the supporting forces prevents the suction of the external pump from being broken. The cassette holder 6 is also provided with a number of lights, such as 7, for lightening the sampling device 1 and the visual inspection of the cassette 6a. The lights 7 allow in particular to inspect the amount of material present on the filter. A support 3 may also be mounted on the sampler 2. The support 3 comprises a first horizontal zone 3a for mounting on the sampler 2, and a second vertical zone 3b serving to support the entire device being provided with, for example, holes, such as 4, for fixing the device 1 for example on a strap or a badge, to allow the transport of the device 1 shoulder strap or for attachment to any suitable support member. As can be seen, the sampler 2 is here kept suspended on the upper surface 5, by bolting into lights, such as 8, in the shape of a circular arc, allowing adjustment of the orientation of the sampler 2. A substantial part of the sampling member and, in particular, the area of the diffuser 9 incorporating the selector 10 protrudes beyond the upper surface of the cassette holder 6, while the zone 3b serving as a support for the entire device 1 extends largely above the selector 10.

Referring now to Figure 2, which illustrates in detail the selector 10, it is seen that this particle selector 10 comprises a selector body 12 and a second plate 13. The body 12 essentially comprises a cylindrical casing 14 surmounted by a first disc-shaped tray 15 comprising a central orifice 16, forming an end of an axial shaft 17 collinear with the casing H. The second plate 13 also has a disc shape. The second plate 13 and the first plate 15 are fixed to each other by means of a spacer 18. An annular slot 19 is thus formed in the space delimited by the first plate 15 and the second plate 13, the annular slot 19 being in communication with the axial well 17. A suction phenomenon is created at the bottom of the axial well 17, when the suction pump is running. The surrounding aerosol is then drawn in a pluridirectional manner in the horizontal plane between the two plates and is brought in the radial direction towards the axial well 17 of flow recovery. The radial movement ensures an acceleration of the aerosol between the trays. The acceleration obeys a hyperbolic power function y = f (x-1), and the instantaneous velocity v inversely proportional to the diameter r can be expressed by the following equation:

v = k / r

with k: a proportionality constant.

For a circular slit, the proportionality constant k can be expressed as the following equation: k = Q (Eq 1) 2rr-h

with Q the suction flow,

h the height of the slot and

the number of Ludolf.

This acceleration prevents the sedimentation of the particles between the trays and thus ensures a transit of the particles without loss from the periphery of the annular slot 19 to the axial well 17.

In order to avoid disturbing the flow between the two plates (13 and 15), the spacer 18 is formed in the form of a disk sector covering an angle α substantially close to 90 °, selected in a range between 60 ° and about 120 °. This sector matches the contours of the plates 13 and 15 and the contour of the orifice 16. Its thickness is equal to the expected height of the slot 19.

As seen in Figure 2, the spacer 18 has in fact a base 18a of convex shape corresponding to the peripheral shape of the plates 13 and 15, a vertex 18b truncated to form a concave surface extending into the extension axial well 17 and two side edges 18c and 18d converging towards the top 18b.

Under these conditions, the expression of the proportionality constant k is modified as follows: k = Q (Eq.2) (2n-a) h with the angle corresponding to the disk sector 18 expressed in radian. It thus emerges from equation 2 that the constant k is increased by a term dependent on the angle α of the disk sector inserted.

The spacer 18 may be independent and be inserted between the two plates 13 and 15, the assembly being secured by different fastening means such as welds, gluing or hardware. The spacer 18 may be integral with one of the trays, the other tray being then fixed by the means mentioned above. Finally, the trays and the spacer 18 may be in one piece, for example forged, molded, machined or cut. The spacer 18 thus makes it possible to maintain the distance between the two plates 13 and 15 and makes it possible to confer a certain rigidity on the assembly. The rigidity of the assembly is also ensured by the thickness of the plates 13 and 15. The plates 13 and 15 are sharpened on their circumference towards the outside of the slot so as to minimize the incidence of the thickness on the properties. aerodynamic. Sharpening ensures a suction efficiency comparable to that of a thin-walled device, with no bounce of particles over its thickness. The slot 19 thus restricted by the spacer 18 nevertheless retains a multi-directional suction and presents no internal obstacle to the flow, thus avoiding the formation of turbulence and the deposition of particles on the plates 13 and 15.

When the selector is installed on the sampling member 2, the particle selector sees its axial well being the seat of a depression under the action of an auxiliary pump. The aerosols captured by the particle selector 10 are then collected in a trap placed in the filter holder for later analysis. The portable sampling device being intended to be worn by a human operator, for example by shoulder strap, the particle selector 10 may be close to the user. In order to avoid contamination of the aerosols taken up by rejects of the operator's clothing, it is proposed to arrange the spacer 18 of the particle selector 10 towards the operator, so that the section of the annular gap 19 which is no longer the seat of a suction is turned towards the operator. The particle selector thus adapted to a portable sampling device is protected from contamination of the aerosols taken. This is an advantage over omnidirectional suction. It will be noted that the particle selector 10, and more particularly the annular slot 19, remain fragile elements. An accidental fall of the device may result in a change in the spacing of the plates 13 and 15, and therefore a change in the flow. To avoid such a situation, the support 3 for attaching the device to the operator is designed such that it extends widely above the particle selector. The support can then absorb any accidental impact due to a fall, thus protecting the annular slot. This support 3, which is based on the operator, is large enough to also limit dust emissions from the operator's clothing to the particle selector.

According to another embodiment not illustrated, the sampler 2 comprises a sampling cup enclosed in a cup holder and mechanically connected to a motor associated with a source of electrical power supply and control circuits, also enclosed in the sampler 2, and adapted to drive in rotation the sampling cup and thus create the air suction. The sampler 2 further comprises a particle selector 10 fixedly mounted on the cup holder via the diffuser 9, in order to select the particles, in particular depending on their size, to trap in the cup. Note that, as is conventional, the sampling cup may be provided with a particle trap or a body delimiting a particle trapping housing, this body may comprise an upper rim provided with an axial passage for the passage of an air flow. The upper rim may also advantageously be provided with a set of channels defining fins forming, on the upper face of the cup, a centrifugal fan capable of creating a radial air flow on this surface when the cup is rotated. by the engine. The suction is generated by the rotation of the cup. The cup also acts as a filter by collecting the offending particles. Such an embodiment also benefits from the flow improvements resulting from the use of the particle selector described above in connection with FIG. 2.

Claims (10)

REVENDICATIONS1. Particle selector for a device for sampling particles suspended in an atmosphere, for sampling the inhalable aerosol fraction of the atmosphere, comprising a selector body (12) carrying a first plate (15) in communication with an axial well (17) and a second plate (13) delimiting with the first plate (15) an annular slot (19) for selecting the particles opening into the axial well (17), characterized in that the second plate (13) ) is mounted on the selector body (12) by means of a spacer (18) disposed between the second plate (13) and the first plate (15), the spacer (18) having a disc sector shape of which the top is turned towards the axial well (17). 2. Selector according to claim 1, characterized in that the spacer (18) covers an angle of between 60 ° and 120 °. 3. Selector according to one of claims 1 and 2, characterized in that the spacer (18) covers an angle substantially close to 90 °. 4. Selector according to any one of the preceding claims, characterized in that the spacer (18) has a thickness equal to the expected height of the annular slot (19). 5. A selector according to any one of the preceding claims, characterized in that the second plate (13) and the first plate (15) have plane facing surfaces parallel to each other which extend perpendicular to the general axis of the axial shaft (17). 6. Selector according to any one of the preceding claims, characterized in that the planar and parallel facing surfaces of the second plate (13) and the first plate (15) are sharpened on their circumference towards the outside of the annular slot ( 19). 7. Selector according to any one of the preceding claims, characterized in that the selector body (12), the first plate (15) and the second plate (13) are made of non-electrostatic plastic material or polished metal, particularly in polished stainless steel. 8. Selector according to any one of claims 1 to 7, characterized in that the selector body (12) and the first plate (15) are made of a first material, the second plate (13) being made in a second material different from the first material, the first material and the second material being selected from non-electrostatic plastics or polished metals, especially polished stainless steel. Portable device for sampling particles suspended in an atmosphere, comprising a diffuser (9), a cassette holder (6), a cassette (6a), an end flange (6b) and a particle selector ( 10) mounted on the diffuser (9) and in communication with the cassette (6a), characterized in that the particle selector (10) is constituted by a selector according to any one of claims 1 to 8. 10. Portable device according to claim 9, comprising a support (3) fixed on the cassette holder (6) for attaching the apparatus to an operator, said support (3) extending over the particle selector ( 10).