Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B03—SEPARATION OF SOLID MATERIALS USING LIQUIDS OR USING PNEUMATIC TABLES OR JIGS; MAGNETIC OR ELECTROSTATIC SEPARATION OF SOLID MATERIALS FROM SOLID MATERIALS OR FLUIDS; SEPARATION BY HIGH-VOLTAGE ELECTRIC FIELDS
  • B03C—MAGNETIC OR ELECTROSTATIC SEPARATION OF SOLID MATERIALS FROM SOLID MATERIALS OR FLUIDS; SEPARATION BY HIGH-VOLTAGE ELECTRIC FIELDS
  • B03C3/00—Separating dispersed particles from gases or vapour, e.g. air, by electrostatic effect
  • B03C3/02—Plant or installations having external electricity supply
  • B03C3/025—Combinations of electrostatic separators, e.g. in parallel or in series, stacked separators, dry-wet separator combinations
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B03—SEPARATION OF SOLID MATERIALS USING LIQUIDS OR USING PNEUMATIC TABLES OR JIGS; MAGNETIC OR ELECTROSTATIC SEPARATION OF SOLID MATERIALS FROM SOLID MATERIALS OR FLUIDS; SEPARATION BY HIGH-VOLTAGE ELECTRIC FIELDS
  • B03C—MAGNETIC OR ELECTROSTATIC SEPARATION OF SOLID MATERIALS FROM SOLID MATERIALS OR FLUIDS; SEPARATION BY HIGH-VOLTAGE ELECTRIC FIELDS
  • B03C3/00—Separating dispersed particles from gases or vapour, e.g. air, by electrostatic effect
  • B03C3/02—Plant or installations having external electricity supply
  • B03C3/04—Plant or installations having external electricity supply dry type
  • B03C3/06—Plant or installations having external electricity supply dry type characterised by presence of stationary tube electrodes
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B03—SEPARATION OF SOLID MATERIALS USING LIQUIDS OR USING PNEUMATIC TABLES OR JIGS; MAGNETIC OR ELECTROSTATIC SEPARATION OF SOLID MATERIALS FROM SOLID MATERIALS OR FLUIDS; SEPARATION BY HIGH-VOLTAGE ELECTRIC FIELDS
  • B03C—MAGNETIC OR ELECTROSTATIC SEPARATION OF SOLID MATERIALS FROM SOLID MATERIALS OR FLUIDS; SEPARATION BY HIGH-VOLTAGE ELECTRIC FIELDS
  • B03C3/00—Separating dispersed particles from gases or vapour, e.g. air, by electrostatic effect
  • B03C3/02—Plant or installations having external electricity supply
  • B03C3/04—Plant or installations having external electricity supply dry type
  • B03C3/12—Plant or installations having external electricity supply dry type characterised by separation of ionising and collecting stations
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B03—SEPARATION OF SOLID MATERIALS USING LIQUIDS OR USING PNEUMATIC TABLES OR JIGS; MAGNETIC OR ELECTROSTATIC SEPARATION OF SOLID MATERIALS FROM SOLID MATERIALS OR FLUIDS; SEPARATION BY HIGH-VOLTAGE ELECTRIC FIELDS
  • B03C—MAGNETIC OR ELECTROSTATIC SEPARATION OF SOLID MATERIALS FROM SOLID MATERIALS OR FLUIDS; SEPARATION BY HIGH-VOLTAGE ELECTRIC FIELDS
  • B03C3/00—Separating dispersed particles from gases or vapour, e.g. air, by electrostatic effect
  • B03C3/34—Constructional details or accessories or operation thereof
  • B03C3/36—Controlling flow of gases or vapour
  • B03C3/368—Controlling flow of gases or vapour by other than static mechanical means, e.g. internal ventilator or recycler
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B03—SEPARATION OF SOLID MATERIALS USING LIQUIDS OR USING PNEUMATIC TABLES OR JIGS; MAGNETIC OR ELECTROSTATIC SEPARATION OF SOLID MATERIALS FROM SOLID MATERIALS OR FLUIDS; SEPARATION BY HIGH-VOLTAGE ELECTRIC FIELDS
  • B03C—MAGNETIC OR ELECTROSTATIC SEPARATION OF SOLID MATERIALS FROM SOLID MATERIALS OR FLUIDS; SEPARATION BY HIGH-VOLTAGE ELECTRIC FIELDS
  • B03C3/00—Separating dispersed particles from gases or vapour, e.g. air, by electrostatic effect
  • B03C3/34—Constructional details or accessories or operation thereof
  • B03C3/40—Electrode constructions
  • B03C3/41—Ionising-electrodes
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B03—SEPARATION OF SOLID MATERIALS USING LIQUIDS OR USING PNEUMATIC TABLES OR JIGS; MAGNETIC OR ELECTROSTATIC SEPARATION OF SOLID MATERIALS FROM SOLID MATERIALS OR FLUIDS; SEPARATION BY HIGH-VOLTAGE ELECTRIC FIELDS
  • B03C—MAGNETIC OR ELECTROSTATIC SEPARATION OF SOLID MATERIALS FROM SOLID MATERIALS OR FLUIDS; SEPARATION BY HIGH-VOLTAGE ELECTRIC FIELDS
  • B03C3/00—Separating dispersed particles from gases or vapour, e.g. air, by electrostatic effect
  • B03C3/34—Constructional details or accessories or operation thereof
  • B03C3/40—Electrode constructions
  • B03C3/45—Collecting-electrodes
  • B03C3/49—Collecting-electrodes tubular
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B03—SEPARATION OF SOLID MATERIALS USING LIQUIDS OR USING PNEUMATIC TABLES OR JIGS; MAGNETIC OR ELECTROSTATIC SEPARATION OF SOLID MATERIALS FROM SOLID MATERIALS OR FLUIDS; SEPARATION BY HIGH-VOLTAGE ELECTRIC FIELDS
  • B03C—MAGNETIC OR ELECTROSTATIC SEPARATION OF SOLID MATERIALS FROM SOLID MATERIALS OR FLUIDS; SEPARATION BY HIGH-VOLTAGE ELECTRIC FIELDS
  • B03C3/00—Separating dispersed particles from gases or vapour, e.g. air, by electrostatic effect
  • B03C3/34—Constructional details or accessories or operation thereof
  • B03C3/38—Particle charging or ionising stations, e.g. using electric discharge, radioactive radiation or flames
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B03—SEPARATION OF SOLID MATERIALS USING LIQUIDS OR USING PNEUMATIC TABLES OR JIGS; MAGNETIC OR ELECTROSTATIC SEPARATION OF SOLID MATERIALS FROM SOLID MATERIALS OR FLUIDS; SEPARATION BY HIGH-VOLTAGE ELECTRIC FIELDS
  • B03C—MAGNETIC OR ELECTROSTATIC SEPARATION OF SOLID MATERIALS FROM SOLID MATERIALS OR FLUIDS; SEPARATION BY HIGH-VOLTAGE ELECTRIC FIELDS
  • B03C3/00—Separating dispersed particles from gases or vapour, e.g. air, by electrostatic effect
  • B03C3/34—Constructional details or accessories or operation thereof
  • B03C3/40—Electrode constructions
  • B03C3/45—Collecting-electrodes
  • B03C3/47—Collecting-electrodes flat, e.g. plates, discs, gratings

Definitions

• the present invention relates to the field of the collection and analysis of particles that may be present in suspension in an aerosol.
• It relates more particularly to the production of an electrostatic device for collecting particles by electrostatic precipitation, including nanoparticles contained in aerosols.
• the present invention aims to allow a collection of particles in suspension in aerosols which is simultaneous but selective depending on their dimensions, the selectivity preferably aimed at collecting, by separating them, the particles of micron and submicron size, ie greater than or equal to at 300 nm, and nanoscale particles.
• Nanoparticle means the usual definition according to the standard
• ISO TS / 27687 a nano-object whose three dimensions are nanoscale, ie a particle whose nominal diameter is less than about 100 nm.
• this high electric field (several thousands to tens of thousands of volts per centimeter in the vicinity of the discharge electrode) is induced by two electrodes arranged close to each other: a first polarized electrode or electrode of discharge, generally in the form of wire or tip, being disposed opposite a second electrode, the latter being in the form of a counter-electrode, generally flat or cylindrical geometry.
• the electric field existing between the two electrodes ionizes the volume of gas located in the inter-electrode space, and in particular a sheath or ring of ionized gas located around the discharge electrode.
• the charged particles thus created migrate to the counter electrode, where they can be collected.
• This counterelectrode is usually called a collection electrode.
• the discharge electrodes encountered are therefore generally either fine points or small diameter wires. So, through a process which originates from the electrons and ions created by natural irradiation, the electrons are accelerated in the intense electric field created in the vicinity of the electrode with (very) small radius of curvature. By the high voltage imposed, if this field exceeds a critical value, an avalanche effect causes the ionization of the air in this space. This phenomenon is called corona discharge.
• FIGS. 1A to 1E show a few configurations of electrodes most suitable for obtaining a corona discharge, namely respectively a tip-plane arrangement (FIG. 1A), plate-plane (FIG. 1B), wire-plane (Figure 1C), wire-wire (Figure 1D), wire-cylinder ( Figure 1E).
• a wind of ions also called ionic wind, is established, characterized by a flow of air directed from the point towards the plane, having as origin the shocks of the positive ions with the surrounding neutral molecules.
• the tip is negative to the plane, the positive ions move toward the tip, and the electrons move toward the plane by attaching themselves to the air molecules to form negative ions.
• the unipolar ions migrate from the tip to the plane with a high concentration of the order of 10 6 to 10 9 / cm 3 and, whatever the polarity, there appears an electric wind directed from the point towards the plane.
• the introduction of aerosol particles in the tip-plane space makes it possible to charge them with the same polarity as the tip, according to a field charging process.
• the field used to create the corona effect and the electric wind also participate in the field charging process.
• FIG. 15.9 on page 341 of the publication [1] already cited shows an arrangement allowing the deposition of aerosol particles on a grid of electron microscope, the particles being charged and precipitated in a tip-plane configuration.
• the unipolar ion diffusion charging mechanism applies predominantly to the finest particles.
• This mechanism is increasingly used in the metrology of nanoparticles, in particular to determine their particle size.
• many authors have studied and are still studying devices capable of conferring high electrical mobilities on the finest particles, in order to be able to select them in instruments adapted to this new domain.
• FIG. 2 schematically reproduces a charging device, also known as a charger, for unipolar ion diffusion whose geometry is of the wire-cylinder type, as illustrated in the publication [4].
• the charger 10 comprises a two-part symmetrical body of revolution 1 which holds a hollow metal cylinder 11 forming an external electrode connected to an AC power supply and a central wire 12 arranged along the axis of the body and connected to a power supply. high voltage not shown.
• Around the central wire 12 is also annularly arranged a cylindrical grid 14 forming an inner electrode.
• the aerosol containing the particles to be charged flows in the charger 10 from the inlet orifice 17 to the outlet orifice 18 by passing through the space delimited between the inner electrode 14 formed by the gate and the outer electrode 11 formed by the cylinder.
• this charger 10 The operation of this charger 10 is as follows: ions are produced by corona effect at the central wire 12 and are collected by the inner mesh electrode 14 brought to a low potential, typically grounded. Part of these ions out of this gate 14 to go to the inner surface of the peripheral cylinder 11 due to the voltage applied to the latter. The aerosol particles pass through the space between grid 14 and cylinder 11 and are thus charged by diffusion by unipolar ions.
• the diffusion loading mechanism operates according to the product N * t, where N represents the concentration of unipolar ions and t the residence time of the particles.
• the diffusion charging mechanism is the only one that can occur because there can be no field charge mechanism since the electric field is very small in space 15.
• DMA differential electric mobility analyzers
• the general object of the invention is then to respond at least in part to this need.
• the invention firstly relates to a method for collecting particles that may be present in an aerosol, comprising the following steps:
• the method further comprises the following steps:
• the invention also relates to a device for collecting particles that may be present in an aerosol, comprising:
• a duct comprising an inlet orifice and an outlet orifice between which the aerosol can circulate;
• suction means for circulating the aerosol from the inlet orifice to the outlet orifice
• a unipolar ion diffusion charger comprising an electrode in the form of a wire surrounded by an electrode in the form of a gate, the charger being adapted to charge the particles finer in the space separating the gate from a first conductive portion of the inner wall of the conduit, by diffusion of unipolar ions through the gate;
• an electrode downstream of the diffusion charger, an electrode adapted to generate, without a corona effect, an electric field in the space separating the electrode from a second portion conductive inner wall of the conduit and thus collect the finest particles, previously loaded by the diffusion charger, by depositing on a first collection zone (Zn);
• an electric field charger comprising an electrode in the form of a wire or a tip adapted to generate a field in the space between the wire or tip of a third conductive portion of the inner wall of the conduit and thereby charge and collect the largest particles, by depositing on a second collection zone (Zm) distinct from the first zone collection.
• the invention consists in an electrostatic collection of all the particles present in an aerosol, but with a decoupling of the mechanisms on the one hand charge of the particles by diffusion of unipolar ions to charge and then collect the finest particles and on the other hand corona charging electric field charge to charge and collect the largest particles in a different area of the collection area of the finest particles.
• the invention consists in first electrically charging the fine particles by diffusion of unipolar ions, then charging the large particles by an electric field and collecting each group of charged particles according to their size on a adequate support.
• the invention makes it possible judiciously to classify the particles according to their particle size, by depositing them in physically distinct zones.
• the deposition of the particles may be carried out according to concentric rings in different locations of the same plane substrate arranged orthogonal to the direction of circulation of the aerosol.
• the substrate or substrates on which the particle deposition collection zones are defined can then be analyzed by conventional physical or physico-chemical characterization techniques, such as optical microscopy or electronics, surface scanner, ⁇ , ⁇ , ⁇ spectrometry if the particles are radioactive, X-ray fluorescence spectroscopy (XRF), X-ray fluorescence ( ⁇ -XRF), laser-induced plasma spectroscopy (X-Ray Fluorescence) LIBS for "Laser-Induced Breakdown Spectroscopy”) ...
• XRF X-ray fluorescence spectroscopy
• ⁇ -XRF X-ray fluorescence
• X-Ray Fluorescence laser-induced plasma spectroscopy
• a collection device is particularly well suited for the sampling of particles in gaseous media, in particular the air of premises or the environment in order to know the concentration, the particle size distribution, the composition of the particles of aerosol that can be inhaled.
• the duct is a hollow cylinder of revolution about a longitudinal axis
• the suction means consist of a pump
• the first, second and third wall conducting portions are cylinder portions constituting part of the duct;
• the field charger comprises an electrode in the form of a thread in wire-cylinder configuration with the corresponding cylinder portion;
• the wire of the ion diffusion charger, the electrode making it possible to generate an electric field without corona effect and the wire of the charger per field are distinct parts and successively arranged one behind the other along the axis (X).
• the duct comprises a hollow element of revolution about a longitudinal axis (X) and a planar substrate arranged at one end of the hollow element being orthogonal to the axis (X), the distance separating the hollow element from the planar substrate and its optional support defining the dimensions of the outlet orifice, the planar substrate forming a collection substrate defining both the first (Zn) and the second collection zone (Zm);
• the suction means consist of the outlet orifice
• the first conducting portion of the wall is a portion of revolution constituting the conduit
• the second and third conductive portions are gathered on the same collection substrate;
• the field charger comprises an electrode in the form of a tip in planar configuration with the collection substrate; the tip being adapted to generate a corona effect participating in the field charge of the particles but also to create an electric field promoting the collection of species previously loaded by the charger by ion diffusion.
• the wire of the ion diffusion charger, the electrode and the tip of the field charger are portions of the same part having an electrical continuity which extends along the axis (X).
• the device according to this second mode may comprise plasma actuators arranged near the outlet.
• the wire of the ion diffusion charger, the electrode for generating an electric field without a corona effect and the wire or the tip of the charger per field are connected to a high voltage power supply, preferably between 2 and 6 kV. .
• the gate is preferably connected to a low voltage supply, preferably of the order of 100 V.
• the first, second and third conductive portions are preferably connected to the zero potential. It is also possible to supply the first conductive portion at low voltage, typically at about 50V.
• the collection device may constitute, after a prior collection, an ionization chamber and a radioactive particle detector with an alarm function in the event of exceeding a predetermined threshold.
• the invention finally relates to the use of a device described above to collect while separating nanoparticles in the first collection zone (Zn) and micron-sized particles in the second collection zone (Zm).
• the use of the device can also be done as an ionization chamber.
• An advantageous use of the device according to the invention is to evaluate the individual exposure of workers or consumers to nanoparticles.
• FIG. 2 is a longitudinal sectional view of a charging device, or unipolar ion diffusion charger
• FIG. 3 is a diagrammatic longitudinal sectional view of a first example of a particle collection device according to the invention.
• FIG. 4 is a diagrammatic view in longitudinal section of a second example of a device for collecting particles according to the invention.
• FIG. 5 is a view showing the simulation carried out using a finite element calculation software for determining the electric field lines in the downstream part of the device;
• FIG. 6 is a view showing the forces to which the particles are subjected as well as examples of trajectories of two types of particles in the downstream part of a device according to the invention
• FIG. 7 is a graph characterizing the influence on the collection efficiency of the voltage applied to the peak electrode for obtaining the corona effect in a device according to FIG. 4, for different distances between the tip electrode and the collection substrate according to the invention (negative polarity);
• FIG. 8 is a graph characterizing the influence on the collection efficiency of the aerosol flow rate in a device according to FIG. 4 for different distances between the tip electrode and the collection substrate according to the invention, and different polarities;
• FIG. 9 is a photographic reproduction of a collection substrate implemented in a device according to the invention as illustrated in FIG. 4, FIG. 9 showing a collection zone Zm of particles of micron size (latex polystyrene beads). 2 ⁇ in diameter);
• FIG. 10 is a view showing the description of models used to perform a simulation using a finite element calculation software for determining the flows and electric fields that occur in a device according to the invention as illustrated. in Figure 4;
• FIG. 11 is a view derived from the simulation by the finite element calculation software for determining the particle velocity profiles as well as the ion wind produced in a device according to the invention as illustrated in FIG. 4;
• FIG. 12 is yet another view resulting from the simulation by the finite element calculation software which illustrates the trajectories of particles of diameter equal to 100 nm (left part of the figure) and equal to 10 nm (right part of the figure) in a device according to the invention as illustrated in FIG. 4;
• inlet refers to the orifice of the device by which the aerosol containing the particles is sucked while the outlet means the one through which the air flow exits.
• FIG. 3 shows a first example of an electrostatic device 1 according to the invention for the selective collection of particles that may be contained in an aerosol.
• Such a device according to the invention makes it possible to collect at the same time the finest particles, such as the nanoparticles and the larger particles, such as those of micron size while separating them from one another according to their range of cut.
• the collection device 1 comprises firstly a conduit 11 which is a hollow cylinder of revolution about the longitudinal axis X and which is electrically connected to a low voltage, for example at a voltage of 50 volts or zero potential .
• the collection device 1 comprises inside the duct 11, upstream to downstream, between its inlet orifice 17 and its outlet orifice 18, four distinct stages 10, 20, 30, 40.
• the first stage consists of a unipolar ion diffusion charger 10, and is similar to that previously described in connection with FIG.
• the charger 10 thus comprises a central electrode which extends along the X axis in the form of a wire 12 connected to a supply delivering a high voltage 13, adapted to thereby create a corona discharge in the vicinity of the wire 12.
• It also comprises a peripheral electrode in the form of a gate 14 connected to a low voltage supply 16.
• the stage 20, downstream of the charger 10, comprises a central electrode which extends along the X axis in the form of a rod 22 connected to a power supply delivering a medium voltage 23, adapted to create a corona-free field electrical collection in the space 21 separating the central electrode 22 and the wall of the conduit 11.
• a hollow cylinder 24 conforming to the wall of the conduit and constituting a first collection zone Zn is arranged around the rod 22 opposite the this.
• the stage 30, downstream of the stage 20, comprises a central electrode which extends along the X axis in the form of a wire 32 connected to a high voltage supply 33, adapted to create a corona effect in the vicinity wire 32 and therefore an intense electric field in the space 31 between the central wire 32 of the conduit 11.
• a hollow cylinder 34 conforming to the wall of the conduit and constituting a second collection zone Zm is arranged around the wire 32 opposite the one -this.
• Stage 40 comprises a structure 41, for example "honeycomb", adapted to prevent the appearance of a vortex in the conduit 11, and downstream a suction device 42.
• the collecting device according to the invention can overcome the structure 41.
• the air containing the particles to be collected is sucked by the inlet orifice 17 by the action of the suction device 42.
• the finest particles of the aerosol are electrically charged by diffusion of unipolar ions in the space 15 separating the gate 14 from the conduit 11.
• the other larger particles are not collected and still present in the aerosol that enters the third stage 30.
• the purified air of both the finest particles deposited in the first collection zone Zn and the larger particles Zm is then discharged through the outlet orifice 18 of the device.
• Each of the zones Zn and Zm can then be analyzed by conventional physical or physico-chemical characterization techniques, such as optical or electronic microscopy, surface scanner, ⁇ , ⁇ , ⁇ spectrometry if the particles are radioactive, X-ray fluorescence spectroscopy ( XRF for "X-Ray Fluorescence"), micro-fluorescence X ( ⁇ -XRF), laser-induced plasma spectroscopy (LIBS for "Laser-Induced Breakdown Spectroscopy”), etc., to determine the particle size on the one hand. the finest particles and on the other hand the largest particles, their concentration, their chemical composition and / or their morphology.
• XRF X-ray Fluorescence
• ⁇ -XRF micro-fluorescence X
• LIBS laser-induced plasma spectroscopy
• the collection cylinder 24 and the 34 are constituted by a single piece which thus forms a single collection substrate, which can be easily extracted from the conduit once the targeted collection performed.
• FIG. 4 shows another advantageous example of a collection device 1 according to the invention making it possible to collect the particles not on a cylinder or cylinders arranged along the axis of flow of the aerosol as illustrated in FIG. 3, but on the same disk-shaped substrate 6 placed on its support 5 and arranged orthogonal to the axis of symmetry of the collection device.
• the collection device illustrated in FIG. 4 has the advantage, compared with that illustrated in FIG. 3, of being able to collect all the particles on the same plane surface of the substrate according to concentric rings as a function of their relative dimensions. the largest particles being collected preferentially at the center of the surface while the finest are collected preferentially at the periphery.
• the collection device illustrated in FIG. 4 advantageously makes it possible to take advantage of the ionic wind created by the tip-plane configuration for the collection of the largest particles, and thus to induce a flow of air through the device in its part. downstream.
• This circulation of air can go as far as to make it possible to overcome the presence of a suction pump, which considerably lighten the collection device according to the invention and also makes it possible to reduce its nuisances (vibrations, noise, ).
• the collecting disk 6 is preferably conductive, typically of metal, or even semiconductor. Its diameter is preferably between 10 and 25 mm, more preferably of the order of 20 mm.
• the collection device 1 has a cylindrical geometry of revolution about the longitudinal axis X and comprises an elongated hollow body 11 surrounded by a casing 110 which may or may not be conductive and surmounted by an electrically insulating body 3 in which the electrodes are fixed and by which the power supplies are realized.
• the body 11 and the envelope 110 may be one and the same piece.
• the conductive envelope 110, as well as the body 11 and the support 5 can be connected to the zero potential by the power supply terminal 2. It is also possible to use a casing 110 and the body 11 of insulating material thus brought to potential floating and maintain the support 5 at zero potential by an electrical wire connecting it to the power terminal 2.
• the hollow body 1 1 defines, within it, with an insulating element 4, and a collection substrate 6 and its support 5, the aerosol circulation duct from the inlet orifice 17 to the outlet orifice. 18.
• the collecting device 1 according to FIG. 4 comprises the same elements as that of FIG. 3 as explained above but essentially differs in that:
• the part to create the corona effect for the collection of the largest particles is in tip-plane configuration, the tip 32 being at a distance from the plane of the collection substrate 6 arranged orthogonal to the X axis; the central corona wire 12 for the diffusion of unipolar ions, the rod 22 making it possible to generate a non-corona electric field for collecting the fine particles and the crown effect tip 32 for the collection of the largest particles forming a single central electrode with portions 12, 22, 32 continuous but of different geometry.
• the unipolar ion diffusion charger consists of a portion of the central electrode in the form of a wire 12 and a gate 14 arranged around the central wire 12.
• the central wire 12 preferably has a diameter less than 50 ⁇ .
• an insulating element 4 judiciously makes it possible to ensure both the centering and the fixing of the electrode portion in the form of a rod 22 thus electrically connected to the wire 12.
• the rod 22 terminates in a tapered point 32 facing the collecting disk 6.
• the angle of the tip is less than 35 ° and its apex (vertex) has its largest width less than 50 ⁇ .
• the collection device 1 may advantageously comprise in its downstream part, that is to say in the widened part of the aerosol circulation duct, downstream of the gate 14, plasma actuators 8 which make it possible to control the flow of the purified air of the particles in this downstream part, before its evacuation through the outlet orifice 18, as explained later.
• a single high voltage supply 13, 23, 33 makes it possible to perform both the corona effect in the vicinity of the wire 12 and in the vicinity of the tip 32.
• the high voltage is chosen preferred between 2 and 6 kV, more preferably at about 4 kV.
• a low voltage power supply 16 of the order of 100V, makes it possible to polarize the gate 14 to control the production of unipolar ions in the diffusion charge space 15.
• the dimensioning is carried out taking care not to introduce excessive shrinkage with a reduced section. This minimizes the pressure drop of the assembly vis-à-vis the air flowing in the annular space 15.
• the aerosol flows from the inlet orifice 17 to the outlet orifice 18 because the suction is carried out at the latter.
• the finest particles are electrically charged by diffusion of unipolar ions in the annular space 15 while the larger particles are electrically charged under the action of the intense electric field in the space 31 between the tip 32 generating the effect crown and collection substrate 6.
• FIG. 4 illustrates a possible embodiment of the collection device 1 which makes it possible not to use an auxiliary suction pump. Under the effect of the ionic wind created in the gap 31 between the tip 32 and the collection substrate 6, a vacuum appears in the annular charge charging gap 15, which creates flow at the rate q in the device.
• the suction can be optimized by the more or less wide opening of the outlet orifice 18, by the choice of the high voltage applied to the tip 32 as well as by the distance between the tip 32 and the plane 6.
• plasma actuators 8 are advantageously of the type used in microelectronics for cooling microcomponents.
• the flow of collection q which runs through the device is generally increased. In the end, with defined geometry and high voltage, there is a collection flow q that can be set.
• FIG. 5 illustrates the electric field lines that take place in the downstream part of the aerosol circulation duct. Field lines being perpendicular to the equipotential lines, it is possible to achieve a confinement of the field lines by the equipotentials internal to the collection zones.
• the tip 32 makes it possible to obtain a very intense electric field locally, which allows the ionization of the air and the charge of the microparticles. But moving away vertically, it decreases very rapidly to a value of about 0.5 * 10 6 V / m where the particles pass.
• the radius of curvature of 1 mm at the bottom of the wall of the hollow body 11 is sufficient at the critical point to avoid any breakdown problem up to 4000 V.
• a thin particle, of high mobility, is immediately subjected to the action of the surrounding radial electric field, which results in a radial outward speed w, while being transported by the aeraulic field, which results in a radial velocity inward v.
• the vector resultant, velocity u thus defines the trajectory and the point of impact of this particle on the disk 6 of collection.
• the point of impact defines an impact circumference or Zn ring on the substrate 6, given the symmetry of revolution of the device.
• the larger particles of lower mobility, they are not charged by diffusion, arrive in the vicinity of the tip 32, are charged electrically by bombarding the ions produced locally by the corona effect between the tip 32 and the substrate 6, and are thus deposited on the latter in the vicinity of the X axis on impact circumferences Zm of radius all the smaller as their size is large.
• the particles are collected on the disc in concentric circles according to their particle size, the finest on the outside, the largest in the center.
• the inventors have sought to quantitatively evaluate the efficiency of a collection device 1 which has just been described with reference to FIGS. 4 to 6.
• a first evaluation was made from air loaded with latex-polystyrene beads (PSL) of 2 ⁇ in diameter, sold by ABCR under the name ABCR 210832.
• PSL latex-polystyrene beads
• This first evaluation makes it possible to illustrate the field effect charging mechanism of the micron-sized particles in the space 31 between the tip 32 and the metal collection substrate 6 and their deposit on the latter.
• the inventors proceeded as follows.
• An aqueous suspension of PSL beads is atomized using an aerosol generator, brand TSI, model 3076, then dried by a desiccant column, brand TSI, model 3062.
• the aerosol thus generated is then introduced into a chamber in which the collection device 1 as illustrated in FIGS. 4 to 6 is located, at a flow rate of 3.6 L / min.
• the chamber is provided with an outlet orifice making it possible to avoid an overpressure since the flow rate imposed by a pump external to the collection device, in the range of 0.4 to 1.4 L / min, is always lower than the flow rate. aerosol entering the room.
• an imposed flow rate Q is applied to the collection device 1 to force a flow to flow from the inlet port 17 to the outlet port 18 by means of a variable flow pump which is controlled by a flowmeter.
• the high voltage 13, 23, 33 applied to the central electrode 12, 22, 32 is studied for positive (+) and negative (-) polarities of 1500 V at 4000 V and for different distances z between the end of the tip 32 and the collection substrate 6.
• Figure 7 shows that for a constant flow rate of 1.4 L / min, the collection efficiency that results in the ratio expressed as a percentage between the number of particles leaving the device and the number of particles entering, increases when the voltage applied (in absolute value) increases.
• the collection efficiency peaks around 90% irrespective of the distance between tip 32 and plane of the substrate 6, which is varied by 2.5 mm. at 6.5 mm.
• the collection efficiency is highest when the flow rate is low, which is particularly the case for a flow rate of 0.4 L / min. Moreover, it is observed that for a fixed flow the collection efficiency is higher when the polarity used is negative and when the distance tip-plane is large.
• FIG. 9 shows the photograph of a 20 mm diameter copper collection substrate 6 on which the micron particles have been collected: it is clearly seen that they are deposited according to a Zm ring concentric with the X axis. the device or the tip 32.
• This white crown Zm corresponds to the deposition of PSL particles of 2 ⁇ in diameter.
• the inventors have also simulated the operation of the collection device according to the invention as illustrated in FIGS. 4 to 6 using a finite element calculation software marketed under the name "COMSOL Multiphysics”.
• the collection device 1 with the same geometry as that shown in FIGS. 4 to 6 can be studied under the COMSOL software by looking at the flows, the electric fields, the particle trajectories as well as the ionic wind produced.
• Fig. 10 is a view showing the description of models used to perform a simulation using finite element computing software to determine the flows and electric fields that occur in a device according to the invention as illustrated in Figs. figure 4.
• the enlarged wall portion 111 is brought to the same potential as the tip 32.
• this portion 11 1 may be at a different potential from tip 32.
• FIG. 11 shows the simulation of the flow for a distance z between tip 32 and plane 31 of 4 mm and an applied voltage U at the tip 32 and at the portion 11 of + 4000 V.
• FIG. 11 clearly shows the generation of a plasma produced by the corona effect under point 32 where the electric fields are the most high, this plasma inducing an ionic wind towards the collecting disc 6.
• the jet thus produced blooms on the surface of the collection disc.
• this ionic wind sucks the aerosol upstream of the tip 32 towards the charge zone 31 by a field effect and therefore contributes to the excellent collection efficiencies encountered for the larger particles.
• the portion 111 makes it possible to create an aerosol circulation in the device 1 according to the invention.
• a flow rate of about 0.5 L / min, which is a value very correct to obtain collection efficiencies greater than 94%.
• the finite element software "Comsol” shows that the nanoparticles are well precipitated, i.e. deposited by electrostatic precipitation.
• the collection device according to the invention is particularly well suited for the sampling of particles in gaseous media, in particular the air of the premises or the environment in order to know the concentration, the particle size, the morphology and the composition. aerosol particles likely to be inhaled ... Because of its small size and its reduced power consumption, this device could be portable and therefore deployable on a large scale for a moderate cost.
• the collection device according to the invention can operate as an ionization chamber.
• the device can operate as an aerosol collector for a time t ls and then as a pulse counter for a time t 2 .
• the ionization current collected by the tip 32 can then be detected by an appropriate electronic system, of the type commonly used in conventional ion chambers.
• radioactive aerosols such an ionization chamber can thus constitute a radioactive contamination detector with an alarm function in case of exceeding a predetermined threshold.

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• 2015
  • 2015-07-28 FR FR1557221A patent/FR3039435B1/fr active Active
• 2016
  • 2016-07-28 CN CN201680044319.1A patent/CN107921444B/zh not_active Expired - Fee Related
  • 2016-07-28 EP EP16744761.4A patent/EP3328548B1/de active Active
  • 2016-07-28 WO PCT/EP2016/067992 patent/WO2017017179A1/fr active Application Filing
  • 2016-07-28 US US15/744,332 patent/US10814335B2/en active Active

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