EP4680934A1 - Appareil et procédés de conditionnement de charge - Google Patents

Appareil et procédés de conditionnement de charge

Info

Publication number
EP4680934A1
EP4680934A1 EP24714015.5A EP24714015A EP4680934A1 EP 4680934 A1 EP4680934 A1 EP 4680934A1 EP 24714015 A EP24714015 A EP 24714015A EP 4680934 A1 EP4680934 A1 EP 4680934A1
Authority
EP
European Patent Office
Prior art keywords
region
flow
gas
conditioning chamber
charge
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Pending
Application number
EP24714015.5A
Other languages
German (de)
English (en)
Inventor
Tyler James Johnson
Robert Nishida
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Atmose Ltd
Original Assignee
Atmose Ltd
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Atmose Ltd filed Critical Atmose Ltd
Publication of EP4680934A1 publication Critical patent/EP4680934A1/fr
Pending legal-status Critical Current

Links

Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N15/00—Investigating characteristics of particles; Investigating permeability, pore-volume or surface-area of porous materials
    • G01N15/02—Investigating particle size or size distribution
    • G01N15/0266—Investigating particle size or size distribution with electrical classification
    • 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
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N15/00—Investigating characteristics of particles; Investigating permeability, pore-volume or surface-area of porous materials
    • G01N15/06—Investigating concentration of particle suspensions
    • G01N15/0656—Investigating concentration of particle suspensions using electric, e.g. electrostatic methods or magnetic methods
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
    • G01N27/62—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating the ionisation of gases, e.g. aerosols; by investigating electric discharges, e.g. emission of cathode
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N15/00—Investigating characteristics of particles; Investigating permeability, pore-volume or surface-area of porous materials
    • G01N2015/0003—Determining electric mobility, velocity profile, average speed or velocity of a plurality of particles
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01T—SPARK GAPS; OVERVOLTAGE ARRESTERS USING SPARK GAPS; SPARKING PLUGS; CORONA DEVICES; GENERATING IONS TO BE INTRODUCED INTO NON-ENCLOSED GASES
    • H01T23/00—Apparatus for generating ions to be introduced into non-enclosed gases, e.g. into the atmosphere

Definitions

  • the present invention relates to the field of charge conditioning, typically of aerosol particles. to the invention
  • Aerosols consist of solid and/or liquid particles (aerosol particles) suspended in a gaseous medium, for example air. Aerosols can adversely affect the climate, environment and human health, and are commonly emitted as a by-product of combustion or industrial processes. Thus, it is advantageous to quantify aerosol particles and it is known to electrically charge aerosols in a charge conditioner for analysis.
  • Existing sensors range from high-resolution devices for characterising particle size or surface area for regulatory monitoring or experimental purposes to low- resolution, low-cost devices for monitoring averaged particle properties whether indoors or outdoors, sometimes as part of a network of sensors. Such devices aim to provide measurements with high spatial and time resolution.
  • Aerosol sensors which seek to provide information on particle size, surface area, mass and/or number concentration, commonly comprise a charging region which applies a discrete and often known electrical charge level (e.g. -1, 0, +1 , +2 charges etc.) to aerosols, typically with a probability distribution.
  • Charge conditioning may be accomplished by mixing, typically flowing, aerosol particles, with ions. Ions may, for example, be generated in a gas by ionizing radiation from a radioactive (alpha or beta) source.
  • a classification region typically selects specific particles by a characteristic parameter, involving a balance of ferees acting on individual particles in continuous flow, typically involving electrostatic versus drag or inertial forces. After classification, particles are typically counted with a particle counter.
  • detection and classification may be combined, using an ion trap which capture highly mobile, excess ions, downstream of the charging region using an externally applied electrical field, and the remaining particles are sensed via electrical currents, using sensitive electrometers.
  • Aerosol particles may also be engineered for the production of materials with unique properties and aerosol charge conditioners may be used to characterise, manufacture or use such materials.
  • charge neutralisers are used to neutralise the charge on aerosols used in spray painting or prior to sampling/collecting of the particles using electrostatic methods.
  • bipolar charge conditioners are typically used in configurations where the particle charging process reaches a steady-state. Otherwise, the charge distribution of charge conditioned aerosols is sensitive to parameters such as: particle concentration; ion concentration (and so source strength, where ions for charging are generated using an ionizing radiation source, such as a radioactive isotope, x-ray or corona discharge);
  • the performance of the charge conditioners using bipolar charging typically limits the sensitivity, capacity or response time of sensors and other apparatus for working with aerosol particles.
  • Some embodiments of the invention seek to address one or more of these limitations.
  • Some embodiments of the invention seek to improve the cost, sensitivity, reliability, capacity or footprint of charge conditioners using bipolar charging.
  • Some embodiments of the invention seek to facilitate the use of smaller or lower-activity ionizing sources (such as radioactive isotopes below the IAEA exemption limit) than are in common use.
  • ions of one polarity i.e. either positive or negative
  • Unipolar charging does not reach a steady-state and so the process typically requires calibration due to sensitivity to the rate of ion generation and the efficiency of charge transfer to the aerosol particles.
  • Some embodiments of the invention seek to expand the sensitivity, reliability, performance or footprint of unipolar charging by using a more stable ion generator (e g. radioactive isotope), while accounting for the effect of ions of both polarities initially being generated.
  • Some embodiments of the invention intend to operate in a regime between traditional bipolar and unipolar charging, resulting in a highly-asymmetric bipolar charge distribution that is advantageous for many applications (e.g. particle manufacture or sensing), while recognizing the benefits of reaching a steady-state charge distribution previously mentioned.
  • Some embodiments of the invention are also relevant to static neutralisers which operate on gases with minimal aerosol particle content.
  • the invention extends in a first aspect to apparatus comprising: a body having an inlet and an outlet and a conditioning chamber therebetween, the body defining a flow-through path for a gas from the body inlet and through the conditioning chamber to the body outlet; the conditioning chamber having an inlet and an outlet, the apparatus comprising an ion generator, the conditioning chamber defining a charging region receiving generated ions; the conditioning chamber comprising a flow expansion region between the inlet of the conditioning chamber and a maximum cross sectional area region, the flow expansion region configured to increase the cross-sectional area of gas flowing through the conditioning chamber, wherein the charging region is within or overlaps the maximum cross sectional area region and the mean position of generated ions in the charging region is closer to the outlet of the conditioning chamber than to the inlet of the conditioning chamber.
  • the invention extends to a method of charge conditioning a gas (typically a gas comprising aerosol particles), the method comprising: providing a body comprising a conditioning chamber, the conditioning chamber having an inlet and an outlet, receiving a flowing gas (typically a gas comprising aerosol particles) into the conditioning chamber through the inlet of the conditioning chamber, expanding the cross-sectional area of the flowing gas within the conditioning chamber, generating ions mixed with the expanded flowing gas, the ions colliding with aerosol particles within the gas and thereby charge conditioning the charge distribution of the aerosol particles within the gas, the charging process progressing towards a steady-state, wherein the charging process is ongoing when either (i) the gas flows out of the conditioning chamber through the outlet of the conditioning chamber, or (ii) ions are removed from the flow gas in a quenching region defined between at least two electrodes.
  • a gas typically a gas comprising aerosol particles
  • the apparatus may be a particle charge conditioner.
  • the gas may comprise aerosol particles.
  • the gas may be an aerosol.
  • the apparatus may be for charge conditioning a sample of aerosol particles in an aerosol to have a controlled charge distribution.
  • the apparatus may comprise a processor programmed to determine a particle size, surface area and/or concentration parameter (of aerosol particles in an aerosol) taking into account the flow rate of gas through the apparatus.
  • the method may comprise determine a particle size, surface area and/or concentration parameter (of aerosol particles in an aerosol) taking into account the flow rate of gas through the apparatus.
  • the gas may be a sample gas.
  • the gas may be an aerosol sample.
  • the apparatus may be a static eliminator.
  • the gas may be air.
  • the flow expansion region is at least 3.25 times longer axially than the maximum cross sectional area region.
  • the flow expansion region has an internal volume at least 1.25 times the volume of the maximum cross sectional area region.
  • the generated ions may be received from the ion generator.
  • the ion generator may generate the ions within the charging region (for example, the ion generator may comprise a radioactive source which emits radiation which ionizes gas molecules in the charging region). Ions may be mixed with the flowing gas by being generated in the flowing gas. For example, ions may be generated in the charging region by irradiating or ionizing the charging region.
  • the apparatus may comprise a radioactive source, which may be in the conditioning chamber.
  • the charging region is the volume within which a density of generated ions is at least 1%, or at least 5%, of the highest density of generated ions
  • an ion generator typically an ionizing radiation source
  • the majority of the generation of ions, by an ion generator takes place after the cross-sectional area of the gas has expanded to a maximum cross-sectional area.
  • the mean position of the generated ions within the chamber is within a maximum cross sectional area region of the chamber, and is closer to the outlet of the chamber than to the inlet of the chamber.
  • the mean position of the generated ions may be determined by calculating the mean of the x, y and z coordinates of the generated ions within the chamber.
  • the ionizing radiation source is located closer to the flow contracting region than the flow expansion region.
  • the apparatus may comprise an electrometer to measure the charge of aerosol particles captured by the electrometer or remaining in the flow gas within a measurement region.
  • the electrometer may comprise at least two electrodes defining the measurement region.
  • the apparatus may comprise a circuit to generate a potential difference between the at least two electrodes of the electrometer to remove charged aerosol particles (i.e. some or all of the charged aerosol particles) from flowing gas and measure the resulting current of aerosol particles captured by the electrodes or remaining in the flowing gas.
  • the electrometer may comprise a Faraday cage (in which case one electrode may function as the Faraday cage and another electrode as a reference, and there is no need to generate a potential difference between the electrodes).
  • the method comprises measuring a current at at least one electrode of the electrometer and a current at at least one electrode which defines the quenching region, and processing both of the measured currents to determine one or more parameters.
  • the determined parameters may comprise one or more of ion mobility (Zj), mean ion concentration n, or interaction time t, and the nt product.
  • the electrometer may be operated in a pulsed mode to improve the signal to noise ratio, for example, it may be that the electrometer alternately receives only positively charged aerosol particles and then only negatively charged aerosol particles.
  • the apparatus may comprise a particle diverter or trap to remove or divert along a path select positively or negatively charged aerosol particles at any time.
  • an apparatus for charge conditioning a sample of aerosol particles to have a controlled charge distribution comprising: a body having an inlet and an outlet and a conditioning chamber therebetween, the body defining a flow-through path for a gas, comprising aerosol particles, from the body inlet and through the conditioning chamber to the body outlet; wherein the conditioning chamber comprises first and second electrodes, a controller configured to apply a potential difference (which may be constant or variable) between the first and second electrodes, the first electrode having an ion generator (typically an ionizing radiation source) adjacent or integrated therewith, the conditioning chamber and ion generator (typically an ionizing radiation source) defining a charging region within the conditioning chamber, the conditioning chamber configured to define a flow path for aerosol particles therethrough from the inlet to the outlet, through the charging region, the controller being configured to select the potential difference between the first and second electrodes to thereby control the distribution of positively and negatively charged ions and thereby control the balance between unipolar and bipolar
  • the conditioning chamber is configured such that aerosol particles at the outlet will on average have been closer to the second electrode than the first.
  • the configuration such that aerosol particles will have on average been closer to the second electrode than the first could cause them to pass through more ions of one polarity than the other, depending on potential difference between the first and second electrodes.
  • the apparatus is a bipolar charger, or operated as a bipolar charger, typically the charge distribution of aerosol particles progresses towards a steady-state as they flow along the flow-through path.
  • the apparatus is a bipolar charger, or is operated as a bipolar charger, it may be that the charge distribution of aerosol particles does reach the steady-state or it may be that the charge distribution of aerosol particles does not reach the steady-state. (In the case of a unipolar charger or device operated a unipolar charger, such as a variable charger, this reasoning does not apply).
  • the apparatus may further comprise at least two electrodes which define a quenching region, the quenching region overlapping or downstream of the charging region, the apparatus comprising a circuit to generate a potential difference between the at least two electrodes and thereby remove ions from the gas in the quenching region.
  • the removal of ions by the quenching region preserves the asymmetry of the charge distribution of the aerosol particles in the gas whether not a steady-state charge distribution is reached.
  • the at least two electrodes are configured such that the potential gradient generated between them in use crosses the direction of flow of gas along the flow- through path.
  • the at least two electrodes are configured such that the potential gradient generated between them in use is within 10% of perpendicular, or is perpendicular to the direction of flow of gas along the flow-through path.
  • the at least two electrodes are configured such that the potential gradient generated between them in use is within 10% of perpendicular, or is perpendicular to a longitudinal axis of the charging chamber.
  • the quenching region may overlap with the outlet of the chamber.
  • the apparatus may be configured such that the quenching region removes ions from the gas after charge conditioning in the charge conditioning zone.
  • quenching region is located at the outlet of the conditioning chamber and/or overlaps with the charging region.
  • the mean position of generated ions within the region of maximum crosssection of the conditioning chamber and is closer to the outlet of the conditioning chamber than to the inlet of the conditioning chamber.
  • the charging region comprises a variable potential gradient region defined by the first and second electrodes and wherein the volume of the conditioning chamber between the variable potential gradient region and the quenching region is less than the volume of the variable potential gradient region.
  • the ionizing source comprises a radioactive material coated on the first or second electrode.
  • the apparatus comprises at least two electrodes which define a quenching region overlapping or downstream of the charging region, the apparatus comprising a circuit to generate a potential difference between the at least two electrodes and thereby remove ions from the gas in the quenching region and it may be that the removal of ions by the quenching region preserves the asymmetry of the charge distribution of the aerosol particles in the gas whether not a steady-state charge distribution is reached.
  • a method of charge conditioning a sample of aerosol particles, in a gas comprising: providing a body having an inlet and an outlet and a conditioning chamber therebetween, the body defining a flow-through path for a gas from the body inlet and through the conditioning chamber to the body outlet; causing a gas comprising aerosol particles (e.g.
  • an aerosol to flow along the flow-through path, through the conditioning chamber at a known flow rate; causing the gas to contain ions of both positive and negative polarity in a charging region of the conditioning chamber; the ions colliding with the aerosol particles and thereby charge conditioning the charge distribution of the aerosol particles in the gas; the charge distribution of the aerosol particles progressing towards a steadystate as they flow along the flow-through path.
  • the charge distribution of the aerosol particles does not reach a steady state. It may be that the method comprises the step of removing some or all of the remaining free ions from the gas within or downstream of the conditioning chamber to at least partially quench the charging conditioning process without the charge distribution of the aerosol particles reaching the steady state.
  • the invention extends in a sixth aspect to an apparatus for charge conditioning a sample of aerosol particles, in a gas, to have a controlled charge distribution (a charge conditioner), the apparatus comprising: a body having an inlet and an outlet and a conditioning chamber therebetween, the body defining a flow-through path for a gas from the body inlet and through the conditioning chamber to the body outlet; an ion generator to cause the gas to contain ions of both positive and negative polarity in a charging region of the conditioning chamber; either or both (i) an actuator to cause a gas to flow along the flow-through path, through the conditioning chamber at a known flow rate and (ii) a sensor to measure the flow rate of gas flowing along the flow-through path; the apparatus configured such that in use the ions collide with the aerosol particles and thereby charge conditioning the charge distribution of the aerosol particles in the gas, the charge distribution of the aerosol particles progressing towards but not reaching a steady-state as they flow along the flow-through path.
  • a charge conditioner a controlled charge distribution
  • charge conditioning due to the collision of ions with the aerosol particles stops while > o.oi, or while : > o.O2 or while 0.05, or while
  • Charge conditioning may stop before the steady state due to the provision of a restricted density of ions (for a given flow rate, body geometry).
  • the method comprises the step of at least partially quenching the charge conditioning due to the collision of ions with the aerosol particles by removal of the ions from the flowing gas before the charge distribution of the aerosol particles reaches the steady state.
  • the charge distribution will remain relatively constant for a longer period of time than would be the case were ions still present.
  • the charge conditioned aerosol particles may be transported further or maintained for longer before they are measured or used for an end application, than would be the case without the quenching step.
  • the at least partial quenching takes place within or at the outlet from the conditioning chamber.
  • the quenching may take place in a quenching region.
  • the at least partial quenching may completely quench the charge conditioning. Typically, the at least partial quenching removes at least 50% or at least 75% of the ions which flow into a quenching zone.
  • the apparatus may further comprise at least two electrodes which define a quenching region, the quenching region overlapping or downstream of the charging region, the apparatus comprising a circuit to generate a potential difference between the at least two electrodes and thereby remove ions from the gas in the quenching region.
  • the ions which are removed may be some (for example at least 50%, at least 75%, at least 90%, at least 95%, or at least 99%) or all of the ions present in the gas at the quenching region.
  • the apparatus may comprise a current sensor to measure a current arising from quenching.
  • the quenching region may be located at the outlet of the conditioning chamber.
  • the quenching region may overlap with the outlet of the chamber.
  • the quenching region may overlap with the charging region.
  • the quenching region may be adjacent to the charging region.
  • the quenching region may define the downstream end of the charging region.
  • the apparatus may be configured such that the quenching region removes ions from the gas after charge conditioning in the charge conditioning zone but before the charge distribution of the aerosol particles reaches a steady-state.
  • the charge conditioning is at least partially quenched by removal of the ions from the flowing gas before the charge distribution of the aerosol particles, q, has proceeded more than 99%, more than 98%, more than 95%, more than 90%, more than 80% or more than 75% of the way to the steady state, (typically from initial state q ⁇ ) (but does not reach steady-state).
  • the charge transfer is at least partially quenched while: > 0.01. It may be that charge transfer is at least partially quenched while: > o.O2. It may be that charge transfer is at least partially quenched while: > °- 05 - It ma Y be that charge transfer is at least partially quenched while: > 0.1. It may be that charge transfer is at least partially quenched while: > o.2. It may be that charge transfer is at
  • the flow rate we refer to the volumetric flow rate through the apparatus. This determines the flow velocity at each location within the apparatus at a fixed geometry and so the aerosol particle residence time.
  • the method may comprise the step of measuring the flow rate.
  • the apparatus may comprise an air flow rate sensor.
  • Figure 1 (a) is an illustration of bipolar charging of aerosol particles, showing a positively-charged particle, a negatively-charged particle and an uncharged particle surrounding and interacting with positive and negative ions.
  • Figure 1(b) shows the distribution of charge on samples of bipolar charged aerosol particles.
  • Figure 2 shows the mean charge per particle on aerosol particles as they flow progressively through a charging regime, a steady-state regime, and a discharging regime. Each of the charging regime and the steady-state regime are within the charging region of the charger.
  • Figure 3 shows (a) experimental and (b) numerical results of mean charge per particle as a function of convective time in tubing between charging region and ion trap. Data were gathered for a wide range of tube lengths and flow rates for the same Kr-85 charger and 217 nm diameter particles.
  • Figure 4 shows a first embodiment of a bipolar charger apparatus.
  • FIG. 5 shows a bipolar charger apparatus utilised within a scanning mobility particle size spectrometer (SMPS).
  • SMPS scanning mobility particle size spectrometer
  • Figure 11 shows a method of designing an apparatus.
  • a bipolar charge conditioner otherwise known as a neutralizer, is commonly operated using an alpha or beta radioactive or X-ray ionization source, although various other ion generators may be used.
  • the neutralizer first ionizes gas molecules which subsequently transfer charge to the sampled aerosol particles, resulting in a distribution of aerosol particles which are variously positively charged 3, negatively charged 5 and uncharged 2, as illustrated in Figure 1(a).
  • the fraction of total particle concentration at each discrete charge level tends to follow an asymmetric Boltzmann distribution centred near neutral, though negative on average, as shown in Figure 1(b).
  • the charge levels acquired by particles must be known, predicted, or calibrated as a function of particle diameter (or other particle properties, such as surface area) in order to interpret measurements.
  • Bipolar charging is often used for aerosol instruments and applications in part because it is generally understood that a well-defined steady-state charge distribution is achievable and that this steady-state distribution provides a known distribution of charges, enabling repeatable and reliable measurements.
  • FIG. 2 shows the development of mean charge per aerosol particle for particles moving through a charger and into a tubing region downstream of the charger, and illustrates these three regimes.
  • Particles acquire charge in the charging/ionizing region (i.e. ’’charging regime”), eventually developing a steady-state charge distribution (i.e. ’’steady-state regime”).
  • the discharge regime explains at least some of the unreliability of known devices which have assumed that the steady state is maintained once it has been reached.
  • the charger may be configured to operate in any of these three regimes depending on the charge levels and properties of the charge distribution desired.
  • the charging regime refers to particle charging while its steady-state charge distribution is developing. Operating a charge conditioner solely within this regime, for example by quenching the charging process before the steady-state charge distribution is reached, represents a new mode of operation for low-cost sensing or high-resolution instrumentation depending on the desired outcome.
  • the primary advantage of operating a charge conditioner in the charging regime is that there is no minimum requirement for the product of ion concentration, ni, and ion-particle interaction time, t, (nit product), as is required for reaching a steady-state distribution. Consequently, chargers can be operated with:
  • the present inventors are not aware that anyone has intentionally stopped the charging process by removing the ions before a steady-state bipolar charge distribution is reached. This operation can be considered a quenching operation.
  • the remaining free ions diffuse and are captured at the walls of the charger housing or downstream tubing/volumes due to their high diffusivity.
  • negative ions are usually significantly more mobile than positive ions, and as a result diffuse more readily to the charger/tubing walls.
  • positive ions remain convected in the flow with the particles longer, producing a shift in the charge distribution relative to its state at the outlet of the ionizing region.
  • the ion imbalance becomes appreciable and affects the charge of the aerosol particles rapidly downstream of the ionization/charging region.
  • the present inventors are the first to fully characterize this effect experimentally by controlling the time the free ions downstream of the ionization/charging region remain with the aerosol particles and measuring the mean charge of the particles.
  • volumetric flow rates and tube lengths were varied to assess the dependence of mean charge on convective time in the tubing between the charger and where the mean charge is sampled.
  • the results are shown in Figure 3a for a given chargerand particles of 217 nm in diameter.
  • the data fall on a consistent curve, which is further supported by modelling results shown in Figure 3b. That the position of the mean charge peak does not occur at the exit of the charger indicates that the charger was operated in the charging regime.
  • the peak mean charge in this figure represents sampling at the steady-state regime.
  • the effect of downstream ions discharging reduces the asymmetry of mean charge towards neutral.
  • FIG. 4 A first embodiment of an apparatus for charge conditioning is illustrated in Figure 4.
  • the apparatus 1 comprises body 4 which has an inlet 17 through which an aerosol, being a gas with a suspension of aerosol particles therein, enters the apparatus.
  • an aerosol being a gas with a suspension of aerosol particles therein
  • a flow regulator 25 is positioned shortly after the apparatus input 17.
  • the flow regulator 25 may be used to control the velocity of the aerosol within the apparatus. It may take the form of a fan or a pump, for example.
  • the flow regulator may alternatively be positioned in a downstream position, for example downstream of the electrometer 27.
  • the flow regulator is typically controlled by a processor. There may also, or alternatively, be a flow rate sensor.
  • the flow transitions from an inlet 17 to a charging region 33 in a charger, where charge conditioning takes place.
  • the inlet tube 43 has a small diameter and the charging region 33 is maximized to maximize the effectiveness of the (low-activity) source. It is critical to consider the flow of the aerosol/gas in the expansion from the inlet 17 to the charging region 33 to avoid any adverse pressure gradient which would causes zones of flow recirculation and to ensure particles have consistent exposure to the ionization/charging region 33.
  • An aerosol entering the apparatus passes the flow regulator 25 and then enters into the conditioning chamber 13 of the apparatus.
  • the aerosol enters the conditioning chamber 13 through conditioning chamber inlet 21 and into charging region 33 within the conditioning chamber.
  • Conditioning chamber inlet 21 comprises a flow expansion region 35 between the inlet of the apparatus inlet 17 and the charging region 33.
  • Flow expansion region 35 is configured to increase the cross-sectional area of gas flowing through the charging region 33.
  • the flow expansion region is defined by a frusto-conical section of a diameter which increases in the direction of flow. Flow expansion is achieved without the introduction of vortex flow into the flow of the aerosol through the apparatus.
  • a source of ionizing radiation such as a low activity radioactive source 11 , is sited within the conditioning chamber 13.
  • the radioactive source 11 emits radiation which ionises gas molecules in the charging region 33 of the conditioning chamber 13, thereby generating ions.
  • the ionized gas molecules subsequently transfer charge to the aerosol particles.
  • this conditioning results in a distribution of positively charged aerosol particles 3, negatively charged aerosol particles 5 and uncharged aerosol particles 2 as discussed above.
  • Examples of radiation sources which are suitable for ion generation are Am-241 (preferably ⁇ 0.27 pCi/10 kBq) and Ni-63 (preferably ⁇ 2.7 mCi/100 MBq).
  • the conditioned aerosol particles exit the conditioning chamber 13 through the conditioning chamber outlet 23.
  • the conditioned aerosol particles enter quenching region 37.
  • Situated in quenching region 37 are two electrodes 15a, 15b.
  • the application of a potential difference across these electrodes creates an electric field in the quenching region 37, forming an ion filter which serves to remove ions.
  • the aerosol particles have a much lower electrical mobility than the ions and because of this they are effectively uninfluenced by the electric field of the ion filter.
  • the ion filter 15a, 15b therefore enables the charge conditioning process to be stopped (quenched), preventing or minimising aerosol particle charge state varying downstream in a discharge zone.
  • the aerosol, having been quenched in the quenching region 37 then exits the apparatus via outlet 19.
  • the device illustrated in Figure 4 is shown in use with a Faraday cup type electrometer 27, called a Faraday cup aerosol electrometer, situated at the outlet 19 of the apparatus.
  • a Faraday cup aerosol electrometer situated at the outlet 19 of the apparatus.
  • Charged aerosol particles which have been conditioned and quenched of ions within the apparatus exit the apparatus and are collected and detected at the electrometer 27.
  • a Faraday cage electrometer Alternative to a Faraday cup electrometer is a Faraday cage electrometer. This consists of a cylinder through which charged particles flow and induce a charge on the cylinder. The electrometer detects the change in charge that passes through the cylinder, and not the absolute flux of charge as in a Faraday cup Electrometer. For this reason, a Faraday cage electrometer can be configured to detect successive clouds of positively, then negatively charged particles. The change in signal is approximately twice that of going from uncharged to unipolarly charged, providing the additional advantage of ⁇ 2x the signal of a conventional Faraday cup electrometer. Furthermore, Faraday cages are advantageous because they avoid drift in signal because it is the change in current that matters, not a current offset (which may drift over time). Finally, use of a Faraday cage is also advantageous because it avoids the need for maintenance (i.e. replacement of a filter in a Faraday Cup Electrometer due to fouling).
  • a Faraday based electrometer positioned at the outlet of the apparatus enables the charged aerosol particles exiting the apparatus to be detected. This enables the dependence of the output of the apparatus on various design parameters to be measured. Such design parameters include the relative locations of the charging region and the quenching region, the form of the flow in the flow contraction region 39, should one be present, and length of the outlet tube 41 which culminates in the apparatus outlet 19.
  • volume downstream of the ionization/charging region e.g. downstream tube lengths
  • FIG. 5 illustrates the use of an apparatus of the type described above in one such high-resolution instrument.
  • SMPS Scanning Mobility Particle Size Spectrometer
  • the SMPS follows an ISO standard for measuring aerosol particle size distributions and is widely used. It combines a bipolar charge conditioner, Differential Mobility Analyzer (DMA) and a particle counter such as Condensation Particle Counter (CPC).
  • DMA Differential Mobility Analyzer
  • CPC Condensation Particle Counter
  • particles of one polarity pass through a sheath flow, resisted by a drag force, towards a slit at the end of the DMA and are then counted by the CPC.
  • Particles within a particular range of electrical mobility travel through the DMA to be counted at the CPC, while those particles outwith the range of electrical mobility are filtered out and do not pass through for counting.
  • the particle size distribution, or the particle concentration at each mobility is determined. If all particles were singly-charged, interpretation of this measurement would be straightforward.
  • the present invention enables charge conditioning a sample of aerosol particles to a known charge distribution that can be controlled.
  • Free ions can be removed utilising the ion filter before a steady state regime is reached (i.e. quenching). Free ions can also be removed during a steady state regime, or during a discharge regime to stop the effect of the remaining free ions downstream of the charging region on the charge distribution.
  • FIG. 6 A second embodiment of an apparatus for charge conditioning is illustrated in Figure 6.
  • the region immediately after the inlet 21 to the conditioning chamber is tapered outwards, forming a flow expansion region 35, to enable a more uniform flow expansion near the radiation source, i.e. to avoid flow recirculation which can cause large differences in particle residence time which causes major uncertainty in temporal response and charge levels (due to differences in nt product, this being the product of the concentration of ions and the interaction time between ions and aerosol particles).
  • the tapering at the inlet constitutes a flow expansion region which increases the cross-sectional area of the flow. The cross-sectional area of the flow reaches a maximum at the charging region in a maximum cross-sectional area region 47.
  • the chamber Downstream of the maximum cross-sectional area region 47 the chamber tapers and the cross-section of the flow decreases in a flow contraction region 39.
  • the expansion region is substantially longer, for example 5x the length, of the flow contraction region to facilitate the provision of a relatively large charge conditioning volume followed by rapid quenching of the charging process.
  • the conditioning chamber has a large volume near the radiation source. This is to maximise the ionizing effect of the radiation since the nt product is proportional to chamber diameter to power of 4 (until reaching the maximum penetration distance of the radiation in the gas).
  • the radiation source 11 in this embodiment is placed near the outlet. This contrasts with conventional bipolar chargers, in which the radiation source is situated in the middle or at the inlet.
  • the arrangement in the presently described embodiment minimises the opportunity for preferential ion loss to walls by diffusion. Consequently, charge asymmetry and the intended charge states are preserved.
  • the mean position 45 of generated ions in the charging region is closer to the outlet 23 of the conditioning chamber than to the inlet 21 of the conditioning chamber.
  • the embodiment also shows an ion trap comprising electrodes 15a and 15b connected directly downstream of the conditioning chamber 13.
  • An electrostatic classifier (such as an DMA) may also be similarly connected to the apparatus. These are options.
  • the Faraday cup electrometer 27 of the figure is also a possible option.
  • the second embodiment has a conditioning chamber outlet which defines a flow contracting region.
  • FIG. 7 A modification of the second embodiment is illustrated in Figure 7.
  • the electrodes 15a and 15b which form the ion trap are positioned in the flow contracting region 39.
  • the electrodes 15a and 15b encroach into conditioning chamber 13.
  • the electrodes 15a and 15b which form the ion trap are positioned after the radioactive source, but upstream of the flow contracting region 39. This alternative arrangement is illustrated in Figure 8.
  • the apparatus illustrated in Figure 6 may also be operated as a static eliminator, with no potential across electrodes 15a and 15b.
  • the aim is to produce an output of ions of both polarities which deposit on a surface in order to neutralise the surface from static/electrostatic charges.
  • a gas is passed through the apparatus. Deposition can occur by convection or diffusion. Static elimination is used in the art to minimize the electrostatic charge, e.g. for analytical balances laboratory settings, or for conditioning a surface (e.g. of an automobile) prior to painting.
  • any of the conditioning devices presently disclosed may be operated as a static eliminator.
  • gas is passed though the device instead of an aerosol and the ion trap is not utilised.
  • Figure 9 illustrates an alternative modification of the second embodiment, which corresponds to a static eliminator.
  • the static eliminator of Figure 9 has no ion trap electrodes, and no flow contracting region is included in this static eliminator.
  • This configuration utilises a radioisotope 11 electro-plated onto an electrically conductive surface 16b, which makes up one of two electrodes 16a, 16b.
  • the radioactive source need not form one of the electrodes as illustrated. Other arrangements are possible.
  • the critical aspect is the introduction of an electric field in the charging region, as this enables control of the charging of the aerosol particles.
  • the outlet 23 of the conditioning chamber in this illustrated embodiment is positioned away from the main central axis 31 of the apparatus 1 , close to one of the two electrodes 16a.
  • the flow through path, which in the previously described embodiments follows the main central axis, in this third embodiment passes through the conditioning chamber outlet 23 and thereby deviates away from the central axis 31.
  • the present embodiment By combining an electric field in the charging region the present embodiment generates an output of charged aerosol particles with known charge levels either bipolar or unipolar. This contrasts with conventional chargers which are either unipolar or bipolar.
  • the polarity of the output is also adjustable (either positive, negative or a combination of both).
  • the conditioning chamber can have other shapes, and may for example be axisymmetric, in the present example, the use of a conditioning chamber outlet which is offset towards one of the electrodes producing the electric field has the effect that the flow path for aerosol particles through the conditioning chamber is inherently closer to one electrode than the other, facilitating controllable charging with a selectable ratio of positive to negative ions.
  • the apparatus is less sensitive to initial charge than conventional unipolar chargers since some bipolar charging still typically occurs.
  • High charge levels are possible with this embodiment, thereby increasing signal significantly, e.g. 4x bipolar.
  • Further advantages of this embodiment include the nt product (and charge levels) being controllable over a wide range, providing control over charge levels and charge polarity, and a low level of particle loss at walls (>95% penetration).
  • the apparatus of the third embodiment may be operated the charger in any of the three bipolar regimes, charging, steady-state or discharging, with the associated benefits.
  • the particle charging is fully quenched by the ion trap in the quenching region, for some applications it is sufficient to partially quench the charging process by removing most, e.g. 90% or 99% of ions.
  • Method of design Figure 11 shows a schematic diagram of a method of designing an apparatus for conditioning a sample of aerosol particles, in an aerosol, with a controlled charge distribution.
  • the apparatus comprises: a body having an inlet and an outlet and a conditioning chamber there between, the body defining a flow-through path for an aerosol from the body inlet and through the conditioning chamber to the body outlet.
  • Step 101 of the method is a step of modelling, simulating or experimentally determining the charge distribution of aerosol particles, in the aerosol, passing through a charging region of the conditioning chamber due to ions in the charging region colliding with the aerosol particles.
  • step 105 a selection is made of one or more parameters of the apparatus, whereby according to the selected one or more parameters the charge distribution of the aerosol particles remains such that > 0.05.
  • step 107 an apparatus having the selected parameters is provided (e.g. manufactured).
  • a method of charge conditioning a sample of aerosol particles, in a gas, to have a controlled charge distribution comprising: providing a body having an inlet and an outlet and a conditioning chamber therebetween, the body defining a flow-through path for a gas from the body inlet and through the conditioning chamber to the body outlet; causing a gas comprising aerosol particles to flow along the flow-through path, through the conditioning chamber at a known flow rate; causing the gas to contain ions of both positive and negative polarity in a charging region of the conditioning chamber; the ions colliding with the aerosol particles and thereby charge conditioning the charge distribution of the aerosol particles in the gas; the charge distribution of the aerosol particles progressing towards a steadystate as they flow along the flow-through path; and removing some or all of the remaining free ions from the gas within or downstream of the conditioning chamber to at least partially quench the charging conditioning process without the charge distribution of the aerosol particles reaching the steady state.
  • a method comprising the steps of measuring the charge of a portion of the charge-conditioned aerosol particles with an electrometer which generates a current and calculating one or more parameters of the size and concentration of the aerosol particles by processing both the measured current and the known flow rate.
  • a method of designing an apparatus for conditioning a sample of aerosol particles, in a gas, with a controlled charge distribution comprising: a body having an inlet and an outlet and a conditioning chamber therebetween, the body defining a flow-through path for a gas from the body inlet and through the conditioning chamber to the body outlet, the method comprising modelling, simulating or experimentally determining the charge distribution of aerosol particles, in a gas, passing through a charging region of the conditioning chamber due to ions in the charging region colliding with the aerosol particles, and then passing through a quenching region within or downstream of the conditioning chamber in which ions are removed, and varying one or more parameters of the apparatus, the parameters comprising one or more of: the shape of the conditioning chamber, the rate of flow of gas sample along the flow-through path, and the concentration of ions in the charging region, selecting one or more parameters of the apparatus, whereby according to the selected one or more parameters the charge distribution of the aerosol particles remains such that > 0.05, and in ss providing an apparatus having the selected

Landscapes

  • Chemical & Material Sciences (AREA)
  • Analytical Chemistry (AREA)
  • Physics & Mathematics (AREA)
  • Health & Medical Sciences (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Biochemistry (AREA)
  • General Health & Medical Sciences (AREA)
  • General Physics & Mathematics (AREA)
  • Immunology (AREA)
  • Pathology (AREA)
  • Dispersion Chemistry (AREA)
  • Electrochemistry (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Other Investigation Or Analysis Of Materials By Electrical Means (AREA)

Abstract

L'invention concerne un appareil et un procédé de conditionnement de charge de particules d'aérosol dans une particule d'aérosol contenant du gaz pour produire une distribution de charge contrôlée.
EP24714015.5A 2023-03-17 2024-03-15 Appareil et procédés de conditionnement de charge Pending EP4680934A1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
GB202303960 2023-03-17
PCT/GB2024/050721 WO2024194614A1 (fr) 2023-03-17 2024-03-15 Appareil et procédés de conditionnement de charge

Publications (1)

Publication Number Publication Date
EP4680934A1 true EP4680934A1 (fr) 2026-01-21

Family

ID=90468507

Family Applications (1)

Application Number Title Priority Date Filing Date
EP24714015.5A Pending EP4680934A1 (fr) 2023-03-17 2024-03-15 Appareil et procédés de conditionnement de charge

Country Status (2)

Country Link
EP (1) EP4680934A1 (fr)
WO (1) WO2024194614A1 (fr)

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN120870477B (zh) * 2025-09-26 2026-01-09 中国核动力研究设计院 适用于蒸汽流动体系的气溶胶取样测量系统及其控制方法

Family Cites Families (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5973904A (en) * 1997-10-10 1999-10-26 Regents Of The University Of Minnesota Particle charging apparatus and method of charging particles
CA2317830C (fr) * 2000-09-08 2009-10-20 Her Majesty The Queen In Right Of Canada As Represented By The Minister Of The Environment Concentrateur de particules
US8044350B2 (en) * 2007-11-29 2011-10-25 Washington University Miniaturized ultrafine particle sizer and monitor
JP2011112026A (ja) * 2009-11-30 2011-06-09 Denso Corp 排気浄化装置用電力供給装置

Also Published As

Publication number Publication date
WO2024194614A1 (fr) 2024-09-26

Similar Documents

Publication Publication Date Title
US8044350B2 (en) Miniaturized ultrafine particle sizer and monitor
Alonso et al. Penetration of nanometer-sized aerosol particles through wire screen and laminar flow tube
Fissan et al. Experimental comparison of four differential mobility analyzers for nanometer aerosol measurements
US10429366B2 (en) Methods and systems for detection of non-volatile solutes
US9207207B2 (en) Drift tube ion mobility spectrometer for aerosol measurement
EP4680934A1 (fr) Appareil et procédés de conditionnement de charge
JP2011511293A (ja) 多元的エアロゾル特性決定のための測定システム
US3449667A (en) Electrogasdynamic method and apparatus for detecting the properties of particulate matter entrained in gases
Toffoletto et al. Design criteria for an angle resolved electron spectrometer of novel toroidal geometry
Simones et al. Measurements of charged aerosol coagulation
Barillon et al. Track etch velocity study in a radon detector (LR 115, cellulose nitrate)
Santos et al. Performance evaluation of a high-resolution parallel-plate differential mobility analyzer
Attoui et al. Flow driven transmission of charged particles against an axial field in antistatic tubes at the sample outlet of a Differential Mobility Analyzer
RU2531369C2 (ru) Масс-спектрометр и способ масс-спекрометрического анализа
US10801992B2 (en) Drift tubes, ion mobility spectrometers systems, and methods of classifying charged particles
Jidenko et al. Post-corona unipolar chargers with tuneable aerosol size-charge relations: Parameters affecting ion dispersion and particle trajectories for charger designs
Dwivedi et al. Optimization of controlling parameters of plasma torch aerosol generator and characteristics of synthesized metal oxide aerosols in context of NAF program
Notis Charge Exchange Ion Energy Analyzer for the PFRC-2 Plasma Device
Jidenko et al. Effect of aerosol concentration on post-corona unipolar diffusion charging: Ion density retro-controlled by aerosol space charge versus geometry of ion-aerosol mixing
US20240298399A1 (en) Apparatus, arrangement and method for the production of an aerosol of charged nanoparticles
EP4007904B1 (fr) Capteur de particules et procédé de détection
Mei et al. A cost-effective differential mobility analyzer (cDMA) for multiple DMA column applications
Ober et al. Aerosol Measurement in Low‐Pressure Systems with Standard Scanning Mobility Particle Sizers
Simones MEASUREMENT OF COAGULATING SILVER AND CARBON AEROSOLS USING A TANDEM DIFFERENTIAL MOBILITY ANALYZER _ A Dissertation
Intra et al. An electrical mobility spectrometer for aerosol size distribution measurement

Legal Events

Date Code Title Description
STAA Information on the status of an ep patent application or granted ep patent

Free format text: STATUS: UNKNOWN

STAA Information on the status of an ep patent application or granted ep patent

Free format text: STATUS: THE INTERNATIONAL PUBLICATION HAS BEEN MADE

PUAI Public reference made under article 153(3) epc to a published international application that has entered the european phase

Free format text: ORIGINAL CODE: 0009012

STAA Information on the status of an ep patent application or granted ep patent

Free format text: STATUS: REQUEST FOR EXAMINATION WAS MADE

17P Request for examination filed

Effective date: 20251014

AK Designated contracting states

Kind code of ref document: A1

Designated state(s): AL AT BE BG CH CY CZ DE DK EE ES FI FR GB GR HR HU IE IS IT LI LT LU LV MC ME MK MT NL NO PL PT RO RS SE SI SK SM TR