A bipolar multi-stage DMA, particle size spectrum measuring device and particle size spectrum measuring method

Abstract

This invention relates to a bipolar multi-stage DMA, a particle size distribution measurement device, and a particle size distribution measurement method. The DMA includes an inlet stage, a sieving stage, and an outlet stage arranged sequentially. The inlet stage includes a sheath gas inlet mixing chamber and a laminar flow device disposed within the sheath gas inlet mixing chamber. The sieving stage includes a sieving chamber connected to the sheath gas inlet mixing chamber and a nozzle installed within the sieving chamber. The outlet stage includes a sheath gas outlet mixing chamber connected to the sieving chamber and a mixer installed within the sheath gas outlet mixing chamber. The bipolar multi-stage DMA of this invention can simultaneously sieve multiple groups of bipolar monodisperse particles, that is, simultaneously sieve positively charged and negatively charged particles, obtain the measured number concentrations, and sum them, thereby reducing the measurement error caused by the change in unipolar charge probability and improving the accuracy of particle size distribution measurement.

Description

Technical Field

[0001] This invention relates to the field of atmospheric ultrafine particulate matter size spectrum measurement technology, specifically to a bipolar multi-stage DMA, a size spectrum measurement device, and a size spectrum measurement method. Background Technology

[0002] The Differential Mobility Analyzer (DMA) is a fundamental instrument in the field of atmospheric ultrafine particulate matter size spectrum measurement. Its function is to sieve monodisperse particles of a specific size from a group of polydisperse particulate matter samples. When combined with bipolar charge generators and particulate matter detection instruments (such as condensation nucleus particle counters, CPC, condensation particle counters, aerosol electrometers, and aerosol electrometers), the DMA forms a "charge-sieving-measurement" system, which is widely used in particle size spectrum measurement.

[0003] Traditional DMA (Differential Mobility Analyzer) is primarily a single-stage DMA, which simultaneously sieves a group of monodisperse particles carrying only one type of charge (positive or negative). DMA is often coupled with CPC (Cyclic Electromigration) to form a Scanning Mobility Particle Sizer (SMPS), commonly used in laboratory settings for particle size distribution measurements. DMA is also frequently coupled with AE (Anaerobic Analyzer) to create portable particle size distribution measuring instruments. To improve the measurement speed, single-stage DMA has been extended to multi-stage DMA (MDMA), capable of simultaneously sieving multiple groups of monodisperse particles carrying the same charge (positive or negative) and coupled with multiple particle detection instruments. For example, Chinese patent CN202011547243.9 discloses a rapid high-temperature particle size distribution measurement device and method based on multi-stage differential electromigration. However, existing DMAs often suffer from reduced accuracy in particle size distribution measurements due to the influence of charge efficiency during particle size spectrum inversion.

[0004] Currently, both traditional single-stage DMA and extended multi-stage DMA can only simultaneously sieve particles carrying the same charge (positive or negative). Studies have shown that aging of the charger, changes in experimental conditions, and alterations in particle type can all cause variations in the unipolar charge probability, leading to inaccurate particle size distribution inversion. Therefore, measurement results based on unipolar DMA (including single-stage and multi-stage) particle size distributions are easily affected. However, when the unipolar charge probability changes, the total charge probability often remains relatively stable; that is, the "positive charge probability + negative charge probability" remains essentially unchanged. Therefore, it is necessary to design a bipolar multi-stage DMA, a particle size distribution measurement device, and a particle size distribution measurement method that can simultaneously sieve positively and negatively charged particles, obtain the measured number concentrations, and sum them, thereby reducing the measurement error caused by changes in the unipolar charge probability and improving the accuracy of particle size distribution measurements. Summary of the Invention

[0005] The purpose of this invention is to provide a bipolar multi-stage DMA, a particle size distribution measurement device and a particle size distribution measurement method. This bipolarity can overcome the shortcomings of the prior art, realize bipolar multi-channel sieving of atmospheric particulate matter, and thus achieve rapid and accurate measurement of particle size distribution.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] In a first aspect of the invention, a bipolar multilevel DMA is provided.

[0008] The DMA includes an inlet stage, a sieving stage, and an outlet stage set sequentially.

[0009] The inlet stage includes a sheath gas inlet mixing chamber and a laminar flow device disposed in the sheath gas inlet mixing chamber;

[0010] The sieving stage includes a sieving chamber connected to the sheath gas inlet mixing chamber and a sample gas nozzle installed in the sieving chamber.

[0011] The outlet stage includes a sheath gas outlet mixing chamber connected to the screening chamber and a mixer installed in the sheath gas outlet mixing chamber.

[0012] Furthermore, a sheath gas inlet is provided on the sheath gas inlet mixing chamber;

[0013] The laminar flow device uses nylon or polyester yarn with a mesh count higher than 300 mesh;

[0014] The vertical distance between the sheath gas inlet and the laminar flow device is not less than 50 mm.

[0015] Furthermore, the screening chamber includes an insulating shell and two high-voltage plates respectively disposed on two opposite sides of the inner wall of the insulating shell, one of the high-voltage plates being connected to a positive high voltage and the other high-voltage plate being connected to a negative high voltage.

[0016] The high-voltage plate is connected to a positive or negative high voltage via a high-voltage connector.

[0017] The insulating outer shell has a fixing groove, the high-voltage connector is installed in the fixing groove, and the inner end of the high-voltage connector is in contact with the high-voltage plate through a spring; the spring is made of stainless steel.

[0018] The sieving chamber is provided with a sample gas inlet and multiple gas outlets;

[0019] The gas outlet is located through the high-voltage electrode plate and the insulating outer shell wall where the high-voltage electrode plate is located.

[0020] The gas outlet portion on the high-voltage plate has a chamfer.

[0021] Furthermore, both the sheath gas inlet mixing chamber and the sheath gas outlet mixing chamber are connected to the screening chamber via connectors;

[0022] The connector is made of angle aluminum.

[0023] Furthermore, the sample gas nozzle includes a nozzle base and an orifice mounted on the nozzle base; dividing the nozzle into two parts, the nozzle base and the orifice, is for ease of processing.

[0024] The sample gas nozzle adopts a semi-rotary structure, including a cuboid first nozzle portion and a triangular prism-shaped second nozzle portion connected to the first nozzle portion. The thickness of the second nozzle portion gradually decreases from the connection point with the first nozzle portion, and the apex angle of the tip of the second nozzle portion is no greater than 15°. The function of the nozzle is to disperse the sample gas from the sample gas inlet and guide it into the flow field through a flat nozzle orifice. By adopting the above-described nozzle structure, the sample gas can be dispersed from the inlet and guided to the flat nozzle orifice.

[0025] The nozzle is provided with a sample gas inlet cavity and a nozzle slit; an opening is made in the nozzle as the sample gas inlet cavity, and the nozzle slit is processed by wire cutting process, with a slit width of less than 2mm.

[0026] The nozzle base has a sample gas inlet channel corresponding to the sample gas inlet cavity; an opening is made on the nozzle base as the sample gas inlet channel, which is directly opposite the sample gas inlet cavity on the nozzle.

[0027] Furthermore, the insulating outer shell is made of POM (polypropylene oxide) board;

[0028] The high-voltage electrode plate is made of stainless steel.

[0029] Both the positive and negative high voltage grounds are connected to the sample gas nozzle base.

[0030] Furthermore, the sheath gas outlet mixing chamber is made of metal.

[0031] The sheath gas outlet mixing chamber is provided with a sheath gas main outlet;

[0032] The mixer includes a mixer body and a plurality of openings evenly distributed on the mixer body; the mixer body is made of a metal plate, and the total area of ​​the openings on the metal plate is less than 25%.

[0033] In a second aspect of the invention, a particle size distribution measuring device is disclosed.

[0034] The device includes the aforementioned bipolar multi-stage DMA, bipolar particulate charge device, and particulate number concentration detector;

[0035] The sample gas inlet of the bipolar multistage DMA is connected to the outlet of the bipolar particulate charge generator, and each gas outlet of the bipolar multistage DMA is connected to a particulate number concentration detector. The bipolar particulate charge generator includes a charging chamber and a charging sheath gas inlet and a charging sheath gas outlet disposed on the charging chamber. The charging chamber is connected to a positive high-voltage source and a negative high-voltage source to generate a charging electric field.

[0036] In a third aspect of the present invention, a particle size distribution measurement method for the above-described particle size distribution measurement device is disclosed.

[0037] The method includes:

[0038] (1) Sheath gas is introduced into the sheath gas inlet mixing chamber. After the sheath gas is mixed in the sheath gas inlet mixing chamber, it enters the screening chamber through the laminar flow device.

[0039] (2) Sample gas is introduced into the bipolar charge device. The bipolar charge device undergoes a charging reaction, which charges the particulate matter in the sample gas. The sample gas carrying the charged particulate matter flows from the bipolar charge device to the sieving chamber and merges with the sheath gas in the sieving chamber.

[0040] (3) The sample gas and sheath gas carrying charged particles flow from the sieving stage to the outlet stage in a laminar flow state. The charged particles are deflected by the electric field force generated by a pair of high-voltage plates. Charged particles of different sizes are screened out from the corresponding gas outlet.

[0041] (4) The number concentration of charged particles screened out of the corresponding gas outlet is detected by each particle number concentration detector to determine the particle size spectrum.

[0042] Furthermore, the step of using each particulate number concentration detector to detect the number concentration of charged particles sieved from the corresponding gas outlet and determining the particle size distribution includes:

[0043] (41) Flow rate setting: The number of particulate number concentration detectors is 2M, where M is a positive integer. M of the particulate number concentration detectors are connected to the positive high voltage plate, and the other M of the particulate number concentration detectors are connected to the negative high voltage plate. The flow rate at the inlet of the bipolar multistage DMA sheath gas is set to Q, the flow rate of the 2M particulate number concentration detectors is set to q, and the flow rate at the outlet of the bipolar multistage DMA sheath gas is set to Q-(2M-1)q. Therefore, the flow rate at the sample gas inlet is passively set to q, where Q, q and Q-(2M-1)q are all greater than 0.

[0044] (42) Set the voltage on the positive high-voltage plate of the bipolar multi-stage DMA to +Ui and the voltage on the negative high-voltage plate to -Ui. Under the flow rate setting in step (41), record the sieve particle size at different gas outlets corresponding to the voltage |Ui| as d. p1 d p2 , ...,d pM At this time, the particulate number concentrations measured by the M particulate number concentration detectors connected to the positive high voltage plate are N. 测量A1 (d p 1), N 测量A2 (d p2 ), ..., N 测量AM (d pM The particulate number concentrations measured by the M particulate number concentration detectors connected to the negative high-voltage plate are N. 测量B1 (d p1 ), N 测量B2 (d p2 ), ..., N 测量BM (d pM );

[0045] Using formula Calculate d in the particle size spectrum p1 d p2 、…、d pM The height at which dN is obtained Ui (d p1 ),dN Ui (d p2 ), ..., dN Ui (d pM Let D be the set. Ui ={dN Ui (d p1 ),dN Ui (d p2 ),…,dN Ui (dpM )};

[0046] Wherein dN Ui (d pM ) represents the particle size distribution channel height at the corresponding particle size of the Mth particulate number concentration detector when the high voltage is set to +Ui and -Ui, p(n,d) p ) represents the particle size d p The probability that a particulate matter carries n charges after passing through a bipolar charge, η(d p () is a particulate number concentration detector for particles with a diameter of d p The detection efficiency of particulate matter, h(d p ) is a bipolar multilevel DMA at d p The height of the transfer function, w(d) p ) is a bipolar multilevel DMA at d p The full width at half maximum (FWHM) of the transfer function, w'(d p ) represents the particle size distribution d p The channel width at the location, w and w' are in the same unit.

[0047] (43) Change the voltage values ​​of the positive and negative high-voltage plates, obtain the particle size distribution height corresponding to each particle size at the current voltage value, and determine the set D corresponding to the current voltage value. Ui .

[0048] (44) Repeat steps (42) and (43) until all D values ​​are obtained. Ui The included dN U (d p It covers the entire particle size spectrum to be measured, thus obtaining complete particle size spectrum measurement results.

[0049] Compared with the prior art, the advantages of the present invention are:

[0050] (1) The present invention is a multi-stage DMA for symmetrical sieving of positive and negative electrode particles. The technical problem it is used to solve is that particle size spectrum inversion is greatly affected by the working state of the charge. The technical effect to be achieved is to reduce the influence of the working state of the charge on particle size spectrum inversion by using the characteristic of "the total positive charge of the charge remains unchanged". Such structure and method improve the accuracy and stability of particle size spectrum inversion.

[0051] (2) The bipolar multi-stage DMA described in this invention utilizes the characteristic of "constant total bipolar charge" to suppress particle size distribution inversion errors caused by changes in charge state. Traditional DMA can only use high pressure of one polarity to screen particles. When "unipolar charge is affected by experimental conditions", inversion errors will occur due to the uncertainty of charge. Compared with traditional DMA, the bipolar multi-stage DMA described in this invention adopts a symmetrical structure, introducing particles from the sample gas inlet into the middle of the flow field. The sample gas nozzle is electrically grounded, and the positive and negative high-pressure plates are located on both sides. Therefore, it can simultaneously screen multiple groups of bipolar monodisperse particles, that is, simultaneously screen positively charged and negatively charged particles, obtain the measured number concentration and sum them. Since "the total bipolar charge remains constant", this invention can effectively reduce the measurement error caused by changes in unipolar charge probability and improve the accuracy of particle size distribution measurement.

[0052] (3) The bipolar multi-stage DMA described in this invention can preliminarily distinguish the types of particulate matter in the sample gas. Since different types of particulate matter have different positive charge ratios when passing through the bipolar charger, under the condition that the positive charge ratios of the charger for different types of particulate matter are known, it is possible to distinguish the types of particulate matter by using N... 测量A (d p ) / N 测量B (d p The value of ) can be used to make a preliminary judgment on the type of particulate matter. Attached Figure Description

[0053] Figure 1 This is a schematic diagram of the three-dimensional structure of DMA in this invention;

[0054] Figure 2 This is a partial cross-sectional view of the DMA in this invention;

[0055] Figure 3 This is a side cross-sectional view of the bipolar multilevel DMA in this invention;

[0056] Figure 4 This is a schematic diagram of the nozzle installation structure in this invention;

[0057] Figure 5 This is a schematic diagram of the particle size distribution measuring device in this invention.

[0058] in:

[0059] 101. Bipolar multi-stage DMA; 102. Sample gas; 103. Bipolar particulate charge generator; 104. Charged sheath gas inlet; 105. Charged sheath gas outlet; 106. Positive high-voltage source; 107. Negative high-voltage source; A01~A0M. Particulate number concentration detectors; B01~B0M. Particulate number concentration detectors; 201. Sheath gas inlet mixing chamber; 202. Sheath gas inlet; 203. Connector; 204. Sample gas inlet; 205. Slit (sample gas outlet); 206. First high-voltage connector; 207. Sheath gas outlet mixer; 208. Sheath gas outlet mixing chamber; 209. Sheath gas outlet; 210. Front of insulating shell; 211. Back of insulating shell; 212. Left side of insulating shell; 213. Right side of insulating shell; 214. Second high-voltage electrode plate; 215. Sample gas nozzle base; 216. Nozzle; 217. Laminar flow device; 218. First high-voltage electrode plate; 219. Second high-voltage connector; 220. Stainless steel spring; 301. Chamfer; 302. Schematic diagram of sample gas flow direction at the outlet; 303. Schematic diagram of sample gas flow direction at the nozzle; 304. Schematic diagram of sheath gas flow direction; 305. Axis of symmetry; 401. Sample gas inlet channel; 402. Sample gas inlet cavity. Detailed Implementation

[0060] The present invention will be further described below with reference to the accompanying drawings:

[0061] like Figures 1-3 The illustrated bipolar multistage DMA includes an inlet stage, a sieving stage, and an outlet stage. The inlet stage includes a sheath gas inlet mixing chamber 201 and a laminar flow device 217. The sieving stage includes a sample gas nozzle (composed of a sample gas nozzle base 215 and an orifice 216), an insulating shell (composed of four POM plates: a front side 210, a back side 211, a left side 212, and a right side 213), and two high-voltage plates mounted on the inner walls of opposite sides of the insulating shell (the high-voltage plate mounted on the front side 210 of the insulating shell is the first high-voltage plate 218, and the high-voltage plate mounted on the back side 211 of the insulating shell is the second high-voltage plate 214). The outlet stage includes a sheath gas outlet mixer 207 and a sheath gas outlet mixing chamber 208. The separate design of the inlet, sieving, and outlet stages facilitates manufacturing and installation.

[0062] The cuboid region enclosed by the sheath gas inlet mixing chamber 201 and the laminar flow device 217 in the inlet stage is the sheath gas inlet mixing region. The upper end of the sheath gas inlet mixing chamber 201 is opened as the sheath gas inlet 202.

[0063] The insulating shell in the screening stage is composed of four acetal-POM plates (one for the front, one for the back, and two for the sides). The acetal-POM plates on the front (210) and back (211) are respectively embedded with a first high-voltage electrode plate 218 and a second high-voltage clamp 214 made of stainless steel. The first high-voltage electrode plate 218(A) and the second high-voltage electrode plate 214(B) are connected to positive and negative high voltages respectively via a first high-voltage connector 206 and a second high-voltage connector 219. The high-voltage grounds of both high voltages are connected to the sample gas nozzle base 215. Two million slits are symmetrically formed on the two high-voltage electrodes and the acetal-POM plates on the front and back of the insulating shell, serving as sample gas outlets 205. The symmetrical structural design of the screening stage allows outlets on the positive and negative high-voltage plates at vertically aligned positions to screen particles of the same size with opposite polarities of charge. Acetal-POM material is used because it releases static electricity quickly, minimizing particle loss due to charge accumulation, thus improving accuracy and stability.

[0064] The sample gas nozzle in the sieving stage is installed at the upper end of the sieving stage, with the nozzle direction consistent with the sheath gas flow direction. The nozzle is installed at the center of the top view projection of the flow field to ensure that the positive and negative high-voltage plates are structurally symmetrical.

[0065] The cuboid region enclosed by the sheath gas outlet mixing chamber 208 and the sheath gas outlet mixer 207 in the outlet stage is the sheath gas outlet mixing region. The lower end of the sheath gas outlet mixing chamber has an opening, which serves as the sheath gas main outlet 209. The function of the sheath gas outlet mixer is to disperse the pressure at this location and maintain the stability of the flow field.

[0066] The inlet stage and screening stage, and the screening stage and outlet stage are connected together by connectors 203. Connectors 203 are made of angle aluminum.

[0067] like Figure 3 As shown, dashed line 305 represents the axis of symmetry of the bipolar multistage DMA. The entire bipolar multistage DMA is a symmetrical structure with dashed line 305 as the axis of symmetry; the inlet stage, sieving stage, and outlet stage are all symmetrical about axis 305. Because of the symmetrical structure, the sample gas enters the flow field vertically downwards from the sample gas nozzle, and the distance from the sample gas inlet to the positive and negative high-pressure plates is the same. Furthermore, because of the symmetrical structure, the sample gas and sheath gas are uniformly distributed in the flow field. Therefore, the symmetrical structure makes the transfer function corresponding to the m-th outlet of the positive high-pressure surface (denoted as A) the same as the transfer function corresponding to the m-th outlet of the negative high-pressure surface (denoted as B). According to the particle size distribution inversion formula... and If and only if h B (d p ) = h A (d p ), w B (dp ) = w A (d p That is, when the transfer functions are the same, these two equations can be combined into one. Where [p(1,d] p )+p(-1,d p The term does not change with the operating state of the load (studies show that p(1,d)) p ) and p(-1,d p Each of them is affected by the changes in the operating state of the load, but their sum is unaffected. In other words, p(1,d) p ) and p(-1,d p (This is a zero-sum relationship, where one increases at the expense of the other, and the total remains constant). Therefore, in this invention, by setting the bipolar multilevel DMA to a symmetrical structure, the p(-1,d) condition is eliminated. p ) or p(1,d p The changes have improved the accuracy and stability of particle size distribution inversion.

[0068] Furthermore, the vertical distance between the sheath gas inlet 202 and the laminar flow device 217 shall not be less than 50 mm. This design allows the sheath gas to diffuse fully and the pressure to be evenly distributed when it reaches the laminar flow device 217, so as to ensure the uniformity of the flow field.

[0069] Furthermore, the laminar flow device 217 is made of nylon or polyester mesh with a mesh count higher than 300. The high mesh count ensures the quality of laminar flow, and the nylon or polyester mesh has a larger opening area ratio than the steel mesh, which can reduce air resistance and increase the adjustment range of the sheath gas.

[0070] Furthermore, the sample gas nozzle in the sieving stage is composed of a sample gas nozzle base 215 and a nozzle 216. For example... Figure 4 As shown, after the sample gas nozzle base 215 and sample gas nozzle 216 are assembled together, the gap is sealed with liquid adhesive to ensure airtightness. Dividing the sample gas nozzle into two parts, the nozzle base and the nozzle, facilitates processing. The sample gas nozzle has a semi-rotary structure, and the apex angle of the nozzle 216 must not exceed 15°. The sample gas nozzle adopts a semi-rotary structure, including a cuboid-shaped first nozzle part and a triangular prism-shaped second nozzle part connected to the first nozzle part; the thickness of the second nozzle part gradually decreases from the connection point with the first nozzle part, and the apex angle of the tip of the second nozzle part does not exceed 15°. The function of the nozzle is to disperse the sample gas from the sample gas inlet and guide it into the flow field through the flat nozzle. By adopting the above-described nozzle structure, the sample gas can be dispersed from the inlet and guided to the flat nozzle.

[0071] The nozzle is provided with a sample gas inlet chamber and a nozzle slit; an opening is made in the nozzle as the sample gas inlet chamber, and the nozzle slit is machined by wire cutting, with a slit width of less than 2mm. The nozzle base has a sample gas inlet channel corresponding to the sample gas inlet chamber; an opening is made in the nozzle base as the sample gas inlet channel, which is directly opposite the sample gas inlet chamber on the nozzle.

[0072] Furthermore, a chamfer 301 is provided on the inner side of the high-voltage electrode slit, the purpose of which is to reduce particulate matter loss at the sample gas outlet.

[0073] Furthermore, the sheath gas outlet mixer 207 is a porous metal plate with uniform openings and a total opening area of ​​less than 25%. The lower opening area increases gas resistance, allowing the sheath gas to flow out of the laminar flow field uniformly.

[0074] Furthermore, the sheath gas inlet mixing chamber 201 is made of metal, the sample gas nozzle base 215 and the nozzle 216 are both made of metal, the first high-pressure plate 218 and the second high-pressure plate 214 are both made of stainless steel, the sheath gas outlet mixer 207 is made of metal, and the sheath gas outlet mixing chamber 208 is made of metal.

[0075] The function of a bipolar multistage DMA is to sieve charged ultrafine particles in a sampling gas flow. "Bipolar" means the device can simultaneously sieve ultrafine particles with a single positive charge and a single negative charge; "multistage" means the device can simultaneously sieve multiple groups of monodisperse ultrafine particles of different sizes. A bipolar multistage DMA includes an inlet stage, a sieving stage, and an outlet stage. The inlet stage includes a sheath gas inlet mixing chamber and a laminar flow device; the sieving stage includes a sample gas nozzle, an insulating shell, and a high-voltage electrode; the outlet stage includes a sheath gas outlet mixer and a sheath gas outlet mixing chamber. The inlet stage introduces the sheath gas into the flow field through the sheath gas inlet and ensures it moves in a laminar flow state; the sieving stage introduces the sampling gas into the flow field through the sample gas inlet and sieves monodisperse ultrafine particles; the outlet stage guides the sheath gas from the flow field to the sheath gas outlet.

[0076] like Figure 5 The particle size distribution measurement device shown includes a bipolar particulate charge device, a bipolar multistage DMA, and 2M particulate number concentration detectors, where M is a positive integer and its value is determined by the number of outlets of the bipolar multistage DMA. The sample gas inlet of the bipolar multistage DMA is connected to the outlet of the bipolar particulate charge device, and each gas outlet of the bipolar multistage DMA is connected to a particulate number concentration detector. The bipolar particulate charge device includes a charging chamber and a charged sheath gas inlet 104 and a charged sheath gas outlet 105 disposed on the charging chamber. The charging chamber is connected to a positive high-voltage source 106 and a negative high-voltage source 107 to generate a charging electric field.

[0077] This invention addresses the shortcomings of existing technologies, enabling bipolar multichannel sieving of atmospheric particulate matter, and thus achieving rapid and accurate measurement of particle size distribution.

[0078] The present invention also relates to a method of using the above-described apparatus, the method comprising the following steps:

[0079] (1) Connect the bipolar multistage DMA in the order of “sample gas 102 – bipolar charge 103 – sample gas inlet 204”; connect the 2M sample gas outlets to the 2M particulate number concentration detectors A01~A0M and B01~B0M respectively. The particulate number concentration detectors can be CPC, aerosol electrometer, etc.

[0080] (2) Flow rate setting: The flow rate at the bipolar multistage DMA sheath gas inlet 202 is set to Q, the flow rate of the 2M number concentration detectors is set to q, and the flow rate at the bipolar multistage DMA sheath gas outlet 209 is set to Q-(2M-1)q. Therefore, the flow rate at the sample gas inlet is passively set to q, where Q, q, and Q-(2M-1)q are all greater than 0. The positive high pressure is set to U1, and the negative high pressure is set to -U1. In this method, the absolute values ​​of the positive and negative high pressures are always equal.

[0081] (3) The sheath gas enters the mixing region from the sheath gas inlet 202. After mixing, the sheath gas passes through the laminar flow device 217 and enters the sieving stage. The trajectory after entering the sieving stage is as follows: Figure 3 As shown in 304.

[0082] (4) After being mixed by the sheath gas outlet mixer 207, the sheath gas enters the sheath gas outlet mixing chamber 208 and flows out of the outlet stage from the sheath gas outlet 209 via the sheath gas outlet mixing chamber.

[0083] (5) The sample gas enters the sample gas inlet channel 401 on the nozzle base through the sample gas inlet 204, then enters the sample gas inlet cavity 402 on the nozzle, and then enters the sieving stage through the slit on the nozzle, where it merges with the sheath gas. The trajectory of the sample gas at the nozzle is as follows: Figure 3 As shown in 303 in Figure 3. Subsequently, the sheath gas and sample gas flow towards the outlet stage in a laminar flow state. The charged particles are deflected by the electric field force generated by the high-voltage plate and are finally screened out through 2M outlets. The sample gas trajectory at the sample gas outlet is shown in 302 in Figure 3.

[0084] The positive high-voltage plate voltage of the bipolar multi-stage DMA is set to +U1, and the negative high-voltage plate voltage is set to -U1. Under the flow rate setting of (41), the sieve particle size corresponding to the voltage |U1| at different gas outlets is d. p1 d p2 , ...,d pM At this time, the M particulate number concentration detectors connected to the positive high voltage plate measured N. 测量A1(d p1 ), N 测量A2 (d p2 ), ..., N 测量AM (d pM M particulate number concentration detectors connected to the negative high-voltage plate measured N. 测量B1 (d p1 ), N 测量B2 (d p2 ), ..., N 测量BM (d pM ). Using formula Calculate d in the particle size spectrum p1 d p2 、…、d pM The height at which dN is obtained U1 (d p1 ),dN U1 (d p2 ), ..., dN U1 (d pM Let D be the set. U1 ={dN U1 (d p1 ),dN U1 (d p2 ),…,dN U1 (d pM )}.

[0085] Wherein dN U1 (d pM p(n,d) represents the particle size distribution channel height at the corresponding particle size of the Mth particle number concentration detector when the high voltage settings are +U1 and -U1. p ) represents the particle size d p The probability that a particulate matter carries n charges after passing through a bipolar charge, η(d p () is a particulate number concentration detector for particles with a diameter of d p The detection efficiency of particulate matter, h(d p ) is a bipolar multilevel DMA at d p The height of the transfer function, w(d) p ) is a bipolar multilevel DMA at d p The full width at half maximum (FWHM) of the transfer function, w'(d p ) represents the particle size distribution d p The width of the passage at that location, w and w' have the same unit;

[0086] (5) Change the voltage values ​​of the positive and negative high voltages to obtain the D values ​​corresponding to each voltage value. U1 D U2 ... D UY Until each D is measured U The included dN U (dp It covers the entire particle size spectrum to be measured, thus obtaining complete particle size spectrum measurement results.

[0087] Because the bipolar multi-stage DMA described in this invention has a symmetrical structure, when the high voltage is set to +U and -U, the outlet at the same vertical position can separate particles with the same particle size but different polarities. This, in turn, causes the nuclear charge probability distribution term in the particle size distribution inversion process to change from p(1, d... p ) is converted to [p(1,d p )+p(-1,d p )], where p(1,d p The single positively charged particles represented by ) are screened out by the negative high-voltage plate, p(-1,d p The single-charge particulate matter represented by ) is screened out by the positive high-voltage plate. Because p(1,d) p ) is more susceptible to the effects of load aging and experimental environment, while [p(1,d p )+p(-1,d p The value of )] is relatively stable. Therefore, the present invention reduces the error, improves the inversion accuracy and the stability of the particle size distribution measurement device during the particle size distribution inversion process.

[0088] The above-described embodiments are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A particle size distribution measurement method using a particle size distribution measurement device, characterized in that, The particle size distribution measurement device includes a bipolar multistage DMA, a bipolar particulate charge, and a particulate number concentration detector. The sample gas inlet of the bipolar multistage DMA is connected to the outlet of the bipolar particulate charge, and each gas outlet of the bipolar multistage DMA is connected to a particulate number concentration detector. The bipolar multistage DMA includes an inlet stage, a sieving stage, and an outlet stage arranged sequentially. The inlet stage includes a sheath gas inlet mixing chamber and a laminar flow device disposed within the sheath gas inlet mixing chamber. The sieving stage includes a sieving chamber connected to the sheath gas inlet mixing chamber and a sample gas nozzle installed within the sieving chamber. The outlet stage includes a sheath gas outlet mixing chamber connected to the sieving chamber and a mixer installed within the sheath gas outlet mixing chamber. The particle size distribution measurement method of this particle size distribution measurement device includes: (1) Sheath gas is introduced into the mixing chamber of sheath gas inlet. After the sheath gas is mixed in the mixing chamber of sheath gas inlet, it enters the screening chamber through the laminar flow device. (2) The sample gas is introduced into the bipolar charge, and the bipolar charge reacts to charge the particles in the sample gas. The sample gas carrying the charged particles flows from the bipolar charge to the sieving chamber and merges with the sheath gas in the sieving chamber. (3) The sample gas and sheath gas carrying charged particles flow from the sieving stage to the outlet stage in a laminar flow state. The charged particles are deflected by the electric field force generated by a pair of high-voltage plates. Charged particles of different sizes are screened out from the corresponding gas outlet. (4) The number concentration of charged particles screened out of the corresponding gas outlet is detected by each particle number concentration detector to determine the particle size distribution; The method of using each particulate number concentration detector to detect the number concentration of charged particles sieved from the corresponding gas outlet and determining the particle size distribution includes: (41) Flow rate setting: Assume the number of particulate number concentration detectors is 2M, where M is a positive integer. M of these detectors are connected to the positive high-voltage plate, and the other M detectors are connected to the negative high-voltage plate. Set the flow rate at the inlet of the bipolar multi-stage DMA sheath gas to... ,Will The flow rate setting for each particulate number concentration detector is... The flow rate at the outlet of the bipolar multistage DMA sheath gas is set to Therefore, the flow rate at the sample gas inlet is passively set to ,in, , and All are greater than 0; (42) Set the voltage on the positive high voltage plate of the bipolar multi-stage DMA to Set the voltage on the negative high-voltage plate to Under the flow rate setting in step (41), the voltage is recorded. The corresponding sieve particle sizes for different gas outlets are as follows: , , ..., At this time, the particulate number concentrations measured by the M particulate number concentration detectors connected to the positive high voltage plate are respectively , , ..., The particulate number concentrations measured by the M particulate number concentration detectors connected to the negative high voltage plate are respectively , , ..., ; Using formula In calculating particle size distribution , … At the height of the location, obtain , … , denoted as set ; in, Set the high voltage to and The height of the particle size distribution channel at the corresponding particle size of the Mth particle number concentration detector. For particle size Particulate matter passes through a bipolar charge belt The probability of a charge, For particulate number concentration detectors, the particle size is The particle detection efficiency, For bipolar multilevel DMA The height of the transfer function, For bipolar multilevel DMA The full width at half maximum (FWHM) of the transfer function. Particle size spectrum The width of the passageway at that location, and Same units; (43) Change the voltage values ​​of the positive high-voltage plate and the negative high-voltage plate, obtain the particle size distribution height corresponding to each particle size at the current voltage value, and determine the set corresponding to the current voltage value. ; (44) Repeat steps (42) and (43) until all the individual items are obtained. Included It covers the entire particle size spectrum to be measured, thus obtaining complete particle size spectrum measurement results.

2. The particle size distribution measurement method of the particle size distribution measurement device according to claim 1, characterized in that, The sheath gas inlet mixing chamber is provided with a sheath gas inlet; The laminar flow device uses nylon or polyester yarn with a mesh count higher than 300 mesh; The vertical distance between the sheath gas inlet and the laminar flow device is not less than 50 mm.

3. The particle size distribution measurement method of the particle size distribution measurement device according to claim 1, characterized in that, The screening chamber includes an insulating shell and two high-voltage plates respectively disposed on two opposite sides of the inner wall of the insulating shell, one of the high-voltage plates being connected to a positive high voltage and the other high-voltage plate being connected to a negative high voltage. The high-voltage plate is connected to a positive or negative high voltage via a high-voltage connector. The insulating outer shell has a fixing groove, the high-voltage connector is installed in the fixing groove, and the inner end of the high-voltage connector is in contact with the high-voltage plate through a spring; the spring is made of stainless steel. The sieving chamber is provided with a sample gas inlet and multiple gas outlets; The gas outlet is located through the high-voltage electrode plate and the insulating outer shell wall where the high-voltage electrode plate is located. The gas outlet portion on the high-voltage plate has a chamfer.

4. The particle size distribution measurement method of the particle size distribution measurement device according to claim 1, characterized in that, The sheath gas inlet mixing chamber and the sheath gas outlet mixing chamber are both connected to the sieving chamber via connectors. The connector is made of angle aluminum.

5. The particle size distribution measurement method of the particle size distribution measuring device according to claim 1, characterized in that, The sample gas nozzle includes a nozzle base and a nozzle mounted on the nozzle base; The nozzle is provided with a sample gas inlet cavity and a nozzle slit; The nozzle base has a sample gas inlet channel corresponding to the sample gas inlet oral cavity; The sample gas nozzle adopts a semi-rotary structure, including a cuboid nozzle first part and a triangular prism nozzle second part connected to the nozzle first part; the thickness of the nozzle second part gradually decreases from the connection point with the nozzle first part, and the apex angle of the tip of the nozzle second part is no greater than 15°.

6. The particle size distribution measurement method of the particle size distribution measuring device according to claim 3, characterized in that, The insulating outer shell is made of POM (polypropylene) board. The high-voltage electrode plate is made of stainless steel. Both the positive and negative high voltage grounds are connected to the sample gas nozzle base.

7. The particle size distribution measurement method of the particle size distribution measurement device according to claim 1, characterized in that, The sheath gas outlet mixing chamber is made of metal. The sheath gas outlet mixing chamber is provided with a sheath gas main outlet; The mixer includes a mixer body and a plurality of openings evenly distributed on the mixer body; the mixer body is made of a metal plate, and the total area of ​​the openings on the metal plate is less than 25%.

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