CN114088590A - Differential electromigration-based aerosol particle grading device - Google Patents
Differential electromigration-based aerosol particle grading device Download PDFInfo
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- 229920006324 polyoxymethylene Polymers 0.000 claims description 10
- 239000011347 resin Substances 0.000 claims description 8
- 229920005989 resin Polymers 0.000 claims description 8
- 229930040373 Paraformaldehyde Natural products 0.000 claims description 7
- -1 polyoxymethylene Polymers 0.000 claims description 6
- 229910000838 Al alloy Inorganic materials 0.000 claims description 4
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- 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
Abstract
The invention relates to an aerosol particle grading device based on differential electromigration, which comprises a sheath gas cavity, a nylon filter screen, an annular grading area, an aerosol cavity, an aerosol outlet slit, an inner electrode, an outer electrode, an aerosol collecting slit, an aerosol collecting hole, a current limiting device, a residual cavity device and a residual gas outlet channel, wherein the sheath gas cavity is provided with a plurality of air holes; the gas introduced into the sheath gas cavity is air without particles; sheath gas introduced into the sheath gas cavity enters the annular classification area through the nylon filter screen, aerosol enters the annular classification area through the aerosol outlet slit, and aerosol with specific electric mobility enters the aerosol collecting hole; according to the relation between the particle size of the aerosol particles to be separated and the power supply voltage, the classification of the aerosols with different particle sizes is realized by controlling the gas flow of the sheath gas flow entering the sheath gas cavity and flowing out from the residual gas outlet channel. The invention improves the measurement range of the aerosol particle size and improves the grading precision of the aerosol particles with small particle size.
Description
Technical Field
The invention relates to the technical field of particulate matter detection, in particular to an aerosol particle grading device based on differential electromigration.
Background
Measurement of aerosol particle size distribution is crucial to understanding the impact of aerosols on human health and global climate. Electromigration technology has been widely used for size measurement of ultra-fine aerosols, nanoparticles, and sub-micron aerosols due to its unique advantages over inertial or optical techniques. The differential mobility analyzer plays a key role in aerosol science, and can classify particles according to the electrical mobility of the particles.
At present, a differential mobility analyzer has certain limitations in particle size measurement range and resolution, and cannot accurately screen aerosol particles in the atmosphere. For small particle size particles, especially particles below the nanometer level, the resolution of the differential mobility analyzer is extremely low due to the intense brownian motion.
Disclosure of Invention
The invention aims to provide an aerosol particle grading device based on differential electromigration, which improves the measurement range of the particle size of aerosol particles and improves the grading precision of small-particle size aerosol particles.
In order to achieve the purpose, the invention provides the following scheme:
an aerosol particle grading device based on differential electromigration comprises a sheath gas cavity, a nylon filter screen, an annular grading area, an aerosol cavity, an inner electrode, an outer electrode, an aerosol collecting slit, an aerosol collecting hole, an aerosol channel, a current limiting device, a residual cavity device and a residual gas outlet channel;
the nylon filter screen is arranged between the sheath gas cavity and the annular grading area, the sheath gas cavity, the nylon filter screen and the annular grading area are sequentially arranged from top to bottom, the aerosol cavity is arranged on the side wall of the annular grading area, the aerosol cavity is communicated with the annular grading area through an aerosol outlet slit, the outer electrode is an annular cylinder, the inner electrode is a cylinder, the outer electrode is arranged on the outer side of the inner electrode, an annular area between the outer electrode and the inner electrode is the annular grading area, and the outer electrode is positioned below the aerosol cavity;
the inner electrode comprises an upper half part of the inner electrode, an inner electrode connecting part and a lower half part of the inner electrode which are arranged from top to bottom in sequence; the upper half part of the inner electrode, the lower half part of the inner electrode and the inner electrode connecting part are coaxially arranged, the diameters of the upper half part of the inner electrode and the lower half part of the inner electrode are the same, the diameter of the inner electrode connecting part is smaller than that of the upper half part of the inner electrode, a slit between the upper half part of the inner electrode and the lower half part of the inner electrode is an aerosol collecting slit, and a plurality of aerosol collecting holes are horizontally arranged in the connecting part; one end of the aerosol collecting hole is communicated with the aerosol collecting slit, and the other end of the aerosol collecting hole is communicated with the aerosol channel; the inner electrode is connected with a power supply, and the outer electrode is grounded;
the current limiting device is arranged below the annular grading area, the current limiting device surrounds the outer side of the inner electrode, the upper part of the current limiting device is connected with the outer electrode, the lower part of the current limiting device is connected with the residual cavity device, and the residual gas outlet channel is connected with the residual cavity device;
the gas introduced into the sheath gas cavity is air without particles;
according to the relation between the particle size of the aerosol particles to be separated and the power supply voltage, the grading of the aerosol with different particle sizes is realized by controlling the sheath gas flow entering the sheath gas cavity and the gas flow flowing out of the residual gas outlet channel, and the gas flowing out of the residual gas outlet channel is the mixed gas of the sheath gas and the aerosol.
Optionally, the upper part of the flow limiting device is in threaded connection with the outer electrode, the lower part of the flow limiting device is in threaded connection with the rest cavity device, and the vertical distance between the top of the flow limiting device and the aerosol collecting hole is 10 mm; a plurality of through holes are uniformly distributed on the flow limiting device, one end of each through hole is communicated with the annular classification area, the other end of each through hole is communicated with the cavity in the rest cavity device, every two adjacent through holes form a group, the angle between the two through holes in each group is 15 degrees, the diameters of the through holes are the same, and the diameter of each through hole is 0.8mm to 1 mm; the residual cavity device surrounds the outer side of the inner electrode;
the material of the current limiting device and the material of the residual cavity device are polyformaldehyde resin.
Optionally, the outer radius of the inner electrode is 33mm, the inner portion of the upper half portion of the inner electrode is hollow, and the outer wall of the inner electrode and the inner wall of the outer electrode are both mirror surfaces.
Optionally, the differential electromigration-based aerosol particle classification device further includes two aerosol inlet channels, and the two aerosol inlet channels are symmetrically disposed on two sides of the aerosol cavity;
the inner surface of the aerosol inlet passage is a polished surface.
Optionally, the number of the residual gas outlet channels is 2, and the 2 residual gas outlet channels are symmetrically arranged on two sides of the residual cavity device.
Optionally, the differential electromigration-based aerosol particle classification device further includes a bell mouth device, a top device, an upper aerosol cavity half and a lower aerosol cavity half, where a cavity between the upper aerosol cavity half and the lower aerosol cavity half is the aerosol cavity, the top device is a shell of the sheath gas cavity, and the annular classification region is between an outer wall of the inner electrode and an inner wall of the outer electrode;
the bell mouth device is fixed below the top device through threads, the upper half part of the aerosol cavity is connected below the bell mouth device through threads, the upper half part of the aerosol cavity is connected with the lower half part of the aerosol cavity through threads, and the outer electrode is connected below the lower half part of the aerosol cavity through threads.
Optionally, the material of the bell mouth device is an aluminum alloy, and the material of the top device is polyoxymethylene resin.
Optionally, the aerosol particle classification device based on differential electromigration further includes a base, the base is disposed below the inner electrode, and the base is made of polyoxymethylene resin.
Optionally, the inner surface of the aerosol chamber is a polished surface.
Optionally, the aerosol collection slit has a vertical height of 1.59mm and the aerosol outlet slit has an axial width of 1.8 mm.
According to the specific embodiment provided by the invention, the invention discloses the following technical effects:
the gas introduced into the sheath gas cavity is air without particles; sheath gas introduced into the sheath gas cavity enters the annular classification area through the nylon filter screen, aerosol enters the annular classification area through the aerosol outlet slit, and aerosol with specific electric mobility enters the aerosol collecting hole; according to the relation between the particle size of the aerosol particles to be separated and the power supply voltage, the grading of the aerosol with different particle sizes is realized by controlling the sheath gas flow entering the sheath gas cavity and the gas flow flowing out from the residual gas outlet channel, the measurement range of the particle size of the aerosol particles is enlarged, and the grading precision of the aerosol particles with small particle sizes is improved.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings needed to be used in the embodiments will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings without inventive exercise.
FIG. 1 is a schematic diagram of a differential electromigration-based aerosol particle classification apparatus according to the present invention;
FIG. 2 is a schematic view of the structure of an aerosol collection slit and an aerosol collection hole according to the present invention;
FIG. 3 is a schematic diagram of the differential electromigration-based aerosol particle classification principle of the present invention;
FIG. 4 is a graph showing the relationship between the concentration of the center point of the aerosol collection slit and the distance from the bottom of the collection slit to the top of the flow restriction device according to the present invention;
FIG. 5 is a velocity profile of the horizontal inward electrode direction in the annular staging area 50mm above the center point of the aerosol collection slit according to the present invention;
description of the symbols: 1-top device, 2-sheath gas inlet channel, 3-bell mouth device, 4-ring, 5-nylon filter screen, 6-aerosol cavity device upper half part, 7-aerosol inlet channel, 8-aerosol cavity device lower half part, 9-outer electrode, 10-inner electrode, 11-current limiting device, 12-residual cavity device, 13-residual gas outlet channel, 14-base, 15-aerosol outlet device, 16-sheath gas cavity, 17-aerosol cavity, 18-aerosol outlet slit, 19-annular grading zone, 20-aerosol collecting slit, 21-aerosol collecting hole, 22-aerosol channel.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
The invention aims to provide an aerosol particle grading device based on differential electromigration, which improves the measurement range of the particle size of aerosol particles and improves the grading precision of small-particle size aerosol particles.
In order to make the aforementioned objects, features and advantages of the present invention comprehensible, embodiments accompanied with figures are described in further detail below.
Fig. 1 is a schematic diagram of an aerosol particle classifying device based on differential electromigration, and as shown in fig. 1, the aerosol particle classifying device based on differential electromigration includes a sheath gas cavity 16, a nylon filter screen 5, an annular classifying region 19, an aerosol cavity 17, an aerosol outlet slit 18, an inner electrode 10, an outer electrode 9, an aerosol collecting slit 20, an aerosol collecting hole 21, an aerosol channel 22, a current limiting device 11, a residual cavity device 12, and a residual gas outlet channel 13.
The nylon filter screen 5 is arranged between the sheath gas cavity 16 and the annular grading area 19, the sheath gas cavity 16, the nylon filter screen 5 and the annular grading area 19 are sequentially arranged from top to bottom, the aerosol cavity 17 is arranged on the side wall of the annular grading area 19, the aerosol cavity 17 is communicated with the annular grading area 19 through an aerosol outlet slit 18, the outer electrode 9 is an annular cylinder, the inner electrode 10 is a cylinder, the outer electrode 9 is arranged on the outer side of the inner electrode 10, the annular area between the outer electrode 9 and the inner electrode 10 is the annular grading area 19, and the outer electrode 9 is located below the aerosol cavity 17.
The inner electrode 10 comprises an upper half part of the inner electrode, an inner electrode connecting part and a lower half part of the inner electrode which are arranged from top to bottom in sequence; the upper half part of the inner electrode, the lower half part of the inner electrode and the inner electrode connecting part are coaxially arranged, the diameters of the upper half part of the inner electrode and the lower half part of the inner electrode are the same, the diameter of the inner electrode connecting part is smaller than that of the upper half part of the inner electrode, a slit between the upper half part of the inner electrode and the lower half part of the inner electrode is an aerosol collecting slit 20, and a plurality of aerosol collecting holes 21 are horizontally arranged on the connecting part; one end of the aerosol collecting hole 21 is communicated with the aerosol collecting slit 20, and the other end is communicated with the aerosol passage 22.
The upper half part of the internal electrode, the internal electrode connecting part and the lower half part of the internal electrode are integrally arranged, namely the upper half part of the internal electrode, the internal electrode connecting part and the lower half part of the internal electrode are integrally arranged.
The inner part of the upper half part of the inner electrode is hollow. Thereby the device has light weight and is convenient to carry.
The inner electrode 10 is connected to a power supply, specifically, the inner electrode 10 is connected to a high voltage power supply, and the outer electrode 9 is grounded, wherein the high voltage power supply is shown as h.v. in fig. 1.
The outer electrode 9 is annular, and the inner electrode 10 and the outer electrode 9 are coaxially arranged.
The utility model provides an aerosol particle grading plant based on difference electromigration still includes sheath gas inlet channel 2, aerosol outlet means 15, horn mouth device 3, ring 4, top device 1, aerosol cavity 17 upper half, aerosol cavity 17 lower half and base 14.
The sheath gas inlet channel 2 is connected to the side of the top unit 1 by means of metal glue. To ensure uniform diffusion of the sheath gas in the sheath gas chamber 16, the volume of the sheath gas chamber 16 is sufficiently large. Wherein the sheath gas inlet channel 2 is made of stainless steel, and the top device 1 is made of Polyoxymethylene (POM).
The cavity between the upper half part of the aerosol cavity 17 and the lower half part of the aerosol cavity 17 is the aerosol cavity 17, the top device 1 is the shell of the sheath gas cavity 16, and an annular grading zone 19 is arranged between the outer wall of the inner electrode 10 and the inner wall of the outer electrode 9.
The bell mouth apparatus 3 is fixed below the top apparatus 1 by screw threads, the upper half of the aerosol chamber 17 is fixedly connected below the bell mouth apparatus 3 by screw threads, the upper half of the aerosol chamber 17 is fixedly connected with the lower half of the aerosol chamber 17 by screw threads, and the external electrode 9 is fixedly connected below the lower half of the aerosol chamber 17 by screw threads.
The nylon filter screen 5 is fixed in the slot formed by the bell mouth unit 3, the ring 4 and the top unit 1. The bell mouth device 3 is made of aluminum alloy.
The current limiting device 11 is arranged below the annular grading zone 19, the current limiting device 11 surrounds the outer side of the inner electrode 10, the upper part of the current limiting device 11 is in threaded connection with the outer electrode 9, the lower part of the current limiting device 11 is in threaded connection with the rest cavity device 12, and the vertical distance between the top of the current limiting device 11 and the aerosol collecting hole 21 is 10 mm; a plurality of through holes are uniformly distributed on the flow limiting device 11, one end of each through hole is communicated with the annular classification area 19, the other end of each through hole is communicated with the cavity in the rest cavity device 12, every two adjacent through holes form a group, the angle between the two through holes in each group is 15 degrees, the diameters of the through holes are the same, and the diameter of each through hole is 0.8mm to 1 mm; the remaining cavity means 12 surrounds the outside of the inner electrode 10.
The differential electromigration-based aerosol particle grading device further comprises two aerosol inlet channels 7, wherein the two aerosol inlet channels 7 are symmetrically arranged on two sides of the aerosol cavity 17.
The differential electromigration-based aerosol particle grading device further comprises two residual gas outlet channels 13, wherein the two residual gas outlet channels 13 are symmetrically arranged on two sides of the residual cavity device 12.
The mount 14 is disposed under the inner electrode 10.
The inner surfaces of the aerosol chamber 17 are polished, i.e. the inner surfaces of the upper part 6 of the aerosol chamber and the lower part 8 of the aerosol chamber are polished, and the inner surfaces of the polydispersed aerosol inlet channels (aerosol inlet channels 7) are polished, wherein the roughness of the polishing is below 0.2um, so as to ensure that the aerosol particles are not seriously lost before entering the annular classification zone 19.
The inner wall of the outer electrode 9 is a polished surface, and the inner wall of the outer electrode 9 is required to meet the mirror surface standard, so as to ensure the continuity of the airflow on the inner wall of the outer electrode 9, prevent aerosol particles from being trapped in the inner wall of the outer electrode 9 and realize the uniformity of the internal electric field.
The outer wall of the inner electrode 10 and the inner wall of the outer electrode 9 are mirror surfaces.
The inner electrode 10 is fixed between the residual cavity device 12 and the base 14, the outer electrode 9, the current limiting device 11, the residual cavity device 12, the base 14 and the aerosol outlet device 15 are fixedly connected through threads, and the residual gas outlet channel 13 is connected to the side surface of the residual cavity device 12 through metal glue.
The current limiting device 11, the residual cavity device 12 and the base 14 are all made of polyoxymethylene resin and are used for insulating the voltage of the inner electrode 10 so as to ensure the safety of the device. The outer wall of the inner electrode 10 needs to be polished to meet the mirror standard, so as to ensure the continuity of the air flow on the inner wall, prevent the aerosol particles from being trapped in the inner wall of the inner electrode 10, and realize the uniformity of the internal electric field. Wherein the inner electrode 10 and the aerosol outlet device 15 are both made of stainless steel.
The aerosol inlet channel 7, the upper half part 6 of the aerosol cavity device, the lower half part 8 of the aerosol cavity device and the outer electrode 9 are all made of stainless steel.
The vertical height of the aerosol collection slit 20 is 1.59 mm.
An aerosol outlet device 15 is connected to the outlet of the aerosol passage 22, the aerosol outlet device 15 being connected by a screw thread to the underside of the base 14.
The connection between the above parts needs to be added with an O-shaped rubber ring to ensure good air tightness.
The gas introduced into the sheath gas cavity 16 is air free of particulate matter.
And determining the limit range of the sum of the sheath gas flow entering the sheath gas cavity 16 and the aerosol flow passing through the aerosol outlet slit 18 when the airflow in the aerosol collection slit 20 is in a laminar state according to the outer radius of the inner electrode 10, the inner radius of the outer electrode 9 and the viscosity coefficient of the sheath gas.
In the limit range of the sum of the sheath gas flow entering the sheath gas cavity 16 and the aerosol flow passing through the aerosol outlet slit 18, classification of aerosols with different particle sizes is realized by controlling the sheath gas flow entering the sheath gas cavity 16 and the gas flow flowing out from the residual gas outlet channel 13 according to the relationship between the particle size of the aerosol particles to be separated and the power supply voltage, and the gas flowing out from the residual gas outlet channel 13 is the mixed gas of the sheath gas and the aerosols.
When the aerosol particle grading device based on differential electromigration is used for grading aerosol, the specific operation process, namely the gas flow direction, is as follows:
the sheath gas (air without particulate matter) is introduced into the sheath gas cavity 16 from the sheath gas inlet channel 2, and a first flow meter is installed at the air inlet of the sheath gas inlet channel 2 and used for monitoring the flow of the sheath gas.
The aerosol is passed from the aerosol inlet passage 7 into the aerosol chamber 17 and the aerosol gas passed into the aerosol chamber 17 passes through the aerosol outlet slit 18 into the annular staging zone 19. The aerosol entering from the aerosol inlet passage 7 into the aerosol chamber 17 is a polydisperse aerosol, i.e. an aerosol comprising a plurality of particle sizes.
The sheath gas that gets into sheath gas cavity 16 gets into horn mouth device 3 through nylon filter screen 5, and the sheath gas carries out the rectification through nylon filter screen 5, and the sheath gas after the rectification gets into the horn mouth device and carries out further rectification, makes the air current that gets into in the annular classification district be stable laminar flow.
The aerosol entering the annular classification zone 19 is dispersed at the outer side of the annular classification zone 19, and the sheath gas entering the annular classification zone 19 is dispersed at the inner side of the annular classification zone 19, namely the aerosol in the annular classification zone 19 is at the periphery of the sheath gas; the aerosol entering the annular classification zone 19 moves in the electric field formed by the inner electrode and the outer electrode, and the aerosol (the aerosol to be separated corresponding to the expected particle size range) meeting the specific electric mobility enters the aerosol channel from the aerosol collecting slit through the aerosol collecting hole and is finally discharged from the aerosol outlet device. The gas (residual gas) other than that entering the aerosol passage through the aerosol collection orifice passes through the flow restriction device and enters the residual cavity device, and the residual gas is discharged from the residual gas outlet passage.
The residual gas outlet passage 13 is provided with a second flow meter for monitoring the flow rate of the gas in the residual gas outlet passage. The flow restriction is arranged to control the flow of gas in the residual gas outlet passage.
The invention starts from the basic theory of a differential electromigration analyzer, calculates the flow rate and the maximum voltage of sheath gas and aerosol airflow and the particle size detection range of aerosol particles, selects air without particles after filtration as the sheath gas from the viewpoint of restraining Brownian diffusion, and optimizes the structure size from the viewpoint of numerical simulation. The invention has the advantages of high safety, compact and small structure, light weight, easy disassembly and cleaning, economy, high efficiency, reliable grain size classification of sampled gas and the like.
The basic principle of the present invention is that the Differential Mobility Analyzer (DMA) is mainly composed of two concentric metal electrodes, the outer radius of the inner electrode 10 is R1The inner radius of the outer electrode 9 is R2The effective fractionation zone has a length L, which is the vertical distance between the center point of the aerosol outlet slit 18 and the center point of the aerosol collection slit 20, as shown in fig. 2 and 3. Aerosol and sheath gases with Q, respectivelyaAnd QcThe collected particles have an electrical mobility that is a function of the DMA size, including the outer radius R of the inner electrode 10, the applied supply voltage and the fluid flow rate1The inner radius of the outer electrode 9 is R2And an effective classification zone of length L, of the particles of the inventionThe electrical mobility was:
where V is a power supply voltage, i.e., a voltage applied to the inner electrode 10.
According to the definition of the electrical mobility of the particles, the electrical mobility of the particles is:
where q is the number of charges of the particles and e is the base charge (1.6 x 10)-9) U is the gas viscosity coefficient, dp is the particle size of the particles, C*For the cunningham correction factor, is given by:
wherein k isnExpressing the number of knudsen, α, β and r are correction coefficients, α is 1.155, β is 0.471, and r is 0.596.
The relationship between the particle size of the particles separated by the DMA and the voltage under the condition that the size of the DMA and the flow rate of the fluid are fixed can be obtained by the above equations (1) and (2), and is given by the following formula:
the gas flow in the annular staging zone of the present invention is required to be in laminar flow, i.e., Reynolds number R is requiredeLess than or equal to 2300, the reynolds number for the flow in the annular staging zone of a cylindrical DMA according to the invention has the form:
the maximum electric field strength requirement of the invention is less than the breakdown strength, for a cylindrical structured DMA, the highest electric field strength is at the surface of the central electrode, and the breakdown strength has the following form:
wherein, EbIndicating the electric field strength at breakdown.
For a cylindrical structured DMA, the electric field strength and voltage have the following form:
wherein R isiIndicating the distance from a point in the annular staging area to the central axis.
For small particle size aerosol particles, whose brownian motion becomes intense with decreasing particle size, the brownian diffusion coefficient has the following form:
where D represents a brownian diffusion coefficient, K represents a boltzmann constant, and T represents an absolute temperature.
Q in FIG. 3sIndicating the flow rate, Q, of the aerosol being separatedmIndicating the flow of the remaining gas other than the separated aerosol, i.e. the flow of the remaining sheath gas and the aerosol. The ordinate of fig. 4 is concentration, the ordinate of fig. 5 is velocity, the abscissa of fig. 5 is horizontal width of the annular grading zone, the difference between the inner radius of the outer electrode and the outer radius of the inner electrode, i.e. equal to R2-R1。
The sheath gas cavity 16 has an inner diameter of 45.8mm and a height of 45 mm. So that the sheath gas is uniformly diffused in the sheath gas cavity 16. Wherein the material of the sheath gas inlet channel 2 is stainless steel.
The tapering angle of the bell mouth device 3 is 45 degrees, and the distance from the tapering starting point to the bottom of the circular ring 4 is 45 mm. Wherein the bell mouth is made of aluminum alloy.
The net surface thickness of the nylon screen is 0.1mm, 400 meshes, and in order to enable the rectification effect to be better, the number of layers of the nylon screen can be increased to 2-3 layers. The nylon screens of each layer are kept at a set distance, which is between 5mm and 10 mm.
The upper half part 6 of the aerosol cavity device, the lower half part 8 of the aerosol cavity device and the polydisperse aerosol inlet channel 7 are all made of stainless steel.
The inner radius of the outer electrode 9 is 25 mm. The material of the outer electrode 9 is stainless steel.
The outer radius of the inner electrode 10 is 33mm, the axial width of the aerosol collecting slit 20 on the inner electrode 10 is 1.59mm, the inner diameter of the aerosol collecting hole 21 is 1.59mm, 12 aerosol collecting small holes are uniformly distributed on the aerosol outlet slit 18, and the angle between every two adjacent aerosol collecting small holes is 30 degrees. The material of the inner electrode 10 is stainless steel.
The aerosol outlet slit 18 has an axial width of 1.8mm to reduce penetration of the electric field.
The small holes 2 and 24 groups of small holes on the flow limiting device 11 are uniformly distributed on the flow limiting device 11, and the angle between every two adjacent groups of small holes is 15 degrees. The orifices in the flow restriction 11 are all of the same diameter, between 0.8mm and 1mm in diameter.
The distance from the centre point of the aerosol outlet slit 18 to the centre point of the aerosol collection slit 20 is 110 mm.
The distance from the bottom of the aerosol-collecting slit 20 to the top of the flow restriction 11 is 10 mm.
The material of the current limiting device 11, the material of the residual cavity device 12 and the material of the base 14 are all polyformaldehyde resin, so that the use safety of the instrument is ensured.
From the formula (9), in order to suppress the brownian diffusion of the aerosol particles having a small particle diameter, a gas having a large gas viscosity coefficient is selected as the sheath gas, and from the viewpoint of viscosity coefficient and economy, the present invention selects air which is filtered and does not contain particulate matter as the sheath gas.
As can be seen from equation (6), the maximum flow rate of the gas stream in the annular staging zone 1919 of the present invention is 399L/min, and for small particle size aerosol particles, the gas stream is sheathedGas flow rate Qc10L/min, aerosol flow QaIs 1L/min; taking sheath gas flow Q for large-particle aerosol particlesc1L/min, aerosol flow QaIs 0.1L/min.
As can be seen from equation (7), the highest electric field strength of the present invention is 35.68KV/cm, and in practice, the breakdown strength may be much lower than that calculated from equation (7), mainly due to defects in electrode alignment or surface finish during manufacturing, or the presence of excess moisture or volatile substances in the sampled aerosol. Currently, commercial DMA designs on the market do not exceed a maximum electric field strength of about 15KV/cm, and the present invention assumes the same limitations.
From the formula (8), the maximum voltage allowed by the present invention is 10.4KV, and the upper limit of the power supply voltage adopted by the present invention is 10 KV.
As shown in formula (5), the particle size of the aerosol particles which can be classified according to the present invention is in the range of 4nm to 1531 nm.
The invention has the beneficial effects that:
1. according to a formula for calculating the Brown diffusion coefficient of particles, from the viewpoint of inhibiting the Brown diffusion of small-particle-size aerosol particles, gas with a large gas viscosity coefficient is selected as sheath gas.
2. From the angle of numerical simulation, the distance from the bottom of the aerosol collecting slit to the top of the current limiting device 11 is determined to be 10mm, and the loss of aerosol particles caused by the uneven tail of an electric field in the DMA is avoided.
3. The invention calculates the flow of the maximum Reynolds number of the differential electromobility analyzer in the state of keeping laminar flow through theory, thereby determining the flow in actual working, filtering through 4 layers of 400-mesh nylon filter screens, and finally enabling the airflow in the annular classification area to be stable laminar flow through a bell mouth device.
4. The maximum voltage allowed by the invention is determined by calculating the highest electric field intensity which can be borne by the invention, and the safety of the instrument is improved.
5. The invention adopts different sheath gases and aerosol flow rates for aerosol particles with different particle sizes, thereby ensuring the improvement of the grading precision of the aerosol particles with small particle sizes and widening the grading range of the particle sizes.
6. The invention is connected by the screw and the thread, and is easy to disassemble and clean.
7. The inner electrode is hollow, light in weight and convenient to carry. The required flow is moderate, and a fan and a filter which have high requirements on the matching of high sheath gas flow are not needed.
The embodiments in the present description are described in a progressive manner, each embodiment focuses on differences from other embodiments, and the same and similar parts among the embodiments are referred to each other.
The principles and embodiments of the present invention have been described herein using specific examples, which are provided only to help understand the method and the core concept of the present invention; meanwhile, for a person skilled in the art, according to the idea of the present invention, the specific embodiments and the application range may be changed. In view of the above, the present disclosure should not be construed as limiting the invention.
Claims (10)
1. The differential electromigration-based aerosol particle grading device is characterized by comprising a sheath gas cavity, a nylon filter screen, an annular grading region, an aerosol cavity, an inner electrode, an outer electrode, an aerosol collecting slit, an aerosol collecting hole, an aerosol channel, a current limiting device, a residual cavity device and a residual gas outlet channel;
the nylon filter screen is arranged between the sheath gas cavity and the annular grading area, the sheath gas cavity, the nylon filter screen and the annular grading area are sequentially arranged from top to bottom, the aerosol cavity is arranged on the side wall of the annular grading area, the aerosol cavity is communicated with the annular grading area through an aerosol outlet slit, the outer electrode is an annular cylinder, the inner electrode is a cylinder, the outer electrode is arranged on the outer side of the inner electrode, an annular area between the outer electrode and the inner electrode is the annular grading area, and the outer electrode is positioned below the aerosol cavity;
the inner electrode comprises an upper half part of the inner electrode, an inner electrode connecting part and a lower half part of the inner electrode which are arranged from top to bottom in sequence; the upper half part of the inner electrode, the lower half part of the inner electrode and the inner electrode connecting part are coaxially arranged, the diameters of the upper half part of the inner electrode and the lower half part of the inner electrode are the same, the diameter of the inner electrode connecting part is smaller than that of the upper half part of the inner electrode, a slit between the upper half part of the inner electrode and the lower half part of the inner electrode is an aerosol collecting slit, and a plurality of aerosol collecting holes are horizontally arranged in the connecting part; one end of the aerosol collecting hole is communicated with the aerosol collecting slit, and the other end of the aerosol collecting hole is communicated with the aerosol channel; the inner electrode is connected with a power supply, and the outer electrode is grounded;
the current limiting device is arranged below the annular grading area, the current limiting device surrounds the outer side of the inner electrode, the upper part of the current limiting device is connected with the outer electrode, the lower part of the current limiting device is connected with the residual cavity device, and the residual gas outlet channel is connected with the residual cavity device;
the gas introduced into the sheath gas cavity is air without particles;
according to the relation between the particle size of the aerosol particles to be separated and the power supply voltage, the grading of the aerosol with different particle sizes is realized by controlling the sheath gas flow entering the sheath gas cavity and the gas flow flowing out of the residual gas outlet channel, and the gas flowing out of the residual gas outlet channel is the mixed gas of the sheath gas and the aerosol.
2. The differential electromigration-based aerosol particle classification device of claim 1, wherein the upper side of the flow limiting device is in threaded connection with the outer electrode, the lower side of the flow limiting device is in threaded connection with the remaining cavity device, and the vertical distance between the top of the flow limiting device and the aerosol collection hole is 10 mm; a plurality of through holes are uniformly distributed on the flow limiting device, one end of each through hole is communicated with the annular grading area, the other end of each through hole is communicated with the cavity in the rest cavity device, every two adjacent through holes form a group, the angle between every two through holes in each group is 15 degrees, the diameters of the through holes are the same, and the diameter of each through hole is 0.8 mm-1 mm; the residual cavity device surrounds the outer side of the inner electrode;
the material of the current limiting device and the material of the residual cavity device are polyformaldehyde resin.
3. The differential electromigration-based aerosol particle classification device of claim 1, wherein the outer radius of the inner electrode is 33mm, the inner portion of the upper half of the inner electrode is hollow, and the outer wall of the inner electrode and the inner wall of the outer electrode are both mirror surfaces.
4. The differential electromigration-based aerosol particle classification device of claim 1 further comprising two aerosol inlet channels symmetrically disposed on either side of the aerosol cavity;
the inner surface of the aerosol inlet passage is a polished surface.
5. The differential electromigration-based aerosol particle classification apparatus of claim 2 wherein the number of the residual gas outlet channels is 2, and 2 of the residual gas outlet channels are symmetrically disposed on both sides of the residual cavity apparatus.
6. The differential electromigration-based aerosol particle classification device of claim 1 further comprising a flare, a top, an aerosol cavity top and an aerosol cavity bottom, wherein the cavity between the aerosol cavity top and the aerosol cavity bottom is the aerosol cavity, the top is the sheath gas cavity housing, and the annular classification region is between the outer wall of the inner electrode and the inner wall of the outer electrode;
the bell mouth device is fixed below the top device through threads, the upper half part of the aerosol cavity is connected below the bell mouth device through threads, the upper half part of the aerosol cavity is connected with the lower half part of the aerosol cavity through threads, and the outer electrode is connected below the lower half part of the aerosol cavity through threads.
7. The differential electromigration-based aerosol particle classification device of claim 6 wherein the material of the bell mouth piece is aluminum alloy and the material of the top piece is polyoxymethylene resin.
8. The differential electromigration-based aerosol particle classification device of claim 1 further comprising a base disposed below the inner electrode, the base being made of a polyoxymethylene resin.
9. The differential electromigration-based aerosol particle classification device of claim 1, wherein an inner surface of the aerosol chamber is a polished surface.
10. The differential electromigration-based aerosol particle classification device of claim 1 wherein the aerosol collection slit has a vertical height of 1.59mm and the aerosol outlet slit has an axial width of 1.8 mm.
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