CN111122396A - Differential high-concentration particulate matter measuring system and method based on dynamic Faraday cup - Google Patents
Differential high-concentration particulate matter measuring system and method based on dynamic Faraday cup Download PDFInfo
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- 239000013618 particulate matter Substances 0.000 title claims abstract description 35
- 238000000034 method Methods 0.000 title claims abstract description 14
- 239000002245 particle Substances 0.000 claims abstract description 118
- 238000005259 measurement Methods 0.000 claims abstract description 33
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- 238000007664 blowing Methods 0.000 claims description 11
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- 239000013589 supplement Substances 0.000 claims description 7
- 229910001220 stainless steel Inorganic materials 0.000 claims description 4
- 239000010935 stainless steel Substances 0.000 claims description 4
- RYGMFSIKBFXOCR-UHFFFAOYSA-N Copper Chemical compound [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 claims description 3
- 239000004696 Poly ether ether ketone Substances 0.000 claims description 3
- 229910052802 copper Inorganic materials 0.000 claims description 3
- 239000010949 copper Substances 0.000 claims description 3
- 229920002530 polyetherether ketone Polymers 0.000 claims description 3
- WFKWXMTUELFFGS-UHFFFAOYSA-N tungsten Chemical compound [W] WFKWXMTUELFFGS-UHFFFAOYSA-N 0.000 claims description 3
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- 238000009792 diffusion process Methods 0.000 description 7
- 238000005516 engineering process Methods 0.000 description 6
- 150000002500 ions Chemical class 0.000 description 6
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- 239000011882 ultra-fine particle Substances 0.000 description 4
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Abstract
The invention relates to a differential high-concentration particulate matter measuring system and method based on a dynamic Faraday cup. The measuring system comprises a first dynamic Faraday cup and a second dynamic Faraday cup. The dynamic Faraday cup comprises a first unipolar charge device, a first electromigration classifier and a first shielding box covering the first unipolar charge device and the first electromigration classifier. The second dynamic Faraday cup comprises a second unipolar charge device, a second electromigration classifier and a second shielding box which covers the second unipolar charge device and the second electromigration classifier. The measuring system and the measuring method can solve the defects in the prior art, meet the continuous measurement of high-concentration particles, accurately invert the measurement of the number concentration and the median diameter of the particles, effectively eliminate system errors and ensure the measuring precision.
Description
Technical Field
The invention relates to the technical field of high-concentration particulate matter number concentration and median diameter measurement, in particular to a differential high-concentration particulate matter measurement system and method based on a dynamic Faraday cup.
Background
Aiming at the emission of high-temperature and high-concentration particulate matters of combustion sources such as diesel vehicles, engineering machinery, coal-fired power plants and the like, the traditional method firstly dilutes the high-concentration particulate matters and then carries out measurement, two measurement technologies at the rear end are divided into two types, one type is that the particulate matters to be measured enter a condensation growth chamber through a condensation counting technology, enter an optical measurement chamber after growing up, and invert the concentration value of the particulate matters through the light scattering intensity of the particulate matters; the other type is that through a diffusion charging technology, particles to be measured enter a charging chamber to charge the particles, and then a filter screen collects the charged particles to measure the current value of the particles; the main defects of the condensation counting technology are that the concentration of the particles cannot be higher than 1E6#/cm3, the particles with high concentration must be diluted to be measured, and the median particle size of the particles cannot be obtained by the technology. Although the diffusion charge technology is improved in the measurement range of the particulate matter concentration, the collection filter screen for measuring the charge quantity of the particulate matter at the rear end is easy to block in the measurement of the particulate matter with high concentration, the continuous measurement is not suitable, and the maintenance period is short.
Disclosure of Invention
The invention aims to provide a differential high-concentration particulate matter measuring system and method based on a dynamic Faraday cup, which can solve the defects in the prior art, meet the continuous measurement of high-concentration particulate matters, accurately invert the measurement of the number concentration and the median diameter of the particulate matters, effectively eliminate system errors and ensure the measuring precision.
In order to achieve the purpose, the invention adopts the following technical scheme:
the invention relates to a differential high-concentration particulate matter measuring system based on a dynamic Faraday cup.
Specifically, the first dynamic Faraday cup comprises a first unipolar charge device, a first electromigration classifier and a first shielding box covering the outer sides of the first unipolar charge device and the first electromigration classifier; the shielding box comprises a horizontally arranged shielding cavity I and a shielding cavity II which is arranged above the left end of the shielding cavity I and communicated with the shielding cavity I; the unipolar charge device I comprises a unipolar charge device shell I and a discharge shell I which are sequentially arranged in a shielding cavity I from left to right, an insulation sleeve I with the right end fixed on the inner side of the right end of the shielding cavity I and the left end extending into the discharge shell I, a high-voltage electrode I with the right end embedded and installed in the insulation sleeve I and the left end extending into the inner cavity of the discharge shell I, and a discharge needle I with the right end embedded and installed at the left end of the high-voltage electrode I and the left end extending out of the left end of the discharge shell I; the inner cavity of the first unipolar charger shell is communicated with the inner cavity of the first discharge shell; the left end of the first discharge shell is fixed at the inner side of the right end of the first unipolar charger shell; the electromigration classifier I comprises an insulation sleeve II, an electromigration classifier shell I and a trapping electrode I, wherein the upper end of the insulation sleeve II is fixed on the inner side of the upper end of the shielding cavity II, the upper end of the electromigration classifier shell I is fixed on the inner wall of the shielding cavity II, the upper end of the electromigration classifier shell I is sleeved outside the lower end of the insulation sleeve II, the lower end of the electromigration classifier shell I is connected with the unipolar charge device shell I, and the upper end of the electromigration classifier shell I is embedded in the insulation sleeve II, and the lower end of the; a first gas outlet communicated with the inside of the first electromigration classifier shell is arranged on the first electromigration classifier shell; the left end of the shielding cavity I is provided with a sample gas inlet I communicated with the interior of the unipolar charger shell I; and a first clean air inlet communicated with the inside of the first discharge shell is formed below the right end of the first shielding cavity.
The second dynamic Faraday cup comprises a second unipolar charge device, a second electromigration classifier and a second shielding box which covers the second unipolar charge device and the second electromigration classifier; the shielding box comprises a horizontally arranged shielding cavity III and a shielding cavity IV which is arranged below the left end of the shielding cavity III and is communicated with the shielding cavity III; the unipolar charge device II comprises a unipolar charge device shell II and a discharge shell II which are sequentially arranged in a shielding cavity III from left to right, an insulating sleeve III with the right end fixed on the inner side of the right end of the shielding cavity III and the left end extending into the discharge shell II, a high-voltage electrode II with the right end embedded and installed in the insulating sleeve III and the left end extending into the inner cavity of the discharge shell II, and a discharge needle II with the right end embedded and installed at the left end of the high-voltage electrode II and the left end extending out of the left end of the discharge shell II; the inner cavity of the second unipolar charger shell is communicated with the inner cavity of the second discharge shell; the left end of the discharge shell II is fixed at the inner side of the right end of the unipolar charger shell II; the second electromigration classifier comprises an insulation sleeve IV, an electromigration classifier shell II and a collecting electrode II, wherein the upper end of the insulation sleeve IV is fixed on the inner side of the lower end of the shielding cavity IV, the lower end of the electromigration classifier shell II is fixed on the inner wall of the shielding cavity IV and is sleeved outside the upper end of the insulation sleeve IV, the upper end of the electromigration classifier shell II is connected with the unipolar current-carrying device shell II, and the lower end of the electromigration classifier shell II is embedded in the insulation sleeve IV, and the upper end of the electromigration classifier shell II extends upwards; a second gas outlet communicated with the inside of the second electromigration classifier shell is arranged on the second electromigration classifier shell; the left end of the shielding cavity III is provided with a sample gas inlet II communicated with the interior of the unipolar charger shell II; and a second clean air inlet communicated with the inside of the second discharge shell is formed above the right end of the third shielding cavity.
And a shielding pipe is connected between the first clean air inlet and the second clean air inlet, and a main clean air inlet communicated with the inside of the shielding pipe, the first clean air inlet and the second clean air inlet is arranged on the shielding pipe.
Further, the first gas outlet and the second gas outlet are both connected with an air suction pump; the clean air main inlet is connected with a blowing pump.
Furthermore, the first shielding box, the second shielding box and the shielding pipe are all solid, and the first shielding box, the second shielding box and the shielding pipe are all made of stainless steel.
Furthermore, the first unipolar charger shell, the second unipolar charger shell, the first discharge shell, the second discharge shell, the first electromigration classifier shell and the second electromigration classifier shell are all connected with a virtual ground.
Furthermore, the collecting electrode I, the collecting electrode II, the high-voltage electrode I and the high-voltage electrode II are made of copper materials.
Furthermore, the first insulating sleeve, the second insulating sleeve, the third insulating sleeve and the fourth insulating sleeve are all made of polyether-ether-ketone materials.
Furthermore, the first discharge needle and the second discharge needle are both made of tungsten.
Furthermore, the measuring system also comprises a micro-current signal detecting unit I for detecting the induced current in the first dynamic Faraday cup and a micro-current signal detecting unit II for detecting the induced current in the second dynamic Faraday cup.
Furthermore, the first unipolar charger and the second unipolar charger are both powered by high-voltage sources; the first electromigration classifier and the second electromigration classifier both adopt linear power supplies for power supply; the collecting electrode I is connected with the linear power supply I, and the collecting electrode II is connected with the linear power supply II; the high-voltage electrode I is connected with a high-voltage source I, and the high-voltage electrode II is connected with a high-voltage source II; and the grounding electrodes of the first linear power supply, the second linear power supply, the first high-voltage power supply and the second high-voltage power supply are all connected with virtual ground.
The measuring system integrates the unipolar diffusion charging device and the electromigration classifier into the Faraday cup to form a dynamic Faraday cup, and can effectively overcome the interference of the outside on current signals in the Faraday cup. After the sample gas flows into the dynamic Faraday cup, the particulate matters firstly pass through the unipolar diffusion charging device and collide with free ions generated by ionizing clean air by the discharge needles to charge the particulate matters; free ions and charged particles with a certain particle size below can be removed through an electromigration classifier; eventually the non-trapped charged particulates flow out of the dynamic faraday cup. Because the particulate matter takes away the electric charge and makes the inside electric charge of whole dynamic Faraday cup reduce, can produce the electric charge of induction charge replenishment reduction, and then produce induced current. The measuring system is suitable for continuous long-time measurement of high-concentration particles, and can simultaneously measure the number concentration and the median particle size of the particles.
The invention also relates to a method of the above measuring system, comprising the steps of:
(1) setting the voltage of a linear power supply I connected with a trapping electrode I as V1, and the voltage of a linear power supply II connected with a trapping electrode II as V2, wherein V1 is not equal to V2; namely the trapping voltage accessed by the trapping electrode I is V1, and the trapping voltage accessed by the trapping electrode II is V2; the first high-voltage electrode is connected with a first high-voltage source, and the second high-voltage electrode is connected with a second high-voltage source. V1 and V2 are obtained through system calibration, when the trapping voltage connected to the trapping electrode I is V1, only free charges are trapped by the trapping electrode I, and all charged particulate matters flow out of the sample gas outlet I along with the gas flow; when the trapping voltage applied to the second trapping electrode is V2, the free charges and part of the charged particulate matter (charged particulate matter having a particle size smaller than a certain particle size) are trapped by the second trapping electrode.
(2) Under the action of the air suction pump and the air blowing pump, sample gas enters an inner cavity of the first unipolar charger shell and an inner cavity of the second unipolar charger shell from the first sample gas inlet and the second sample gas inlet respectively; clean air enters the shielding tube from the clean air main inlet, and then enters the inner cavity of the first discharge shell and the inner cavity of the second discharge shell through the clean air inlet I and the clean air inlet II respectively.
Under the action of an air suction pump and an air blowing pump, clean air entering an inner cavity of a first discharge shell flows leftwards, and when the clean air passes through a first discharge needle, the clean air is discharged from the tip of the first discharge needle connected with a first high-voltage electrode connected with a first high-voltage source to ionize part of the clean air to generate free charges; when the free charges continuously flow leftwards along with the unionized clean air, the free charges collide with particles in the sample gas entering the inner cavity of the first unipolar charger shell, and part of the free charges are adhered to the particles so as to charge the particles; charged particles and free charges which are not trapped by the particles enter an inner cavity of a first electromigration classifier shell along with airflow, a first trapping electric field is formed between a first trapping electrode connected to a first linear power supply and a first electromigration classifier shell connected to virtual ground, all the free charges which are not adhered by the particles are adsorbed to the first trapping electrode under the action of the first trapping electric field, and all the charged particles flow out from a first gas outlet along with the airflow.
(4) Under the action of the air suction pump and the air blowing pump, clean air entering the inner cavity of the second discharge shell flows leftwards, and when the clean air passes through the second discharge needle, the clean air is discharged from the tip of the second discharge needle connected with the second high-voltage electrode connected with the second high-voltage source, so that part of the clean air is ionized to generate free charges; when the free charges continuously flow leftwards along with the unionized clean air, the free charges collide with particles in the sample gas entering the inner cavity of the unipolar charger shell II, and part of the free charges are adhered to the particles so as to charge the particles; charged particles and free charges which are not trapped by the particles can enter an inner cavity of the second electromigration classifier shell along with the airflow, a second trapping electric field is formed between a second trapping electrode connected to the second linear power supply and the second electromigration classifier shell connected to virtual ground, all the free charges which are not adhered by the particles and charges on part of the charged particles are adsorbed to the second trapping electrode under the action of the second trapping electric field, and the rest charged particles and the particles without charges lost flow out of the second gas outlet along with the airflow.
(5) The first dynamic Faraday cup shell connected with the virtual ground can generate induced charges to supplement the reduced charge quantity in the first dynamic Faraday cup shell, so that the flow of the induced charges is generated between the first dynamic Faraday cup shell and the first shielding box to form induced currents, and the induced currents are collected and set as I1。
A cavity formed by enclosing the unipolar charger shell II, the electromigration classifier shell II and the discharge shell II is a dynamic Faraday cup shell II, the charged particles flowing out of the gas outlet II can reduce the charges in the dynamic Faraday cup II, the dynamic Faraday cup shell II connected with the virtual ground can generate induced charges to supplement the reduced charges in the dynamic Faraday cup II, so that the induced charges flow between the dynamic Faraday cup shell II and the shielding box II to form induced currents, and the induced currents are collected and set as I2。
(6) Using formula I1-I2And (4) solving the total number concentration N of the particulate matters as AN, wherein A is a system calibration value.
(7) Using a formula
Finding the median particle diameter D of the particlespWhere c is the system calibration value and e is the element charge (1.6X 10)-19C)。
According to the technical scheme, the two dynamic Faraday cups are used for carrying out differential measurement on the atmospheric particulate matters, induced current signals generated by the flow of induced charges between the dynamic Faraday cup shells of the two dynamic Faraday cups and the shielding box are monitored in real time, and the measured induced current signals of the two dynamic Faraday cups are subjected to differential operation, so that the accurate measurement of the number concentration and the median diameter of the high-concentration particulate matters can be realized. The invention adopts a non-collection measurement mode, does not block a measurement system, and can meet the continuous measurement of high-concentration particles. The invention adopts two dynamic Faraday cups to carry out differential measurement, can effectively eliminate system errors, ensures the measurement precision and accurately invert the number concentration and the median diameter of particulate matters.
Drawings
FIG. 1 is a schematic block diagram of a measurement system of the present invention;
FIG. 2 is a schematic diagram of the structure of the measuring system of the present invention;
fig. 3 is a schematic diagram of the operation of the first dynamic faraday cup of the present invention.
Wherein:
1. the device comprises a sample gas main inlet 2, a sample gas inlet I, a sample gas outlet I, an insulating sleeve II, a sample gas outlet II, a shielding box I, a shielding box 6, a collecting electrode I, a shielding box 7, an electromigration classifier shell I, a unipolar charge device shell I, a high-voltage electrode I, a discharge shell I, a discharge sleeve I, a clean air inlet II.
Detailed Description
The invention is further described below with reference to the accompanying drawings:
the invention relates to a differential high-concentration particulate matter measuring system based on a dynamic Faraday cup, which comprises a first dynamic Faraday cup and a second dynamic Faraday cup. The invention combines the unipolar charger and the electromigration classifier together to form a dynamic Faraday cup structure, and the electromigration classifier II only collects the charges in part of the charged particles to lose the charges, so that the particles are not left in the whole dynamic Faraday cup II, thereby meeting the long-term continuous measurement of high-concentration particles.
Specifically, the first dynamic faraday cup comprises a first unipolar charger, a first electromigration classifier and a first shielding box 5 which covers the first unipolar charger and the first electromigration classifier. The shielding box I5 comprises a shielding cavity I and a shielding cavity II, wherein the shielding cavity I is horizontally arranged, and the shielding cavity II is arranged above the left end of the shielding cavity I and communicated with the shielding cavity I. The unipolar charge ware one includes unipolar charge ware casing 8 and discharge casing 11 that sets gradually in shielding chamber one from left hand right side, right-hand member fix the right-hand member of shielding chamber one inboard and the left end stretch into the insulation sleeve 12 in discharge casing 11, the right-hand member embedding is installed in insulation sleeve 12 and the left end stretches into the high voltage electrode 10 in discharge casing 11 inner chamber and the right end embedding is installed in the left end portion of high voltage electrode 10 and the discharge needle 9 that the left end stretches out from the left end of discharge casing 11. The inner cavity of the unipolar charger shell I8 is communicated with the inner cavity of the discharge shell I11. The left end of the discharge casing I11 is fixed on the inner side of the right end of the unipolar charger casing I8. The electromigration classifier I comprises an insulation sleeve II 4, an electromigration classifier shell I7 and a trapping electrode I6, wherein the upper end of the insulation sleeve II 4 is fixed on the inner side of the upper end of the shielding cavity II, the upper end of the electromigration classifier shell I is fixed on the inner wall of the shielding cavity II, the upper end of the electromigration classifier shell I is sleeved outside the lower end of the insulation sleeve II 4, the lower end of the electromigration classifier shell I is connected with a unipolar current-carrying device shell I8, the upper end of the electromigration classifier shell I is embedded in the insulation sleeve II 4, and the lower end of; and a first gas outlet 3 communicated with the inside of the first electromigration classifier shell 7 is arranged on the first electromigration classifier shell 7. And the left end of the shielding cavity I is provided with a sample gas inlet I2 communicated with the inside of a unipolar charger shell I8. And a first clean air inlet 13 communicated with the inside of the first discharge shell 11 is formed below the right end of the first shielding cavity.
The second dynamic Faraday cup comprises a second unipolar charge device, a second electromigration classifier and a second shielding box which covers the second unipolar charge device and the second electromigration classifier; the second shielding box 22 comprises a third shielding cavity and a fourth shielding cavity, wherein the third shielding cavity is horizontally arranged, and the fourth shielding cavity is arranged below the left end of the third shielding cavity and is communicated with the three phases of the shielding cavities. The unipolar charge device II comprises a unipolar charge device shell II 20 and a discharge shell II 18 which are sequentially arranged in a shielding cavity III from left to right, an insulating sleeve III 16 with the right end fixed on the inner side of the right end of the shielding cavity III and the left end extending into the discharge shell II 18, a high-voltage electrode II 17 with the right end embedded in the insulating sleeve III 16 and the left end extending into the inner cavity of the discharge shell II 18, and a discharge needle II 19 with the right end embedded in the left end of the high-voltage electrode II 17 and the left end extending out of the left end of the discharge shell II 18; the second unipolar charger shell 20 is communicated with the inner cavity of the second discharge shell 18; the left end of the discharge shell II 18 is fixed at the inner side of the right end of the unipolar charger shell II 20; the electromigration classifier II comprises an insulation sleeve IV 23, an electromigration classifier shell II 27 and a collecting electrode II 21, wherein the upper end of the insulation sleeve IV 23 is fixed on the inner side of the lower end of the shielding cavity IV, the lower end of the electromigration classifier shell II is fixed on the inner wall of the shielding cavity IV, the lower end of the electromigration classifier shell II is sleeved outside the upper end of the insulation sleeve IV 23, the upper end of the electromigration classifier shell II is connected with the unipolar current-carrying device shell II 20, the lower end of the electromigration classifier shell II is embedded in the insulation sleeve IV 23, and the upper end; a second gas outlet 24 communicated with the interior of the second electromigration classifier shell 27 is arranged on the second electromigration classifier shell 27; the left end of the shielding cavity III is provided with a sample gas inlet II 25 communicated with the interior of the unipolar charger shell II 20; and a second clean air inlet 15 communicated with the inside of the second discharge shell 18 is formed above the right end of the third shielding cavity.
The measuring system also comprises a sample gas main inlet 1 which is respectively communicated with the sample gas inlet I2 and the sample gas inlet II 25.
A shielding pipe 26 is connected between the first clean air inlet 13 and the second clean air inlet 15, and a total clean air inlet 14 communicated with the interior of the shielding pipe 26, the first clean air inlet 13 and the second clean air inlet 15 is installed on the shielding pipe 26.
Further, the first gas outlet 3 and the second gas outlet 24 are both connected with an air suction pump; the clean air inlet 14 is connected to a blower pump.
Furthermore, the first shielding box 5, the second shielding box 22 and the shielding pipe 26 are all solid, and the first shielding box 5, the second shielding box 22 and the shielding pipe 26 are all made of stainless steel materials
Further, the first unipolar charger housing 8, the second unipolar charger housing 20, the first discharge housing 11, the second discharge housing 18, the first electromigration classifier housing 7 and the second electromigration classifier housing 27 are all connected to virtual ground, and specifically, ground electrodes of the first linear power supply, the second linear power supply, the first high voltage supply and the second high voltage supply are all connected to virtual ground. The first unipolar charger shell 8 is connected with the grounding electrode of the first high-voltage source, the second unipolar charger shell 20 is connected with the grounding electrode of the second high-voltage source, the first discharge shell 11 is connected with the grounding electrode of the first linear power supply, and the second discharge shell 18 is connected with the grounding electrode of the second linear power supply.
Furthermore, the first collecting electrode 6, the second collecting electrode 21, the first high-voltage electrode 10 and the second high-voltage electrode 17 are made of copper materials.
Further, the first insulating sleeve 12, the second insulating sleeve 4, the third insulating sleeve 16 and the fourth insulating sleeve 23 are all made of polyether ether ketone.
Furthermore, the first discharge needle 9 and the second discharge needle 19 are made of tungsten.
Furthermore, the measuring system also comprises a micro-current signal detecting unit I for detecting the induced current in the first dynamic Faraday cup and a micro-current signal detecting unit II for detecting the induced current in the second dynamic Faraday cup. The first micro-current signal detection unit and the second micro-current signal detection unit both adopt a micro-ammeter. A cavity surrounded by the first unipolar charger shell, the first electromigration classifier shell and the first discharge shell is a first dynamic Faraday cup shell; and a cavity surrounded by the unipolar charger shell II, the electromigration classifier shell II and the discharge shell II is a dynamic Faraday cup shell II. The first micro-current signal detection unit is used for measuring induced current flowing between the first dynamic Faraday cup shell and the first shielding box; and the second micro-current signal detection unit is used for measuring the induced current flowing between the second dynamic Faraday cup and the second shielding box.
Furthermore, the first unipolar charger and the second unipolar charger are both powered by high-voltage sources. And the first electromigration classifier and the second electromigration classifier both adopt a linear power supply for supplying power. The first collecting electrode 6 is connected with a first linear power supply, and the second collecting electrode 21 is connected with a second linear power supply. The first high-voltage electrode 10 is connected with the first high-voltage source, and the second high-voltage electrode 17 is connected with the second high-voltage source. The first unipolar charger and the second unipolar charger are both unipolar diffusion chargers.
When the measuring system works, the sample gas is divided into two paths and enters the first dynamic Faraday cup and the second dynamic Faraday cup in parallel. The two dynamic faraday cups are identical except that the voltage of the linear power supply connected to the collecting electrode is different. To better describe the working principle of the system, taking a dynamic faraday cup as an example, as shown in fig. 1-3, a sample gas flows into the dynamic faraday cup from a sample gas inlet one 2, particles in the sample gas firstly enter a unipolar charger one, a high-voltage electrode one 10 in the unipolar diffusion charger one is connected with a high-voltage source one, and after the high-voltage source one is connected, a discharge needle one 9 connected with the high-voltage electrode one 10 discharges to generate a large amount of free charges. Part of the particles in the sample gas collide with free charges, and the free charges are adsorbed on part of the particles, so that part of the particles are charged. Under the action of the airflow, free charges, charged particles and uncharged particles enter the first electromigration classifier. A first collecting electrode 6 in the first electromigration classifier is connected with a first linear power supply, and after the first linear power supply is connected, the first collecting electrode 6 can adsorb free ions and charged particles with particle sizes below a certain specific particle size. Eventually, the uncaptured free ions, charged particulate matter, anduncharged particles flow out of the dynamic faraday cup. In the process, the charge inside the first dynamic faraday cup is taken away by the charged particles and the free ions, so that the charge inside the first dynamic faraday cup is reduced, induced charge is generated on the first dynamic faraday cup (namely virtual ground) to supplement the reduced charge inside the first dynamic faraday cup, and the induced charge flows to generate induced current. The grounding electrodes of the high voltage source and the linear power supply for supplying power to the unipolar diffusion charge device I and the electromigration classifier I are connected with virtual ground, one end of the micro-current signal detection unit I is connected with virtual ground, and the other end of the micro-current signal detection unit I is grounded and is used for monitoring an induced current value I caused by the fact that charges are carried away by particles entering and exiting the dynamic Faraday cup in real time1. The stability of discharge is controlled by controlling the output voltage of the first high-voltage source, and the stability of the concentration of free charges in the first unipolar charger is further ensured.
And the trapping electrodes I and II of the first electro-migration classifier and the second electro-migration classifier are respectively connected with different trapping voltages to control the trapping lower limits of different particle sizes. The constant temperature control circuit is adopted to carry out constant temperature control on the whole measuring system, and the sample gas is ensured not to generate new nuclear mode particles in the measuring system. Because the micro-current signal is easily influenced by temperature and external signals, the stainless steel shell is adopted to encapsulate the first micro-current signal detection unit and the second micro-current signal detection unit for electromagnetic shielding, and the constant temperature control circuit is adopted to carry out constant temperature control on the two micro-current signal detection units, so that the accuracy of micro-current signal measurement is ensured.
The invention also relates to a method of the measuring system, which comprises the following steps:
(1) setting the voltage of a linear power supply I connected with a trapping electrode I as V1, and the voltage of a linear power supply II connected with a trapping electrode II as V2, wherein V1 is not equal to V2; namely the trapping voltage accessed by the trapping electrode I is V1, and the trapping voltage accessed by the trapping electrode II is V2; the first high-voltage electrode is connected with a first high-voltage source, and the second high-voltage electrode is connected with a second high-voltage source. V1 and V2 are obtained through calibration, when the trapping voltage connected to the trapping electrode I is V1, the trapping electrode I traps only free charges, and all charged particulate matters flow out of the sample gas outlet I along with the gas flow; when the trapping voltage applied to the second trapping electrode is V2, the free charges and part of the charged particulate matter (charged particulate matter having a particle size smaller than a certain particle size) are trapped by the second trapping electrode.
The trapping voltage connected to the trapping electrode is set as above, so that the trapping electrode I in the first dynamic Faraday cup can trap free charges, and the interference of the free charges on the actually measured particulate matter charge amount is eliminated; the setting of V2 can correct the current value measured after the setting of V1, and can eliminate the system error; it is also possible to calculate the median particle diameter of the particulate matter by setting the two trapping voltages to appropriate values.
(2) Under the action of the air suction pump and the air blowing pump, sample gas enters an inner cavity of the first unipolar charger shell and an inner cavity of the second unipolar charger shell from the first sample gas inlet and the second sample gas inlet respectively; clean air enters the shielding tube from the clean air main inlet, and then enters the inner cavity of the first discharge shell and the inner cavity of the second discharge shell through the clean air inlet I and the clean air inlet II respectively.
Under the action of an air suction pump and an air blowing pump, clean air entering an inner cavity of a first discharge shell flows leftwards, and when the clean air passes through a first discharge needle, the clean air is discharged from the tip of the first discharge needle connected with a first high-voltage electrode connected with a first high-voltage source to ionize part of the clean air to generate free charges; when the free charges continuously flow leftwards along with the unionized clean air, the free charges collide with particles in the sample gas entering the inner cavity of the first unipolar charger shell, and part of the free charges are adhered to the particles so as to charge the particles; charged particles and free charges which are not trapped by the particles enter an inner cavity of a first electromigration classifier shell along with airflow, a first trapping electric field is formed between a first trapping electrode connected to a first linear power supply and a first electromigration classifier shell connected to virtual ground, all the free charges which are not adhered by the particles are adsorbed to the first trapping electrode under the action of the first trapping electric field, and all the charged particles flow out from a first gas outlet along with the airflow.
(4) Under the action of the air suction pump and the air blowing pump, clean air entering the inner cavity of the second discharge shell flows leftwards, and when the clean air passes through the second discharge needle, the clean air is discharged from the tip of the second discharge needle connected with the second high-voltage electrode connected with the second high-voltage source, so that part of the clean air is ionized to generate free charges; when the free charges continuously flow leftwards along with the unionized clean air, the free charges collide with particles in the sample gas entering the inner cavity of the unipolar charger shell II, and part of the free charges are adhered to the particles so as to charge the particles; charged particles and free charges which are not trapped by the particles can enter an inner cavity of the second electromigration classifier shell along with the airflow, a second trapping electric field is formed between a second trapping electrode connected to the second linear power supply and the second electromigration classifier shell connected to virtual ground, all the free charges which are not adhered by the particles and charges on part of the charged particles are adsorbed to the second trapping electrode under the action of the second trapping electric field, and the rest charged particles and the particles without charges lost flow out of the second gas outlet along with the airflow.
(5) The first dynamic Faraday cup shell connected with the virtual ground can generate induced charges to supplement the reduced charge quantity in the first dynamic Faraday cup shell, so that the flow of the induced charges is generated between the first dynamic Faraday cup shell and the first shielding box to form induced currents, and the induced currents are collected and set as I1。
A cavity formed by enclosing the unipolar charger shell II, the electromigration classifier shell II and the discharge shell II is a dynamic Faraday cup shell II, the charged particles flowing out of the gas outlet II can reduce the charges in the dynamic Faraday cup II, the dynamic Faraday cup shell II connected with the virtual ground can generate induced charges to supplement the reduced charges in the dynamic Faraday cup II, so that the induced charges flow between the dynamic Faraday cup shell II and the shielding box II to form induced currents, and the induced currents are collected and set as I2。
(6) Using formula I1-I2And (4) solving the total number concentration N of the particulate matters as AN, wherein A is a system calibration value.
(7) Using a formula
Finding the median particle diameter D of the particlespWhere c is the system calibration value and e is the element charge (1.6X 10)-19C)。
The design principle of the measuring method is as follows:
after the particles in the sample gas pass through the unipolar charger, the average charge carried by the particles
And its particle diameter DpApproximately proportional, satisfying the relation (1):
when the trapping voltages of the first electromigration classifier and the second electromigration classifier are respectively set to be V1 and V2, the currents I measured by the first micro-current detection unit and the second micro-current detection unit1And I2The following formula is satisfied:
wherein n is the charged number of the particles, and e is the elementary charge (1.6 × 10)-19C)，Pn(Niontr，Dp) Is a particle diameter of DpIn the presence of NionIs staying in the environment of (t)rProbability of n ions after time, fn(Dp,V2) To trap a voltage of V2When the particle diameter is DpThe probability of losing charge after the particle deflection strikes the electromigration classifier two, N (D)p) Is a granuleDiameter of DpThe number concentration of the particulate matter of (a).
According to the theory of electromigration, fn(Dp,V2) The following relation is satisfied:
wherein, CcThe Canning index, η is the air viscosity, L is the length of the electromigration region, d is the inner diameter of the electromigration region, and v is the average particle velocity.
For polydisperse particles, the total number concentration of particles N is:
the current difference value measured by the two micro-current signal detection units satisfies the following relational expression:
the difference value I of the currents measured by the two micro-current signal detection units can be seen from the formula (5) and the formula (6)1-I2Proportional to the number concentration of particulate matter N, so:
I1-I2＝AN (7)
with the combination of the formula (5), the current value of the particulate matter detected by the first micro-current signal detection unit and the median diameter of the particulate matter satisfy the following relation:
I1＝ceNDp(8)
from equations (7) and (8), the median particle size of the particulate matter is:
wherein, the parameters A and c are system calibration values and can be obtained through a system calibration experiment.
According to the charge characteristics of the particles and the micro-electric quantity information obtained by classification detection, a particle size inversion algorithm of high-precision ultrafine particles is researched, and the method is a key step for finally realizing the particle size spectrum measurement of the ultrafine particles. Firstly, based on a standard monodisperse particulate matter generating source, carrying out high-temperature ultrafine particulate matter charging, grading and calibration experiments of a micro-current detection module. Through a high-temperature ultrafine particle charging calibration experiment, key charging parameters such as charge distribution, average charging number and charging efficiency of ultrafine particles with different particle sizes can be obtained; secondly, obtaining a corresponding relation between the particle size of the charged particles and the grading voltage of the electromigration classifier based on a particle size grading calibration experiment of a standard monodisperse source; and thirdly, calibrating and measuring the detection efficiency of the Faraday cup and the micro-current signal detection unit. Finally, after the series of calibration experiments are completed to obtain performance parameters of each module, the charge efficiency, the average charge number, the particle size grading voltage and the detection efficiency of the particles are obtained, and the value of the number concentration and the median particle size of the particles can be obtained by combining the quantitative function relationship between the difference value of the inlet current and the outlet current of the dynamic Faraday cup and the number concentration of the particles.
The above-mentioned embodiments are merely illustrative of the preferred embodiments of the present invention, and do not limit the scope of the present invention, and various modifications and improvements of the technical solution of the present invention by those skilled in the art should fall within the protection scope defined by the claims of the present invention without departing from the spirit of the present invention.
Claims (9)
1. Differential formula high concentration particulate matter measurement system based on developments Faraday cup, its characterized in that: comprises a first dynamic Faraday cup and a second dynamic Faraday cup;
the dynamic Faraday cup comprises a first unipolar charge device, a first electromigration classifier and a first shielding box covering the outer sides of the first unipolar charge device and the first electromigration classifier; the shielding box comprises a horizontally arranged shielding cavity I and a shielding cavity II which is arranged above the left end of the shielding cavity I and communicated with the shielding cavity I; the unipolar charge device I comprises a unipolar charge device shell I and a discharge shell I which are sequentially arranged in a shielding cavity I from left to right, an insulation sleeve I with the right end fixed on the inner side of the right end of the shielding cavity I and the left end extending into the discharge shell I, a high-voltage electrode I with the right end embedded and installed in the insulation sleeve I and the left end extending into the inner cavity of the discharge shell I, and a discharge needle I with the right end embedded and installed at the left end of the high-voltage electrode I and the left end extending out of the left end of the discharge shell I; the inner cavity of the first unipolar charger shell is communicated with the inner cavity of the first discharge shell; the left end of the first discharge shell is fixed at the inner side of the right end of the first unipolar charger shell; the electromigration classifier I comprises an insulation sleeve II, an electromigration classifier shell I and a trapping electrode I, wherein the upper end of the insulation sleeve II is fixed on the inner side of the upper end of the shielding cavity II, the upper end of the electromigration classifier shell I is fixed on the inner wall of the shielding cavity II, the upper end of the electromigration classifier shell I is sleeved outside the lower end of the insulation sleeve II, the lower end of the electromigration classifier shell I is connected with the unipolar charge device shell I, and the upper end of the electromigration classifier shell I is embedded in the insulation sleeve II, and the lower end of the; a first gas outlet communicated with the inside of the first electromigration classifier shell is arranged on the first electromigration classifier shell; the left end of the shielding cavity I is provided with a sample gas inlet I communicated with the interior of the unipolar charger shell I; a first clean air inlet communicated with the inside of the first discharge shell is formed below the right end of the first shielding cavity;
the second dynamic Faraday cup comprises a second unipolar charge device, a second electromigration classifier and a second shielding box which covers the second unipolar charge device and the second electromigration classifier; the shielding box comprises a horizontally arranged shielding cavity III and a shielding cavity IV which is arranged below the left end of the shielding cavity III and is communicated with the shielding cavity III; the unipolar charge device II comprises a unipolar charge device shell II and a discharge shell II which are sequentially arranged in a shielding cavity III from left to right, an insulating sleeve III with the right end fixed on the inner side of the right end of the shielding cavity III and the left end extending into the discharge shell II, a high-voltage electrode II with the right end embedded and installed in the insulating sleeve III and the left end extending into the inner cavity of the discharge shell II, and a discharge needle II with the right end embedded and installed at the left end of the high-voltage electrode II and the left end extending out of the left end of the discharge shell II; the inner cavity of the second unipolar charger shell is communicated with the inner cavity of the second discharge shell; the left end of the discharge shell II is fixed at the inner side of the right end of the unipolar charger shell II; the second electromigration classifier comprises an insulation sleeve IV, an electromigration classifier shell II and a collecting electrode II, wherein the upper end of the insulation sleeve IV is fixed on the inner side of the lower end of the shielding cavity IV, the lower end of the electromigration classifier shell II is fixed on the inner wall of the shielding cavity IV and is sleeved outside the upper end of the insulation sleeve IV, the upper end of the electromigration classifier shell II is connected with the unipolar current-carrying device shell II, and the lower end of the electromigration classifier shell II is embedded in the insulation sleeve IV, and the upper end of the electromigration classifier shell II extends upwards; a second gas outlet communicated with the inside of the second electromigration classifier shell is arranged on the second electromigration classifier shell; the left end of the shielding cavity III is provided with a sample gas inlet II communicated with the interior of the unipolar charger shell II; a second clean air inlet communicated with the inside of the second discharge shell is formed above the right end of the third shielding cavity;
and a shielding pipe is connected between the first clean air inlet and the second clean air inlet, and a main clean air inlet communicated with the inside of the shielding pipe, the first clean air inlet and the second clean air inlet is arranged on the shielding pipe.
2. The differential high concentration particulate matter measurement system based on dynamic faraday cup of claim 1, wherein: the first gas outlet and the second gas outlet are both connected with a gas suction pump; the clean air main inlet is connected with a blowing pump.
3. The differential high concentration particulate matter measurement system based on dynamic faraday cup of claim 1, wherein: the shielding box I, the shielding box II and the shielding pipe are all grounded, and the shielding box I, the shielding box II and the shielding pipe are all made of stainless steel.
4. The differential high concentration particulate matter measurement system based on dynamic faraday cup of claim 1, wherein: the first unipolar charger shell, the second unipolar charger shell, the first discharge shell, the second discharge shell, the first electromigration classifier shell and the second electromigration classifier shell are all connected with virtual ground.
5. The differential high concentration particulate matter measurement system based on dynamic faraday cup of claim 1, wherein: the collecting electrode I, the collecting electrode II, the high-voltage electrode I and the high-voltage electrode II are made of copper materials, and the discharge needle I and the discharge needle II are made of tungsten materials.
6. The differential high concentration particulate matter measurement system based on dynamic faraday cup of claim 1, wherein: the first insulating sleeve, the second insulating sleeve, the third insulating sleeve and the fourth insulating sleeve are all made of polyether-ether-ketone materials.
7. The differential high concentration particulate matter measurement system based on dynamic faraday cup of claim 1, wherein: the measuring system also comprises a first micro-current signal detecting unit for detecting the induced current in the first dynamic Faraday cup and a second micro-current signal detecting unit for detecting the induced current in the second dynamic Faraday cup.
8. The differential high concentration particulate matter measurement system based on dynamic faraday cup of claim 1, wherein: the first unipolar charger and the second unipolar charger are both powered by high-voltage sources; the first electromigration classifier and the second electromigration classifier both adopt linear power supplies for power supply; the collecting electrode I is connected with the linear power supply I, and the collecting electrode II is connected with the linear power supply II; the high-voltage electrode I is connected with a high-voltage source I, and the high-voltage electrode II is connected with a high-voltage source II; and the grounding electrodes of the first linear power supply, the second linear power supply, the first high-voltage power supply and the second high-voltage power supply are all connected with virtual ground.
9. The method of the differential high concentration particulate matter measurement system based on the dynamic faraday cup of any one of claims 1 to 8, wherein: the method comprises the following steps:
(1) setting the voltage of a linear power supply I connected with a trapping electrode I as V1, and the voltage of a linear power supply II connected with a trapping electrode II as V2, wherein V1 is not equal to V2; namely the trapping voltage accessed by the trapping electrode I is V1, and the trapping voltage accessed by the trapping electrode II is V2; connecting a first high-voltage electrode to a first high-voltage source, and connecting a second high-voltage electrode to a second high-voltage source;
(2) under the action of the air suction pump and the air blowing pump, sample gas enters an inner cavity of the first unipolar charger shell and an inner cavity of the second unipolar charger shell from the first sample gas inlet and the second sample gas inlet respectively; clean air firstly enters the shielding tube from the clean air main inlet, and then respectively enters the inner cavity of the first discharge shell and the inner cavity of the second discharge shell through the first clean air inlet and the second clean air inlet;
under the action of an air suction pump and an air blowing pump, clean air entering an inner cavity of a first discharge shell flows leftwards, and when the clean air passes through a first discharge needle, the clean air is discharged from the tip of the first discharge needle connected with a first high-voltage electrode connected with a first high-voltage source to ionize part of the clean air to generate free charges; when the free charges continuously flow leftwards along with the unionized clean air, the free charges collide with particles in the sample gas entering the inner cavity of the first unipolar charger shell, and part of the free charges are adhered to the particles so as to charge the particles; charged particles and free charges which are not trapped by the particles enter an inner cavity of a first electromigration classifier shell along with airflow, a first trapping electric field is formed between a first trapping electrode connected to a first linear power supply and the first electromigration classifier shell connected to virtual ground, all the free charges which are not adhered by the particles are adsorbed to the first trapping electrode under the action of the first trapping electric field, and all the charged particles flow out from a first gas outlet along with the airflow;
(4) under the action of the air suction pump and the air blowing pump, clean air entering the inner cavity of the second discharge shell flows leftwards, and when the clean air passes through the second discharge needle, the clean air is discharged from the tip of the second discharge needle connected with the second high-voltage electrode connected with the second high-voltage source, so that part of the clean air is ionized to generate free charges; when the free charges continuously flow leftwards along with the unionized clean air, the free charges collide with particles in the sample gas entering the inner cavity of the unipolar charger shell II, and part of the free charges are adhered to the particles so as to charge the particles; charged particles and free charges which are not trapped by the particles enter an inner cavity of a second electromigration classifier shell along with airflow, a second trapping electric field is formed between a second trapping electrode connected to a second linear power supply and the second electromigration classifier shell connected to virtual ground, all the free charges which are not adhered by the particles and charges on part of the charged particles are adsorbed onto the second trapping electrode under the action of the second trapping electric field, and the rest charged particles and the particles without charges lost flow out of a second gas outlet along with the airflow;
(5) the first dynamic Faraday cup shell connected with the virtual ground can generate induced charges to supplement the reduced charge quantity in the first dynamic Faraday cup shell, so that the flow of the induced charges is generated between the first dynamic Faraday cup shell and the first shielding box to form induced currents, and the induced currents are collected and set as I1；
A cavity formed by enclosing the unipolar charger shell II, the electromigration classifier shell II and the discharge shell II is a dynamic Faraday cup shell II, the charged particles flowing out of the gas outlet II can reduce the charges in the dynamic Faraday cup II, the dynamic Faraday cup shell II connected with the virtual ground can generate induced charges to supplement the reduced charges in the dynamic Faraday cup II, so that the induced charges flow between the dynamic Faraday cup shell II and the shielding box II to form induced currents, and the induced currents are collected and set as I2；
(6) Using formula I1-I2Obtaining the total number concentration N of the particulate matters as AN, wherein A is a system calibration value;
(7) using a formula
Finding the median particle diameter D of the particlespWhere c is the system calibration value and e is the element charge (1.6X 10)-19C)。
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