JP2008096168A - Particle classifier - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a particle classifier capable of measuring the supply amount of sample gas without installing a flowmeter in a main channel where the sample gas flows. <P>SOLUTION: The particle classifier includes a charging mechanism 33 for charging aerosol, a particle classifying mechanism PD for classifying the charged particle in the charged aerosol by electro-migration degree, and a detector FCE for measuring the number of classified and taken particles. A sheath gas supply mechanism 31 for supplying sheath gas is connected to the particle classifying mechanism PD. A half-closed piping system is employed where the sample gas is supplied from an aerosol supply section 11, gas is exhausted at a flow rate Qe from a first exhaust section 13, and part of sheath gas flow rate Qs is circulated and re-supplied at a flow rate Qc into the particle classifier. Accordingly, using indirect flow rate relation of Qa = Qe allows more accurate determination of sample gas supply amount Qa than before. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an apparatus for measuring a sample gas supply amount, for example, a particle classification apparatus for measuring the number of particles contained in an environmental gas.

Aerosol generally means a colloid in which the dispersion medium is a gas and the dispersoid is a liquid or a solid, and indicates an environmental gas such as an automobile exhaust gas.
As an apparatus for measuring the number of particles, an electric mobility measuring apparatus is used that measures particles after charging the particles in the aerosol to be measured and classifying the charged charged particles using the difference in moving speed in the electric field. Yes. Since there is a certain relationship between the electric mobility and the particle diameter, the particle diameter can be specified by specifying the electric mobility.

  As the electric mobility measuring device, a differential mobility analyzer (DMA) capable of selecting fine particles having a specific electric mobility and an electric mobility in the vicinity thereof (see Patent Document 1). Then, there is an integral type electric mobility measuring device that can select fine particles having an electric mobility smaller than a certain electric mobility.

For example, when evaluating the health effects of fine particles in automobile exhaust gas, counting the number of particles in a certain particle size range, that is, a predetermined particle size range in which particles having a particle size greater than or equal to a certain particle size are removed It is necessary to detect the particle distribution (this is called a box-type transfer function).
In particular, in recent years, health effects due to ultrafine particles having a diameter in the range of several nanometers to several hundred nanometers have been discussed, and a device that measures them is required to have quick responsiveness corresponding to the driving state of an automobile.

DMA has been used as a reliable apparatus for counting ultrafine particles having a diameter of about several nanometers as described above. In this case, the particle size distribution is a specific electric mobility and the electric mobility in the vicinity thereof. (See Non-Patent Document 1).
And in order to obtain a result corresponding to a desired box-type transfer function, it is necessary to scan the particle size, but this method cannot obtain a quick response corresponding to the driving state of the automobile. There's a problem.

Some particle classifiers enable high-speed response. However, since the minute ammeter electrode is installed in a strong electric field, the minimum resolution may be limited (see Non-Patent Documents 2 and 3).
In addition, if a discontinuous structure such as an electrode is brought into the apparatus, it will be difficult to maintain a laminar flow of gas, and the classified particles will be collected on the surface of the flat electrode that forms part of the structure of the apparatus. For this reason, it may not be available for reuse or analysis by another method.

Japanese Patent No. 3449359 Knutson, E.O. and Whitby, K.T. (1975). "Aerosol Classification by Electric Mobility: Apparatus, Theory, and Applications," J. Aerosol Sci., Vol.6, pp.453-460. Mirme A., Noppel M., Peil I., Salm J., Tamm E. and Tammet H. (1984) "Multi-channel electric aerosol spectrometer." In 11th int. Conf. On Atmospheric Aerosols. Condensation and Ice Nuclei, Budapest, 2, pp.155-159 Mirme A. and Tamm E. (1991) "Comparison of sequential and parallel measurement principles in aerosol spectrometry." J. Aerosol Sci., 22Sl, pp.S331-S334 JP 2003-326192 A

When a flow meter is installed in the flow path through which the sample gas flows and the supply amount of the sample gas (aerosol) is measured, an error in flow measurement and deterioration of the flow meter occur due to the influence of fine particles, and the flow of particles to the flow measurement mechanism May induce sample alteration due to adhesion.
Therefore, in order to know the sample gas flow rate, there is a method of calculating it from the mass balance of the apparatus without directly measuring it.
Here, when the sheath gas flow rate with a large absolute value of the flow rate is used for the balance calculation, the absolute accuracy of the measuring instrument indicated value is relatively inferior as the indicated value is large, and thus the calculation result includes a large error.

Therefore, an object of the present invention is to provide a particle classifier that can accurately measure the amount of sample gas supplied without installing a flow meter in the main flow path through which the sample gas flows.
Moreover, when using DMA for a particle classifier, it aims at ensuring the coincidence of the particle diameter measurement in sample gas.

The particle classifying device of the present invention charges a classifying region having a pair of counter electrodes arranged to face each other to generate an electric field for classifying charged particles by electric mobility, and charged sample gas. It has a charging mechanism for generating a charged aerosol, has an inlet in the vicinity of one electrode of the counter electrode or in the vicinity of the electrode, and has an aerosol supply part that supplies charged aerosol from the inlet to the classification region, and a sheath gas supply mechanism, A sheath gas supply unit that supplies uncharged sheath gas at a flow rate Qc from the upstream side of the classification region to the classification region, and a discharge port on one electrode of the counter electrode or in the vicinity of the electrode on the downstream side of the aerosol supply unit. A first discharge unit that discharges gas from the discharge port to the outside of the classification region at a flow rate Qe, and a sheath gas supply machine that discharges gas at a flow rate Qs on the downstream side of the sheath gas flow And a second discharge unit for supplying to.
Then, a first discharge unit flow meter for measuring the gas flow rate Qe discharged from the first discharge unit is provided, and the gas supply to the particle classifier is only the sample gas supply to the aerosol supply unit, and from the particle classifier to the outside The gas discharge to is a semi-closed piping system in which only the gas discharge from the first discharge section is performed, and the measured flow rate Qe by the first discharge section flowmeter is set as the sample gas supply amount Qa to the classification region.

  In order to indirectly measure and calculate the flow rate, a branch flow channel for supplying a part of the gas flow rate Qe discharged from the first discharge unit to the sheath gas supply mechanism, and a branch flow for measuring the flow rate Qb flowing through the branch flow channel A road flow meter is further provided, and Qa = Qe−Qb may be used instead of Qa = Qe.

  When a flow meter that can measure without a differential pressure is available, an atmospheric pressure flow meter that measures the gas flow rate Qo discharged from the first discharge unit to the atmospheric pressure is further provided, and instead of setting Qa = Qe, It is good also as Qa = Qo.

  When a flow meter that can measure without a differential pressure is available, an atmospheric pressure flow meter that measures the gas flow rate Qo discharged from the first discharge part to the atmospheric pressure is further provided, and Qa = Qe−Qb Thus, Qa = Qo may be set.

  A branch channel that supplies a part of the gas flow rate Qe discharged from the first discharge unit to the sheath gas supply mechanism, a branch channel flow meter that measures the flow rate Qb flowing through the branch channel, and a discharge from the second discharge unit A third discharge unit that branches and discharges a part of the gas flow rate Qs before being supplied to the sheath gas supply mechanism, and a third discharge unit flow meter that measures the flow rate Qr discharged from the third discharge unit. Further, Qa = Qr + Qe−Qb may be used instead of Qa = Qe.

  When a part of the charged gas is used in another analyzer, a third discharge unit that branches and discharges a part of the gas flow rate Qs discharged from the second discharge unit before supplying the sheath gas supply mechanism; A third discharge unit flow meter for measuring the flow rate Qr discharged from the third discharge unit may be provided, and Qa = Qr + Qe-Qb may be used instead of Qa = Qe-Qb.

  When a part of the charged gas is used in another analyzer, a third discharge unit that branches and discharges a part of the gas flow rate Qs discharged from the second discharge unit before supplying the sheath gas supply mechanism; A third discharge unit flow meter that measures the flow rate Qr discharged from the third discharge unit may be provided, and instead of setting Qa = Qo, Qa = Qr + Qe−Qb may be used.

  In the particle classifier of the present invention, the sample gas is supplied from the aerosol supply unit, the gas is discharged from the first discharge unit at the flow rate Qe, and the sheath gas flow rate Qs is circulated and re-supplied into the device at the flow rate Qc. Since the piping system has fewer parts such as flowmeters, the indirect flow relationship of Qa = Qe is used without using large flow Qc and Qs with large absolute values of measurement errors. The sample gas supply amount Qa can be obtained with high accuracy.

  When a part of the gas flow rate Qe discharged from the first discharge unit of the particle classifier is branched and supplied to the sheath gas supply mechanism, the sample gas supply amount is measured by measuring the flow rate Qb flowing through the branch flow path. Qa can be indirectly measured as Qa = Qe−Qb.

  If an atmospheric pressure flow meter for measuring the gas flow rate Qo discharged to the atmospheric pressure is provided, the sample gas supply amount Qa in the semi-closed system can be calculated as Qa = Qo from the gas discharge amount Qo.

  A third discharge unit that branches and discharges a part of the gas flow rate Qs discharged from the second discharge unit before supplying it to the sheath gas supply mechanism, and a third flow rate that measures the flow rate Qr discharged from the third discharge unit. When a discharge flow meter is provided, the sample gas supply amount Qa can be indirectly measured by setting Qa = Qr + Qe-Qb, and a part of the charged gas can be measured by another analyzer. Can be used.

The present invention is described in detail below.
[Piping system of particle classifier]
As shown in FIG. 1, the particle classification device according to the present invention is classified and taken out by a charging mechanism 33 for charging the aerosol, a particle classification mechanism PD for classifying charged particles in the charged aerosol by electric mobility. A detector FCE (Faraday cup electrometer) for measuring the number of particles is provided. In addition, a sheath gas supply mechanism 31 that supplies a sheath gas is connected to the particle classification mechanism PD.

The connection part of the particle classification mechanism PD with the sheath gas supply mechanism 31 is a sheath gas supply part 7, which supplies uncharged sheath gas at a flow rate Qc.
Further, the connection part of the particle classification mechanism PD with the charging mechanism 33 is an aerosol supply part 11 so that the charged aerosol charged by the charging device INZ is supplied into the particle classification mechanism PD with the sample gas supply amount Qa. It has become. The flow rate Qa is not directly obtained.

  A pair of counter electrodes is provided in the particle classification mechanism PD, and a classification region for classifying charged particles by electric mobility is formed by an electric field generated between the counter electrodes. The description in the particle classification mechanism PD will be described later. A description of the charging mechanism 33 and the sheath gas supply mechanism 31 will also be given later.

A first discharge unit (large particle size discharge unit) 13 that discharges gas at a flow rate Qe to the outside of the classification region is provided in the vicinity of the counter electrode on the downstream side of the aerosol supply unit 11.
Downstream of the first discharge unit 13, a filter F3 for removing fine particles, a flow rate adjusting unit (first discharge unit flow meter) MFC1 for measuring and adjusting the gas flow rate Qe, and a pump P3 are provided, and the gas flowing through these is The gas is discharged from the gas discharge unit 35 at the flow rate Qo.

  Further, the connection part of the particle classification mechanism PD with the detector FCE is a second discharge part (sheath gas discharge part) 17, and the sheath gas in the particle classification mechanism PD is discharged at a flow rate Qs.

  Gas supply into the particle classification mechanism PD is only sample gas supply to the aerosol supply unit 11, and gas discharge from the particle classification mechanism PD to the outside is only gas discharge from the first discharge unit 13. A part of the flow path connected from the first discharge unit 13 becomes a branch flow path 39 and is connected to the flow rate adjusting unit (branch flow rate meter) MFC3, and the downstream thereof is connected to the sheath gas supply mechanism 31.

  Further, between the second discharge unit 17 and the detector FCE, a third discharge unit 37 that branches and discharges a part of the gas flow rate Qs and a flow rate Qr that is discharged from the third discharge unit 37 are measured. A three-discharge unit flow meter (not shown) is provided so that the gas flow rate Qr can be measured.

[Sheath gas supply mechanism]
The sheath gas supply mechanism 31 includes a flow path that connects the detector FCE that is upstream to the sheath gas supply unit 7 that is downstream, and a pump or the like disposed there. A buffer tank BT for storing the sheath gas is provided downstream of the detector FCE. The pump P1 that transports the sheath gas, the cooling tank CT that keeps the sheath gas near room temperature, and particulates mixed in the sheath gas are sequentially removed downstream of the detector FCE. A filter F1, a flow rate adjusting valve NV1 for adjusting the flow rate of the sheath gas flow, and a flow meter MFM1 for measuring the sheath gas flow rate Qc are provided.

[Particle classification mechanism PD]
2A and 2B are schematic views of the particle classification mechanism, in which FIG. 2A is a vertical sectional view and FIG. 2B is a horizontal sectional view taken along line XX ′ in FIG.
A cylindrical center electrode 3 is provided inside the cylindrical housing 1 so as to coincide with the central axis of the housing 1. The inner surface of the housing 1 is an outer electrode 4, and the counter electrode is constituted by the center electrode 3 and the outer electrode 4. A rotating space formed by the center electrode 3 and the outer region 4 is a classification region 5, and charged particles in the classification region 5 are classified by electric mobility in response to an electric field generated between the electrodes 3 and 4. To do.

A sheath gas supply unit 7 for introducing an uncharged gas as a sheath gas at a flow rate Qc is provided at the top of the housing 1, and an insulator commutator 9 for laminating the sheath gas at the upper end of the classification region 5. Is provided. The sheath gas that has passed through the commutator 9 is supplied to the classification region 5.
The charged aerosol is introduced from the aerosol introduction part 11 in a direction crossing the sheath gas flow at a flow rate Qa, and the upper part on one electrode side (the outer electrode 4 side in FIG. 2) of the classification region 5 is for introducing the aerosol. It is an introduction port 11a.

Part of the charged particles in the charged aerosol that has passed through the classification region 5 is discharged at a flow rate Qe from the first discharge portion (large particle size discharge portion) 13, and one electrode side of the classification region 5 ( The lower part of the outer electrode 4 side in FIG. 2 is a gas discharge port 13a.
A second discharge portion 17 is provided outside the lower end of the classification region 5 at the lower portion of the casing 1, that is, downstream of the sheath gas flow, and is sent together with the sheath gas at a flow rate Qs downstream of the second discharge portion 17. A detector FCE for detecting the remaining number of charged particles as an electric quantity is arranged.

  The upper end of the center electrode 3 is supported on the housing 1 by an insulating member 10 and an insulator commutator 9, and the lower end of the center electrode 3 is a support member 16 that also serves as an insulating member 19 and a commutator for laminating the flow of sheath gas. The center electrode 3 and the casing 1 serving as an external electrode are electrically insulated from each other.

The diameter of the center electrode 3 is 25 mm and the inner diameter of the outer electrode 4 is 33 mm. In the columnar portion of the center electrode 3, the distance between the center electrode 3 and the outer electrode 4 is constant at about 4 mm. For example, a classification voltage of 1000 to 1500 V is applied between the electrodes 3 and 4.
The introduction port 11 a and the discharge port 13 a have a width of 0.5 mm and are formed in a ring shape surrounding the center electrode 1 along the inner peripheral surface of the outer electrode 4. The distance between the introduction port 11a and the discharge port 13a is about 100 mm. The introduction port and the discharge port may be slits.

[Charging mechanism]
Next, the charging mechanism will be described with reference to FIGS.
The particles become charged particles by, for example, diffusion charging by gas ions. This is because a part of the neutral gas such as the atmosphere is ionized by americium (Am) or corona discharge, and the gas ion collides with the particle by diffusion, and it adheres to the particle or exchanges its charge. The particles are charged.

However, when Am or soft X-rays are used, there is a risk of exposure to radiation during handling and storage. Further, in the conventional method in which corona discharge is directly performed in a sample gas containing particles to be measured, there is a risk of generation of secondary particles, decomposition of substances constituting the particles, and modification.
On the other hand, Patent Document 2 proposes a method in which a charged gas and particles are mixed by discharging into a charged gas in a separate chamber instead of directly discharging into the sample gas.
However, when charged gas is taken in from the outside air, the mixing portion with the sample gas tends to be positive pressure, and it is necessary to limit the amount of sample gas introduced, or to increase the size of the subsequent classification unit pump. It was.

In addition, since the number of particles is conventionally expressed in the dimension of pcs / cc or pcs / m ³ , it is necessary to measure and control the specific volume of the sample gas for accurate particle count measurement. Become. Typical factors affecting the specific volume include temperature and humidity.
In addition, when the sample gas is highly humid, condensed water may be generated by compression by the pump, and this condensed water may be converted into particles by scattering or condensed with the particles as nuclei. It may be misidentified or adversely affect the measurement.

When a dehumidifying mechanism is arranged in the sample gas, any dehumidifying mechanism may function as a particle filter. When the dehumidifying mechanism is installed in the main flow path through which the sample gas flows, the dehumidifying mechanism having a large capacity is required because the flow rate is large.
In addition, many dehumidifiers require regeneration gas, dry gas, and high-temperature gas to maintain the capacity of the dehumidification mechanism. In the case of regeneration gas, the lower the dew point temperature, the better the performance of the dehumidification mechanism can be maintained.

  In other words, as a device for charging the particles, it is preferable that the mixing portion is less likely to be at a positive pressure, and that the main flow path through which the sample gas flows is not provided with a dehumidifying mechanism.

Therefore, as shown in FIG. 3, the charging device INZ used in the particle classification device of the present invention is provided with a charging unit 41 that generates a charged gas by charging a supplied charging target gas, and downstream of the charging unit 41. And a mixing part 43 for generating a charged aerosol by mixing the sample gas introduced at the flow rate Qa ′ with the charged gas and discharging it further downstream.
Further, downstream of the mixing unit 43, a pump P2 that sucks a part of the charged aerosol from the downstream of the mixing unit 43 and transports the charged aerosol to the upstream of the charging unit 41, and when the pump P2 transports the charged aerosol, A filter F2 for removing particles and a flow rate adjustment unit MFC2 that measures and adjusts the flow rate of the charge target gas are provided, which form a semi-closed flow path. The sample gas is introduced from the upstream of the mixing unit 43. As shown in FIG. 1, a temperature / humidity measuring unit SU for measuring the temperature or humidity of the sample gas may be provided on the flow path.

  Further, a dehumidifying mechanism D1 for drying the charge target gas is provided between the downstream side of the pump P2 and the flow rate adjusting unit MFC2. Examples of the dehumidifying mechanism D1 include a hollow fiber membrane dryer and an adsorption dryer. By providing the dehumidifying mechanism D1, a dry gas can be supplied to the charging unit 41, and a charged aerosol with a small amount of water can be discharged. The charged aerosol discharged at the flow rate Qa is supplied to the particle classification mechanism PD, for example.

[Control of particle classifier]
As shown in FIG. 1, the particle classifying apparatus of the present invention includes an analog input / output device AI / O (one-dot chain line in the drawing) and a digital input / output device DI / O (two-dot chain line in the drawing) from a personal computer PC. By connecting to each device or mechanism. Thereby, each device is controlled by an analog or digital signal.

Next, the operation of the present invention will be described with reference to FIGS.
[Operation of particle classifier]
[Sample gas amount calculation method 1]
A sheath gas having a flow rate Qc = 100 L is supplied from the sheath gas supply mechanism 31 into the particle classification mechanism PD via the sheath gas supply unit 7. Charged aerosol 33 is supplied from the charging mechanism 33 to the particle classification mechanism PD via the aerosol supply unit 11 at a flow rate Qa (for example, 2 L, which cannot be directly measured).
102 L of gas is supplied into the particle classification mechanism PD, and the flow rate Qe = 3 L is discharged from the first discharge unit 13 to the outside. The remaining flow rate Qs = 99L is discharged from the second discharge unit 17 and circulates to the sheath gas supply mechanism 31 via the detector FCE.

  In the sheath gas supply mechanism 31, the sheath gas is taken into the buffer tank BT by being transported by the pump P1, cooled to near room temperature in the cooling tank CT, fine particles are removed by the filter F1, and then the flow rate is adjusted by the flow rate adjusting valve NV1. The flow rate Qc is measured by the flow meter MFM1.

  The gas discharged at the flow rate Qe from the first discharge unit 13 passes through the filter F3 by transport by the pump P3, fine particles are removed, and the flow rate is measured and adjusted by the flow rate adjustment unit MFC1. Of the gas flow rate Qe, the gas for the flow rate Qb = 1L flowing through the branch flow path 39 is supplied to the sheath gas supply mechanism 31 together with the gas for the flow rate Qs = 99L. The remaining gas flow 2L is discharged to the outside from the discharge port 35 at a flow rate Qo as exhaust gas.

  In the particle classifier of the present invention, the sample gas is supplied from the aerosol supply unit 11 and the gas is discharged from the discharge port 35 at the flow rate Qo, and a part of the sheath gas flow rate Qs is circulated and re-supplied into the device at the flow rate Qc. Since it is a closed piping system and parts such as a flow meter are reduced, Qo is measured without using large flow Qc and Qs with large absolute values of measurement errors, and an indirect flow relationship of Qa = Qo is established. By using it, the sample gas supply amount Qa can be obtained with higher accuracy than before.

[Sample gas amount calculation method 2]
In order to indirectly measure and calculate the flow rate, the branch flow channel 39 that supplies a part of the gas flow rate Qe discharged from the first discharge unit 13 to the sheath gas supply mechanism 31 and the flow rate Qb that flows through the branch flow channel 39 are calculated. A branch flow meter MFC3 for measurement may be further provided, and Qa = Qe−Qb may be set. In this way, the gas flow rate can be indirectly measured.

At this time, if there is sufficient pressure loss between the branch 39 and the discharge port 35, the branch 39 side of the MFC 3 is the discharge side of the pump P3, and the pressure is high.
The side where MFC3 joins Qs is the pump P1 suction side, which is at a low pressure.
As a result, a sufficient differential pressure is generated at both ends of the MFC 3, and a stable operation is brought about in the MFC 3.

[Sample gas amount calculation method 3]
When a flow meter that can measure without a differential pressure is available, an atmospheric pressure flow meter (not shown) that measures the gas flow rate Qo discharged from the first discharge unit 13 to the atmospheric pressure via the discharge port 35 is further provided. It is good also as Qa = Qo. In this way, the gas supply amount Qa in the semi-closed system can be calculated from the gas discharge amount Qo.

In calculation method 2, two measured values were used for calculating Qa. For this reason, each flow meter error is added to the calculation result.
On the other hand, in the present invention, since Qa is directly obtained from one measurement value, it can be said that the error included in the result is small.

[Sample gas amount calculation method 4]
When a part of the charged gas is used in another analyzer, a third discharge that branches and discharges a part of the flow rate before supplying the gas flow rate Qs discharged from the second discharge unit 17 to the sheath gas supply unit. And a third discharge portion flow meter (not shown) for measuring the flow rate Qr discharged from the third discharge portion 37, and Qa = Qr + Qe−Qb may be provided. In this way, the sample gas supply amount Qa can be indirectly measured, and a part of the charged gas (flow rate Qr) can be used for other analyzers.

When calculating the sample gas supply amount Qa in the calculation methods 1 to 4, a calculation function for calculating Qa from each flow rate or the like may be further provided to calculate the flow rate.
In order to realize the box-type transfer function, it is preferable that Qe ≧ Qa and Qs ≠ Qs as described above. Further, when obtaining a sensitive classification characteristic, there is a tendency that Qc≈Qs >> Qa.

[Operation of charging device INZ]
Next, the operation of the charging device INZ will be described with reference to FIG.
The sample gas is introduced into the mixing unit 43 in the charging device INZ at a flow rate Qa ′. The charged gas charged by the charging unit 41 is mixed with the introduced sample gas to generate a charged aerosol, which is taken out as a charged aerosol at a flow rate Qa. The flow rates Qa ′ and Qa are not directly measured.

  At that time, a part of the charged aerosol is sucked into the semi-closed flow path by the pump P2, and the fine particles in the aerosol are removed through the filter F2. The gas from which the fine particles have been removed is dried by the dehumidifying mechanism D1, adjusted to a predetermined flow rate by the flow rate adjusting unit MFC2, supplied to the charging unit 41 as a charge target gas, and circulated. The charge target gas becomes a charged gas in the charging unit 41.

By adopting a semi-closed flow path configuration in which a part of the charged aerosol released from the mixing unit 43 is transported to the charging unit 41 by the pump P2, a certain amount of gas is always sucked from the downstream of the mixing unit 43. The pressure increase downstream of the mixing unit 43 is suppressed.
Further, the charge target gas can be dried by providing the dehumidifying mechanism D1 in the semi-closed flow path.

  In this embodiment, if the gas amount Qc of the charged aerosol discharged from the mixing unit 43 is 2 L, the gas in the semi-closed system flow channel is flowed at a flow rate of about 1 L. Therefore, it is necessary to calculate the number of particles contained in the aerosol supplied at the flow rate Qa in consideration of the influence of the dilution rate in the semi-closed flow path described above.

  The charging device INZ used in the particle classifier of the present invention includes a charging unit 41, a mixing unit 43, a pump P2, and a filter F2, and pumps a part of the gas from the downstream of the mixing unit 43 to the charging unit 41. Therefore, the pressure increase in the mixing portion 43 is suppressed, and it becomes easy to release the charged aerosol.

  Until now, in the method of disposing the dehumidifying mechanism in the flow path through which the sample gas flows, any dehumidifying mechanism may function as a particle filter, but the downstream of the pump P2 and the upstream of the charging unit 41 If the dehumidifying mechanism D1 is provided in the semi-closed system channel, the gas can be dehumidified while avoiding the filter effect. When the charged aerosol is introduced into the particle classification mechanism PD, the inside of the particle classification mechanism PD is kept at a low humidity, and the aerosol can be classified in a normal state.

  If the flow rate adjustment unit MFC2 is provided in the semi-closed system flow path between the downstream of the pump P2 and the upstream of the charging unit 41, the dilution rate of the charged aerosol released from the downstream of the mixing unit 43 can be calculated. And the amount of fine particles in the sample gas can be measured more accurately.

  If the temperature / humidity measuring unit SU is provided in the sample introduction channel into which the sample gas is introduced, the temperature or humidity of the sample gas introduced into the mixing unit 43 can be measured in advance.

  Since the inside of the charging device INZ is always kept at a low humidity, the particle classification device of the present invention can always use a low-humidity charged aerosol.

[Operation of particle classification mechanism PD]
Next, the operation of the particle classification mechanism PD shown in FIG. 2 will be described.
When a voltage is applied between the electrodes 3 and 4, a horizontal electric field that classifies charged particles according to electric mobility is generated in the classification region 5.

  In this embodiment, among the aerosols introduced into the classification region 5 from the inlet 11a of the aerosol supply unit 11, charged particles having a particle size of about 20 nm reach near the center electrode 3 on the opposite bank and have a particle size smaller than 20 nm. Charged particles are captured by the central electrode 3 and removed. Charged particles having a particle size larger than 20 nm are distributed from the vicinity of the center of the sheath gas flow to the vicinity of the outer electrode 4 having the introduction port 11a.

  The discharge port 13a is provided on the downstream side of the same outer electrode 4 as the introduction port 11a, and a portion having a predetermined particle diameter or more of the charged particles in the charged aerosol is sucked and discharged together with the sheath gas from the discharge electrode 13a. Fine particles larger than (for example, 100 nm) are removed. In order to realize this, for example, at a relatively small classification voltage at which charged particles having a particle size of 20 nm reach the opposite bank, the distribution of charged particles having a particle size of about 100 nm is different from the charged particles having a particle size of about 130 nm in the sheath gas flow. It is necessary to exclude from the discharge port 13a only the gas flow in which the particles are completely separated and distributed, and the fine particles having a particle diameter of more than 100 nm are distributed.

  The particle classification mechanism PD constituting the particle classification apparatus of the present invention includes a counter electrode 3, 4, a sheath gas supply unit 7, an aerosol supply unit 11, and a detector FCE, and is in a charged aerosol according to the basic principle of an electric mobility measurement device. The charged fine particles are classified by the first discharge portion (large particle size side discharge portion) 13 so that the portions of the classified charged fine particles having a predetermined particle diameter or more are removed. When the fine particles on the small particle size side are removed by being sucked and adsorbed by the other electrode, the total amount of charged fine particles having a particle size in a predetermined range in the charged aerosol can be measured. . At this time, the particle size range to be measured is a particle size range on the large particle size side and a particle size range on the small particle size side to be removed depending on the sheath gas flow rate, the charged aerosol flow rate, and the discharge flow rate from the first discharge unit 13. Since it can be set, the measurement range can be set to a sufficiently wide range such as 30 to 100 nm.

[Calculation of particles within a predetermined particle size range]
Next, an example of calculating the particle size distribution of the fine particles in the particle classifier of the present invention will be described.
In a particle classifier that classifies particles according to electric mobility and counts the number of particles, it is important to know the charge rate of the particles and the distribution of their charge valences when converting from the electric mobility distribution to the particle size distribution. It is.

So far, a theoretical model by Wiedensohler has been developed for positive and negative charge valence distribution including zero valence.
On the other hand, an approximate expression (1) based on the extended theory of Fuck in the submicron region is shown, and is applied to a charged valence within ± 2 including zero valence.

この近似式（１）において、ａｉ（N）は表１に示される係数を、Ｎは微粒子の電荷価数を、Ｄｐは微粒子の平均粒径を、（Ｄｐ／ｎｍ）はＤｐの単位がｎｍであることをそれぞれ意味している。

In this approximate expression (1), ai (N) is the coefficient shown in Table 1, N is the charge valence of the fine particles, Dp is the average particle diameter of the fine particles, and (Dp / nm) is the unit of Dp in nm. Each means.

この近似式（２）において、ｅは素電荷、ε₀は空気中の誘電率、Ｄｐは粒子直径、ｋはボルツマン定数、Ｎは電荷数、（Ｚ_i+/Ｚ_i-）はイオン移動度を意味する。 For those with a charge valence of +3 or higher or −3 or lower, the approximate expression (2) derived by Gunn is used.

In this approximate expression (2), e is the elementary charge, ε ₀ is the dielectric constant in air, Dp is the particle diameter, k is the Boltzmann constant, N is the number of charges, and (Z _{i +} / Z _i− ) is the ion mobility. means.

  Conventionally, the particle size distribution has been obtained by applying correction by various mathematical methods to the distribution measurement result of the electric mobility using the above formulas (1) and (2). In this mathematical method, the particle size distribution is calculated once assuming that all of the count values for each electric mobility are monovalent, and the charge rate and polyvalent charge are calculated based on the equations (1) and (2). In consideration of the above, the particle size distribution is recalculated, and the difference from the initial assumed distribution is evaluated by, for example, the residual sum of squares for each classification. There is also a method in which the calculation is repeated until the evaluation value reaches a certain value.

When the particle size distribution of the measurement target gas is known or when there is data that can estimate the particle size distribution, the above equations (1) and (2) can be used.
However, in the case of a box-type transfer function DMA that counts the number of particles having a certain particle size distribution, for example, it is impossible in principle to derive the particle size width or number from the measurement result by a conventional method.
Therefore, when converting the width of a certain electric mobility into a particle size width and calculating the number of particles from the measured number of charges, it is necessary to calculate using a mathematical method in which a correction coefficient is introduced.

In the particle classification device of the present invention, the following particle number calculation examples 1 to 3 are proposed.
[Particle number calculation example 1]
Let Ea be the average valence of particles in the box-type transfer function particle size band, and Ca be the average charge rate.
Let Nel (number / second) be the number of large charged polyvalent charged particles per second flowing into the box-type transfer function particle size band, and let nl be the average valence.
Let Ne (number / second) be the number of small charged polyvalent charged particles per second flowing out of the box-type transfer function particle size band.
In addition, the elementary electric quantity is e, and the current measured by the detector is Imfce (A).

Using these, the particle number Na is calculated from the following relational expression (3).
Na = (Imfce-e * nl * Nel) / (e * Ea * Ca) + Nes (3)
These Nel, nl, Nes, Ca, and Ea are specified by the measurer.

FIG. 4 is a schematic diagram of particle distribution for explaining the above example of calculating the number of particles.
(A) is the figure which showed the particle distribution in the particle size distribution of 10 nm-1000 nm of the particle | grains of all the valences contained in aerosol. With the abundance of particles (number / cc) having a particle diameter of 100 nm as a peak, the number decreases as the distance approaches 10 nm or 1000 nm.

(B) is a particle distribution diagram in which a particle size distribution of 20 nm to 100 nm is displayed by classifying 0 valence to 3 valence or more (without distinguishing +-).
The valence distribution of the particles is known, and as shown in the lower part of (B), when the particle size is 20 nm, the 0 valence is 80%, the 1 valence is 15%, the 2 valence is 4.5%, the 3 valence or more is When the particle size is 100 nm, the zero value is 50%, the first value is 30%, the second value is 15%, and the third value or more is 5%.

  “Nl × Nel” in the relational expression (3) indicates “210 nm × 3 valence” or “120 nm × 2 valence”, which are large-sized multivalent charged particles per second that are mixed into the box-type transfer function band. “Nes” indicates “30 nm × 2 valence” which is a small charged multivalent charged particle per second flowing out of the box-type transfer function band.

[Particle number calculation example 2]
In addition, since experience shows that Imfce and Nel often have a proportional relationship, the number of particles Na may be calculated by the following relational expression (4). This equation (4) is empirically derived from the fact that Nel in equation (3) is proportional to the measured current value Imfce.
Na = (Imfce (1−e × n1 × k)) / (e × Ea × Ca) + Nes (4)
Here, k represents a proportional constant of the current value.

[Particle number calculation example 3]
Further, Ea, Ca, Nel, nl, Nel, and Nes may be expressed using a general variable.
By combining a plurality of unknown variables based on experience or theory, it is possible to reduce the load of calculation and setting.
For example, it can be expressed as Na = A × Imfce-B.
Here, A and B are constants specified by the measurer.
Depending on the particle size distribution of the particles, Nel × nl = 0, Nes = 0, nl × k = 0, or Ea × Ca = 1 may be used.

In the particle classification device of the present invention, when detecting the number of particles in a predetermined particle size range from which particles having a certain particle size or more and a certain particle size or less are removed, the equation using the number of particles, the average charging rate, and the average valence is used. Since it is calculated, even when measuring a sample whose particle size distribution is unknown or a sample whose particle size distribution cannot be estimated, the number of particles in a predetermined particle size range can be calculated easily and quickly. It also eliminates the need for iterative calculations.
When calculating the actual particle concentration in the sample gas, it is necessary to consider the influence of dilution in the charging mechanism 33 in the examples of FIGS.

  The present invention can be used for an apparatus for measuring the number of fine particles contained in environmental gas, for example, an apparatus for measuring the number of fine particles contained in automobile exhaust gas in real time.

It is a figure which shows the piping system of the whole particle classification apparatus. The schematic of a particle classification mechanism is shown, (A) is a vertical sectional view, (B) is a horizontal sectional view in X-X 'of (A). It is a block diagram of charging device INZ used for a particle classification device. It is the schematic explaining the particle number calculation example of particle distribution, (A) is the figure which showed the particle distribution in the particle size distribution of 10 nm-1000 nm of the particle | grains contained in aerosol, (B) is particle size distribution 20 nm- It is a figure of the particle distribution which classified and displayed 0 valence-3 valence or more (not distinguishing +-) in 100 nm.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Housing | casing 3 Center electrode 4 Outer electrode 5 Classification area | region 7 Sheath gas supply part 9 Commutator 11 Aerosol supply part 11a Inlet 12, 24 Convergent electrode 13 1st discharge part 13a Discharge port 14 Small particle size side discharge part 14a Discharge port 16 Detector inlet slit 17 Second discharge portion 19 Insulator 31 Sheath gas supply mechanism 33 Charging mechanism 35 Gas discharge port 37 Third discharge portion 39 Branch flow path 41 Charging portion 43 Mixing portion INZ charging device PD Particle classification mechanism P1 to P3 Pump F1 ~ F3 filter MFC1 ~ MFC2 Flow rate adjuster

Claims (7)

A classification region comprising a pair of counter electrodes arranged opposite to each other to generate an electric field for classifying charged particles according to electric mobility;
It has a charging mechanism that charges the supplied sample gas to generate a charged aerosol, and has an inlet at or near one of the counter electrodes, and supplies the charged aerosol from the inlet to the classification region An aerosol supply,
A sheath gas supply mechanism that includes a sheath gas supply mechanism, and supplies an uncharged sheath gas from the upstream side of the classification region to the classification region at a flow rate Qc;
A first discharge unit having a discharge port at one electrode of the counter electrode or in the vicinity of the electrode on the downstream side of the aerosol supply unit, and discharging gas from the discharge port to the outside of the classification region at a flow rate Qe; ,
A second discharge unit that discharges gas at a flow rate Qs on the downstream side of the sheath gas flow and supplies the gas to the sheath gas supply mechanism,
A first discharge unit flow meter for measuring a gas flow rate Qe discharged from the first discharge unit;
Gas supply to the particle classifier is only sample gas supply to the aerosol supply unit, and gas discharge from the particle classifier to the outside is only gas discharge from the first discharge unit,
A particle classification apparatus characterized in that a measurement flow rate Qe by the first discharge unit flow meter is set as a sample gas supply amount Qa to the classification region. A branch flow path for supplying a part of the gas flow rate Qe discharged from the first discharge section to the sheath gas supply mechanism, and a branch flow rate meter for measuring the flow rate Qb flowing through the branch flow path,
The particle classifier according to claim 1, wherein Qa = Qe−Qb instead of Qa = Qe. An atmospheric pressure flow meter for measuring a gas flow rate Qo discharged from the first discharge portion to atmospheric pressure;
The particle classifier according to claim 1 or 2, wherein Qa = Qo instead of Qa = Qe. An atmospheric pressure flow meter for measuring a gas flow rate Qo discharged from the first discharge portion to atmospheric pressure;
3. The particle classifier according to claim 2, wherein Qa = Qo instead of Qa = Qe-Qb. A branch flow channel for supplying a part of the gas flow rate Qe discharged from the first discharge unit to the sheath gas supply mechanism, a branch flow meter for measuring the flow rate Qb flowing through the branch flow channel, and the second discharge A third discharge part for branching and discharging a part of the gas flow rate Qs discharged from the part before supplying to the sheath gas supply mechanism, and a third discharge part for measuring the flow rate Qr discharged from the third discharge part A flow meter,
The particle classifier according to claim 1, wherein Qa = Qr + Qe-Qb is used instead of Qa = Qe. Before the gas flow rate Qs discharged from the second discharge portion is supplied to the sheath gas supply mechanism, a third discharge portion is branched and discharged, and the flow rate Qr discharged from the third discharge portion is measured. A third discharge flow meter,
The particle classifier according to claim 2, wherein Qa = Qr + Qe-Qb is used instead of Qa = Qe-Qb. Before the gas flow rate Qs discharged from the second discharge portion is supplied to the sheath gas supply mechanism, a third discharge portion is branched and discharged, and the flow rate Qr discharged from the third discharge portion is measured. A third discharge flow meter,
The particle classifier according to claim 3 or 4, wherein Qa = Qr + Qe-Qb is used instead of Qa = Qo.

Images