JP4221501B2 - Aerosol charge neutralizer - Google Patents

Description

The present invention relates to a technique for neutralizing the charge distribution of an aerosol, and is used to easily realize a known charge distribution amount in the particle size distribution measurement of particles in an aerosol.

  The amount of charge of aerosol constituent particles generally has a distribution, but neutralization technology that makes the average of the distribution almost zero (uncharged) is an important technique for measuring the particle size distribution of aerosol particles by electromobility classification. Widely used. Electric mobility distribution measurement using a neutralization technique has been discussed in detail (see Non-Patent Document 1) and has been commercialized by a number of manufacturers including US TSI. Such a measuring apparatus is widely used for measuring particle size distribution during a manufacturing process using fine particles, particle size distribution of fine particles in atmospheric aerosol or automobile exhaust gas, and the like.

  The aerosol in the neutralized charge distribution state is almost uncharged, but at the same time, some of the particles are positively or negatively charged with a monovalent or multivalent charge. The number of particles of each valence is approximately the same number, the frequency distribution with the charged valence on the horizontal axis and the existence frequency of each charged valence on the vertical axis is positive and negative with zero as the mode value. Symmetric distribution. Such a charge distribution state is referred to as a neutralized state. In the neutralized state, since the distribution of the number of charges and the charge / uncharge rate are known for each particle size, the particle size distribution of the charged particles measured by the electromobility method can be used to determine the total number including uncharged particles. The particle size distribution of the particles can be converted and obtained accurately.

  For neutralization of aerosol particles, a device using a radioactive substance is most frequently used. Such a neutralization apparatus is described in detail in, for example, Non-Patent Document 1, and an example of the configuration is shown in FIG. In this apparatus, high-energy particles emitted from the radioactive substance 24 collide with gas molecules, and a large number of ions are generated in almost the same number. The bipolar ions generated in this way adhere to the suspended particles in the process of Brownian motion and change the charge amount of the particles. In the situation where there are almost the same number of positive and negative ions, the probability of attachment of ions to charged particles is greater than the probability of attachment of ions having the opposite polarity to the charge of the particles. As a result, the adhesion reaction between the bipolar ions and the particles renders the majority of the particles uncharged. However, some particles are charged positively or negatively monovalently, and a small number of particles are charged positively or negatively multivalently, and the particles as a whole reach the neutralized charge state described above.

  In order to generate bipolar ions for the purpose of neutralizing the aerosol, it is also possible to use electric discharge. For example, using a DC corona discharge, positive ions are generated simultaneously by a positive DC corona discharge and negative ions are generated by a negative DC corona discharge. By mixing these ions, the positive and negative ions are substantially the same. Bipolar ions including the amount are generated. In this apparatus, the ion generation field and the field for neutralizing the particles are separated. This separation is necessary to prevent the loss of particles in the DC corona discharge field (see Non-Patent Document 2). In addition, a bipolar ion generator using AC corona discharge and its application to neutralization of aerosol particles have been discussed. In this neutralization method, the bipolar ion generator is separated from the particle charge neutralization field. (See Patent Document 1).

As another technique for neutralizing aerosol by generating bipolar ions, there is a technique using generation of positive ions and photoelectrons using photoelectron emission by ultraviolet irradiation (Patent Document 2).
However, in this method, due to the principle that a DC electric field is generated in the neutralizing device to adjust the number of positive and negative ions, the charged particles are transported to the device wall by the electric field in the neutralizing device and lost. This neutralization method is not suitable for use in combination with electromobility measurements because electromobility measurements are only effective on charged particles.

Many other techniques for adjusting the charge distribution of aerosol particles have been proposed and put to practical use. Most of such techniques are not intended to neutralize, but are intended to charge non-charged particles using positive or negative monopolar ions.
As a result of the electrification of particles, the purpose is to facilitate the transport control of particles in the space. Such charging technology and transport control technology can improve the production efficiency in the manufacturing process using particles as a material element (Patent Literature 3), control of toner particles in a copying machine (see Patent Document 4), removal of particles from the air by electric dust collection (see Patent Document 5), and particle measuring apparatus having sensitivity only to charged particles. It is used for applications such as an increase in measurement sensitivity (see Patent Document 6).
Among these charging technologies, there are those using unipolar ions generated from direct current discharge (see Patent Document 7) or those obtained by extracting only the unipolar components from bipolar ions generated from radioactive substances (see Patent Document 8). is there.
However, in such a method for the purpose of charging uncharged particles, in any case, the charge distribution of the particles is biased from zero to either positive or negative, and the charge distribution in a neutralized state is not reached. In addition, since many polyvalent charged particles are generated, in the particle size distribution measurement by the electromobility method, coarse particles having multivalent charges and monovalent charged microparticles are measured as the same electric mobility. Cause problems. Therefore, it is difficult to use such a particle charging technique as it is as a neutralization technique for the purpose of measuring the particle diameter by the electric mobility method.

Japanese Patent No. 3393270 Japanese Patent No. 2670942 JP 2002-190258 A JP 2000-187369 A JP 52-99480 A Special Table 2000-504111 Japanese Patent No. 62-19033 Japanese Patent Laid-Open No. 7-24357 Knutson, EO (1976) .Extended electric mobility method for measuring aerosol particle size and concentration.Fine Particles, Aerosol Generation, Measurement, Sampling, and Analysis.BYH Liu.New York, NY, Academic Press: 740-762. Adachi, M. et al. (1993). "Aerosol charge neutralization by a corona ionizer." Aerosol Sci. Technol. 18: 48-58.

  The neutralizing device using the radioactive substance has a limitation that it can be used only in a place where the use of the radioactive substance is approved and only by a person who has received the authorization for handling the radioactive substance. Even when the conditions for approval were satisfied, special handling was required for safety management and storage to eliminate the health effects on the human body associated with the use of radioactive materials.

  Moreover, in the neutralization apparatus using the corona discharge of Non-Patent Document 2 and Patent Document 1, the ion generation part is separated from the aerosol flow path, and the ions generated in the ion generation part are mixed with the neutralized aerosol. Therefore, it is necessary to introduce gas and control the flow rate unique to the ion generation unit, which complicates the structure of the neutralizer. Further, mixing of the gas containing ions into the neutralized aerosol dilutes the aerosol and causes a decrease in the particle concentration. Furthermore, in patent document 2, the loss of the charged particle by the direct current electric field in an apparatus arises.

The present invention neutralizes the aerosol charge distribution by generating bipolar ions from an ion generator using alternating current discharge. In other words, since an AC voltage with zero DC component (unbiased) can be applied, particle loss does not occur around the electrode even if discharge is used. In other words, it was possible to have an ion generation function at the center of the field for neutralizing the charge of the particles, so we succeeded in creating an aerosol charge neutralization device that is simple in structure, easy to control and easy to handle.
That is, this application provides the following inventions.
<1> An aerosol charge neutralization device comprising an aerosol inlet and an aerosol outlet at both ends, a conductive container with a branch pipe at the center, an ion generator by alternating current, and an alternating current power source,
An aerosol charge neutralization apparatus comprising the following requirements:
(I) The field where positive ions and negative ions are generated using AC discharge is at the center of the field where the particles are charged and neutralized, and both fields are in the same space.
(Ii) An alternating current ion generator includes a discharge electrode and a ground electrode, and the discharge electrode has a structure having fine protrusions on the surface, and the ground electrode is only locally in the space near the electrode pair. to be able to form an electric field, it is provided so as to surround the discharge electrodes via the thin insulating layer, and (iii) an ion generating apparatus according to the alternating current of the aerosol through the branch pipe of the container central portion that it is provided perpendicular to the flow path direction subjected to <2> discharge electrode alternating current, charge neutralization apparatus of the aerosol according to <1>, which comprises using an alternating current bias is not applied.
<3> During the charging of the aerosol according to <1> or <2>, the applied AC voltage and frequency are set so that the number of positive and negative ions generated by the discharge is substantially the same. Japanese equipment.

  In this invention, since the ion generator by alternating current is used, since a radioactive substance is not used, the restriction | limiting of the neutralization apparatus use by use authorization or handling authorization is lost. In addition, handling and storage of the neutralizer is easier than using a radioactive substance.

  In the present invention, an alternating current ion generator uses a discharge electrode having a structure having fine protrusions on the surface, and discharges by applying an alternating voltage with zero direct current component (not biased). Since no particle loss occurs around the electrode even if is used, the discharge electrode can be placed in the neutralized aerosol flow path. As a result, it is not necessary to separate the ion generating part from the aerosol flow path, it is not necessary to introduce a new gas, and the apparatus structure such as flow rate control can be simplified.

  In the present invention, since the power source for generating the applied voltage used for the discharge is a power source that can control the generation / stop of the normal voltage, the operation of such a power source can be performed without the removal of the device. Can be controlled.

In the present invention, there is an ion generator at the center of a field for generating positive ions and negative ions using AC discharge, and an aerosol charge neutralizing device in which a conductive material constituting the space is grounded can be obtained. .
In the present invention, an ion generator using alternating current is composed of a discharge electrode and a ground electrode, and the discharge electrode having a structure having fine protrusions on the surface thereof is used. The ground electrode surrounds the discharge electrode through a thin insulating layer, and is an aerosol charge neutralization device in which the electrode pair is provided so that an electric field can be formed only locally in the space near the electrode pair. it can.
Such a discharge electrode is placed in the flow path of the aerosol to be neutralized, and an AC voltage having a DC component of zero is applied. The voltage and frequency are set to appropriate values in order to generate approximately the same amount of positive and negative ions.

The aerosol charge neutralization apparatus used in the present invention will be described with reference to FIGS.
FIG. 1 shows an overall view of the configuration of an aerosol charge neutralization apparatus. The neutralizer container has a metal container 11 having a cylindrical tube attached with a branch pipe, metal aerosol inlets 12 and outlets 13 at both ends thereof, and an ion generator 14 is installed inside the container. It is necessary to use the ion generator 14 that can maintain a stable discharge when an AC voltage is applied. In the present invention, the structure of a creeping corona discharge electrode is used.
The conducting wire 19 to the discharge electrode is connected to an external AC power supply 16 through a current introduction terminal 15. In order not to generate a DC electric field in the space between the lead wire 19 to the discharge electrode and the cylindrical vessel, the lead wire 17 to the ground electrode connected to one side of the ion generator 14 is electrically connected to the cylindrical vessel via the lead wire 18. Connect to. The conducting wire 19 connected to the discharge electrode is disposed in the vessel branch pipe part and separated as much as possible from the flow of the neutralized aerosol to suppress particle loss due to the electric field generated around the conducting wire 19. For the same reason, the length of the conductive wire 19 is made as short as possible. The aerosol flow rate flowing in the neutralization device is determined by the flow rate control of the device downstream of the aerosol flow path connected to the outlet 13.

FIG. 3 shows the structure of the ion generator. The alternating voltage is applied to the discharge electrode 31 via the conducting wire 32. A ground electrode 33 is arranged around the discharge electrode 31 so as to surround the thin insulating layer. The interval between the discharge electrode 31 and the ground electrode 33 is made as small as possible within a range where stable discharge can be obtained. The ground electrode 33 is grounded via a conducting wire 34.

In the apparatus of the present invention, in order to optimize the voltage and frequency applied to the discharge electrode in order to generate approximately the same number of positive and negative ions, the ion number concentration by polarity is measured as a function of voltage and frequency.
Examples of such measurement results are shown in Table 1. There were many cases where the negative ion concentration was slightly higher than the positive ion concentration. However, under the conditions where the voltage was 3 kV and the frequency was 50 Hz, almost the same positive and negative ion concentrations were observed, and operating conditions aimed at neutralization. You can see that Moreover, although the ion concentration which the neutralization apparatus using a radioactive substance (Americium 241) generate | occur | produced was shown in the lowest part of Table 1, it was generated by the ion concentration and radioactive substance which were generated by discharge from comparison with these. It can be seen that the ion concentration is almost the same amount, and it can be analogized that the neutralizing device by discharge will have the same neutralizing performance as the neutralizing device using radioactive material.

  Optimum conditions are determined with reference to Table 1 (3 kV, 50 Hz), and the neutralization device of the present invention is applied to the uncharged silver particle aerosol generated from the particle generator so that some of the particles are charged. The state was measured with a differential electric mobility classifier, and the charged particle number concentration for each particle size was determined positively and negatively. The result is shown in FIG. The amount of positive and negative charged particles is almost the same in each particle size, and it is considered that the charge distribution is a positive and negative symmetric type centered on zero due to bipolar ions.

  Since the aerosol charge neutralization apparatus of the present invention uses an alternating current ion generator, it does not use a radioactive substance, so that there is no restriction on the use of the neutralization apparatus due to use authorization or handling authorization. In addition, since the handling and storage of the neutralization device is easier than those using radioactive materials, it is possible to give epoch-making convenience to aerosol measurement using charge neutralization.

1 is a schematic diagram of an aerosol charge neutralization apparatus according to an embodiment of the present invention. Schematic diagram of conventional aerosol charge neutralization equipment using radioactive materials Schematic diagram of electrode structure of ion generator Concentration distribution of distinct number of positively charged particles generated as a result of passing an uncharged silver particle aerosol through the aerosol charge neutralizer of the present invention (Table 1) Positive and negative ions generated from the aerosol charge neutralizer of the present invention Dependence of concentration on applied voltage and frequency, and concentration of positive and negative ions generated from neutralizers using radioactive materials

Explanation of symbols

11 Neutralizer container 12 Aerosol inlet 13 Aerosol outlet 14 Ion generator 15 Current introduction terminal 16 AC power source 17 Conductor 18 Conductor 19 Conductor 21 Conventional neutralizer container 22 Aerosol inlet 23 Aerosol outlet 24 Containing radioactive substance Radiation source 31 Discharge electrode 32 Conductor 33 Ground electrode 34 Conductor 35 Electrode substrate

Claims (3)

An aerosol charge neutralization device comprising an aerosol inlet and an aerosol outlet at both ends, a conductive container with a branch pipe at the center, an ion generator by alternating current, and an alternating current power source,
An aerosol charge neutralization apparatus comprising the following requirements:
(I) The field where positive ions and negative ions are generated using AC discharge is at the center of the field where the particles are charged and neutralized, and both fields are in the same space.
(Ii) An alternating current ion generator includes a discharge electrode and a ground electrode, and the discharge electrode has a structure having fine protrusions on the surface, and the ground electrode is only locally in the space near the electrode pair. to be able to form an electric field, it is provided so as to surround the discharge electrodes via the thin insulating layer, and (iii) an ion generating apparatus according to the alternating current of the aerosol through the branch pipe of the container central portion Provided perpendicular to the flow path direction 2. The aerosol charge neutralization apparatus according to claim 1, wherein an alternating current applied to the discharge electrode is an alternating current that is not biased. 3. The aerosol charge neutralization apparatus according to claim 1, wherein the applied AC voltage and frequency are set so that the number of positive and negative ions generated by the discharge is substantially the same.

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