JPH0522183B2 - - Google Patents

Description

Detailed Description of the Invention A two-stage electrostatic precipitator or electrostatic air filter has a charging section that charges particles in the air and a collection section that collects the charged particles. In order to maintain high collection performance, not only the performance of the collection section but also the performance of the charging section is important.

What is important in the characteristics of a charged part is how to load a large amount of charge onto particles in a short time, and how to eliminate uncharged particles.

Due to the structure of a charging device that uses corona discharge, it is difficult to completely eliminate particles that bypass the ionization region because they apply a high voltage and maintain an insulating distance. Particles that have passed through the charging device tend to include uncharged particles or particles with a small amount of charge.

There is a so-called mobility analyzer as a conventional device for measuring the amount of charge of fine particles in the air.

This is done by applying a voltage between cylindrical electrodes or flat plate electrodes to make the particles have a known amount of charge in advance, that is, to make them singly charged, and then generating a current due to the charged particles being collected by the electrodes. The particle size and concentration are measured by measuring while changing the voltage applied between the electrodes.

In this mobility analyzer, particles are counted by measuring current, so if the particle concentration is low, the current becomes extremely small and measurement becomes impossible. Measurable particle size is 0.003
It is in a limited range of about ~0.3 μm. Since radiation is used to uniformly charge particles, there are various disadvantages such as the equipment is difficult to handle and expensive.

The present invention can measure the number of particles in air or other fluids and determine the proportion of uncharged particles contained in a group of charged particles, and can measure even when the particle concentration is extremely low. The purpose of this invention is to provide a device for measuring the amount of charge of charged particles that is expected to have many applications.

Embodiments of the present invention will be described below based on the drawings. In FIG. 1, 1 is an electrode section through which air containing charged particles passes, and 2 is a high-voltage power source used to apply a high voltage to the electrode section 1. , 3 is a light scattering particle counter that counts the number of particles by sucking air containing charged particles that has passed through the electrode section 1, and 4 is a data processing device.

FIG. 2 shows an example of the electrode section 1,
To explain this, a coaxial double cylindrical electrode, that is, an outer cylindrical electrode 6 is provided at intervals around the outer periphery of an inner cylindrical electrode 5,
The electrodes 5 and 6 are electrically insulated by an insulating material, and flanges 7 and 8 are provided at both ends of the outer cylinder electrode 6. Insulating plate 1 having openings 9, 10 of diameter
1 and 12, and gas such as air containing charged particles is applied to the outside of one insulating plate 11, and both electrodes 5,
The flange 14 provided at the rear end of the inlet pipe 13 introduced between the electrodes 5 and 6 is placed on the outside of the other insulating plate 12. Flange 1 provided at the rear end
6, the ends of the stud bolts 17, 17 inserted between the insulating plates 11, 12 protrude to the outside of the flanges 14 and 16, and nuts 18, 19 are screwed into each of the protruding parts, respectively. An inlet pipe 13 and an outlet pipe 15 are integrally connected to both ends of the electrode 6 via insulating plates 11 and 12, and a gas flow passing between the inner and outer electrodes 5 and 6 is connected to both ends of the inner cylinder electrode 5. A rectifier head 20 and a rectifier tail 21 are provided to prevent air from leaking, and between the flange 7 and the insulating plate 11 and between the flange 14 and the insulating plate 11, there are O-rings 22 to prevent air leakage.
23 between the flange 8 and the insulating plate 12,
O-rings 24 and 25 are also fitted between the flange 16 and the insulating plate 12 to prevent air leakage, the inner tube electrode 5 is grounded 26, and the outer tube electrode 6 is connected to a high voltage power source 2 that applies high voltage. It has been done. This high-voltage power supply 2 is variable from 0V to several kilovolts. Incidentally, a light scattering type particle counter capable of counting the number of particles is connected to the outlet pipe 15.

Next, to explain the measurement method using the charged particle charge measuring device having the above-mentioned configuration, polydisperse charged particles of unknown particle size contained in the air pass through the inlet pipe 13 to the inner tube electrode 5 and the outer tube electrode 5. When the air enters between the cylindrical electrodes 6, it receives a Coulomb force due to the electric field caused by the high voltage applied between the two electrodes 5 and 6, and is collected by the opposite polarity electrode, but the degree of this collection depends on the airflow velocity v. , or sampling suction amount Q, electrode distance (size),
It depends on the applied voltage V, the particle diameter D _p and the charge amount n of the particles.

Therefore, while changing the applied voltage V,
When the ratio of the number of particles that have passed through the particle is counted using a particle counter 3 for a certain particle size range, for example, 0.1 to 0.2 μm, the result is as shown in the graph of FIG. The applied voltage V ^* , ie, the limit voltage, determined by the dotted line in FIG. 3 is obtained by removing the voltage from FIG. 3, and the amount of charge on the particles is measured using the following equation.

n=4πακV ^* /Q[e] (1) However, α is a constant determined by the electrode shape, and is determined by the following equation.

α=l/21log(r _p ÷ r _i ) (2) r _p : Outer cylinder radius r _i : Inner cylinder radius l : Cylinder length Q : Suction amount κ : Mobility of single charge Mobility of single charge κ is given by the Stokes-Cunningham equation as a function of particle size, and is determined by the following equation.

κ＝C _n e／3πμD _p (3) C _n : Cunningham correction coefficient e : Elementary charge of electron D _p : Particle diameter μ : Viscosity coefficient of air Here, depending on which channel of the particle counter is used, If the particle size category of interest is determined, and it is 0.1 to 0.2 μm, the Cunningham correction coefficient C _n and single charge mobility κ are determined with D _p =0.15 μm. The suction amount Q is equal to the suction amount of the particle counter 3.

Then, it can be seen from equation (1) that the amount of charge on a particle of the particle size of interest is determined by V ^* .

The electric field inside the cylindrical electrode generated by the applied voltage bends the trajectory of the particles and they are collected within the cylindrical electrode, but V ^* This is the limit voltage at which particles are collected.

The actual method for determining V ^* is the removal method shown in FIG. 3, which is performed by the data processing device 4.

That is, the number of particles in the cylindrical electrode when the applied voltage V ₁
C _po (V ₁ ), the number of particles in the cylindrical electrode when the applied voltage V ₂
From the data of C _po (V ₂ ) and the number of particles C _pff when no voltage is applied, it is determined as V ^* V ₂ × C _pff / C _po (V ₂ ) = V ₁ × C _pff / C _po (V ₁ ) .

By the way, the reciprocal of 4πακ/Q in equation (1) is a quantity having the unit of voltage. Therefore, if this is set as V ₀ , then V ₀ =Q/4πακ (4).

The physical meaning of this equation (4) corresponds to the limiting voltage in the case of a single charged particle. If it is known that the amount of charge is a single charge, it can be determined by theoretical calculation for the particle size of interest, and it is
This is the theoretical limit voltage shown in equation (4).

Looking at it in this way, equation (1) becomes the following equation (5): n=V ^* /V ₀ (5) The limit voltage V ^* determined by measurement and the limit voltage of a single charge determined theoretically. It can be seen that the ratio is

An example of the results of measuring the amount of charge of particles that have passed through a certain charging device using the device according to the present invention is shown in the graph of FIG. This graph shows particle sizes of 0.1-0.2μm, 0.2-0.3μm, 0.3-0.4μm.
The transmittance is determined using a particle counter as shown in FIG. 3 while changing the applied voltage for each range of 0.4 to 0.5 μm, V ^* is determined, and the amount of charge is determined. Next, an example of the results of measuring the proportion of uncharged particles is as shown in the graph in Figure 5. The fine particles that have passed through a charging device with the normal number of discharge lines (18) are not charged. The transmittance decreases as the voltage applied to the cylindrical electrode increases. In other words, uncharged particles that have passed through the part where the discharge wire is removed are not collected within the cylindrical electrode, so when air containing both charged and uncharged particles is passed through the cylindrical electrode, even if the applied voltage is increased, no amount of permeation occurs. The rate remains almost constant. The value of the transmittance at this time becomes the proportion of uncharged particles, and this proportion is shown by the 5% dashed line in the graph of FIG.

In the graph of Fig. 3, C _po indicates the particle concentration at the outlet of the electrode section 1 when a voltage is applied, C _pff indicates the particle concentration at the outlet of the electrode section 1 when no voltage is applied, and the fourth In the figure and the graph of Fig. 5, I _p indicates the discharge current of the charging device, Q indicates the air volume passing through the charging device, and in the graph of Fig. 5, wires indicates the number of discharge wires in the charging device, and DOP indicates the test The fine particles of dioctyl phthalate used in the above are shown below.

In addition to the embodiments described above, the present invention connects a high voltage power source 2 that applies a high voltage to the cylindrical electrode 5, and
The design can be changed as appropriate, such as by grounding the electrode part 1 or configuring the electrode part 1 with a flat plate electrode.

Since the present invention is constructed as described above, 0.1 μm
It is possible to measure the amount of charge of particles with a diameter of ~10 μm while they are suspended in the air. In particular, the amount of charge can be measured even when the particle concentration is low. The proportion of uncharged particles contained in a group of charged particles can be measured. Unlike conventional mobility analyzers, there is no need for extremely high insulation between electrodes to measure minute currents; all you need to do is apply an electric field, so the structure is simple, easy to manufacture, and easy to handle. It has the following advantages.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the configuration of the device of the present invention, FIG. 2 is a sectional view showing an example of the electrode section,
Figure 3 is a graph showing the transmittance of charged particles passing through the electrode section, Figure 4 is a graph showing an example of the measurement results of particle charging characteristics, and Figure 5 is the ratio of uncharged particles included in charged particles. 2 is a graph showing an example of measurement results. DESCRIPTION OF SYMBOLS 1... Electrode part, 2... High-voltage power supply, 3... Particle counter, 4... Data processing device, 5... Cylindrical electrode, 6... External cylindrical electrode.

Claims (1)

[Scope of Claims] 1. Electrodes supported by an insulating material at intervals through which air containing charged particles passes, an electrode part that creates a potential difference between the electrodes, and a high voltage applied to this electrode part. a high-voltage power supply connected to the electrode section, a particle counter that counts the number of particles in the gas that has passed between the electrodes of the electrode section, a particle counter that counts the number of particles at the electrode outlet when no high voltage is applied to the electrode section, and a particle counter that counts the number of particles in the gas that has passed between the electrodes of the electrode section; Data that calculates the limit voltage determined from the data on the number of particles at the electrode exit when high voltage is applied to the electrode part, and calculates and outputs the amount of charge of the particles calculated from the ratio of this limit voltage and the theoretical limit voltage of a single charge. A charged particle charge amount measuring device comprising a processing device. 2. The device for measuring the amount of electric charge of charged particles according to claim 1, wherein the electrode portion comprises a double cylindrical electrode. 3. The device for measuring the amount of charge of charged particles according to claim 1, wherein the electrode portion is a flat plate electrode.