RU1800321C - Aerosol concentration determining method - Google Patents

Abstract

SUMMARY OF THE INVENTION: Aerosol particles are deposited during electro-precipitation on a metal or metallized tape with a mirror surface. 1 ill.

Description

The invention relates to the protection of the environment, and more particularly to the control of aerosol pollution of atmospheric air.

The purpose of the invention is to increase sensitivity.

This goal is achieved in that in the device for determining the concentration of aerosols, including a sampler with a substrate in the form of a tape for the deposition of particles and a photometer for recording the intensity of light scattering of particles, the sampler is made in the form of an electric precipitator with a cylindrical flow chamber made of fluoroplastic, along the axis of which there is a needle corona electrode while a substrate made of metal or metallized with a mirror surface is used as a precipitation electrode.

It is known to deposit particles on a substrate by inertia, thermophoresis, under the influence of gravity (gravitational sedimentation), as well as the deposition of pre-charged particles in an electric field (electrorecipitation).

As a result of studies, it was found that sampling by electroprecipitation is most effective.

As is known, the Coulomb force, defined by the expression, acts on a charged particle in an electric field

Fk Eqp,

where E is the electric field strength;

qp is the charge of the particle.

Particles are charged by depositing ions from the surrounding gas volume on their surface. A corona discharge is usually used as a source of ions. The magnitude of the limiting charge of a particle placed in the corona discharge field is easy to estimate. Indeed, the flow of ions falling under the action of an external electric field onto the particle surface will cease when the electric field created by ions deposited on the particle surface becomes equal to the external field, i.e.

ate

WITH

00

oh oh

Cj

Yu

OR

Ј0 d p

 Ek

whence for the ultimate charge of the particle we obtain the expression:

q p jre0d p E k.

A more detailed analysis, taking into account the dielectric properties of the material of the particles, leads to the following expression for the value of the limiting charge:

q p le 0 d p E kf e,

Where

B - 1

fe 1 +2, о .Ј - relative

Ј + 2

dielectric constant of the particle material.

Since for most non-conductive substances, Ј varies from 2 to 5, the factor f e will vary from 1.5 to 2. For conductors, Ј and, respectively, fg 3.

Taking into account the Stokes law for the resistance force, it is easy to determine the rate of electric drift of charged particles:

Vk -f dpfЈEl,

Let us estimate the values of charge, coulomb force, and particle drift velocity in an electric field under normal atmospheric conditions in the following case:

dp, Ek 106B, fe 3.

Using the obtained expressions, we find:

-17

qp 8 10 cells, Fk 8 10

-eleven

Vk 0.5m-s

-1

Thus, despite the fact that the Coulomb force acting on particles in the corona discharge field is much less than the inertia force in impactors, it nevertheless exceeds the thermophoretic force by more than two orders of magnitude and by more than four pores q is the force of gravity. Therefore, electrical precipitation is the most effective method of depositing particles on a substrate. In addition, the proposed metal or metallized substrate has high electrical conductivity and can be directly used as a precipitation electrode. This does not require lubrication to hold the particles on the substrate, and the relatively low speed of electric particle drift eliminates the possibility of abrasive destruction of the mirror surface.

In addition, the use of the proposed device as a precipitation electrode of a metal or metallized substrate with a mirror surface allows one to obtain an additional positive effect by increasing

5 of the luminous flux incident on individual aerosol particles due to additional light reflected from the substrate.

The drawing shows a device for determining the concentration of aerosol, General view. ,

The device comprises a housing 1, in which a tape 2 for deposition of aerosol particles and a tape drive 5 are placed 3. In the upper wall of the housing 1 immediately above the surface of the tape 2, an electric precipitator 4, a photodetector 5, and a illuminator 6 are sequentially installed.

0 The electric precipitator 4 is made in the form of a cylindrical flow chamber 7 of fluoroplastic, along the axis of which a needle-shaped corona electrode 8 is mounted, mounted in a metal holder 9,

5 pressed into the upper base of the chamber 7. The lower open base of the chamber 7 is placed directly above the tape 2, which serves as a precipitation electrode, which is made of metal or metallized with a mirror surface and is connected via a current collector contact 10 by a high-voltage electric circuit 11 to the corona electrode 8. In the upper part camera 7 protruding from the housing 1

5 of the device, an inlet pipe 12 is installed connecting the internal volume of the chamber 7 with the volume of the air under investigation.

The lighter 6 is made in the form of a tube 13, along the axis of which a superminiature SMN10-55 incandescent lamp 14, a collecting lens 15 and an aperture system 16 are sequentially arranged. Moreover, the light body of the lamp 14 is located in the focus of the lens 15, and the axis of the tube 13 coincides with the axis of the lens

5 and makes an angle of 30 ° with the surface of the tape 2.

The photodetector 5 is made in the form of a tube 17, along the axis of which a sensing element 18 is sequentially mounted, which is used as a photodiode

FD-7K, diaphragm 19 and collecting lens 20. Moreover, the axis of the tube 17, which coincides with the axis of the lens 20, makes an angle of 30 ° with the surface of the tape 2 and runs perpendicular to the center line of the tape, intersecting it at two focal lengths from the lens 20. and the sensing element 18 is mounted on the opposite side of the lens 20 also at two focal lengths from it. In this case, the axes of the photodetector 5 and the illuminator 6 lie in two mutually perpendicular planes. The photodetector 5 is connected by an electric circuit 21 to a recording device 22, in which the recorder VD41 from KIPP ZONEN (input resistance 1 MOhm) is used.

. An outlet pipe 23 is installed in the housing 1 of the device, to which a small-sized centrifugal fan 24 is connected, driven by an electric motor 25.

The device operates as follows. The centrifugal fan 24 is turned on, and the high voltage from the high voltage power supply unit (not shown) is applied to the corona electrode 8 of the electric precipitator 4, while the tape 2 is maintained at zero potential. Under the action of the vacuum created by the centrifugal fan 24 in the device body 1 and in the flow chamber 7, the test air enters the electric receiver 4 through the inlet 12. Aerosol particles passing through the flow chamber 7 fall into the region of the corona discharge arising between the tip the corona electrode 8 and the tape 2, where they are charged by the flow of ions and deposited by the electric field on the mirror surface of the tape. Purified air through an annular gap between the lower base of the chamber 7 and the tape 2 enters the device body 1, from where it is then ejected by a centrifugal fan 24 through the outlet pipe 23.

After a predetermined sampling time, the centrifugal fan 24 and the electric precipitator 4 are turned off. The tape drive 3, the illuminator 6, the photodetector 5 and the recording device 22 are turned on. The section is moving

tapes with a sample taken into the registration zone and measuring the intensity of the scattered light sample.

The use of a metallized tape with a mirror surface allows one to reliably record aerosol concentrations from 5 μg and higher, since the signal from the aerosol sample is no less than twice the value of the background signal from a clean tape. At the same time, we can conclude that when using filter tapes for sampling, the background signal will correspond to the signal from the aerosol sample at concentrations of 40Q. 1200 μg / m3. Thus, the proposed device for determining the concentration of aerosol has about 100 times more higher sensitivity than the device adopted as a prototype.

Concentration determination device

the aerosol will provide, in comparison with the known ones, more reliable and express control of aerosol pollution of atmospheric air by industrial emissions, in particular in the case of

particularly harmful emissions, the maximum permissible concentrations of which lie in the range of 5 ... 50 μg.m.

Claims (1)

SUMMARY OF THE INVENTION Concentration Detection Device an aerosol comprising a sampler with a substrate in the form of a tape for particle deposition and a photometer for recording the intensity of light scattering of particles, characterized in that, in order to increase sensitivity, the sampler is made in the form of an electric precipitator with a cylindrical flow chamber made of fluoroplastic, along the axis of which there is a needle a corona electrode, and a substrate made of metal or metallized with a mirror surface is used as a precipitation electrode.