RU2231771C1 - Method of measurement of concentration and fraction dispersed composition of aerosols and device for realization of this method - Google Patents

Abstract

FIELD: measurement of concentration of non-conducting particles in gaseous mixtures.

SUBSTANCE: proposed method consists in passing the aerosol particles preliminarily charged in alternating coronal discharge chamber through area of permanent external magnetic field whose vector of magnetic induction is directed perpendicularly relative to flow of particles and recording on measuring electrodes. Device proposed for realization of this method is made in form of bipolar charging chamber with permanent magnet , two measuring induction electrodes shielded on the outside and located symmetrically relative to axis of charging chamber in plane perpendicular to vector of magnetic induction of external magnetic field.

EFFECT: enhanced accuracy of measurement at simultaneous obtaining of information pertaining to fraction dispersed composition of aerosol under test.

3 cl, 1 dwg

Description

The invention relates to the field of determining particle sizes and their concentrations and can be used in various fields of science, technology and medicine, for example, for measuring the concentration and fractional dispersed composition (FDS) of aerosols used as air treatment respiratory mixtures.

There is a method of continuous measurement of the concentration of the dispersed phase of aerosols, based on the charging of aerosol particles in the field of an alternating current corona discharge and the subsequent measurement of the emf induced by them on the measuring electrode [1].

When using this method, the measured EMF is proportional to the total surface area of the charged aerosol particles passing the measuring electrode. But since the particle’s charge is proportional to the square of its diameter, and the particle’s volume is proportional to the cube of its diameter, the accuracy of measuring the calculated concentration of aerosols inhomogeneous in the dispersed composition of their constituent particles is small.

The disadvantage of this method is the low accuracy of measuring the concentration of aerosol with unknown FDS.

Closest to the technical nature of the present invention is a method of measuring the mass of the dispersed phase of an aerosol [2], based on the preliminary charge of the aerosol particles in the field of a unipolar corona discharge, the impact on the stream of a unipolar-charged aerosol of a deflecting electric field of a capacitor directed perpendicular to the flow, causing a transverse deviation a charged aerosol stream, and subsequent registration and processing of the charge induced by the stream at two induction electrodes, is located s symmetrically relative to the axis of the charging chamber and spaced from each other in the plane of the electric field vector of the deflecting capacitor. Each of the electrodes through its charge-sensitive amplifier is connected to one of the two inputs of the subtraction circuit and to one of the two inputs of the summation circuit. The output signal of the subtraction circuit is proportional to the deviation of the charged stream in the capacitor field, and the output signal of the summing circuit characterizes the magnitude of the deflected charge. Method [2] allows to slightly improve, compared with the previous one, the accuracy of measuring the calculated concentration of aerosols with a wide range of particle size changes, however, it does not allow to obtain information about the FDS of the studied aerosol.

The aim of the invention is to improve the accuracy of the method of measuring the calculated concentration of the aerosol and at the same time measuring its FDS.

This goal is achieved by the fact that a stream of aerosol particles preliminarily alternately charged in the charging chamber of an AC corona discharge is passed through an applied adjustable external constant magnetic field, the magnetic induction vector of which is directed perpendicular to the aerosol stream, in which the spatial separation of charged particles into fractions and along the sign of the charge due to the Lorentz force, moreover, by regulating the magnetic induction of the applied field, it is possible to ensure a consistent The motion of the different fractions of the test aerosol for the same chosen path. Particles of different signs of charge but of the same FDS move along trajectories symmetrical about the axis of the ionization chamber in a plane perpendicular to the magnetic induction vector of the applied field.

Separation of particles by sign allows the use of separate, symmetrically located relative to the charging chamber, measuring electrodes for particles charged positively and negatively, and by differential processing (subtraction) of the emf of different signs induced by them on the measuring electrodes, double the value of the useful signal while suppressing spurious EMF of the same sign induced on the measuring electrodes by corona discharge.

Thus, spatial separation in a magnetic field of charged particles of different fractions provides a sequential measurement of the counted concentration of particles for each fraction, calculation of the total counted concentration for all fractions of particles, as well as measurement with high accuracy of the photographic function of the studied aerosol.

The drawing shows a device whose operating principle is based on the proposed method.

In the dielectric casing (not shown in the drawing), a charging chamber consisting of two electrodes is installed sequentially along the laminar flow of aerosol: the outer one, for example, in the form of a hollow metal cylinder and the inner one (not shown in the drawing) in the form of a metal needle located along the cylinder axis . An alternating pulse voltage from a high voltage source (not shown in the drawing) is supplied to the electrodes of the charging chamber, which ensures the formation of an alternating electrostatic field in the chamber due to corona discharge.

The charging chamber provides a charge of aerosol particles passing through the chamber section to saturation. At the chamber exit, in the laminar flow of aerosol particles having some intrinsic background charge, a cylindrical region is formed, consisting of space charge packets moving with the flow with an alternating charge sign.

Following the charging chamber, poles 2 and 3 of the permanent magnet are arranged on the path of the laminar aerosol flow in such a way that the magnetic induction vector is directed perpendicular to the aerosol flow. Charged aerosol particles move perpendicular to the magnetic lines of force, with the Lorentz force acting in them in the direction perpendicular to the magnetic field induction vector and the charged particle velocity vector. The trajectory of a charged particle in a constant magnetic field is a circle whose radius is proportional to the ratio of the particle diameter to the magnetic field induction and does not depend on the particle velocity. Charged particles of different fractions passing the magnet poles are shifted to different angles from the axis of the charging chamber with constant induction of the magnetic field.

Next, on the path of the aerosol flow, at the same distance, symmetrically relative to the axis of the charging chamber, the first 4 and second 5 induction measuring electrodes are placed in the form of hollow metal shielded cylinders with an inner diameter equal to the inner diameter of the outer electrode 1 of the charging chamber.

By changing the magnetic field between the poles 2 and 3 of the permanent magnet, it is possible to ensure through the induction measuring electrodes 4 and 5 packets of charged particles of a selected size (fraction), and packets of particles carrying a charge of a different sign, but of the same magnitude, will be shifted in opposite directions from the axis of the charging chamber at equal angles and each passing inside its electrode, inducing an emf in it, proportional to the total surface area of the particles of this packet (this fraction). In the intervals between the packets, an aerosol stream uncharged in the charging chamber passes through the measuring electrodes 4 and 5 with some own background charge, which induces a background emf on the electrodes 4 and 5.

The first induction measuring electrode 4 is connected to a non-inverting input of a subtractor 6, for example, an instrumental amplifier, and the second electrode 5 is connected to its inverting input. The instrumental amplifier 6 performs the operation of subtracting the EMF induced in the measuring electrodes 4 and 5, while the EMF induced by the packets of charged particles (different in sign) are added, and the EMF induced by the background charge on the electrodes are subtracted and suppressed by the instrumental amplifier 6, as in-phase component. The leads from the charging chamber to the induction measuring electrodes 4 and 5 are the same (due to the symmetry of the location of the electrodes and the same distance of each of them to the charging chamber - the source of pickups) and are suppressed by the instrumental amplifier 6, as a common-mode component.

Measurements are carried out at various values of the magnetic field strength, i.e. for different fractions of the aerosol, and calculated for each fraction, the counted concentration of particles, as well as the integral counted concentration of the aerosol as the sum of the counted concentrations of all fractions and the FDS of the studied aerosol.

Thus, a device that implements the proposed method improves the accuracy of measuring the concentration and provides information on the aerosol FDS.

Sources of information

1. Device for continuous measurement of gas dust by A. with. USSR No. 113558, class G 01 N 15/02, Vysotsky D.I. et al. 10.23.56.

2. Device for measuring the mass of the dispersed phase of the aerosol by AS USSR No. 693165, cl. G 01 N 15/02, Napalkov E.G., publ. 10/25/79, bull. No. 39 is a prototype.

Claims (2)

1. A method of measuring the concentration and fractionally dispersed composition of aerosols, based on the charge of aerosol particles using a corona discharge, followed by registration of the emf induced by them on two measuring electrodes symmetrically spaced at the same distance relative to the axis of the corona discharge chamber, each electrically connected to its input subtractor device, characterized in that, in order to improve the accuracy of measuring the concentration and fractionally dispersed composition of the aerosol, its charge is carried out in the sign field a pulsed corona discharge, and the aerosol flux modulated by the sign of the charge is processed in a controlled constant magnetic field, the magnetic induction vector of which is directed perpendicular to the flux to separate particles in space in sign and fractional composition under the action of the Lorentz force, the measuring electrodes are shielded from the outside and spaced apart in a plane perpendicular to the magnetic induction vector, providing separate registration of EMF induced by positively and negatively charged particles with the same howl dispersion, which is regulated over the entire range of possible change of the measured aerosol dispersion variation of the applied magnetic field, electromotive force measurement electrodes of opposite sign are algebraically summed by the subtractor. 2. The device for implementing the method according to claim 1, comprising a dielectric housing with a bipolar charging chamber for aerosol particles sequentially installed along the aerosol stream, permanent magnet poles with adjustable magnetic induction, the vector of which is directed perpendicular to the flow, and two measuring induction electrodes shielded from the outside, located symmetrically with respect to the axis of the particle charging chamber in a plane perpendicular to the magnetic induction vector of the permanent magnet, are electrically connected each with its own input of a subtractor, for example, an instrument amplifier.