RU2810026C1 - Method and device for determining the concentration of suspended particles in a flow - Google Patents

Abstract

FIELD: suspended particles concentration determination.

SUBSTANCE: invention relates to a method and device for determining the concentration of suspended particles in a stream. A device for determining the concentration of suspended particles in a stream contains a pipeline designed to pass a stream with suspended particles; a laser source configured to irradiate the pipeline with a beam at a predetermined angle to the flow direction, the pipeline and the flow being transparent to this beam; the first lens placed in the wall of the pipeline at the point of incidence of said beam and focused in the middle of the pipeline in the direction of propagation of the said beam; a second lens placed in the opposite wall of the pipeline opposite the focal point of the first lens; the first optical receiver located on the opposite side of the laser source on the propagation line of said beam; the second optical receiver located on the opposite side of the laser source at the focal point of the second lens; a flow meter designed to determine the volume of flow that has passed through the pipeline for a given period of time; computing means connected to both optical receivers and the flow meter and configured to detect a signal received by the second optical receiver from radiation scattered by each suspended particle in said flow, and simultaneously register a signal received by the first optical receiver from radiation transmitted through the flow; as well as calculating the size of each suspended particle from simultaneously measured signals from both optical receivers and determining the concentration of suspended particles in the flow by dividing the number of suspended particles registered over a given period of time by the volume of flow that passed through the flowmeter during the same period of time.

EFFECT: expansion of the arsenal of technical means.

4 cl, 6 dwg

Description

Field of technology to which the invention relates

The present invention relates to a method for determining the concentration of suspended particles in a stream and to a device for its implementation.

State of the art

Various methods and devices are known for determining the concentration of suspended particles in a flow.

RF patents No. 2485481 (published on June 20, 2013), No. 2622494 (published on June 15, 2017) and No. 2626750 (published on July 31, 2017) describe variants of the method for analyzing suspended particles, implemented using a device in which, through a flow with suspended The particles are passed through a multiply reflected laser beam, the reflections of which from the suspended particles are recorded by a video camera. The disadvantage of these solutions is that they are extremely difficult to implement.

RF patents No. 2767953 (published on March 22, 2022) and No. 2770567 (published on April 18, 2022) disclose a similar method and device for analyzing suspended particles, where the flow is irradiated with a laser beam, divided into reference and object beams to form holographic images on the matrix from charge-coupled devices of a video camera. These solutions are even more complex.

As the closest analogue, the Russian Federation patent for utility model No. 186970 (published on February 12, 2019) was adopted, revealing a sensor for measuring dust concentration, in the measuring chamber of which an air sample is irradiated with an infrared laser beam, and part of the radiation scattered from suspended particles and passed through the sample recorded by optical receivers. The ratio of attenuated and reflected radiation provides the computing device with information about the dispersed composition of dust in a given range.

The disadvantage of this technical solution is that it works only in a stationary volume, as well as the impossibility of determining how suspended particles in the flow are distributed in size.

Disclosure of the Invention

The objective of the present invention is to overcome the shortcomings of the closest analogue and expand the arsenal of technical means to achieve a technical result in the form of expanded functionality, which consists in determining the concentration of suspended particles in the flow and their size distribution.

To solve the noted problem and achieve the specified technical result, the first object of the present invention proposes a method for determining the concentration of suspended particles in a stream, in which: a stream flowing through a pipeline with suspended particles in it is irradiated with a laser source beam, and the stream and the pipeline are transparent to the said beam incident onto the pipeline at a given angle to the direction of flow; a first lens is placed in the pipeline wall at the point where said beam falls, focused into the middle of the pipeline in the direction of propagation of said beam; a second lens is placed in the opposite wall of the pipeline opposite the focal point of the first lens; placing the first optical receiver on the side opposite from the laser source on the line of propagation of the said beam; a second optical receiver is located on the side opposite to the laser source at the focal point of the second lens; registering with a second optical receiver a signal from radiation scattered by each suspended particle in said flow, and simultaneously registering with a first optical receiver a signal from radiation passing through the flow; calculating the size of each suspended particle from simultaneously measured signals from both optical receivers; - determine the concentration of suspended particles in the flow by dividing the number of suspended particles recorded over a given period of time by the volume of flow passing through the flow meter over the same period of time.

A feature of the method according to the first object of the present invention is that the incidence of the laser source beam on the pipeline at a given angle to the flow direction can be ensured by means of a mirror.

To solve the same problem and achieve the same technical result, the second object of the present invention proposes a device for determining the concentration of suspended particles in a stream, comprising: a pipeline designed to pass a stream with suspended particles; a laser source designed to irradiate the pipeline with a beam at a given angle to the direction of the flow, and the pipeline and the flow are transparent to this beam; a first lens placed in the pipeline wall at the point of incidence of said beam and focused into the middle of the pipeline in the direction of propagation of said beam; a second lens placed in the opposite wall of the pipeline opposite the focal point of the first lens; a first optical receiver located on the opposite side from the laser source on the line of propagation of said beam; a second optical receiver located on the side opposite to the laser source at the focal point of the second lens; a flow meter designed to determine the volume of flow passing through a pipeline over a given period of time; a computing means connected to both optical receivers and a flow meter and configured to: register a signal received by the second optical receiver from radiation scattered by each suspended particle in said flow, and simultaneously register a signal received by the first optical receiver from radiation passed through the flow; calculating the size of each suspended particle from simultaneously measured signals from both optical receivers; determining the concentration of suspended particles in a stream by dividing the number of suspended particles recorded over a given period of time by the volume of flow that passed through the flow meter over the same period of time.

A feature of the device according to the second object of the present invention is that a mirror can be installed in the path of the laser source beam, deflecting this beam at a given angle to the flow direction.

Brief description of drawings

The present invention is illustrated by the accompanying drawings, in which like elements are designated by the same reference numerals.

In FIG. 1 is a diagram of a device according to a second aspect of the present invention.

In FIG. 2 illustrates the path of rays in the circuit shown in FIG. 1.

In FIG. Figure 3 shows graphs of the beam intensity distribution when passing through the lens.

In FIG. Figure 4 shows the distribution of scattered light as a function of the ratio of suspended particle size to wavelength.

In FIG. Figures 5 and 6 show the analog signal shapes from the second optical receiver for suspended particles of different sizes.

Detailed Description of Embodiments

The device according to the second object of the present invention contains (Fig. 1) a pipeline 1 designed to pass a flow of suspended particles, which are designated by the reference numeral 2. Arrows 3 indicate the direction of flow.

The device further contains a laser source 4 designed to irradiate the pipeline 2 with a beam at a given angle to the flow direction 3. We especially note that pipeline 2 and the flow in it are transparent to this beam, i.e. laser source 4 was chosen specifically to illuminate this flow. For example, this could be an optical radiation source, the choice of wavelength of which is explained below. The laser source 4 can be installed at the above-mentioned predetermined angle to the flow direction 3, or a mirror 5 can be used to rotate the beam of the laser source 4. The predetermined angle in the preferred embodiment is close to 45°, although it can be other value, for example, 30° or 60° (not equal to 90°).

In the place of the pipeline wall to which the beam of the laser source 4 is directed, a first lens 6 is placed, focused into the middle of the pipeline 1 in the direction of propagation of the said beam. In the opposite wall of the pipeline opposite the focal point of the first lens 6 there is a second lens 7.

The device contains a first optical receiver 8 located on the side opposite from the laser source 4 on the line of propagation of its beam, and a second optical receiver 9 located on the side opposite from the laser source 4 at the focal point of the second lens 7.

The device further comprises a flow meter (not shown) designed to determine the volume of flow passing through the pipeline 1 over a given period of time, and a computing means (not shown) connected to both optical receivers 8 and 9 and to the flow meter. This computing means may be, for example, a computer, a processor with memory, a controller, or the like. The computing device is configured (programmed) with the ability to perform the following operations:

- registration of the signal received by the second optical receiver 9 from radiation scattered by each suspended particle 2 in the flow, with simultaneous registration of the signal received by the first optical receiver 8 from radiation passed through the flow;

- calculating the size of each suspended particle 2 from simultaneously measured signals from both optical receivers 8 and 9;

- determination of the concentration of suspended particles 2 in the flow by dividing the number of suspended particles recorded over a given period of time by the volume of flow passing through the flow meter over the same period of time.

Fig. 2 explains the path of the beams in the device according to the second aspect of the present invention and the selection of appropriate dimensions. In a particular case, these dimensions can be, for example:

D0=7 mm - pipeline diameter 1;

L0=30 mm - distance from laser source 4 to mirror 2;

L1=10 mm - distance from mirror 3 to first lens 6;

F0=4.95 mm - focal length of the first lens 6;

L3=3.57 mm - distance from the focal point of the first lens 6 to the center of the optical axis of the second lens 7;

F1=8 mm - the distance between the focus of the second lens 7 and the second optical receiver 9;

L2=16.26 mm - distance from the focal point of the first lens 6 to the first optical receiver 8.

Graphs of the intensity distribution I of the laser source 4 beam when passing through the first lens 6 are presented in Fig. 3. This drawing indicates:

2w ₀ - minimum beam diameter at the focus of the first lens 6;

z _R is the distance at which the beam intensity drops by half compared to the focal point;

r is the distance from the focus.

Now let us explain the choice of laser source 4. The wavelength of its radiation should preferably not exceed ~ 650 nm to reduce the size of 2w ₀ , but, at the same time, should be as close as possible to the maximum spectral sensitivity of optical receivers 8 and 9. For this wavelength, the indicated the dimensions are 2w ₀ ≈ 20 µm and z _R ≈ 100 µm.

When a particle passes through the focus, we can observe the physical phenomenon illustrated in Fig. 4, which shows the scatter diagrams, i.e. distribution of intensity I of scattered light depending on the ratio of the size of the suspended particle to the wavelength λ. From Fig. 4 it can be seen that the distribution of scattered light by a suspended particle depends on the ratio of the characteristic size of the particle itself to the wavelength λ. The characteristic size refers to the particle diameter, since in calculations it is conventionally assumed that all particles have a spherical shape.

In the direct beam area, the intensity of the scattered radiation is too high and will not differ much from the intensity of the incident beam when there is nothing obstructing it, which will lead to problems reading the signal. That is why the second optical receiver 9 is installed in the forward scattering zone, i.e. preferably at an angle of 45° from the direction of the beam of the laser source 4.

Calculating the quantitative concentration of suspended particles 2 by the optical method comes down to the classical problem of electrodynamics, solved back in 1908 by Gustav Mie, which works very well with particles whose characteristic size does not exceed 10 microns. After 10 µm, the quantitative concentration is calculated by a special case of Mie scattering - the Fraunhofer approximation.

Let I ₀ be the intensity of the incident light, I the intensity of the scattered light at a certain point at a large distance r from the particle, and k the wave number determined by the relation k=2π/λ, where λ is the wavelength in the medium surrounding the particle. Since I must be proportional to I ₀ and r, we can write:

Here F(θ, ϕ) is a dimensionless function of direction and does not depend on r. It depends on the orientation of the particle relative to the incident wave and on the polarization state of the incident wave. Relative values can be plotted on a polar diagram as a function of angle for a fixed scattering plane containing the direction of the incident light beam. This diagram is called the scattering diagram of a given particle (Fig. 4). In practice, the most important result of light scattering in dispersed media is the energetic weakening of the incident flux due to the redistribution (scattering) of part of this flux in all directions. To quantitatively characterize such attenuation, one can introduce the concepts of absorption and scattering (attenuation) coefficients. The electromagnetic energy of the total flux scattered in all directions to the ratio of the intensity of the incident flux is called the particle scattering coefficient σ _p .

A similar ratio with a minus sign of the total energy flux (incident and scattered) through a large sphere with the center located at the center of the particle to the intensity of the incident flux is called the particle absorption coefficient σ _p . If we take into account the intensity of the flow and the dimension of the energy flow, then for the dimension of the scattering coefficients by a particle we have the area. Therefore, these coefficients are called effective scattering or absorption cross sections. Scattering and attenuation measurements enable us to determine (at least in principle) the size and size distribution of particles, their shape and orientation.

It follows from Mie theory that the angular distribution of light scattered by particles of a dispersed medium is uniquely related to the radius R of the particle. The intensity of light scattered by one particle at different angles to the direction of the incident beam (light scattering indicatrix) is determined by the following relationship:

where m is the refractive index of the particle substance; z is the distance from the particle to the recording device, λ is the wavelength, I ₀ and I are the intensities of the incident and scattered emitters, respectively, γ is the angle at which the intensity of the scattered radiation is measured relative to the direction of the incident radiation.

From this equation we can calculate the dependence of the particle radius on the amplitude values of the light intensity that will excite the current in the optical receiver:

When a particle reaches a size where the Mie theory cannot reliably calculate the particle size (i.e., the particle size exceeds 10 μm), a special case of the Mie theory is used - the Fraunhofer approximation.

Since the scattering indicatrix is focused on the optical receiver, the calculation of the particle size is reduced to solving the Fredholm integral equation of the first kind:

Where: - parameter of radiation diffraction by particles; d is the characteristic particle size; λ - wavelength; I(θ) is the intensity of radiation incident on the particle; I ₀ - intensity of scattered light; ƒ(p) - particle size distribution function; k(р,θ) - Fredholm kernel (kernel of the integral equation).

These relationships form the basis for programming the computing power in the device of the present invention.

The method according to the first object of the present invention is implemented using the described device as follows.

The laser source 4 is installed so that its beam falls on the pipeline 1 at a given angle. It is possible to use a mirror 5 for this purpose. In the wall of the pipeline 1, at the point of incidence of this beam, a first lens 6 is placed, focused in the middle of the pipeline 1 in the direction of propagation of the said beam, and in the opposite wall of the pipeline 1, opposite the focal point of the first lens 6, a second lens 7 is placed. The first optical receiver 8 is located on the side opposite from the laser source 4 on the line of propagation of its beam, the second optical receiver 9 is located on the side opposite from the laser source 4 at the focal point of the second lens 7.

The flow with suspended particles 2 flowing through pipeline 1 is irradiated with the beam of the laser source 4, and the flow and pipeline 1 are transparent to the beam of the laser source 4.

The second optical receiver 9 registers the signal from the radiation scattered by each suspended particle 2 in the flow, and simultaneously registers the signal from the radiation passing through the flow with the first optical receiver 8. The measured values are recorded in the memory of the computing device.

Using simultaneously measured signals from both optical receivers 8 and 9, the size of each suspended particle 2 that falls into the focus of the first lens 6 is calculated using a computer, and the number of suspended particles passing through the focus of the first lens 6 for a given period of time is determined.

A flow meter is used to record the volume of flow that has passed through the flow meter over the same period of time. The computational tool determines the concentration of suspended particles in a stream by dividing the number of suspended particles recorded over a given period of time by the recorded volume of the stream.

Since the diameter of the pipeline is quite small, those particles that pass by the focal point of the first lens 6 can be neglected. As experiments have shown, the method according to the first object of the present invention makes it possible to determine the concentration of suspended particles with an accuracy of no worse than ±10%.

Thus, the present invention expands the arsenal of technical means and ensures the achievement of a technical result in the form of expanded functionality, which consists in determining the concentration of suspended particles in the flow and their size distribution.

Claims (23)

1. A method for determining the concentration of suspended particles in a stream in which: - irradiate the flow with suspended particles in it flowing through the pipeline with a laser source beam, and the flow and the pipeline are transparent to the said beam incident on the pipeline at a given angle to the direction of the flow; - a first lens is placed in the wall of the pipeline at the point of incidence of the said beam, focused into the middle of the pipeline in the direction of propagation of the said beam; - place a second lens in the opposite wall of the pipeline opposite the focal point of the first lens; - the first optical receiver is placed on the side opposite from the laser source on the line of propagation of the said beam; - a second optical receiver is placed on the side opposite to the laser source at the focal point of the second lens; - registering with a second optical receiver the signal from radiation scattered by each suspended particle in said flow, and simultaneously registering with the first optical receiver the signal from radiation passing through the flow; - calculate the size of each suspended particle from simultaneously measured signals from both optical receivers; - determine the concentration of suspended particles in the flow by dividing the number of suspended particles recorded over a given period of time by the volume of flow passing through the flow meter over the same period of time. 2. The method according to claim 1, in which the incidence of the laser source beam on the pipeline at a given angle to the flow direction is ensured by means of a mirror. 3. A device for determining the concentration of suspended particles in a stream, containing: - a pipeline designed to pass a flow with suspended particles; - a laser source designed to irradiate the pipeline with a beam at a given angle to the direction of flow, and the pipeline and flow are transparent to this beam; - a first lens placed in the pipeline wall at the point of incidence of said beam and focused into the middle of the pipeline in the direction of propagation of said beam; - a second lens placed in the opposite wall of the pipeline opposite the focal point of the first lens; - a first optical receiver located on the side opposite to the laser source on the line of propagation of said beam; - a second optical receiver located on the side opposite to the laser source at the focal point of the second lens; - a flow meter designed to determine the volume of flow passing through the pipeline for a given period of time; - a computing means connected to both optical receivers and a flow meter and configured to: - registering the signal received by the second optical receiver from radiation scattered by each suspended particle in said flow, and simultaneously registering the signal received by the first optical receiver from radiation passing through the flow; - calculating the size of each suspended particle using simultaneously measured signals from both optical receivers; - determining the concentration of suspended particles in a flow by dividing the number of suspended particles recorded over a given period of time by the volume of flow passing through the flow meter over the same period of time. 4. The device according to claim 3, in which a mirror is installed in the path of the laser source beam, deflecting this beam at a given angle to the direction of flow.