JPS6244646A - Method and apparatus for measuring concentration and grain size of suspended particles - Google Patents

Abstract

PURPOSE:To measure the concn. and grain size of pulverous suspended particles by irradiating a laser beam on the pulverous particle group to be measured, condensing the light scattered forward at slight angles, detecting the collected light with an annular photodetector having at least three channels and analyzing the detected respective channel signals. CONSTITUTION:The laser beam 1' from a helium neon laser oscillator 1 is expanded by a beam expander or collimator lens 5 and the expanded laser beam is irradiated on the particle group 2 to be measured. The components in the direction of the scattering angle theta out of the scattered light of the laser beam colliding against the particle group 2 are collected onto the circumference of a prescribed radius at the focal plane of a photodetecting lens 3 regardless of the position or speed of the particles. The annular photodetector 6 of a concentrical circular shape having at least three channels of the photodetecting parts is positioned to the focal plane thereof to directly detect the intensity I(theta) of the light. The output from the detector 6 is inputted to an instrument 7 for measuring the quantity of light energy, by which the concn. and particle size of the suspended particles are determined.

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to a method and apparatus for simultaneously measuring the concentration and particle size of sprayed suspended particles. [Prior art] Generally, the spray combustion method, in which liquid fuel is injected into a room and burned as minute particles, is widely used in diesel engines, gas turbines, industrial furnaces, etc., and the particle size distribution of the sprayed fuel is It is well known that it plays an important role in the ignition performance of various combustors, flame stability, combustion efficiency, and control of emissions of air pollutants such as NOx and soot. However, the reality is that the above-mentioned relationship between spray and combustion is only understood in terms of situation, and it is difficult to measure particle size distribution with high precision to be fully useful for combustor design J1 and the development of a combustion model for this purpose. Through this development, it is hoped that a routine and universal relationship between spray and combustion will be established. i Eh... :,. Methods for measuring the particle size and spatial distribution of particles have been considered. The first method is called the immersion method, which has been used for a long time. This method involves placing particles in a suitable liquid and measuring their size using a microscope.If the correct sample can be collected, the measurement accuracy, resolution, and reliability are excellent, and the labor is not required.

[This method has the feature that particle size can be measured without using expensive equipment or requiring a high degree of skill. However, there are inherent problems common to direct methods, such as droplets coalescing and splitting during sampling, and measurement in high-pressure, high-temperature atmospheres being extremely difficult. Therefore, an optical measurement method was considered that has the potential to alleviate the limitations and drawbacks of such direct measurement methods. This optical measurement method includes a method of measuring the size of the droplet image and a method of determining the particle size from physical quantities related to the size of the droplet. The TV imaging method, or holography, belongs to the former category, while most of the latter utilize the light scattering properties of particles. Research in this field has been active since monochromatic, coherent laser light sources became readily available1=. Traditionally, scattering methods that utilize the light scattering properties of fine particles mainly target particles that are not very large compared to the wavelength, but recently they have been used to measure particles that are more than 100 times the wavelength, such as particles in atomized spray. An attempt was made. One method for measuring the particle size distribution of a particle group consisting of particles that are sufficiently large compared to the wavelength is to determine the particle size distribution from changes in the intensity of forward scattered light. This calculates the distribution function using an inverse transformation formula within the range of diffraction approximation. However, this method has the problem that it is extremely difficult to accurately evaluate the differential coefficient of the light intensity with respect to the angle required for this conversion. Another method is to determine the shape parameters of a particle size distribution function from the intensity distribution of scattered light and measure the particle size distribution of lEi atomized granules, instead of using an inverse transformation formula. Although the parameters themselves cannot be determined by this method, the Sallator mean particle diameter (hereinafter referred to as SMD1) can be determined relatively easily from the attenuation of the scattered light intensity. However, when analyzing the formula I(θ) of Mie's scattering theory, which expresses the intensity of scattered light, the influence of the central region, which is susceptible to direct light interference, becomes large. Furthermore, an effective method for obtaining the weight particle size distribution from the scattered light intensity distribution has not been established. [Object of the Invention] This invention has been made in view of the above circumstances, and when measuring the particle size distribution of sprayed particles using the light scattering characteristics from the particles, the intensity of the scattered light is calculated based on Mie's scattering theory. Rather than analyzing the diffraction pattern of the formula I(θ), which is the integrand with respect to the angle θ of the scattered light energy, ■(θ)
・This method attempts to measure by analyzing the diffraction pattern of θ, which solves all the problems of conventional spray particle size measurement methods and makes it easy to measure the concentration and particle size distribution of sprayed particulates. Moreover, it is an object of the present invention to provide a method and apparatus for accurate measurement. [Structure of the Invention] The present invention, which has been made to achieve the above-mentioned object, focuses the forward small-angle scattered light obtained by irradiating a laser beam onto a group of particles to be measured using a lens, and places it on the focal point position. Light is received by an annular photodetector consisting of at least three channels of concentric photoelectric conversion elements, and the microcurrent signal photoelectrically converted by the photodetector is amplified, sampled and held, and the scattered light pattern received by the photodetector is patterned. Floating particles characterized in that the signal from each channel proportional to In this method, the concentration and particle size distribution of particles can be measured by analyzing the diffraction pattern of the integrand of the scattered light energy depending on the scattering angle of the scattered light intensity of the sprayed particle group. It is. Furthermore, the apparatus for carrying out the above method includes a laser emitter and a device that collects forward small angle scattered light from a group of measured microparticles irradiated with a laser beam.
* 9 V > X k・H'/e 'l L/ >
-2" (7) lx a 41.?i An annular photodetector consisting of photoelectric conversion elements such as at least three concentric silicon photodetectors arranged in an annular photodetector, and a microphotograph of each channel photoelectrically converted by the photodetector. The number of amplifiers that are the same as the number of channels of the optical detector that simultaneously amplifies the current signal, and the current signal that is amplified by the amplifier is 13.
A circuit that samples and holds the signal for each channel, an A/D converter that converts the FLR signal of each channel into a digital signal, and an optical detector that converts the optical energy received by each channel into a digital signal. A device for measuring the concentration and particle size of suspended particles is specified, comprising a microcomputer in which a procedure for analysis is stored based on the scattered light intensity of the mother and 0 is the scattered light intensity, and 0 is the scattering light intensity.
Accurate measurement is possible because the optical energy converted by the /D converter is simply analyzed and calculated based on a computer program. [Example] - The present invention will be explained in detail below based on the measurement principle and the illustrated example. When a single isotropic spherical particle with a diameter D is irradiated with an unpolarized laser beam of wavelength λ, the intensity distribution of the light scattered by the spherical particle is determined by the refractive index m and the particle size parameter α (
= πD/λ). As the value of the particle size parameter α increases, the amount of light scattered toward a small angle forward of the totally scattered light source increases rapidly, and the shape of the scattered light intensity distribution with respect to the angle in this region is sensitive to the particle size parameter α. It begins to change. The forward small-angle scattering method in a broad sense uses this property to determine the particle size or particle size distribution of a particle group consisting of particles larger than the wavelength λ of light. The key point of this invention is to measure the particle size distribution from As shown in Figure 1, the laser beam (monochromatic parallel beam)
1' is irradiated onto the particle group 2, and a lens 3 is placed in front of it to collect the scattered light, among the scattered light from each particle, the scattering angle θ
The directional components are collected on the circumference having a radius of γ=f−sinθ=j·0 at the focal plane 4 of the light-receiving lens, regardless of the position and velocity of the particles. The distribution of the scattered light intensity I(θ) at the focal plane 4 can be considered to be a combination of the scattered light intensities I(θ, α) from individual single particles if the influence of multiple scattering can be ignored. In other words, if the number particle size distribution is N(α), the following relationship holds true: (1)
l(0, α) is calculated as a pre-series of the scattering equation given by Mie. ■Determining the particle size distribution from the measurement of (θ) is nothing but solving the integral equation of equation (1). Furthermore, if we use the solution to obtain the weight particle size distribution from the scattered light intensity distribution, ■(θ)・θ will always have a peak value at a certain scattering angle, which is very convenient for understanding the characteristics of the distribution. Good. Here, the expression I(θ)·θ is an integrand with respect to the scattering angle θ of the scattered light energy. There is also the advantage that the influence of the central area, which is susceptible to direct light interference, can be reduced in analysis. When the diffraction approximation holds, equation (1) becomes ■ (θ)・θ− ・・・・・・・・・・・・・・・ (2), and this is given by the weighted distribution group number W(α). When , I(θ)・θ=C= becomes. Determining W(α) from equation (3) is the symmetric kernel [
This corresponds to solving an Andholm integral equation of the first kind with 2J1 (α, θ)]/αθ. From this relationship, the concentration of particles can be obtained. The present invention will be explained in more detail below based on the apparatus of the embodiment. FIG. 2 shows the basic concept of an apparatus for implementing the method of the present invention, in which a laser beam 1' from a helium-neon laser oscillator (hereinafter simply referred to as a He-Ne laser) 1 is passed through a beam expander or collimator lens. 5, and when the laser beam is irradiated onto the particle group 2 to be measured, the component of the scattering angle in the θ direction of the scattered light of the laser beam that collided with the particle group 2 is related to the position and velocity of the particles. In the focal plane of the light receiving lens 3, γ+f−sinθ=j・0
are collected on the circumference of a circle with radius. By positioning an annular optical detector 6 such as a concentric silicon photodetector having at least three channels of light receiving sections on this focal plane, a light intensity distribution can be obtained that can be considered as a superposition of the scattered light intensities of individual particles as described above! (θ) can be directly received. The intensity distribution of the scattered light received by the annular photodetector 6 is photoelectrically converted and becomes an input to the optical energy suspension measuring device 7 as a minute current signal. As shown in the block diagram in FIG.
) corresponding amplifiers 711 to 71 and sample and hold circuits 121 to 72°, and an A/D converter 73;
It consists of a computer interface 74 and a microcomputer 75. The analysis procedure on the microcomputer-75 is as follows. First, in order to analyze the above equation (3), Ro
The sim-Rammler distribution function was adopted. The reason for this is that the parameters x2 and
This is because it is easy to understand that the weight is 1/e of the total weight. C=×2/X3 (C: constant), small proportionality constant×1
When introducing , equation (4) becomes. Parameter X2. By changing X3, the above l(θ
)・θ equation pattern is determined by equation (5). From the measured pattern of 1(θ)・θ equation, ×1. ×2. Find ×3. The average particle size is x2. From X3, it is calculated from the following formula. SMD=X3/r' (1-1/X2): Gamma function (6) In the case of an annular optical detector, the particle size distribution is based on the optical energy ff1Ei to the ill-th channel. Determine. Ei is given by the following equation: θ・and θ・ are the outer shape of the annular optical detector ROUT, 1
÷ 1- If the inner diameter is R1o1 and the focal length of the light receiving lens is f, then θ
i+=Rout'', 0i-=Rin'' and are the scattering angles. When the particle size parameter α=πD/λ is sufficiently large and the diffraction approximation holds true, using the approximation of equation (3), W(α
)dαdO・・・・・・・・・・・・ (8)・・・
...... (9), and integrating this gives J (αθ・)−J2 (α0.,)−J 2(αθ・
))/Ddα (10)11+ The required value based on the optical energy aEi can be obtained from equation (10). That is, data based on the angle from the center and the 11] of each channel of the annular optical detector 6,
By storing the calculation procedure of equation (10) in the memory of the microcomputer 75, it is possible to simultaneously measure the particle concentration and particle size from the scattered light pattern received by the annular light detector. Furthermore, the meanings of the symbols used in each of the above formulas are as follows. α: particle size parameter, C2 constant, D2 particle size, Ei:
Light energy 1! I (θ), ■ (α, θ): intensity of scattered light from a single particle, ■ (θ): intensity of scattered light from a group of particles, Jo (α, θ): first type O order, Be5sellll
number, Jl((Z, θ): first type linear Be5se I function, N(D), N(α): number particle size distribution function, SMD:
Zallator average particle diameter, W (D), W (α) double particle size distribution function, ×1: Parameter of weight proportionality constant, ×2 Parameter of two distribution spreads, ×3 Parameter of two representative particle diameters Parameter, f: focal length of lens, θ: scattering angle, θ1-
: Scattering angle corresponding to the inner diameter of the i-channel of the annular light detector, θi+: Scattering angle corresponding to the outer diameter of the i-channel of the annular light detector, λ: Wavelength of the rape light, ": Gamma function. [Effects of the invention] As explained above, the method for measuring the concentration and particle size of suspended particles according to the present invention involves irradiating a group of particles to be measured sprayed into the air with a laser beam, and focusing the scattered light emitted through the group of particles with a lens. , the light is received by an annular light detector of at least three channels arranged on the focal position of the lens, and the signal from each channel proportional to the scattered light pattern received by the light detector is analyzed using the formula I(θ)·θ. This has the excellent effect of making it possible to easily measure the diameter of suspended particles, which has been considered extremely difficult in the past.In addition, the apparatus for carrying out the measurement method includes a laser oscillator and a laser beam. an expander, an optical lens that condenses the scattered light that has passed through the microparticles, an annular optical detector with at least three channels arranged at its focal position, an amplifier, a circuit for holding signals, and an A/D converter. The device is configured with a computer that analyzes and calculates the integrand function based on the scattered light intensity and the scattering angle of the A/D converted light energy, and has a simple structure yet accurate Furthermore, the effectiveness of the above measurements increases the combustion efficiency of various combustors that use the spray combustion method, contributing to energy conservation and greatly reducing air pollutant emissions. It also has various excellent effects such as contributing to

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram for explaining the invention in detail, and FIG.
The figure is a schematic configuration diagram of an apparatus for carrying out the method of the present invention, and FIG. 3 is a block diagram of a light energy measuring device in the same apparatus. 1... Oscillator 2... Particle group 3...
Light receiving lens 4...Focal plane 5...] Remeter lens 6...Annular light detector...Light energy measuring device 711-71. ...Amplifier, 721-72. ... Zumble and hold circuit 73
...A/D converter 74...Interface

Claims (3)

[Claims] (1) An annular optical detector consisting of at least three channels of concentric photoelectric conversion elements arranged above the focal point of a lens that focuses the forward small-angle scattered light obtained by irradiating a laser beam onto a group of particles to be measured. After amplifying, sampling and holding the minute current signal received by the photodetector and photoelectrically converted by the photodetector, the signal from each channel proportional to the pattern of scattered light received by the photodetector is A method for measuring the concentration and particle size of suspended particles, characterized in that the analysis is performed based on the following formula: [In the formula (2) (θ) is the intensity of scattered light from a group of particles, and θ is the scattering angle]. (2) a laser oscillator, an optical lens that condenses forward small angle scattered light from a group of measured microparticles irradiated with a laser beam, and at least three lenses arranged at the focal position of the optical lens;
An annular photodetector consisting of a photoelectric conversion element such as a silicon photodetector having concentric channels, an amplifier of the same number as the number of channels of the photodetector that simultaneously amplifies minute current signals of each channel photoelectrically converted by the photodetector, and the amplifier. A circuit that samples and holds the current signal amplified by each channel for each channel, and an A/D converter that converts the current signal of each channel into a digital signal.
The amount of light energy received by each channel of the optical detector converted into a digital signal is calculated by the formula ■(θ)・θ (in the formula ■(θ
) is the intensity of scattered light from a group of particles, and θ is the scattering angle.) A device for measuring the concentration and particle size of suspended particles, which consists of a microcomputer that stores an analysis procedure based on the scattering angle. (3) The second device further includes a collimator lens for collimating the laser beam of the laser oscillator.
Device for measuring the concentration and particle size of suspended particles as described in 2.