On-line measurement system and method for particle size and component of fogdrop

Abstract

The invention discloses an on-line measurement system and method for particle size and composition of fog drops, and relates to the technical field of on-line measurement of fog drops, the system comprises a laser, a scattered light receiving assembly, a light trap and a fog drop sampling channel cylinder; the laser is used for emitting laser, and scattered light is obtained after the laser is scattered by fogdrops in the fogdrop sampling channel cylinder; the four independently-arranged scattered light receiving assemblies are arranged on the outer side of the fogdrop sampling channel cylinder in a surrounding mode in the axial direction of the fogdrop sampling channel cylinder so as to receive scattered light, the detectors in all the scattered light receiving assemblies and laser beams emitted by the lasers are located on the same plane A, and the movement direction of fogdrops in the fogdrop sampling channel cylinder is perpendicular to the plane A; light beam focuses of scattered light received by all the scattered light receiving assemblies are located at the central position of the fogdrop sampling channel cylinder on the plane A; the light trap is used for absorbing laser directly penetrating through the fog drop sampling channel cylinder; according to the online measurement system and method, real-time non-contact measurement of the particle size and the chemical components of a single fog drop can be realized at the same time.

Description

Technical Field

[0001] The invention relates to the technical field of droplet online measurement, and in particular to a system and method for online measurement of droplet particle size and composition. Background Art

[0002] Fog is a natural weather phenomenon. It is an aerosol system composed of a large number of small water droplets or ice crystals with a particle size distribution of 2-100μm. Continuous fogging will harm people's health and affect the economic development of society, mainly in the following aspects:

[0003] (1) Heavy fog can significantly reduce air visibility, causing traffic accidents on land, flight delays at airports, and ship suspensions at sea, seriously affecting traffic safety and operational efficiency;

[0004] (2) Pollutant particles in fog will shorten the sunshine time and affect the photosynthesis of crops, thus greatly increasing the probability of crop diseases and insect pests, affecting the quality of crops and causing a reduction in grain production;

[0005] (3) Some harmful substances will combine with water vapor in foggy weather, making them more toxic. The particles that make up the fog will be inhaled and retained in the human body, causing upper respiratory tract infections and seriously damaging human health.

[0006] (4) In dense fog, the insulation level of insulators is greatly reduced, which may cause short circuits in transmission lines and power outages in the power grid, affecting the normal electricity use of people in all walks of life and causing serious economic losses;

[0007] (5) Fog can also affect satellite and microwave communications, causing a sharp drop in signals and reduced communication quality.

[0008] The spectral distribution of droplets is an important parameter of fog. Research on the droplet spectrum helps people understand the physical and chemical changes in the atmosphere and the mechanisms and laws of fog generation, improve human prediction capabilities for fog, and enhance people's defense capabilities against fog damage, so as to reduce the losses caused by fog damage.

[0009] In addition, the composition of fog droplets is complex and diverse, and is not just composed of water. They are affected by geographical location, seasonal changes, and a variety of environmental factors, resulting in significant differences in composition. In arid and desert areas, dust is one of the common components of fog droplets. These dust particles can be blown up by the wind and captured by fog droplets. In coastal areas, due to the influence of seawater evaporation, the content of chloride salts (such as sodium chloride) in sea fog is significantly higher than that in inland fog. Dust generated by industrial activities, such as coal smoke and industrial dust, is also one of the components of fog droplets, especially near industrial areas. In addition, fog droplets may also contain salts, which may come from seawater evaporation, salt in the soil, and industrial emissions.

[0010] In addition to the above ingredients, fog droplets may also contain sand, sea salt, industrial dust, nitrates, ammonium salts, carbon black, etc. The sources of these ingredients are diverse, including waste gas and smoke emitted by human life and production, sulfates ejected from volcanic eruptions, and gases discharged by microbial metabolism. The chemical composition of fog droplets is related to the location of the fog. For example, the chloride content in sea fog is significantly higher than that in inland fog, while sulfate is common in fog in different regions, and the content does not vary much. In addition, the concentration of ions contained in small and large fog droplets is also different. The concentration of ions contained in small fog droplets is generally higher than that in large fog droplets, but the concentration of acetate in large fog droplets is higher than that in small fog droplets.

[0011] When the droplets contain organic matter, the surface tension of the droplets is reduced, resulting in more droplets being generated under supersaturated conditions of water vapor. On the contrary, when the droplets contain inorganic matter, the surface tension of the droplets increases, resulting in a decrease in the concentration of droplets. The diversity and complexity of these components make the study of droplets an interdisciplinary field involving multiple disciplines such as environmental science and meteorology, and is of great significance for understanding atmospheric chemical processes, climate change, and its impact on human health.

[0012] With the increasing development of optical technology, light scattering technology has become a non-contact rapid measurement technology for droplets, and has gradually become one of the mainstream measurement methods of laser particle counters. The American DMT company has also launched commercial instruments. In the 1970s, with the development of laser measurement technology, laser technology was applied to the measurement of droplets, and the particle size and distribution information of droplets were solved by digital signal processing methods, which greatly improved the accuracy of droplet size measurement and made the measurement operation process simple. There are two principles for measuring droplets by laser method: one is laser holography, which uses laser negatives to record the spatial holographic image of the measured droplets, and can accurately measure the particle size and concentration of droplets. When the movement speed of droplets is within a certain range, the droplets can also be dynamically measured. One is light scattering method: European and American countries have successfully developed optical droplet spectrometers based on the Mie scattering principle. It calculates the particle size of droplets based on the scattered light intensity of the particles to the incident light, and the measurement range is between 2μm and 50μm.

[0013] At present, in the online monitoring of droplets, light scattering technology still has the following problems and shortcomings:

[0014] (1) The droplet sampling system must determine whether the sampled droplets pass through the sampling point in order to accurately carry out the subsequent scattered light calculation. Existing droplet sampling systems are difficult to implement the sampling method of a single droplet passing through, that is, the method of a group of droplets passing through the sampling channel tube. Therefore, it is difficult to accurately obtain the position of the droplet passing through the sampling channel, which makes it difficult to locate the sampled single particle.

[0015] Although the FM120 of DMT Instruments of the United States uses the method of calculating the splitting ratio of the scattered light beam after passing through the beam splitting glued prism to determine whether the particles are within the depth of field of the system and determine the specific position of the droplets, the optical path is complex and the error is large in actual application.

[0016] (2) The existing technology can only measure the particle size and number concentration of droplets, but it is difficult to obtain information such as the chemical composition of the droplets;

[0017] (3) The existing light scattering particle size measurement results are easily affected by parameters such as the refractive index of the particles and the particle shape, thereby reducing the accuracy of the particle size measurement. Summary of the invention

[0018] Based on the technical problems existing in the background technology, the present invention proposes an online measurement system and method for droplet size and composition, which can simultaneously realize real-time non-contact measurement of the particle size and chemical composition of a single droplet.

[0019] The invention provides an online measurement system for droplet particle size and composition, comprising a laser, a scattered light receiving component, a light trap and a droplet sampling channel tube;

[0020] The laser is used to emit laser light, and the laser light is scattered by the droplets in the droplet sampling channel tube to obtain scattered light;

[0021] Four independently arranged scattered light receiving components are arranged around the outside of the droplet sampling channel tube along the axial direction of the droplet sampling channel tube to receive scattered light, and the detectors in all scattered light receiving components and the laser beam emitted by the laser are on the same plane A, the movement direction of the droplets in the droplet sampling channel tube is perpendicular to the plane A, and the focus of the scattered light beam received by all scattered light receiving components is located at the center of the droplet sampling channel tube on the plane A;

[0022] The light trap is used to absorb the laser light that directly passes through the droplet sampling channel cylinder.

[0023] Further, each scattered light receiving assembly includes a detector, a signal processing circuit and a computer, the input of the signal processing circuit is connected to the output of the detector, and the output is connected to the input of the computer;

[0024] The receiving ends of the four detectors are respectively 15 degrees, 30 degrees, 140 degrees, and 160 degrees to the laser emission direction to receive scattered light from different directions.

[0025] Furthermore, the four detectors convert the scattered light signals I1, I2, I3, and I4 received at four angles into electrical signals respectively and input them into the signal processing circuits connected to them respectively, the signal processing circuit amplifies the signal change and inputs the obtained signal peaks P1, P2, P3, and P4 at the four angles into the computer respectively, the computer compares the peak value P4 with the standard light intensity-particle size relationship curve to obtain the droplet particle size, and compares the ratios of P1 / P4, P2 / P4, and P3 / P4 with the standard peak value ratio-chemical composition database to obtain the chemical composition information of the droplets; wherein, I1 is received by a detector at an angle of 160 degrees to the laser emission direction, I2 is received by a detector at an angle of 140 degrees to the laser emission direction, I3 is received by a detector at an angle of 30 degrees to the laser emission direction, and I4 is received by a detector at an angle of 15 degrees to the laser emission direction.

[0026] Furthermore, the receiving angles of the detectors in all scattered light receiving assemblies are less than ±4 degrees to ensure the spatial resolution and validity of each measurement value.

[0027] Furthermore, the online measurement system also includes a collimating lens and an aperture. The laser light emitted by the laser passes through the collimating lens and the aperture in sequence and then is collimated and incident on the droplets in the droplet sampling channel tube to obtain scattered light.

[0028] Furthermore, the collimating lens is an aspherical collimating lens, and the absorption efficiency of the light trap to the laser is greater than 0.99.

[0029] A method for online measurement of droplet size and composition, characterized in that each scattered light receiving assembly includes a detector, a signal processing circuit and a computer, the input of the signal processing circuit is connected to the output of the detector, and the output is connected to the input of the computer, and the measurement method includes the following steps:

[0030] Step 1, four detectors receive scattered light after the laser emitted by the laser is scattered by the droplets in the droplet sampling channel tube, and the scattered light signals I1, I2, I3, and I4 at four angles are respectively converted into electrical signals and input into the respectively connected signal processing circuits, and the signal processing circuit amplifies the signal change and inputs the obtained signal peaks P1, P2, P3, and P4 at the four angles into the computer, wherein I1 is received by the detector at an angle of 160 degrees to the laser emission direction, I2 is received by the detector at an angle of 140 degrees to the laser emission direction, I3 is received by the detector at an angle of 30 degrees to the laser emission direction, and I4 is received by the detector at an angle of 15 degrees to the laser emission direction;

[0031] Step 2: After preprocessing the signal peaks P1, P2, P3, and P4, if all the preprocessed signal peaks are greater than the preset signal strength threshold, the droplet passes through the center of the droplet sampling channel tube, and then proceed to step 3; if all the preprocessed signal peaks have a signal peak value less than or equal to the preset signal strength threshold, the droplet does not pass through the center of the droplet sampling channel tube, and then return to step 1;

[0032] Step 3: Measure the relationship between the standard particle size and the signal peak value P4 under the same droplet sampling environment, and obtain the standard light intensity-particle size relationship curve through third-order linear fitting;

[0033] Step 4: Measure the direct relationship between the standard particle composition and the P1 / P4, P2 / P4, and P3 / P4 ratios under the same droplet sampling environment to obtain a standard peak ratio-chemical composition database;

[0034] Step 5: The scattered light receiving component measures the scattered light signal of a single droplet passing through the laser spot during the sampling process, and compares the signal peak value P4 with the standard light intensity-particle size relationship curve to obtain the required droplet size information;

[0035] Step 6: The scattered light receiving component measures the scattered light signal of a single droplet passing through the laser spot during the sampling process, and compares the signal peak ratios P1 / P4, P2 / P4, P3 / P4 with the standard peak ratio-chemical composition database to obtain the chemical composition information of the required droplets.

[0036] Furthermore, in step 3, in obtaining the standard light intensity-particle size relationship curve by third-order linear fitting, the third-order linear fitting formula is as follows:

[0037] y=B0+B1*x+B2*x 2 +B3*x 3

[0038] Among them, y is the standard light intensity, x is the standard particle size, and B0, B1, B2, and B3 are fitting parameters respectively.

[0039] Furthermore, in step 2, the comparison process of the signal peak values ​​P1, P2, P3, and P4 with the preset signal strength threshold is as follows:

[0040] The computer obtains the signal strength S1, S2, S3, S4 of each detector based on the acquired signal peak values ​​P1, P2, P3, P4;

[0041] The signal strengths S1, S2, S3, and S4 are smoothed to reduce noise, thereby standardizing the signal strengths;

[0042] Set the signal strength threshold T to determine whether the droplets pass through the center of the droplet sampling channel;

[0043] Compare the signal intensities after each normalization and determine the detector with the minimum signal intensity.

[0044] If the minimum signal strength is greater than the preset signal strength threshold, the droplet passes through the center of the droplet sampling channel cylinder;

[0045] If the minimum signal strength is less than or equal to the preset signal strength threshold, the droplet has not passed through the center position of the droplet sampling channel tube.

[0046] The advantages of the online measurement system and method for droplet size and composition provided by the present invention are as follows: the online measurement system and method for droplet size and composition provided in the structure of the present invention, (1) adopts a method of jointly detecting the sampling point position by four detectors, which can accurately determine the droplets passing through the sampling point. This method can solve the actual position by intensity by using the distribution model of the light signals of the four detectors, thereby improving the accuracy of droplet sampling. The offset can be calculated by the output current of the four detectors, thereby realizing center positioning. This method can improve the positioning accuracy of a single sampled droplet, and help solve the problem of incorrect measurement and positioning of a single droplet particle caused by a group of droplets passing through the sampling channel in the prior art; (2) by using the characteristics that the scattering signal of the droplet is positively correlated with the particle size under small-angle light scattering, and the scattering signal is related to the chemical composition of the particle under specific multi-angle light scattering, the particle size spectrum and chemical composition of a single droplet can be measured online at the same time; it plays a good technical support role in the change characteristics and source analysis of atmospheric fine particles; (3) it is simple to achieve, does not require membrane sampling and offline analysis, and effectively expands the real-time online sensing method of multiple physical and chemical parameters of droplets based on the principle of light scattering. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Figure 1 It is a structural schematic diagram of the present invention;

[0048] Figure 2 This is the distribution structure diagram of four detectors;

[0049] Figure 3 This is the corresponding relationship diagram between the scattering signal intensity and scattering angle of sand, sea salt, industrial dust, salt, and water;

[0050] Among them, 1-laser, 2-scattered light receiving component, 3-light trap, 4-droplet sampling channel tube, 5-straight lens, 6-aperture, 7-droplet, 21-detector, 22-signal processing circuit, 23-computer, 211-first detector, 212-second detector, 213-third detector, 214-fourth detector 214. DETAILED DESCRIPTION

[0051] Below, the technical solution of the present invention is described in detail through specific embodiments. Many specific details are set forth in the following description to facilitate a full understanding of the present invention. However, the present invention can be implemented in many other ways different from those described herein, and those skilled in the art can make similar improvements without violating the connotation of the present invention. Therefore, the present invention is not limited to the specific implementation disclosed below.

[0052] like Figures 1 to 3 As shown, a system and method for online measurement of droplet particle size and composition proposed by the present invention include a laser 1, a scattered light receiving component 2, a light trap 3 and a droplet sampling channel tube 4; the laser 1 is used to emit laser light, and the laser light is scattered by droplets 7 in the droplet sampling channel tube 4 to obtain scattered light; four independently arranged scattered light receiving components 2 are arranged along the axial direction of the droplet sampling channel tube 4 and around the outside of the droplet sampling channel tube 4 to receive scattered light, and the detectors 21 in all scattered light receiving components 2 are on the same plane A as the laser light beam emitted by the laser 1, the movement direction of the droplets 7 in the droplet sampling channel tube 4 is perpendicular to the plane A, and the focus of the scattered light beam received by all scattered light receiving components 2 is located at the center of the droplet sampling channel tube 4 on the plane A; the light trap 3 is used to absorb the laser light that directly passes through the droplet sampling channel tube 4.

[0053] In this embodiment, each scattered light receiving component 2 includes a detector 21, a signal processing circuit 22 and a computer 23. The input of the signal processing circuit 22 is connected to the output of the detector 21, and the output is connected to the input of the computer 23. The receiving ends of the four detectors 21 are respectively 15 degrees, 30 degrees, 140 degrees and 160 degrees to the laser emission direction to receive scattered light in different directions.

[0054] This embodiment uses a method in which four detectors 21 jointly detect the sampling point position (the sampling point is located at the center of the droplet sampling channel tube on plane A), which can accurately determine the droplets passing through the sampling point. This method uses the structural distribution of scattered light received by the four detectors 21 to calculate the actual position by intensity, thereby improving the accuracy of droplet sampling. The offset can be calculated through the output current of the four detectors to achieve center positioning. This method can improve the positioning accuracy of a single sampled droplet, which helps to solve the accuracy problem caused by a group of droplets passing through the droplet sampling channel tube 4 in the prior art.

[0055] In this embodiment, the laser 1 adopts a semiconductor laser to output a laser with stable light intensity to improve the measurement accuracy of the particle size of the droplets; the receiving angle of the detector 21 in all scattered light receiving components 2 is less than ±4 degrees to ensure the spatial resolution and effectiveness of each measurement value; the absorption efficiency of the light trap 3 for laser is greater than 0.99 to avoid the interference of stray light on the measurement results of each detector signal; the light trap 3 adopts a Brewster light trap.

[0056] It should also be noted that the droplet 7 at the measurement point should ensure that the focus of the scattered light beam received by the four detectors is at the center of the droplet sampling channel tube on plane A, so as to achieve real-time measurement and analysis of single droplet information.

[0057] It can be understood that in order to improve the ability of the laser to be collimated and incident on the droplet sampling channel tube 4, the present embodiment further provides a collimating lens 5 and an aperture 6. The laser emitted by the laser 1 passes through the collimating lens 5 and the aperture 6 in sequence and is collimated and incident on the droplets 7 in the droplet sampling channel tube 4 to obtain scattered light, wherein the collimating lens 5 adopts a non-spherical collimating lens to achieve the best laser collimation effect.

[0058] For ease of explanation, the four detectors 21 are respectively a first detector 211, a second detector 212, a third detector 213, and a fourth detector 214, wherein the first detector 211 is at an angle of 160 degrees to the laser emission direction to receive the scattered light signal I1; the second detector 212 is at an angle of 140 degrees to the laser emission direction to receive the scattered light signal I2; the third detector 213 is at an angle of 30 degrees to the laser emission direction to receive the scattered light signal I3; and the fourth detector 214 is at an angle of 15 degrees to the laser emission direction to receive the scattered light signal I4.

[0059] According to the attached Figure 2 In this embodiment, the first detector 211 and the third detector 213 are preferably arranged on one side of the laser emission direction, which is recorded as the B side, and the second detector 212 and the fourth detector 214 are arranged on the other side of the laser emission direction, which is recorded as the C side. On the B side, based on the laser emission direction, the direction of the scattered light received by the first detector 211 is 160 degrees to the laser emission direction, and the direction of the scattered light received by the third detector 213 is 30 degrees to the laser emission direction; on the C side, based on the laser emission direction, the direction of the scattered light received by the second detector 212 is 140 degrees to the laser emission direction, and the direction of the scattered light received by the fourth detector 214 is 15 degrees to the laser emission direction; thus, scattered light in four directions is received by the four detectors 21.

[0060] A method for online measurement of droplet size and composition comprises the following steps:

[0061] Step 1, four detectors 21 receive scattered light after the laser emitted by the laser 1 is scattered by the droplets 7 in the droplet sampling channel tube 4, and convert the scattered light signals I1, I2, I3, and I4 at four angles into electrical signals and input them into the respectively connected signal processing circuits 22, and the signal processing circuit 22 amplifies the signal change and inputs the obtained signal peak values ​​P1, P2, P3, and P4 at the four angles into the computer 23, wherein I1 is received by the first detector 211, I2 is received by the second detector 212, I3 is received by the third detector 213, and I4 is received by the fourth detector 214.

[0062] Step 2: After preprocessing the signal peaks P1, P2, P3, and P4, if all the preprocessed signal peaks are greater than the preset signal strength threshold, the droplet 7 passes through the center of the droplet sampling channel tube 4, and then the process goes to step 3; if all the preprocessed signal peaks have a signal peak value that is less than or equal to the preset signal strength threshold, the droplet 7 does not pass through the center of the droplet sampling channel tube 4, and then the process goes back to step 1;

[0063] The comparison process of the signal peak values ​​P1, P2, P3, and P4 with the preset signal strength threshold values ​​is as follows: the computer 23 obtains the signal strength S1, S2, S3, and S4 of each detector 21 based on the acquired signal peak values ​​P1, P2, P3, and P4; the signal strengths S1, S2, S3, and S3 are smoothed respectively to reduce noise, thereby standardizing the signal strength; a signal strength threshold T is set to determine whether the droplet 7 passes through the center position of the droplet sampling channel tube 4; each standardized signal strength is compared to determine the detector 21 corresponding to the minimum signal strength; if the minimum signal strength is greater than the preset signal strength threshold value, the droplet 7 passes through the center position of the droplet sampling channel tube 4; if the minimum signal strength is less than or equal to the preset signal strength threshold value, the droplet 7 does not pass through the center position of the droplet sampling channel tube 4.

[0064] The formula for normalized signal strength is as follows:

[0065]

[0066] Among them, S norm is the standardized signal strength, S i is the signal strength, i∈[1,4], μ is the mean of the signal strength, and σ is the standard deviation of the signal strength.

[0067] Step 3: Measure the relationship between the standard particle size and the signal peak value P4 under the same droplet 7 sampling environment, and obtain the standard light intensity-particle size relationship curve through third-order linear fitting;

[0068] The third-order linear fitting formula is as follows:

[0069] y=B0+B1*x+B2*x 2 +B3*x 3

[0070] Among them, y is the standard light intensity, x is the standard particle size, and B0, B1, B2, and B3 are fitting parameters respectively.

[0071] Step 4: Measure the direct relationship between the standard particle composition and the P1 / P4, P2 / P4, and P3 / P4 ratios under the same droplet 7 sampling environment to obtain a standard peak ratio-chemical composition database;

[0072] Step 5, the scattered light receiving component 2 measures the scattered light signal of a single droplet passing through the laser spot during the sampling process, compares the signal peak value P4 with the standard light intensity-particle size relationship curve, and obtains the required particle size information of the droplet 7;

[0073] Step 6: The scattered light receiving component 2 measures the scattered light signal of a single droplet passing through the laser spot during the sampling process, and compares the signal peak ratios P1 / P4, P2 / P4, P3 / P4 with the standard peak ratio-chemical composition database to obtain the chemical composition information of the required droplet 7.

[0074] The basic principle of the droplet composition discrimination in this embodiment is:

[0075] The scattered light intensity I at point P in the droplet scattered light field s :

[0076]

[0077] Among them, r is the distance from the center of the droplet to the field point P, λ is the wavelength of the incident light, I0 is the incident light intensity, I H3 is the relative intensity of polarized light parallel to the incident light direction; I VV is the relative intensity of polarized light perpendicular to the direction of the incident light;

[0078] I HH =i1(θ)=|S1(θ)| 2 ;I VV =i2(θ)=|S2(θ)| 2 ;

[0079] Among them, S1(θ) and S2(θ) are two amplitude functions related to the scattering angle, and θ is the angle between the scattered light and the incident light. It can be expressed as:

[0080]

[0081] in:

[0082] Among them, πn , τ n is an auxiliary angle function related to the scattering angle, used to describe the scattering directionality of light, P n , are Legendre function and first-order associated Legendre function, respectively, and the Mie scattering coefficient a n , b n It can be expressed as

[0083]

[0084] Where:

[0085] Among them, φ n (x)ξ n , ξ' n (x) represents φ n (x) and ξ n The derivatives of (x) with respect to x represent the rate of change of these two functions at a specific point and are usually used to calculate the relative changes in the scattering or transmission process. n+1 / 2 (x) and are the half-integer-order Bessel functions of the first kind and the half-integer-order Hankel functions of the second kind, φ n (x), ξ n (x), J n+1 / 2 (x), It is usually used to describe the propagation of spherical waves. m is the relative complex refractive index, that is, the ratio of the refractive index of the scatterer to the refractive index of the surrounding medium.

[0086] That is, when the components of the mist droplets 7 are different, their complex refractive indices are also different. When the distribution of the mist droplet scattering phase function is calculated according to the Mie scattering theory, there is a certain correlation between the scattered light intensity ratio at different angles and the mist droplet components, so the mist droplet components can be distinguished.

[0087] As an example:

[0088] The online measurement system includes a laser 1, a light trap 3, a droplet sampling channel tube 4, a collimating lens 5 and an aperture 6, a first detector 211, a second detector 212, a third detector 213, a fourth detector 214, a signal processing circuit 22 and a computer 23.

[0089] Laser 1 uses a 650nm, 30mW semiconductor laser; light trap 3 uses a Brewster light trap; all detectors use high-sensitivity avalanche photodiodes; collimating lens 5 uses an aspheric collimating lens that matches the divergence angle of laser 1; light trap 3 should achieve an absorption efficiency of the emitted laser greater than 0.99 to avoid stray light interfering with the signal measurement results of each detector. Fog droplet 7 should ensure that it passes through the laser beam individually to avoid achieving real-time measurement and analysis of single fog droplet information.

[0090] The laser emitted by the laser 1 is collimated and incident on the mist droplet 7 after passing through the collimating lens 5 and the aperture 6. The scattered light is received by the fourth detector 214, the third detector 213, the second detector 212, and the first detector 211, which are respectively received at directions of approximately 15 degrees, 30 degrees, 140 degrees, and 160 degrees to the laser emission angle. The receiving angles of the first detector 211, the second detector 212, the third detector 213, and the fourth detector 214 are less than ±4 degrees to ensure the spatial resolution and validity of each measurement value. The directly transmitted laser is absorbed by the light trap 3, and the first detector 211, the second detector 212, the third detector 213, and the fourth detector 214 convert the light signals I1, I2, I3, and I4 received at various angles into electrical signals and input them into the signal processing circuit 9, which amplifies the signal variation and inputs the signal peak values ​​P1, P2, P3, and P4 into the computer 23, respectively. P4 is substituted into the standard light intensity-particle size relationship fitting function to obtain the measured particle size, and the ratios of P1 / P4, P2 / P4, and P3 / P4 are compared with the standard peak value ratio-chemical composition database to determine the chemical composition information of the droplets.

[0091] like Figure 3 As shown in the figure, sand, sea salt, industrial dust, salt, etc. all have specific light scattering phase functions, that is, there is a specific correspondence between the intensity of the scattering signal and the scattering angle. The scattered light at about 15 degrees is less affected by the droplet composition and is used as a signal to measure the particle size; at 30 degrees, 140 degrees, and 160 degrees, there are different ratios, which are used as signals for analyzing the composition of the particle.

[0092] Then, the required droplet size information and chemical composition information are obtained through steps one to six.

[0093] This embodiment uses a single laser 1 and four detectors 21, and performs data comparison and analysis to achieve simultaneous online measurement of a single droplet size and chemical composition signal. This embodiment is simple, does not require film sampling and offline analysis, and effectively expands the online sensing method of multiple physical and chemical parameters of droplets based on the principle of light scattering, especially providing reliable data for real-time monitoring and source analysis of droplets; the spectral distribution and component analysis of droplets are key parameters for studying fog. In-depth exploration of the spectral distribution and composition of droplets not only helps to deepen the understanding of atmospheric physical and chemical change processes, but also promotes the understanding of the formation mechanism and laws of fog; by improving the ability to predict fog, this embodiment enhances human defense capabilities against fog damage, thereby helping to reduce losses caused by fog damage, and has important practical application value and scientific significance.

[0094] Therefore, this embodiment also has the following advantages:

[0095] (1) It makes up for the deficiency of the common droplet sampling system in determining whether the sampled droplets pass through the sampling point;

[0096] The droplet sampling system must determine whether the sampled droplets pass through the sampling point in order to accurately carry out the subsequent scattered light calculation. The existing droplet sampling system is difficult to achieve the sampling method of a single droplet passing through, that is, the method of a group of droplets passing through the sampling channel tube, so it is difficult to accurately obtain the position of the droplet passing through the sampling channel, which makes it difficult to locate the sampling single particle.

[0097] Although the American instrument FM120 uses the method of calculating the splitting ratio of the scattered light beam after passing through the beam splitting glued prism to determine whether the particles are within the system depth of field and determine the specific location of the droplets, the optical path is complex and the error is large in actual application.

[0098] This embodiment uses a method in which four detectors jointly detect the position of the sampling point, which can accurately determine the droplets passing through the sampling point. This method uses the distribution model of the light signals of the four detectors to calculate the actual position by intensity, thereby improving the accuracy of droplet sampling. The offset can be calculated through the output current of the four detectors to achieve center positioning. This method can improve the positioning accuracy of a single sampled droplet, which helps to solve the accuracy problem caused by a group of droplets passing through the sampling channel in the prior art.

[0099] (2) This embodiment makes up for the shortcomings of the ordinary light scattering method in measuring droplet parameters. For example, the single-angle light scattering method can only realize the particle (droplet) size measurement. The previous multi-angle detection scheme is only based on the design of different particle shapes without in-depth analysis of the relationship between the chemical composition of the particles and the light scattering signals at different angles. This embodiment uses the characteristics that the scattering signal of the droplet is positively correlated with the particle size under small-angle light scattering, and the scattering signal is related to the chemical composition of the particle under specific multi-angle light scattering, to achieve simultaneous online measurement of the particle size spectrum and chemical composition of a single droplet. This method plays a good technical support role in the change characteristics and source analysis of atmospheric fine particulate matter.

[0100] (3) The present invention is simple to implement, does not require membrane sampling and offline analysis, and effectively expands the real-time online sensing method of multiple physical and chemical parameters of droplets based on the principle of light scattering.

[0101] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. An online measurement system for droplet size and composition, characterized in that: It comprises a laser (1), a scattered light receiving component (2), a light trap (3) and a droplet sampling channel tube (4); The laser (1) is used to emit laser light, and the laser light is scattered by the mist droplets (7) in the mist droplet sampling channel tube (4) to obtain scattered light; Four independently arranged scattered light receiving components (2) are arranged around the outside of the droplet sampling channel tube (4) along the axial direction of the droplet sampling channel tube (4) to receive scattered light, and the detectors (21) in all the scattered light receiving components (2) and the laser light beam emitted by the laser (1) are on the same plane A, the movement direction of the droplets (7) in the droplet sampling channel tube (4) is perpendicular to the plane A, and the focus of the scattered light beam received by all the scattered light receiving components (2) is located at the center of the droplet sampling channel tube (4) on the plane A; The light trap (3) is used to absorb the laser light that directly passes through the mist drop sampling channel tube (4).

2. The online measurement system for droplet size and composition according to claim 1, characterized in that: Each scattered light receiving assembly (2) comprises a detector (21), a signal processing circuit (22) and a computer (23), wherein the input of the signal processing circuit (22) is connected to the output of the detector (21), and the output is connected to the input of the computer (23); The receiving ends of the four detectors (21) are respectively at 15 degrees, 30 degrees, 140 degrees and 160 degrees to the laser emission direction so as to receive scattered light in different directions.

3. The online measurement system for droplet size and composition according to claim 2, characterized in that: The four detectors (21) convert the scattered light signals I1, I2, I3, and I4 received at four angles into electrical signals and input them into the signal processing circuits (22) connected to them respectively. The signal processing circuits (22) amplify the signal variation and input the obtained signal peak values ​​P1, P2, P3, and P4 at the four angles into the computer (23). The computer (23) compares the peak value P4 with the standard light intensity-particle size relationship curve to obtain the particle size of the droplet (7). P1 / P 4. The ratios of P2 / P4 and P3 / P4 are compared with the standard peak ratio-chemical composition database to obtain the chemical composition information of the droplet (7); wherein I1 is received by the detector (21) at an angle of 160 degrees to the laser emission direction, I2 is received by the detector (21) at an angle of 140 degrees to the laser emission direction, I3 is received by the detector (21) at an angle of 30 degrees to the laser emission direction, and I4 is received by the detector (21) at an angle of 15 degrees to the laser emission direction.

4. The online measurement system for droplet size and composition according to claim 1, characterized in that: The receiving angles of the detectors (21) in all scattered light receiving components (2) are less than ±4 degrees, so as to ensure the spatial resolution and validity of each measurement value.

5. The online measurement system for droplet size and composition according to claim 1, characterized in that: The online measurement system further comprises a collimating lens (5) and an aperture (6). The laser light emitted by the laser (1) passes through the collimating lens (5) and the aperture (6) in sequence and then collimated and incident on the mist droplets (7) in the mist droplet sampling channel tube (4) to obtain scattered light.

6. The online measurement system for droplet size and composition according to claim 5, characterized in that: The collimating lens (5) is a non-spherical collimating lens, and the absorption efficiency of the light trap (3) for laser light is greater than 0.

99.

7. The measuring method of the online measurement system for droplet size and composition according to claim 1, characterized in that: Each scattered light receiving assembly (2) comprises a detector (21), a signal processing circuit (22) and a computer (23), the input of the signal processing circuit (22) is connected to the output of the detector (21), and the output is connected to the input of the computer (23), and the measuring method comprises the following steps: Step 1, four detectors (21) receive scattered light after the laser emitted by the laser (1) is scattered by the droplets (7) in the droplet sampling channel tube (4), and the scattered light signals I1, I2, I3, and I4 at four angles are respectively converted into electrical signals and input into the signal processing circuits (22) connected to them respectively, and the signal processing circuits (22) amplify the signal variation and input the obtained signal peak values ​​P1, P2, P3, and P4 at the four angles into the computer (23), wherein I1 is received by the detector (21) at an angle of 160 degrees to the laser emission direction, I2 is received by the detector (21) at an angle of 140 degrees to the laser emission direction, I3 is received by the detector (21) at an angle of 30 degrees to the laser emission direction, and I4 is received by the detector (21) at an angle of 15 degrees to the laser emission direction; Step 2: After preprocessing the signal peaks P1, P2, P3, and P4, if all the signal peaks after preprocessing are greater than a preset signal strength threshold, the droplet (7) passes through the center of the droplet sampling channel tube (4), and the process proceeds to step 3; if all the signal peaks after preprocessing have a signal peak less than or equal to the preset signal strength threshold, the droplet (7) does not pass through the center of the droplet sampling channel tube (4), and the process returns to step 1; Step 3: The scattered light receiving component (2) measures the relationship between the standard particle size and the signal peak value P4 under the same droplet (7) sampling environment, and obtains a standard light intensity-particle size relationship curve through third-order linear fitting; Step 4: The scattered light receiving component (2) measures the direct relationship between the standard particle composition and the P1 / P4, P2 / P4, and P3 / P4 ratios under the same droplet (7) sampling environment, and obtains a standard peak ratio-chemical composition database; Step 5, the scattered light receiving component (2) measures the scattered light signal of a single droplet passing through the laser spot during the sampling process, compares the signal peak value P4 with the standard light intensity-particle size relationship curve, and obtains the required particle size information of the droplet (7); Step 6: The scattered light receiving component (2) measures the scattered light signal of a single droplet passing through the laser spot during the sampling process, and compares the signal peak ratios P1 / P4, P2 / P4, P3 / P4 with the standard peak ratio-chemical composition database to obtain the chemical composition information of the required droplet (7).

8. The measuring method according to claim 7, characterized in that: In step 3, the standard light intensity-particle size relationship curve is obtained by third-order linear fitting. The third-order linear fitting formula is as follows: y=B0+B1*x+B2*x 2 +B3*x 3 Among them, y is the standard light intensity, x is the standard particle size, and B0, B1, B2, and B3 are fitting parameters respectively.

9. The measuring method according to claim 7, characterized in that: In step 2, the comparison process of the signal peak values ​​P1, P2, P3, P4 with the preset signal strength threshold is as follows: The computer (23) obtains the signal strength S1, S2, S3, S4 of each detector (21) based on the acquired signal peak values ​​P1, P2, P3, P4; The signal strengths S1, S2, S3, and S4 are smoothed to reduce noise, thereby standardizing the signal strengths; A signal strength threshold T is set to determine whether the mist droplet (7) passes through the center position of the mist droplet sampling channel tube (4); Compare each normalized signal intensity and determine the detector corresponding to the minimum signal intensity (21). If the minimum signal strength is greater than a preset signal strength threshold, the droplet (7) passes through the center of the droplet sampling channel cylinder (4); If the minimum signal strength is less than or equal to a preset signal strength threshold, the mist droplet (7) has not passed through the center position of the mist droplet sampling channel cylinder (4).

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