CN107192648B - Method and system for measuring uncertainty of D50 of PM2.5 cutter - Google Patents
Method and system for measuring uncertainty of D50 of PM2.5 cutter Download PDFInfo
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- CN107192648B CN107192648B CN201710416703.6A CN201710416703A CN107192648B CN 107192648 B CN107192648 B CN 107192648B CN 201710416703 A CN201710416703 A CN 201710416703A CN 107192648 B CN107192648 B CN 107192648B
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N15/00—Investigating characteristics of particles; Investigating permeability, pore-volume, or surface-area of porous materials
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
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- G01N15/06—Investigating concentration of particle suspensions
Abstract
The invention provides a method and a system for measuring uncertainty of D50 of a PM2.5 cutter. The method for measuring the D50 uncertainty of the PM2.5 cutter adopts a method of key section-taking fitting to analyze and evaluate the uncertainty of D50 in the research of the cutting characteristics of the PM2.5 cutter, replaces a complex cutting efficiency standard characteristic fitting curve with a linear curve, measures the uncertainty of the obtained linear curve through linear regression analysis, further determines the uncertainty of D50, greatly simplifies the analysis and calculation process, can accurately analyze and measure the uncertainty of D50 in the research of the cutting characteristics of the PM2.5 cutter, meets the requirement of magnitude traceability in the detection process of the PM2.5 cutter in China, and can provide reliable technical service for atmospheric environment monitoring.
Description
Technical Field
The invention relates to the technical field of air quality detection methods, in particular to a method and a system for measuring uncertainty of a PM2.5 cutter D50.
Background
PM2.5 is particulate matter having an aerodynamic diameter of less than or equal to 2.5 μm in the atmosphere, also known as accessible lung particulate matter. The PM2.5 has small particle size, is rich in a large amount of toxic and harmful substances, has long retention time in the atmosphere and long conveying distance, and thus has larger influence on human health and atmospheric environmental quality. PM2.5 particulate matters are used as the first pollutants of air pollution in China. PM2.5 monitoring and effective treatment are important targets of environmental protection departments and national governments in China. Currently, research work in the related field of PM2.5 is of great concern from countries to places, from environmental protection and environmental monitoring departments, to metering technology supervision agencies at all levels. Following HJ618-2011 ambient air PM10And PM2.5, GB 3095-environmental airThe promulgation and implementation of gas quality standards, the monitoring of PM2.5 particulate matter mass concentrations, has become a major concern for government work.
The PM2.5 measuring instrument is a necessary means for monitoring PM2.5 particles in air and evaluating the indoor and outdoor air quality, and the quality of the measuring performance of the PM2.5 measuring instrument directly relates to the reliability of monitoring data. The PM2.5 measuring instrument consists of a sampling device, a particle separator (PM2.5 cutter) and a testing and data processing system. The PM2.5 cutter is a core device of a PM2.5 measuring instrument, the size of collected particulate matters is determined, and the PM2.5 cutter cutting characteristic detection is a key point for researching the accuracy of PM2.5 monitoring results. At present, the domestic PM2.5 cutter lacks corresponding technical standards and a uniform instrument inspection detection means, so that the reliability of the domestic PM2.5 cutter is low, most of measurement data cannot be accepted by the public, and most of PM2.5 monitoring stations select to purchase the foreign PM2.5 cutter. Therefore, an effective analysis and evaluation means is urgently needed to comprehensively evaluate the performance of the PM2.5 cutter.
In recent years, with the increase of the national investment on the environmental protection industry, the monitoring technology research of PM2.5 is increasingly gaining attention. HJ618-2011 ambient air PM implemented by Ministry of environmental protection in 201110And PM2.5 gravimetric method of determination the performance of the cutter was specified as follows: particle aerodynamic equivalent diameter D corresponding to a cutter cutting efficiency of 50% on the particles50It should be in the range of (2.5. + -. 0.2) μm. Therefore, D50The uncertainty is an important index to examine the cutting performance of the PM2.5 cutter, however, related research and analysis are not available in the prior art.
In view of the above, the present invention is particularly proposed.
Disclosure of Invention
The invention aims to provide a method for measuring uncertainty of D50 of a PM2.5 cutter, which is simple and convenient, can accurately analyze and measure uncertainty of D50 in the research of cutting characteristics of the PM2.5 cutter, meets the requirement of quantity value tracing in the detection process of the PM2.5 cutter in China, and can provide reliable technical service for atmospheric environment monitoring.
The second purpose of the invention is to provide a measuring system adopting the method for measuring the uncertainty of the D50 of the PM2.5 cutter, and the measuring system can rapidly and accurately analyze and measure the uncertainty of the D50 in the research of the cutting characteristics of the PM2.5 cutter, meet the requirement of quantity value traceability in the detection process of the PM2.5 cutter in China, and provide reliable technical service for atmospheric environment monitoring.
In order to achieve the above purpose of the present invention, the following technical solutions are adopted:
a PM2.5 cutter D50 uncertainty determination method, adopt PM2.5 cutter cutting characteristic detection device to measure and calculate the average cutting efficiency of different particle size standard granules of PM2.5 cutter selected, and fit the standard characteristic fitting curve of cutting efficiency;
a method of taking a section for fitting is mainly adopted, a gravity center point of a whole cutting efficiency standard characteristic fitting curve is taken as a center, a plurality of experimental points are respectively taken before and after the gravity center point, each taken experimental point is fitted to obtain a linear curve, the uncertainty of the obtained linear curve is measured through linear regression analysis, and then the uncertainty of D50 is determined.
The method for measuring the D50 uncertainty of the PM2.5 cutter adopts a method of key section-taking fitting to analyze and evaluate the uncertainty of D50 in the research of the cutting characteristics of the PM2.5 cutter, replaces a complex cutting efficiency standard characteristic fitting curve with a linear curve, measures the uncertainty of the obtained linear curve through linear regression analysis, further determines the uncertainty of D50, greatly simplifies the analysis and calculation process, can accurately analyze and measure the uncertainty of D50 in the research of the cutting characteristics of the PM2.5 cutter, meets the requirement of magnitude traceability in the detection process of the PM2.5 cutter in China, and can provide reliable technical service for atmospheric environment monitoring.
Preferably, the cutting efficiency of the standard particles with different particle sizes can be obtained by the following formula:
in the formula: i … … … point of aerosol particle size;
j … … … number of measurements per particle size point;
N1ij… … PM2.5 concentration of solid monodisperse particles upstream of the cutter;
N2ij… … PM2.5 cutter downstream solid monodisperse particulate matter concentration;
ηij… … … single measured capture efficiency per particle size point;
respectively calculating the cutting efficiency of different particle size points according to the formula (1);
the average cutting efficiency at each particle size point was calculated as follows:
in the formula:
… … … … … … … … average cutting efficiency per particle size point.
Preferably, the equation of the cutting efficiency standard characteristic fitting curve is as follows:
wherein the values of a, b, c, d and e are all determined directly by fitting.
Preferably, the experimental points are taken between 10% and 90% of the cutting efficiency in a standard characteristic fit curve of cutting efficiency.
Preferably, the equation of the linear curve is:
y＝ax+b；
where the values of a and b are both determined directly by fitting.
Preferably, said determining the uncertainty of the resulting linear curve by linear regression analysis comprises:
substituting the standard particle size and the corresponding average cutting efficiency into the fitted linear curve equation, and calculating a regression standard deviation estimated value s:
in the above formula, yiCutting efficiency values corresponding to different standard particle sizes;
is taken from a linear curve with xiCorresponding to yiCalculating a value; n is the number of tests.
Preferably, the uncertainty of D50 is further determined
Then calculating the corresponding particle size x when the cutting efficiency is 50 percent0S (x) is the standard deviation estimate of0)：
In the above formula, the first and second carbon atoms are,the average of all x values used for fitting the linear curve;is the average of all y values; y is0Representing a cutting efficiency of 50%; b is the slope of the linear curve; m is the number of parallel tests;
then selecting confidence level, checking t distribution table, determining degree of freedom, and comparing D50The extended uncertainty of (a) is calculated.
Preferably, the adopted PM2.5 cutter cutting characteristic detection device comprises an air source device, an atomized aerosol generator, a dryer, an electrostatic neutralizer, a mixing pipe, an aerosol particle size spectrometer, an air pump, a first valve, a second valve, a third valve and a fourth valve;
the output end of the air source device is communicated with the input end of the atomized aerosol generator, the output end of the atomized aerosol generator is communicated with the input end of the dryer, the output end of the dryer is communicated with the input end of the static neutralizer, and the output end of the static neutralizer is communicated with the input end of the mixing pipe;
the output end of the blending pipe is communicated with the input end of the first valve, and the output end of the first valve is communicated with the aerosol particle size spectrometer;
the output end of the blending pipe is also communicated with the input end of a PM2.5 cutter to be detected, the output end of the PM2.5 cutter to be detected is communicated with the input end of the second valve, and the output end of the second valve is communicated with the aerosol particle size spectrometer;
the input end of the first valve is also communicated with the input end of the third valve, and the output end of the third valve is communicated with the input end of the air pump;
the input end of the second valve is also communicated with the input end of the fourth valve, and the output end of the fourth valve is communicated with the input end of the air suction pump.
Preferably, the method for detecting the cutting characteristic of the PM2.5 cutter comprises the following steps:
adding ultrapure water and a standard particle suspension into the atomizing aerosol generator to generate monodisperse solid aerosol particles, wherein the standard particle suspension contains a plurality of standard particles with different particle sizes, and the content of the standard particles with different particle sizes is a fixed value;
opening the first valve and the third valve, closing the second valve and the fourth valve, and reading the aerosol particle number concentration value measured by the aerosol particle size spectrometer;
and opening the second valve and the fourth valve, closing the first valve and the third valve, and reading the aerosol particle number concentration value measured by the aerosol particle size spectrometer.
A measurement system using the above-described method for measuring the uncertainty of D50 on the PM2.5 cutter.
The measuring system can rapidly and accurately analyze and measure the uncertainty of D50 in the research of the cutting characteristics of the PM2.5 cutter, meets the quantity value tracing requirement in the detection process of the PM2.5 cutter in China, and can provide reliable technical service for atmospheric environment monitoring.
Compared with the prior art, the invention has the beneficial effects that:
the method for measuring the D50 uncertainty of the PM2.5 cutter adopts a method of key section-taking fitting to analyze and evaluate the uncertainty of D50 in the research of the cutting characteristics of the PM2.5 cutter, replaces a complex cutting efficiency standard characteristic fitting curve with a linear curve, measures the uncertainty of the obtained linear curve through linear regression analysis, further determines the uncertainty of D50, greatly simplifies the analysis and calculation process, can accurately analyze and measure the uncertainty of D50 in the research of the cutting characteristics of the PM2.5 cutter, meets the requirement of magnitude traceability in the detection process of the PM2.5 cutter in China, and can provide reliable technical service for atmospheric environment monitoring.
The measuring system can rapidly and accurately analyze and measure the uncertainty of D50 in the research of the cutting characteristics of the PM2.5 cutter, meets the quantity value tracing requirement in the detection process of the PM2.5 cutter in China, and can provide reliable technical service for atmospheric environment monitoring.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, and it is obvious that the drawings in the following description are some embodiments of the present invention, and other drawings can be obtained by those skilled in the art without creative efforts.
Fig. 1 is a schematic structural diagram of a PM2.5 cutter cutting characteristic detection apparatus provided in embodiment 1 of the present invention;
FIG. 2 is a schematic view showing the structure of a gas source apparatus in example 1 of the present invention;
FIG. 3 is a schematic structural view of a mixing tube in example 1 of the present invention;
fig. 4 is a flowchart of a detection method of the PM2.5 cutter cutting characteristic detection apparatus according to embodiment 2 of the present invention;
FIG. 5 is a graph of the standard cut efficiency characteristic obtained in example 3 of the present invention;
FIG. 6 is a graph of a fitted linear curve on a fitting curve of standard characteristics of cutting efficiency obtained in example 3 of the present invention;
reference numerals: 100-gas source device; 102-an atomized aerosol generator; 103-a dryer; 104-an electrostatic neutralizer; 105-a mixing tube; 106-aerosol particle size spectrometer; 107-an air pump; 108-a first valve; 109-a second valve; 110-a third valve; 111-a fourth valve; 112-mass flow controllers; 113-an air compressor; 114-a gas storage tank; 115-three-stage high-efficiency filter; 116-a freeze dryer; 117-first make-up air conduit; 118-a second air make-up conduit; 119-a fifth valve; 120-a sixth valve; 121-inverted cone structure; 122-an air flow splitter; 123-air supplement end; 124-PM 2.5 cutter to be detected; 125-seventh valve.
Detailed Description
The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings and the detailed description, but those skilled in the art will understand that the following described embodiments are some, not all, of the embodiments of the present invention, and are only used for illustrating the present invention, and should not be construed as limiting the scope of the present invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention. The examples, in which specific conditions are not specified, were conducted under conventional conditions or conditions recommended by the manufacturer. The reagents or instruments used are not indicated by the manufacturer, and are all conventional products available commercially.
In the description of the present invention, it should be noted that the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc., indicate orientations or positional relationships based on the orientations or positional relationships shown in the drawings, and are only for convenience of description and simplicity of description, but do not indicate or imply that the device or element being referred to must have a particular orientation, be constructed and operated in a particular orientation, and thus, should not be construed as limiting the present invention. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and are not to be construed as indicating or implying relative importance.
In the description of the present invention, it should be noted that, unless otherwise explicitly specified or limited, the terms "mounted," "connected," and "connected" are to be construed broadly, e.g., as meaning either a fixed connection, a removable connection, or an integral connection; can be mechanically or electrically connected; they may be connected directly or indirectly through intervening media, or they may be interconnected between two elements. The specific meanings of the above terms in the present invention can be understood in specific cases to those skilled in the art.
The PM2.5 cutting characteristic detection device mainly comprises an air source generating device, an atomization generator, a dryer, an electrostatic neutralizer, a mixing pipe, a flow divider and an aerosol particle size spectrometer. Compressed clean air passes through an atomization generator to form monodisperse polystyrene aerosol, and the monodisperse polystyrene aerosol is dried and destaticized to be diluted and uniformly mixed in a uniformly mixing pipe to achieve a uniform and stable state. The aerosol particle number concentration measuring instrument is divided into an upstream branch and a downstream branch after passing through a flow divider, the upstream branch is directly connected to a particle size spectrometer, the downstream branch is connected to the particle size spectrometer after passing through a PM2.5 cutter to be measured, and the aerosol particle number concentration in the two branches is alternately measured by the particle size spectrometer by switching an electromagnetic valve.
Example 1
Referring to fig. 1 to 3, a first embodiment of the present invention provides a PM2.5 cutter cutting characteristic detection apparatus, including an air supply apparatus 100, an atomized aerosol generator 102, a dryer 103, an electrostatic neutralizer 104, a blending pipe 105, an aerosol particle size spectrometer 106, an air pump 107, a first valve 108, a second valve 109, a third valve 110, and a fourth valve 111; the output end of the air source device 100 is communicated with the input end of the atomized aerosol generator 102, and specifically, a fifth valve 119 is communicated between the output end of the air source device 100 and the input end of the atomized aerosol generator 102; the output end of the atomized gas generator is communicated with the input end of the dryer 103, the output end of the dryer 103 is communicated with the input end of the static neutralizer 104, and the output end of the static neutralizer 104 is communicated with the input end of the blending pipe 105; the output end of the blending pipe 105 is communicated with the input end of a first valve 108, and the output end of the first valve 108 is communicated with an aerosol particle size spectrometer 106; the output end of the blending pipe 105 is also communicated with the input end of a PM2.5 cutter to be detected, the output end of the PM2.5 cutter to be detected is communicated with the input end of a second valve 109, and the output end of the second valve 109 is communicated with an aerosol particle size spectrometer 106; the input end of the first valve 108 is also communicated with the input end of the third valve 110, the output end of the third valve 110 is communicated with the input end of the air pump 107, specifically, the connecting point of the input end of the first valve 108 and the output end of the blending pipe 105 is communicated with the input end of the third valve 110; the input end of the second valve 109 is also communicated with the input end of the fourth valve 111, the output end of the fourth valve 111 is communicated with the input end of the air pump 107, and specifically, the connection point of the input end of the second valve 109 and the output end of the PM2.5 cutter to be detected is communicated with the input end of the fourth valve 111.
In this embodiment, the apparatus for detecting the cutting characteristics of the PM2.5 cutter further includes a mass flow controller 112, an input end of the air pump 107 is communicated with an output end of the mass flow controller 112, and an output end of the fourth valve 111 and an output end of the third valve 110 are respectively communicated with an input end of the mass flow controller 112. Specifically, the connection point between the output of the fourth valve 111 and the output of the third valve 110 is communicated with the input of a mass flow controller 112, and the output of the mass flow controller 112 is communicated with the input of the suction pump 107.
In this embodiment, the air source device 100 includes an air compressor 113, an air storage tank 114, a three-stage high-efficiency filter 115 and a freeze dryer 116, wherein the air compressor 113, the air storage tank 114, the three-stage high-efficiency filter 115 and the freeze dryer 116 are sequentially communicated, and the freeze dryer 116 is further communicated with the aerosol atomizer 102.
Specifically, the output end of the air compressor 113 and the input end of the air tank 114 are connectedThe output end of the gas storage tank 114 is communicated with the input end of the three-stage high-efficiency filter 115, the output end of the three-stage high-efficiency filter 115 is communicated with the input end of the freeze dryer 116, and the output end of the freeze dryer 116 is communicated with the input end of the atomization aerosol generator 102. The air compressor 113 compresses air into an air storage tank 114, the air is filtered by a three-stage high-efficiency filter 115 to obtain a clean air source with the particle size of less than 0.3 mu m, a freeze dryer 116 freezes a water-containing substance in the clean air source into a solid state, and the water in the water-containing substance is sublimated from the solid state into a gas state, so that the drying purpose is achieved, wherein the air flow processed by the freeze dryer 116 is 1.5m3/min。
In this embodiment, a pressure sensor is mounted on the gas tank 114 for detecting the pressure of the gas in the gas tank 114. The device for detecting the cutting characteristics of the PM2.5 cutter further comprises a controller, and the air compressor 113, the freeze dryer 116 and the suction pump 107 are respectively and electrically connected with the controller. The pressure of the gas in the gas storage tank 114 can be controlled within a set range by the gas pressure sensor, so that a continuous and stable gas source is provided for the subsequent process. The specific process is as follows: the air storage tank 114 and the air compressor 113 have an automatic adjustment function, when the pressure in the air storage tank 114 reaches 0.6MPa, the air pressure sensor sends pressure information to the controller, and the controller stops the operation of the air compressor 113 after receiving the pressure information sent by the air pressure sensor, so that the pressure in the air storage tank 114 is in a safety range. Along with the continuous use of the air source, the pressure in the air storage tank 114 is gradually reduced, when the pressure sensor detects that the pressure in the air storage tank 114 is reduced to 0.4MPa, the pressure sensor sends pressure information to the controller, and after the controller receives the pressure information sent by the pressure sensor, the air compressor 113 is enabled to work again, dry clean air is continuously manufactured, and therefore the fact that a stable air source is continuously provided for the subsequent process can be guaranteed.
In this embodiment, a first air supply pipeline 117 is further connected between the output end of the air supply device 100 and the input end of the static neutralizer 104, and the clean air can be directly input into the static neutralizer 104 through the first air supply pipeline 117 to dilute the concentration of the particulate matters in the air. The first air make-up duct 117 is provided with a sixth valve 120.
In this embodiment, the top of the mixing tube 105 has an inverted conical structure 121, and the input end of the mixing tube 105 is located at the end of the inverted conical structure 121.
Specifically, a second air supply pipe 118 is further communicated between the air supply device 100 and the blending pipe 105, wherein an output end of the air supply device 100 is communicated with one end of the second air supply pipe 118, the other end of the second air supply pipe 118 is communicated with an air supply end 123 of the blending pipe 105, and the air supply end extends into the conical surface of the inverted cone-shaped structure 121, so that the air flowing out of the second air supply pipe 118 flows along the conical surface of the inverted cone-shaped structure 121. The input end of the first valve 108 and the input end of the cutter for detecting PM2.5 are both communicated with the output end of the blending pipe 105 through the airflow splitter 122. The second air make-up pipe 118 is provided with a seventh valve.
By the detection test, when the length of the mixing tube 105 is 100mm, the volume fraction of the aerosol on the cross section of the mixing tube 105 does not change. The volume fraction on each section remains constant as the distance increases. Indicating that complete mixing of the aerosol and diluent gas entering from the end of the supply takes place over a short distance.
In this embodiment, the dryer 103 is filled with silica gel; the electrostatic neutralizer 104 is an aerosol electrostatic neutralizer. The generated monodisperse solid aerosol particles generated by the aerosol generator, each particle being surrounded by 5 water molecules, cause aggregation of the particles and adhesion on the tube wall, and therefore with the dryer 103 filled with silica gel, moisture can be effectively removed. After passing through the dryer 103, the drying effect can reach 99.5%, the monodisperse aerosol is very dry, the particle size range of particles used in the experiment is 1.5-4.5 μm, the particle size is small, static electricity is easily generated, monodisperse solid aerosol particles with charges can be adsorbed on the tube wall to cause loss and influence the number concentration value of the aerosol particles to be detected, the aerosol static electricity neutralizer can process solid or liquid aerosol, the particle size range is 0.1-150 μm, and the principle of static electricity removal is as follows: the aerosol enters the mixing chamber of the aerosol static neutralizer and is fully mixed with the charged clean gas entering from the first air supply pipeline 117, and then the static attached to the particles is eliminated.
In this embodiment, the three-stage high efficiency filter 115 is a HEPA filter.
In this embodiment, the first valve 108, the second valve 109, the third valve 110, and the fourth valve 111 are all solenoid valves; the fifth valve 119, the sixth valve 120 and the seventh valve are all solenoid valves, and the solenoid valves are electrically connected with the controller. By adopting the electromagnetic valve, the influence of human factors on the measurement time can be reduced as much as possible.
In this embodiment, the treated gas source should not contain particles above 0.3 μm, depending on the detection requirements; therefore, the particle size distribution experiment of the processed air source is detected by the aerosol particle size spectrometer 106. The aerosol particle size spectrometer 106 is a typical instrument for measuring aerosol particle counts using the principle of light scattering, with particle sizes ranging from 0.3 μm to 20 μm.
The atomization aerosol generator 102 is removed, the output end of the freeze dryer 116 is directly connected to the input end of the dryer 103, and the aerosol enters the aerosol particle size spectrometer 106 after passing through the static neutralizer 104 and the mixing tube 105. And filling the gas path with gas, ventilating for half an hour, removing residual particles adhered to the tube wall, and measuring the counting concentration of the particles in the gas source at the moment by using an aerosol particle size spectrometer 106. The test results are shown in table 1.
Table 1 shows the concentration of particles of 0.3 μm or more in a clean gas source
| Number of measurements | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 |
| Concentration of particulate matter of 0.3 μm or more | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
As can be seen from Table 1, the filtered clean gas meets the requirements of EPA and national environmental protection standards on the content of gas source particles.
In this example, in the process of testing the cutting characteristics of the PM2.5 cutter, the polystyrene suspension, i.e., the standard particle suspension, was dispersed in the ultrapure water, so it was first necessary to test the content of particles in the ultrapure water using the aerosol particle size spectrometer 106 to verify whether particles affecting the experiment were present in the ultrapure water.
Only 20mL of ultrapure water is added into an atomization aerosol generator 102, and then dry clean gas is introduced into the atomization aerosol generator, passes through a dryer 103, an electrostatic neutralizer 104 and a mixing tube 105, and enters an aerosol particle size spectrometer 106. The results of 8 tests are shown in table 2.
Table 2 shows the number of particles in ultrapure water (one test volume of 15 cm)3)
| Number of times | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 |
| Total number of |
0 | 1 | 1 | 0 | 1 | 0 | 1 | 0 |
As can be seen from Table 2, the amount of particles contained in the ultrapure water was almost zero and was negligible relative to the amount of the polystyrene aerosol of high concentration. Ultrapure water can be used as a dispersion medium for the suspension of the atomizing aerosol generator 102.
The volumetric flow rate of the aerosol generator is controlled by controlling the pressure of the gas within the reservoir 114, which has been tested to be between 2lpm and 20lpm at pressures between 0.5psi and 20 psi. In the flow interval, adding fixation aiming at different particle diametersThe standard particles with the volume can reach 1.5 particles/cm through the detection of an aerosol particle size spectrometer 1063And meets the requirement of EPA on the detection of the concentration of the aerosol.
Example 2
Referring to fig. 4, a second embodiment of the present invention provides a detection method using the device for detecting a cutting characteristic of a PM2.5 cutter according to the first embodiment, the detection method including the steps of:
200, adding ultrapure water and standard particle floating liquid into an atomizing aerosol generator 102 to generate monodisperse solid aerosol particles, wherein the standard particle floating liquid contains a plurality of standard particles with different particle sizes, and the content of the standard particles with different particle sizes is a fixed value;
specifically, in this example, 8 kinds of standard particles of the prior art having an aerodynamic equivalent particle diameter in the range of (1.5 to 4.0) μm were used. The content of each standard particle with different particle sizes is a fixed value.
and step 203, finally, analyzing whether the cutting characteristic of the PM2.5 cutter meets the requirement or not according to the aerosol particle number concentration values measured in the two states.
Specifically, different trapping efficiencies corresponding to particles with different aerodynamic equivalent diameters are obtained by alternately measuring the number concentration of aerosol particles in two states; then, an orthogonal coordinate system is established by taking the aerodynamic equivalent diameter as an abscissa and the trapping efficiency as an ordinate, a cutting characteristic curve of the PM2.5 cutter is obtained by using TableCURVE2D software in a fitting mode, and whether the cutting performance of the PM2.5 cutter meets the relevant standard requirements or not is judged by analyzing D50 and the geometric standard deviation of the cutting characteristic curve, wherein D50 represents the corresponding particle aerodynamic equivalent diameter with the unit of mum when the trapping efficiency of the cutter on the particulate matters is 50%.
Example 3
First, the standard particles (polystyrene particles) having different particle diameters were atomized into monodisperse solid aerosols using the PM2.5 cutter cutting characteristic measuring device. After drying and static electricity removing, the mixture is diluted and mixed in a mixing tube to reach a stable state. Then, a selected PM2.5 cutter is added into the gas path, the aerosol particle numbers at the upstream of the PM2.5 cutter and the downstream of the PM2.5 cutter are alternately measured by a real-time aerosol particle size spectrometer, and N is respectively recorded1iAnd N2i. Obtaining N until the test of the atomized monodisperse solid aerosol particles with different particle diameters is finished1ijAnd N2ij. Repeating the operation for three times, and calculating according to the following formula to obtain the cutting efficiency of the standard particles with different particle sizes:
in the formula: i … … … (different particle size numbers, i is a positive integer);
j … … … number of measurements per particle size point (j is a positive integer);
N1ij… … PM2.5 cutter upstream solid monodisperse particulate matter concentration (number concentration value);
N2ij… … PM2.5 cutter downstream solid monodisperse particulate matter concentration (number concentration value);
ηij… … … single measured capture efficiency per particle size point;
respectively calculating the cutting efficiency of different particle size points according to the formula (1);
the average cutting efficiency at each particle size point was calculated as follows:
in the formula:… … … … … … … … average cutting efficiency per particle size point.
And then fitting a corresponding cutting efficiency standard characteristic fitting curve by taking the obtained average cutting efficiency numerical value as a vertical coordinate and taking the corresponding standard particle size as a horizontal coordinate. And fitting a curve according to the standard cutting efficiency characteristic, and obtaining the corresponding particle size value under the relevant cutting efficiency condition by reverse extrapolation.
As can be seen from the fitted cutting efficiency standard characteristic fitted curve (as shown in table 3), the cutting efficiency of PM2.5 is gradually decreased as the particle size is increased. The larger the particle size is, the larger the inertia is, and the particles are more likely to impact on the capture plate or be captured in the sand settling tank to be deposited in the process of moving along with the airflow; and the smaller the particle size, the easier it will move through with the gas flow.
TABLE 3 cutting efficiency at different particle sizes
The cutting efficiency standard characteristic fitting curve equation obtained by fitting according to the experimental data is as follows:
wherein a is 99.418; -98.304; c is 2.493; d is 0.268; and e-2.513. It can be seen that the cutting efficiency standard characteristic fitting curve equation is too complex, and the relevant uncertainty of the analysis cannot be directly and effectively evaluated by using the traditional regression analysis method.
The quality of the PM2.5 cutter performance was assessed by examining the uncertainty of D50, which is the uncertainty of the particle size corresponding to a cutting efficiency of 50%. By observing and analyzing the standard characteristic fitting curve of the cutting efficiency (as shown in figure 5), the linear characteristic of the curve (occupying the middle and most parts of the whole characteristic curve) with the cutting efficiency between 10% and 90% is obvious. And the more toward its center of gravity, the more pronounced the linear characteristic. And point D50 is exactly the center of gravity point of the characteristic curve. And D50 is taken as a center, a plurality of experimental points are extended from top to bottom, a corresponding linear curve is made, the uncertainty of the straight line is evaluated through straight line regression analysis, and the uncertainty of the key point D50 is further determined.
The corresponding experimental points, i.e. the particle sizes corresponding to different cutting efficiencies, are plotted on the standard characteristic fitting curve of the cutting efficiency, as shown in fig. 6. The middle point (D50) is taken as the center, the curve linear characteristics obtained by the two-end extension are obvious, so the middle five experimental points are taken as parameters (underlined parts in the table 3), the least square method is sampled, and a linear curve is drawn to obtain a related linear curve equation:
y＝288.436-96.054x (4)
the correlation coefficient of the obtained linear curve is 0.993, which shows that the linear characteristic is good. When y0 is 50 (i.e. the cutting efficiency is 50%), the x0 is 2.482 by substituting equation (4), i.e. the D50 coordinate is (2.482,50), which is also the center of gravity point of the whole linear curve. In the linear curve uncertainty investigation, the closer to the center of gravity, the higher the accuracy of the data uncertainty. Therefore, the uncertainty of the D50 can be effectively analyzed and evaluated on the basis of a linear curve after linear regression.
The regression standard deviation estimate s was calculated by first substituting the relevant experimental data in table 3 into the fitted linear curve equation (4):
in the above formula, yiCutting efficiency values corresponding to different standard particle sizes;
is taken from a linear curve with xiCorresponding to yiCalculating a value; n is the number of tests.
Then calculating the corresponding particle size x when the cutting efficiency is 50 percent0S (x) is the standard deviation estimate of0)：
In the above formula, the first and second carbon atoms are,
the average of all x values used for fitting the linear curve;
is the average of all y values; y is0Representing a cutting efficiency of 50%; b is the slope of the linear curve; m is the number of parallel tests;
when cutting efficiency y0When 50%, the particle diameter x of the corresponding fine particle can be found by substituting the linear equation (4)02.482 μm, its expansion uncertainty is denoted as U (m50) Selecting confidence level p as 95% (significance level α as 0.05), looking up t distribution table, and obtaining t with degree of freedom v as n-295(13) 1.771. Therefore, D50Extended uncertainty U of95(50)＝t95(13)×s(x0) 1.771 × 0.02469 ═ 0.012133006 μm. Namely: d50＝(2.482±0.012)μm。
Further from the linear curves of fig. 2, the PM2.5 cutter cutting efficiencies were 16%, and the particle aerodynamic diameters at 50% and 84%, respectively, were: d162.828 μm and D842.122 μm. According to U.S. EPA-related regulations, the Geometric Standard Deviation (GSD) of a cutting characteristic curve can be calculated as:
according to the United states EPA and the national environmental protection regulation HJ618-2011 environmental air PM10And PM2.5 gravimetric method of determination "requirements: d50μ m (2.5 ± 0.2) and a geometric standard deviation GSD of 1.2 ± 0.1. From the above discussion, it can be seen that D is obtained in the present subject50The product (2.482 + -0.057) mu m and the GSD (1.154) meet the requirements of United states EPA and national environmental protection regulations.
According to the invention, the evaluation on the cutting characteristic of the PM2.5 cutter is realized by analyzing and evaluating the uncertainty of D50. In the D50 uncertainty analysis and evaluation process, a method of key section-taking fitting is adopted, the center of gravity point of the whole cutting efficiency standard characteristic fitting curve is taken as the center, limited experimental points are respectively taken up and down, and the curve obtained by fitting the taken series of experimental points is good in linearity. Further, linear regression processing is carried out to obtain a linear curve, the linear characteristic is prominent, and the correlation coefficient is close to 1. The method for analyzing and evaluating the uncertainty of the D50 by using the method of the key-section linear regression analysis can be effectively used. The method can meet the quantity value tracing requirement in the PM2.5 cutter detection process in China, and can provide reliable technical service for atmospheric environment monitoring.
While particular embodiments of the present invention have been illustrated and described, it will be appreciated that the above embodiments are merely illustrative of the technical solution of the present invention and are not restrictive; those of ordinary skill in the art will understand that: modifications may be made to the above-described embodiments, or equivalents may be substituted for some or all of the features thereof without departing from the spirit and scope of the present invention; the modifications or the substitutions do not make the essence of the corresponding technical solutions depart from the scope of the technical solutions of the embodiments of the present invention; it is therefore intended to cover in the appended claims all such alternatives and modifications that are within the scope of the invention.
Claims (7)
1. A method for measuring uncertainty of D50 of a PM2.5 cutter is characterized in that a PM2.5 cutter cutting characteristic detection device is adopted to test and calculate the average cutting efficiency of selected PM2.5 cutters on standard particles with different particle sizes, and a cutting efficiency standard characteristic fitting curve is fitted;
the PM2.5 cutter cutting characteristic detection device comprises an air source device, an atomized aerosol generator, a dryer, an electrostatic neutralizer, a mixing pipe, an aerosol particle size spectrometer, an air suction pump, a first valve, a second valve, a third valve and a fourth valve;
the output end of the air source device is communicated with the input end of the atomized aerosol generator, the output end of the atomized aerosol generator is communicated with the input end of the dryer, the output end of the dryer is communicated with the input end of the static neutralizer, and the output end of the static neutralizer is communicated with the input end of the mixing pipe;
the output end of the blending pipe is communicated with the input end of the first valve, and the output end of the first valve is communicated with the aerosol particle size spectrometer;
the output end of the blending pipe is also communicated with the input end of a PM2.5 cutter to be detected, the output end of the PM2.5 cutter to be detected is communicated with the input end of the second valve, and the output end of the second valve is communicated with the aerosol particle size spectrometer;
the input end of the first valve is also communicated with the input end of the third valve, and the output end of the third valve is communicated with the input end of the air pump;
the input end of the second valve is also communicated with the input end of the fourth valve, and the output end of the fourth valve is communicated with the input end of the air suction pump;
the equation of the cutting efficiency standard characteristic fitting curve is as follows:
wherein the values of a, b, c, d and e are directly determined by fitting, x represents the standard particle size, and y represents the cutting efficiency;
a method of taking a section for fitting is mainly adopted, a gravity center point of a whole cutting efficiency standard characteristic fitting curve is taken as a center, a plurality of experimental points are respectively taken before and after the gravity center point, each taken experimental point is fitted to obtain a linear curve, the uncertainty of the obtained linear curve is measured through linear regression analysis, and then the uncertainty of D50 is determined;
and taking the experimental points when the cutting efficiency is 10% -90% in the standard characteristic fitting curve of the cutting efficiency.
2. The method for measuring uncertainty of D50 on the PM2.5 cutter according to claim 1, wherein the cutting efficiency of standard particles with different particle sizes is calculated according to the following formula:
in the formula: i … … … point of aerosol particle size;
j … … … number of measurements per particle size point;
N1ij… … PM2.5 concentration of solid monodisperse particles upstream of the cutter;
N2ij… … PM2.5 cutter downstream solid monodisperse particulate matter concentration;
ηij… … … single measured capture efficiency per particle size point;
respectively calculating the cutting efficiency of different particle size points according to the formula (1);
the average cutting efficiency at each particle size point was calculated as follows:
in the formula:
… … … … … … … … average cutting efficiency per particle size point.
3. A method of determining D50 uncertainty in a PM2.5 cutter as claimed in claim 1, wherein the equation for the linear curve is:
y＝ax+b；
where the values of a and b are both determined directly by fitting.
4. The method of claim 1, wherein said determining the uncertainty of the resulting linear curve by linear regression analysis comprises:
substituting the standard particle size and the corresponding average cutting efficiency into the fitted linear curve equation, and calculating a regression standard deviation estimated value s:
in the above formula, yiCutting efficiency values corresponding to different standard particle sizes;
is taken from a linear curve with xiCorresponding to yiCalculating a value; n is the number of tests.
5. The method of claim 4, wherein the D50 uncertainty of the PM2.5 cutter is further determined according to the D50 uncertainty,
then calculating the corresponding particle size x when the cutting efficiency is 50 percent0S (x) is the standard deviation estimate of0)：
In the above formula, the first and second carbon atoms are,
the average of all x values used for fitting the linear curve;
is the average of all y values; y is0Indicating that the cutting efficiency was 50%,
is all y0An average of the values; b is the slope of the linear curve; m is the number of parallel tests;
then selecting confidence level, checking t distribution table, determining degree of freedom, and comparing D50The extended uncertainty of (a) is calculated.
6. The method for measuring uncertainty of D50 on the PM2.5 cutter according to claim 1, wherein the method for detecting by using the PM2.5 cutter cutting characteristic detecting device comprises the following steps:
adding ultrapure water and a standard particle suspension into the atomizing aerosol generator to generate monodisperse solid aerosol particles, wherein the standard particle suspension contains a plurality of standard particles with different particle sizes, and the content of the standard particles with different particle sizes is a fixed value;
opening the first valve and the third valve, closing the second valve and the fourth valve, and reading the aerosol particle number concentration value measured by the aerosol particle size spectrometer;
and opening the second valve and the fourth valve, closing the first valve and the third valve, and reading the aerosol particle number concentration value measured by the aerosol particle size spectrometer.
7. A system for determining the uncertainty of D50 on a PM2.5 cutter according to any one of claims 1 to 6.
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| CN107271345B (en) * | 2017-06-15 | 2019-07-19 | 中国食品药品检定研究院 | Two method combined calibrating oxygen transit dose standard films of one kind and preparation method thereof |
| CN107421863A (en) * | 2017-09-25 | 2017-12-01 | 北京航空航天大学 | It is a kind of to combine the PM that monodisperse aerosol occurs1Cutting head Performance Test System |
| CN108169101B (en) * | 2018-01-18 | 2023-12-19 | 广州纤维产品检测研究院 | Anti-haze window screening filtering effect testing device and testing method |
| CN108499382A (en) * | 2018-04-24 | 2018-09-07 | 北京市计量检测科学研究院 | A kind of dust generating system and a kind of dust instrument calibration method |
| CN111812002A (en) * | 2020-06-29 | 2020-10-23 | 上海交通大学 | Small flow aerosol measuring method |
| CN111982784A (en) * | 2020-08-28 | 2020-11-24 | 中国环境监测总站 | PM2.5 cutterbar characteristic calibrating device |
| CN112229772A (en) * | 2020-09-04 | 2021-01-15 | 中国原子能科学研究院 | Radioactive aerosol source preparation system |
| CN111965083A (en) * | 2020-09-17 | 2020-11-20 | 青岛市计量技术研究院 | Particulate matter calibration system |
| CN113310856B (en) * | 2021-05-26 | 2022-08-26 | 常熟理工学院 | Particle generation method and device of heat flow generator for thermal vibration test |
| CN113635383B (en) * | 2021-07-02 | 2022-09-06 | 北京九州鹏跃科技有限公司 | Aerosol cutter |
| CN113457479B (en) * | 2021-07-22 | 2022-09-23 | 上海交通大学 | Dust aerosol generating system with constant and stable quantitative concentration |
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