Method for measuring average particle size of particulate matter

Abstract

The invention discloses a method for measuring the average particle size of particulate matter, which belongs to the technical field of particle size measurement, and comprises the following steps: selecting a cylindrical flat-bottom silo which is vertically placed, the bottom of the cylindrical flat-bottom silo is provided with a diameter-adjustable round hole, and the diameter of the silo is 2.5 times larger than that of the round hole; the method comprises the following steps: uniformly mixing particulate matters, and loading into a silo, wherein the particle stacking height is 1.2 times greater than the diameter of the silo; the maximum value Dmax of the diameter of the round hole is set as the calibration diameter D0, and the corresponding particle flow Q0 is measured as the calibration flow; adjusting the diameter of the round hole to different set values D, measuring the mass Q of particles flowing out in unit time for each value D, and recording data; performing normalization processing on the Q value obtained by measurement, calculating q = Q / Q0, and constructing a q-D relation graph; software is used for fitting a q-D relation graph, and the average particle size of the particles can be calculated. The method has the advantages of good stability, low cost, simple operation and the like.

Description

Technical Field

[0001] The present invention belongs to the technical field of particle size measurement, and in particular, relates to a method for measuring the average particle size of a particulate matter. Background Art

[0002] In daily production and life, we often encounter various granular materials, such as soybeans, glass beads, sand and gravel, coal powder, etc. They are often numerous and small in size, and measuring their average particle size has become a difficult problem.

[0003] To address this problem, existing technologies such as AI image recognition, ultrasonic and laser diffuse reflection measurement have been applied to average particle size measurement. However, these solutions also have some defects, such as the instruments are too expensive, the threshold for use is too high, and they can only be measured in the laboratory. Summary of the invention

[0004] The purpose of the present invention is to propose a method for measuring the average particle size of particulate matter, which has the advantages of good stability, low cost, and easy operation, as the existing instruments for measuring the average particle size of particulate matter are too expensive and have too high a threshold for use.

[0005] To achieve the above object, the present invention adopts the following technical solution: A method for measuring the average particle size of particulate matter, comprising the following steps:

[0006] Step S1: Select a vertically placed cylindrical flat-bottom silo with a circular hole of adjustable diameter at the bottom, and ensure that the silo diameter is greater than 2.5 times the diameter of the circular hole;

[0007] Step S2: Mix the granular material and load it into the silo, and the granular stacking height is greater than 1.2 times the diameter of the silo;

[0008] Step S3: Set the maximum value D of the circular hole diameter max As the calibration diameter D0, and measure the corresponding particle flow Q0 as the calibration flow;

[0009] Step S4: adjusting the diameter of the circular hole to different set values ​​D, measuring the mass Q of the particles flowing out per unit time for each D value, and recording the data;

[0010] Step S5: normalize the measured Q value, calculate q=Q / Q0, and construct a qD relationship diagram;

[0011] Step S6: Use software to fit the qD relationship diagram to obtain fitting parameters c and k, and calculate the average particle size of the particles based on the k value obtained by fitting.

[0012] Furthermore, the method for measuring the average particle size of the particulate matter satisfies the following equation for the flow rate of spherical particles passing through the circular hole at the bottom of the silo: Q = C0ρg 1 / 2 (D-kd) 5 / 2 ; Among them, Q is the mass of particles flowing out per unit time, ρ is the density of the particle accumulation, g is the acceleration of gravity, D is the diameter of the circular hole, d is the particle size, and C0 and k are dimensionless parameters.

[0013] Furthermore, the method for measuring the average particle size of the particulate matter is as follows for non-spherical particles and mixed particles of different particle sizes:

[0014]

[0015] Among them, Q is the mass of particles flowing out per unit time, ρ is the density of the particle accumulation, g is the acceleration of gravity, D is the diameter of the circular hole, is the equivalent diameter of the ith particle, which is defined as the diameter of a sphere with the same volume as the particle, p i is the total proportion of the i-th particle, obviously is the weighted average particle size of the mixed particles, C0 and k are dimensionless parameters;

[0016] right Normalize it and get The relationship is fitted as follows:

[0017]

[0018] Where c is the fitting parameter, is the normalized particle flow rate, Q0 is the particle flow measurement value corresponding to the calibrated diameter D0.

[0019] Furthermore, the method for measuring the average particle size of the particulate matter is to measure the particle size in the range of 0.5 mm to 0.22 mm. min , where D min is the minimum value of D.

[0020] Through the above-mentioned design scheme, the present invention can bring the following beneficial effects: the present invention proposes a method for measuring the average particle size of particulate matter, which method only requires loading a sufficient amount of mixed particles in the silo, measuring the particle flow corresponding to several groups of bottom circular holes with different diameters, and thus completing the measurement of the average particle size of the particles. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The accompanying drawings herein are used to provide a further understanding of the present invention and constitute a part of the present application. The exemplary embodiments of the present invention and their descriptions are used to understand the present invention and do not constitute improper limitations of the present invention. In the accompanying drawings:

[0022] Figure 1 This is a flow chart of the method for measuring the average particle size of particulate matter proposed by the present invention;

[0023] Figure 2 For experimental results Figure 1 ;

[0024] Figure 3 For experimental results Figure 2 . DETAILED DESCRIPTION

[0025] In order to make the purpose, features and advantages of the present invention more obvious and easy to understand, the technical scheme in the present invention is clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the present invention is not limited to the following embodiments, and the specific implementation method can be determined according to the technical scheme of the present invention and the actual situation. In order to avoid confusing the essence of the present invention, the known methods and processes are not described in detail.

[0026] In view of the defects of existing instruments for measuring the average particle size of particulate matter, such as being too expensive, having a high threshold for use, and being able to only be measured in laboratories, the present invention proposes a method for measuring the average particle size of particulate matter, which has the advantages of good stability, low cost, and easy operation. According to this method, it is only necessary to load a sufficient amount of mixed particles in the silo and measure the particle flow rates corresponding to several groups of circular holes of different diameters opened at the bottom of the silo to complete the measurement of the average particle size of the particles.

[0027] The principle is described in detail below:

[0028] For a vertical cylindrical flat-bottom silo placed vertically with a circular hole at the bottom, according to the Beverloo formula, the flow rate of the spherical particles loaded therein through the circular hole opened at the bottom of the silo satisfies:

[0029] Q=C0ρg 1 / 2 (D-kd) 5 / 2

[0030] Wherein, Q is the mass of particles flowing out per unit time, ρ is the density of the particle accumulation body, g is the acceleration of gravity, D is the diameter of the circular hole, d is the particle size, C0 and k are fitting parameters obtained by fitting software, which are dimensionless parameters. The fitting software used in the present invention is origin, but it is not limited to this, as long as the method steps proposed in the present invention can be executed.

[0031] Due to the Janssen effect, there is a stress saturation phenomenon in the particle accumulation body, that is, when the particle accumulation height is high enough, the pressure at the bottom of the accumulation body is independent of its height. In the present invention, the particle accumulation height is greater than 1.2 times the silo diameter D, and the silo diameter is greater than 2.5 times the circular hole diameter D, which can ensure that the particle flow rate Q remains stable.

[0032] For non-spherical particles and mixed particles of different diameters, there is a generalized Beverloo formula

[0033]

[0034] Among them, Q is the mass of particles flowing out per unit time, ρ is the density of the particle accumulation, g is the acceleration of gravity, D is the diameter of the circular hole, is the equivalent diameter of the ith particle, which is defined as the diameter of a sphere with the same volume as the particle, p i is the total proportion of the i-th particle, obviously is the weighted average particle size of the mixed particles, C0 and k are dimensionless parameters,

[0035] In practice, it is found that the Beverloo formula will have obvious deviations in predicting the particle flow rate Q when D is small. Mankoc et al. proposed a correction for this.

[0036]

[0037] Among them, b is the fitting parameter, and the lower limit of the applicable range of the revised formula can reach The deviation is eliminated. Therefore, the relationship between the mass Q of particles flowing out per unit time and the diameter D of the circular hole can be fitted. In order to avoid the fitting formula from being over-parameterized and unable to converge, the present invention normalizes the original formula to obtain The relationship is fitted as follows:

[0038]

[0039] Where c is the fitting parameter, is the normalized particle flow rate, Q0 is the particle flow measurement value corresponding to a selected circular hole diameter D0, which can also be called the calibration flow. In actual operation, the maximum value of D can be selected, that is, D max , which is least affected by parameter b.

[0040] Through this method, the present invention only needs to load a sufficient amount of mixed particles in the silo, measure the Q corresponding to several groups of different D, obtain the qD data graph after normalization with the calibration flow, and then use the software to fit the values ​​of c and k to calculate The average particle size can be completed measurement.

[0041] Recommended measurement range of particle size: 0.5mm-0.22D min , where D minIt is the minimum value of D. If the particle size is lower than this range, it will be significantly affected by air resistance and intermolecular forces. If it is higher than this range, intermittent flow or even blockage will occur.

[0042] The present invention utilizes the flow rate of particles in a vertical cylindrical flat-bottom silo equipped with a circular hole at the bottom to satisfy the Beverloo formula, and fits the equivalent diameter (average particle size) by measuring the relationship between the mass Q of particles flowing out per unit time and the diameter D of the circular hole. For non-spherical particles and mixed particles of different diameters, there is a generalized Beverloo formula. However, in practice, it is found that the Beverloo formula will have obvious deviations when D is small, so a correction formula is proposed. In the end, it is only necessary to load a sufficient amount of mixed particles in the silo, measure the Q corresponding to several groups of different D, normalize it with the calibrated flow rate to obtain the qD data graph, and then use the software to fit the values ​​of c and k to calculate the average particle size of the particles. Where c is the fitting parameter, The recommended particle size range is 0.5mm-0.22D min , where D min It is the minimum value of D. If it is lower than this range, it will be affected by air resistance, and if it is higher than this range, intermittent flow or even blockage will occur.

[0043] like Figure 1 As shown, the present invention provides a method for measuring the average particle size of particulate matter, comprising:

[0044] Step S1: Select a vertically placed cylindrical flat-bottom silo with a circular hole of adjustable diameter at the bottom, and ensure that the silo diameter is greater than 2.5 times the diameter of the circular hole;

[0045] Step S2: Mix the granular material and load it into the silo, and the granular stacking height is greater than 1.2 times the diameter of the silo;

[0046] Step S3: Set the maximum value D of the circular hole diameter max As the calibration diameter D0, and measure the corresponding particle flow Q0 as the calibration flow;

[0047] Step S4: adjusting the diameter of the circular hole to different set values ​​D, measuring the mass Q of the particles flowing out per unit time for each D value, and recording the data;

[0048] Step S5: normalize the measured Q value, calculate q=Q / Q0, and construct a qD relationship diagram;

[0049] Step S6: Use software to fit the qD relationship diagram to obtain fitting parameters c and k, and calculate the average particle size of the particles based on the k value obtained by fitting.

[0050] from Figure 2 and Figure 3 It can be seen that the particle size fitting value obtained by the method of the present invention is close to the actual measured value of the particle size.

[0051] In summary, the method proposed in the present invention only requires loading a sufficient amount of mixed particles in the silo and measuring the particle flow rates corresponding to several groups of bottom circular holes with different diameters to complete the measurement of the average particle diameter.

Claims

1. A method for measuring the average particle size of particulate matter, characterized in that: The steps include: Step S1: Select a vertically placed cylindrical flat-bottom silo with a circular hole of adjustable diameter at the bottom, and ensure that the silo diameter is greater than 2.5 times the diameter of the circular hole; Step S2: Mix the granular material and load it into the silo, and the granular stacking height is greater than 1.2 times the diameter of the silo; Step S3: Set the maximum value D of the circular hole diameter max As the calibration diameter D0, and measure the corresponding particle flow Q0 as the calibration flow; Step S4: adjusting the diameter of the circular hole to different set values ​​D, measuring the mass Q of the particles flowing out per unit time for each D value, and recording the data; Step S5: normalize the measured Q value, calculate q=Q / Q0, and construct a qD relationship diagram; Step S6: Use software to fit the qD relationship diagram to obtain fitting parameters c and k, and calculate the average particle size of the particles based on the k value obtained by fitting.

2. The method for measuring the average particle size of particulate matter according to claim 1, characterized in that: The flow rate of spherical particles through the circular hole at the bottom of the silo satisfies: Q = C0ρg 1 / 2 (D-kd) 5 / 2 ; Among them, Q is the mass of particles flowing out per unit time, ρ is the density of the particle accumulation, g is the acceleration of gravity, D is the diameter of the circular hole, d is the particle size, and C0 and k are dimensionless parameters.

3. The method for measuring the average particle size of particulate matter according to claim 1, characterized in that: For non-spherical particles and mixed particles of different particle sizes: Among them, Q is the mass of particles flowing out per unit time, ρ is the density of the particle accumulation, g is the acceleration of gravity, D is the diameter of the circular hole, is the equivalent diameter of the ith particle, which is defined as the diameter of a sphere with the same volume as the particle, p i is the total proportion of the i-th particle, obviously is the weighted average particle size of the mixed particles, C0 and k are dimensionless parameters; right Normalize it and get The relationship is fitted as follows: Where c is the fitting parameter, is the normalized particle flow rate, Q0 is the particle flow measurement value corresponding to the calibrated diameter D0.

4. The method for measuring the average particle size of particulate matter according to claim 1, characterized in that: The measured particle size range is 0.5mm-0.22D min , where D min is the minimum value of D.

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