A method for analyzing and calculating particle size distribution and solid content using the optical path difference method in two-phase flow

Abstract

The present invention provides a method for analyzing and calculating particle size grading and solid content in two-phase flow using the optical path difference method. The method comprises: varying the measurement zone width of a laser particle size analyzer to collect extinction values ​​at two different optical path lengths and scattered light intensity signals from each detector; subtracting the scattered light intensity signal from the shorter optical path length from the scattered light intensity signal from the longer optical path length on each detector to obtain a new set of scattered light intensity signals; using the resulting set of scattered light intensity signals for particle size distribution inversion calculation to obtain grading data; subtracting the shorter optical path length from the longer optical path length extinction value to obtain a new extinction value; and calculating the solid content based on the resulting new extinction value and the grading data. In the present invention, neither the scattered light intensity signal used to calculate grading data nor the extinction value signal used to calculate solid content is affected by window lens contamination. A pure scattered light intensity signal can be obtained without measuring background signals from a pure medium. This method enables online, real-time monitoring and long-term operation underwater or in the atmosphere.

Description

Technical Field

[0001] The invention relates to the field of underwater sand content and particle size distribution monitoring, and relates to an optical path difference method particle size distribution and solid content analysis and calculation method in two-phase flow. Background Art

[0002] In hydrological monitoring, the analysis of particle grading and sediment content in rivers, oceans, and ports is an important task, which is of great significance for preventing soil erosion, dam sand discharge and siltation, and river and waterway regulation and dredging.

[0003] Sediment in rivers flows as a liquid-solid two-phase flow. Current underwater online laser particle size analyzers for monitoring sediment concentration and particle size distribution suffer from two drawbacks in both the measurement process and application, impacting their effectiveness. First, because river water is not a pure medium, the instrument's background signal cannot be measured in real time. Instead, a fixed background signal is used as an offset, which impacts the acquisition of the actual scattering signal from the sediment. Second, prolonged immersion of the test window lens in water can contaminate it, leading to errors in the measured extinction value and scattering signal, affecting the accuracy of the calculated particle size distribution and solids content.

[0004] Airborne particulate matter also belongs to gas-solid two-phase flow, and its quality monitoring suffers from the same drawbacks as liquid-solid two-phase flow monitoring. Therefore, a more accurate and convenient method is urgently needed to improve the monitoring accuracy of particle size distribution and solid content in two-phase flow. Summary of the Invention

[0005] The purpose of the present invention is to provide a method for analyzing and calculating particle size distribution and solid content using the optical path difference method in two-phase flow, so as to solve the error problem in the calculation of particle size distribution and solid content caused by the use of a fixed background signal and contamination of the test window lens.

[0006] The present invention provides a method for analyzing and calculating particle size distribution and solid content using an optical path difference method in a two-phase flow, comprising the following steps:

[0007] Step 1: Change the measurement area width of the laser particle size analyzer and collect the extinction values ​​at two different optical path lengths and the scattered light intensity signals on each detector during monitoring;

[0008] Step 2: Subtract the scattered light intensity signal with a short optical path from the scattered light intensity signal with a long optical path on each detector to obtain a new set of scattered light intensity signals with the background subtracted;

[0009] Step 3: Use the obtained set of new scattered light intensity signals for particle size distribution inversion calculation to obtain the gradation data of solid particles;

[0010] Step 4: Subtract the logarithm of the extinction value of the short optical path from the logarithm of the extinction value of the long optical path to obtain the new extinction value related data;

[0011] Step 5: Calculate the solid content based on the new extinction value and gradation data.

[0012] In the optical path difference method for particle size distribution and solid content analysis and calculation in two-phase flow of the present invention, the calculation process of the new scattered light intensity signal on the detector in step 2 is as follows:

[0013] S=A1-A2=(S1+B)-(S2+B)=S1-S2

[0014] Among them, A1 is the scattered light intensity signal with background on the long optical path on the detector, A2 is the scattered light intensity signal with background on the short optical path on the detector, B is the background signal, S1 is the scattered light intensity signal after subtracting the background from the long optical path, S2 is the scattered light intensity signal after subtracting the background from the short optical path, and S is the scattered light intensity signal of the optical path difference, that is, the new scattered light intensity signal; the new scattered light intensity signal on each detector constitutes a new set of scattered light intensity signals.

[0015] In the optical path difference method for particle size distribution and solid content analysis and calculation in two-phase flow of the present invention, the new extinction value is calculated in step 4 as follows:

[0016]

[0017]

[0018]

[0019] Among them, I1 is the long light path transmission signal, I2 is the short light path transmission intensity signal, I0 is the initial light intensity signal, D is the surface area average diameter of the solid particles calculated by inversion of scattered light intensity in step 3, K ext is the extinction coefficient, L1 is the long optical path length, L2 is the short optical path length, C v is the volume concentration of solid particles.

[0020] In the optical path difference method for particle size distribution and solid content analysis and calculation in two-phase flow of the present invention, the solid content H is calculated according to the following formula in step 5:

[0021]

[0022] Here, ρ is the density of the solid particles.

[0023] A method for analyzing and calculating particle size distribution and solid content using the optical path difference method in two-phase flow has at least the following beneficial effects:

[0024] The scattering signals with long and short optical paths are both scattering signals with background. When taking the difference between them, it is equivalent to subtracting the background from the two scattering signals with background. The remaining signal is the difference in scattering signal intensity, which is also the scattering signal of the particle group in the two-phase flow system, and it completely contains the particle size distribution information. If the window lens is contaminated, the scattering signal generated by the contamination is in the background and can be completely subtracted. The resulting scattering signal is the true scattering signal of the sediment in the two-phase flow. The extinction value is also measured by subtracting the extinction value under the short optical path from the extinction value under the long optical path. In this way, the part of the extinction value that is not caused by sediment particles due to window lens contamination will be subtracted, and the extinction value will not be affected by window lens contamination.

[0025] The present invention is not affected by window lens contamination whether measuring the scattered light intensity signal of particle grading or the extinction value signal of solid content, can realize long-term operation of underwater or atmospheric online monitoring, and can obtain a simple scattered light intensity signal without measuring the background signal under pure medium. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is a flow chart of a method for analyzing and calculating particle size distribution and solid content using an optical path difference method in a two-phase flow according to the present invention;

[0027] Figure 2 The particle size distribution diagram was obtained based on Mie scattering theory. DETAILED DESCRIPTION

[0028] like Figure 1 As shown, a method for analyzing and calculating particle size distribution and solid content using an optical path difference method in a two-phase flow according to the present invention comprises the following steps:

[0029] Step 1: Change the measurement area width of the laser particle size analyzer and collect the extinction values ​​at two different optical path lengths and the scattered light intensity signals on each detector during monitoring;

[0030] In this embodiment, as shown in Table 1, the scattered light intensity distributions collected at two different optical path lengths are as follows:

[0031]

[0032]

[0033]

[0034] Step 2: Subtract the scattered light intensity signal of the detector with a short optical path from the scattered light intensity signal of the detector with a long optical path to obtain a new set of scattered light intensity signals with the background subtracted, i.e., the scattered light signal difference of each detector in the third column of Table 1;

[0035] In specific implementation, the calculation process of the new scattered light intensity signal in step 2 is as follows:

[0036] S=A1-A2=(S1+B)-(S2+B)=S1-S2

[0037] Among them, A1 is the scattered light intensity signal with background in the long optical path, A2 is the scattered light intensity signal with background in the short optical path, B is the background signal, S1 is the scattered light intensity signal after subtracting the background from the long optical path, S2 is the scattered light intensity signal after subtracting the background from the short optical path, and S is the scattered light intensity signal of the optical path difference, that is, the new scattered light intensity signal.

[0038] Step 3: Use the obtained set of new scattered light intensity signals for particle size distribution inversion calculation to obtain the gradation data of solid particles.

[0039] In specific implementation, a new set of scattered light intensity signals is used to obtain the particle size distribution according to Mie scattering theory. Figure 2 As shown, typical characteristic values ​​are calculated, including volume average diameter, surface area average diameter, length average diameter, number average diameter, peak particle size, specific surface area, and span grade matching data. See Table 2 below for details.

[0040] D00 0.205μm Volume mean diameter D[4,3] 21.15μm D10 2.208μm Surface area average diameter D[3,2] 5.013μm D16 3.817μm Length average diameter D[2,1] 0.936μm D25 6.599μm Number mean diameter D[1,0] 0.500μm D50 16.67μm Peak particle size 24.39μm D75 30.37μm Specific surface area <![CDATA[443.2m 2 / kg]]> D84 38.37μm span 2.640 D90 46.23μm D100 151.1μm

[0041] Step 4: Subtract the logarithm of the extinction value of the short optical path from the logarithm of the extinction value of the long optical path to obtain a new extinction value. The new extinction value is calculated as follows:

[0042]

[0043]

[0044]

[0045] Among them, I1 is the long light path transmission signal, I2 is the short light path transmission intensity signal, I0 is the initial light intensity signal, D is the surface area average diameter of the solid particles calculated by inversion of scattered light intensity in step 3, K ext is the extinction coefficient, L1 is the long optical path length, L2 is the short optical path length, C v is the volume concentration of solid particles.

[0046] Step 5: Calculate the solid content based on the new extinction value and gradation data.

[0047] During specific implementation, the solid content H is calculated according to the following formula:

[0048]

[0049] Here, ρ is the density of the solid particles.

[0050] The value of D in the formula is 5.013 μm in the typical value of particle size distribution data; K ext is the extinction coefficient corresponding to D[3,2]5.013μm, which is 2.0015 according to Mie scattering calculation; L1=3mm, L2=2mm, Parameters are put into the formula to calculate C v The value is: 0.000322. In this embodiment, the test sample is sediment, and the density is taken as a constant of 2.4. Substituting this into the formula, the solid content is 0.000775. The unit of solid content is usually g / L. After conversion, the solid content of this test is 0.775 g / L.

[0051] The present invention discloses a method for analyzing and calculating particle size grading and solid content using the optical path difference method in two-phase flow, which belongs to the field of underwater sand content and particle size grading measurement. The optical path difference sand content and particle size grading monitoring method collects the extinction values ​​under two optical path lengths and the scattered light intensity signal on the detector, and subtracts the signal with the short optical path from the signal with the long optical path (scattered light intensity signal and extinction value) to obtain a new set of scattered light intensity signals and extinction values. The scattered light intensity signal is the scattered signal of the particle group in the two-phase flow system, which contains particle size distribution information. The sand content can be obtained by calculation based on the scattered light intensity signal and the extinction value. Whether measuring the scattered light intensity signal of the particle grading or the extinction value signal of the solid content, the present invention is not affected by the contamination of the window lens, and can achieve long-term operation of underwater or atmospheric online monitoring, and can obtain a simple scattered light intensity signal without measuring the background signal in the pure medium state.

[0052] The above description is only a preferred embodiment of the present invention and is not intended to limit the concept of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for analyzing and calculating particle size distribution and solid content using the optical path difference method in two-phase flow, characterized in that: The steps include: Step 1: Change the measurement area width of the laser particle size analyzer and collect the extinction values ​​at two different optical path lengths and the scattered light intensity signals on each detector during monitoring; Step 2: Subtract the scattered light intensity signal with a short optical path from the scattered light intensity signal with a long optical path on each detector to obtain a new set of scattered light intensity signals with the background subtracted; Step 3: Use the obtained set of new scattered light intensity signals for particle size distribution inversion calculation to obtain the gradation data of solid particles; Step 4: Subtract the logarithm of the extinction value of the short optical path from the logarithm of the extinction value of the long optical path to obtain the new extinction value related data; The new extinction value calculated in step 4 is specifically: Among them, I1 is the long light path transmission signal, I2 is the short light path transmission intensity signal, I0 is the initial light intensity signal, D is the surface area average diameter of the solid particles calculated by inversion of scattered light intensity in step 3, K ext is the extinction coefficient, L1 is the long optical path length, L2 is the short optical path length, C v is the volume concentration of solid particles; Step 5: Calculate the solid content based on the new extinction value and gradation data; In step 5, the solid content H is calculated according to the following formula: Here, ρ is the density of the solid particles.

2. The method for analyzing and calculating particle size distribution and solid content in two-phase flow using the optical path difference method according to claim 1, wherein: The calculation process of the new scattered light intensity signal on the detector in step 2 is as follows: S=A1-A2=(S1+B)-(S2+B)=S1-S2 Among them, A1 is the scattered light intensity signal with background on the long optical path on the detector, A2 is the scattered light intensity signal with background on the short optical path on the detector, B is the background signal, S1 is the scattered light intensity signal after subtracting the background from the long optical path, S2 is the scattered light intensity signal after subtracting the background from the short optical path, and S is the scattered light intensity signal of the optical path difference, that is, the new scattered light intensity signal; the new scattered light intensity signal on each detector constitutes a new set of scattered light intensity signals.

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