Method of Utilizing Optical Path Difference in Two-phase Flow for Analytical Calculation of Particle Size Gradation and Solid Content

Description

FIELD OF INVENTION

The present invention relates to the field of underwater sand content and particle size grading monitoring, and is related to a method of utilizing optical path difference in two-phase flow for analytical calculation of particle size gradation and solid content.

DESCRIPTION OF RELATED ARTS

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

Sediment in rivers belongs to two-phase flow of liquid-solid. From the measurement process and application, there are two aspects in the current underwater online laser particle size analyzer, the sand content and particle size gradation monitoring instrument where there are drawbacks that affect the actual application effect. First, because river water is not a pure medium environment, the background signal of the instrument cannot be measured in real time but a fixed background signal is used as a penalty, which will have a certain impact on collecting the actual scattering signal of sediment. Second, contamination will occur if the test window lens is immersed in water for a long time, and there will be certain errors in the measured extinction value and scattering signal, which will affect the accuracy of the calculation results of particle size gradation and solid content.

Particulate matter in the air also belongs to two-phase flow of gas-solid, and its quality monitoring also has the same drawbacks as two-phase flow of liquid-solid monitoring. Therefore, there is an urgent need for a method with higher accuracy and more convenient to use to improve the monitoring accuracy of particle size gradation and solid content in two-phase flow.

SUMMARY OF THE PRESENT INVENTION

An object of the present invention is to provide a method utilizing optical path difference in two-phase flow for analytical calculation of particle size gradation and solid content to solve the problem of errors in the calculation of particle size gradation and solid content caused by the use of fixed background signals and contamination of the test window lens (of the laser particle size analyzer).

According to the present invention, a method utilizing optical path difference in two-phase flow for analytical calculation of particle size gradation and solid content comprises the following steps:

- Step 1: Changing a width of measurement area of a laser particle size analyzer, and collecting extinction values at two different optical path lengths and a scattered light intensity signal on each detector during monitoring;
- Step 2: the scattered light intensity signal with a short optical path is subtracted from the scattered light intensity signal with a long optical path on each detector to obtain a set of new scattered light intensity signals with background subtracted;
- Step 3: processing particle size distribution inversion calculations for the set of scattered light intensity signals with background subtracted to obtain gradation data of solid particles;
- Step 4: Processing subtraction of 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 new extinction value related data;
- Step 5: Processing calculation of the solid content based on the new extinction value related data and the gradation data obtained from the above steps.

According to the method utilizing optical path difference in two-phase flow for analytical calculation of particle size gradation and solid content of the present invention, in step 2, the new scattered light intensity signals on the detector is calculated by the followings:

$S = A_{1} - A_{2} = (S_{1} + B) - (S_{2} + B) = S_{1} - S_{2}$

- wherein A₁refers to a scattered light intensity signal with long optical path and background on the detector, A₂refers to a scattered light intensity signal with short optical path and background on the detector, B refers to the background signal, S₁refers to a scattered light intensity signal with long optical path after the background is subtracted, S₂refers to a scattered light intensity signal with short optical path after the background is subtracted, S refers to a scattered light intensity signal difference for scattered light intensity signal with different optical paths, 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.

According to the method utilizing optical path difference in two-phase flow for analytical calculation of particle size gradation and solid content of the present invention, in step 4, the specific calculation of the new extinction value is:

$\ln (\frac{I_{1}}{I_{0}}) = - \frac{3 C_{v} L_{1} K_{ext}}{2 D}$

$\ln (\frac{I_{2}}{I_{0}}) = - \frac{3 C_{v} L_{2} K_{ext}}{2 D}$

$\ln (\frac{I_{1}}{I_{0}}) - \ln (\frac{I_{2}}{I_{0}}) = - \frac{3 C_{v} L_{1} K_{ext}}{2 D} + \frac{3 C_{v} L_{2} K_{ext}}{2 D} = - \frac{3 C_{v} K_{ext}}{2 D} (L_{1} - L_{2})$

Wherein I₁refers to transmitted signal for long optical path, I₂refers to transmitted signal for short optical path, I₀refers to the initial light intensity signal, D refers to the surface area mean diameter of the solid particles calculated by the scattered light intensity inversion in step 3, and Kext refers to the extinction coefficient, L₁refers to a length of the long optical path, L₂refers to a length of the short optical path, Cv refers to a volume concentration of solid particles.

According to the method utilizing optical path difference in two-phase flow for analytical calculation of particle size gradation and solid content of the present invention, in step 5, the solid content H is calculated according to the following formula:

$H = C_{v} \times ρ = - \frac{[\ln (\frac{I_{1}}{I_{0}}) - \ln (\frac{I_{2}}{I_{0}})] 2 D}{3 K_{ext} (L_{1} - L_{2})} \times ρ$

- Wherein ρ refers to a density of solid particle.

The method utilizing optical path difference in two-phase flow for analytical calculation of particle size gradation and solid content at least has the following advantageous effect:

The scattered signals with long optical path and short optical path are both scattered signals with background. When they are compared, it is equivalent to subtracting the background from the two scattered signals with background. The remaining signal is the difference in intensity of the scattered signal, which is also the scattered signal of the group of particles in the two-phase flow system and completely contains the particle size distribution information. If the window lens (of the laser particle size analyzer) is contaminated, then the scattered signal generated by the contaminant is in the background and can be completely subtracted. The resulting scattered signal is the true scattered 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, due to the contamination of the window lens (of the laser particle size analyzer), the part of the extinction value that is not caused by sediment particles will be subtracted, and the extinction value will not be affected by the contamination of window lenses.

The present invention is not affected by window lens contamination (of the laser particle size analyzer), whether it is the measured the scattered light intensity signal of particle gradation or the extinction value signal of measured solid content, and can obtain simple and pure scattered light intensity signal without the step of measuring the background signal in pure medium, thereby realizing a long-term operation of underwater or atmospheric online monitoring (through the laser particle size analyzer).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flowchart of method utilizing optical path difference in two-phase flow for analytical calculation of particle size gradation and solid content according to the present invention.

FIG. 2 is a particle size distribution diagram obtained based on Mie scattering theory.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to FIG. 1, a method utilizing optical path difference in two-phase flow for analytical calculation of particle size gradation and solid content according to the present invention comprises the following steps:

Step 1: The width of measurement area of a laser particle size analyzer is changed. During monitoring, the extinction values at two different optical path lengths and a scattered light intensity signal on each detector are collected.

According to this embodiment, as shown in Table 1, the collected scattered light intensity distributions at two different optical path lengths are as follows

Difference

Calculation

Length of Measurement
Length of Measurement
Extinction Value

Area: 2 mm Optical Path
Area: 3 mm Optical Path
Difference=−

Measured Extinction
Measured Extinction
Difference

Value ln(I₂/I0) = −0.0943
Value ln(I₁/I0) = −0.287
between the

The Scattered Light
The Scattered Light
Scattered Signals

Intensity of each
Intensity of each
of each

Detector is as follows:
Detector is as follows:
Detector is as

5167.23
3588.963
−1578.267

3956.379
3260.721
−695.658

1534.273
1364.772
−169.501

1001.801
909.718
−92.083

548.776
513.048
−35.728

490.915
450.363
−40.552

354.166
331.968
−22.198

333.446
309.917
−23.529

280.98
266.197
−14.783

270.817
257.28
−13.537

241.91
235.644
−6.266

248.5
245.216
−3.284

237.408
240.078
2.67

260.722
268.173
7.451

259.116
274.643
15.527

272.375
295.618
23.243

292.769
325.546
32.777

328.452
373.51
45.058

383.206
443.302
60.096

427.557
505.911
78.354

523.84
628.434
104.594

601.167
730.885
129.718

689.158
848.572
159.414

802.222
999.399
197.177

944.272
1186.075
241.803

1097.906
1391.366
293.46

1296.674
1645.303
348.629

1514.234
1932.2
417.966

1762.493
2267.687
505.194

2043.676
2647.561
603.885

2359.548
3069.963
710.415

2654.656
3463.351
808.695

2941.415
3851.256
909.841

3631.194
4604.883
973.689

3483.78
4572.389
1088.609

3896.296
5083.865
1187.569

4161.654
5492.191
1330.537

4535.62
5984.344
1448.724

4965.422
6563.453
1598.031

5308.882
7008.687
1699.805

5715.995
7537.142
1821.147

6192.446
8062.983
1870.537

6415.429
8468.343
2052.914

6758.973
8871.968
2112.995

7041.008
9275.152
2234.144

7321.049
9634.642
2313.593

7599.674
10002.993
2403.319

7853.106
10327.616
2474.51

8054.424
10594.912
2540.488

8361.472
11011.056
2649.584

8699.398
11440.092
2740.694

9034.359
11891.172
2856.813

9366.257
12313.862
2947.605

9786.41
12867.667
3081.257

10131.857
13363.827
3231.97

10481.914
13843.943
3362.029

10888.937
14362.57
3473.633

11217.049
14871.9
3654.851

11489.425
15283.211
3793.786

11750.904
15701.206
3950.302

12036.368
16150.397
4114.029

12305.886
16663.214
4357.328

12468.702
16999.625
4530.923

12724.211
17504.46
4780.249

12783.646
17725.052
4941.406

12938.338
18047.344
5109.006

13229.308
18599.631
5370.323

13396.673
18970.73
5574.057

13583.191
19354.514
5771.323

13830.258
19772.346
5942.088

14019.414
20226.03
6206.616

14237.112
20583.46
6346.348

12258.941
17791.09
5532.149

11868.634
17245.083
5376.449

11496.996
16693.347
5196.351

10812.336
15682.237
4869.901

10083.973
14549.012
4465.039

9318.834
13421.222
4102.388

8500.133
12219.003
3718.87

7884.584
11274.975
3390.391

7032.316
10043.987
3011.671

6343.078
9034.326
2691.248

5460.253
7724.258
2264.005

4737.527
6678.556
1941.029

4119.438
5824.263
1704.825

3747.709
5303.985
1556.276

2893.277
3339.839
446.562

1503.234
1983.828
480.594

1137.452
1524.015
386.563

816.863
1115.841
298.978

534.471
737.838
203.367

283.284
385.478
102.194

Step 2: On each detector (of the laser particle size analyzer), subtracts the scattered light intensity signal with a short optical path from the scattered light intensity signals with a long optical path to obtain a set of new scattered light intensity signals with background being subtracted.

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

$S = A_{1} - A_{2} = (S_{1} + B) - (S_{2} + B) = S_{1} - S_{2}$

- wherein A₁refers to a scattered light intensity signal with long optical path and background, A₂refers to a scattered light intensity signal with short optical path and background, B refers to the background signal, S₁refers to a scattered light intensity signal with long optical path after the background is subtracted, S₂refers to a scattered light intensity signal with short optical path after the background is subtracted, S refers to a scattered light intensity signal difference for scattered light intensity signals with different optical paths, that is, the new scattered light intensity signal.

Step 3: For the new set of scattered light intensity signals, process particle size distribution inversion calculation to obtain gradation data of solid particles.

In specific implementation, through the new set of scattered light intensity signals, the particle size distribution is obtained according to Mie scattering theory, which is shown in FIG. 2 of the drawings. The typical characteristic values are calculated, which includes grading data such as volume mean diameter, surface area mean diameter, length mean diameter, number mean diameter, peak particle size diameter, specific surface area, span, and etc. The details are shown in Table 2 as follows:

D00
0.205
μm
volume mean
21.15
μm

diameter D[4,3]

D10
2.208
μm
surface area mean
5.013
μm

diameter D[3,2]

D16
3.817
μm
length mean
0.936
μm

diameter D[2,1]

D25
6.599
μm
number mean
0.500
μm

diameter D[1,0]

D50
16.67
μm
peak particle
24.39
μm

size diameter

D75
30.37
μm
specific surface
443.2
m²/kg

area

D84
38.37
μm
Span
2.640

D90
46.23
μm

D100
151.1
μm

Step 4: Process subtraction of 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 new extinction value. In particular, the calculation of the new extinction value is as follows:

Step 5: Process calculation of the solid content based on the new extinction value and the gradation data obtained from the above steps.

In specific implementation, the solid content H is calculated according to the following formula:

$H = C_{v} \times ρ = - \frac{[\ln (\frac{I_{1}}{I_{0}}) - \ln (\frac{I_{2}}{I_{0}})] 2 D}{3 K_{ext} (L_{1} - L_{2})} \times ρ$

Wherein ρ refers to the density of solid particles.

In the formula, the value of D is D[3,2] in the typical value of particle size distribution data, which is 5.013 μm. K_extis an extinction coefficient corresponding to D[3,2] 5.013 μm, based on Mie scattering calculation, it is 2.0015 . . . L₁=3 mm, L₂=2 mm,

$\frac{I_{1}}{I_{0}} = 0.75, \frac{I_{2}}{I_{0}} = 0.91 .$

The parameters are brought into the formula to calculate the Cv value, which is 0.000322. According to this embodiment, the test sample is sediment, and the density is taken as a constant of 2.4. When put into the formula, the solid content is 0.000775, usually the unit of solid content is g/L, and the solid content of this test is 0.775 g/L after unit conversion.

The present invention is a method for analyzing and calculating particle size gradation and solid content using optical path difference method in two-phase flow, which belongs to the field of underwater sand content measurement and particle size gradation.

This sand content and particle size gradation monitoring method with optical path difference collects the extinction values at two optical path lengths and the scattered light intensity signal on the detector, and subtracts the short optical path signal from the long optical path signal to obtain a new set of scattered light intensity signals and extinction values. The scattered light intensity signal is the scattering signal of the particle group in the two-phase flow system, including particle size distribution information. The sediment content can be calculated based on the scattered light intensity signal and extinction value. Whether it is the measured scattered light intensity signal of particle gradation or the extinction value signal of measured solid content, they are not affected by window lens contamination, and can realize long-term operation of underwater or atmospheric online monitoring. There is no need to measure the background signal in the pure medium state, and a pure scattered light intensity signal can be obtained.

The above description includes the preferred embodiments of the present invention only and is not intended to be limiting the concept of the present invention. Within the spirit and principle of the present invention, any modifications, equivalent substitutions, improvements, etc., shall be included in the protection scope of the present invention.

Claims

1. A method utilizing optical path difference in two-phase flow for analytical calculation of particle size gradation and solid content, characterized in that, said method comprises the following steps: step 1: changing a width of measurement area of a laser particle size analyzer, and during monitoring, collecting extinction values at two different optical path lengths and a scattered light intensity signal on each detector at two different optical path lengths;step 2: utilizing the scattered light intensity signal with a long optical path to subtract the scattered light intensity signal with a short optical path on each detector to obtain a set of new scattered light intensity signals with background subtracted;step 3: processing particle size distribution inversion calculations for the set of scattered light intensity signals with background subtracted to obtain gradation data of solid particles;step 4: processing subtraction of 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 new extinction value related data;step 5: processing calculation of the solid content based on the new extinction value related data and the gradation data obtained.
2. The method utilizing optical path difference in two-phase flow for analytical calculation of particle size gradation and solid content according to claim 1, characterized in that: in step 2, the new scattered light intensity signals on the detector is calculated by the followings:
3. The method utilizing optical path difference in two-phase flow for analytical calculation of particle size gradation and solid content according to claim 1, characterized in that: in step 4, a specific calculation of the new extinction value is: ▪▪▪wherein I1 refers to transmitted signal for long optical path, I2 refers to transmitted signal for short optical path, I0 refers to the initial light intensity signal, D refers to the surface area mean diameter of the solid particles calculated by the scattered light intensity inversion in step 3, and Kext refers to the extinction coefficient, L1 refers to a length of the long optical path, L2 refers to a length of the short optical path, Cv refers to a volume concentration of solid particles.
4. The method utilizing optical path difference in two-phase flow for analytical calculation of particle size gradation and solid content according to claim 3, characterized in that: in step 5, the solid content H is calculated according to the following formula:

Priority Claims (1)

Number	Date	Country	Kind
202310226531.1	Mar 2023	CN	national

PCT Information

Filing Document	Filing Date	Country	Kind
PCT/CN2023/083037	3/22/2023	WO

Method of Utilizing Optical Path Difference in Two-phase Flow for Analytical Calculation of Particle Size Gradation and Solid Content

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