A particle multi-parameter in-situ measurement method and device based on double-pulse digital holography

Abstract

The application discloses a kind of particle multi-parameter in-situ measurement method based on double-pulse digital holography: two laser beams emitted by double-pulse light source are combined, filtered, expanded and collimated to form parallel light;Parallel light irradiates moving particle flow, and single-camera records single-frame double-pulse particle hologram;The hologram is reconstructed, and three-dimensional particle field information is obtained by inversion, to obtain the particle size and concentration information of particle;The three-dimensional position of particle is obtained, so as to calculate the actual position of particle, and the three-dimensional velocity of particle is obtained by using particle matching algorithm.The application also discloses a kind of particle multi-parameter in-situ measurement device based on double-pulse digital holography: double-pulse light source system, laser modulation system, measurement probe system, interference fringe recording system and particle multi-parameter processing system.The method and device realize multi-parameter, in-situ measurement of particle, are simple to operate, and have high test precision;Single-frame double-pulse mode greatly enriches the information of test speed, and has wide adaptability.

Description

Technical Field

[0001] This invention relates to the field of online measurement of gas-solid two-phase flow, and specifically to a method and apparatus for in-situ measurement of multiple parameters of particles based on dual-pulse digital holography. Background Technology

[0002] Gas-solid two-phase flow (GSB) is a two-phase flow formed by the mixing of gas and solid particles. Its research and applications are widespread, encompassing energy conversion, chemical processes, environmental pollution control, and materials preparation, where it plays a crucial role. Measuring the particle parameters of GSB is one of the core issues in this field. Accurate measurement helps in understanding the behavioral characteristics of GSB and predicting and controlling its flow properties. GSB particle parameter measurement has broad application value in many fields, including industrial production and environmental protection, and is of great significance for improving production efficiency, enhancing environmental quality, and promoting scientific and technological progress.

[0003] In pneumatic particle transport, parameters such as particle size, morphology, concentration, and velocity play a crucial role in addressing issues such as particle classification and wear, flow characteristics, blockage, and accumulation. Existing particle measurement technologies include ultrasonic methods, acoustic emission techniques, electrostatic methods, and imaging methods, enabling simultaneous measurement of single or multiple parameters. For example, ultrasonic methods can simultaneously measure particle size and concentration, acoustic emission techniques combined with electrostatic sensors can simultaneously measure particle size and velocity, and imaging methods can simultaneously measure particle size and morphology. However, these methods have some limitations. For instance, the inversion models of ultrasonic and acoustic emission technologies have limited accuracy and require complex calibration processes. Electrostatic methods are limited by particle morphology and color, making them unsuitable for practical production environments. Simultaneous measurement of multiple parameters such as particle size, morphology, concentration, and velocity remains a challenging problem in the field of multiphase flow testing.

[0004] Digital holography is a high-precision three-dimensional measurement technology that uses digital recording and reconstruction techniques to conveniently record and save holograms. Digital holography can measure each particle in a particle field, including its motion, geometry, and position information. While sampling-based holographic particle size analyzers can achieve accurate particle size measurement, the accuracy of particle concentration measurement still needs improvement. One major reason is that the sampling and dilution process can amplify errors; therefore, avoiding the sampling process can ensure the accuracy of concentration measurement.

[0005] Conventional methods for measuring particle velocity in pipelines employ correlation velocimetry, which derives the overall velocity based on the time correlation of upstream and downstream signals. Digital particle holography, however, can combine PTV or PIV technologies to achieve three-dimensional velocity field measurement, providing richer velocity information beyond simply measuring the overall velocity. Depending on the light source characteristics and the number of frames acquired, recording modes can be categorized into four types: single-frame continuous light, single-frame multi-pulse, multi-frame continuous light, and multi-frame multi-pulse. For particle velocity measurement in industrial pipelines, multi-frame optical path systems are difficult to deploy and prohibitively expensive; therefore, single-frame multi-pulse is more suitable and can be achieved using a standard industrial camera and a multi-pulse laser.

[0006] For example, the specification of Chinese Patent Publication No. CN106323825A discloses a pipeline pulverized coal particle size measurement device and method using digital holographic technology. This method employs sampling to achieve online measurement of pulverized coal particle size and concentration within the pipeline. However, since the pulverized coal concentration and particle size distribution data are calculated based on the dilution ratio of the measured sample, its accuracy is relatively poor. Similarly, the specification of Patent Publication No. CN106290078A discloses a method and device for simultaneous measurement of multiple parameters of gas-solid two-phase flow particle clusters. This method utilizes multiple laser light sources and an equal number of photodetectors to obtain multiple parameters, including the velocity, height, and volume concentration of gas-solid two-phase flow particle clusters. However, this system has a complex structure and high measurement costs.

[0007] Therefore, it is essential to develop a method and apparatus that is simple to use, easy to operate, and capable of performing multi-parameter, in-situ measurements of particles in gas-solid two-phase flow. Summary of the Invention

[0008] The purpose of this invention is to provide a method and device for in-situ measurement of multiple parameters of particles based on dual-pulse digital holography, which realizes multi-parameter in-situ measurement of particles, and is simple to operate and has high testing accuracy.

[0009] To solve the above-mentioned technical problems, the specific technical solution adopted by the present invention is as follows:

[0010] A method for in-situ measurement of multiple parameters of particles based on dual-pulse digital holography, the method comprising the following steps:

[0011] (1) The two laser beams emitted by the dual-pulse laser are combined to form a single beam. The single beam passes through a spatial filter and a collimating lens in sequence to form parallel light that illuminates the moving particles in the measurement area.

[0012] (2) Two laser beams in a single beam are irradiated onto the moving particle in succession. Within one frame, through two exposures, a single camera records the interference fringes to form a single-frame double-pulse particle hologram. Among them, the laser beam is scattered by the particle to form the object beam, and the laser beam that has not passed through the particle is used as the reference beam. The object beam and the reference beam interfere to form interference fringes.

[0013] (3) Reconstruct the single-frame double-pulse particle hologram to retrieve the three-dimensional particle field information within the measurement area and obtain the particle size and concentration information; and obtain the three-dimensional position of the particle to calculate the actual position of the particle. Based on the different gray values ​​of the particle image caused by the different energies of the two pulse lasers, the particle matching algorithm is used to further calculate the three-dimensional velocity of the particle.

[0014] The dual-pulse laser in step (1) is composed of two pulse lasers, and the time interval between the two pulses is adjustable. The pulse interval can be adjusted according to the particle velocity and particle size range so that the particle movement distance between the two pulses is greater than the particle size, thereby avoiding particle overlap and affecting the particle recognition effect.

[0015] In step (3), the reconstruction process includes: first, preprocessing the hologram to remove noise; then performing holographic reconstruction, which can be done using a wavelet reconstruction algorithm; obtaining the binary image of the particle through particle identification and particle localization; and finally obtaining particle size and concentration information through computer image processing technology, and calculating the three-dimensional velocity of the particle using a particle matching algorithm.

[0016] The particle matching algorithm utilizes the difference in grayscale values ​​of corresponding particle images caused by the different intensities of dual-pulse lasers for analysis and matching. By pre-calibrating and setting the energy magnitude and emission order of the two pulses, the three-dimensional velocity of the particles can be calculated after matching.

[0017] The present invention also provides an in-situ particle multi-parameter measurement device based on dual-pulse digital holography, the in-situ measurement device comprising:

[0018] The dual-pulse light source system emits two laser beams, which are combined into a single beam and then transmitted to the laser modulation system.

[0019] In the laser modulation system, a single beam is converted into a clean Gaussian beam by a spatial filter, then collimated into parallel light by a collimating lens, and finally illuminated to the measurement probe system by a light guide tube.

[0020] The measurement probe system includes a measurement probe inserted into a pipe. The particle to be measured passes through the measurement area inside the measurement probe by its own velocity, and parallel light is irradiated onto the moving particle in the measurement area.

[0021] In the interference fringe recording system, two laser beams in a single beam are sequentially irradiated onto a moving particle. Within one frame, through two exposures, a single camera records the interference fringes to form a single-frame double-pulse particle hologram. The laser beam that passes through the particle and is scattered becomes the object beam, while the laser beam that does not pass through the particle serves as the reference beam. The object beam and the reference beam interfere with each other to form interference fringes.

[0022] The particle multi-parameter processing system reconstructs a single-frame dual-pulse particle hologram, retrieves the three-dimensional particle field information within the measurement area, and obtains the particle size and concentration information. It also obtains the three-dimensional position of the particle, thereby calculating the actual position of the particle. Based on the difference in grayscale value of the particle image caused by the different energies of the two pulsed lasers, the particle matching algorithm is used to further calculate the three-dimensional velocity of the particle.

[0023] During measurement, the measuring probe of the device is first inserted into the pipe. The particle passes through the measuring area of ​​the probe by its own velocity, and the device performs in-situ measurement on it. The laser beams emitted by the dual-pulse light source system are combined and first have stray light removed by the laser modulation system to become a clean Gaussian parallel beam. The parallel beam passes through the light guide tube and illuminates the moving particle in the measuring probe, and finally reaches the interference fringe recording system. The system records the particle hologram and transmits it to the particle multi-parameter processing system. After processing, the three-dimensional particle field information in the measurement area can be retrieved, realizing multi-parameter, in-situ measurement of the particle.

[0024] The dual-pulse light source system uses a dual-pulse laser, which is composed of two pulse lasers combined. After beam combining, the two laser beams form a single beam.

[0025] The laser modulation system includes an objective lens, a pinhole, and a lens; the objective lens and pinhole together form a spatial filter. Simultaneously, a mirror can be used to adjust the optical path structure.

[0026] The measurement probe system includes a light guide tube, a measurement probe, and optical windows located on both sides of the measurement probe.

[0027] The measuring probe has a measuring area in the middle, which can be adjusted according to the actual situation. The particles being measured flow through the measuring area of ​​the probe by their own speed.

[0028] The measuring probe is also equipped with protective gas inlets and cooling gas inlets on both sides. Cooling gas is introduced into one side of the camera for camera cooling, and protective gas is introduced into the optical channel to prevent the measured particles from contaminating the optical components. Specifically, a protective gas inlet is provided on each side of the measuring probe, and a cooling gas inlet is provided on one side of the measuring probe.

[0029] The flow rates of the protective gas and cooling gas can be adjusted according to actual conditions.

[0030] The interference fringe recording system includes an industrial camera.

[0031] The particle multi-parameter processing system consists of a computer equipped with a digital holographic reconstruction program. The program algorithm includes a localization part, an identification part, a matching part, and a multi-parameter calculation part for particle size, morphology, concentration, and velocity.

[0032] The main problem this invention addresses is the low accuracy, complex operation, and high cost of existing technologies in simultaneously measuring multiple parameters such as particle size, morphology, concentration, and velocity. It achieves multi-parameter, in-situ measurement of particles. Furthermore, it overcomes the limitation of conventional pipeline particle velocity measurement methods, which can only measure the overall velocity. By utilizing dual-pulse digital holography, it enables the measurement of the velocity distribution of individual particles in three-dimensional space, providing richer velocity information and extending beyond simply measuring the overall velocity.

[0033] The advantages of this invention are as follows: 1. The particle measurement method and device based on dual-pulse digital holography provided by this invention realizes multi-parameter, in-situ measurement of particles, with simple operation and high testing accuracy; 2. The single-frame dual-pulse digital holography method provided by this invention uses only a single camera to realize the velocity distribution measurement of a single particle in three-dimensional space, greatly enriching the information of the test velocity, and making the device compact and portable; 3. This invention has strong applicability and is suitable for online measurement of multi-parameter particles in various industrial processes, and can effectively solve the problems of optical element contamination caused by the measured particles affecting the shooting and increasing the measurement error. Attached Figure Description

[0034] Figure 1 This is a schematic diagram of the structure of a dual-pulse digital holographic particle multi-parameter in-situ measurement device provided by the present invention.

[0035] Figure 2 This is a cross-sectional view of the measuring probe section of the device.

[0036] Figure 3 Examples of dual-pulse holograms and reconstruction results are provided.

[0037] Among them, 1. dual-pulse laser system, 2. reflector, 3. beam splitter, 4. laser modulation system, 5. objective lens, 6. pinhole, 7. lens, 8. parallel light, 9. light guide tube, 10. measuring probe, 11. optical window, 12. industrial camera, 13. pipeline, 14. particle flow, 15. protective gas, 16. cooling gas. Detailed Implementation

[0038] The specific embodiments of the present invention will be further described below with reference to the accompanying drawings.

[0039] like Figure 1 and Figure 2 As shown, the device provided in this embodiment of the invention includes: a dual-pulse light source system, a laser modulation system, a measurement probe system, an interference fringe recording system, and a particle multi-parameter processing system.

[0040] 1. A dual-pulse light source system 1 consists of two pulsed lasers placed side-by-side on the same horizontal plane. One laser beam is reflected by a mirror 2 and intersects with the other laser beam. A suitably sized beam splitter 3 is placed at the intersection of the two laser beams. By adjusting the angle and horizontal position of the beam splitter 3, the two laser beams are combined into a single beam. The laser wavelength is 532nm, the single-pulse energy is adjustable with a maximum value of approximately 120μJ, and the time interval between the two pulses is adjustable. During use, the pulse interval is selected according to the particle velocity and particle size range, ensuring that the particle movement distance between the two pulses is greater than the particle size to avoid particle overlap affecting particle recognition. In this embodiment, the pulse interval is 20μs.

[0041] 2. The laser modulation system 4 includes an objective lens 5, a pinhole 6, and a lens 7. The three are arranged on the same horizontal line and adjusted to a suitable interval. The laser beam after beam combining is transformed into a clean Gaussian parallel beam 8 by removing stray light from the laser modulation system 4.

[0042] 3. The measuring probe system includes a light guide tube 9, a measuring probe 10, and optical windows 11 located on both sides of the measuring probe. This device is also arranged on the same horizontal plane as described above. A Gaussian parallel beam 8 passes through the light guide tube 9, through the optical windows 11, and illuminates the moving particles in the measuring probe 10.

[0043] 4. An interference fringe recording system, including a standard industrial camera 12, records particle holograms and transmits them to a particle multi-parameter processing system. The camera used has a maximum resolution of 2048×2048 and a pixel size of 5.5μm×5.5μm; in actual use, a ROI of 1200×1200 is selected. Theoretically, the system can measure particle velocities ranging from 0.001m / s to 5600m / s.

[0044] 5. Particle multi-parameter processing system: processes particle holograms, retrieves three-dimensional particle field information within the measurement area, and realizes multi-parameter, in-situ measurement of particles.

[0045] During measurement, the measuring probe 10 of the device is first inserted into the pipe, and the particles pass through the measuring area of ​​the measuring probe 10 by their own speed.

[0046] In this embodiment, two protective gas inlets and one cooling gas inlet are also provided on both sides of the measuring probe 10. Cooling gas 16 is introduced into one side of the camera 12 to cool the camera 12, and protective gas 15 is introduced into the optical channel to prevent the measured particles from contaminating the optical components, such as the laser modulation system 4 and the camera 12.

[0047] The in-situ measurement method for multiple parameters of particles based on dual-pulse digital holography provided in this invention includes the following steps:

[0048] (1) The two laser beams emitted by the dual-pulse light source system 1 are first combined to form a single beam, which is then filtered by a spatial filter (composed of objective lens 5 and pinhole 6) to become a clean Gaussian beam. It is then collimated into a parallel beam 8 by a collimating lens 7, and finally illuminated by a light guide tube 9 onto the moving particle flow 14 in the measurement area of ​​the measuring probe 10.

[0049] (2) The laser beam, after passing through the scattered light of the particles, forms the object beam. The laser beam without particles serves as the reference beam. The object beam and the reference beam interfere to form interference fringes. Two laser beams in a single beam sequentially illuminate the moving particle stream 14. Within one frame, through two exposures, a single camera 12 records the formation of... Figure 3 The image shown is a single-frame dual-pulse particle hologram.

[0050] (3) The particle multi-parameter processing system reconstructs the single-frame double-pulse particle hologram, retrieves the three-dimensional particle field information in the measurement area, and obtains the particle size and concentration information; it can also obtain the three-dimensional position of the particle, thereby calculating the actual position of the particle. Based on the different gray values ​​of the particle image caused by the different energies of the two pulse lasers, the particle matching algorithm is used to further calculate the three-dimensional velocity of the particle.

[0051] In step (3), the reconstruction process includes: first, preprocessing the hologram to remove noise; then performing holographic reconstruction, which can be done using wavelet reconstruction algorithm; obtaining the binary image of the particle through particle identification and particle localization; and finally obtaining particle size and concentration information through computer image processing technology, and calculating the three-dimensional velocity of the particle using particle matching algorithm.

[0052] The particle matching algorithm utilizes the difference in intensity of dual-pulse lasers to analyze and match the grayscale values ​​of corresponding particle images. By pre-calibrating and setting the energy magnitude and emission order of the two pulses, the three-dimensional velocity of the particles can be calculated after matching.

[0053] The above description represents the preferred embodiments of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications are also considered to be within the scope of protection of the present invention.

Claims

1. A method for in-situ measurement of multiple parameters of particles based on dual-pulse digital holography, characterized in that, The method includes the following steps: (1) The two laser beams emitted by the dual-pulse laser are combined to form a single beam. The single beam passes through a spatial filter and a collimating lens in sequence to form parallel light that illuminates the moving particles in the measurement area. (2) Two laser beams in a single beam are irradiated onto the moving particle in succession. Within one frame, through two exposures, a single camera records the interference fringes to form a single-frame double-pulse particle hologram. Among them, the laser beam is scattered by the particle to form the object beam, and the laser beam that has not passed through the particle is used as the reference beam. The object beam and the reference beam interfere to form interference fringes. (3) Reconstruct the single-frame double-pulse particle hologram to retrieve the three-dimensional particle field information within the measurement area and obtain the particle size and concentration information; and obtain the three-dimensional position of the particle to calculate the actual position of the particle. Based on the different gray values ​​of the particle image caused by the different energies of the two pulse lasers, the particle matching algorithm is used to further calculate the three-dimensional velocity of the particle.

2. The in-situ multi-parameter particle measurement method based on dual-pulse digital holography according to claim 1, characterized in that, In step (1), the dual-pulse laser is composed of two pulse lasers. The time interval between the two pulses is adjusted according to the particle velocity and particle size range so that the particle movement distance between the two pulses is greater than the particle size.

3. The in-situ measurement method for multiple parameters of particles based on dual-pulse digital holography according to claim 1, characterized in that, In step (3), noise is removed by preprocessing the single-frame double-pulse particle hologram before three-dimensional reconstruction is performed; then, the binary image of the particle is obtained through particle recognition and particle localization processes. Particle size and concentration are obtained from binary images.

4. The in-situ measurement method for multiple parameters of particles based on dual-pulse digital holography according to claim 3, characterized in that, The analysis and matching are based on the different gray values ​​of the corresponding particle images caused by the different intensities of the dual-pulse laser in the binary image. The energy magnitude and emission order of the two pulses are pre-calibrated and set, and the three-dimensional velocity of the particles is calculated after matching.

5. A particle multi-parameter in-situ measurement device based on dual-pulse digital holography, characterized in that, The device includes: The dual-pulse light source system emits two laser beams, which are combined into a single beam and then transmitted to the laser modulation system. In the laser modulation system, a single beam is converted into a clean Gaussian beam by a spatial filter, then collimated into parallel light by a collimating lens, and finally illuminated to the measurement probe system by a light guide tube. The measurement probe system includes a measurement probe inserted into a pipe. The particle to be measured passes through the measurement area inside the measurement probe by its own velocity, and parallel light is irradiated onto the moving particle in the measurement area. In the interference fringe recording system, two laser beams in a single beam are sequentially irradiated onto a moving particle. Within one frame, through two exposures, a single camera records the interference fringes to form a single-frame double-pulse particle hologram. The laser beam that passes through the particle and is scattered becomes the object beam, while the laser beam that does not pass through the particle serves as the reference beam. The object beam and the reference beam interfere with each other to form interference fringes. The particle multi-parameter processing system reconstructs a single-frame dual-pulse particle hologram, retrieves the three-dimensional particle field information within the measurement area, and obtains the particle size and concentration information. It also obtains the three-dimensional position of the particle, thereby calculating the actual position of the particle. Based on the difference in grayscale value of the particle image caused by the different energies of the two pulsed lasers, the particle matching algorithm is used to further calculate the three-dimensional velocity of the particle.

6. The in-situ particle multi-parameter measurement device based on dual-pulse digital holography according to claim 5, characterized in that, The dual-pulse light source system includes two pulsed lasers.

7. The in-situ particle multi-parameter measurement device based on dual-pulse digital holography according to claim 5, characterized in that, The laser modulation system includes an objective lens, a pinhole, and a lens, wherein the objective lens and the pinhole form a spatial filter.

8. The in-situ particle multi-parameter measurement device based on dual-pulse digital holography according to claim 5, characterized in that, The measurement probe system includes a light guide tube, a measurement probe, and optical windows located on both sides of the measurement probe, with the measurement area located in the middle of the measurement probe.

9. The in-situ particle multi-parameter measurement device based on dual-pulse digital holography according to claim 5, characterized in that, The measuring probe has protective gas inlets on both sides, through which protective gas is introduced into the measuring area; the measuring probe also has a cooling gas inlet on one side, through which cooling gas is introduced to the side of the interference fringe recording system.

10. The in-situ particle multi-parameter measurement device based on dual-pulse digital holography according to claim 5, characterized in that, The interference fringe recording system is an industrial camera.

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