CN1252451C - Particle field total-field measurement process and apparatus based on laser sheet optical image-forming - Google Patents

Abstract

The present invention is based on the particle field full-field measurement method of laser sheet light imaging and its measurement device, which is characterized in that mutually orthogonal laser sheet light is used to illuminate the particles in the test flow field, and two CCD cameras are used to obtain the cross-section perpendicular to the direction of the flow field respectively. The image of the particles in the image and the trajectory image of the particles in the plane parallel to the direction of the flow field are determined by identifying the image of the particle and statistically analyzing the number of pixels it occupies to determine the size of its equivalent diameter. The magnitude and direction of particle motion velocity give the scale spectrum and velocity field distribution of particles in the imaging plane. The invention only takes the particles in the flow field as the imaging object, does not need to artificially apply tracer particles, avoids the interference caused by the application of tracer particles to the flow field, and can be widely used in the study of two-phase or multiphase flow. The multi-parameter, full-field dynamic measurement has broad application prospects in the fields of energy and environment, national defense, machinery, chemical industry, metallurgy, medicine and food.

Description

Particle field full-field measurement method and device based on laser sheet optical imaging

Technical field:

The invention relates to a method and device for measuring particle size and velocity in two-phase or multiphase flow.

Background technique:

Proceedings of the 15th International Conference on Fire Safety Research (15th meeting of the UJNR panel on fire research and safety, March 1-7, 2000, pp.471-481.) and Proceedings of the 8th International Conference on Liquid and Spray Systems (8thInternational Conference on Liquid and Spray Systems, Pasadena, USA, 2000, 886-892.) pointed out that although the Digital Particle Image Velocimetry (DPIV) method developed in recent years can do dynamic full-field measurement of the flow field , but because it uses the particle image cross-correlation technique to reconstruct the velocity of the flow field, it is required that the laser sheet light must be parallel to the direction of the flow field, and it is required to apply tracer particles with good followability and light scattering characteristics to the test flow field , usually only the two-dimensional velocity distribution of the flow field can be obtained; although the stereoscopic particle image velocimetry (Stereoscopic PIV, SPIV for short) technology realizes the three-dimensional measurement of the flow field velocity by using two CCD cameras for stereoscopic imaging, it still requires The laser sheet light must be parallel to the direction of the flow field, and it is required to apply tracer particles with good followability and light scattering characteristics to the test flow field. Only the velocity of the flow field can be obtained but the particle size of the particles in the flow field cannot be measured. Feature parameters. In addition, for two-phase or multiphase flow fields (such as spray fields, etc.), because the density of particles in them is often much smaller than the density of tracer particles in DPIV and SPIV methods, the image of particles in the flow field image The density cannot meet the requirements of the cross-correlation algorithm in the DPIV and SPIV methods for the particle number density in the query window, that is, for the measurement of the two-phase or multi-phase flow field velocity, the above method is also difficult to achieve.

In the study of two-phase or multi-phase flow, such as spray combustion, spray cooling of hot surfaces in micromachining, water mist fire extinguishing and performance design of spray systems, it is very concerned about the transient measurement of flow field velocity and the particle size. real-time diagnosis. Especially in the performance design and flight test of airplanes and other aircraft, it is often necessary to conduct experimental measurements on the flow field in the wind tunnel and the distribution of particles; in the research of fuel engines, in order to save energy, improve efficiency and reduce pollution, It is usually necessary to study the atomization and diffusion process of the fuel in the combustion chamber and measure the particle size and velocity distribution of the oil droplets, so as to provide an experimental basis for the correct design of the fuel nozzle and the shape of the combustion chamber and the selection of an appropriate fuel-air mixing ratio; in various explosion studies In the process of explosion, it is necessary to study the particle number, spectral distribution and diffusion law of aerosol particles in the explosion process; in the study of water mist fire extinguishing and spray cooling of hot surfaces, it is necessary to measure the velocity distribution, particle size distribution and atomization of droplets Characteristic parameters such as cone angle, etc. However, as mentioned above, some of the existing technologies can only measure the flow field at a single point, and some can only measure the velocity distribution of the flow field, which cannot meet the requirements of multi-parameters and full-field dynamics in the study of two-phase or multiphase flow. measurement requirements.

Invention content:

The present invention proposes a flow field multi-parameter full-field measurement method and its measurement device based on laser sheet light imaging and digital image analysis and processing to solve the shortcomings of the existing single-point measurement technology, and DPIV and SPIV technology in the flow field measurement The limitation that only the velocity of the flow field can be obtained in .

The particle field full-field measurement device based on laser sheet optical imaging of the present invention includes a laser sheet optical system 1, a digital imaging system 2 and an image data acquisition system 3; it is characterized in that: the laser sheet optical system 1 is composed of a laser power supply 4, A laser 5, two cylindrical lenses 6 and 7, a beam splitter 8 and a mirror 9 are formed, wherein the beam splitter 8 is placed on the optical axis of the laser, the mirror 9 is placed on the optical axis of the split beam, and the first cylindrical lens 6 is placed on the optical axis of the transmitted beam of the laser beam through the beam splitter 8, and the second cylindrical lens 7 is placed on the optical axis of the beam of the laser split beam reflected by the total reflection mirror 9; the digital imaging system 2 adopts two A CCD camera 10 and 11, wherein the first CCD camera 10 is perpendicular to the sheet light produced by the laser transmission beam through the cylindrical lens 6, and the second CCD camera 11 is perpendicular to the sheet light produced by the split beam through the cylindrical lens 7; Described image data acquisition system 3 comprises computer 14 and the image card 13 that is inserted on the main board of computer; Image card 13 is connected with the output end of two CCD camera heads 10 and 11 respectively by video transmission line; Two CCD camera heads 10 and 11 respectively Connect with the same controller 12 through the data control line; two beams of laser sheet light are in the flow field area 16 generated by the two-phase or multiphase flow field generating device 15, and one of the laser sheet light surfaces is parallel to the flow direction of the flow field 16, The other bundle is perpendicular to the flow direction of the flow field 16 .

Laser light source 5 of the present invention can be Ar+laser, also can be semiconductor laser or other pulsed laser light source; Add a collimating lens group between the beam splitter 8 and between the second cylindrical lens 7 and the reflector 9, so that the thickness of the laser sheet light is as thin as possible (less than 1 millimeter or less); two cylindrical lenses 6 and 7, beam splitter 8 and reflecting mirror 9 placement positions are determined according to the size of the experimental test space and the requirements for the optical thickness of the laser sheet from the distance of the laser outlet; two CCD cameras 10 and 11 can be CCD and optical camera lenses ( fixed focal length or adjustable focal length) assembly, it can also be a digital camera or a digital video camera; in order to clearly image particles with a diameter of tens of microns or smaller, one can also be added to the entrance pupil of the CCD camera Microscopic imaging lens; two CCD cameras 10 and 11 can be separated from the distance of the laser sheet light produced by the first cylindrical lens 6 and the second cylindrical lens 7 respectively according to the size of the particle in the flow field, the exposure amount and the size of the imaging area It depends on the requirements; there is no special requirement for the position of the two-phase or multi-phase flow field generating device 15 from the two laser sheet lights, as long as the position of the flow field generating device 15 or the incident position of the laser sheet light is adjusted so that the laser sheet light can fully illuminate the The imaged flow field area is sufficient.

The measuring object of the measuring method and device thereof of the present invention can be the solid particles in the gas-solid or gas-liquid two-phase flow field produced by the two-phase or multi-phase flow field generating device 15, such as dust particles in dust explosion, food processing process solid particles and smoke particles in early fire detection, etc., can also be liquid particles in gas-liquid two-phase or multi-phase flow field, such as various liquid fuel spray droplets in the spray combustion process, fine water mist fire extinguishing system The fine water mist droplets, the spray droplets in the spraying process, and the spray cooling system droplets in the micromachining process, etc.

The particle field full-field measurement method based on laser sheet light imaging in the present invention is characterized in that the particles in the test flow field are illuminated by mutually orthogonal laser sheet light, and two CCD cameras are used to respectively obtain the particles in the section perpendicular to the direction of the flow field. Image and trajectory images of particles in a plane parallel to the direction of the flow field, by identifying the images of particles and statistically analyzing the number of pixels it occupies to determine the size of its equivalent diameter, analyzing and identifying particle trajectory images to determine the particle velocity The size and direction of , give the scale spectrum distribution and velocity vector field distribution of particles in the imaging plane.

Compared with the prior art, since the present invention adopts the orthogonal arrangement of the light incident direction of the laser sheet, that is, the light surface of the laser sheet can be incident either parallel to the flow direction of the flow field or perpendicular to the flow direction of the flow field, so both vertical The particles in the plane of the flow field can be clearly imaged, and the trajectory of the particles in the plane parallel to the flow field can also be obtained, and then the particle size and its size can be obtained through direct identification and statistical analysis of the single particle image. Scale spectrum distribution, and through the identification and statistical analysis of particle trajectory images to determine the velocity and distribution of particles in the flow field, which not only solves the shortcomings of the single-point measurement method in the flow field test, but also solves the DPIV/SPIV method The limitation that it can only measure and obtain the velocity of the flow field makes it have the advantages of multi-parameter and full-field dynamic measurement.

Since only the particles in the flow field are used as imaging objects in the present invention, there is no need to artificially apply any tracer particles, which avoids the analysis and requirements of tracer particle follow-up and light scattering in DPIV/SPIV technology, and more importantly, The problem of interference to the flow field caused by the application of the tracer particles is avoided, and at the same time, the technical and financial problems faced by the preparation and application of the tracer particles are avoided.

Based on the above advantages, the present invention can be widely used in two-phase or multiphase flow research (such as spray cooling of hot surfaces in spray combustion, micromachining, identification and analysis of smoke particles in early fire detection, water mist fire extinguishing, etc.) Multi-parameter and full-field dynamic measurement of the flow field in the performance design of its spray system. Therefore, the full-field particle field measurement method developed by the present invention has very broad application prospects and scientific value in research fields such as energy and environment, national defense, machinery, chemical industry, metallurgy, medicine and food.

Description of drawings:

Fig. 1 is the particle field measurement method and device schematic diagram based on laser sheet light imaging of the present invention;

Fig. 2 is the measuring device schematic diagram of standard glass ball particle size and velocity in embodiment 1;

Fig. 3 is the experimental measurement device schematic diagram of fine water mist droplet characteristic in embodiment 2;

Detailed ways:

The specific embodiments of the present invention will be described below in conjunction with the accompanying drawings.

Embodiment 1: Measurement of particle size and velocity distribution of solid particles in two-phase flow field

In the present embodiment, the laser sheet optical system 1 is made up of a laser power supply 4, a semiconductor laser 5 with a wavelength of 650nm, two cylindrical lenses 6 and 7, a beam splitter 8 and a mirror 9, and the beam splitter 8 is placed in the laser 5 At about 200mm on the optical axis of the laser, the first cylindrical lens 6 is placed at about 150mm on the optical axis of the transmitted beam after the laser passes through the beam splitter 8, and the mirror 9 is placed on the optical axis of the split beam after the laser passes through the beam splitter 8 At about 250mm above, the second cylindrical lens 7 is placed at about 250mm on the optical axis of the light beam after the split beam is reflected by the reflector 9; the digital imaging system 2 adopts two CCD cameras 10 and 11 with a resolution of 1024×768, Wherein the first CCD camera 10 is perpendicular to the sheet light produced by the first cylindrical lens 6 by the laser transmission beam, and the second CCD camera 11 is perpendicular to the sheet light produced by the split beam through the second cylindrical lens 7, and the CCD camera is at a distance from the laser beam. The distance of sheet light is about 100mm respectively; Image data acquisition system 3 comprises computer 14 and the image card 13 that is inserted on the main board of computer; Image card 13 is connected with the output end of two CCD cameras 10 and 11 respectively by video transmission line; Two CCD cameras 10 and 11 are respectively connected with the same controller 12 through data control lines; two-phase or multi-phase flow field generating device 15 is placed under the light of the two laser sheets, and the flow field 16 produced by it is connected with the flow field 16 by the first cylindrical lens. The plane of the laser sheet light generated by 6 is perpendicular to the plane of the sheet light generated by the second cylindrical lens 7, and it is placed about 100 mm from the latter.

The two-phase or multiphase flow field generating device 15 in the present embodiment is a glass tube container with openings at both ends, and the diameter of the middle section of the glass tube is 5 to 6 times the diameter of the two opening sections; The standard glass ball particle of known average particle diameter at place produces uniform particle field at the upper opening end place under the effect of blower 17; Support 22 is fixed on a horizontal platform, and the glass tube container of flow field generating device 15 is fixed on support On 22; blower 17 is connected with glass container by plastic hose 18.

When measuring, turn on the power of the blower, laser, CCD camera and computer, start the image card to obtain the image of standard glass ball particles; then determine the size of the area by counting the number of pixels occupied by the image of a single particle, and calculate according to the area of the circle The method determines the equivalent diameter of a single particle, and then gives its particle size distribution through the statistical analysis of all particle diameters in the imaging area; first determines the movement speed of a single particle according to the length of the movement track of a single particle and the exposure time of the imaging system, and then Through the statistical analysis of the velocity of all particles in the imaging area, the distribution of the particle velocity in the whole field is given.

As the experimental verification of the device and method of the present invention, the standard glass ball particles with an average particle diameter of 115 microns are used in this embodiment; the maximum particle diameter of the measurement results using the above-mentioned device and method is 121 microns, and the minimum particle diameter is 78 microns , The average particle size is 111.6 microns; the speed of the airflow used in the experiment is 0.22m/s, and the average value of the experimental measurement results is 0.21m/s. The above results show that the present invention is reliable in measuring the particle size and velocity of solid particles in the gas-solid two-phase flow field, and the relative errors are not more than 3% and 5% respectively.

Embodiment 2: Measurement of the particle size of liquid particles in the gas-liquid two-phase flow field (fine water mist droplet flow field)

The composition and layout of the measuring device in this embodiment are basically the same as those in Embodiment 1, the difference is that in this embodiment the sheet light generated by the first cylindrical lens 6 is parallel to the direction of the flow field, while the sheet light generated by the second cylindrical lens 7 is parallel to the direction of the flow field. The sheet light is perpendicular to the direction of the flow field; in this embodiment, a collimator lens 21 with a diameter of 300 mm is arranged at about 200 mm on the transmitted light path of the second cylindrical lens 7, in order to collimate the fan-shaped sheet light into parallel sheet light , so that the light intensity distribution of the laser sheet light is as uniform as possible.

In this embodiment, the two-phase or multi-phase flow field generating device 15 is a combination system of a water storage device and a fine water mist nozzle 19, which are connected by a stainless steel pipe 20, and the two-phase flow field is about The fine water mist droplet flow field 16 generated by spraying in the fine water mist nozzle 19 at 1 meter.

When measuring, turn on the power of the laser, CCD camera and computer, turn on the switch of the water storage device, start the image card to obtain the image of fine water mist droplets; then determine the area size by counting the number of pixels occupied by a single particle image 1. Determine the equivalent diameter of a single particle according to the circle area calculation method, and then give its particle size distribution through the statistical analysis of all particle diameters in the imaging area; first determine the single particle according to the length of the single particle trajectory and the exposure time of the imaging system The motion velocity of all particles in the imaging area is then statistically analyzed to give the distribution of particle motion velocities in the entire field.

In this embodiment, the working pressure of the water supply system is adjusted within the range of 0.1 to 1.0 MPa, and the images of the fine water mist droplets under different pressure conditions and their motion trajectory images can be obtained by using the above-mentioned measuring device, and then according to the above-mentioned method, the images can be obtained The particle size distribution and average particle size, the velocity distribution vector diagram and the average velocity of the fine water mist droplets; this embodiment simultaneously illustrates that the device and method of the present invention can be used to simultaneously measure and obtain fine particles without artificially applying any tracer substances. The size and distribution of droplet size and velocity in water mist field.

Claims (2)

1. A particle field full-field measurement device based on laser sheet light imaging, comprising a laser sheet light system (1), a digital imaging system (2) and an image data acquisition system (3); it is characterized in that: the laser sheet light The system (1) consists of a laser power supply (4), a laser (5), two cylindrical lenses (6, 7), a beam splitter (8) and a mirror (9), wherein the beam splitter (8) is placed on the laser On the optical axis, the reflecting mirror (9) is placed on the optical axis of the split beam, the first cylindrical lens (6) is placed on the optical axis of the transmitted beam after the laser passes through the beam splitter (8), and the second cylindrical lens (7 ) is placed on the optical axis of the light beam reflected by the total reflection mirror (9) of the laser split beam; the digital imaging system (2) adopts two CCD cameras (10,11), wherein the first CCD camera (10) Perpendicular to the sheet of light produced by the laser transmission beam through the first cylindrical lens (6), and the second CCD camera (11) is perpendicular to the sheet of light produced by the split beam through the second cylindrical lens (7); the image data Acquisition system (3) comprises computer (14) and the image card (13) that is inserted on the computer mainboard; Image card (13) is connected with the first CCD camera head (10) and the second CCD camera head (11) respectively by video transmission line The output terminal of the first CCD camera (10) and the second CCD camera (11) are respectively connected with the same controller (12) by the data control line; 15) In the generated flow field area (16), the optical surface of one laser sheet is parallel to the flow direction of the flow field (16), and the other is perpendicular to the flow direction of the flow field (16). 2. A particle field full-field measurement method based on laser sheet light imaging, which is characterized in that the particles in the test flow field are illuminated by mutually orthogonal laser sheet light, and two CCD cameras are used to obtain the cross-section perpendicular to the direction of the flow field respectively. The image of the particle and the image of the trajectory of the particle in the plane parallel to the direction of the flow field, through the identification of the image of the particle and statistical analysis of the number of pixels it occupies to determine the size of its equivalent diameter, and the analysis and identification of the trajectory of the particle to determine the size of the particle The size and direction of the moving velocity give the scale spectrum distribution and velocity vector field distribution of particles in the imaging plane.

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