A device and method for measuring two-dimensional rainbow refraction of liquid droplets in a plane

Abstract

The present invention discloses a two-dimensional refraction device for measuring droplets in a plane: a laser sheet light source emission and atomized droplet generation system, including a laser, a beam modulation element and an atomization device; a rainbow signal acquisition system, including a convex lens, a horizontal slit aperture, a cylindrical lens and a digital camera in sequence; a rainbow signal processing system, which processes a two-dimensional rainbow image. The present invention also discloses a two-dimensional rainbow refraction method for measuring droplets in a plane: a sheet light source is used to illuminate the atomized droplets in the plane to generate a rainbow signal and record it on pixel blocks of different rows and columns of the camera; a two-dimensional scattering angle calibration is performed on the plane to be measured; the two-dimensional position of the droplet is determined according to the plane position of the rainbow signal, and the rainbow signal is extracted and inverted in combination with the two-dimensional scattering angle calibration result to obtain droplet information such as refractive index and particle size. The device and method have the characteristics of non-contact, two-dimensional, high precision and in-situ online, and can analyze fluid multiphase flow involving droplets.

Description

Technical Field

[0001] The invention relates to the field of gas-liquid two-phase flow measurement, and in particular to a two-dimensional rainbow refraction measurement device and method capable of measuring the two-dimensional position, particle size and refractive index of atomized liquid droplets in a plane. Technical Background

[0002] Liquid atomization is a gas-liquid two-phase flow phenomenon that is widely present in the energy, power, environment and other industrial fields, such as liquid fuel atomization evaporation combustion, gas-liquid mixing and absorption in desulfurization and denitrification spray equipment, etc. Accurate measurement of gas-liquid two-phase flow field parameters such as velocity, particle size, concentration, temperature, and composition helps people understand the complex gas-liquid two-phase flow mechanism, thereby guiding industrial optimization design and manufacturing.

[0003] Relevant researchers have invented and applied a variety of droplet measurement methods, which can be mainly divided into mechanical contact method, electromagnetic field method, and optical measurement method (including infrared, visible light and X-ray, etc.). Although the principle and operation of the traditional mechanical contact method are relatively simple, its contact measurement method always inevitably destroys the original distribution structure of the flow field. The optical measurement method does not interfere with the original gas-liquid two-phase flow, and usually has the advantages of high measurement accuracy, real-time and fast, and large amount of information. It has been widely used in various research fields in recent years. Among them, the measurement methods of macro parameters such as spray penetration depth, injection velocity and atomization cone angle are relatively mature. However, in actual research, it is hoped to further understand the droplet atomization inside the flow field, especially the evaporation rate of the droplets; under the condition of certain chemical composition, it mainly depends on the two parameters of the contact surface area with the surrounding environment and the droplet temperature. Therefore, it is very necessary to develop an optical measurement method for simultaneous online measurement of droplet size, temperature distribution and its evolution law.

[0004] In recent years, the optical methods commonly used to measure the droplet size in research include: high-speed photography technology, Malvern particle size analyzer, laser Mie scattering technology, laser induced fluorescence, digital holography, interference particle imaging technology, etc.; the methods that can be used to measure the droplet temperature include: two-color laser induced fluorescence, laser induced phosphorescence, Raman scattering, etc. Compared with the above measurement methods, rainbow refraction technology has the characteristics of accurately measuring the particle size and temperature of atomized droplets and their evolution laws at the same time. In recent years, it has been rapidly developed in the field of atomized gas-liquid two-phase flow. When a monochromatic laser irradiates a droplet, the second-order scattered light of the droplet interferes with each other to form gradually attenuated light and dark stripes, called Airy structures. The position and shape of this structure are very sensitive to the droplet characteristic parameters such as the droplet refractive index and particle size. Therefore, by inverting the rainbow signal, the particle size and refractive index of the droplet are obtained at the same time, and then the parameters such as the droplet temperature or concentration related to the droplet refractive index are derived.

[0005] Roth et al. first proposed the standard rainbow refraction method for studying monodisperse droplets. However, high-frequency ripple structures and non-spherical droplets will greatly affect the measurement accuracy of this technology. On this basis, Van Beeck et al. further proposed the full-field rainbow refraction method for the measurement of polydisperse droplet groups. By extending the exposure time and expanding the aperture, the smooth rainbow of thousands of droplet groups with a certain particle size distribution is recorded simultaneously, and then the average refractive index and particle size distribution of the droplet group are obtained. Polydisperse droplets eliminate the high-frequency ripple structure that is particularly sensitive to particle size; at the same time, because the synthetic rainbow image of thousands of droplets is recorded, the influence of a very small number of non-spherical droplets is smoothed. The full-field rainbow refraction technology solves the problem of high-frequency ripple structure and non-spherical droplets affecting measurement, and has been widely used in the diagnosis of spray evaporation and combustion. Although the full-field rainbow refraction technology measures atomized droplet groups, it still belongs to the category of "single-point" zero-dimensional measurement like the standard rainbow refraction technology. Wu Xuecheng et al. proposed a one-dimensional rainbow refraction method, which can simultaneously obtain the parameters of droplets at different heights on the measurement line, achieving a breakthrough in the measurement from "zero dimension" to "one dimension", and providing a favorable tool for continuously tracking the evolution of droplet size and temperature. Based on the one-dimensional rainbow refraction method, Wu Yingchun et al. proposed a phase rainbow refraction method, which can measure the refractive index, particle size and their tiny changes of droplets, and then measure the heat and mass transfer parameters such as the transient evaporation rate of droplets. However, the measurement area of ​​these technologies is limited to a single point or a one-dimensional line segment, and it is impossible to obtain the droplet size and refractive index in two-dimensional space that are widely present under realistic conditions.

[0006] In order to provide better testing methods for the study of non-steady-state complex spray flow fields, rainbow refraction technology needs to be further developed into two or even three dimensions, which is of great significance for a more comprehensive and in-depth study of the spray mechanism. Summary of the invention

[0007] The purpose of the present invention is to overcome the defect that the existing single-point / one-dimensional rainbow refraction method is limited to single-point / one-dimensional measurement, and to provide a two-dimensional rainbow refraction device and method for measuring droplets in a plane, which can measure the two-dimensional position, particle size and refractive index of atomized droplets in the plane, analyze the multiphase flow of the fluid involving droplets, and realize online measurement of fuel atomization field, droplet evaporation and combustion and other processes, and has the characteristics of two-dimensional plane, high precision and non-contact.

[0008] The specific technical solution adopted by the present invention to solve the above technical problems is:

[0009] A two-dimensional rainbow refraction device for measuring a droplet in a plane, comprising:

[0010] A laser sheet light source emission and atomized droplet generation system comprises a laser, a beam modulation element and an atomization device; the laser beam emitted by the laser is modulated into a vertically polarized sheet light source by the beam modulation element, and irradiates the atomized droplets generated by the atomization device in the plane to be measured, forming a rainbow signal of the droplets; the beam modulation element comprises a vertical polarizer, a plano-concave cylindrical lens and a plano-convex cylindrical lens in sequence;

[0011] The rainbow signal acquisition system includes a convex lens, a horizontal slit aperture, a cylindrical lens and a digital camera in sequence, and is used to separate and image the rainbow signals of the atomized droplets at different heights and different horizontal positions, record and obtain a two-dimensional rainbow image, and transmit it to the rainbow signal processing system;

[0012] The rainbow signal processing system processes the two-dimensional rainbow image to obtain the position, particle size and refractive index of the atomized droplets in the plane to be measured.

[0013] The laser beam emitted by the laser becomes a vertical linear polarized laser beam after passing through a vertical polarizer, and then is expanded by a plano-concave cylindrical lens and a plano-convex cylindrical lens into a vertical light source for irradiating atomized droplets in the plane to be measured. The laser is a continuous laser or a pulsed laser; the atomizing device is a pneumatic or pressure-type atomizing nozzle. Specifically, the continuous laser or pulsed laser is used to generate a coherent light beam with adjustable intensity and good beam characteristics; the atomizing device, such as a pneumatic or pressure-type atomizing nozzle, is used to spray out a solid cone atomized droplet group.

[0014] Preferably, the continuous laser is a semiconductor laser with adjustable light intensity of 0mW to 5000mW, a wavelength in the visible light band of 400nm to 760nm, and a beam waist radius of 0.4mm to 2mm; the pulse laser is a solid laser with adjustable single pulse energy of 0mJ to 100mJ, a pulse width between 1ns and 500ns, a wavelength in the visible light band of 400nm to 760nm, and a beam waist radius of 0.4mm to 2mm.

[0015] Preferably, the focal length of the plano-concave cylindrical lens is -20 mm to -5 mm, and the focal length of the plano-convex cylindrical lens is 50 mm to 200 mm; the height of the vertically polarized light source is not less than 10 mm, and the thickness is not more than 2 mm.

[0016] A horizontal slit aperture is provided at the rear focal length of the convex lens, so that only scattered light vertically incident on the convex lens in the height direction can pass through, thereby filtering scattered light in other directions, so that rainbow signals of atomized droplets at different heights are separately imaged and recorded on different rows of pixels of the digital camera, and rainbow signals of atomized droplets at different horizontal positions are separately imaged and recorded in the form of stripe blocks on different columns of pixel blocks of the digital camera; a vertically placed cylindrical lens is provided behind the horizontal slit aperture, which is used to adjust the width of the rainbow signal on the digital camera in the horizontal direction.

[0017] The width of the horizontal slit aperture is variable, ranging from 0.1mm to 10mm; the diameter of the convex lens is 50mm to 200mm, and the focal length is 50mm to 250mm; the cylindrical lens is a vertical plano-concave cylindrical lens, and the focal length is -200mm to -5mm; the digital camera is an area array camera (such as CCD or CMOS), with a pixel range of 1M to 16M, a recording scattering angle range of 6° to 20°, an angular resolution of not less than 0.002°, and an exposure time adjustable from 1μs to 1000ms. According to different measurement objects and measurement conditions, the camera exposure time can be adjusted to achieve the best measurement effect.

[0018] The rainbow signal processing system includes a computer and a synchronous controller; the computer is connected to and synchronously controls a laser and a digital camera through the synchronous controller, including controlling the switch and intensity of the laser and the switch and exposure time of the digital camera (when the laser is a pulse laser, the frequency of the pulse light and the digital camera is also synchronously controlled); and processes the two-dimensional rainbow image to obtain the position, particle size and refractive index of the atomized droplets in the plane to be measured.

[0019] For the atomized droplets located in the plane to be measured, their position on the plane passing through the droplets and perpendicular to the optical axis is recorded, which is proportional to the position recorded on the digital camera. By calibrating the relationship between them, the plane position of the droplets can be determined.

[0020] The present invention also provides a method for measuring the two-dimensional rainbow refraction of a droplet in a plane using the above device, the method comprising the following steps:

[0021] (1) Calibrate the two-dimensional scattering angle of the two-dimensional rainbow refraction measurement device at different vertical measurement line positions in the plane to be measured;

[0022] (2) Turn on the atomization device and adjust the atomized droplet group to a stable working state;

[0023] (3) Turn on the laser, and the laser beam emitted by the laser is modulated by the polarizer, the plano-concave cylindrical lens, and the plano-convex cylindrical lens, and then irradiated to the atomized droplets in the plane to be measured in the form of a light source perpendicular to the polarizer, forming a rainbow signal;

[0024] (4) The rainbow signal is collected by a convex lens and converged to propagate backward, and sequentially passes through a horizontal slit aperture and a vertical plano-concave cylindrical lens so that the rainbow signals of atomized droplets at different heights are separated and imaged on different rows of pixels of a digital camera, and the rainbow signals of atomized droplets at different horizontal positions are separated and imaged in the form of stripe blocks on different columns of pixel blocks of a digital camera;

[0025] (5) adjusting the width of the horizontal slit aperture and the position of the vertical plano-concave cylindrical lens to control the height and position of the rainbow stripe block until a clear and appropriately sized two-dimensional rainbow image of the atomized droplets in the plane to be measured is obtained;

[0026] (6) Combined with the two-dimensional scattering angle calibration results, the rainbow signal processing system processes the recorded two-dimensional rainbow image to obtain the position, particle size and refractive index of the atomized droplets in the plane to be measured.

[0027] The two-dimensional scattering angle calibration described in step (1) is to obtain the relationship between the scattering angles at different positions in the plane to be measured and the corresponding pixel positions of the digital camera. The calibration method is as follows:

[0028] (1-1) Using a monodisperse droplet generation system, a monodisperse droplet flow with known particle size D and refractive index n is generated;

[0029] (1-2) In the incident direction of the laser light source, a three-dimensional translation stage is used to sequentially move the monodisperse droplet flow from the edge of the plane to be measured to different vertical measurement line positions. After being irradiated by the vertical polarizer light source, a calibration experimental rainbow signal for two-dimensional scattering angle calibration is collected and recorded by a rainbow signal acquisition system. The calibration experimental rainbow signal is a function of the scattering intensity distribution with respect to the pixel position of the digital camera.

[0030] (1-3) Based on the known particle size D and refractive index n of the droplet flow, the Mie theory is used to simulate and calculate the accurate calibration theoretical rainbow signal, which is a function of the scattering intensity distribution with respect to the scattering angle;

[0031] (1-4) Combined with the global optimization algorithm, the calibration experimental rainbow signal collected at each vertical measurement line position is fitted and matched with the calibration theoretical rainbow signal, and the calibration relationship between the scattering angle and the pixel position at each vertical measurement line is obtained in turn;

[0032] (1-5) The interpolation method is further used to fit the scattering angle-pixel position calibration relationship at other vertical measurement line positions, thus completing the two-dimensional scattering angle calibration.

[0033] Wherein, in step (1-1), the monodisperse droplet generating system includes a monodisperse droplet generator, a high-pressure injection pump, a signal generator and an adapter, etc.

[0034] The method for processing the recorded two-dimensional rainbow image in step (6) includes:

[0035] (6-1) Based on the recorded two-dimensional rainbow image, image recognition locates the position of the rainbow signal of each droplet in the measurement area on the digital camera (x r ,y r );

[0036] For the atomized droplet located in the plane to be measured, its position on the plane passing through the droplet and perpendicular to the optical axis is recorded as (x s ,y s ), the light transmission matrices from the droplet to the digital camera in the horizontal and vertical directions are and For the angles (θ s , ) of the geometric rainbow angle, the scattered light passes through the rainbow signal acquisition system and is recorded on the digital camera at the position (x r ,y r ) can be expressed as:

[0037]

[0038]

[0039] In the implementation of the light transmission matrix system, A x ≠0, to ensure that they are at the same height y s , different horizontal positions x s The rainbow signal of the droplet can be separated in the horizontal direction by a digital camera; A y ≠0, to ensure that they are at the same horizontal position x s , different heights s The rainbow signal of the droplets can be separated in the vertical direction of the digital camera;

[0040] (6-2) Combined with the transmission matrix parameter A in the rainbow signal acquisition system x , A y , B x , B y The angles of the rainbow signal in the horizontal and vertical directions (θ s , ), the plane position (x s ,y s ), where x s =(x r -B x θ s ) / A x ,

[0041] (6-3) Combined with the pre-calibrated relationship of the two-dimensional scattering angle, the linear equation of the light intensity of the rainbow signal of each droplet in the measurement area is iteratively calculated on the computer at the same time:

[0042]

[0043] Among them, I r (θ) is the rainbow signal collected in the experiment, I f(D, n, θ) is the rainbow signal of inversion fitting, θ is the scattering angle of the rainbow signal, D is the droplet diameter, and n is the refractive index;

[0044] (6-4) When the difference between the rainbow signal collected experimentally and the rainbow signal obtained by inversion fitting is less than a preset threshold, the inversion ends, and the position, particle size, and refractive index of each measured atomized droplet in the measured plane are obtained.

[0045] Compared with the prior art, the beneficial effects of the present invention are: it overcomes the defect that the existing single-point / one-dimensional rainbow refraction method is limited to single-point / one-dimensional measurement, and proposes a two-dimensional rainbow refraction measurement device and method. It can simultaneously measure the position, particle size, and refractive index of atomized droplets at different positions in the plane to be measured; through time-continuous measurement, the two-dimensional distribution evolution law of these key parameters can be further obtained. The device of the present invention has the characteristics of simple structure and suitability for industrial online applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 It is a schematic diagram of the overall structure and optical path system of an embodiment of a two-dimensional rainbow refraction measurement device of the present invention;

[0047] Figure 2 It is a schematic diagram of the enlarged structure of the atomized droplet group and the droplet rainbow signal image in the present invention;

[0048] Figure 3 It is a schematic diagram of the monodisperse droplet generation system used in the two-dimensional scattering angle calibration process;

[0049] Among them, 1. laser, 2. vertical polarizer, 3. plano-concave cylindrical lens, 4. plano-convex cylindrical lens, 5. laser sheet light source, 6. plane to be measured, 7. atomized droplets, 8. rainbow signal, 9. convex lens, 10. horizontal slit aperture, 11. vertical plano-concave cylindrical lens, 12. digital camera, 13. collected rainbow signal, 14. computer, 15. synchronous controller, 16. atomization device, 17. measurement area, 18. two-dimensional rainbow image, 19. monodisperse droplet flow, 20. monodisperse droplet generator, 21. three-dimensional translation stage, 22. adapter, 23. high-pressure injection pump, 24. signal generator. DETAILED DESCRIPTION

[0050] The specific implementation of the technical solution of the present invention is further described below through examples and in conjunction with the accompanying drawings.

[0051] like Figure 1 As shown, a two-dimensional rainbow refraction measuring device comprises:

[0052] a. Laser sheet light source emission and atomized droplet generation system, the laser beam emitted by the laser 1 is modulated by the beam modulation element into a vertically polarized laser sheet light source 5, which irradiates the atomized droplets 7 generated by the atomization device 16 in the plane to be measured 6, forming a rainbow signal 8. The laser sheet light source emission and atomized droplet generation system consists of three parts:

[0053] Laser 1, used to generate a coherent light beam with adjustable intensity and good beam characteristics; the semiconductor laser 1 of this embodiment is a laser with adjustable light intensity from 0mW to 2000mW, a wavelength of 532nm, and a beam waist radius of 1mm;

[0054] The beam modulation element includes a vertical polarizer 2, a plano-concave cylindrical lens 3 and a plano-convex cylindrical lens 4, which are used to modulate the outgoing laser beam into a vertically polarized sheet light source 5; the focal length of the plano-concave cylindrical lens 3 is -5mm, and the focal length of the plano-convex cylindrical lens 4 is 200mm; the laser sheet light source 5 propagates in parallel, has a height of 41mm and a thickness of 1mm.

[0055] The atomizing device 16 is used to spray out a solid cone atomized droplet group, and in this embodiment, it is a pneumatic nozzle.

[0056] b. A rainbow signal acquisition system, which is used to record the rainbow signals 8 generated by the atomized droplets 7 at different positions in the plane to be measured 6 separately on a digital camera 12 through the signal acquisition system to obtain a two-dimensional rainbow image 18. The rainbow signal acquisition system includes a convex lens 9, a horizontal slit 10, a vertical plano-concave cylindrical lens 11 and a digital camera 12. The rainbow signals 8 of the atomized droplets 7 at different positions in the plane to be measured 6 are collected by the convex lens 9 and converged to propagate backward. A horizontal slit aperture 10 is provided at the rear focal length of the convex lens 9. The horizontal slit aperture 10 allows only the scattered light that is vertically incident on the convex lens to pass in the height direction, thereby filtering the scattered light in other height directions. The vertical plano-concave cylindrical lens 11 is placed between the horizontal slit aperture 10 and the digital camera 12, and is used to adjust the width of the rainbow signal in the horizontal direction without affecting the propagation of the collected rainbow signal 13 in the vertical direction. The rainbow signals 8 of the atomized droplets 7 at different heights are imaged separately on different rows of pixels of the digital camera 12; the rainbow signals 8 of the atomized droplets 7 at different horizontal positions are imaged separately on different columns of pixel blocks of the digital camera 12 in the form of stripe blocks. The convex lens 9 has a diameter of 100 mm and a focal length of 150 mm; the width of the horizontal slit aperture 10 is variable, ranging from 0.1 mm to 2 mm. The digital camera 12 is a planar array CMOS camera with 8M pixels. The acquisition system records a scattering angle range of 15° and an angular resolution of 0.002°.

[0057] The rainbow signal processing system obtains the position, particle size and refractive index of the atomized droplet 7 in the plane 6 to be measured by sequentially identifying, locating and inverting the two-dimensional rainbow image 18. The rainbow signal processing system comprises a computer 14 and a synchronous controller 15. The computer 14 is connected to and synchronously controls the laser 1 and the digital camera 12 through the synchronous controller 15, including controlling the switch and intensity of the laser 1 and the switch and exposure time of the digital camera 12 (when the laser 1 is a pulsed laser, the frequency of the pulsed light and the digital camera 12 is also synchronously controlled).

[0058] The method for measuring the two-dimensional rainbow refraction of a droplet in a plane using the above device comprises the following steps:

[0059] (1) Calibrate the two-dimensional scattering angles of vertical measurement lines at different positions of the two-dimensional rainbow refraction measurement device. The calibration method of this embodiment is as follows:

[0060] like Figure 3 As shown, a monodisperse droplet generation system composed of a monodisperse droplet generator 20, a high-pressure injection pump 23, a signal generator 24 and an adapter 22 is used to generate a monodisperse droplet flow 19 with a known particle size D and a refractive index n. In the incident direction of the laser sheet light source 5, a three-dimensional displacement stage 21 is used to sequentially move the monodisperse droplet flow 19 from the edge of the plane to be measured to different vertical measurement line positions. After being irradiated by the vertically polarized laser sheet light source 5, the monodisperse droplet flow 19 is collected and recorded by the rainbow signal acquisition system as a calibration experimental rainbow signal for two-dimensional scattering angle calibration. The calibration experimental rainbow signal is a function of the scattering intensity distribution with respect to the pixel position of the digital camera. According to the known particle size D and refractive index n of the droplet flow, the Mie theory is used to simulate and calculate an accurate calibration theoretical rainbow signal. The calibration theoretical rainbow signal is a function of the scattering intensity distribution with respect to the scattering angle. Combined with the global optimization algorithm, the calibration experimental rainbow signal collected at each vertical measurement line position is fitted and matched with the calibration theoretical rainbow signal, and the calibration relationship between the scattering angle and the pixel position at each vertical measurement line is obtained in turn. The interpolation method is further used to fit the scattering angle-pixel position calibration relationship at other vertical measurement line positions, thus completing the two-dimensional scattering angle calibration.

[0061] (2) Open Figure 2 The atomizing device 16 shown adjusts the atomized droplet group to a stable working state;

[0062] (3) Turn on the laser 1. The laser beam emitted by the laser 1 is modulated by the vertical polarizer 2, the plano-concave cylindrical lens 3, and the plano-convex cylindrical lens 4, and then irradiated onto the atomized droplets 7 in the plane to be measured 6 in the form of a vertical polarizer light source 5. The rainbow signals 8 of the droplets 7 at different plane positions are collected by the rainbow signal collection system;

[0063] (4) Adjust the width of the horizontal slit aperture 10 and the position of the vertical plano-concave cylindrical lens 11 to control the height and position of the rainbow stripe block until a clear and appropriately sized image is obtained. Figure 2 A two-dimensional rainbow image 18 produced by atomized droplets in the measurement area 17 is shown;

[0064] (5) Turn on the digital camera 12, and separate the rainbow signals 8 of the atomized droplets 7 at different positions in the plane 6 to be measured into images in the form of stripe blocks on pixel blocks of different rows and columns of the digital camera 12;

[0065] (6) The rainbow signal processing system sequentially identifies, locates and inverts the rainbow signal 13 of each droplet recorded in the two-dimensional rainbow image 18 to obtain the position, particle size and refractive index of the droplet;

[0066] According to the recorded two-dimensional rainbow image 18, the position (x r ,y r );

[0067] Among them, for the atomized droplet located in the plane to be measured, its position on the plane passing through the droplet and perpendicular to the optical axis is recorded as (x s ,y s ), the light transmission matrices from the droplet to the digital camera in the horizontal and vertical directions are and For the angles (θ s , ) of the geometric rainbow angle, the scattered light passes through the rainbow signal acquisition system and is recorded on the digital camera at the position (x r ,y r ) can be expressed as:

[0068]

[0069]

[0070] In the implementation of the light transmission matrix system, A x ≠0, to ensure that they are at the same height y s , different horizontal positions x s The rainbow signal of the droplet can be separated in the horizontal direction by a digital camera; A y ≠0, to ensure that they are at the same horizontal position x s , different heights s The rainbow signal of the droplets can be separated in the vertical direction of the digital camera;

[0071] Combined with the transmission matrix parameter A in the rainbow signal acquisition system x , A y , Bx , B y The angles of the rainbow signal in the horizontal and vertical directions (θ s , ), the plane position (x s ,y s ), where x s =(x r -B x θ s ) / A x ,

[0072] On this basis, combined with the pre-calibrated relationship of the two-dimensional scattering angle, the linear equation of the light intensity of the rainbow signal of each droplet in the measurement area 17 is iteratively calculated on the computer 14 at the same time: The particle size and refractive index of each droplet in the measurement area 17 are obtained by inversion; through time-continuous measurement, the two-dimensional distribution evolution law of the key parameters of the atomized droplet group can also be obtained.

[0073] In addition to the above-mentioned embodiments, within the scope disclosed in the claims and the specification of the present invention, the technical features or technical data of the present invention can be reselected and combined to form new embodiments, which can be achieved by those skilled in the art without creative work. Therefore, these embodiments that are not described in detail in the present invention should also be regarded as specific embodiments of the present invention and within the protection scope of the present invention.

Claims

1. A two-dimensional rainbow refraction device for measuring droplets in a plane, characterized in that: The device comprises: A laser sheet light source emission and atomized droplet generation system comprises a laser, a beam modulation element and an atomization device; the laser beam emitted by the laser is modulated into a vertically polarized sheet light source by the beam modulation element, and irradiates the atomized droplets generated by the atomization device in the plane to be measured, forming a rainbow signal of the droplets; the beam modulation element comprises a vertical polarizer, a plano-concave cylindrical lens and a plano-convex cylindrical lens in sequence; The rainbow signal acquisition system includes a convex lens, a horizontal slit aperture, a cylindrical lens and a digital camera in sequence, and is used to separate and image the rainbow signals of the atomized droplets at different heights and different horizontal positions, record and obtain a two-dimensional rainbow image, and transmit it to the rainbow signal processing system; The rainbow signal processing system processes the two-dimensional rainbow image to obtain the position, particle size and refractive index of the atomized droplets in the plane to be measured; The focal length of the plano-concave cylindrical lens is -20mm to -5mm, and the focal length of the plano-convex cylindrical lens is 50mm to 200mm; the height of the vertically polarized light source is not less than 10mm, and the thickness is not more than 2mm; A horizontal slit aperture is provided at the rear focal length of the convex lens, so that only scattered light vertically incident on the convex lens in the height direction can pass through, thereby filtering scattered light in other directions, so that rainbow signals of atomized droplets at different heights are separately imaged and recorded on different rows of pixels of the digital camera, and rainbow signals of atomized droplets at different horizontal positions are separately imaged and recorded in the form of stripe blocks on different columns of pixel blocks of the digital camera; a vertically placed cylindrical lens is provided behind the horizontal slit aperture, which is used to adjust the width of the rainbow signal on the digital camera in the horizontal direction.

2. The two-dimensional rainbow refraction device for measuring droplets in a plane as claimed in claim 1, characterized in that: The laser is a continuous laser or a pulsed laser; the atomizing device is a pneumatic or pressure atomizing nozzle.

3. The two-dimensional rainbow refraction device for measuring droplets in a plane as claimed in claim 2, characterized in that: The continuous laser is a semiconductor laser with adjustable light intensity from 0mW to 5000mW, a wavelength in the visible light band of 400nm to 760nm, and a beam waist radius of 0.4mm to 2mm; the pulse laser is a solid laser with adjustable single pulse energy from 0mJ to 100mJ, a pulse width between 1ns and 500ns, a wavelength in the visible light band of 400nm to 760nm, and a beam waist radius of 0.4mm to 2mm.

4. The two-dimensional rainbow refraction device for measuring droplets in a plane as claimed in claim 1, characterized in that: The width of the horizontal slit aperture is variable, ranging from 0.1 mm to 10 mm; the diameter of the convex lens is 50 mm to 200 mm, and the focal length is 50 mm to 250 mm; the cylindrical lens is a vertical plano-concave cylindrical lens, and the focal length is -200 mm to -5 mm; the digital camera is an area array camera, with a pixel range of 1M to 16M, a recorded scattering angle range of 6° to 20°, an angular resolution of not less than 0.002°, and an exposure time adjustable from 1μs to 1000ms.

5. The two-dimensional rainbow refraction device for measuring droplets in a plane as claimed in claim 4, characterized in that: The rainbow signal processing system includes a computer and a synchronous controller; the computer is connected to and synchronously controls a laser and a digital camera through the synchronous controller, including controlling the switch and intensity of the laser and the switch and exposure time of the digital camera; when the laser is a pulse laser, the frequency of the pulse light and the digital camera is also synchronously controlled; and the two-dimensional rainbow image is processed to obtain the position, particle size and refractive index of the atomized droplets in the plane to be measured.

6. A method for measuring the two-dimensional rainbow refraction of a droplet in a plane using the device described in any one of claims 1 to 5, characterized in that: The method comprises the following steps: (1) Calibrate the two-dimensional scattering angle of the two-dimensional rainbow refraction measurement device at different vertical measurement line positions in the plane to be measured; (2) Turn on the atomization device and adjust the atomized droplet group to a stable working state; (3) Turn on the laser, and the laser beam emitted by the laser is modulated by the polarizer, the plano-concave cylindrical lens, and the plano-convex cylindrical lens, and then irradiated to the atomized droplets in the plane to be measured in the form of a light source perpendicular to the polarizer, forming a rainbow signal; (4) The rainbow signal is collected by a convex lens and converged to propagate backward, and sequentially passes through a horizontal slit aperture and a vertical plano-concave cylindrical lens so that the rainbow signals of atomized droplets at different heights are separated and imaged on different rows of pixels of a digital camera, and the rainbow signals of atomized droplets at different horizontal positions are separated and imaged in the form of stripe blocks on different columns of pixel blocks of a digital camera; (5) adjusting the width of the horizontal slit aperture and the position of the vertical plano-concave cylindrical lens to control the height and position of the rainbow stripe block until a clear and appropriately sized two-dimensional rainbow image of the atomized droplets in the plane to be measured is obtained; (6) Combined with the two-dimensional scattering angle calibration results, the rainbow signal processing system processes the recorded two-dimensional rainbow image to obtain the position, particle size and refractive index of the atomized droplets in the plane to be measured.

7. The method for measuring the two-dimensional rainbow refraction of a droplet in a plane as claimed in claim 6, characterized in that: The two-dimensional scattering angle calibration described in step (1) is to obtain the relationship between the scattering angles at different positions in the plane to be measured and the corresponding pixel positions of the digital camera. The calibration method is as follows: (1-1) Using a monodisperse droplet generation system, a monodisperse droplet flow with known particle size D and refractive index n is generated; (1-2) In the incident direction of the laser light source, a three-dimensional translation stage is used to sequentially move the monodisperse droplet flow from the edge of the plane to be measured to different vertical measurement line positions. After being irradiated by the vertical polarizer light source, a calibration experimental rainbow signal for two-dimensional scattering angle calibration is collected and recorded by a rainbow signal acquisition system. The calibration experimental rainbow signal is a function of the scattering intensity distribution with respect to the pixel position of the digital camera. (1-3) Based on the known particle size D and refractive index n of the droplet flow, the Mie theory is used to simulate and calculate the accurate calibration theoretical rainbow signal, which is a function of the scattering intensity distribution with respect to the scattering angle; (1-4) Combined with the global optimization algorithm, the calibration experimental rainbow signal collected at each vertical measurement line position is fitted and matched with the calibration theoretical rainbow signal, and the calibration relationship between the scattering angle and the pixel position at each vertical measurement line is obtained in turn; (1-5) The interpolation method is further used to fit the scattering angle-pixel position calibration relationship at other vertical measurement line positions, thus completing the two-dimensional scattering angle calibration.

8. The method for measuring the two-dimensional rainbow refraction of a droplet in a plane as claimed in claim 7, characterized in that: The method for processing the recorded two-dimensional rainbow image in step (6) includes: (6-1) Based on the recorded two-dimensional rainbow image, image recognition locates the position of the rainbow signal of each droplet in the measurement area on the digital camera (x r ,y r ); For the atomized droplet located in the plane to be measured, its position on the plane passing through the droplet and perpendicular to the optical axis is recorded as (x s ,y s ), the light transmission matrices from the droplet to the digital camera in the horizontal and vertical directions are and For the angles in the horizontal and vertical directions After the scattered light near the geometric rainbow angle passes through the rainbow signal acquisition system, the position (x r ,y r ) is expressed as: In the implementation of the light transmission matrix system, A x ≠0, to ensure that they are at the same height y s , different horizontal positions x s The rainbow signal of the droplet can be separated in the horizontal direction by a digital camera; A y ≠0, to ensure that they are at the same horizontal position x s , different heights s The rainbow signal of the droplets can be separated in the vertical direction of the digital camera; (6-2) Combined with the transmission matrix parameter A in the rainbow signal acquisition system x , A y , B x , B y The horizontal and vertical angles of the rainbow signal The plane position (x s ,y s ), where x s =(x r -B x θ s ) / A x , (6-3) Combined with the pre-calibrated relationship of the two-dimensional scattering angle, the linear equation of the light intensity of the rainbow signal of each droplet in the measurement area is iteratively calculated on the computer at the same time: Among them, I r (θ) is the rainbow signal collected in the experiment, I f (D, n, θ) is the rainbow signal of inversion fitting, θ is the scattering angle of the rainbow signal, D is the droplet diameter, and n is the refractive index; (6-4) When the difference between the rainbow signal collected experimentally and the rainbow signal obtained by inversion fitting is less than a preset threshold, the inversion ends, and the position, particle size, and refractive index of each measured atomized droplet in the measured plane are obtained.

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