PIV and shadow imaging technology coupled gas-liquid two-phase flow measurement system and method

Abstract

The embodiment of the present application provides a kind of gas-liquid two-phase flow measurement system and method based on PIV and shadow imaging technology coupling, the gas-liquid two-phase flow measurement system includes: high-frequency LED, synchronizer, double-cavity diode-pumped laser, data processing device and high-speed camera with high-pass filter.High-frequency LED and the double-cavity diode-pumped laser are connected with the synchronizer;The high-speed camera with high-pass filter is operated by double-frame mode, and high-pass filter is installed in front of lens, and the high-speed camera is connected with the data processing device and synchronizer respectively;The synchronizer is connected with the data processing device.The technical scheme of the present application can measure the size, position, shape, velocity and other characteristics of gas phase, and measure the liquid phase flow field structure, and accurately measure the interface of gas-liquid two-phase.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of underwater flow field test, and particularly relates to a gas-liquid two-phase flow measurement system and method based on coupling of PIV and shadow imaging technology. BACKGROUND

[0002] Gas-liquid two-phase flow test has an important role in many fields such as energy power, ocean engineering, chemical industry, etc. PIV (Particle Image Velocimetry) is a non-contact, instantaneous and full-field flow field test technology, which can accurately obtain the velocity distribution characteristics of the flow field. When applied to gas-liquid two-phase flow, it is difficult to identify the two-phase interface boundary, and the reflection of bubbles will produce glare, so that the geometric size of the bubbles and other gas phase characteristics cannot be obtained, and the flow field structure at the gas-liquid interface is difficult to obtain. The shadow imaging technology can obtain the characteristics of the bubbles, but cannot obtain the dynamic flow field distribution of the liquid phase, and further cannot obtain the interaction at the interface between the bubbles and the fluid.

[0003] The existing gas-liquid two-phase flow test method based on coupling of PIV and shadow imaging technology records PIV images and shadow images through two cameras, which has the disadvantages of high cost and complex experimental device structure. The images captured by the two cameras are difficult to ensure time synchronization and the same range, and the image processing is difficult. At the same time, there is signal interference between multiple cameras, resulting in inaccurate measurement results.

[0004] Therefore, how to provide a gas-liquid two-phase flow measurement system and method based on coupling of PIV and shadow imaging technology has become a technical problem to be solved, which can measure the size, position, shape, velocity and other characteristics of the gas phase, measure the flow field structure of the liquid phase, and accurately measure the interface between the gas-liquid two phases. SUMMARY

[0005] The embodiment of the application provides a gas-liquid two-phase flow measurement system and method based on coupling of PIV and shadow imaging technology, which can measure the size, position, shape, velocity and other characteristics of the gas phase, measure the flow field structure of the liquid phase, and accurately measure the interface between the gas-liquid two phases.

[0006] In one embodiment of the application, a gas-liquid two-phase flow measurement system based on coupling of PIV and shadow imaging technology is provided, which comprises a high-frequency LED, a synchronizer, a double-cavity diode-pumped laser, a data processing device and a high-speed camera with a high-pass filter.

[0007] The high-frequency LED and the double-cavity diode-pumped laser are connected with the synchronizer; the high-speed camera with the high-pass filter operates in a double-frame mode and is installed with a high-pass filter in front of the lens, and the high-speed camera is connected with the data processing device and the synchronizer respectively; the synchronizer is connected with the data processing device;

[0008] The fluorescent particles are evenly distributed and suspended in the water tank to be measured, the double-cavity diode-pumped laser is used to emit green light of a first wavelength, the high-pass filter of the high-speed camera allows light of a second wavelength to pass through; the Q1 signal is sent to the high-frequency LED by pulse modulation, and the Q2 signal is sent to the double-cavity diode-pumped laser, the double-cavity diode-pumped laser and the high-frequency LED intermittently work at the same frequency, respectively; the high-speed camera operates in a double-frame mode, and the frequency of the high-speed camera and the frequencies of the laser and the high-frequency LED are set so that two frames of images continuously captured by the high-speed camera are a PIV image and a shadow image of a backlight source.

[0009] Further, the fluorescent particles are evenly distributed and suspended in the water tank to be measured, and the method comprises the following steps:

[0010] The fluorescent particles are rhodamine 6G which absorbs green light of the first wavelength and emits red light of the second wavelength.

[0011] Further, the first wavelength is 527 nm, and the second wavelength is 590 nm.

[0012] Further, the intensities of the high-frequency LED and the double-cavity diode-pumped laser are controlled by pulse width.

[0013] Further, the high-speed camera captures a shadow image in the environment of a backlight source, the shadow image is a gas phase in the water tank to be measured, the phase boundary is determined by setting global threshold values and local threshold values through phase interface detection, the captured shadow image is converted into a black-and-white image, data information including at least bubble size, position, shape and speed is obtained through image morphological operation filtering.

[0014] In another embodiment of the present application, a gas-liquid two-phase flow measurement method based on coupling of PIV and shadow imaging technology is provided, comprising:

[0015] The fluorescent particles are evenly distributed in the water tank to be measured, the pulse width of the high-frequency LED and the double-cavity diode-pumped laser and the working frequency of the high-frequency LED and the double-cavity diode-pumped laser and the high-speed camera with a high-pass filter are set according to experimental requirements, each part is triggered in sequence in the same acquisition cycle through a synchronizer, it is ensured that one frame of image captured by the camera in a double-frame mode is a shadow image in a backlight source, and the other frame is a PIV particle image in a laser irradiation environment, and the laboratory is kept in dark conditions;

[0016] When the experiment starts, the switches of the double-cavity diode-pumped laser and the high-frequency LED are turned on, the double-cavity diode-pumped laser and the high-frequency LED are controlled through a data processing device and a synchronizer, two-phase flow experiments are carried out in the camera shooting range in the water tank to be measured, repeated experiments are carried out after the flow field is stable, and the power supply of the double-cavity diode-pumped laser and the high-frequency LED is turned off after the experiment is completed.

[0017] The shadow image is processed, the global threshold and the local threshold are determined through the phase interface detection, the phase boundary is determined, the captured shadow image is converted into a black and white image, after filtering through image morphological opening operation, the bubble size, position and shape are obtained, and the bubble center is identified, and then the bubble speed can be calculated through the PTV method.

[0018] The gas phase profile obtained from the shadow image performs dynamic masking on the PIV particle images of adjacent frames, generates a dynamic mask from the shadow image by isolating the moving gas phase to be masked, and removes the gas phase information in the particle image through the mask, and obtains the liquid phase flow field structure through post-processing of the particle image.

[0019] The beneficial effects brought by the present application are as follows:

[0020] As can be seen from the above scheme, the present application provides a gas-liquid two-phase flow measurement system and method based on coupling of PIV and shadow imaging technology, which comprises a high-frequency LED, a synchronizer, a double-cavity diode-pumped laser, a data processing device and a high-speed camera with a high-pass filter. The high-frequency LED and the double-cavity diode-pumped laser are connected with the synchronizer; the high-speed camera with a high-pass filter operates in a double-frame mode and is installed with a high-pass filter in front of the lens, and the high-speed camera is connected with the data processing device and the synchronizer respectively; the synchronizer is connected with the data processing device. The technical scheme of the present application can measure the size, position, shape and speed of the gas phase and measure the liquid phase flow field structure, and accurately measure the interface of the gas-liquid two-phase flow. BRIEF DESCRIPTION OF DRAWINGS

[0021] Figure 1 A structure schematic diagram of a gas-liquid two-phase flow measurement system based on coupling of PIV and shadow imaging technology according to an embodiment of the present application is shown;

[0022] Figure 2 A time sequence diagram of an LED, a laser and a high-speed camera of a gas-liquid two-phase flow measurement system based on coupling of PIV and shadow imaging technology according to an embodiment of the present application is shown;

[0023] Figure 3 An original particle image captured by a high-speed camera in a gas-liquid two-phase flow measurement system based on coupling of PIV and shadow imaging technology according to an embodiment of the present application is shown;

[0024] Figure 4 An original shadow image captured by a high-speed camera in a gas-liquid two-phase flow measurement system based on coupling of PIV and shadow imaging technology according to an embodiment of the present application is shown;

[0025] Figure 5A processed shadow image in a gas-liquid two-phase flow measurement system based on coupling of PIV and shadow imaging technology according to the embodiment of the application is shown;

[0026] In the figure: 1 is a water tank to be measured, 2 is a high-frequency LED, 3 is a synchronizer, 4 is a double-cavity diode-pumped laser, 5 is a data processing device, and 6 is a high-speed camera with a high-pass filter. DETAILED DESCRIPTION

[0027] To make the objectives, technical solutions and advantages of the application clearer, the technical solutions in the embodiments of the application will be described clearly and completely below with reference to the accompanying drawings of the embodiments of the application. Obviously, the described embodiments are some but not all of the embodiments of the application. Based on the embodiments in the application, all other embodiments obtained by those of ordinary skill in the art without creative work fall within the protection scope of the application.

[0028] In the embodiments of the application, a gas-liquid two-phase flow measurement system and method based on coupling of PIV and shadow imaging technology are provided, which can realize measurement of characteristics such as size, position, shape and speed of the gas phase and measurement of the liquid phase flow field structure, and can also realize accurate measurement of the interface between the gas and liquid phases.

[0029] A gas-liquid two-phase flow measurement system based on coupling of PIV and shadow imaging technology mainly comprises a water tank to be measured, a high-frequency LED, a synchronizer, a double-cavity diode-pumped laser, a data processing device and a high-speed camera with a high-pass filter. The water tank to be measured is provided with fluorescent particles that are uniformly distributed and have good suspension properties. The high-frequency LED and the diode-pumped laser are connected with the synchronizer. The high-speed camera is operated in a double-frame mode, and a high-pass filter is installed in front of the lens. The high-speed camera is connected with the data processing device and the synchronizer. The synchronizer is connected with the data processing device. The diode-pumped laser can generate green light with a wavelength of 527 nm. The fluorescent particles used in the PIV test are rhodamine 6G that absorbs green light with a wavelength of 527 nm and emits red light with a wavelength not less than 590 nm. The high-pass filter of the high-speed camera allows light with a wavelength exceeding 590 nm to pass through.

[0030] Q1 signals are sent to the high-frequency LED and Q2 signals are sent to the diode-pumped laser in a pulse modulation mode, so that the laser and the LED intermittently work at the same frequency. The intensity of the LED and the laser can be controlled by the pulse width. The high-speed camera is operated in a double-frame mode. By setting the camera shooting frequency and the frequency of the laser and the LED, the two frames of images continuously shot by the double-frame camera are one PIV image and one shadow image of the backlight source. This unique timing design and simple experimental device setting reduce the experimental cost and simplify the hardware configuration structure, and the measurement is accurate and can be applied to various experimental environments.

[0031] In the embodiment of the present application, the data processing device is a computer. It can be understood that in other embodiments of the present application, other devices with data processing functions can also be selected, and the present application does not make specific limitations here.

[0032] In another embodiment of the present application, a gas-liquid two-phase flow measurement method based on coupling of PIV and shadow imaging technology is provided. That is, a high-speed camera shoots a shadow image in a back light source environment as a gas phase in a water tank to be measured. A phase boundary is determined by setting a global threshold value and a local threshold value through phase interface detection. The shot shadow image can be converted into a black and white image. After filtering through image morphological opening operation, the gas bubble size, position, shape, speed and the like can be obtained. Since the interval between two frames in the double frame mode is extremely short, the gas phase profile obtained from the shadow image can dynamically mask the PIV particle image, and then the particle image is post-processed to obtain the liquid phase flow field structure. This method has a simple image processing process. The gas phase characteristics can be measured through the shadow image, and the shadow image can also be applied as a mask image to the PIV image. The accurate gas-liquid two-phase flow structure can also be obtained at the gas-liquid boundary.

[0033] As shown in Figures 1 to 5 , Figure 1 , a structure schematic diagram of a gas-liquid two-phase flow measurement system based on coupling of PIV and shadow imaging technology according to an embodiment of the present application is shown, Figure 2 , a time sequence diagram of an LED, a laser and a high-speed camera of a gas-liquid two-phase flow measurement system based on coupling of PIV and shadow imaging technology according to an embodiment of the present application is shown, Figure 3 , an original particle image shot by a high-speed camera in a gas-liquid two-phase flow measurement system based on coupling of PIV and shadow imaging technology according to an embodiment of the present application is shown, Figure 4 , an original shadow image shot by a high-speed camera in a gas-liquid two-phase flow measurement system based on coupling of PIV and shadow imaging technology according to an embodiment of the present application is shown, Figure 5 , a processed shadow image in a gas-liquid two-phase flow measurement system based on coupling of PIV and shadow imaging technology according to an embodiment of the present application is shown.

[0034] A gas-liquid two-phase flow measurement system based on coupling of PIV and shadow imaging technology is connected in the manner as shown in Figure 1 . After connection, fluorescent particles are scattered in the water tank to be measured. The pulse width of the high-frequency LED and the double-cavity diode-pumped laser, and the working frequency of the high-speed camera with a high-pass filter are set according to the experimental requirements. Each part is controlled through a synchronizer to be triggered in sequence in the same acquisition cycle as shown in Figure 2 . It is ensured that one of the images shot by the high-speed camera in the double frame mode is a shadow image in the back light source, and the other is a PIV particle image in the laser irradiation environment. The laboratory is kept in dark conditions, and the experimental results are shown in FIG. 8.Figure 3 and Figure 4 as shown.

[0035] After starting the experiment, the switch of the double-cavity diode-pumped laser and the high-frequency LED is opened, and the control is performed through the data processing device and the synchronizer, the two-phase flow experiment is performed in the camera shooting range in the water tank to be tested, the repeated experiment is performed after the flow field is stable, and the power supply of the double-cavity diode-pumped laser and the high-frequency LED is turned off after the experiment is completed, and the experimental data is processed.

[0036] First, the shadow image is processed, the phase boundary is determined by phase interface detection setting global threshold and local threshold, the shot shadow image is converted into a black and white image, after filtering through image morphological opening operation, the acquisition of bubble size, position and shape is realized, and the bubble centroid is identified, and the bubble speed can be calculated through the PTV method.

[0037] In the embodiment of the present application, since the interval between the two frames in the double-frame mode is extremely short, the gas phase profile obtained from the shadow image can dynamically mask the PIV particle image of the adjacent frame, the moving gas phase to be masked is isolated, a dynamic mask can be generated from the shadow image, the gas phase information in the particle image can be removed through the mask, and then the liquid phase flow field structure is obtained through post-processing of the particle image.

[0038] The above is the preferred embodiment of the present application, and it should be noted that for ordinary skilled in the art, without departing from the principles of the present application, a number of improvements and refinements can be made, and these improvements and refinements should be considered as the protection scope of the present application.

Claims

1. A gas-liquid two-phase flow measurement system based on coupling of PIV and shadow imaging technology, characterized in that, The measurement system comprises a high-frequency LED, a synchronizer, a double-cavity diode-pumped laser, a data processing device and a high-speed camera with a high-pass filter; The high-frequency LED and the double-cavity diode-pumped laser are connected with the synchronizer; the high-speed camera with the high-pass filter operates in a double-frame mode, a high-pass filter is installed in front of a lens, and the high-speed camera is connected with the data processing device and the synchronizer respectively; the synchronizer is connected with the data processing device; The fluorescent particles that are evenly distributed and suspended are added in a to-be-measured tank, the double-cavity diode-pumped laser is used to emit green light of a first wavelength, and the high-pass filter of the high-speed camera allows light of a second wavelength to pass through; a Q1 signal is sent to the high-frequency LED in a pulse modulation mode, and a Q2 signal is sent to the double-cavity diode-pumped laser, the double-cavity diode-pumped laser and the high-frequency LED intermittently work at the same frequency respectively; the high-speed camera operates in a double-frame mode, and the shooting frequency of the high-speed camera and the frequencies of the laser and the high-frequency LED are set so that two frames of images continuously shot by the high-speed camera are a PIV image and a shadow image of a backlight source respectively; The shadow image shot by the high-speed camera in the environment of the backlight source is a gas phase in the to-be-measured tank, the phase boundary is determined by phase interface detection by setting a global threshold value and a local threshold value, the shot shadow image is converted into a black-and-white image, and data information including at least bubble size, position, shape and speed is obtained after image morphology operation and filtering.

2. The gas-liquid two-phase flow measurement system based on the coupling of PIV and shadow imaging technology according to claim 1, characterized in that, The fluorescent particles that are evenly distributed and suspended are added in a to-be-measured tank, the double-cavity diode-pumped laser is used to emit green light of a first wavelength, and the high-pass filter of the high-speed camera allows light of a second wavelength to pass through; a Q1 signal is sent to the high-frequency LED in a pulse modulation mode, and a Q2 signal is sent to the double-cavity diode-pumped laser, the double-cavity diode-pumped laser and the high-frequency LED intermittently work at the same frequency respectively; the high-speed camera operates in a double-frame mode, and the shooting frequency of the high-speed camera and the frequencies of the laser and the high-frequency LED are set so that two frames of images continuously shot by the high-speed camera are a PIV image and a shadow image of a backlight source respectively; The first wavelength is 527 nm, and the second wavelength is 590 nm.

3. The gas-liquid two-phase flow measurement system based on the coupling of PIV and shadow imaging technology according to claim 1, characterized in that, The intensities of the high-frequency LED and the double-cavity diode-pumped laser are controlled by pulse width.

4. The gas-liquid two-phase flow measurement system based on the coupling of PIV and shadow imaging technology according to claim 1, characterized in that, The method comprises:

5. A method for measuring gas-liquid two-phase flow based on coupling of PIV and shadow imaging technology, based on the gas-liquid two-phase flow measurement system according to any one of claims 1 to 4, characterized in that, The fluorescent particles are distributed in a to-be-measured tank, the pulse widths of the high-frequency LED and the double-cavity diode-pumped laser and the working frequencies of the high-frequency LED, the laser and the high-speed camera with the high-pass filter are set according to experimental requirements, each part is triggered in sequence in a same acquisition cycle by a synchronizer, it is ensured that one frame of image shot by the high-speed camera in a double-frame mode is a shadow image in a backlight source, and the other frame is a PIV particle image in a laser irradiation environment, and a laboratory is kept in dark conditions; After the experiment starts, the switches of the laser and the high-frequency LED are turned on, the data processing device and the synchronizer are controlled, two-phase flow experiments are carried out in a camera shooting range in the to-be-measured tank, repeated experiments are carried out after a flow field is stable, and the power supplies of the laser and the high-frequency LED are turned off after the experiment is completed; The shadow image is processed, the phase boundary is determined by phase interface detection by setting a global threshold value and a local threshold value, the shot shadow image is converted into a black-and-white image, and bubble size, position and shape are obtained after image morphology operation and filtering, and bubble speed is calculated by a PTV method after bubble centers are recognized. ​ The shadow image obtains the gas phase profile to dynamically mask the PIV particle images of adjacent frames, generates a dynamic mask from the shadow image by isolating the moving gas phase to be masked, removes the gas phase information in the particle image by masking, and obtains the liquid phase flow field structure by post-processing the particle image.

Images