Observation Device for Droplet Collision with Metal Bottom Plate and Its Application

Abstract

The present invention belongs to the field of engineering thermophysics / aircraft safety technology, and relates to an observation device for droplet collision with a metal bottom plate and its application. The observation device of the present invention includes a lifting table, a data acquisition device, and a data analysis system. The experimental device can quantitatively measure the dynamic parameters such as the spreading radius, movement and sliding distance, and rebound height of the liquid droplet on the surface of the sample stage. At the same time, based on the light transmittance of the liquid droplet measured by a high-speed camera and the surface temperature of the liquid droplet measured by a high-speed infrared camera, the surface temperature distribution and phase change time of the liquid droplet can be studied. The data analysis uses a MATLAB program independently developed by the laboratory, which ensures the convenience and accuracy of data analysis. The entire system is of great significance for the research on the motion and phase change heat characteristic behaviors, laws, and mechanisms of water droplets impacting a solid cold surface or metal droplets impacting the surfaces of different metal materials.

Description

Technical Field

[0001] The present invention belongs to the technical field of engineering thermophysics / aircraft safety, and relates to an observation device for liquid droplets colliding with a metal bottom plate and its application. Background Technique

[0002] Aircraft have the characteristics of high speed and comfort, and play an indispensable role in the current global economic development. The "Statistical Bulletin on the Development of the Civil Aviation Industry in 2018" released by the Civil Aviation Administration of China shows that: in the past five years, the average annual growth rate of passenger transportation in the entire industry has exceeded 10%, and the average annual growth rate of cargo transportation has also exceeded 5%. The "Expected Report on Air Passenger Transportation in the Next 20 Years" released by the International Air Transport Association shows that the aviation industry will still maintain a strong development momentum, and at the same time, China is expected to become the world's largest civil aviation passenger market within 5 years. However, it is worth noting that once an aircraft accident occurs, it often causes heavy property and economic losses and casualties. For example, on November 21, 2004, the air crash of China Eastern Airlines Flight MU5210 resulted in a tragic accident in which a total of 57 passengers, crew members and ground staff on board died. After investigation, the expert group believed that the frost formation on the wing caused by the aircraft staying overnight in Baotou led to a decrease in the critical angle of attack of the wing stall, aircraft stall, and finally crash. Another example is the cargo hold fire accident of Air China CA183 on August 27, 2019. After investigation, it was found that a large amount of aluminum alloy materials were melted and dripped on the sandwich insulation material, interior decoration and goods, inducing a rapid development of the fire.

[0003] The accident analysis of aircraft wing icing, high-temperature molten droplets, etc. shows that the research on the dynamic and thermodynamic behaviors of metal droplets or water droplets falling on the surface of solid materials is of great significance for improving the safety performance of civil aircraft. At present, Patent CN109253947A discloses "an experimental device and method for high-temperature molten metal droplets hitting a wall under a negative pressure environment", which provides a method for quantitatively studying the dynamic characteristics of high-temperature droplets colliding with a metal bottom plate. However, this patent does not involve the temperature change of the droplets themselves during the process of droplet falling, rebounding and spreading. Considering that the droplets will be affected by air resistance during the falling process, the velocity of the droplets immediately before collision is generally calculated by the following formula. The calculation method is: let the droplets fall with an initial velocity U0 and collide with the metal bottom plate, and the falling velocity of the droplets is:

[0004]

[0005] where g is the acceleration due to gravity, H0 is the falling height of the droplets, α is a dimensionless constant, α = 3ρ α C f / (8ρ w R0), ρ α 、ρ ωrespectively represent the air density and the droplet density, and R0 is the ideal gas constant. According to the empirical formula, in the embodiments of the present invention, since the Reynolds number Re < 1000, C f generally takes a value of 0.44.

[0006] Patent CN106682380A discloses a "method and device for obtaining the maximum spreading diameter of a droplet hitting a wall", which considers the influence of the wall wetting effect on the maximum value of the spreading diameter and improves the calculation accuracy of the maximum spreading diameter, but does not involve the phase change process of the droplet itself and the research on its heat transfer characteristics to the bottom plate. Summary of the Invention

[0007] The object of the present invention is to propose an observation device for a droplet colliding with a metal bottom plate and its application, which is used to study the coupled influence of the collision motion and phase change heat exchange of the droplet, in order to master the mechanism, critical conditions, evolution laws and control methods, etc. when the droplet collides with the metal plate.

[0008] The observation device for a droplet colliding with a metal bottom plate proposed by the present invention includes a lifting table device, a high-speed camera, a high-speed infrared camera and a data analysis system; a stepping motor is provided on the lifting table, and the top of the lifting table is provided with an upper working surface of the lifting table with a temperature control coil. The metal bottom plate is nested in the upper working surface of the lifting table. At the same time, the temperature control coil on the upper working surface of the lifting table is connected to a temperature controller with adjustable voltage magnitude, and a patch thermocouple is embedded at the center position of the metal bottom plate; the high-speed camera and the high-speed infrared camera are respectively located on both sides of the lifting table device, and the data analysis system is respectively connected to the high-speed camera and the high-speed infrared camera through signal lines.

[0009] Using the observation device for a droplet colliding with a metal bottom plate of the present invention to observe the initial velocity when the droplet collides with the metal bottom plate includes the following steps:

[0010] (1) Record the video of the droplet falling process, and read the video frame by frame, that is, split the video into consecutive photos;

[0011] (2) Select two photos before and after the droplet collides with the metal bottom plate from the consecutive photos;

[0012] (3) According to the pixel positions of the droplet in the two photos before and after, use the following formula to calculate the initial velocity U0 of the droplet when it collides with the metal bottom plate:

[0013]

[0014] where P2 and P1 are the pixel coordinates of the bottom of the droplet in the height direction in the two frames of images before and after the bottom of the droplet collides with the metal bottom plate, r is the ratio of the unit pixel length to the actual length, and f is the sampling frame rate of the high-speed camera used to obtain the video of the droplet falling process.

[0015] The observation device for droplets colliding with a metal bottom plate of the present invention is used to observe the spreading length and rebound height when the droplets collide with the metal bottom plate, and includes the following steps:

[0016] (1) Use a high-speed camera to record the video of the process of droplets colliding with the metal bottom plate, and obtain a series of consecutive photos of the droplets changing on the metal bottom plate frame by frame from the video, that is, a series of three-base images including red, green, and blue. Respectively convert the series of three-base images into grayscale graphics;

[0017] (2) Perform binarization processing on all the grayscale graphics in step (1) to obtain black-and-white images, and record the value of the black pixel points in all the black-and-white images as 0 and the value of the white pixel points as 1;

[0018] (3) When the stepping motor 6 of the lifting table 2 makes the metal bottom plate in a horizontal state, process all the black-and-white images in step (2): that is, for the white pixel points assigned a value of 1, multiply the maximum value x of the white pixel points in the X direction by the ratio r of the unit pixel length to the actual length, and calculate to obtain the actual spreading length D of the droplet. Multiply the maximum value y of the single row of white pixel points in the Y direction by the ratio r of the unit pixel length to the actual length, and calculate to obtain the actual rebound height H of the droplet:

[0019]

[0020] When the stepping motor of the lifting table makes the metal bottom plate in an inclined state, use the following formula to calculate the actual spreading length D of the droplet:

[0021] D = X α +X β =(x α +x β )×r

[0022] where X α is the upper sliding distance X α of the droplet on the inclined bottom plate, X β is the lower sliding distance of the droplet on the inclined bottom plate, x α , x β are respectively the maximum values of the number of pixels in the single rows of the upper and lower inclined planes with the center point of the droplet hitting the metal bottom plate as the boundary in the black-and-white image of step (2), and r is the ratio of the unit pixel length to the actual length.

[0023] The observation device for droplets colliding with a metal bottom plate of the present invention is used to determine the solid-liquid interface during the phase change of the droplet when it collides with the metal bottom plate. The specific process is as follows:

[0024] The droplet phase change refers to the process in which a water droplet releases heat and freezes on the surface of a low-temperature metal material, or a metal droplet releases heat and condenses into a solid state. For the condensation of a water droplet into ice, an image captured by a high-speed camera is used. The turbid part of the droplet in the image is determined as the ice body. The turbidity of the droplet means that an ice-water mixture is formed inside the droplet, that is, re-vaporization occurs. For a metal droplet, according to the metal melting point, the metal droplet has different light transmittances at different temperatures. Through a high-speed infrared camera, the solid-liquid interface of the metal melt droplet is observed when the metal droplet collides with the metal bottom plate.

[0025] Using the observation device for droplet collision with a metal bottom plate of the present invention to determine the nucleation temperature of the bottom plate droplet, the start time of the phase change, and the phase change time when the droplet collides with the metal bottom plate, includes the following steps:

[0026] (1) Record the video of the process of the droplet colliding with the metal bottom plate with a high-speed camera to obtain a video frame sequence;

[0027] (2) When the droplet collides with the metal bottom plate, measure the temperature T at the bottom of the droplet during the change process of the droplet when the droplet collides with the metal bottom plate through a 1 cm × 1 cm patch thermocouple on the surface of the metal bottom plate;

[0028] (3) Compare the temperature T at the bottom of the droplet in step (1) with the nucleation temperature T0 of the metal droplet. When T = T0, record this moment as t0, and t0 is the start time of the droplet phase change process;

[0029] (4) Continue to record the temperature T at the bottom of the droplet at different moments during the change process of the droplet, and use the following formula to obtain the time interval t when the droplet condenses from the bottom to different heights:

[0030] t = n / f - t0

[0031] Wherein, f is the sampling frequency of the high-speed camera, n is the serial number of the video frame in step (1) corresponding to when the droplet phase change condenses to the set height, and the serial number of the photo frame when the droplet touches the metal top plate is 0.

[0032] In the application of the above observation device for droplet collision with a metal bottom plate, the droplet material is deionized water or a high-temperature melt of aluminum, tin, or magnesium alloy.

[0033] In the application of the above observation device for droplet collision with a metal bottom plate, the metal bottom plate is a typical material for aircraft such as copper, aluminum, or magnesium alloy, and the surface texture and shape of the metal bottom plate are processed.

[0034] The observation device for droplet collision with a metal bottom plate and its application proposed by the present invention have the following advantages:

[0035] The observation device for a droplet colliding with a metal bottom plate of the present invention is an experimental device that can quantitatively study the movement and phase change process of droplets on the surface of a metal plate. It is used to analyze the influence of the bottom plate platform material, height, inclination angle, and shape on the movement and spreading and shrinking behavior characteristics of dripping droplets under different temperature metal bottom plate conditions. Based on the images of a high-speed camera and a high-speed infrared camera, it can more accurately study the advancement of the solid-liquid interface of the droplet and the phase change time. The device of the present invention is used to study the subject of the coupled influence of droplet collision movement and phase change heat exchange, in order to master the occurrence mechanism, critical conditions, evolution laws, and control methods of physical phenomena such as aircraft wing icing and secondary ignition. The surface temperature of the droplet measured by the high-speed infrared camera of the device of the present invention can study the surface temperature distribution and phase change time of the droplet. The data analysis uses a MATLAB program independently developed by the laboratory, ensuring the convenience and accuracy of data analysis. The entire system is of great significance for the study of the movement, phase change heat characteristics, behaviors, laws, and mechanisms of water droplets impacting a solid cold surface or metal droplets impacting the surface of different metal materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 FIG. is a schematic structural diagram of the observation device for a droplet colliding with a metal bottom plate proposed by the present invention.

[0037] Figure 2 FIG. is a schematic principle diagram of using the device of the present invention to observe the spreading and sliding of a droplet impacting a horizontal metal bottom plate.

[0038] Figure 3 FIG. is a schematic principle diagram of using the device of the present invention to observe the spreading and sliding of a droplet impacting an inclined metal bottom plate.

[0039] Figures 1 - 3 In FIG., 1 is a droplet, 2 is a lifting table device, 3 is the upper working surface of the lifting table with a temperature control coil, 4 is a patch thermocouple, 5 is a metal bottom plate, 6 is a stepping motor, 7 is a high-speed camera, 8 is a high-speed infrared camera, 9 is a data analysis system, 10 is a thermostat that can adjust the voltage magnitude, 11 is the phase change volume of the droplet, 12 is the spreading distance D of the droplet, 13 is the rebound height H of the droplet, 14 is the left sliding distance x of the droplet α , 15 is the right sliding distance x of the droplet β . DETAILED DESCRIPTION OF THE EMBODIMENTS

[0040] The observation device for a droplet colliding with a metal bottom plate proposed by the present invention has a schematic structural diagram as shown in Figure 1As shown in the figure, it includes a lifting table device 2, a high-speed camera 7, a high-speed infrared camera 8, and a data analysis system 9; a stepping motor 6 is provided on the lifting table 2, and a working surface on the upper layer of the lifting table with a temperature control coil is provided at the top of the lifting table 2. The metal bottom plate 5 is nested in the working surface on the upper layer of the lifting table. At the same time, the temperature control coil on the working surface on the upper layer of the lifting table is connected to a thermostat 10 whose voltage magnitude can be adjusted. The patch thermocouple 4 is embedded at the center position of the metal bottom plate 5; the high-speed camera 7 and the high-speed infrared camera 8 are respectively located on both sides of the lifting table device 2, and the data analysis system 9 is respectively connected to the high-speed camera 7 and the high-speed infrared camera 8 through signal lines.

[0041] The application of the observation device for a droplet colliding with a metal bottom plate proposed by the present invention is for observing the initial velocity when a droplet collides with a metal bottom plate, and includes the following steps:

[0042] (1) Record the video of the droplet falling process, and read the video frame by frame, that is, split the video into consecutive photos;

[0043] (2) Select two photos before and after the droplet collides with the metal bottom plate from the consecutive photos;

[0044] (3) According to the pixel positions of the droplet in the two photos before and after, use the following formula to calculate the initial velocity U0 of the droplet when it collides with the metal bottom plate:

[0045]

[0046] Where P2 and P1 are the pixel coordinates of the bottom of the droplet in the height direction in the two frames of images before and after the bottom of the droplet collides with the metal bottom plate, r is the ratio of the unit pixel length to the actual length, and f is the sampling frame rate of the high-speed camera used to obtain the video of the droplet falling process.

[0047] After calculation, the speed obtained through the above pixel analysis differs from the speed calculated in the background technology by within 0.01 m / s.

[0048] Using the observation device for a droplet colliding with a metal bottom plate of the present invention to observe the spreading length and rebound height when a droplet collides with a metal bottom plate, includes the following steps:

[0049] (1) Use the high-speed camera 8 to record the video of the process of the droplet 1 colliding with the metal bottom plate 5, and obtain a series of consecutive photos of the change of the droplet on the metal bottom plate from the video, that is, a series of three-primary color images including red, green, and blue, and convert the series of three-primary color images into grayscale graphics respectively;

[0050] (2) Perform binarization processing on all the grayscale graphics in step (1) to obtain black-and-white images, and record the value of the black pixel points in all the black-and-white images as 0 and the value of the white pixel points as 1;

[0051] (3) When the stepping motor 6 of the lifting platform 2 makes the metal bottom plate in a horizontal state, as Figure 2 shown, process all the black and white images in step (2): that is, for the white pixel points assigned a value of 1, multiply the maximum value x of the white pixel points in the X direction by the ratio r of the unit pixel length to the actual length to calculate the actual spreading length D of the droplet, and multiply the maximum value y of the single row of white pixel points in the Y direction by the ratio r of the unit pixel length to the actual length to calculate the actual rebound height H of the droplet:

[0052]

[0053] When the stepping motor 6 of the lifting platform 2 makes the metal bottom plate in an inclined state, as Figure 3 shown, use the following formula to calculate the actual spreading length D of the droplet:

[0054] D = X α + X β = (x α + x β ) × r

[0055] where X α is the upward sliding distance X α of the droplet on the inclined bottom plate, X β is the downward sliding distance of the droplet on the inclined bottom plate, x α , x β are respectively the maximum values of the number of pixels in the single rows of the upper and lower inclined planes bounded by the center point of the droplet hitting the metal bottom plate in the black and white image of step (2), and r is the ratio of the unit pixel length to the actual length.

[0056] Use the observation device for droplet collision with the metal bottom plate of the present invention to measure the solid-liquid interface during the phase change of the droplet colliding with the metal bottom plate. The specific process is as follows:

[0057] The droplet undergoes a phase change where a water droplet releases heat and freezes on the surface of a low-temperature metal material, or a metal droplet releases heat and condenses into a solid state. For the condensation of a water droplet into ice, use the image captured by the high-speed camera 7 and determine the turbid part of the droplet in the image as the ice crystal body. The turbidity of the droplet means that an ice-water mixture is formed inside the droplet, that is, re-evaporation occurs; for a metal droplet, according to the melting point of the metal, the metal droplet has different light transmittances at different temperatures. Observe the solid-liquid interface of the molten metal droplet when it collides with the metal bottom plate through the high-speed infrared camera 8.

[0058] Use the observation device for droplet collision with the metal bottom plate of the present invention to determine the nucleation temperature of the bottom plate droplet, the start time of the phase change, and the phase change time when the droplet collides with the metal bottom plate, including the following steps:

[0059] (1) Use a high-speed camera 8 to record the video of the process of the droplet 1 colliding with the metal bottom plate 5 to obtain a video frame sequence;

[0060] (2) When the droplet collides with the metal bottom plate, use the 1 cm × 1 cm patch thermocouple 4 on the surface of the metal bottom plate to measure the temperature T at the bottom of the droplet during the change process of the droplet when the droplet 1 collides with the metal bottom plate 5;

[0061] (3) Compare the temperature T at the bottom of the droplet in step (1) with the nucleation temperature T0 of the metal droplet. When T = T0, since the droplet under study cools from the bottom under the cooling effect on the surface of the droplet, record this moment as t0, and t0 is the start time of the droplet phase change process;

[0062] (4) Continue to record the temperature T at the bottom of the droplet at different moments during the change process of the droplet. Use the following formula to obtain the time interval t when the droplet condenses from the bottom to different heights:

[0063] t = n / f - t0

[0064] where f is the sampling frequency of the high-speed camera 8, n is the serial number of the video frame in step (1) corresponding to when the droplet phase change condenses to the set height, and the serial number of the photo frame when the droplet touches the metal top plate is 0;

[0065] In the application of the above-described observation device for a droplet colliding with a metal bottom plate, the material of the droplet is deionized water or a high-temperature melt of aluminum, tin, or magnesium alloy.

[0066] In the application of the above-described observation device for a droplet colliding with a metal bottom plate, the metal bottom plate is a typical material for aircraft such as copper, aluminum, or magnesium alloy, and the surface texture and shape of the metal bottom plate are processed.

[0067] The following will describe the content of the present invention in detail with reference to the accompanying drawings:

[0068] The observation device for a droplet colliding with a metal bottom plate of the present invention, as Figure 1As shown in the figure, it includes a lifting platform, a data acquisition device, and a data analysis system. The lifting platform can be used to adjust the temperature, height, and tilt angle of the bottom plate. The lifting platform with adjustable height is controlled by a stepper motor 6 to precisely control the distance between the liquid droplet and the metal bottom plate, thereby changing the initial collision velocity of the liquid droplet. Its height change range is 5 - 80 cm, and the corresponding liquid droplet velocity range is 1 - 4 m / s. At the same time, the sample stage bottom plate on the upper working surface of the lifting platform with a temperature control coil has a temperature control coil, and the temperature change range is 30 - 400 °C. The tilt angle of the lifting platform is adjustable, and it can also move horizontally within a certain range, so as to adjust the position where the liquid droplet drops on the solid surface. During the experiment, first nest the metal bottom plate on the lifting platform at a certain height, and then control the tilt angle of the solid surface to change within the range of 0° to 180° by adjusting the angle of the lifting platform. In addition, the lifting platform can move horizontally within a certain range, so as to adjust the position where the liquid droplet drops on the solid surface. The inlaid design of the test bench surface ensures that metals with different materials and different textured surfaces can be replaced and used according to experimental requirements, as well as the adjustment of the working tilt angle of the metal bottom plate.

[0069] In the data acquisition device, the high-speed camera and the high-speed infrared camera are arranged on both sides of the lifting platform. Figure 2 、 Figure 3 respectively show the changes in the droplet shape and position during the process of the liquid droplet dropping and hitting the horizontal bottom plate and the inclined bottom plate recorded by the high-speed camera (i.e., the actual spreading distance (D) of the liquid droplet in the horizontal top plate, the upper and lower droplet displacement distances x α 、x β , and the liquid droplet rebound height H). The high-speed infrared camera records the change in the surface temperature of the liquid droplet during the experiment to distinguish between the solid and liquid states of the liquid droplet. The patch thermocouple continuously records the temperature of the liquid droplet on the bottom plate surface. The sampling frame rate of the high-speed camera is 2000 Hz to 4000 Hz, and the resolution is 1280 pixels × 1024 pixels. Using it, the collision of the liquid droplet, this short-term instantaneous physical phenomenon, can be completely and detailedly recorded. The resolution of the high-speed infrared camera is 1024 pixels × 96 pixels, the frame rate is 232 Hz, and at 1 / 4 frame 1024 × 96 pixels, the real-time acquisition rate can reach 2300 Hz. The temperature measurement range is 40 - 3000 degrees Celsius, and the measurement accuracy is ±1 °C. A 1 cm × 1 cm K-type chrome-plated aluminum patch thermocouple is placed in the exact middle of the metal bottom plate, directly below the liquid droplet, to measure the temperature in contact with the bottom plate during the phase change process of the liquid droplet movement, and finally determine the nucleation temperature of the liquid droplet on the bottom plate.

[0070] The data analysis system in the observation device of the present invention refers to the use of a MATLAB program independently developed by the laboratory to analyze the dynamic and thermodynamic coupling process of liquid droplets colliding with a solid wall. The data analysis system is used to quantitatively calculate and analyze the initial velocity, spreading distance, rebound height, phase change time, and solid-liquid interface during the process of liquid droplets impacting a metal bottom plate.

[0071] The specific experimental steps are as follows:

[0072] (1) Before the experiment starts, nest the experimental metal material on the lifting platform and adjust the required angle.

[0073] (2) Adjust the intensity of the background light source and the positions of the high-speed camera and the high-speed infrared camera, and focus on the center position of the experimental table to ensure that a clear and complete picture can be recorded.

[0074] (3) Turn on the temperature control coil of the metal bottom plate.

[0075] (4) After the temperature reading of the metal bottom plate reaches the experimental set value and stabilizes, trigger the liquid droplet dropping device, and at the same time use a patch thermocouple and a camera to record the entire change process of the liquid droplet.

[0076] (5) Analyze the collision, movement, and phase change processes of the liquid droplets involved in the process of the liquid droplets colliding with the metal bottom plate.

Claims

1. An observation device for a droplet colliding with a metal bottom plate, characterized in that The device includes a lifting table device, a high-speed camera, a high-speed infrared camera, and a data analysis system; a stepping motor is provided on the lifting table, and an upper working surface of the lifting table with a temperature control coil is provided at the top of the lifting table. A metal bottom plate is nested in the upper working surface of the lifting table. At the same time, the temperature control coil on the upper working surface of the lifting table is connected to a thermostat that can adjust the voltage magnitude. A patch thermocouple is embedded at the center position of the metal bottom plate; the high-speed camera and the high-speed infrared camera are respectively located on both sides of the lifting table device, and the data analysis system is respectively connected to the high-speed camera and the high-speed infrared camera through signal lines; The observation device for droplet impacting the metal bottom plate is used to observe the initial velocity when the droplet impacts the metal bottom plate, including the following steps: (1) Record the video of the droplet falling process, and read the video frame by frame, that is, split the video into consecutive photos; (2) Select two photos before and after the droplet impacts the metal bottom plate from the consecutive photos; (3) Based on the pixel positions of the droplet in the front and rear photos, the initial velocity of the droplet when it collides with the metal bottom plate is calculated using the following formula :[[]]END]] Among them, , are the pixel coordinates of the bottom of the droplet in the height direction in two frames of images before and after the bottom of the droplet collides with the metal bottom plate respectively, is the ratio of the unit pixel length to the actual length, is the sampling frame rate of the high-speed camera used to obtain the video of the droplet falling process.

2. Application of an observation device for droplet collision with a metal bottom plate as described in claim 1, characterized in that The observation device for droplet impacting the metal bottom plate is used to observe the spreading length and rebound height when the droplet impacts the metal bottom plate, including the following steps: (1) Use a high-speed camera to record the video of the droplet impacting the metal bottom plate process, and obtain a series of consecutive photos of the droplet changing on the metal bottom plate from the video, that is, a series of three-base images containing red, green, and blue. Respectively convert a series of three-base images into grayscale graphics; (2) Perform binarization processing on all the grayscale graphics in step (1) to obtain black-and-white images, and record the value of the black pixel points in all the black-and-white images as 0 and the value of the white pixel points as 1; When the stepping motor of the lifting platform makes the metal bottom plate in a horizontal state, all the black and white images obtained in step (2) are processed: for the white pixel points assigned a value of 1, the maximum value of the white pixel points in the X direction is multiplied by the ratio of the unit pixel length to the actual length to calculate the actual spreading length of the droplet ; the maximum value of the single column of white pixel points in the Y direction is multiplied by the ratio of the unit pixel length to the actual length to calculate the actual rebound height of the droplet : When the stepper motor of the lifting platform makes the metal bottom plate in an inclined state, the actual spreading length of the droplet is calculated using the following formula : wherein, is the upward sliding distance of the droplet on the inclined bottom plate , is the downward sliding distance of the droplet on the inclined bottom plate, , are respectively the maximum values of the number of pixels in the single rows of the upper and lower inclined planes bounded by the center point of the droplet hitting the metal bottom plate in the black and white image of step (2), is the ratio of the unit pixel length to the actual length.

3. An application of an observation device for droplet impinging on a metal bottom plate as claimed in claim 1, characterized in that The observation device for droplet impacting the metal bottom plate is used to determine the solid-liquid interface during the phase change of the droplet impacting the metal bottom plate. The specific process is as follows: The droplet undergoes a phase change where a water droplet releases heat and freezes on the surface of a low-temperature metal material, or a metal droplet releases heat and condenses into a solid state. For the water droplet condensing into ice, using the image captured by the high-speed camera, the turbid part of the droplet shown in the image is determined as the ice body. The droplet becoming turbid means that an ice-water mixture is formed inside the droplet, that is, re-evaporation occurs; for the metal droplet, according to the metal melting point, the metal droplet has different light transmittances at different temperatures. Through the high-speed infrared camera, observe the solid-liquid interface of the metal melt droplet when it impacts the metal bottom plate.

4. Application of an observation device for droplet collision with a metal bottom plate as described in claim 1, characterized in that The observation device for droplet impacting the metal bottom plate is used to determine the nucleation temperature of the bottom plate droplet, the start time of the phase change, and the phase change time when the droplet impacts the metal bottom plate, including the following steps: (1) Use a high-speed camera to record the video of the droplet impacting the metal bottom plate process to obtain a video frame sequence; (2) When the droplet impacts the metal bottom plate, measure the temperature T at the bottom of the droplet during the change process of the droplet when the droplet impacts the metal bottom plate through a 1 cm × 1 cm patch thermocouple on the surface of the metal bottom plate; (3) Compare the bottom temperature T of the droplet in step (2) with the nucleation temperature of the metal droplet and when T = , record this moment as , which is the start time of the droplet phase change process; (4) Continuously record the bottom temperature T of the droplet at different moments during the change process of the droplet, and use the following formula to obtain the time interval when the droplet condenses from the bottom to different heights. : Among them, is the sampling frequency of the high-speed camera, is the serial number of the video frame in step (1) corresponding to when the droplet phase change condensation reaches the set height. The serial number of the photo frame when the droplet touches the metal top plate is 0.

5. Application of an observation device for droplet collision with a metal bottom plate as described in claim 1, characterized in that Wherein the droplet material is deionized water or a high-temperature melt of aluminum, tin, or magnesium alloy.

6. An application of the observation device for droplet impacting a metal bottom plate according to claim 1, characterized in that Wherein the metal bottom plate is a typical material of copper, aluminum, or magnesium alloy for aircraft, and the surface texture and shape of the metal bottom plate are processed.

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