CN118032660A - Liquid drop bottom air film interference experimental device and method under high pressure condition - Google Patents
Liquid drop bottom air film interference experimental device and method under high pressure condition Download PDFInfo
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Abstract
The invention discloses a device and a method for testing gas film interference at the bottom of a liquid drop under a high pressure condition, which belong to the field of visual research of liquid drops and gas films.
Description
Technical Field
The invention belongs to the field of visual research of liquid drops and air films, in particular to a visual method in a liquid drop impact process, and mainly relates to visual research of macroscopic morphology of liquid drops and micron-sized air film contours at the bottom of the liquid drops in the liquid drop impact process.
Background
Droplet impingement is common in industrial applications such as spray coating, spray cooling, nuclear power safety, and spray combustion. At present, the research on droplet impact is mostly carried out under normal pressure environment, but the impact behavior of fuel droplets in a combustion chamber of an actual internal combustion engine is often in a high-pressure environment. Therefore, research on droplet impingement in high pressure environments is particularly important.
In the process of impacting the liquid drops, the liquid drops are not fused with the surface of the impacted object at once, and a very thin air film is extruded between the liquid drops and the impacted object, and the air film is of a micron level, but can prevent the liquid drops from being fused with the impacted object, so that the phenomenon of rebound of the liquid drops occurs. The liquid drop rebound caused by the air film can prevent the contact between the liquid drop of the fuel oil and the inner wall surface of the combustion chamber, reduce the generation of an oil film with the wall, promote the evaporation of the fuel oil and the generation of the mixed gas, and improve the combustion efficiency of the fuel oil to a certain extent. Therefore, the gas film profile and thickness measurement at the bottom of the liquid drop under high pressure are of great significance.
However, the existing droplet impact research is mostly carried out under normal pressure environment, and the traditional research adopts high-speed photographic technology to shoot the macroscopic form of the droplet in the droplet impact process under normal pressure from the side, so as to extract the change process of the droplet profile, but the droplet impact behavior under high pressure and the measurement of the micron-sized air film profile at the bottom of the droplet are not paid enough attention. However, the dynamic process of the liquid drop and the air film can be changed in a high-pressure environment, and the liquid drop impact behavior in practical engineering application is often in the high-pressure environment, so that the liquid drop impact process under the high-pressure condition and the measurement of the micron-sized air film are particularly important. The prior art is difficult to realize the requirements of regulating and controlling the impact of liquid drops in the research of gas film dynamics under the high pressure condition and the practical engineering application.
Therefore, the invention provides the measuring device capable of simultaneously obtaining the macroscopic morphology of the liquid drop and the micron-sized air film profile at the bottom of the liquid drop under the high-pressure condition, and the measuring device has important significance for researching the flow heat and mass transfer characteristics in the impact process of the liquid drop under the high-pressure condition. The invention can regulate and control the rebound and fusion process of the liquid drops by regulating the thickness of the air film at the bottom of the liquid drops, further regulate and control the contact process of the liquid drops of the fuel oil of the internal combustion engine and the inner wall surface of the combustion chamber, reduce the generation of the oil film with the wall, promote the evaporation of the fuel oil and the generation of the mixed gas, and improve the combustion efficiency of the fuel oil.
Disclosure of Invention
In view of the above, the invention aims to provide a device and a method for testing the gas film at the bottom of a liquid drop under a high pressure condition, so as to solve the problem that the macroscopic morphology of the liquid drop and the outline of the micron-sized gas film at the bottom of the liquid drop can not be measured simultaneously under the high pressure condition in the existing liquid drop impact research.
In order to achieve the above purpose, the present invention provides the following technical solutions:
The device comprises a constant volume bomb internal pressure control system and a liquid drop generating device; the pressure control system comprises a vacuum pump for vacuumizing the constant volume bomb and a high-pressure nitrogen cylinder for inflating the constant volume bomb; the output end of the liquid drop generating device is communicated with the top end of the constant volume bomb, and liquid drops emitted by the liquid drop generating device vertically fall down along the center of the constant volume bomb; the inside of the constant volume bomb is fixedly provided with ultra-white glass which is horizontally placed and used for receiving the impact of liquid drops; the periphery surface of the constant volume bomb is provided with two side perspective windows symmetrically distributed about the constant volume bomb, and the bottom center of the constant volume bomb is provided with a bottom perspective window;
The side surface of the constant volume bomb is provided with a first image acquisition system for observing the macroscopic form of the liquid drop, and the first image acquisition system comprises an LED lamp and a monochromatic high-speed camera which are respectively arranged outside the side perspective window; the centers of the LED lamp, the monochromatic high-speed camera and the two side perspective windows are all on the same straight line, and the upper surface of the ultra-white glass is positioned below the center line of the side perspective window;
The bottom of the constant volume bomb is provided with a second image acquisition system for observing the micron-sized air film outline at the bottom of the liquid drop, and the second image acquisition system comprises a metal halide lamp, a color high-speed camera and an optical path conversion unit; the light path conversion unit comprises a support piece arranged right below the bottom perspective window and a semi-transparent and semi-reflecting mirror fixedly arranged on the support piece; the semi-transparent semi-reflecting mirror is obliquely arranged towards the metal halide lamp, and the centers of the metal halide lamp and the semi-transparent semi-reflecting mirror are on the same horizontal line.
Further, a liquid drop collector for screening liquid drops is arranged in the constant volume bomb, and the liquid drop collector comprises a rotating motor and a bracket arranged at the output end of the rotating motor; the bracket is fixedly connected with a collecting tank for collecting liquid drops; the collecting tank is positioned above the ultra-white glass.
Further, the light path conversion unit further comprises a plane mirror arranged right below the half mirror; the plane mirror is obliquely arranged towards the color high-speed camera, and the centers of the color high-speed camera and the plane mirror are on the same horizontal line; the plane mirror reflects the light passing through the half mirror to the color high-speed camera.
Further, the constant volume bomb is made of stainless steel materials and comprises a support column, an upper cover plate and a lower cover plate which are fixedly connected to the upper end and the lower end of the support column; sealing gaskets are arranged at the joints of the support columns, the upper cover plate and the lower cover plate, and the support columns, the upper cover plate and the lower cover plate form a high-pressure-resistant sealing chamber together.
Further, a pressure gauge for measuring internal pressure is connected to the constant volume bomb.
The invention also provides a liquid drop bottom air film interference experiment method under the high pressure condition, which comprises the following steps:
s1, adjusting the positions and connection relations of all the components, pumping air into the constant volume bomb by using a vacuum pump to enable the inside of the constant volume bomb to be in a vacuum environment, then inflating the inside of the constant volume bomb by using a high-pressure nitrogen cylinder to change the internal pressure of the constant volume bomb, and enabling a droplet impact experiment to be carried out in the high-pressure nitrogen environment;
S2, controlling a droplet generation device to emit droplets towards the surface of the ultra-white glass, screening the fallen droplets by a droplet collector, removing the droplets with irregular spheres, and starting a rotating motor and driving a bracket and the collector to rotate when continuous droplets with regular spheres appear, so that the droplets with regular spheres fall down and strike the surface of the ultra-white glass;
S3, enabling the liquid drops moving towards the ultra-white glass to pass through a side perspective window of the constant volume bomb, then irradiating the liquid drop impact process, then entering a single-color high-speed camera, recording macroscopic morphological changes in the liquid drop impact process from the side, extracting the liquid drops in the side view image through a self-defined Matlab image processing program, and measuring the size and the speed of the liquid drops;
And S4, when the liquid drops fall and strike on the surface of the ultra-white glass, white light emitted by the metal halide lamp is reflected to the ultra-white glass through the semi-transparent semi-reflective mirror, one part of the white light is reflected from the upper surface of the ultra-white glass, the other part of the white light passes through the ultra-white glass to irradiate the bottom surface of the liquid drops and is reflected from the bottom surface of the liquid drops, two light beams reflected from the ultra-white glass and the bottom of the liquid drops interfere to form interference fringes with different colors, the interference fringes pass through the semi-transparent semi-reflective mirror, then enter the color high-speed camera through the plane mirror, interference fringes of an air film are obtained, and then the interference fringes are processed to obtain the profile curve of the air film at the bottom of the liquid drops.
Further, in the step 3, after the impact process of the side recording droplet is converted into image processing, the edge of the droplet is extracted according to a brightness detection algorithm, and after the hole in the droplet area in the binary image is filled, the pixel number S and centroid coordinates (x, y) of the droplet are calculated, and since the droplet is not completely spherical, the characteristic diameter calculation method of the droplet is as follows:
Wherein, Is the magnification obtained in the calibration process.
Further, in the step 3, the method for calculating the velocity of the droplet includes:
Wherein, And/>Respectively, the ordinate of the mass center of the liquid drop on two continuous images before the liquid drop impact,/>Is the shooting frame rate of the camera.
Further, in the step 4, before extracting the outline of the micron-sized air film at the bottom of the liquid drop, firstly, shooting interference fringes at the bottom of the lens by adopting a white light color interference technology, then calculating the outline distribution of the air film at the bottom of the lens by adopting a MATLAB image processing program, and then calibrating the outline of the air film at the bottom of the liquid drop by using the thickness of the air film corresponding to the interference fringes; the thickness of the air film at the bottom of the lens corresponds to the interference fringe in the radial direction, then the interference fringe of the air film at the bottom of the liquid drop is processed, tangential average is carried out by taking the center of the interference fringe as the center of a circle, then the RGB mode is converted into the CIE1976 color mode, the interference fringe at the bottom of the lens is converted into the CIE1976 color mode from the RGB mode, finally the distance is calculated by using the Euclidean algorithm, the chromatic aberration is calculated, and one of the clearest dark continuous curves in the chromatic aberration diagram is the contour curve of the air film at the bottom of the liquid drop.
The invention has the beneficial effects that:
1. the invention can realize the precise measurement of the micron-sized air film at the bottom of the liquid drop under the high-pressure condition by using the constant-volume elastic fit interference experimental device;
2. the liquid drop collector is arranged in the constant volume bomb, so that not only can redundant liquid drops generated due to the change of the environmental pressure be collected, but also regular spherical liquid drops can be screened out;
3. Two paths of pulse signals of the synchronous control device are adopted to synchronously trigger two high-speed cameras, so that synchronous measurement of macroscopic morphology of the side surface of the liquid drop and the bottom micron-sized air film can be realized.
Additional advantages, objects, and features of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from practice of the invention. The objects and other advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out in the specification.
Drawings
In order to make the objects, technical solutions and advantageous effects of the present invention more clear, the present invention provides the following drawings for description:
FIG. 1 is a schematic illustration of an apparatus for measuring droplet macroscopic morphology and droplet bottom micron-sized gas film profile in accordance with the present invention;
FIG. 2 is a schematic diagram of a constant volume bomb according to the present invention;
FIG. 3 is a schematic diagram of the structure of the optical path conversion unit;
Fig. 4 is a schematic diagram of a droplet generator.
The figures are marked as follows:
1 constant volume bullet, 101 support column, 102 upper cover plate, 103 lower cover plate, 2 drop generating device, 201 power switch, 202 piston, 203 nozzle, 204 propeller, 3 vacuum pump, 4 high pressure nitrogen gas cylinder, 5 ultra white glass, 6 side perspective window, 7 bottom perspective window, 8LED lamp, 9 monochromatic high-speed camera, 10 metal halide lamp, 11 color high-speed camera, 12 light path conversion unit, 1201 support, 1202 semi-transparent semi-mirror, 1203 plane mirror, 13 drop collector, 1301 rotating electrical machine, 1302 support, 1303 collecting tank, 14 manometer, 15 drop.
Detailed Description
As shown in fig. 1 to 4,
The device comprises a constant volume bomb 1, a pressure control system and a liquid drop generating device 2, wherein the pressure control system is communicated with the inside of the constant volume bomb 1; the pressure control system comprises a vacuum pump 3 for vacuumizing the constant volume bomb 1 and a high-pressure nitrogen cylinder 4 for inflating the constant volume bomb 1; the output end of the liquid drop generating device 2 is communicated with the center of the top end of the constant volume bomb 1, and liquid drops 15 emitted by the liquid drop generating device 2 vertically drop along the center of the constant volume bomb 1; the inside of the constant volume bomb 1 is fixedly provided with ultra-white glass 5 which is horizontally placed and used for receiving liquid drops 15; the periphery surface of the constant volume bomb 1 is provided with two side perspective windows 6 symmetrically distributed about the constant volume bomb 1, the bottom center of the constant volume bomb 1 is provided with a bottom perspective window 7, and the perspective windows are all made of quartz glass;
The side surface of the constant volume bomb 1 is provided with a first image acquisition system for observing the macroscopic form of liquid drops 15, and the first image acquisition system comprises an LED lamp 8 and a single-color high-speed camera 9 which are respectively arranged outside the side perspective window 6; the centers of the LED lamp 8, the monochromatic high-speed camera 9 and the two side perspective windows 6 are all on the same straight line, and the upper surface of the ultra-white glass 5 is positioned below the center line of the side perspective window 6;
The bottom of the constant volume bomb 1 is provided with a second image acquisition system for observing the micron-sized air film outline at the bottom of the liquid drop 15, and the second image acquisition system comprises a metal halide lamp 10, a color high-speed camera 11 and an optical path conversion unit 12; the optical path conversion unit 12 includes a support 1201 provided right below the bottom perspective window 7, and a half mirror 1202 fixedly mounted on the support 1201; the half mirror 1202 is obliquely arranged towards the metal halide lamp 10, the oblique angle is 45 degrees, the centers of the metal halide lamp 10 and the half mirror 1202 are on the same horizontal line, the light emitted by the metal halide lamp 10 irradiates the reflecting surface on the half mirror 1202, and the reflecting surface reflects the light to the ultra-white glass 5;
The structure of the droplet generator 2 is shown in fig. 4, and specific device components include a power switch 201, a piston 202, a nozzle 203 and a propeller 204, an inner chamber of the droplet generator 2 is filled with a liquid working medium, the piston 202 is controlled by the power switch 201 to generate droplets 15, the power switch 201 of the droplet generator 2 is a normally open switch, and the opening and closing of the power switch are controlled by a current signal. The magnitude and the energizing time of the current can be regulated and controlled by the switch controller, and the droplet generation device 2 can stably generate droplets 15 at 4000 times per second under the limit working condition. The diameter of the liquid drop 15 is controlled by changing the size of the nozzle 203, and the diameter of the liquid drop 15 can be adjusted to be 0.01-10 mm.
After the constant volume bomb 1 is vacuumized by the vacuum pump 3, pressurizing (0-100 bar) the inside of the constant volume bomb 1 by the high-pressure nitrogen bottle 4, and enabling a droplet 15 impact experiment to be carried out in a nitrogen environment, wherein the impact experiment of the droplet 15 in the nitrogen environment can eliminate the interference of external factors such as ambient humidity and viscosity due to the stable chemical property of nitrogen, the droplet 15 generated by the droplet generating device 2 moves towards the super white glass 5, the light emitted by the LED lamp 8 passes through the side perspective window 6 in the falling process of the droplet 15, irradiates the falling and impact process of the droplet 15, then enters the single-color high-speed camera 9, records macroscopic form change in the impact process of the droplet 15 from the side, and can measure the speed and size of the droplet 15; while the liquid drop 15 strikes the ultra-white glass 5, white light emitted by the metal halide lamp 10 passes through the semi-transparent mirror 1202 and then passes through the perspective window 7 on the bottom surface of the constant volume bomb 1 and is reflected to the ultra-white glass 5, one part of the white light is reflected from the upper surface of the ultra-white glass 5, the other part of the white light passes through the ultra-white glass 5 and irradiates the bottom surface of the liquid drop 15, and is reflected from the bottom surface of the liquid drop 15, two beams of light reflected from the ultra-white glass 5 and the bottom of the liquid drop 15 interfere and enter the color high-speed camera 11, interference fringes of the liquid drop 15 air film are obtained, and then the interference fringes are processed to obtain the profile curve of the liquid drop 15 bottom air film, so that the simultaneous measurement of the macroscopic form of the liquid drop 15 and the micron-level air film profile on the bottom of the liquid drop 15 can be realized.
In this embodiment, a droplet collector 13 for screening the droplets 15 is further disposed in the constant volume bomb 1, and the droplet collector 13 includes a rotating motor 1301 and a bracket 1302 mounted at an output end of the rotating motor 1301; a collecting groove 1303 for collecting the liquid drops 15 is fixedly connected to the bracket 1302; the collecting vat 1303 is located above the ultrawhite glass 5.
Because there is pressure difference between the inside and the outside of the constant volume bullet 1, after the liquid drop 15 sent by the liquid drop generating device 2 enters the high pressure environment from the external normal pressure environment, the shape of the liquid drop 15 produced in the earlier stage may be irregular, or bubbles may exist in the liquid drop 15 and do not meet the test standard, therefore, the liquid drop collector 13 is adopted to screen the spherical regular liquid drop 15, the collecting tank 1303 moves onto the falling track of the liquid drop 15, the irregular liquid drop produced in the earlier stage is collected, when the spherical regular liquid drop 15 is screened, the rotating motor 1301 starts and drives the bracket 1302 and the collecting tank 1303 to rotate, the collecting tank 1303 is not in the moving track of the liquid drop 15, the liquid drop 15 can freely fall onto the surface of the ultra-white glass 5 for the impact test, and the accuracy of data acquisition after the impact test of the liquid drop 15 is ensured.
In this embodiment, the optical path conversion unit 12 further includes a plane mirror 1203 disposed directly below the half mirror 1202; the plane mirror 1203 is obliquely arranged towards the direction of the color high-speed camera 11, the inclination angle is 45 degrees, and the centers of the color high-speed camera 11 and the plane mirror 1203 are on the same horizontal line; the plane mirror 1203 reflects the light passing through the transparent portion of the half mirror 1202 to the color high speed camera 11.
In practical application, because the color high-speed camera 11 is vertically placed below the constant volume bullet 1 to increase the operation difficulty, and the back of the color high-speed camera 11 is provided with a plurality of connectors, the camera can be damaged by inversion, and the optical path needs to be very accurately adjusted during the test, therefore, the angle of the adjusting plane mirror 1203 is more convenient than the angle of the color high-speed camera 11, the moving color high-speed camera 11 can be reduced, the workload is reduced, the beam line can be effectively adjusted, and the accuracy of data acquisition is further improved.
In this embodiment, the constant volume bomb 1 is made of stainless steel material, and comprises a support column 101, and an upper cover plate 102 and a lower cover plate 103 fixedly connected to the upper end and the lower end of the support column 101 through bolts; the connection parts of the support column 101, the upper cover plate 102 and the lower cover plate 103 are respectively provided with a sealing gasket, the support column 101, the upper cover plate 102 and the lower cover plate 103 jointly form a high-pressure-resistant sealing chamber, and a plurality of through holes are formed in the surface of the upper cover plate 102 and are used for connecting external equipment.
In this embodiment, the constant volume bomb 1 is connected with a pressure gauge 14 for measuring internal pressure, wherein the top of the constant volume bomb 1 is further provided with an air inlet valve and an air outlet valve.
The invention also provides a liquid drop bottom air film interference experimental method under the high pressure condition, which comprises the following steps:
s1, adjusting the positions and connection relations of all the components, pumping air in the constant volume bomb 1 by using a vacuum pump 3 to enable the inside of the constant volume bomb 1 to be in a vacuum environment, then inflating the constant volume bomb 1 by using a high-pressure nitrogen cylinder 4 to change the internal pressure of the constant volume bomb, and enabling a droplet 15 impact experiment to be carried out in the high-pressure nitrogen environment;
S2, controlling the droplet generation device 2 to emit droplets 15 towards the surface of the ultra-white glass 5, screening the fallen droplets 15 by the droplet collector 13, removing the droplets 15 with irregular spheres in the early stage, and starting the rotary motor 1301 and driving the bracket 1302 and the collector to rotate when continuous regular spherical droplets 15 appear, so that the regular spherical droplets 15 fall and impact on the surface of the ultra-white glass 5;
S3, enabling light rays emitted by the LED lamp 8 to pass through the lateral perspective window 6 of the constant volume bomb 1 and then irradiate the liquid drops 15 to strike, then entering the single-color high-speed camera 9, recording macroscopic morphological changes in the liquid drops 15 striking process from the lateral surface, extracting the liquid drops 15 in the side view image through a self-defined Matlab image processing program, and measuring the size and the speed of the liquid drops 15;
S4, when the liquid drop 15 falls down and impinges on the surface of the ultrawhite glass 5, white light emitted by the metal halide lamp 10 is reflected to the ultrawhite glass 5 through the half mirror 1202, a part of the light is reflected from the upper surface of the ultrawhite glass 5, the other part of the light passes through the ultrawhite glass 5 to irradiate the bottom surface of the liquid drop 15 (as shown in combination with FIG. 3, a broken line represents a light propagation path), and the two light beams reflected from the bottoms of the ultrawhite glass 5 and the liquid drop 15 interfere to form interference fringes with different colors, pass through the half mirror 1202, enter the color high-speed camera 11 through the plane mirror 1203, obtain interference fringes of an air film, and process the interference fringes to obtain a profile curve of the air film at the bottom of the liquid drop 15.
In this embodiment, in the step 3, after the impact process of the side recording droplet 15 is converted into image processing, the edge of the droplet 15 is extracted according to the brightness detection algorithm, the pixel number S and the centroid coordinates (x, y) of the droplet 15 are calculated after the hole in the region of the droplet 15 in the binary image is filled, and the characteristic diameter calculation method of the droplet 15 is as follows: ; wherein/> Is the magnification obtained in the calibration process.
In this embodiment, in the step 3, the method for calculating the velocity of the droplet 15 is as follows: ; wherein, And/>Respectively the ordinate of the centroid of the drop 15 on two consecutive images before the drop 15 strikes,/>Is the shooting frame rate of the camera.
In the embodiment, in the step 4, before extracting the outline of the micron-sized air film at the bottom of the droplet 15, firstly, shooting interference fringes at the bottom of a lens (with known curvature radius) by adopting a white light color interference technology, then calculating the outline distribution of the air film at the bottom of the lens by adopting a MATLAB image processing program, and then calibrating the outline of the air film at the bottom of the droplet 15 according to the thickness of the air film corresponding to the interference fringes; the thickness of the air film at the bottom of the lens corresponds to the interference fringes in the radial direction, then the interference fringes of the air film at the bottom of the liquid drop 15 are processed, tangential average is carried out by taking the center of the interference fringes as the center of a circle, then the interference fringes at the bottom of the lens are converted into a CIE1976 color mode from an RGB mode, then the interference fringes at the bottom of the lens are converted into the CIE1976 color mode from the RGB mode, finally the distance is calculated by adopting a Euclidean algorithm, the chromatic aberration is calculated, and one of the clearest dark continuous curves in the chromatic aberration diagram is the contour curve of the air film at the bottom of the liquid drop 15.
Finally, it is noted that the above-mentioned preferred embodiments are only intended to illustrate rather than limit the invention, and that, although the invention has been described in detail by means of the above-mentioned preferred embodiments, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the scope of the invention as defined by the appended claims.
Claims (9)
1. The utility model provides a liquid drop bottom air film interference experimental apparatus under high pressure condition which characterized in that: comprises a constant volume bomb internal pressure control system and a liquid drop generating device; the pressure control system comprises a vacuum pump for vacuumizing the constant volume bomb and a high-pressure nitrogen cylinder for inflating the constant volume bomb; the output end of the liquid drop generating device is communicated with the top end of the constant volume bomb, and liquid drops emitted by the liquid drop generating device vertically fall down along the center of the constant volume bomb; the inside of the constant volume bomb is fixedly provided with ultra-white glass which is horizontally placed and used for receiving the impact of liquid drops; the periphery surface of the constant volume bomb is provided with two side perspective windows symmetrically distributed about the constant volume bomb, and the bottom center of the constant volume bomb is provided with a bottom perspective window;
The side surface of the constant volume bomb is provided with a first image acquisition system for observing the macroscopic form of the liquid drop, and the first image acquisition system comprises an LED lamp and a monochromatic high-speed camera which are respectively arranged outside the side perspective window; the centers of the LED lamp, the monochromatic high-speed camera and the two side perspective windows are all on the same straight line, and the upper surface of the ultra-white glass is positioned below the center line of the side perspective window;
The bottom of the constant volume bomb is provided with a second image acquisition system for observing the micron-sized air film outline at the bottom of the liquid drop, and the second image acquisition system comprises a metal halide lamp, a color high-speed camera and an optical path conversion unit; the light path conversion unit comprises a support piece arranged right below the bottom perspective window and a semi-transparent and semi-reflecting mirror fixedly arranged on the support piece; the semi-transparent semi-reflecting mirror is obliquely arranged towards the metal halide lamp, and the centers of the metal halide lamp and the semi-transparent semi-reflecting mirror are on the same horizontal line.
2. The device for liquid drop bottom air film interference experiment under high pressure condition as claimed in claim 1, wherein: the constant volume bullet is internally provided with a liquid drop collector for screening liquid drops, and the liquid drop collector comprises a rotating motor and a bracket arranged at the output end of the rotating motor; the bracket is fixedly connected with a collecting tank for collecting liquid drops; the collecting tank is positioned above the ultra-white glass.
3. The device for liquid drop bottom air film interference experiment under high pressure condition as claimed in claim 2, wherein: the light path conversion unit also comprises a plane mirror arranged right below the half-mirror; the plane mirror is obliquely arranged towards the color high-speed camera, and the centers of the color high-speed camera and the plane mirror are on the same horizontal line; the plane mirror reflects the light passing through the half mirror to the color high-speed camera.
4. A droplet bottom gas film interference experimental device under high pressure conditions according to claim 3, wherein: the constant volume bomb is made of stainless steel materials and comprises a support column, an upper cover plate and a lower cover plate, wherein the upper cover plate and the lower cover plate are fixedly connected to the upper end and the lower end of the support column; sealing gaskets are arranged at the joints of the support columns, the upper cover plate and the lower cover plate, and the support columns, the upper cover plate and the lower cover plate form a high-pressure-resistant sealing chamber together.
5. The device for liquid drop bottom gas film interference experiment under high pressure condition as claimed in claim 4, wherein: and the constant volume bomb is connected with a pressure gauge for measuring internal pressure.
6. The method is characterized by being applied to the droplet bottom air film interference experimental device under the high pressure condition, and comprises the following steps:
s1, adjusting the positions and connection relations of all the components, pumping air into the constant volume bomb by using a vacuum pump to enable the inside of the constant volume bomb to be in a vacuum environment, then inflating the inside of the constant volume bomb by using a high-pressure nitrogen cylinder to change the internal pressure of the constant volume bomb, and enabling a droplet impact experiment to be carried out in the high-pressure nitrogen environment;
S2, controlling a droplet generation device to emit droplets towards the surface of the ultra-white glass, screening the fallen droplets by a droplet collector, removing the droplets with irregular spheres, and starting a rotating motor and driving a bracket and the collector to rotate when continuous droplets with regular spheres appear, so that the droplets with regular spheres fall down and strike the surface of the ultra-white glass;
S3, enabling the liquid drops moving towards the ultra-white glass to pass through a side perspective window of the constant volume bomb, then irradiating the liquid drop impact process, then entering a single-color high-speed camera, recording macroscopic morphological changes in the liquid drop impact process from the side, extracting the liquid drops in the side view image through a self-defined Matlab image processing program, and measuring the size and the speed of the liquid drops;
And S4, when the liquid drops fall and strike on the surface of the ultra-white glass, white light emitted by the metal halide lamp is reflected to the ultra-white glass through the semi-transparent semi-reflective mirror, one part of the white light is reflected from the upper surface of the ultra-white glass, the other part of the white light passes through the ultra-white glass to irradiate the bottom surface of the liquid drops and is reflected from the bottom surface of the liquid drops, two light beams reflected from the ultra-white glass and the bottom of the liquid drops interfere to form interference fringes with different colors, the interference fringes pass through the semi-transparent semi-reflective mirror, then enter the color high-speed camera through the plane mirror, interference fringes of an air film are obtained, and then the interference fringes are processed to obtain the profile curve of the air film at the bottom of the liquid drops.
7. The experimental method for gas film interference at the bottom of liquid drops under high pressure condition as defined in claim 6, which is characterized in that: in the step 3, after the impact process of the side recording liquid drop is converted into image processing, the edge of the liquid drop is extracted according to a brightness detection algorithm, and after holes in a liquid drop area in a binary image are filled, the pixel number S and the centroid coordinates (x, y) of the liquid drop are calculated, and the liquid drop is not completely spherical, so that the characteristic diameter calculation method of the liquid drop is as follows:
Wherein, Is the magnification obtained in the calibration process.
8. The experimental method for gas film interference at the bottom of liquid drops under high pressure condition as defined in claim 7, wherein the experimental method comprises the following steps: in the step3, the method for calculating the speed of the liquid drop is as follows:
Wherein, And/>Respectively, the ordinate of the mass center of the liquid drop on two continuous images before the liquid drop impact,/>Is the shooting frame rate of the camera.
9. The experimental method for gas film interference at the bottom of liquid drops under high pressure condition as set forth in claim 8, which is characterized in that: in the step 4, before extracting the outline of the micron-sized air film at the bottom of the liquid drop, firstly, adopting a white light color interference technology to shoot interference fringes at the bottom of the lens, then adopting MATLAB image processing program to calculate the outline distribution of the air film at the bottom of the lens, and then calibrating the outline of the air film at the bottom of the liquid drop according to the thickness of the air film corresponding to the interference fringes; the thickness of the air film at the bottom of the lens corresponds to the interference fringe in the radial direction, then the interference fringe of the air film at the bottom of the liquid drop is processed, tangential average is carried out by taking the center of the interference fringe as the center of a circle, then the RGB mode is converted into the CIE1976 color mode, the interference fringe at the bottom of the lens is converted into the CIE1976 color mode from the RGB mode, finally the distance is calculated by using the Euclidean algorithm, the chromatic aberration is calculated, and one of the clearest dark continuous curves in the chromatic aberration diagram is the contour curve of the air film at the bottom of the liquid drop.
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