JP2007248436A - Method and instrument for measuring internal flow in droplet dropping behavior - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method and an instrument capable of measuring precisely an internal flow of a droplet in a droplet moving behavior on a solid surface or the like, using an original particle image flow velocity measuring (PIV) method. <P>SOLUTION: In this method and instrument for measuring the internal flow in the droplet moving behavior, a particle is mixed in the droplet, the droplet is passed to irradiate a droplet inside with sheet light, and a motion of the droplet in a light emitting cross-sectional image of the particle is visualized regarded as the internal flow in a droplet cross-sectional part when the droplet is moved. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method and apparatus for measuring the internal flow of a droplet in the droplet movement behavior on a solid surface or the like.

  Control of wetting of solid surfaces is a technical issue located at the boundary between physics and chemistry, and its application range is the most fundamental and important research area covering all engineering fields such as surface functions and production processes. Conventionally, wetting of solid surfaces is based on Young's equation, and the relationship between changes in composition and structure and macro wetting obtained from contact angle measurement, etc. has been studied both theoretically and experimentally. It is known that surface roughness, surface shape, electric field, and the like are involved in a complicated manner.

  In addition, “static” wetting by contact angle measurement has been mainly evaluated in the past, but in recent years, the importance of “dynamic” wetting has begun to be recognized in various engineering fields such as construction and transportation machinery. . This “dynamic” wetting does not mean the rate of wetting and spreading on the hydrophilic surface, but mainly “removability of droplets” on the water-repellent surface. The most commonly evaluated dynamic wettability today is the falling angle and contact angle hysteresis. This contact angle hysteresis is the difference between the advancing contact angle and the receding contact angle. FIG. 1 shows the relationship between the drop angle α, the advancing contact angle θa, and the receding contact angle θr for the droplet 2 (for example, a water droplet) on the solid surface 1. Indicates. However, these are used to gradually tilt the horizontally supported sample surface and read the falling angle, forward and backward contact angles when the droplet started to fall, and no information on the droplet removal speed is included. Not. For example, even if the drop angle of the droplet is 1 degree, it is known that it falls on a super water-repellent surface in an instant, but is extremely slow on a smooth polymer surface.

  On the other hand, in actual industrial materials, the inclination angle of the surface is mostly determined by the size, function, design, etc., and not `` how many times the inclination angle falls '' but `` how fast at a certain inclination angle '' The information “whether it will fall down” is becoming more important. For example, measurement examples can be seen in Patent Document 1, Patent Document 2, Patent Document 3, Patent Document 4, and the like. Also, in academic journals, Miwa et al. Reported that water on a super-water-repellent surface falls by non-patent document 1 with a uniform acceleration motion. Glycerol has been reported to fall with constant velocity motion due to viscous resistance. In Non-Patent Document 3 and Non-Patent Document 4, the tendency of acceleration may change depending on the falling condition for water on a smooth water-repellent surface, and the droplet may vibrate while falling. Has been reported.

  However, the measurement method is not constant. There are various combinations of types and shapes of solid surfaces and types of droplets. Furthermore, it is known that the acceleration of droplets on the solid surface varies depending on the size and inclination angle of the droplets and the material of the solid surface. Yes. The drop-down behavior of the droplet cannot be comprehensively evaluated unless the shape change of the droplet is simultaneously evaluated together with the measurement of acceleration. Various measuring devices and measuring principles for contact angle and falling angle are known, and as disclosed in Patent Document 5, a method and apparatus for comprehensively measuring and evaluating the apparent droplet falling behavior has been developed. However, a method and an apparatus for observing the internal flow at the time of dropping the droplet have not been developed yet.

Non-Patent Document 5 describes a general particle image velocimetry (PIV) method (in a broad sense: a flow is visualized by mixing a tracer in a fluid, and a digital image processing technique as a technique related to the present application. , Which extracts multi-point velocity information of a flow field).
JP 2001-259509 A JP 2002-29783 A JP 2002-97192 A Japanese Patent Laid-Open No. 11-116973 Japanese Patent Application 2005-231801 Miwa, M., Nakajima, A., Fujishima, A., Hashimoto, K. and Watanabe, T., Langmuir, Vol 16, p. 5754-5760 (2000) Richard, D. and Quere, D., Europhys. Lett., Vol. 48, p. 286-291 (1999) Nakajima, A, Suzuki, S., Kameshima, Y., Yoshida, N., Watanabe, T. and Okada, K., Chem. Lett., VoL32, P.1148-1149 (2003) Suzuki, S., Kameshima, Y., Nakajima, A and Okada, K., Surf. Sci., Vo1.557 / 1-3.p.L163-L168 (2004) The main points of PIV The Visualization Society of Japan

As described above, considering the case of a drop falling on a solid surface, as described above, there are various combinations of types and shapes of solid surfaces and types of droplets. Is known to vary depending on the size and inclination angle of the droplet and the material of the solid surface. For example, when a droplet falls while “rotating”, the falling speed is said to be fast, but there is no report that has been demonstrated by actually visualizing the internal flow of the droplet. Further, the degree of deformation of the droplets at the time of falling is not necessarily uniform, and may be accompanied by periodic fluctuations depending on the conditions of falling, which may affect the falling acceleration. In order to analyze the periodic fluctuation simultaneously with the measurement of the falling acceleration, the advancing contact angle of the droplet viewed from the side with respect to the falling direction, the receding contact angle of the droplet viewed from the side with respect to the falling direction, The length of the contact portion of the droplet with the solid as viewed from the side with respect to the falling direction, the height of the droplet as viewed from the side with respect to the falling direction, and the falling of the two points where the outer periphery of the droplet intersects with the solid surface It is effective to continuously measure at least one of the accelerations at the point opposite to the direction side along with the falling acceleration. These are illustrated in FIG. In FIG. 2, a _a is the acceleration at the point on the falling direction side at the point where the outer periphery and the solid surface intersect, a _r is the acceleration at the point on the opposite side to the falling direction at the point where the outer periphery and the solid surface intersect, and V _a is the outer periphery. speed of points falling direction of the point of intersection is the solid surface, V _r is the outer circumference and that the solid surface intersects the opposite side speed of the points falling direction of, theta _a is the advancing contact angle of the point of intersection is the outer periphery and the solid surface , Θ _r is the receding contact angle at the point where the outer periphery and the solid surface intersect, h is the height of the droplet, and d is the distance between the two points where the outer periphery and the solid surface intersect.

  In this way, in order to measure the drop falling behavior more accurately, the drop (acceleration) speed is measured and the drop shape change (advance contact angle / retreat contact angle / droplet height / droplet In order to directly observe the interaction from the solid to the liquid, it is necessary to measure the internal flow when the droplet falls. To that end, we have established a method for visualizing the internal flow of a droplet when it falls, and does not hinder the original flow of a droplet with a small mass. Development of an image velocimetry (PIV) method and apparatus is desired.

  The object of the present invention is to establish a unique particle image velocimetry (PIV) method in order to satisfy such demands, and to use it for internal flow of droplets in droplet movement behavior on a solid surface or the like. It is an object to provide a method and an apparatus capable of measuring the temperature with high accuracy.

  In order to solve the above problems, the internal flow measurement method in the droplet movement behavior according to the present invention mixes particles in the droplets, passes the droplets so that the sheet light is irradiated inside the droplets, The movement of the particles in the emission cross-sectional image is visualized by regarding the movement of the particles as the internal flow of the droplet cross-section when the droplet moves. As the sheet light, laser sheet light can be typically used. However, the light source itself can be other than a laser. For example, it is possible to use metal halide illumination that is converted into sheet light using an optical lens.

  The droplet movement in the present invention includes not only the movement (falling) of the droplet on the solid surface (regardless of the upward surface or the downward surface) but also the movement of the droplet in the air.

  The kind of particle to mix is not specifically limited, For example, a polystyrene particle can be used and it is preferable to mix a particle | grain of 1 micrometer-220 micrometers with a density | concentration of 0.01-20 wt%.

  Further, in the internal flow measurement method according to the present invention, the moving velocity component in the traveling direction obtained using the front and / or rear end points of the droplet is subtracted from the total velocity component of the droplet cross-section, Only the velocity component of the flow can be extracted.

  Also, on the side of the moving droplet, a reflection / transmission filter that reflects light of a certain wavelength or more and reflects the remaining light or a reflection / transmission filter that transmits light of a certain wavelength or more and reflects the remainder, The optical system is arranged so that light of the same optical axis is branched and images of the same optical axis can be taken by a plurality of cameras, and a visualization image by the mixed particles and a silhouette image for measuring the droplet movement behavior are provided. You can also shoot at the same time.

  Furthermore, in the internal flow measuring method according to the present invention, it is possible to simultaneously measure the droplet movement behavior and the droplet internal flow.

  The present invention also provides an internal flow measurement device for droplet movement behavior comprising means using at least one of the methods as described above.

  In the method and apparatus for measuring internal flow in the droplet falling behavior according to the present invention as described above, when the droplet moves, for example, sheet light (particularly, sheet laser light) is parallel to the moving direction of the droplet. It is possible to obtain a clear cross-sectional image in which the flow is visualized by the particles irradiated and mixed in the droplets. It is possible to measure only the internal flow of the droplet by pre-processing the acquired image using a unique coordinate transformation algorithm for droplet movement. The particle image velocimetry (PIV) method is a high density PIV (correlation PIV method: calculating the flow velocity by tracking the displacement of the density pattern formed by high density particles) due to the difference between the particle number density and the image processing method. And low-density PIV (PTV method: the flow velocity is calculated by tracking individual particles introduced into the flow), and the method according to the measurement purpose described in Non-Patent Document 5 etc. is used. The internal flow velocity can be measured from the preprocessed video. In addition, by using filters and / or prisms that reflect and transmit light of a specific wavelength range, it is possible to acquire images with the same image quality using two high-speed cameras. It is possible to simultaneously measure the internal flow of the liquid droplets and the movement behavior (drop (acceleration) speed / morphological change) of the liquid droplets.

  According to the present invention, as shown in Examples described later, it is possible to effectively measure and evaluate the internal flow during the movement of the droplet, and even for various combinations of droplets and solid surfaces. It is possible to measure and evaluate the internal flow during droplet movement. Furthermore, the internal flow can be measured simultaneously with the falling behavior and shape change. As a result, we were able to pioneer a new path in the method for evaluating and analyzing the dynamic behavior of droplets.

  Hereinafter, the internal flow measuring method and apparatus in the droplet falling behavior according to the present invention, particularly in the case of using the laser sheet light as the sheet light, especially in the center of the measuring method and apparatus of the droplet falling behavior, It explains in detail with a form.

(Installation of sheet light laser)
As shown in FIG. 3, the laser sheet light 4 is irradiated in parallel to the moving direction of the droplet 2 from the laser sheet light irradiation device 3 so as to pass through the cross section of the droplet 2 moving on the solid surface 1. To do. When droplets 5 are mixed with particles 5 and a cross section of the droplets expressed by the particles projected by the laser sheet light 4 is photographed with a high-speed camera arranged on the side in the movement direction of the droplets 2, A clear image suitable for PIV analysis can be acquired. Reference numeral 7 denotes a screen. At this time, the sheet thickness of the laser sheet light 4 is desirably less than 1 mm, and more desirably, it is preferable to use a stable laser sheet light having a thickness of less than 500 μm. In addition, it is desirable that the intensity of the laser is higher, for example, 250 mW or more, and if it is 1 W or more, the depth of the subject increases, so that a clear sectional image can be acquired. When using particles with a fluorescent paint attached to the surface, it is desirable to install a filter 8 that cuts light having a wavelength less than the emission wavelength of the fluorescent particles between the droplet and the camera.

(Installation of sample when measuring internal flow of liquid droplets on solid surface)
The type of droplet used in the present invention is not particularly limited, but the size is preferably in the range of 1 to 50 mg. The type of the solid surface is not particularly limited, but the contact angle with the droplet is preferably at least 45 degrees or more, more preferably 80 degrees or more. This is because the speed effect of wetting and spreading when the droplet wets the solid surface becomes small. When the contact angle is less than 45 degrees, it becomes difficult to distinguish between the above-described droplet removability and wetting and spreading characteristics. Further, it is desirable that the solid surface during measurement is flat. Further, the inclination angle of the surface at the time of measurement is desirably 10 degrees or more and 80 degrees or less, and more desirably 30 degrees or more and 70 degrees or less. If the tilt angle is low, the drop falls slowly and takes time. Moreover, if the inclination is large, the fall is quick and it becomes difficult to see the difference in characteristics between samples.

(Particle size)
In order to measure the internal flow in the droplet, for example, polystyrene particles having a particle size of 1 μm to 220 μm are mixed in the droplet at a concentration of 0.01 to 20 wt% so as not to disturb the original flow of the droplet, thereby controlling the movement of the particle. The flow inside the droplet can be visualized. Since the particle size hinders the internal flow of the droplets, the particle size is not small, but it is unclear because it depends on the resolution of the camera used for photographing. In the case of a high-speed camera having a resolution of 512 × 512 picel, when the picture quality (for example, picture quality such as image 1 or image 2 shown in FIG. 4) is 15 mm, preferably 10 to In the 40 μm PTV method, it is better to use particles having a diameter of 100 to 220 μm. This is one of the factors governing the drop-falling behavior by measuring the velocity distribution in the droplets by measuring the velocity distribution by image analysis (particle image velocimetry: PIV method). It becomes possible to measure the shear displacement rate between the droplet and the substrate.

(Video analysis method)
When the velocity distribution of the internal flow of the moving droplet is viewed in external coordinates, it is affected by the motion of the droplet itself in addition to the internal flow of the droplet, and only the internal flow cannot be measured. Therefore, it is necessary to acquire an image in which the droplet itself appears to be at a certain position in the picture and the inside is convective. For this purpose, there are two methods: (1) moving the camera in accordance with the movement of the droplet, and (2) extracting an image so as to appear at a certain position by image processing. This time, the measurement was performed by developing an algorithm capable of acquiring the velocity vector using the method (2). In this case, it is necessary to obtain an image in which the droplet itself appears to be at a certain position in the picture and the inside is convective. For this purpose, by developing an algorithm capable of acquiring a velocity vector using a method of extracting an image so that it appears to be at a certain position by image processing, the velocity distribution of the liquid flow inside the droplet is reduced. Can be obtained (FIG. 4).

(Simultaneous measurement of moving speed, shape change and internal flow)
For example, as shown in FIG. 5, the laser sheet light irradiation device 12 irradiates the laser sheet light 13 from the laser sheet light irradiation device 12 so as to cut the cross section with respect to the moving direction of the droplet 11, and the metal halide illumination as the backlight illumination 14 is opposite to the camera. Reflecting light that illuminates backlight through the transmission filter 15 and the diffusion plate 16 and reflects light of a certain wavelength or more between the solid surface 17 on which the droplet 11 moves and the camera, and transmits the rest. A transmission filter or a reflection / transmission filter 18 that transmits light of a certain wavelength or more and reflects the rest is placed on the side of the moving droplet 11 to branch the light of the same optical axis, and to display an image of the same optical axis. Two high-speed cameras 19 and 20 that are synchronized so as to be photographed by a plurality of cameras are arranged, and the wavelength of one laser beam 21 is transmitted through a cross section through which the high-speed camera is transmitted. Was arranged to be taken at 0, was positioned to the silhouette of the droplet 11 which is projected by the other metal halide light 22 can capture a high-speed camera 19. These arrangements enable simultaneous measurement of droplet movement behavior and internal flow.

  Hereinafter, the method and apparatus according to the present invention will be described more specifically with reference to examples of actual measurement and evaluation. In addition, these Examples are only illustrations and do not restrict | limit this invention.

Example 1
FIG. 6 shows an image 31 in which the internal flow is visualized by laser sheet light when a 30 ml water droplet is dropped at an inclination angle of 35 degrees on a silicon substrate coated with octadecyltrimethoxysilane. In the drawing of the image 31 shown in FIG. 6, the mixed particles are slightly difficult to see, but in reality, the mixed particles are clearly dropped as if the mixed particles flow on a two-dimensional plane by the laser sheet light. Was able to visualize the internal flow.

Comparative Example 1
FIG. 7 shows an image 41 in which the internal flow is visualized only by metal halide illumination when a 30 ml water droplet is dropped at an inclination angle of 35 degrees on a silicon substrate coated with octadecyltrimethoxysilane. In the drawing of the image 41 shown in FIG. 7, the mixed particles are slightly difficult to see. Actually, however, the mixed particles present not in the cross section of the liquid droplet but in the substantially entire inside of the liquid droplet are metal halide illumination. Therefore, it was difficult to accurately capture the internal flow of the droplets when viewed from the image side, with the particles overlapping in a complicated manner.

Example 2
FIG. 8 shows a velocity distribution characteristic 51 of a droplet when a 30 ml water droplet is dropped at an inclination angle of 35 degrees on a silicon substrate coated with octadecyltrimethoxysilane.

  The present invention can be applied to all industrial fields in which it is desired to accurately grasp the internal flow during droplet movement.

It is a schematic explanatory drawing which shows the relationship between a forward and backward contact angle, and a fall angle. It is a schematic explanatory drawing which shows the item measured with a movement acceleration (a fall acceleration is included). It is the schematic explanatory drawing (A) which shows the mode of laser sheet light irradiation, and the schematic partial perspective view (B) which looked at it from the side. It is a schematic explanatory drawing which shows the pre-processing method for extracting an internal fluid velocity component. It is a schematic explanatory drawing of the apparatus which has arrange | positioned the illumination for laser sheet light and backlight, and was able to image | photograph with two cameras with the same optical axis using a filter and / or a reflecting plate. It is a figure which shows the cross-sectional image in the droplet when the laser sheet light in Example 1 is used. It is a figure which shows the image of the droplet and particle | grains at the time of using only metal halide illumination in the comparative example 1. FIG. FIG. 9 is a characteristic diagram expressing a droplet internal flow velocity distribution in Example 2.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Solid surface 2 Droplet 3 Laser sheet light irradiation apparatus 4 Laser sheet light 5 Mixed particle 6 High speed camera 7 Screen 8 Filter 11 Droplet 12 Laser sheet light irradiation apparatus 13 Laser sheet light 14 Backlight illumination (metal halide illumination)
DESCRIPTION OF SYMBOLS 15 Transmission filter 16 Diffusion plate 17 Solid surface 18 Reflection / transmission filter 19, 20 High-speed camera 21 Laser light 22 Metal halide light 31 Image 41 in a state of visualizing internal flow of liquid droplet in Example 1 Image 51 in a state of visualizing internal flow Droplet velocity distribution characteristics in Example 2

Claims (8)

  Particles are mixed in the droplet, and the droplet is passed so that the sheet light is irradiated inside the droplet, and the movement of the particle in the emission cross-sectional image of the particle is determined by the internal flow of the droplet cross-section when the droplet moves. A method for measuring internal flow in a droplet movement behavior, characterized in that it is visualized as if it were a droplet.   The method for measuring internal flow in the droplet movement behavior according to claim 1, wherein laser sheet light is used as the sheet light.   The method for measuring internal flow in a droplet movement behavior according to claim 1 or 2, wherein the droplet is moved on a solid surface.   The internal flow measurement method in the droplet movement behavior according to any one of claims 1 to 3, wherein particles of 1 µm to 220 µm are mixed at a concentration of 0.01 to 20 wt%.   The moving velocity component in the traveling direction obtained by using the front and / or rear end points of the droplet is subtracted from the total velocity component of the droplet cross-section, and only the velocity component of the droplet internal flow is extracted. 5. The internal flow measurement method in the droplet movement behavior according to any one of 4 above.   On the side of the moving droplet, a reflection / transmission filter that reflects light of a certain wavelength and transmits the rest or a reflection / transmission filter that transmits light of a certain wavelength and reflects the rest is installed. The optical system is arranged so that images of the same optical axis can be taken by multiple cameras by splitting the light of the axis, and the visualization image by the mixed particles and the silhouette image for measuring the droplet movement behavior are simultaneously shot The internal flow measurement method in the droplet movement behavior according to any one of claims 1 to 5.   The method for measuring internal flow in droplet movement behavior according to any one of claims 1 to 6, wherein the droplet movement behavior and the internal flow of the droplet are measured simultaneously.   An apparatus for measuring internal flow in a droplet movement behavior, comprising means for using at least one of the methods according to claim 1.

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