Method for measuring contact angle of liquid in thin tube

Abstract

The method considers that the obtained gas-liquid interface line of the concave liquid level in the thin tube is refracted twice by liquid-quartz glass and quartz glass-air, so that the directly measured gas-liquid interface line is used as an actual gas-liquid interface line, and errors are brought to the measurement result of the liquid contact angle in the thin tube. The method for measuring the liquid contact angle in the tubule comprises the steps that a clear gas-liquid interface line image of a working medium in a pulsating heat pipe test piece in a measuring system is collected, measuring coordinate points of a gas-liquid interface line are calibrated, actual coordinate points are obtained through calculation with the liquid contact angle measuring method, and the liquid contact angle is measured according to the actual coordinate points. And fitting an actual gas-liquid interface line of the working medium in the tubule, and performing angle measurement on the actual gas-liquid interface line by adopting an angle measurement tool to obtain an actual contact angle of the working medium in the tubule. By using the liquid contact angle measuring method provided by the invention, the error influence caused by the thin tube material and light refraction is effectively reduced, and the method can be used for accurately measuring the static liquid contact angle and the dynamic liquid contact angle.

Description

Technical Field

[0001] The invention relates to the technical field of measuring the contact angle of liquid in a cylindrical capillary tube, in particular to a method for measuring the contact angle of liquid in a capillary tube. Background Art

[0002] The liquid contact angle refers to the angle formed between the solid-liquid interface tangent and the liquid-gas interface tangent at the intersection of the solid, liquid and gas phases of the droplet. It is an important parameter to characterize the degree of wetting of the liquid on the material surface. Since the liquid contact angle is an important parameter to characterize the wettability of the material surface, the interaction between the liquid and the tube wall surface directly affects the efficiency of heat transfer and mass exchange.

[0003] A method for measuring liquid contact angle in the prior art has been applied for inserting a sample tube vertically into a water tank. The depression formed by the sample tube and the liquid surface forms a rectangular projection on the bottom projection of the water tank. The functional relationship between the projection width and the liquid contact angle is obtained by fitting. The projection width is brought into the functional relationship to obtain the liquid contact angle of the sample tube. This scheme aims to obtain the liquid contact angle of the outer surface of the tube and indirectly measure the liquid contact angle by obtaining the bottom projection of the water tank. The disadvantage of this scheme is that the refraction effect of water is not considered during the measurement process.

[0004] Another liquid contact angle measurement method in the prior art is a liquid contact angle measurement method for the gas-liquid interface in a micron capillary channel. This method uses a threshold segmentation algorithm to convert a grayscale image that has been grayscale converted and filtered into a binary image, uses a connected region method to extract the boundary points that constitute the pipeline-shaped boundary image, performs function fitting on the boundary points to obtain the precise coordinates of the interface, and respectively brings them into the derivative of the cubic function to obtain the liquid contact angle at the two end points of the interface. This method aims to provide accurate measurement results for images of poor quality, and the disadvantage of this method is that it does not provide the change in the liquid contact angle during operation of the liquid in the micron capillary channel.

[0005] The above-mentioned prior art liquid contact angle measurement method directly selects the local contour of the droplet for fitting calculation, without considering the error caused by the capillary material and light refraction. At the same time, the existing liquid contact angle measurement method is often used to measure the static liquid contact angle, and does not consider that the dynamic contact angle of the liquid in the capillary is not a constant value when the working fluid is running. Summary of the invention

[0006] The embodiments of the present invention provide a system and method for measuring the contact angle of a liquid in a capillary tube, so as to effectively measure the contact angle of the liquid in a stationary state and the contact angle of the liquid in a running state in the capillary tube.

[0007] In order to achieve the above object, the present invention adopts the following technical scheme.

[0008] A method for measuring the contact angle of a liquid in a capillary tube, comprising:

[0009] After the pulsating heat pipe specimen is evacuated by a vacuum pump, a liquid phase working medium is injected into the pulsating heat pipe specimen by a liquid filling system, and the liquid phase working medium forms gas and liquid columns that are alternately distributed in the pulsating heat pipe;

[0010] A digital camera is used to record the static state and running process of the working fluid in the pulsating heat pipe to obtain the gas-liquid interface line image;

[0011] Based on the gas-liquid interface line image, the measurement coordinate points of the gas-liquid interface line are calibrated, and the refracted light diagram is drawn based on different measurement coordinate points using Snell's law, and the actual coordinate points of each measurement coordinate point are calculated. The actual gas-liquid interface line of the working fluid in the tube is fitted according to each actual coordinate point, and the actual contact angle between the liquid and the glass tube wall is measured using an angle measurement tool.

[0012] Preferably, the method further comprises:

[0013] The top of the pulsating heat pipe specimen is cooled in a water bath by using a cooling system, a heating wire is wound around the bottom of the pulsating heat pipe specimen, the heating power is adjusted by adjusting the input voltage through the heating system, the pulsating heat pipe specimen is heated, and images of the working fluid in the pipe running at different heating powers are obtained;

[0014] LED lights are arranged around the pulsating heat pipe specimen. The LED light creates a light-dark contrast between the working fluid in the pulsating heat pipe and the background, and the gas-liquid interface line of the concave liquid surface of the liquid column can be observed.

[0015] Preferably, the method further comprises:

[0016] The gas-liquid interface line image of the working fluid in the pulsating heat pipe specimen is collected based on a digital camera, and multiple measurement coordinate points are selected on the gas-liquid interface line. According to Snell's law, when the refractive index of the two media is different, the light will be deflected in the normal direction at the interface of the two media. The geometric relationship in the light refraction process is used to draw the refraction light diagram between the working fluid and the recording position in the pulsating heat pipe specimen. The functional relationship for measuring the liquid contact angle is established through the refraction light diagram, and the actual marking point coordinates of each measurement coordinate point are calculated. The actual gas-liquid interface line of the liquid contact angle is fitted, and the angle measurement tool in the ImageJ software is used to measure the actual contact angle between the liquid and the quartz glass tube wall.

[0017] Images of the operation of the working fluid in the pulsating heat pipe at different heating powers are collected. Based on the operation images of the working fluid, the measurement points of the gas-liquid interface lines of the advancing liquid contact angle and the receding liquid contact angle are calibrated respectively. The actual coordinate points are calculated through the functional relationship of the liquid contact angle, and the actual gas-liquid interface lines of the advancing liquid contact angle and the receding liquid contact angle at different heating powers are fitted, thereby obtaining the actual advancing liquid contact angle and the receding liquid contact angle.

[0018] Preferably, the method of using the geometric relationship in the light refraction process to draw a refraction light diagram between the working fluid and the recording position in the pulsating heat pipe specimen, establishing a functional relationship for measuring the liquid contact angle through the refraction light diagram, and calculating the actual marking point coordinates of each measurement coordinate point includes:

[0019] Set the digital camera placement point as point O, set the horizontal distance between the digital camera and the pulsating heat pipe specimen as L, select the lowest point A of the meniscus curve as the coordinate origin, point B as the calibrated measurement coordinate point, point C as the actual coordinate point calculated by the functional relationship of the liquid contact angle, and the horizontal coordinate measurement length of the measurement coordinate point B is L AB , the actual length of the actual coordinate point C on the horizontal axis is L AC , ∠AOB is the angle between the measurement coordinate point B and the digital camera placement point O, ∠β in is the angle between the actual coordinate point C and the digital camera placement point O, and the distance between the actual coordinate point C and the coordinate origin point A is L AC ;

[0020] The horizontal coordinate measurement length of the measured coordinate point B is L AB The horizontal distance L between the digital camera and the pulsating heat pipe specimen is known. According to the Pythagorean theorem in the right triangle, the length L between the measurement coordinate point B and the digital camera placement point O is obtained. BO Size:

[0021]

[0022] For the right triangle ΔOAB, the sine function is defined as:

[0023]

[0024] From the inverse sine function, we can get the angle ∠AOB between the measurement coordinate point B and the digital camera placement point O:

[0025]

[0026] ∠AOB=∠AOE

[0027] In the right triangle ΔOAB, ∠BAO is a right angle, so ∠ABO can be obtained from the triangle interior angle theorem:

[0028]

[0029] ∠ABO=∠ABE

[0030] According to the sine theorem, the size of ∠ABE is known, and the length of the side opposite to ∠ABE is L AE , the length of the side opposite to ∠BEA is L AB , find ∠BEA:

[0031]

[0032] In triangle ΔABE, the magnitudes of ∠ABE and ∠BEA have been determined, and ∠EAB can be obtained from the triangle interior angle theorem:

[0033] ∠EAB=π-∠ABE-∠BEA

[0034] In the triangle ΔABE, since Having found ∠EAB, find ∠OAE:

[0035]

[0036] In triangle ΔAEO, ∠OAE and ∠AOE have been obtained. ∠AEO can be obtained by the triangle interior angle theorem:

[0037] ∠AEO=π-∠OAE-∠AOE

[0038] Because ∠AEO and ∠α re They are complementary angles, and we can find ∠α re :

[0039] ∠α re =π-∠AEO

[0040] Applying Snell's law to the quartz glass-air interface, when light enters the air from the glass, refraction occurs. The sine of the incident angle·the refractive index of the light in the glass = the sine of the refraction angle·the refractive index of the light in the air, we get:

[0041] sin∠α in ·n si = sin∠α re ·n air

[0042]

[0043] Using the triangular cosine theorem to solve for L DE , L DE The range is [L AE -L AD,L AE ), when the solution of the equation does not satisfy it, discard the unsatisfactory solution:

[0044]

[0045] Known L DE , use the law of cosines to find the ADE:

[0046]

[0047] In triangle ΔADE, ∠α has been found in And ∠ADE, we can find ∠EAD by the triangle interior angle theorem:

[0048] ∠EAD=π-∠α in -∠ADE

[0049] Because ∠ADE and ∠β re As complementary angles, we get ∠β re :

[0050] ∠β re =π-∠ACD

[0051] Applying Snell's law to the interface between liquid and quartz glass, light is refracted when it enters the glass from water. The sine of the incident angle·the refractive index of light in water = the sine of the refraction angle·the refractive index of light in glass, and we get:

[0052] sin∠β in ·n water = sin∠β re ·n si

[0053]

[0054] In triangle ΔACD, ∠β has been found in and ∠DAC, we get ∠ACD:

[0055] ∠ACD=π-∠β in -∠DAC

[0056] According to the sine theorem, ∠β in The length of the opposite side is L AC , the length of the side opposite to ∠ACD is L AD , find the distance L between the actual coordinate point C and the coordinate origin point A AC , L AC The range is: [0,L AD ];

[0057]

[0058] Therefore, the actual coordinate point is determined according to the actual length of the actual coordinate point C on the horizontal axis, and the actual gas-liquid interface line of the droplet is fitted according to the actual coordinate point to measure the true liquid contact angle.

[0059] It can be seen from the technical solutions provided by the above-mentioned embodiments of the present invention that the method for measuring the contact angle of liquid in a capillary tube takes into account the error influence caused by the capillary material and light refraction, and can be used for accurate measurement of static liquid contact angle and dynamic liquid contact angle.

[0060] Additional aspects and advantages of the present invention will be given in part in the following description, which will become obvious from the following description, or may be learned through practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0061] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other accompanying drawings can be obtained based on these accompanying drawings without paying creative work.

[0062] Figure 1 A flow chart of a method for measuring the contact angle of a liquid in a capillary provided by an embodiment of the present invention;

[0063] Figure 2 A schematic diagram of the structure of a system for measuring the contact angle of a liquid in a capillary tube provided by an embodiment of the present invention;

[0064] Figure 3 A clear gas-interface line image of an internal working fluid in a system for measuring the contact angle of a liquid in a capillary tube provided by an embodiment of the present invention;

[0065] Figure 4 A refracted light diagram between a meniscus of a liquid contact angle in a capillary and a measurement position provided in an embodiment of the present invention.

[0066] Figure 5 A schematic diagram of a contact angle measurement deviation of a liquid in a capillary tube due to light refraction provided by an embodiment of the present invention;

[0067] Figure 6 A schematic diagram of measurement coordinate points for calibrating the contact angle of a liquid in a capillary tube on a gas-interface line provided in an embodiment of the present invention;

[0068] Figure 7 The embodiment of the present invention provides a contact angle directly measured for the liquid contact angle in a capillary and an actual contact angle measurement result of the gas-liquid interface line fitted according to the actual coordinates.

[0069] In the figure: 1- heating system; 2- cooling system; 3- vacuum pump and liquid filling system; 4- pulsating heat pipe made of quartz glass; 5- data acquisition instrument; 6- transformer; 7- power meter; 8- digital camera; 9- low temperature constant temperature bath; 10- vacuum pump; 11- filling medium inlet; 12- scale paper; 13- LED lamp; 14- data acquisition instrument; 15- computer; 16- T-type thermocouple; C1- water bath cooling inlet; C2- water bath cooling outlet. DETAILED DESCRIPTION

[0070] The embodiments of the present invention are described in detail below, examples of which are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and cannot be interpreted as limiting the present invention.

[0071] It will be understood by those skilled in the art that, unless expressly stated, the singular forms "one", "said", and "the" used herein may also include plural forms. It should be further understood that the term "comprising" used in the specification of the present invention refers to the presence of the features, integers, steps, operations, elements and / or components, but does not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components and / or groups thereof. It should be understood that when we refer to an element as being "connected" or "coupled" to another element, it may be directly connected or coupled to the other element, or there may be intermediate elements. In addition, the "connection" or "coupling" used herein may include wireless connection or coupling. The term "and / or" used herein includes any unit and all combinations of one or more associated listed items.

[0072] It will be understood by those skilled in the art that, unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as those generally understood by those skilled in the art in the art to which the present invention belongs. It should also be understood that terms such as those defined in common dictionaries should be understood to have meanings consistent with the meanings in the context of the prior art, and will not be interpreted with idealized or overly formal meanings unless defined as herein.

[0073] To facilitate understanding of the embodiments of the present invention, several specific embodiments will be further explained below with reference to the accompanying drawings, and each embodiment does not constitute a limitation on the embodiments of the present invention.

[0074] The present invention studies the influence of the tube wall thickness on the measurement result during the liquid contact angle measurement process. Considering that the tube wall thickness will produce light refraction, the obtained gas-liquid interface line is obtained by the working medium in the tube undergoing two refractions of liquid-quartz glass and quartz glass-air, and the liquid contact angle is the angle formed between the solid-liquid interface tangent and the gas-liquid interface tangent. Therefore, the measurement result of the liquid contact angle is also affected by the refraction of light. In view of the above problems, the geometric relationship in the light refraction process is used to draw the refraction light diagram between the working medium in the capillary and the recording position (digital camera), and the position coordinates of the gas-liquid interface of the working medium in the capillary are set as the measurement coordinates. The actual coordinates are calculated through the refraction light diagram, and the actual coordinate points are fitted to obtain the real gas-liquid interface of the liquid in the tube, thereby accurately measuring the contact angle of the liquid in the tube.

[0075] The structure of a system for measuring the contact angle of a liquid in a capillary provided by an embodiment of the present invention is as follows: Figure 2 As shown, it includes: 1-heating system; 2-cooling system; 3-vacuum pump and liquid filling system; 4-pulsating heat pipe made of quartz glass; 5-data acquisition instrument; 6-transformer; 7-power meter; 8-digital camera; 9-low temperature constant temperature bath; 10-vacuum pump; 11-filling medium inlet; 12-scale paper; 13-LED (Lighting Emitting Diode, light emitting diode) lamp; 14-data acquisition instrument; 15-computer; 16-T-type thermocouple; C1-water bath cooling water inlet; C2-water bath cooling water outlet.

[0076] The pulsating heat pipe is a single-circuit closed-loop pipeline with an inner diameter of 3 mm and an outer diameter of 6 mm. The inner diameter of the pulsating heat pipe meets the pipe diameter of the pulsating heat pipe that can form alternating distribution of gas and liquid columns when distilled water is used as the working medium.

[0077] The vacuum pump and liquid filling system uses a vacuum pump to evacuate the pulsating heat pipe, so that the pulsating heat pipe maintains a slightly negative pressure state, and the filled working fluid can form a stable gas and liquid column distribution in the pulsating heat pipe.

[0078] The heating system is used to wind a nickel-chromium resistance wire at the bottom of a pulsating heat pipe, adjust the heating power by adjusting the input voltage through a transformer, and heat the pulsating heat pipe. At the same time, a T-shaped thermocouple is arranged at the bottom of the pulsating heat pipe to collect instantaneous temperature.

[0079] The cooling system is used to cool the top of the pulsating heat pipe using a constant temperature cooling water tank, and the constant temperature cooling water tank is connected to a water bath circulation interface at the top of the pulsating heat pipe.

[0080] The digital camera is used to shoot and record the instantaneous operation process of the working fluid inside the pulsating heat pipe using a digital camera of the Canon 1DX-MarkⅡ model, and convert the visual information into images and transmit them to the computer.

[0081] The computer is used to store instantaneous operation process images of the working fluid inside the pulsating heat pipe, and determine the liquid contact angle at each moment according to the images.

[0082] The LED lamp is used to be arranged around the pulsating heat pipe to provide uniform light intensity for the pulsating heat pipe. The LED light allows the working fluid in the pipe and the background to form a light and dark contrast, illuminating a clear meniscus of the liquid column, and the outermost boundary of the gas-liquid interface is well illuminated to produce a clear gas-liquid interface line.

[0083] To achieve the above purpose, the liquid contact angle measurement method proposed in the present invention follows Snell's law, and draws a refracted light diagram between the working medium in the pulsating heat pipe and the recording position (digital camera) according to the refractive index of different media and the geometric relationship in the light refraction process. The functional relationship of the liquid contact angle measurement is established through the refracted light diagram, and then the accurate measurement result of the liquid contact angle is obtained.

[0084] According to Snell's law:

[0085]

[0086] Where θ in is the incident angle of light in medium 1, θ re is the refraction angle of light in medium 2, n1 is the refractive index of medium 1, n2 is the refractive index of medium 2, and when n1>n2, sin∠2>sin∠1. When light enters a medium with a lower refractive index from a medium with a higher refractive index, the light will cause objects in the two media to appear to change in position and size.

[0087] In a system for measuring the contact angle of a liquid in a capillary tube provided by an embodiment of the present invention, a clear meniscus image of an internal working fluid is provided. Figure 3 As shown, the clear meniscus of the working fluid inside the pulsating heat pipe is selected as the object of reading the marking point. Before reading the coordinates, the computer is used to unify the measurement scale, and then the point selection tool is used to take the lowest point of the meniscus curve as the coordinate origin, and the measurement points are selected to the left and right in sequence. After the point selection is completed, the computer gives the coordinate value of the marking point on the meniscus curve.

[0088] Based on the coordinate values ​​of the points on the meniscus, the actual coordinates of the measuring points are first calculated according to the refraction process of light and the relationship of trigonometric functions, and then the actual gas-liquid interface line of the droplet is fitted. Using the geometric relationship of the working fluid in the pulsating heat pipe during the refraction process, the refraction light diagram between the meniscus and the measuring position is drawn, such as Figure 4 As shown, the angle function relationship of the measured liquid contact angle is obtained, and the actual liquid contact angle can be calculated.

[0089] like Figure 2As shown, the present invention builds a pulsating heat pipe visualization test bench to measure the static liquid contact angle of the liquid when the pulsating heat pipe is not heated, and the dynamic liquid contact angle of the liquid is measured in a stable operating state after heating. The flow chart of a method for measuring the liquid contact angle in a capillary provided by an embodiment of the present invention is shown in FIG. Figure 1 As shown, the following steps are included:

[0090] Step (1): Wrap a heating wire around the bottom of the pulsating heat pipe, adjust the heating power by adjusting the input voltage through the heating system, heat the pulsating heat pipe, and at the same time, arrange a data acquisition instrument at the bottom of the pulsating heat pipe to collect the instantaneous temperature. After the pulsating heat pipe is evacuated with a vacuum pump, a liquid working medium is injected into the pulsating heat pipe using a liquid filling system, and the liquid working medium forms gas and liquid columns that are alternately distributed in the pulsating heat pipe. The pulsating heat pipe is cooled in a water bath using 10°C cooling water provided by the cooling system. The digital camera is 18 cm away from the center of the pulsating heat pipe. The digital camera is used to shoot and record the operation process of the working medium in the pulsating heat pipe, and the digital camera transmits the captured image to a computer for data processing.

[0091] Step (2): Figure 3 A schematic diagram of a clear meniscus photographed by using an LED light to overcome the lens effect caused by the meniscus provided by an embodiment of the present invention. Figure 3 As shown in the figure, LED lights with uniform illumination intensity are arranged around the pulsating heat pipe. The LED light creates a light-dark contrast between the working fluid in the pipe and the background, illuminating a clear meniscus of the liquid column. The outermost boundary of the gas-liquid interface is well illuminated and produces a clear gas-liquid interface line. The gas-liquid interface line directly photographed by a digital camera has been refracted twice by liquid-quartz glass and quartz glass-air. The directly measured meniscus is not the actual meniscus of the working fluid in the pipe.

[0092] Step (3): If Figure 4 As shown, using the geometric relationship of the refraction of the working fluid in the pulsating heat pipe through the liquid-quartz glass and quartz glass-air, the normal line m1 at the interface between the liquid and the quartz glass, the normal line m2 at the interface between the quartz glass and the air, and the refracted light diagram between the meniscus and the measurement position are drawn. According to the selected marking points, the horizontal coordinate measurement length of the measurement coordinate point B on the gas-liquid interface line can be directly measured as L AB , the actual length L of the actual coordinate point C on the horizontal axis is calculated through the geometric relationship of refraction AC ∠AOB is the angle between the mark point B of the liquid contact angle measured directly and the point O where the digital camera is placed, ∠β inThe angle between the marked point C on the actual gas-liquid interface line and the digital camera placement point O is obtained by considering the refraction geometric relationship caused by the capillary material and light refraction. The contact angle measurement method proposed in the present invention is used to calculate the actual coordinates marked on the gas-liquid interface line, and the actual gas-liquid interface line curve of the liquid contact angle is fitted, and the actual contact angle is measured using the angle measurement tool in the software.

[0093] Step (4): Figure 5 A schematic diagram of the contact angle measurement deviation of a liquid in a capillary due to light refraction provided by an embodiment of the present invention. Figure 5 As shown, the actual contact angle measured in the present invention is the angle between the tangent line K2 and the glass tube wall. The present invention discusses the measurement of the contact angle of liquid in a cylindrical capillary made of quartz glass. The contact angle of the liquid in the cylindrical capillary is refracted twice by liquid-quartz glass and quartz glass-air. The refractive index of light in water is known to be n water =1.333, the refractive index n in the glass tube si =1.45847, the refractive index in air n air =1.00029, n water <n si . According to Snell's law, light is deflected toward the normal direction at the interface between the liquid and the glass tube, causing the liquid to appear larger than its actual size. Therefore, a tangent K1 is directly made to the gas-liquid interface curve to obtain the contact angle between the liquid and the glass tube wall. A tangent K2 is made to the actual gas-liquid interface line obtained by fitting the liquid contact angle measurement method proposed in the present invention to obtain the actual contact angle between the liquid and the glass tube wall, and the actual contact angle is smaller than the contact angle directly measured.

[0094] Step (5): Figure 6 A schematic diagram of the coordinate values ​​of the marking points on the meniscus curve provided by an embodiment of the present invention. The relatively clear gas-liquid interface line in the pulsating heat pipe is intercepted as the marking object for measuring the coordinates. In order to unify the measurement scale, the scale is marked on the image before reading the coordinates. From the gas-liquid interface line image taken by a digital camera, each marking point on the gas-liquid interface line (X i ,Y i ), as the measurement coordinate of the liquid contact angle measurement method proposed in the present invention. Measurement coordinate X i The size increases from left to right, Y i The size decreases from bottom to top, such as Figure 6 The measurement results are shown on the left.

[0095] Specific calculation process:

[0096] The horizontal coordinate measurement length of the measured coordinate point B is L ABThe horizontal distance L between the digital camera and the pulsating heat pipe specimen is known. According to the Pythagorean theorem in the right triangle, the length L between the measurement coordinate point B and the digital camera placement point O can be obtained. BO Size:

[0097]

[0098] For the right triangle ΔOAB, the sine function is defined as:

[0099]

[0100] From the inverse sine function, we can find the angle ∠AOB between the measurement coordinate point B and the digital camera placement point O:

[0101]

[0102] ∠AOB=∠AOE

[0103] In the right triangle ΔOAB, ∠BAO is a right angle, so ∠ABO can be obtained from the triangle interior angle theorem:

[0104]

[0105] ∠ABO=∠ABE

[0106] According to the sine theorem, the size of ∠ABE is known, and the length of the side opposite to ∠ABE is L AE , the length of the side opposite to ∠BEA is L AB , find ∠BEA:

[0107]

[0108] In triangle ΔABE, the magnitudes of ∠ABE and ∠BEA have been determined, and ∠EAB can be obtained from the triangle interior angle theorem:

[0109] ∠EAB=π-∠ABE-∠BEA

[0110] In the triangle ΔABE, since Having found ∠EAB, find ∠OAE:

[0111]

[0112] In triangle ΔAEO, ∠OAE and ∠AOE have been obtained. ∠AEO can be obtained by the triangle interior angle theorem:

[0113] ∠AEO=π-∠OAE-∠AOE

[0114] Because ∠AEO and ∠α re They are complementary angles, and we can find ∠αre :

[0115] ∠α re =π-∠AEO

[0116] Applying Snell's law to the quartz glass-air interface, when light enters the air from the glass, refraction occurs. The sine of the incident angle·the refractive index of the light in the glass = the sine of the refraction angle·the refractive index of the light in the air, we get:

[0117] sin∠α in ·n si = sin∠α re ·n air

[0118]

[0119] Using the triangular cosine theorem to solve for L DE , L DE The range is [L AE -L AD ,L AE ), when the solution of the equation does not satisfy it, discard the unsatisfactory solution:

[0120]

[0121] Known L DE , use the law of cosines to find the ADE:

[0122]

[0123] In triangle ΔADE, ∠α has been found in And ∠ADE, we can find ∠EAD by the triangle interior angle theorem:

[0124] ∠EAD=π-∠α in -∠ADE

[0125] Because ∠ADE and ∠β re As complementary angles, we get ∠β re :

[0126] ∠β re =π-∠ADE

[0127] Apply Snell's law to the liquid-quartz glass interface and use Snell's law to draw a refracted light diagram based on different measurement coordinate points. When light enters the glass from water, it is refracted. The sine of the incident angle·the refractive index of light in water = the sine of the refraction angle·the refractive index of light in glass, and we get:

[0128] sin∠β in ·n water = sin∠βre ·n si

[0129]

[0130] In triangle ΔACD, ∠β has been found in and ∠DAC, we get ∠ACD:

[0131] ∠ACD=π-∠β in -∠DAC

[0132] According to the sine theorem, ∠β in The length of the opposite side is L AC , the length of the side opposite to ∠ACD is L AD , find the distance L between the actual coordinate point C and the coordinate origin point A AC , L AC The range is: [0,L AD ];

[0133]

[0134] Step (6): Considering that the gas-liquid interface line of the working fluid in the tube is refracted twice by water-quartz glass-air, the calculation method proposed in the above step (5) is used to calculate the actual coordinate points of each measurement coordinate point marked on the gas-liquid interface line, and fit the actual gas-liquid interface line, such as Figure 7 Finally, the angle measurement tool in the software is used to measure the contact angle of the actual gas-liquid interface line. The measurement results are shown in Figure 7 As shown on the left, 1 and 2 refer to the contact angles of the droplet on the right and left sides respectively measured directly, and 3 and 4 refer to the contact angles of the droplet on the right and left sides measured by the actual gas-liquid interface line respectively. From the measurement results, it can be seen that the actual contact angle value of the droplet is smaller than the directly measured contact angle value. When the working fluid in the tube is at rest, the static liquid contact angle in the capillary is obtained.

[0135] Step (7): Based on the working fluid images collected at different times during the operation of the working fluid, the calculation method proposed in step (4) is used to perform image processing for the advancing liquid contact angle and the receding liquid contact angle, and different gas-liquid interfaces are fitted for calculation to obtain the advancing liquid contact angle and the receding liquid contact angle at different times, thereby obtaining the dynamic liquid contact angle.

[0136] In summary, the embodiments of the present invention specifically consider the measurement error of the liquid contact angle of the liquid in the capillary tube caused by factors such as the tube wall material and light refraction, and propose an operational measurement method for measuring the static liquid contact angle and dynamic liquid contact angle of the upper and lower liquid surfaces of the liquid in the capillary tube.

[0137] Those skilled in the art can understand that the accompanying drawings are only schematic diagrams of an embodiment, and the modules or processes in the accompanying drawings are not necessarily required to implement the present invention.

[0138] It can be known from the description of the above implementation methods that those skilled in the art can clearly understand that the present invention can be implemented by means of software plus a necessary general hardware platform. Based on such an understanding, the technical solution of the present invention is essentially or the part that contributes to the prior art can be embodied in the form of a software product, which can be stored in a storage medium such as ROM / RAM, a magnetic disk, an optical disk, etc., and includes a number of instructions for enabling a computer device (which can be a personal computer, a server, or a network device, etc.) to execute the methods described in the various embodiments of the present invention or certain parts of the embodiments.

[0139] Each embodiment in this specification is described in a progressive manner, and the same or similar parts between the embodiments can be referred to each other, and each embodiment focuses on the differences from other embodiments. In particular, for the device or system embodiment, since it is basically similar to the method embodiment, the description is relatively simple, and the relevant parts can be referred to the partial description of the method embodiment. The device and system embodiments described above are merely schematic, wherein the units described as separate components may or may not be physically separated, and the components displayed as units may or may not be physical units, that is, they may be located in one place, or they may be distributed on multiple network units. Some or all of the modules may be selected according to actual needs to achieve the purpose of the scheme of this embodiment. Ordinary technicians in this field can understand and implement it without paying creative labor.

[0140] The above is only a preferred specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed by the present invention should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

Claims

1. A method for measuring the contact angle of a liquid in a capillary tube, characterized in that: include: After the pulsating heat pipe specimen is evacuated by a vacuum pump, a liquid phase working medium is injected into the pulsating heat pipe specimen by a liquid filling system, and the liquid phase working medium forms gas and liquid columns that are alternately distributed in the pulsating heat pipe; A digital camera is used to record the static state and running process of the working fluid in the pulsating heat pipe to obtain the gas-liquid interface line image; Based on the gas-liquid interface line image, the measurement coordinate points of the gas-liquid interface line are calibrated, and the refracted light diagram is drawn based on different measurement coordinate points using Snell's law, and the actual coordinate points of each measurement coordinate point are calculated. The actual gas-liquid interface line of the working fluid in the tube is fitted according to each actual coordinate point, and the actual contact angle between the liquid and the glass tube wall is measured using an angle measurement tool.

2. The method according to claim 1, further comprising: The top of the pulsating heat pipe specimen is cooled in a water bath by using a cooling system, a heating wire is wound around the bottom of the pulsating heat pipe specimen, the heating power is adjusted by adjusting the input voltage through the heating system, the pulsating heat pipe specimen is heated, and images of the working fluid in the pipe running at different heating powers are obtained; LED lights are arranged around the pulsating heat pipe specimen. The LED light creates a light-dark contrast between the working fluid in the pulsating heat pipe and the background, and the gas-liquid interface line of the concave liquid surface of the liquid column can be observed.

3. The method according to claim 1 or 2, characterized in that: The method further comprises: The gas-liquid interface line image of the working fluid in the pulsating heat pipe specimen is collected based on a digital camera, and multiple measurement coordinate points are selected on the gas-liquid interface line. According to Snell's law, when the refractive index of the two media is different, the light will be deflected in the normal direction at the interface of the two media. The geometric relationship in the light refraction process is used to draw the refraction light diagram between the working fluid and the recording position in the pulsating heat pipe specimen. The functional relationship for measuring the liquid contact angle is established through the refraction light diagram, and the actual marking point coordinates of each measurement coordinate point are calculated. The actual gas-liquid interface line of the liquid contact angle is fitted, and the angle measurement tool in the Image J software is used to measure the actual contact angle between the liquid and the quartz glass tube wall. Images of the operation of the working fluid in the pulsating heat pipe at different heating powers are collected. Based on the operation images of the working fluid, the measurement points of the gas-liquid interface lines of the advancing liquid contact angle and the receding liquid contact angle are calibrated respectively. The actual coordinate points are calculated through the functional relationship of the liquid contact angle, and the actual gas-liquid interface lines of the advancing liquid contact angle and the receding liquid contact angle at different heating powers are fitted, thereby obtaining the actual advancing liquid contact angle and the receding liquid contact angle.

4. The method according to claim 3, characterized in that The method of using the geometric relationship in the light refraction process to draw a refraction light diagram between the working fluid and the recording position in the pulsating heat pipe specimen, establishing a functional relationship for measuring the liquid contact angle through the refraction light diagram, and calculating the actual marking point coordinates of each measurement coordinate point includes: Set the digital camera placement point as point O, set the horizontal distance between the digital camera and the pulsating heat pipe specimen as L, select the lowest point A of the meniscus curve as the coordinate origin, point B as the calibrated measurement coordinate point, point C as the actual coordinate point calculated by the functional relationship of the liquid contact angle, and the horizontal coordinate measurement length of the measurement coordinate point B is L AB , the actual length of the actual coordinate point C on the horizontal axis is L AC , ∠AOB is the angle between the measurement coordinate point B and the digital camera placement point O, ∠β in is the angle between the actual coordinate point C and the digital camera placement point O, and the distance between the actual coordinate point C and the coordinate origin point A is L AC ; The horizontal coordinate measurement length of the measured coordinate point B is L AB The horizontal distance L between the digital camera and the pulsating heat pipe specimen is known. According to the Pythagorean theorem in the right triangle, the length L between the measurement coordinate point B and the digital camera placement point O is obtained. BO Size: For the right triangle ΔOAB, the sine function is defined as: From the inverse sine function, we can get the angle ∠AOB between the measurement coordinate point B and the digital camera placement point O: ∠AOB=∠AOE In the right triangle ΔOAB, ∠BAO is a right angle, so ∠ABO can be obtained from the triangle interior angle theorem: ∠ABO=∠ABE According to the sine theorem, the size of ∠ABE is known, and the length of the side opposite to ∠ABE is L AE , the length of the side opposite to ∠BEA is L AB , find ∠BEA: In triangle ΔABE, the magnitudes of ∠ABE and ∠BEA have been determined, and ∠EAB can be obtained from the triangle interior angle theorem: ∠EAB=π-∠ABE-∠BEA In the triangle ΔABE, since Having found ∠EAB, find ∠OAE: In triangle ΔAEO, ∠OAE and ∠AOE have been obtained. ∠AEO can be obtained by the triangle interior angle theorem: ∠AEO=π-∠OAE-∠AOE Because ∠AEO and ∠α re They are complementary angles, and we can find ∠α re : ∠a re =π-∠AEO Applying Snell's law to the quartz glass-air interface, when light enters the air from the glass, refraction occurs. The sine of the incident angle·the refractive index of the light in the glass = the sine of the refraction angle·the refractive index of the light in the air, we get: sin∠α in ·n si =sin∠α re ·n air Using the triangular cosine theorem to solve for L DE , L DE The range is [L AE -L AD ,L AE ), when the solution of the equation does not satisfy it, discard the unsatisfactory solution: Known L DE , use the law of cosines to find the ADE: In triangle ΔADE, ∠α has been found in And ∠ADE, we can find ∠EAD by the triangle interior angle theorem: ∠EAD=π-∠α in -∠ADE Because ∠ADE and ∠β re As complementary angles, we get ∠β re : ∠β re =π-∠ACD Applying Snell's law to the interface between liquid and quartz glass, light is refracted when it enters the glass from water. The sine of the incident angle·the refractive index of light in water = the sine of the refraction angle·the refractive index of light in glass, and we get: sin∠β in ·n water =sin∠β re ·n si In triangle ΔACD, ∠β has been found in and ∠DAC, we get ∠ACD: ∠ACD=π-∠β in -∠DAC According to the sine theorem, ∠β in The length of the opposite side is L AC , the length of the side opposite to ∠ACD is L AD , find the distance L between the actual coordinate point C and the coordinate origin point A AC , L AC The range is: [0,L AD ]; Therefore, the actual coordinate point is determined according to the actual length of the actual coordinate point C on the horizontal axis, and the actual gas-liquid interface line of the droplet is fitted according to the actual coordinate point to measure the true liquid contact angle.

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