Comprehensive experimental instrument for measuring viscosity coefficient and surface tension coefficient of liquid

Abstract

The invention relates to the technical field of college physics experiment devices, and discloses a liquid viscosity coefficient and surface tension coefficient measurement comprehensive experiment instrument, which comprises a test bed, a first square column container, a second square column container, a timing automatic release device, a force sensor, a metal circular ring, an industrial camera matched with a telecentric lens, a lifting platform and a host. According to the invention, two original experimental devices are combined into one, so that the cost is saved, and the laboratory space is also saved; by designing the timed automatic release device, manpower is saved, and errors caused by manual operation of an original experimental instrument can be reduced; and the instantaneous speed of the small ball on the falling path is measured by using a machine vision technology, so that the selection basis for selecting the constant-speed motion interval of the small ball can be explored.

Description

Technical Field

[0001] The invention relates to the technical field of university physics experimental devices, and more particularly to a comprehensive experimental instrument for measuring liquid viscosity coefficient and surface tension coefficient. Background Art

[0002] The measurement of liquid viscosity is a typical teaching experiment in university physics. It has important guiding significance for the study of force and fluid mechanics. The falling ball method is often used to determine the viscosity of liquids. This experimental method has become a classic method for basic physics experiments in colleges and universities due to its teaching advantages such as intuitive phenomena and clear principles. This method is suitable for transparent or translucent liquids with high viscosity. Other measured quantities in this experiment can be measured relatively conveniently and accurately, but the time of uniform motion of the ball is difficult to measure accurately. The simplest way at present is to select a uniform motion interval and measure its motion time with a stopwatch, but the manual timing error of the stopwatch is large. A more accurate timing method is to use photoelectric gate timing. Its main working principle is to build a photoelectric gate through two upper and lower laser beams. During the falling process of the ball, the light will be blocked twice, and the time when the ball passes through the two laser beams can be obtained, and then the time when the ball falls at a uniform speed can be accurately obtained. However, in the actual experimental operation, the instrument has the following shortcomings:

[0003] 1. Manually releasing the ball is time-consuming and labor-intensive;

[0004] 2. Before conducting the experiment, you first need to adjust the positions of the two photoelectric gates to ensure that the laser beam emitted by the laser transmitter passes through the liquid container and is received by the laser receiver at the other end. Due to the low laser power, the laser receiver has difficulty receiving it, which makes the instrument adjustment cumbersome;

[0005] 3. The two laser beams must be kept on the same vertical plane, and the release position of the ball must also be ensured to be on the corresponding vertical plane. This is to ensure that the ball can successfully block the two laser beams when it falls and complete the timing. The success rate of the ball drop operation is low;

[0006] 4. There's no rationale for choosing the distance between the two lasers. The experiment requires the ball to move at a constant speed, but there's no specific explanation for how to ensure constant movement between the photoelectric gates.

[0007] 5. The non-infinite depth and width of the liquid is handled by correcting the theoretical formula; however, the instrument is only equipped with one specification of container, and it is impossible to explore how the container size affects the viscosity coefficient under non-infinite depth and width conditions.

[0008] At the same time, the molecules in the surface layer of the liquid are subjected to a pulling force directed toward the interior of the liquid, causing the surface of the liquid to tend to shrink. This force acting perpendicularly on a unit length along the surface of the liquid is called surface tension. In the experiment to measure the surface tension coefficient of liquids, when a metal frame (such as a rectangular frame) is slowly pulled up on the liquid surface, a liquid film will form on the metal frame; if the liquid film is to break, the pulling force must overcome the effect of surface tension. The key to this experiment is to measure the difference in pulling force before and after the water film breaks using a force-sensitive sensor. In order to accurately measure the surface tension of the liquid, the water film must be in a vertical direction when it breaks, which places high demands on the experimental operation. In addition, there is no basis for judging whether the water film is vertical or not in the experiment. The water film can only be slowly pulled up, and when it breaks, it is considered to be vertical. But obviously, the water film may not have reached a vertical state at all when it breaks, which brings additional errors to the experiment.

[0009] In addition, in university physics experiments, the measurement of liquid viscosity coefficient and the measurement of liquid surface tension coefficient belong to two different experimental contents, which require two independent sets of experimental equipment to complete, which also adds unnecessary burden to the experimental space layout and experimental funds. Summary of the Invention

[0010] In view of this, the present invention proposes a comprehensive experimental instrument for measuring liquid viscosity coefficient and surface tension coefficient, and its specific technical solution is as follows:

[0011] A comprehensive experimental instrument for measuring liquid viscosity coefficient and surface tension coefficient, comprising a test bench, a first square cylindrical container, a second square cylindrical container, a timed automatic release device, a force-sensitive sensor, a metal ring, an industrial camera with a telecentric lens, a lifting platform, and a host computer;

[0012] The test bench includes a bottom support platform, a support frame mounted on the upper surface of the bottom support platform, a loading platform that can be temporarily placed in the middle section of the support frame, and a top plate mounted on the top of the support frame and having a circular hole. The first and second square cylindrical containers are both open at the top and made of highly transparent acrylic sheet material. The height of the first square cylindrical container is greater than that of the second square cylindrical container. When conducting a liquid viscosity coefficient measurement experiment, the first square cylindrical container is placed on the bottom support platform; when conducting a surface tension coefficient measurement experiment, the second square cylindrical container is placed on the loading platform.

[0013] The timed automatic release device includes a ball container, a ball drop funnel installed in the circular hole of the top plate, and a timer pusher that can push the ball in the ball container into the ball drop funnel according to the set time interval. The ball container, ball drop funnel, and timer pusher can all be detachably installed on the top plate, with the bottom of the circular hole of the top plate facing the upper opening of the square column-shaped container in the experiment. The timer pusher can also be installed in the circular hole of the top plate with the push rod facing downward. In this case, a force sensitive sensor is installed below the push rod of the timer pusher, and a metal ring is suspended horizontally below the force sensitive sensor through several suspension lines.

[0014] The main unit is located outside the test bench, and is equipped with a power switch and a timed automatic release control system electrically connected to the timed automatic release device; the lifting platform is placed on the upper part of the main unit, and the industrial camera equipped with a telecentric lens is placed on the lifting platform, and the telecentric lens is facing one of the side walls of the corresponding square cylindrical container; a background light source is provided on the outer wall of the square cylindrical container away from the industrial camera, and the light in the background light source is vertically incident from one side of the square cylindrical container, passes through the container wall and enters the liquid to be tested, and then is emitted from the container wall on the other side and enters the telecentric lens of the industrial camera.

[0015] Preferably, the timing pusher includes a timing controller and a DC electric push rod, and the timing controller is electrically connected to the timing automatic release control system and the DC motor in the DC electric push rod respectively; the timing automatic release control system pre-sets the push rod time interval, advancement distance and number of push rods, and then the timing controller controls the DC motor to drive the push rod in the DC electric push rod to move forward a set distance, automatically returns to its position after moving the specified distance, waits for the set time interval to perform the next push rod action, and cycles until the set number of push rods is completed; the timing controller can also control the DC electric push rod to forcibly stop the push rod action midway.

[0016] Preferably, the ball container with a top opening is arranged between the ball falling funnel and the timing pusher, and the inner cavity of the ball container can accommodate a plurality of balls in a vertical arrangement; a push rod insertion port is provided at the lower part of the ball container facing the timing pusher, and a ball ejection port is provided at the lower part facing the ball falling funnel, and the push rod insertion port and the ball ejection port are arranged opposite to each other.

[0017] Preferably, the background light source is a blue LED light source with a diffusion plate, and a linear polarizer is installed in the middle of the surface of the diffusion plate.

[0018] Preferably, an outer bracket for temporarily storing the loading platform is installed on the outer side of the support frame.

[0019] Preferably, a circular hole for the ball to pass through is opened on one side of the bottom of the first square cylindrical container, and a vertical connecting tube with an open top is connected to the outside of the circular hole. The connecting tube is fixedly connected to the outer wall of the first square cylindrical container, and the outer wall of the connecting tube can attract magnets.

[0020] Preferably, the first square cylindrical container has multiple specifications with different column widths, and the influence of non-infinite depth and width on the viscosity coefficient of the liquid is explored by selecting first square cylindrical containers of different specifications.

[0021] Preferably, a level is also installed on the bottom support platform of the test bench.

[0022] Preferably, the industrial camera equipped with a telecentric lens is connected to an external computer or an image data processing system in a host computer, and the host computer is also provided with a display screen.

[0023] Compared with the prior art, the comprehensive experimental instrument for measuring liquid viscosity coefficient and surface tension coefficient of the present invention has the following beneficial effects:

[0024] 1. The present invention creatively integrates the liquid viscosity coefficient measuring instrument and the surface tension coefficient measuring instrument through machine vision technology, combining the original two sets of experimental devices into one, saving both cost and laboratory space.

[0025] 2. The present invention utilizes a timed automatic release mechanism, which not only saves manpower but also makes the ball's drop position more controllable. Furthermore, the timed automatic release mechanism can simultaneously control the drop position and time of multiple balls, reducing the errors introduced by manual operation in conventional experimental instruments.

[0026] 3. The present invention uses machine vision technology to measure the instantaneous velocity of the ball on the falling path, which can explore the basis for selecting the uniform motion interval of the ball.

[0027] 4. The present invention can explore the influence of non-infinite depth and width on the viscosity coefficient of liquid by selecting first square cylindrical containers with different column width sizes.

[0028] 5. The present invention can use machine vision to measure the surface tension coefficient of the liquid through simple accessory adjustments; at the same time, the complete change process of the water film can be observed, overcoming the requirement of the original experimental device that the water film should be in a vertical state when it breaks, but cannot determine whether it is vertical. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are merely embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying any creative work.

[0030] Figure 1 This is a schematic diagram of the front structure of the device when the comprehensive experimental instrument of the present invention is used to perform a liquid viscosity coefficient measurement experiment.

[0031] Figure 2 Axonometric view of the device structure when the comprehensive experimental instrument of the present invention is used to measure the liquid viscosity coefficient Figure I .

[0032] Figure 3 This is the axonometric diagram II of the device structure when the comprehensive experimental instrument of the present invention is used to perform a liquid viscosity coefficient measurement experiment.

[0033] Figure 4 This is a schematic diagram of the front structure of the device when the comprehensive experimental instrument of the present invention is used to perform a surface tension coefficient measurement experiment.

[0034] Figure 5 This is an axonometric diagram of the device structure when the comprehensive experimental instrument of the present invention is used to perform a surface tension coefficient measurement experiment.

[0035] In the figure: 1-first square cylindrical container, 2-second square cylindrical container, 3-force sensitive sensor, 4-metal ring, 5-industrial camera with telecentric lens, 6-lifting platform, 7-host, 8-bottom support platform, 9-support frame, 10-loading platform, 11-top plate, 12-ball funnel, 13-small ball container, 14-timing pusher, 15-suspension line, 16-background light source, 17-external bracket, 18-connecting pipe, 19-level. DETAILED DESCRIPTION

[0036] The following describes embodiments of the present invention in detail, 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 intended to be used to explain the present invention, and are not to be construed as limiting the present invention.

[0037] In the description of the present invention, it should be understood that the terms "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", etc., indicating directions or positional relationships, are based on the directions or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific direction, be constructed and operated in a specific direction, and therefore should not be understood as limiting the present invention.

[0038] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of the technical features being referred to. Thus, a feature identified as "first" or "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, "plurality" means two or more, unless otherwise specifically defined.

[0039] Example:

[0040] Based on the deficiencies of liquid viscosity coefficient measuring instruments and surface tension coefficient measuring instruments and the integration of related experimental instruments and equipment, this embodiment provides a set of high-precision liquid viscosity coefficient and surface tension coefficient measurement comprehensive experimental instruments based on machine vision.

[0041] For details, see Figure 1-Figure 5 The comprehensive experimental instrument for measuring liquid viscosity coefficient and surface tension coefficient includes a test bench, a first square cylindrical container 1, a second square cylindrical container 2, a timed automatic release device, a force sensitive sensor 3, a metal ring 4, an industrial camera with a telecentric lens 5, a lifting platform 6 and a host 7.

[0042] Among them, the test bench includes a bottom support platform 8, a support frame 9 installed on the upper surface of the bottom support platform, a loading platform 10 that can be temporarily placed in the middle section of the support frame, and a top plate 11 installed on the top of the support frame and having a circular hole; the first square cylindrical container 1 and the second square cylindrical container 2 are both open at the top and are made of highly transparent acrylic plate material. The height of the first square cylindrical container 1 is greater than that of the second square cylindrical container 2; when conducting a liquid viscosity coefficient measurement experiment, the first square cylindrical container 1 is placed on the bottom support platform 8; when conducting a surface tension coefficient measurement experiment, the second square cylindrical container 2 is placed on the loading platform 10.

[0043] The timed automatic release device includes a ball container 13, a ball dropping funnel 12 installed at the circular hole of the top plate, and a timing pusher 14 that can push the balls in the ball container 13 into the ball dropping funnel 12 according to the set time interval. The ball container 13, the ball dropping funnel 12, and the timing pusher 14 can all be detachably installed on the top plate 11. The bottom of the circular hole of the top plate faces the upper opening of the square cylindrical container in the experiment, that is, in the liquid viscosity coefficient measurement experiment, the bottom of the ball dropping funnel 12 faces the upper opening of the first square cylindrical container 1. The ball dropping funnel 12 can play a role in assisting in positioning the balls.

[0044] The host 7 is arranged outside the test bench, and is provided with a power switch and a timed automatic release control system electrically connected to the timed automatic release device; the host 7 is also provided with a power indicator light and the like.

[0045] This embodiment can improve the convenience and accuracy of releasing the balls by adding a timing pusher 14 and a corresponding ball container 13 on the basis of the existing technology.

[0046] In a further specific embodiment, the timing pusher 14 includes a timing controller and a DC electric push rod, and the timing controller is electrically connected to the timing automatic release control system in the host 7 and the DC motor in the DC electric push rod respectively; the timing automatic release control system pre-sets the push rod time interval, advancement distance and number of push rods, and then the timing controller controls the DC motor to drive the push rod in the DC electric push rod to move forward a set distance, automatically returns to its position after moving the specified distance, and waits for the set time interval to perform the next push rod action, and the cycle continues until the set number of push rods is completed.

[0047] In addition, the timing controller can also control the DC electric push rod to force the push rod to stop midway.

[0048] At the same time, a ball container 13 with an opening at the top is arranged between the ball falling funnel 12 and the timing pusher 14, and the inner cavity of the ball container 13 can accommodate a number of balls in a vertical arrangement; a push rod insertion port is provided at the lower part of the ball container 13 facing the timing pusher, and a ball push-out port is provided at the side facing the ball falling funnel. The push rod insertion port and the ball push-out port are arranged opposite to each other, and the push rod can push the lowest ball in the ball container 13 into the funnel. After the lowest ball is pushed away, the upper balls fall down and continue to be pushed regularly.

[0049] Before the experiment, the required balls are first loaded into the ball container 13 with the top opening, and the time interval for pushing the balls is set. The position of the ball drop funnel 12 is installed, and then the balls can be dropped from the same position during the experiment with the same drop interval time.

[0050] The design of the timing automatic release device in this embodiment not only saves experimental time, but also improves the accuracy of the experiment, allowing the experiment to be carried out more efficiently.

[0051] The lifting platform 6 is placed on the upper part of the main unit 7, and the system for controlling the lifting of the lifting platform 6 is located inside the main unit 7; the industrial camera 5 equipped with a telecentric lens is placed on the lifting platform 6, and the telecentric lens is facing one of the side walls of the corresponding square cylindrical container; a background light source 16 is provided on the outer wall of the square cylindrical container away from the industrial camera. Since the material used for the square cylindrical container in this embodiment is a highly transparent acrylic plate, the light in the background light source 16 is vertically incident from one side of the square cylindrical container, passes through the container wall and enters the liquid to be tested, and then is emitted from the container wall on the other side and enters the telecentric lens of the industrial camera.

[0052] The presence of background light source 16 creates a stable and uniform light field within the square cylindrical container. This eliminates the smear of the ball and the light spots caused by refraction within the liquid, thus preventing localized overly bright or overly dark areas in the image. Furthermore, background light source 16 renders the metal ball as a high-contrast silhouette, facilitating image segmentation and centroid location, enabling accurate measurement of the ball's uniform motion velocity.

[0053] In a further specific embodiment, the background light source 16 is a blue LED light source with a diffuser, and a linear polarizer is installed in the middle of the surface of the diffuser.

[0054] Blue light was chosen because transparent liquids like dishwashing liquid have a low absorption rate for blue light, allowing it to easily penetrate the liquid. The diffuser converts the LED's point light source into a surface light source, allowing the light to penetrate the liquid evenly and enhance the contrast between the ball and the background. The linear polarizer eliminates some polarized light, making the ball's outline clearer.

[0055] The invention discloses a comprehensive experimental instrument for measuring liquid viscosity coefficient and surface tension coefficient, which is suitable for measuring the viscosity coefficient of transparent or translucent liquids (such as detergents and oils). By optimizing the light source and polarizer, environmental interference is eliminated and measurement accuracy is improved.

[0056] The experimental principle for measuring the viscosity coefficient of liquid in this embodiment is:

[0057] A micro-scale fixed ball with mass m and volume V is slowly making quasi-static sedimentation motion in a viscous liquid with density ρ0. At the same time, the liquid satisfies the condition of infinite depth and width. There are three forces acting on the system: the gravity of the ball F a = mg, buoyancy F b =ρ0gV and resistance f. The resistance is caused by the internal friction of the liquid, that is, the viscous resistance. According to Stokes' law, the viscous resistance f is:

[0058] f=6πηυr

[0059] Where η is the viscosity of the liquid, υ is the speed of the falling ball, and r is the radius of the ball.

[0060] The falling of a ball in a liquid can be divided into two processes. The first is the acceleration process, in which gravity is greater than the sum of buoyancy and resistance. However, as the speed of the ball increases, the resistance also increases, and the acceleration decays as the speed increases until it reaches the second process, the equilibrium stage. At this time, gravity is equal to the sum of buoyancy and resistance, achieving a balance of three forces, and the ball begins to fall at a uniform speed.

[0061]

[0062] In fact, the container for liquid has a certain size and depth. The liquid is not infinitely deep and wide. Suppose the height of the liquid in the cylinder with a radius of R0 is h, and the diameter of the ball is d. Then, if the influence of the wall is taken into account and the ball descends along the central axis of the cylinder, the formula is corrected to:

[0063]

[0064] It can be seen that measuring the speed of the ball when it falls at a uniform speed is the key to this experiment.

[0065] The original container is a cylindrical container. In order to prevent the cylindrical container from interfering with the emission and refraction of background light, a square cylindrical container is used. Due to the change in container shape, the revised formula needs to be re-derived.

[0066] For rectangular containers, take the equivalent diameter D of the container d It is 4 times the ratio of the cross-sectional area of ​​the pipe to its perimeter. If the length and width of the rectangular pipe are A and B respectively, then:

[0067]

[0068] The current container is a square. Let the side length of the square cylinder be a, that is, A=B=a. Then the equivalent diameter of the square cylinder is:

[0069]

[0070] Therefore, for a square cylindrical container, the corrected liquid viscosity coefficient calculation formula is:

[0071]

[0072] In the prior art, the diameter of the ball in the original experiment was small, and the laser beam was thin, resulting in a high failure rate in triggering the photoelectric timing, making it impossible to measure the uniform velocity of the ball. Therefore, in order to accurately measure the uniform velocity of the ball, this embodiment uses machine vision technology to measure it.

[0073] Specifically, before conducting the liquid viscosity coefficient measurement experiment, this embodiment first fills a certain amount of detergent liquid into the first square cylindrical container 1, and sets a blue LED light source with a diffuser on one side of the first square cylindrical container. At the same time, a linear polarizer is placed close to the surface of the diffuser. The first square cylindrical container 1 is placed on the bottom support platform 8, and the bottom of the ball dropping funnel 12 is facing the upper opening of the first square cylindrical container 1; then, an industrial camera 5 with a telecentric lens is placed in front of the other side of the first square cylindrical container where the blue LED backlight is installed. The industrial camera 5 with a telecentric lens is externally connected to a computer, and the graphics captured by the lens can be input into the computer. The speed of the ball movement can be accurately measured through processes such as system calibration, image acquisition, image preprocessing, ball center of mass positioning and speed fitting.

[0074] In this embodiment, an image data processing system can be provided within the host computer 7, and the industrial camera 5 equipped with a telecentric lens can be electrically connected to the image data processing system. This allows the host computer 7 to directly perform processes such as system calibration, image acquisition, image preprocessing, ball center of mass location, and velocity fitting, eliminating the need for an external computer. Like a computer, the host computer 7 can also be equipped with a display screen for displaying data processing results.

[0075] This embodiment uses machine vision technology to directly obtain the speed data of the ball's movement using a camera + a corresponding image data processing system, unlike other methods that only measure the time of the ball's movement and then use the movement distance to obtain the speed of the ball.

[0076] In this embodiment, the timing pusher 14 in the timing automatic release device can also be adapted to be installed in the circular hole of the top plate 11 with the push rod facing downward. At this time, the force sensitive sensor 3 is installed below the push rod in the timing pusher 14, and the metal ring 4 is suspended horizontally below the force sensitive sensor 3 through several suspension lines 15. This configuration is used to conduct surface tension coefficient measurement experiments.

[0077] The experimental principle for measuring the surface tension coefficient of liquid in this embodiment is:

[0078] In the liquid surface tension experiment, a clean metal ring 4 is suspended horizontally on the lower side of the force sensor 3, and then the ring is immersed in the liquid to be tested. The ring is slowly pulled up, and the suspended ring will bring up a layer of liquid film. The surface tension f that causes the liquid surface to shrink is along the tangent direction of the liquid surface, and the angle θ is called the wetting angle (or contact angle). When the ring is continued to be lifted, the angle θ gradually becomes smaller and approaches zero. At this time, the tension f on the inner and outer surfaces of the pulled liquid film is vertically downward. Assuming that the pulling force on the force sensor 3 when the liquid film is pulled up and is about to break but does not break is F1, there is

[0079] F1=mg+f

[0080] Where m is the mass of the ring, and the surface tension is proportional to the length of the boundary around the contact surface, then:

[0081] f=π(D 内 +D 外 )·α

[0082] When the water film breaks, the tension on the force sensor 3 is F2, and F2 = mg. Therefore, the difference in tension F between the force sensor 3 before and after the water film breaks is the surface tension of the water on the metal ring 4, that is:

[0083] F=F1-F2=f=π(D 内 +D 外 )·α

[0084] The force applied to the dynamometer of force-sensitive sensor 3 is proportional to the output voltage. Before the water film breaks, the voltage readings are U1 and U2 respectively. Then:

[0085]

[0086] The surface tension coefficient α of water can be measured:

[0087]

[0088] If the contact angle of the surface tension at a certain moment from the time the water film is pulled up to the time the water film has not yet broken is θ, then the surface tension coefficient α is corrected to:

[0089]

[0090] When conducting a surface tension coefficient measurement experiment, first place the loading platform 10 on the platform bracket in the middle of the support frame 9, and adjust the position of the loading platform 10. Place the second square cylindrical container 2 filled with a certain amount of liquid to be tested on the loading platform 10, and hang the metal ring 4 on the force-sensitive sensor 3. Let the lower edge of the metal ring 4 be immersed in the liquid to a position approximately half the height of the ring. The force-sensitive sensor 3 is connected to the push rod in the timing pusher 14 through a hook. Set the retraction speed of the push rod, and slowly retract the push rod to drive the metal ring 4 to slowly rise, thereby pulling up the water film. When the metal ring 4 pulls up the water film and remains stationary for a certain moment, the shape of the water film is determined by the balance of surface tension and gravity. At this time, the angle θ between the water film and the vertical direction is:

[0091] F1=mg+fcosθ

[0092] The shape of the water film at this time is captured by an industrial camera, and the contact angle at this time is analyzed based on the data image captured by the industrial camera, and directly substituted into the corresponding formula to obtain the surface tension coefficient of the liquid.

[0093] In this embodiment, an industrial camera can also be used to capture the shape of the water film at different times to obtain the contact angles at different times, and the correctness of the surface tension coefficient can be verified by comparing the contact angles at different times.

[0094] This embodiment uses machine vision technology to measure the surface tension of the liquid, which not only avoids judging whether the water film is in a vertical state when it breaks, but also allows the entire change process of the water film from being pulled up to breaking to be observed through an industrial camera.

[0095] That is, the comprehensive experimental instrument of the present invention can not only measure the surface tension coefficient of liquid, but also simultaneously observe the entire process of liquid water film from pulling up to rupture, thereby deepening students' intuitive understanding of liquid surface tension.

[0096] After the ball is released, it enters free fall until it contacts the liquid surface. After contacting the liquid surface, its motion trend is to first decelerate and then maintain a constant velocity. Because the solution is not infinitely deep or wide, the ball's velocity decreases further as it approaches the bottom of the container. Therefore, the ball's velocity is not constant throughout its entire fall. However, the experiment requires measuring the ball's velocity over a certain distance of uniform motion during its fall. Therefore, as long as we can determine the ball's instantaneous velocity at different locations during its fall, we can determine which interval is the uniform motion interval.

[0097] In this embodiment, machine vision measurement of a ball's velocity is based on image data and kinematic analysis. First, data is collected and preprocessed. A camera captures each frame of the ball's falling motion, and a centroid positioning algorithm is used to determine the ball's position coordinates and time in each frame. Using the camera's measurement starting point as a reference, the vertical displacement of the ball in each frame is calculated, and the relationship between displacement and time is determined. The velocity of the ball is then determined using a differential method. Because the time interval between each camera frame is very short, the velocity obtained using this method can be considered the instantaneous velocity at that position. The velocity of each frame can be used to determine the interval of the ball's uniform motion.

[0098] In a further specific embodiment, an outer bracket 17 for temporarily storing the loading platform 10 is installed on the outer side of the support frame 9 .

[0099] In a further specific embodiment, a circular hole is provided on one side of the bottom of the first square cylindrical container 1 for the small ball to pass through, and a vertical connecting tube 18 with an open top is connected to the outside of the circular hole. The connecting tube 18 is fixedly connected to the outer wall of the first square cylindrical container, and the outer wall of the connecting tube 18 can attract a magnet (not shown in the figure).

[0100] In this embodiment, the balls that fall to the bottom of the first square-cylindrical container 1 can be recovered by magnetic attraction. The circular hole at the bottom of the first square-cylindrical container and the connecting tube 18 together form a communicating vessel. Specifically, after the experiment is completed, a magnet can be attached to the lower side of the outer wall of the communicating tube 18 to attract the balls from the communicating vessel. The magnet can then be controlled to slide upward to finally remove the balls from the top opening of the communicating tube 18.

[0101] Directly using a magnet to draw the beads from the first cylindrical container 1 would cause bubbles to form in the liquid within the container, potentially affecting the experimental results. This method, however, effectively avoids this by indirectly recovering the beads through a connecting tube 18 on one side. The first cylindrical container 1 in this embodiment is available in various sizes with varying column widths. Operators can select first cylindrical containers 1 of varying sizes and measure the viscosity coefficients for these different container sizes to explore the impact of the non-infinite depth and width of the liquid on the measurement. For first cylindrical containers 1 of varying sizes, the relevant equipment can be installed using the same method.

[0102] In a further specific embodiment, in order to ensure the horizontality of the bottom support platform 8 and the accuracy of the final experimental data, a level 19 is further installed on the bottom support platform 8 of the test bench.

[0103] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. Reference can be made to the common and similar parts between the various embodiments. For the devices disclosed in the embodiments, since they correspond to the methods disclosed in the embodiments, the description is relatively simple, and the relevant parts can be referred to the method description.

[0104] The above description of the disclosed embodiments is intended to enable one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be readily apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention is not limited to the embodiments described herein but is to be construed in the widest possible manner consistent with the principles and novel features disclosed herein.

Claims

1. A comprehensive experimental instrument for measuring liquid viscosity coefficient and surface tension coefficient, characterized in that: It includes a test bench, a first square cylindrical container, a second square cylindrical container, a timed automatic release device, a force-sensitive sensor, a metal ring, an industrial camera with a telecentric lens, a lifting platform, and a host computer; The test bench includes a bottom support platform, a support frame mounted on the upper surface of the bottom support platform, a loading platform that can be temporarily placed in the middle section of the support frame, and a top plate mounted on the top of the support frame and having a circular hole. The first and second square cylindrical containers are both open at the top and made of highly transparent acrylic sheet material. The height of the first square cylindrical container is greater than that of the second square cylindrical container. When conducting a liquid viscosity coefficient measurement experiment, the first square cylindrical container is placed on the bottom support platform; when conducting a surface tension coefficient measurement experiment, the second square cylindrical container is placed on the loading platform. The timed automatic release device includes a ball container, a ball drop funnel installed in the circular hole of the top plate, and a timer pusher that can push the ball in the ball container into the ball drop funnel according to the set time interval. The ball container, ball drop funnel, and timer pusher can all be detachably installed on the top plate, with the bottom of the circular hole of the top plate facing the upper opening of the square column-shaped container in the experiment. The timer pusher can also be installed in the circular hole of the top plate with the push rod facing downward. In this case, a force sensitive sensor is installed below the push rod of the timer pusher, and a metal ring is suspended horizontally below the force sensitive sensor through several suspension lines. The main unit is located outside the test bench, and is equipped with a power switch and a timed automatic release control system electrically connected to the timed automatic release device; the lifting platform is placed on the upper part of the main unit, and the industrial camera equipped with a telecentric lens is placed on the lifting platform, and the telecentric lens is facing one of the side walls of the corresponding square cylindrical container; a background light source is provided on the outer wall of the square cylindrical container away from the industrial camera, and the light in the background light source is vertically incident from one side of the square cylindrical container, passes through the container wall and enters the liquid to be tested, and then is emitted from the container wall on the other side and enters the telecentric lens of the industrial camera.

2. A comprehensive experimental instrument for measuring liquid viscosity coefficient and surface tension coefficient according to claim 1, characterized in that: The timing pusher includes a timing controller and a DC electric push rod. The timing controller is electrically connected to the timing automatic release control system and the DC motor in the DC electric push rod respectively; the timing automatic release control system pre-sets the push rod time interval, advancement distance and number of push rods, and then the timing controller controls the DC motor to drive the push rod in the DC electric push rod to move forward a set distance, automatically returns to its position after moving the specified distance, waits for the set time interval to perform the next push rod action, and repeats until the set number of push rods is completed; the timing controller can also control the DC electric push rod to forcefully stop the push rod action midway.

3. The comprehensive experimental instrument for measuring liquid viscosity coefficient and surface tension coefficient according to claim 2, characterized in that: The ball container with an opening at the top is arranged between the ball falling funnel and the timing pusher, and the inner cavity of the ball container can accommodate a plurality of balls in a vertical arrangement; the lower part of the ball container is provided with a push rod insertion port facing the timing pusher, and a ball ejection port facing the ball falling funnel, and the push rod insertion port and the ball ejection port are arranged opposite to each other.

4. The comprehensive experimental instrument for measuring liquid viscosity coefficient and surface tension coefficient according to claim 1, characterized in that: The background light source is a blue LED light source with a diffuser plate, and a linear polarizer is installed in the middle of the surface of the diffuser plate.

5. The comprehensive experimental instrument for measuring liquid viscosity coefficient and surface tension coefficient according to claim 1, characterized in that: An outer bracket for temporarily storing a loading platform is installed on the outer side of the support frame.

6. A comprehensive experimental instrument for measuring liquid viscosity coefficient and surface tension coefficient according to claim 1, characterized in that: A circular hole for the ball to pass through is provided on one side of the bottom of the first square column container. A vertical connecting pipe with an open top is connected to the outside of the circular hole. The connecting pipe is fixedly connected to the outer wall of the first square column container, and the outer wall of the connecting pipe can attract a magnet.

7. The comprehensive experimental instrument for measuring liquid viscosity coefficient and surface tension coefficient according to claim 1, characterized in that: The first square cylindrical container has various specifications with different column widths. By selecting first square cylindrical containers of different specifications, the influence of non-infinite depth and width on the viscosity coefficient of the liquid is explored.

8. The comprehensive experimental instrument for measuring liquid viscosity coefficient and surface tension coefficient according to claim 1, characterized in that: A level is also installed on the bottom support platform of the test bench.

9. The comprehensive experimental instrument for measuring liquid viscosity coefficient and surface tension coefficient according to claim 1, characterized in that: The industrial camera equipped with a telecentric lens is connected to an external computer or an image data processing system in a host computer, which is also equipped with a display screen.

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