Liquid surface tension coefficient measurement device based on surface waves

Abstract

This invention discloses a device for measuring the surface tension coefficient of liquids based on surface waves. The invention includes a light box, an imaging box, a vibration table, and a signal generator. The light box has a light-emitting hole at the top, housing a built-in light-emitting diode (LED), and a plano-convex lens is arranged in the optical path. The imaging box is a height-adjustable enclosure with an open bottom and a diffuser on the top. The vibration table includes two identical resonant horns positioned on opposite sides of the light-emitting hole, and a light-transmitting plate mounted on the two horns; a light-transmitting water tank is movably mounted on the light-transmitting plate. The two resonant horns are connected to the signal generator via a power amplifier and vibrate at the same frequency. The LED is connected to the signal generator via a strobe light controller and flashes pulses at the same frequency. The diffuser produces bright and dark fringes, and the surface tension coefficient of the liquid under test is obtained by measuring the distance between two bright fringes. This invention achieves high measurement accuracy with a simple device, and has advantages such as safety and reliability, making it suitable for experimental teaching in higher education institutions.

Description

Technical Field

[0001] This invention belongs to the field of experimental and measurement technology, and relates to a liquid surface tension coefficient measuring device, specifically a liquid surface tension coefficient measuring device based on surface waves. Background Technology

[0002] The surface tension coefficient is a physical quantity characterizing the magnitude of surface tension, playing a crucial role in discussing liquid surface phenomena and understanding liquid properties. Surface tension is a macroscopic manifestation of molecular forces; molecules in the liquid surface layer move due to unbalanced attractive forces, minimizing the liquid's surface area. Many phenomena in daily life are related to surface tension, such as the wetting of liquids and solids, and capillary action in liquids.

[0003] Commonly used methods for determining the surface tension coefficient of liquids include the pull-out method, capillary method, and maximum bubble pressure method. Patent No. 201720154685.4 discloses a device for measuring the surface tension coefficient of liquids based on surface capillary wave phenomena. This device measures the surface tension coefficient of liquids based on surface capillary phenomena and includes a storage tank, a rubber tube, an outlet pipe, a calibration scale, a baffle plate, a camera, and a display. The storage tank is connected to the outlet pipe via the rubber tube; a baffle plate is located below the outlet of the outlet pipe; the calibration scale is set parallel to the outlet pipe; the camera is opposite the outlet of the outlet pipe, and the camera's electrical output terminal is connected to the display. This device improves measurement accuracy by improving the stability of the constant current generator (replacing the storage tank) and increasing the resolution of the camera. Patent No. 201920614800.0 discloses a device for determining surface tension using the maximum bubble pressure method. The device includes a support test tube with a capillary tube inserted inside. The upper part of the support test tube is connected to a digital pressure gauge, which is sealed to a dropping funnel. A second beaker is placed at the lower part of the dropping funnel. A heat insulation layer is installed on the outside of the support test tube, and the heat insulation layer is vacuum-sealed. A temperature sensor is installed on the bottom surface of the heat insulation layer. A first beaker is placed at the lower part of the support test tube, and a heating device is installed on the outside of the first beaker. It also includes a PLC controller, a heating device, a temperature sensor, and a contact sensor. An alarm is installed on the contact sensor, and a timer is installed on the digital pressure gauge. Patent No. 202121691489.3 discloses an experimental device for measuring the surface tension coefficient of a liquid using the pull-out method. This device includes an electronic balance, a metal cylinder, and a beaker and a graduated cylinder placed on the electronic balance. The beaker and graduated cylinder have openings in their side walls near the bottom, and are connected by a flexible tube with a shut-off valve. A horizontal support rod is fixed to an iron frame, and a clamping device and a fixed pulley are installed on the horizontal support rod, with the fixed pulley positioned directly above the beaker. A pull rope is fixedly connected to one end of a metal cylinder, passing through the fixed pulley and clamping device. The other end of the metal cylinder contacts the liquid surface inside the beaker. A vernier caliper is also provided for measurement. This device obtains the liquid surface tension and the mass of the pulled-out water film by reading the electronic balance and the height of the water level rise in the graduated cylinder when the water film is pulled out, thereby determining the liquid surface tension coefficient. Summary of the Invention

[0004] The purpose of this invention is to provide a liquid surface tension coefficient measuring device based on surface waves.

[0005] The present invention includes a light box, an imaging box, a vibration table, and a signal generator.

[0006] The light box contains a light-emitting diode (LED), and a plano-convex lens is installed in the light path of the LED. The divergent light emitted by the LED is transformed into quasi-parallel divergent light after passing through the plano-convex lens. A light-emitting hole is opened on the top of the light box, and the quasi-parallel divergent light is directly opposite the light-emitting hole.

[0007] The imaging box is located on top of the light box and is a height-adjustable box. The bottom of the imaging box is open, and the top surface is a diffuser.

[0008] The vibration table is located on the top of the light box. The vibration table includes two resonant speakers with the same specifications and parameters, which are located on opposite sides of the light outlet, and a light-transmitting plate mounted on the two resonant speakers. A light-transmitting water tank is movably installed on the light-transmitting plate. A liquid level line is engraved on the side wall of the light-transmitting water tank. A light-transmitting scale is installed on the light-transmitting plate, and the height of the scale is the same as the height of the liquid level line.

[0009] The signal generator can send sinusoidal electrical signals with frequencies ranging from 30 to 200 Hz. Two resonant speakers are connected to the signal generator via a power amplifier. The power amplifier divides the sinusoidal signal emitted by the signal generator into left and right channels, which are then output to the two resonant speakers respectively. The two resonant speakers vibrate with the same frequency, amplitude, and phase. The light-emitting diodes (LEDs) are connected to the signal generator via a strobe light controller, and the LEDs pulse at the same frequency.

[0010] The light emitted by the light-emitting diode is focused into quasi-parallel light by a short-focal-length plano-convex lens. The light passes through a light-transmitting plate that serves as a support and a light-transmitting water tank containing the liquid to be tested, and is projected onto a diffuser plate. A sine wave signal is input to the resonant horn, and the light-transmitting water tank undergoes simple harmonic vibration at the same frequency. Surface waves are formed on the surface of the liquid in the tank. By adjusting the distance between the diffuser plate and the liquid surface, clear bright and dark fringes are generated on the diffuser plate. The distance between two adjacent bright fringes is the wavelength of one surface wave, and the surface tension coefficient of the liquid can be calculated from this.

[0011] The electronic control and information processing in this invention are mature existing technologies. The inventive point of this invention is to provide a new method for measuring the surface tension coefficient of liquids, which has the advantages of safety, reliability and environmental protection.

[0012] This invention proposes a novel measurement method that differs from the methods and principles described above. It achieves high measurement accuracy using a relatively simple implementation device, making it highly suitable for experimental teaching in higher education institutions. Attached Figure Description

[0013] Figure 1 This is a schematic diagram of the overall structure of the present invention;

[0014] Figure 2 This is a schematic diagram of the control circuit of the present invention;

[0015] Figure 3 This is a circuit diagram of the strobe light controller in an embodiment of the present invention;

[0016] Figure 4 This is a schematic diagram of surface wave imaging using a rectangular transparent water tank;

[0017] Figure 5 This is a schematic diagram of surface wave imaging using a circular transparent water tank. Detailed Implementation

[0018] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0019] like Figure 1 As shown, a liquid surface tension coefficient measuring device based on surface waves includes a light box, an imaging box, a vibration table, and a signal generator.

[0020] A light-emitting diode (LED) D is installed inside the light box 1. A plano-convex lens 2 is placed in the optical path of the LED D. The divergent light emitted by the LED D is transformed into quasi-parallel divergent light with a divergence angle of less than 15° after passing through the plano-convex lens 2. The focal length of the plano-convex lens 2 is less than or equal to 50mm. The inner wall of the light box 1 is covered with light-absorbing cloth, and a light-emitting hole is opened at the top. The quasi-parallel divergent light is directly opposite the light-emitting hole.

[0021] The imaging box is located on top of the light box 1, and the imaging box is a height-adjustable box. In this embodiment, the imaging box includes an inner box 3 and an outer box 4 that are movably connected. The inner box 3 and the outer box 4 adopt a pull-out structure, and the overall height of the telescopic box can be changed by moving the height of the outer box. The bottom of the imaging box is open, and the top surface is a diffuser 5.

[0022] A vibration table is located at the top of the light box. The vibration table includes two identical resonant speakers 6 positioned on opposite sides of the light-emitting aperture, and a light-transmitting plate 7 mounted on the two speakers. The resonant speakers have a power of at least 3W and an impedance of 4Ω or 8Ω. A light-transmitting water tank 8, which can be rectangular or circular, is movably mounted on the light-transmitting plate 7. A liquid level line is engraved on the side wall of the light-transmitting water tank 8, and a light-transmitting scale 9 is mounted on the light-transmitting plate 7 at the same height as the liquid level line.

[0023] Signal generator 10 is capable of sending sinusoidal electrical signals with frequencies ranging from 30 to 200 Hz. In this embodiment, the sinusoidal signal (amplitude range: 0–5V) used for measurement is generated by a function signal generator. For example... Figure 2 As shown, two resonant speakers 6 are connected to a signal generator 10 via a power amplifier 11. The power amplifier 11 divides the sinusoidal signal emitted by the signal generator 10 into left and right channels, which are then output to the two resonant speakers respectively. Since the two resonant speakers have the same specifications, they will vibrate at the same frequency, amplitude, and phase when they are working. An LED D is connected to the signal generator 10 via a strobe light controller 12.

[0024] A light-emitting diode (LED) emits white light as a point light source, which is converged by a short-focal-length plano-convex lens, resulting in slightly divergent, quasi-parallel light. The degree of divergence is not strictly required, but the light must not be parallel or convergent. The light passes through a transparent plate serving as support and a transparent water tank containing the liquid to be tested, ultimately projecting onto a diffuser. When a sinusoidal signal of a certain frequency is input to the resonant horn, the water tank will undergo simple harmonic vibration at the same frequency. This causes undulations on the surface of the liquid in the tank, i.e., surface waves. These undulations affect the refraction of the transmitted light, thus producing bright and dark fringes on the diffuser. The distance between the diffuser and the liquid surface is adjusted by an extendable imaging box to achieve the best effect of clear and sharp bright and dark fringes. Because the liquid surface waves appear as standing waves, the light projection at the same location on the liquid surface will alternate between bright and dark, with the frequency matching the vibration table frequency. To display the projection of the standing wave at a specific moment within one cycle, the light source must pulse and flicker at the same frequency.

[0025] The surface waves generated by the vibration table have relatively small amplitudes, corresponding to small undulations in the liquid surface. Therefore, each wave crest can be considered a convex lens with a relatively long focal length. Light rays refracted through this lens converge, and as long as the display screen is within the focal length, each wave crest corresponds to a bright fringe. Thus, the distance between two adjacent bright fringes is the distance between two adjacent wave crests, i.e., one wavelength. During measurement, adjusting the distance between the display screen and the liquid surface according to the wave amplitude and frequency can effectively improve image quality.

[0026] There are many methods to achieve synchronized flickering of light sources; only one feasible method is introduced below. For example... Figure 3 As shown, the strobe light controller 12 includes a main control chip U (Arduino Nano control board), an N-channel enhancement-mode metal-oxide-semiconductor field-effect transistor (N-MOSFET) (model IRFZ46N) and two push-button switches.

[0027] The gate of an N-channel enhancement-mode metal-oxide-semiconductor field-effect transistor (N-MOSFET) is connected to a signal output pin of the main control chip U, its source is grounded, and its drain is connected to the negative terminal of an LED D. The positive terminal of LED D is connected to a +5V DC power supply through a current-limiting resistor R. One end of each of the two push-button switches B1 and B2 is connected to a signal input pin of the main control chip, and the other end is grounded. The positive terminal of the buzzer is connected to a signal output pin of the main control chip, and its negative terminal is grounded. The signal output pin of the signal generator 10 is connected to a signal input pin of the main control chip U. The strobe light controller 12 converts the sine wave signal into a pulse wave signal of the same frequency, with a duty cycle of 5%. The two buttons on the controller are used to control the excitation time of the pulse relative to the sine wave.

[0028] In this embodiment, the strobe light controller operates at 5V and uses an Arduino Nano control board to process the signal. A 0-5V sine wave signal is input from pin D8, processed by the microcontroller, and a square pulse wave of the same frequency is output from pin D9 with a duty cycle of 5%. For signals below 200Hz, a 5% duty cycle is a reasonable value; too small a duty cycle will result in too low light intensity, while too large a duty cycle will cause the projection to be blurry. The pulse signal output from D9 reaches the gate of an N-channel enhancement-mode metal-oxide-semiconductor field-effect transistor (MOSFET) to control the on / off state of a high-power LED. The LED has a power of 3W, an operating voltage of 3.3V, and a current-limiting resistor R with a resistance of 1.6 ohms and a power of 3W. Switch buttons B1 and B2 are used to control the phase delay of the pulse wave relative to the input sine wave. By default, this delay is zero. That is, when the amplitude of a sine wave with a range of 0-5V reaches the rising edge of 2.5V, a pulse wave with a 5% duty cycle is triggered. Pressing B1 once delays the trigger time by 250 microseconds; pressing it again increases the delay to 500 microseconds, and so on. Pressing B2 reduces the delay time by 250 microseconds until it reaches zero. After the delay time reaches zero, pressing B2 will cause a stable 5V output at pin D9, resulting in a constantly lit LED, which is beneficial for calibration operations during measurement. When B2 is constantly lit, pressing it again will trigger a buzzer indicating that pressing the button is ineffective. Pressing B1 while the LED is constantly lit will exit the constantly lit mode and return to the pulse mode with a zero delay.

[0029] When a liquid surface is disturbed, two restoring forces exist: gravity and surface tension. Under their combined action, the liquid surface returns to its equilibrium position. Considering both forces, the wave velocity v of the liquid surface wave and its wavelength λ follow the following relationship:

[0030] g is the acceleration due to gravity, α is the surface tension coefficient of the liquid, ρ is the density of the liquid, h is the depth of the liquid, and tanh(·) represents the hyperbolic tangent function.

[0031] When the vibration frequency f is 30–200 Hz, the wavelength λ of the liquid surface wave is less than 1 cm, and the set liquid surface height is 1 cm ≤ h ≤ 2 cm, then…

[0032] Since v = f·λ, The formula for calculating the surface tension coefficient after cleaning is as follows:

[0033]

[0034] Therefore, by obtaining the frequency and wavelength of the surface wave, and combining this with the local actual gravitational acceleration and liquid density, the surface tension coefficient α of the liquid can be calculated.

[0035] The following uses a rectangular transparent water tank as an example to illustrate the process of measuring the surface tension coefficient of a liquid, as detailed below:

[0036] 1. Take out the light-transmitting water tank and add the liquid to be tested to the liquid level line (the liquid height should be about 1cm); place the light-transmitting water tank on the light-transmitting plate, with the side wall of the rectangular light-transmitting water tank parallel to the scale, and the liquid level and the scale at the same horizontal plane.

[0037] 2. Turn on the signal generator, adjust the output to a sine wave signal, amplitude 0-5V, frequency 50Hz; turn on the power amplifier power and the strobe light controller power.

[0038] 3. Adjust the signal generator to a suitable output frequency, and gradually increase the output intensity of the power amplifier until stable and distinct square bright and dark stripes are seen on the diffuser. Figure 4 As shown; adjust the height of the diffuser to make the light and dark stripes of the light projection clear, and fix this height; at the same time, project the ruler onto the diffuser.

[0039] 4. Record the vibration frequency f at this time, measure the length of the corresponding squares, and obtain the side length of a square, which is the wavelength λ of the liquid surface wave.

[0040] 5. Through the formula The surface tension coefficient of the liquid was calculated.

[0041] 6. Change the output frequency of the signal generator, perform multiple measurements, calculate the corresponding surface tension coefficient, and finally take the average value.

[0042] If a circular, translucent water tank is used, stable and distinct concentric light and dark stripes can be seen on the diffuser panel, such as... Figure 5 As shown, the difference in radius between two adjacent bright fringe circles is the distance between two adjacent wave crests, which is one wavelength.

Claims

1. A liquid surface tension coefficient measuring device based on surface waves, comprising a light box, an imaging box, a vibration table, and a signal generator; characterized in that: The light box contains a light-emitting diode (LED), and a plano-convex lens is installed in the light path of the LED. The divergent light emitted by the LED is transformed into quasi-parallel divergent light after passing through the plano-convex lens. A light-emitting hole is opened at the top, and the quasi-parallel divergent light is directly opposite the light-emitting hole. The imaging box is located on top of the light box and is a height-adjustable box. The bottom of the imaging box is open and the top is a diffuser. The vibration table is set on the top of the light box. The vibration table includes two resonant speakers with the same specifications and parameters, which are set on opposite sides of the light outlet, and a light-transmitting plate mounted on the two resonant speakers. A light-transmitting water tank is movably set on the light-transmitting plate. A liquid level line is engraved on the side wall of the light-transmitting water tank. A light-transmitting scale is set on the light-transmitting plate. The height of the scale is the same as the height of the liquid level line. The signal generator can send sinusoidal electrical signals with a frequency of 30-200Hz. Two resonant speakers are connected to the signal generator through a power amplifier. The power amplifier divides the sinusoidal signal emitted by the signal generator into left and right channels, which are output to the two resonant speakers respectively. The two resonant speakers vibrate with the same frequency, amplitude, and phase. The light-emitting diodes are connected to the signal generator through a strobe light controller. The light-emitting diodes flash pulses at the same frequency. Light emitted from a light-emitting diode is focused into quasi-parallel light by a short-focal-length plano-convex lens. This light passes through a supporting transparent plate and a transparent water tank containing the liquid to be tested, projecting onto a diffuser. A sinusoidal signal with frequency f is input to a resonant horn, causing the transparent water tank to undergo simple harmonic oscillation at the same frequency. Surface waves are formed on the surface of the liquid in the tank. By adjusting the distance between the diffuser and the liquid surface, clear bright and dark fringes are produced on the diffuser. The distance between two adjacent bright fringes is the wavelength λ of one surface wave, from which the surface tension coefficient of the liquid can be obtained. g is the acceleration due to gravity, and ρ is the density of the liquid.

2. The liquid surface tension coefficient measuring device based on surface waves as described in claim 1, characterized in that: The focal length of the plano-convex lens is less than or equal to 50 mm, and the divergence angle of the quasi-parallel diverging light transmitted through the plano-convex lens is less than 15°.

3. The liquid surface tension coefficient measuring device based on surface waves as described in claim 1, characterized in that: The inner wall of the light box is covered with light-absorbing cloth.

4. The liquid surface tension coefficient measuring device based on surface waves as described in claim 1, characterized in that: The resonant horn has a power of 3W or more and an impedance of 4Ω or 8Ω.

5. The liquid surface tension coefficient measuring device based on surface waves as described in claim 1, characterized in that: The light-transmitting water tank is either rectangular or circular.

6. The liquid surface tension coefficient measuring device based on surface waves as described in claim 1, characterized in that: The strobe light controller includes a main control chip, an N-channel enhancement-mode metal-oxide-semiconductor field-effect transistor (MOSFET), and two push-button switches. The gate of the N-channel MOSFET is connected to a signal output pin of the main control chip, the source is grounded, and the drain is connected to the negative terminal of a light-emitting diode (LED). The positive terminal of the LED is connected to a +5V DC power supply through a current-limiting resistor. One end of each push-button switch is connected to a signal input pin of the main control chip, and the other end is grounded. The signal output pin of the signal generator is connected to a signal input pin of the main control chip. The strobe light controller converts a sine wave signal into a pulse wave signal of the same frequency. The two buttons are used to control the excitation time of the pulse relative to the sine wave; one button increases the delay, and the other decreases the delay. Pressing the delay-decreasing button after the delay time reaches 0 will keep the LED constantly lit.

7. The liquid surface tension coefficient measuring device based on surface waves as described in claim 6, characterized in that: The main control chip is an Arduino Nano control board.

8. The liquid surface tension coefficient measuring device based on surface waves as described in claim 6, characterized in that: The N-channel enhancement-mode metal-oxide-semiconductor field-effect transistor is model IRFZ46N.

9. The liquid surface tension coefficient measuring device based on surface waves as described in claim 6, characterized in that: The aforementioned strobe light controller also includes a buzzer, the positive terminal of which is connected to a signal output terminal of the main control chip, and the negative terminal is grounded; the light-emitting diode is in the on state, and the buzzer is activated when the delay reduction button is pressed.

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