Liquid surface tension measuring system and measuring method

Abstract

The invention discloses a liquid surface tension measuring system and method, and relates to the technical field of liquid physical property measurement. The system comprises a lifting measurement module, a heating temperature control module and a signal acquisition and processing module, the lifting measurement module is used for measuring the surface tension of liquid to be measured, and the heating temperature control module is used for controlling the measurement temperature of the liquid to be measured. The signal collecting and processing module is used for collecting the lifting height of the lifting measuring module, the surface tension of the liquid to be measured and the temperature of the heating temperature control module in real time and controlling the lifting height of the lifting measuring module and the temperature of the heating temperature control module in real time. The device effectively overcomes the problems of poor temperature adaptability, limited lifting stroke, low automation control degree and the like in the prior art, has the characteristics of simple structure, convenience in operation, wide measurement range and high experiment repeatability, and is suitable for accurately measuring the surface tension of liquid in scientific research and industrial production.

Description

Technical Field

[0001] The present invention belongs to the technical field of liquid property measurement, and in particular relates to a liquid surface tension measurement system and a measurement method. Background Art

[0002] The surface tension of a liquid is a manifestation of the forces acting between molecules on the liquid's surface and is the tendency of the liquid's surface to shrink to its minimum area. Liquid surface tension is an important physical parameter that measures the strength of molecular interactions on the liquid's surface. It is not only related to the molecular structure of the liquid itself, but is also significantly affected by external conditions such as temperature. As the temperature rises, the forces between liquid molecules weaken, and molecular motion becomes more active, typically leading to a gradual decrease in surface tension. Therefore, accurately measuring the surface tension of liquids at different temperatures provides data support for analyzing the characteristics of liquids under various operating conditions, and has broad application value in aerospace, biomaterials, petrochemicals, micro-nano coatings and other fields.

[0003] Methods for measuring liquid surface tension include the pull-off method, the pendant drop method, the capillary method, and the maximum bubble pressure method. The pull-off method (such as the Wilhelmy plate method) calculates surface tension by measuring the pull of a liquid on a solid surface (such as a platinum plate or glass plate); the pendant drop method calculates surface tension by analyzing the shape of the pendant drop; the capillary rise method calculates surface tension by measuring the height of a liquid rising in a capillary tube; and the maximum bubble pressure method calculates surface tension by measuring the maximum pressure when a bubble detaches from the liquid surface.

[0004] Among them, the pull-off method is widely used because of its simple operation and high measurement accuracy. The pull-off method is a classic and commonly used surface tension measurement method, and its principle is based on the interaction force between the solid-liquid interface and the liquid-gas interface. When a metal ring is vertically immersed in a liquid and then pulled upward at a constant speed, the liquid will form a liquid film on the surface of the plate due to surface tension. As the pulling process continues, the liquid film gradually becomes thinner until it is broken. At the moment when the liquid film is about to detach from the plate, the pull-off force reaches its maximum value. This method can calculate the surface tension coefficient of the liquid by measuring the maximum pull-off force required for a metal ring or metal sheet of known circumference to detach from the surface of the liquid to be measured. If it is a metal ring of known circumference, the pull-off force ; Where D1 and D2 are the outer diameter and inner diameter of the ring respectively, is the surface tension coefficient of the liquid.

[0005] The pull-off force measurement is realized based on a pressure sensor circuit with a Wheatstone bridge structure. The circuit includes a Wheatstone bridge circuit composed of four force-sensitive resistors connected in a full-bridge manner. When external pressure acts on the elastic metal sheet to produce mechanical deformation, the resistance values ​​of the four force-sensitive resistors will change, breaking the equilibrium state of the Wheatstone bridge and generating a voltage signal at the output end. The amplitude of the output voltage signal is linearly proportional to the external pressure acting on the elastic metal sheet. The change value of the output voltage of the sensor under the action of the pull-off force F is , where k is the sensitivity of the pressure sensor.

[0006] The pull-off method provides an effective means for measuring liquid surface tension. Existing liquid surface tension coefficient testers are designed based on the pull-off method and include a top measuring device and a bottom lifting platform. However, existing liquid surface tension coefficient testers still have the following shortcomings: 1. Lack of effective temperature control and limited measurement range: Most existing measurement systems lack integrated high-precision temperature control modules and can only meet measurement requirements at room temperature. They are unable to accurately obtain liquid surface tension data under different temperature conditions. However, temperature has a significant impact on liquid molecular motion and surface tension, and liquid surface tension and temperature are often significantly negatively correlated.

[0007] 2. Low degree of automation and poor system adaptability: Existing measurement systems mostly rely on manual adjustment, and the lifting stroke is short, making it difficult to flexibly adjust the relative position of the metal ring and the liquid surface, resulting in inconvenient operation and limiting the applicability of surface tension measurement at different liquid levels and different types of liquids.

[0008] 3. Limited experimental repeatability and accuracy: Insufficient temperature control and low degree of automation make the experiment susceptible to environmental interference, affecting the stability and reliability of the measurement results.

[0009] Therefore, the present invention provides a liquid surface tension measurement system and a measurement method for automatically and multiple times measuring the surface tension of liquids at different temperatures. Summary of the Invention

[0010] The purpose of the present invention is to address the defects of the existing technology and propose a liquid surface tension measurement system and measurement method. The pull-off method is used to automatically measure the surface tension of the liquid at different temperatures multiple times, and the change of the liquid surface tension with temperature can be directly obtained.

[0011] In order to achieve the above-mentioned purpose, the present invention proposes the following liquid surface tension measurement system, which includes a lifting and measuring module, a heating and temperature control module and a signal acquisition and processing module. The lifting and measuring module is used to measure the surface tension of the liquid to be measured, the heating and temperature control module is used to control the measurement temperature of the liquid to be measured, and the signal acquisition and processing module is used to collect the lifting height of the lifting and measuring module, the surface tension of the liquid to be measured and the temperature of the heating and temperature control module in real time, and control the lifting height of the lifting and measuring module and the temperature of the heating and temperature control module in real time.

[0012] The lift measurement module consists of a motorized vertical displacement platform, a two-dimensional tilt displacement platform, a pressure sensor, and a platinum metal lifting ring. The two-dimensional tilt displacement platform is mounted on the motorized vertical displacement platform, and the pressure sensor is fixed to the two-dimensional tilt displacement platform. The motorized vertical displacement platform drives the two-dimensional tilt displacement platform and pressure sensor for vertical movement, which in turn drives the pressure sensor for angular adjustment. The pressure sensor and the platinum metal lifting ring are connected using a three-wire structure.

[0013] After leveling the metal platinum ring hanging on the pressure sensor using a two-dimensional tilt displacement platform, the electric vertical displacement platform drives the metal platinum ring in the vertical direction to immerse or detach from the liquid at a uniform speed, thereby measuring the change in tension during the pulling-off process on the liquid surface.

[0014] Furthermore, the platinum ring has a flat surface and uniform inner and outer diameters at all locations, and can be replaced with an ultra-thin ring (<0.5 mm) or a metal sheet when measuring liquids with poor uniformity.

[0015] The heating and temperature control module includes a controllable heating platform and a metal culture dish containing the test liquid. The signal acquisition and processing module uses a PID intelligent temperature control algorithm to control the temperature of the temperature-controlled heating platform with an accuracy of ±0.1°C, enabling continuous adjustment from room temperature to the set temperature. The culture dish containing the test liquid is placed in the heating zone of the temperature-controlled heating platform. The signal acquisition and processing module controls the heating temperature of the heating platform to maintain the test liquid in the culture dish within the set temperature range. Surface tension measurements of the liquid are performed under stable temperature conditions, effectively preventing the influence of temperature fluctuations on the measurement results.

[0016] The signal acquisition and processing module includes a data acquisition card and a computer signal processing system. The acquisition card collects real-time temperature signals from the temperature sensors in the heating and temperature control module, real-time tension signals from the pressure sensors, and position information from the 2D tilt and electric vertical displacement platforms. It converts the voltage signals into digital signals and sends them to the computer signal processing system. Simultaneously, the acquisition card generates analog voltage control signals to the drivers of the 2D tilt and electric vertical displacement platforms, and generates control signals to the heating platform to drive heating.

[0017] The computer signal processing system dynamically adjusts the power of the heating platform through the real-time feedback of the temperature signal from the temperature sensor in the heating and temperature control module to ensure that the liquid temperature remains constant during the experiment.

[0018] The pressure sensor senses the real-time change of tension during the pulling-off process of the metal platinum ring, and converts the original signal into a voltage signal which is input into the acquisition card. The acquisition card converts the voltage signal into a digital signal, and the computer signal processing system processes and calculates the received digital signal to obtain the surface tension data result.

[0019] The computer signal processing system can also generate control signals to the driving motors of the two-dimensional tilt displacement platform and the electric vertical displacement platform to control the movement of the two-dimensional tilt displacement platform and the electric vertical displacement platform.

[0020] The pressure sensor is fixed on the two-dimensional tilt displacement platform through a support rod and a cross clamp with two holes of different diameters. The mounting holes of the cross clamp with two holes of different diameters are tightened by adjusting the looseness of the bolts to achieve a locking effect.

[0021] Furthermore, the electric vertical displacement platform is equipped with a rotating handwheel, which allows manual adjustment of its height. The two-dimensional tilting platform utilizes dual-axis horizontal calibration, and a knob on the side of the platform allows manual adjustment of its tilt angle. This allows for fine-tuning of the measurement system's dual-axis angle to optimize liquid film formation conditions and improve measurement repeatability. It is particularly suitable for measuring systems susceptible to interfacial gradients, such as nanofluids and emulsions.

[0022] Furthermore, the electric vertical displacement platform and the two-dimensional tilt displacement platform are both driven by stepping motors.

[0023] Preferably, the electric vertical displacement platform adopts a ball screw with a self-locking mechanism to have a lifting stroke range of 0~50 mm. It adopts a ball screw with a self-locking mechanism, has a dual-mode adjustment of automatic motor control and a rotary handwheel, and has a visual scale value printed on the surface to achieve micron-level reciprocating lifting control with a maximum displacement speed of 5 mm / s. It is used to accurately control the lifting and lowering of the metal platinum ring to ensure that the lower edge of the metal platinum ring is immersed in the liquid without touching the bottom of the metal culture dish.

[0024] The two-dimensional tilt displacement platform adopts dual-axis horizontal calibration and is driven by a screw and a second stepper motor to achieve high-precision pitch adjustment. The pitch and flip angle travel is ±7.5°. The guide rail is a cross-ball guide rail, which is suitable for frequent adjustments of light loads. When the controller is not powered, manual adjustment function can be achieved through the knob on the side of the platform.

[0025] Furthermore, the two-dimensional tilt displacement platform is internally provided with a limit block to ensure that the lifting and measuring structure will not overturn or shake when the metal platinum ring receives tension from the liquid surface.

[0026] Furthermore, the pressure sensor adopts a high-precision strain gauge pressure sensor, which uses a metal sheet inside to sense resistance changes and is connected in the form of a bridge circuit. Signal amplification is achieved by measuring the voltage difference output by the bridge. The metal sheet and the metal platinum ring in the pressure sensor are connected using a three-wire structure. Three equally spaced small holes are opened on the upper side of the metal platinum ring. After the three metal wires pass through the small holes, they are twisted into a metal wire, and a closed hook is set at the unperforated free end for hanging on the metal sheet hook at the bottom of the pressure sensor.

[0027] Furthermore, the bottom of the metal culture dish fits tightly against the heating platform, ensuring that the liquid can be heated precisely.

[0028] Furthermore, the system is also provided with a thermocouple. After the temperature of the liquid to be measured is increased, the thermocouple directly contacts the liquid to be measured and is connected to the computer signal processing system through an acquisition card to monitor the temperature of the liquid to be measured in real time.

[0029] The present invention further provides a method for measuring the surface tension coefficient based on the pull-off method using the liquid surface tension measurement system described above, which specifically comprises the following steps: Step 1: Prepare the liquid sample. Power on the acquisition card and computer signal processing system. Use a vernier caliper to manually measure the inner and outer diameters and thickness of the selected platinum ring. Before the experiment, soak the ring in a NaOH solution and then thoroughly clean it with deionized water.

[0030] Step 2: Different pressure sensors 1 have different sensitivities. The sensor sensitivity should be calibrated before the experiment.

[0031] Furthermore, the pressure sensor sensitivity calibration process in step 2 is as follows: weights of equal mass are added to the weight plate, and the voltage values ​​under the corresponding weight gravity after stabilization are recorded respectively. After performing a univariate linear fit, the slope of the linear fitting line is obtained, which is the pressure sensor sensitivity k.

[0032] Step 3: Before measuring the liquid's surface tension, adjust the lengths of the three wires of the platinum metal ring until the bottom of the ring is parallel to the liquid surface. To achieve this, place a level on the pressure sensor, control the movement of the two-dimensional tilt displacement platform using a computer signal processing system, and manually adjust the knobs to observe the level until the bottom of the platinum ring is parallel to the liquid surface.

[0033] Step 4: Turn on the heating platform and set the heating temperature. The signal acquisition and processing module generates a control signal through PID based on the deviation between the set heating temperature and the actual temperature to drive the heating temperature control module to work.

[0034] Step 5: Place the metal petri dish on a heating platform and add the liquid to be tested. Use a thermocouple to monitor the liquid temperature in real time in a computer signal processing system. Suspend a platinum ring directly above the center of the liquid in the metal petri dish, close to the liquid surface but not touching it.

[0035] The position of the electric vertical displacement platform at this time is used as the initial position of the measurement, and the position where the lower edge of the metal platinum ring is completely immersed in the liquid surface is used as the measurement position. The descent height of the electric vertical displacement platform is set according to the vertical distance between the liquid surface and the metal platinum ring.

[0036] At the same time, the descending speed of the vertical displacement platform, the voltage difference threshold ΔU of the pressure sensor, and the number of experimental cycles are set.

[0037] Step 6. The signal acquisition and processing module controls the electric vertical displacement platform to set the speed according to the set descent height, and drives the metal platinum ring to descend at a uniform speed to the set descent height; at this time, the lower edge of the metal platinum ring is completely immersed in the liquid to be tested, and the signal acquisition and processing module automatically controls the electric vertical displacement platform to rise, driving the metal platinum ring to rise, and starts measurement; during measurement, when the liquid surface pull-off force acts on the sensor metal sheet, the metal sheet will undergo a slight deformation, causing its resistance value to change and pressure to change. The sensor converts the pressure change into a voltage signal and transmits the signal to the signal acquisition and processing module in real time; the voltage signal is converted into an analog signal through the acquisition card and transmitted to the computer acquisition system.

[0038] When the liquid film of the metal platinum ring is broken, the acquisition card sends the received voltage signal to the computer signal processing system, and the computer signal processing system controls the electric vertical displacement platform to stop moving; After completing a measurement, the computer signal processing system controls the metal platinum ring to descend below the liquid surface to be measured according to the set descent height, and repeats the above measurement process until the set number of measurements is reached.

[0039] After automatically completing multiple repeated measurements, the computer signal processing system obtains the surface tension coefficient results of each group and gives the average value of the surface tension coefficient.

[0040] The present invention has the following beneficial effects: 1. In this invention, a precise temperature control system is integrated to study the specific effects of temperature on surface tension. The liquid sample is placed on a temperature-controlled heating platform. Adjusting the temperature control device maintains the liquid at a constant temperature within a set range. A thermocouple temperature sensor is used for temperature detection, and the temperature data is fed back to a computer in real time, ensuring the reliability and repeatability of the experimental data.

[0041] 2. During the experiment, the metal ring surface must be kept clean, free of oil and impurities. Failure to do so could affect the wettability of the plate and the pull-off force measurement. Furthermore, the pressure sensor is fixedly connected to the 2D tilting platform, effectively locking it during the movement of the electric vertical displacement platform. This prevents premature breakage of the liquid film due to device vibration, which could result in lower measurements.

[0042] 3. The traditional pull-off method for measuring surface tension uses a device that lifts the base. The stroke is small and the lifting of the base is controlled only manually, which cannot guarantee uniform lifting speed. When measuring fluids with relatively high viscosity and tension, such as organic matter and nanofluids, the liquid film often cannot be broken. The present invention expands the lifting range of the metal ring by introducing an adjustable lifting mechanism; by setting a stepper motor and a data acquisition module, the pulling force change can be converted into a voltage signal and the signal can be synchronously output to the computer. At the same time, it can adapt to metal rings of different thicknesses, so that the equipment can adapt to different liquid level conditions and liquid types with different viscosities, thereby improving the convenience and applicability of experimental operations. By setting an automatic measurement program, the problem of uneven speed when personnel adjust the lifting platform can be effectively improved, ensuring the stability of the pull-off process. When the pull-off is too slow, it may be affected by excessive liquid viscosity, resulting in excessive deviation in the results.

[0043] 4. The computer signal processing system uses the tension voltage feedback signal collected by the pressure sensor to identify liquid film rupture. The voltage value fluctuates dramatically before and after the liquid film ruptures. When the difference in the continuous voltage feedback signal exceeds the set threshold, the computer signal processing system controls the electric vertical displacement platform to stop raising and lowering, and records the measurement data. This data can also be transmitted externally for subsequent analysis.

[0044] Overall, the present invention effectively overcomes the problems of low automation, poor temperature adaptability, and limited lift stroke in the prior art. It features a simple structure, convenient program control, a wide measurement range, and high experimental repeatability, making it suitable for precise measurement of liquid surface tension in scientific research and industrial production. The present invention not only measures the surface tension of liquids at different temperatures, but also further analyzes how it changes with temperature. In practical applications, the experimental data provided will be of great reference value for liquid material selection, process parameter adjustment, and related theoretical research. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1 Schematic diagram of the overall structure of the system of the present invention; Figure 2 It is the Visual studio C# data visualization display operation interface of the measurement system in the embodiment; Figure 3 This is a graph showing the surface tension measurement results of deionized water in Application Example 1; Figure 4This is the surface tension measurement result of the nanofluid in Application Example 2. DETAILED DESCRIPTION

[0046] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0047] This embodiment will explain in detail how to complete the variable temperature surface tension measurement process through this system based on the coordination and working principles of the various parts of the equipment.

[0048] like Figure 1 As shown, a liquid surface tension measurement system includes a lifting measurement module, a heating and temperature control module, and a signal acquisition and processing module. The lifting measurement module is used to measure the surface tension of the liquid to be measured, the heating and temperature control module is used to control the measurement temperature of the liquid to be measured, and the signal acquisition and processing module is used to collect the lifting height of the lifting measurement module, the surface tension of the liquid to be measured, and the temperature of the heating and temperature control module in real time, and to control the lifting height of the lifting measurement module and the temperature of the heating and temperature control module in real time.

[0049] The lift measurement module includes a motorized vertical displacement platform 7, a two-dimensional tilt displacement platform 6, a pressure sensor 1, and a platinum metal ring 2. The two-dimensional tilt displacement platform 6 is mounted on the motorized vertical displacement platform 7, to which the pressure sensor 1 is secured via support rods 4 and a cross clamp 3 with two holes of varying diameters. The motorized vertical displacement platform 7 drives the two-dimensional tilt displacement platform 6 and pressure sensor 1 for vertical movement, while the two-dimensional tilt displacement platform 6 drives the pressure sensor 1 for horizontal adjustment. Both displacement platforms are equipped with proprietary stepper motors for independent control.

[0050] The electric vertical displacement platform 7 also features a rotating handwheel 11, which allows manual adjustment of its height. The electric vertical displacement platform 7 utilizes a first stepper motor 12 driving a ball screw with a self-locking mechanism, offering dual-mode adjustment: automatic stepper motor control and manual knob adjustment. The rotating handwheel 11 is printed with a visual scale, and the lifting range is 0–50 mm. The stepper motor converts rotary motion into linear motion by driving the ball screw. The screw utilizes a high-precision, fine-pitch thread, enabling precise and smooth lifting while also ensuring self-locking performance. The first stepper motor 12 receives a low-frequency pulse signal and can be raised and lowered slowly and at a constant speed, ensuring precise adjustment of the lifting system within a narrow range, ensuring accurate liquid film pull-off. The signal acquisition and processing module controls the first stepper motor 12 to adjust the vertical position of the electric vertical displacement platform 7. The vertical position of the electric vertical displacement platform 7 is also fine-tuned by rotating the handwheel 11.

[0051] The two-dimensional tilt displacement platform 6 is placed on the motorized vertical displacement platform 7 and fixed together with M6 hexagon socket bolts, with the center holes of the two platforms aligning. The two-dimensional tilt displacement platform 6 utilizes dual-axis horizontal calibration, driven by a screw and a second stepper motor 13, enabling high-precision pitch adjustment with a pitch and roll angular range of ±7.5°. The guide rails are cross-ball guides, suitable for frequent adjustments with light loads. When the controller is unpowered, manual adjustment is possible using knobs on the side of the platform. This ensures that the lifting and measuring structure remains stable and horizontal during measurement.

[0052] The support rod 4 and the reducing double-hole cross clamp 3 are used to connect the two-dimensional tilt displacement platform 6 and the pressure sensor 1. One end of the support rod 4 is fixed to the two-dimensional tilt displacement platform 6 through a thread, and the other end of the support rod 4 is detachably provided with the pressure sensor 1 through the reducing double-hole cross clamp 3 and the connecting rod. One end of the connecting rod is detachably provided in the mounting hole of the reducing double-hole cross clamp 3, and the mounting hole of the reducing double-hole cross clamp 3 is locked by adjusting the tightness of the bolt.

[0053] The pressure sensor 1 adopts a high-precision strain gauge pressure sensor, with a metal sheet inside to sense resistance changes. It is connected in the form of a bridge circuit and signal amplification is achieved by measuring the voltage difference output by the bridge. The metal sheet inside the pressure sensor 1 and the metal platinum ring 2 are connected using a three-wire structure. Three equally spaced small holes are opened on the upper side of the metal platinum ring 2. After the three metal wires pass through the small holes, they are twisted into a metal wire, and a closed hook is set at the unperforated free end for hanging on the metal sheet hook at the bottom of the pressure sensor 1.

[0054] In order to ensure that the lifting and measuring structure will not overturn or shake when the metal platinum ring 2 is subjected to the pulling force of the liquid surface, a limit block is provided inside the two-dimensional tilt displacement platform 6.

[0055] The heating and temperature control module includes a controllable temperature heating platform 8, model Shanghai Xiniu DB-0AB, which adopts PID intelligent temperature control algorithm, with a temperature control accuracy of up to ±0.1 ° C, and can achieve continuous adjustment from room temperature to 400 ° C, ensuring the stability and consistency of the experimental temperature. The culture dish 5 containing the liquid to be tested is placed on the heating area of ​​the controllable temperature heating platform 8 (the central area in this embodiment to ensure that the temperature is evenly distributed during the heating process and reduce heat loss caused by heat conduction and heat radiation). The heating temperature of the heating platform is controlled by the signal acquisition and processing module to maintain the liquid to be tested in the culture dish within the set temperature range. The surface tension of the liquid is measured under stable temperature conditions, which effectively avoids the influence of temperature fluctuations on the measurement results. At the same time, the bottom of the culture dish is in close contact with the heating platform 8 to ensure that the liquid can be accurately heated.

[0056] Through real-time feedback of temperature data, the signal acquisition and processing module can dynamically adjust the power of the heating platform to ensure that the liquid temperature remains constant during the experiment.

[0057] The signal acquisition and processing module includes a data acquisition card 9 and a computer signal processing system 10 (PC); the real-time change of tension during the pulling-off process of the metal platinum ring 2 is sensed by the pressure sensor and converted into a voltage signal as an original signal and input into the acquisition card 9. The acquisition card 9 converts the voltage signal into a digital signal, and the computer signal processing system 10 processes and calculates the received digital signal to obtain the surface tension data result.

[0058] The acquisition card 9 converts control commands into analog voltage signals through a computer signal processing system and transmits them via an interface to the stepper motor that controls the platform position. Based on the deviation between the set heating temperature and the actual temperature, the acquisition card 9 generates control signals to the heating platform 8 via PID control to drive the heating and temperature control module. Control signals are then generated to the drive motors of the two-dimensional tilt displacement platform 6 and the electric vertical displacement platform 7 to control their movement. Simultaneously, the acquisition card 9 collects the voltage signal from the pressure sensor 1 and the temperature signal from the temperature sensor within the heating platform 8. These two analog signals are then converted into digital signals and recorded in the computer signal processing system 10.

[0059] The computer signal processing system 10 identifies the rupture of the liquid film through the tension voltage value feedback signal collected by the pressure sensor. The voltage value will fluctuate violently before and after the liquid film ruptures. When the difference of the continuous voltage feedback signal is greater than the set threshold, the electric vertical displacement platform 7 is controlled to stop rising and falling, and the measurement data is recorded.

[0060] In addition, to obtain voltage values ​​related to liquid surface tension at different temperatures and ensure data reliability and repeatability, a thermocouple (not shown) is used to monitor the liquid temperature before measurement to further obtain accurate liquid temperature information. The thermocouple is connected to a computer signal processing system 10 via an acquisition card 9 to monitor the temperature of the liquid in real time.

[0061] The metal platinum ring 2 can be replaced with different thicknesses and shapes, suitable for measuring different liquid types. For example, for well-dispersed suspensions, an ultra-thin ring (<0.5 mm) can be replaced. For high-concentration nanofluids, a metal sheet can be replaced to reduce the impact of particle adsorption on measurement accuracy.

[0062] In addition, since the present invention is composed of precise mechanisms, it can be placed on an optical platform. By adding a magnetic base, the stability of the system can be further increased, and the positions of each structure are relatively fixed.

[0063] Based on the above liquid surface tension measurement system, there is a fully automatic liquid surface tension measurement method, which specifically includes the following steps: Step 1: Prepare a liquid sample, turn on the power of the acquisition card 9 and the computer signal processing system 10, and use a vernier caliper to manually measure the inner and outer diameters and thickness of the selected metal platinum ring 2.

[0064] It should be noted that the surface condition of the metal ring has a great influence on the measurement results. Before the experiment, the ring should be soaked in NaOH solution (concentration 5%-10%) for 20 to 30 seconds, and then taken out and thoroughly cleaned with deionized water. Only then can the inner and outer diameters and surface conditions of the metal ring meet the measurement requirements. It's important to note that nanoparticles suspended in nanofluids can alter the fluid's interfacial properties, such as adsorption, Brownian motion, and aggregation. At high concentrations, particles may aggregate, leading to uneven surface tension and fluctuations in measured values. When measuring high-concentration nanofluids, replacing the platinum ring with a metal ring or sheet with a thickness of less than 0.5 mm can reduce the effects of particle aggregation and adsorption on measurement results, further improving accuracy.

[0065] Step 2: Different pressure sensors 1 have different sensitivities. The sensor sensitivity should be calibrated before the experiment. The specific process is as follows: Turn on the power switch of the instrument, preheat the instrument, and adjust the sensor and base to a horizontal level; hang a weight disk in the small hook at the end of the sensor beam, and set the tension voltage value to zero in the computer control system; use tweezers to gently place weights of masses such as 0.5g, 1.0g, 1.5g, 2.0g, 2.5g, and 3.0g into the weight disk. After the shaking stops, the computer records the corresponding voltage representation numbers respectively, measures multiple times to find the average value, and performs a univariate linear fit on the data. The slope of the linear fit line is the pressure sensor sensitivity k.

[0066] The univariate linear fitting is to use the univariate linear regression method y=kx+b to obtain the actual linear fitting curve for the experimental measurement data.

[0067] like Figure 2 As shown, in this embodiment, by turning on the "sensor sensitivity" mode in the visual operation interface of Visual studio C#, the sensitivity measurement requires the use of the voltage monitoring module and parameter setting module of the operation interface. The voltage monitoring module has a built-in univariate linear fitting function. When the sensitivity measurement function is turned on, first hang the weight disk in the small hole of the metal sheet at the end of the sensor 1. After the weight disk stops shaking, click automatic zeroing to set the voltage value under this tension to zero. Before starting the measurement, it is necessary to fill in the mass of the single weight and the gravity coefficient into the parameter setting module, then put 0.5g weights into the weight disk in batches and click the start measurement button. The voltage monitoring module will record the voltage value and automatically match the corresponding tension value. After clicking the measurement end button, the computer signal processing system 10 automatically completes the linear fitting to obtain the pressure sensor sensitivity k, completing the calibration of the pressure sensor 1.

[0068] Step 3. Before starting to measure the surface tension of the liquid, it is necessary to adjust the length of the three pull wires of the metal platinum ring 2 until the bottom of the metal platinum ring 2 is parallel to the liquid surface, so that the metal platinum ring 2 hung on the hook on the top of the pressure sensor 1 can be immersed in and removed from the liquid at a uniform speed in the vertical direction, and then measure the change in tension during the pulling-off process of the liquid surface.

[0069] When leveling, it is necessary to place the level bubble on the pressure sensor 1, control the movement of the two-dimensional tilt displacement platform 6 through the computer signal processing system 10, and manually fine-tune it through the knob, observing the position of the level bubble until the bottom of the metal platinum ring 2 is parallel to the liquid surface.

[0070] Step 4: Turn on the heating platform 8 and set the heating temperature. The signal acquisition and processing module generates a control signal through PID based on the deviation between the set heating temperature and the actual temperature to drive the heating temperature control module to work.

[0071] Step 5: Place the metal Petri dish 5 on a heating platform, add the test liquid, and monitor the liquid temperature in real time using a thermocouple in the computer signal processing system 10. Suspend the metal platinum ring 2 just above the center of the liquid surface in the metal Petri dish 5, close to the liquid surface but not touching it.

[0072] The position of the electric vertical displacement platform 7 at this time is used as the initial position of the measurement, and the position where the lower edge of the metal platinum ring 2 is completely immersed in the liquid surface is used as the measurement position. The descending height of the electric vertical displacement platform 7 is set according to the vertical distance between the liquid surface and the metal platinum ring 2.

[0073] At the same time, experimental parameters such as the descending speed of the vertical displacement platform 7, the voltage difference threshold ΔU of the pressure sensor 1, the number of experimental cycles and the file saving path are set.

[0074] Step 6. The signal acquisition and processing module controls the electric vertical displacement platform 7 to drive the metal platinum ring 2 to descend to the set descent height at a set speed according to the set descent height; at this time, the lower edge of the metal platinum ring 2 is completely immersed in the liquid to be tested, and the signal acquisition and processing module automatically controls the electric vertical displacement platform 7 to rise to drive the metal platinum ring 2 to rise and start measurement; during measurement, when the liquid surface pull-off force acts on the sensor metal sheet, the metal sheet will undergo a slight deformation, causing its resistance value to change and pressure to change. The sensor converts the pressure change into a voltage signal and transmits the signal to the signal acquisition and processing module in real time; the voltage signal is converted into an analog signal through the high-precision A / D conversion module of the acquisition card 9 and transmitted to the computer acquisition system 10. The user can intuitively read the change in the liquid film pull-off force in the visual interface of Visual studio C#.

[0075] When the liquid film of the metal platinum ring 2 is broken, the acquisition card sends the received voltage signal to the computer signal processing system 10, and the computer signal processing system 10 controls the electric vertical displacement platform 7 to stop moving; After completing one measurement, the computer signal processing system 10 controls the metal platinum ring 2 to drop below the liquid level to be measured, and repeats the above measurement process until the set number of measurements is reached.

[0076] After automatically completing multiple repeated measurements, the computer signal processing system 10 obtains the surface tension coefficient results of each group and provides an average value of the surface tension coefficient.

[0077] In this embodiment, the metal platinum ring 2 is an annular hanging piece. It is approximately considered that the detachment force of the metal platinum ring 2 is the surface tension coefficient multiplied by the circumference of the detachment surface, which can be expressed by the formula: , F For the separation force, D 1 and D 2are the outer and inner diameters of the ring, α is the surface tension coefficient of the liquid. During measurement, the computer signal processing system 10 obtains the voltage value U1 just before the liquid film is about to break and the voltage value U2 just after the liquid film is broken according to the set voltage difference threshold ΔU. The corresponding calculation formula of the liquid surface tension coefficient is expressed by the following formula: ; Among them, α is the surface tension coefficient of the liquid, ΔU=(U1-U2) is the difference in voltage values, k is the sensitivity of the pressure sensor, D1 is the outer diameter of the metal platinum ring, and D2 is the inner diameter of the metal platinum ring.

[0078] Application Example 1 In this application example, deionized water is used as the experimental object, and the surface tension is measured by breaking the liquid film with a ring. The average outer diameter of the metal platinum ring used in multiple measurements is 0.0349 m, the average inner diameter is 0.0330 mm, and the ring thickness is 0.8 mm. The above system and method are used to perform data analysis on the surface tension coefficient of the liquid under different temperature conditions. The reference values ​​of the surface tension coefficients of deionized water at different temperatures measured by the present invention are as follows: the surface tension coefficient of deionized water at 20°C is 0.07250 N / m, the surface tension coefficient of deionized water at 40°C is 0.06892 N / m, the surface tension coefficient of deionized water at 60°C is 0.06300 N / m, the surface tension coefficient of deionized water at 80°C is 0.05948 N / m, and the surface tension coefficient of deionized water at 100°C is 0.05783 N / m. The results are compared with the standard value of the surface tension coefficient of pure water, and the error bars are plotted. Figure 3 The error bars (measurement uncertainty) are relatively short, demonstrating that the present invention measures water surface tension with good accuracy at various water temperatures. The measurement method and process are reliable, effectively acquiring water surface tension data. Both the measured and referenced values ​​show a clear downward trend, indicating that increasing temperature decreases the surface tension of water, consistent with the general rule that surface tension decreases with increasing temperature. The data measured by the system and method described in the present invention exhibit an error of <5%.

[0079] It is important to note that in this application example, the surface tension coefficient measurements of deionized water at temperatures above 100°C are not presented. This is because surface tension measurements of water at temperatures above 100°C are subject to significant error. At high temperatures, the evaporation rate of water increases significantly, causing continuous mass loss at the liquid surface. Temperature gradients may also form across the liquid surface, altering the stability of surface tension during measurement. Furthermore, conventional measurement methods struggle to effectively compensate for errors introduced by evaporation. Bubbles or vapor films easily form on the surface of hot deionized water, significantly deviating from the linear relationship between surface tension and temperature.

[0080] Application Example 2 When measuring the surface tension coefficient of liquids using existing methods, deionized water is often used as an ideal experimental subject. Most devices used to measure the surface tension of nanofluids can only perform measurements at room temperature and cannot measure the surface tension of nanofluids at elevated temperatures. This makes it difficult to meet the needs of scientific research and production for the surface tension coefficient of nanofluids at different temperatures. This invention enables continuous measurement and analysis of the surface tension coefficient of nanofluids from room temperature to boiling point (maximum 400°C). This not only fills the technological gap in nanofluid surface tension measurement under elevated temperatures, but also effectively improves the accuracy and reliability of the measurement data through precise temperature control and synchronous measurement.

[0081] This application example measures the surface tension of a nanofluid at various temperatures, using the same ring size as in Application Example 1. This nanofluid is a stable suspension prepared by dispersing a certain proportion of nanoparticles in a traditional heat transfer medium (such as water, alcohol, or oil). It exhibits significant advantages in enhancing heat transfer coefficients, improving combustion efficiency, and reducing pollutants. The nanofluid used in this application example is a 0.5 wt.% Al / OA / JP-10 mixture, prepared using a two-step process. Al is 50 nm aluminum powder; OA is oleic acid, a surfactant; and JP-10 is aviation kerosene, which boils at approximately 185°C.

[0082] The reference values ​​of the surface tension coefficients of 0.5 wt.% Al / OA / JP-10 nanofluids at different temperatures measured by the above system and method are as follows: the surface tension coefficient of 0.5 wt.% Al / OA / JP-10 at 20 ℃ is 0.03266 N / m, the surface tension coefficient of 0.5 wt.% Al / OA / JP-10 at 50 ℃ is 0.02639 N / m, the surface tension coefficient of 0.5 wt.% Al / OA / JP-10 at 80 ℃ is 0.02364 N / m, the surface tension coefficient of 0.5 wt.% Al / OA / JP-10 at 110 ℃ is 0.02144 N / m, the surface tension coefficient of 0.5 wt.% Al / OA / JP-10 at 140 ℃ is 0.01863 N / m, and the surface tension coefficient of 0.5 wt.% Al / OA / JP-10 at 170 ℃ is 0.01737 N / m, sort the results and draw the error bars. Figure 4 ,The surface tension of the nanofluid in this application example decreases with increasing temperature, showing a negative correlation trend.

[0083] To ensure the reliability and accuracy of the experimental results, the present invention performs multiple measurements and averages the results. Through multiple measurements, the experimenter can obtain the variation pattern of the surface tension of the liquid at different temperatures and further verify the trend of the liquid surface tension changing with temperature.

[0084] The heating platform, precision lifting system, and pressure sensor work together to ensure the accuracy of the experimental process. The surface tension of liquids under different temperature conditions can be measured with high precision. The entire experimental process can be automated, reducing manual intervention and improving experimental efficiency.

[0085] The system and method described in the present invention achieve accurate measurement of the surface tension of liquids at different temperatures by precisely controlling the liquid temperature, accurately adjusting the lifting and lowering measurement structure, and a high-sensitivity real-time pressure sensing system. Combining an accurate temperature control system, a precise lifting mechanism, and a high-precision pressure sensor, the system can accurately measure the surface tension of liquids at different temperatures through the organic coordination of various parts. The system not only has efficient experimental capabilities, but also can adapt to different liquid samples and experimental needs. It is suitable for measuring the surface tension of a variety of liquids to be tested, including organic solvents such as water, ethanol, ether, acetone, toluene, as well as dispersed systems such as emulsions and nanofluids, and can measure their surface tension coefficients under different boiling point conditions. It provides reliable data support for the study of liquid physical properties. Its intelligent control, automated operation, and high-precision measurement give it broad prospects in scientific research, industrial production, and other application fields.

[0086] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. A liquid surface tension measurement system, characterized in that: It includes a lifting measurement module, a heating and temperature control module, and a signal acquisition and processing module. The lifting measurement module is used to measure the surface tension of the liquid to be measured, the heating and temperature control module is used to control the measurement temperature of the liquid to be measured, and the signal acquisition and processing module is used to collect the lifting height of the lifting measurement module, the surface tension of the liquid to be measured, and the temperature of the heating and temperature control module in real time, and to control the lifting height of the lifting measurement module and the temperature of the heating and temperature control module in real time; The lifting measurement module includes an electric vertical displacement platform, a two-dimensional tilt displacement platform, a pressure sensor, and a metal platinum ring. The two-dimensional tilt displacement platform is set on the electric vertical displacement platform, and the pressure sensor is fixed on the two-dimensional tilt displacement platform. The electric vertical displacement platform drives the two-dimensional tilt displacement platform and the pressure sensor to move vertically, and the two-dimensional tilt displacement platform drives the pressure sensor to adjust the angle. The pressure sensor and the metal platinum ring are connected with a three-wire structure. After the metal platinum ring hanging on the pressure sensor is leveled using a two-dimensional tilt displacement platform, the electric vertical displacement platform drives the metal platinum ring in the vertical direction to immerse or remove it from the liquid at a uniform speed, thereby measuring the change in tension during the process of pulling it off the liquid surface. The heating and temperature control module includes a temperature-controlled heating platform and a metal culture dish containing the test liquid. The signal acquisition and processing module uses a PID intelligent temperature control algorithm to control the temperature of the temperature-controlled heating platform with an accuracy of ±0.1°C, enabling continuous adjustment from room temperature to the set temperature. The culture dish containing the test liquid is placed in the heating area of ​​the temperature-controlled heating platform. The signal acquisition and processing module controls the heating temperature of the heating platform to maintain the test liquid in the culture dish within the set temperature range. The surface tension of the liquid is measured under stable temperature conditions, effectively avoiding the influence of temperature fluctuations on the measurement results. The signal acquisition and processing module includes a data acquisition card and a computer signal processing system. The acquisition card collects the real-time temperature signal fed back by the temperature sensor in the heating and temperature control module, the real-time tension signal from the pressure sensor, and the position information of the two-dimensional tilt displacement platform and the electric vertical displacement platform, and converts the voltage signal into a digital signal before sending it to the computer signal processing system. At the same time, the acquisition card generates analog voltage control signals to the drivers of the two-dimensional tilt displacement platform and the electric vertical displacement platform, and generates a control signal to the heating platform to drive heating. The computer signal processing system uses the real-time feedback of the temperature signal from the temperature sensor in the heating and temperature control module to dynamically adjust the power of the heating platform to ensure that the liquid temperature remains constant during the experiment; The pressure sensor senses the real-time change of tension during the pull-off process of the platinum metal ring and converts the original signal into a voltage signal which is input into the acquisition card. The acquisition card then converts the voltage signal into a digital signal. The computer signal processing system processes and calculates the received digital signal to obtain the surface tension data result. The computer signal processing system can also generate control signals to the driving motors of the two-dimensional tilt displacement platform and the electric vertical displacement platform to control the movement of the two-dimensional tilt displacement platform and the electric vertical displacement platform.

2. The liquid surface tension measuring system according to claim 1, wherein: The pressure sensor is fixed on the two-dimensional tilt displacement platform through a support rod and a cross clamp with two holes of different diameters. The mounting holes of the cross clamp with two holes of different diameters are tightened by adjusting the looseness of the bolts to achieve a locking effect.

3. The liquid surface tension measuring system according to claim 1, wherein: The electric vertical displacement platform is also equipped with a rotating handwheel, by which the height of the electric vertical displacement platform can be manually adjusted; the two-dimensional tilt displacement platform adopts dual-axis horizontal calibration, and a knob is provided on the side of the platform, by which the tilt angle of the two-dimensional tilt displacement platform can be manually adjusted.

4. The liquid surface tension measuring system according to claim 1 or 3, wherein: The electric vertical displacement platform and the two-dimensional tilt displacement platform are both driven by stepping motors.

5. The liquid surface tension measuring system according to claim 1 or 3, wherein: The two-dimensional tilt displacement platform is internally provided with a limit block to ensure that the lifting and measuring structure will not overturn or shake when the metal platinum ring receives tension from the liquid surface.

6. The liquid surface tension measuring system according to claim 1, wherein: The pressure sensor adopts a high-precision strain gauge pressure sensor, in which a metal sheet is used to sense resistance changes inside, and is connected in the form of a bridge circuit. Signal amplification is achieved by measuring the voltage difference output by the bridge. The metal sheet and the metal platinum ring in the pressure sensor are connected using a three-wire structure. Three equally spaced small holes are opened on the upper side of the metal platinum ring. After the three metal wires pass through the small holes, they are twisted into a metal wire, and a closed hook is set at the unperforated free end for hanging on the metal sheet hook at the bottom of the pressure sensor.

7. The liquid surface tension measurement system according to claim 1, wherein: The bottom of the metal culture dish fits tightly against the heating platform, ensuring that the liquid can be heated precisely.

8. The liquid surface tension measuring system according to claim 1, wherein: A thermocouple is also provided, which is connected to a computer signal processing system through an acquisition card and is used to monitor the temperature of the liquid to be measured in real time.

9. A method for measuring liquid surface tension using the system according to any one of claims 1 to 8, characterized in that: The specific steps include: Step 1: Prepare the liquid sample, power on the acquisition card and computer signal processing system, and manually measure the inner and outer diameters and thickness of the selected platinum metal ring using a vernier caliper. Before the experiment, soak the ring in NaOH solution and then thoroughly clean it with deionized water. Step 2: Different pressure sensors 1 have different sensitivities. The sensor sensitivity should be calibrated before the experiment. Step 3: Before measuring the surface tension of the liquid, adjust the length of the three wires of the platinum metal ring until the bottom of the metal ring is parallel to the liquid surface. When leveling, place the level bubble on the pressure sensor, control the movement of the two-dimensional tilt displacement platform through the computer signal processing system, and manually adjust the knob to observe the position of the level bubble until the bottom of the metal ring is parallel to the liquid surface. Step 4: Turn on the heating platform and set the heating temperature. The signal acquisition and processing module generates a control signal through PID based on the deviation between the set heating temperature and the actual temperature to drive the heating temperature control module to work; Step 5: Place the metal culture dish on a heating platform and add the test liquid. Use a thermocouple to monitor the liquid temperature in real time in a computer signal processing system. Suspend a platinum metal ring directly above the center of the liquid surface in the metal culture dish, close to the liquid surface but not touching it. The position of the electric vertical displacement platform at this time is used as the initial position of the measurement, and the position where the lower edge of the metal platinum ring is completely immersed in the liquid surface is used as the measurement position. The descending height of the electric vertical displacement platform is set according to the vertical distance between the liquid surface and the metal platinum ring; At the same time, set the descending speed of the vertical displacement platform, the voltage difference threshold ΔU of the pressure sensor, and the number of experimental cycles; Step 6. The signal acquisition and processing module controls the electric vertical displacement platform to set the speed according to the set descent height, driving the metal platinum ring to descend at a uniform speed to the set descent height; at this time, the lower edge of the metal platinum ring is completely immersed in the liquid to be measured, and the signal acquisition and processing module automatically controls the electric vertical displacement platform to rise, driving the metal platinum ring to rise, and starts measurement; during measurement, when the liquid surface pull-off force acts on the sensor metal sheet, the metal sheet will undergo a slight deformation, causing its resistance value to change and pressure to change. The sensor converts the pressure change into a voltage signal and transmits the signal to the signal acquisition and processing module in real time; the voltage signal is converted into an analog signal through the acquisition card and transmitted to the computer acquisition system; When the liquid film of the metal platinum ring is broken, the acquisition card sends the received voltage signal to the computer signal processing system, and the computer signal processing system controls the electric vertical displacement platform to stop moving; After completing one measurement, the computer signal processing system controls the metal platinum ring to descend below the liquid surface to be measured according to the set descent height, and repeats the above measurement process until the set number of measurements is reached; After automatically completing multiple repeated measurements, the computer signal processing system obtains the surface tension coefficient results of each group and gives the average value of the surface tension coefficient.

10. The method for measuring liquid surface tension according to claim 9, wherein: The pressure sensor sensitivity calibration process in step 2 is as follows: add weights of equal mass to the weight plate, record the voltage values ​​under the gravity of the corresponding weights after stabilization, and perform a linear fit to obtain the slope of the linear fit line, which is the pressure sensor sensitivity k.

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