CN112098272A - Method and device for simultaneous online measurement of liquid surface tension and viscosity - Google Patents

Abstract

The invention discloses a method for simultaneous online measurement of liquid surface tension and viscosity: a droplet generating unit generates droplets that oscillate in a second-order mode; laser irradiates the oscillating droplets and their motion tracks to generate rainbow signals; recording oscillations The rainbow image of the spherical droplet formed from the ellipsoidal droplet from the ellipsoid droplet to the steady state; the calibration curve of the pixel column and the scattering angle is obtained; the signal in the rainbow image is extracted and corresponding to the calibration curve, and the rainbow image is inverted to obtain the spherical droplet. The refractive index and radius of the droplet; then according to the rainbow angle offset of the rainbow image, the evolution of the ellipsoid degree during the droplet falling process is obtained; the ellipsoid degree is converted into the oscillation amplitude information and the oscillation of the damped oscillation function is obtained by fitting The frequency and time constants are used to obtain the surface tension and viscosity values of the liquid, respectively. The invention also discloses a device for simultaneous online measurement of liquid surface tension and viscosity. The method and device realize the tracking of droplet oscillation in microseconds, and improve the spatiotemporal resolution of measurement.

Description

Method and device for simultaneous online measurement of liquid surface tension and viscosity

technical field

The invention relates to the field of on-line measurement of liquid thermal properties, in particular to a method and a device for simultaneous on-line measurement of liquid surface tension and viscosity.

Background technique

Surface tension and viscosity are important physical and chemical properties of liquids, and are basic data commonly used in many scientific research and engineering applications such as medicine, food, fuel atomization, and multiphase reactions. At present, the commonly used methods for measuring the surface tension and viscosity of liquids are: the capillary rise method, which drives the liquid to flow through the capillary by external pressure, and measures the height and flow rate of the liquid in the capillary to calculate the surface tension and viscosity of the liquid; the maximum bubble method, which measures the bubbles. The inner radius of the capillary when the pressure in the bubble is maximum; the drop weight method is used to measure the mass of the droplet when the liquid is dropped from the capillary. The common problems of these methods are the large consumption of samples, the easy contamination of samples by contact measurement, and the long measurement time. In terms of the time resolution of measurement, the capillary rise method is a static method. Although other methods can be used to measure the dynamic surface tension, the time accuracy can only reach 1ms.

The oscillating droplet method obtains the surface tension and viscosity values of the liquid by observing the shape and time evolution of the oscillating droplets formed after the jet is split. For example, the Chinese patent document with publication number CN108007825A discloses a liquid viscosity testing method based on mechanical vibration of droplets, which specifically includes the following steps: placing a hydrophobic substrate on an ultrasonic probe of a Doppler ultrasound instrument, and generating droplets through a micro-injector On the hydrophobic substrate; the droplet is vibrated by the vibration triggering device with automatic rebound function, and then the vibration triggering device is rebounded, and the droplet vibrates freely; the ultrasonic probe adopts the non-focusing continuous wave Doppler method to capillary the droplet surface. The free vibration of the wave is converted into an ultrasonic Doppler frequency shift signal and amplified; the computer signal processing module collects and processes the Doppler frequency shift signal to obtain the free vibration characteristic map of the droplet; the droplet is obtained by fitting the free vibration characteristic map. The decay rate of the amplitude with time, and then the liquid viscosity is calculated. In addition, the oscillating droplet method is also suitable for liquid parameter measurement under extreme conditions (supercooling, high temperature, high pressure environment). At present, direct imaging methods such as high-speed photography are mostly used to observe droplet morphological changes, but this method is limited by the size of pixels and the size of the field of view, and requires the fitting of droplet contours, which makes data processing more complicated. Therefore, it is of great scientific significance and practical value to develop a fast, efficient, accurate and reliable on-line measurement method and device for liquid dynamic surface tension and viscosity.

SUMMARY OF THE INVENTION

In view of the superiority of the oscillating droplet method for measuring liquid interface parameters, the purpose of the present invention is to provide a method and device for simultaneous online measurement of liquid surface tension and viscosity, which realizes the tracking of droplet oscillation in microseconds and improves the measurement accuracy. spatiotemporal resolution.

To achieve the above object, the present invention provides the following technical solutions:

A method for simultaneous online measurement of liquid surface tension and viscosity, comprising the following steps:

(1) The droplet generating unit generates droplets oscillating in the second-order mode, and the cross-section of the droplets is ellipsoid;

(2) The laser beam expanding unit generates a piece of laser light and irradiates the oscillating droplet and its motion trajectory to generate a rainbow signal; the signal processing and acquisition unit records the rainbow image of the oscillating ellipsoid droplet to the steady state spherical droplet;

(3) Calibrate the height of the rainbow signal and the scattering angle in the rainbow image, and obtain the calibration curve of the pixel row and the scattering angle; extract the signal in the rainbow image and correspond to the calibration curve, and invert the rainbow image in the steady state , the refractive index and radius of spherical droplets are obtained;

(4) Combined with the refractive index and radius of the spherical droplet, according to the offset of the rainbow angle between the oscillating ellipsoid droplet and the rainbow image of the spherical droplet in steady state, the evolution of the ellipsoid degree during the droplet falling process was obtained; The droplet ellipsoid information is converted into oscillation amplitude information, and the damped oscillation function is used for fitting; the oscillation frequency and time constant of the damped oscillation function are obtained by fitting, and the surface tension and viscosity of the liquid are obtained respectively.

Further, the method for calibrating the rainbow signal height and scattering angle in step (3) is:

Set a mirror with a rotating displacement stage in the droplet measurement area in the extension direction of the main optical axis of the laser beam expander unit, and adjust the rotating displacement stage to make the light reflected by the mirror coincide with the main optical axis of the optical system unit. And record the initial angle of the rotary stage, fine-tune the rotation angle of the rotary stage, record the rotation angle and the position of the reflected light on the digital camera, and combine the laser beam emitted by the laser in the droplet generation unit with the main optical axis of the optical system unit. Angle, the scattering angle of the calibration point can be obtained, and then the relationship between the digital camera pixels in the signal processing and acquisition unit and the scattering angle can be obtained. Synchronously adjust the upper and lower heights of the mirror and the laser, measure the change in height and repeat the above measurement process to obtain the corresponding relationship between the measurement points of different heights on the one-dimensional line and the digital camera pixels up and down.

公式计算：Further, the relationship between the angular offset of the ellipsoid droplet and the droplet ellipsoid degree is given by

Formula calculation:

Among them, θ _gn , θ _rg are the geometric rainbow angles of ellipsoid droplets and spherical droplets of the same volume, respectively; ξ is the ellipsoid degree of ellipsoid droplets; β, θ _rg are obtained by the following formulas, respectively:

where m is the refractive index of the droplet.

Further, the polar radius of the droplet can be expressed by the following formula:

Among them, r ₀ is the radius of the spherical droplet of the same volume; θ is the polar angle of the ellipsoid; A(t) is the change function of the droplet oscillation amplitude with time, and its relationship with the droplet ellipsoid degree can be expressed as:

and fitted by the following formula:

A(t)=A ₀ exp(-t/τ)·sin[Ω·t+φ]+c (6)

Among them, A ₀ , φ are the amplitude and phase of droplet oscillation at time 0; τ and Ω are the time constant and frequency of oscillation; c is the offset of asymmetric oscillation.

Based on Rayleigh and Lamb's description of the free oscillation of the droplet, the time constant and frequency of the oscillation are related to the liquid viscosity μ and the surface tension σ, respectively, and in the second-order oscillation mode, are determined by the following equations:

修正，ρ为液体密度，r₀为液滴在稳态时的半径。Among them, Ω is given by the formula

Correction, ρ is the liquid density, r ₀ is the radius of the droplet at steady state.

The invention also provides a device for simultaneous online measurement of liquid surface tension and viscosity, comprising a droplet generating unit, a sheet laser beam expanding unit and a signal acquisition and processing unit;

The droplet generating unit includes a droplet generator, a syringe pump and a piezoelectric driver. The syringe pump sends the liquid to be tested into the droplet generator and generates oscillating droplets of the liquid to be tested under the action of the piezoelectric driver;

The chip laser beam expanding unit includes a laser, a beam expanding element and a reflector. The laser beam emitted by the laser is modulated into a chip laser by the beam expanding element, and is irradiated to the oscillating droplet through the reflector to generate a rainbow signal;

The signal acquisition and processing unit, including a digital camera and a field lens, images the rainbow signals of the oscillating droplets of different heights on different pixel rows of the digital camera through optical filtering, and outputs them in the form of data.

Further, the droplet generator may be a monodisperse droplet stream generator or a single droplet generator for generating an oscillating droplet stream and a single droplet, respectively.

Among them, the laser is a continuous laser, which is used to generate a laser beam with adjustable intensity. The beam expanding element expands the emitted laser beam into a piece of laser light. The mirror is installed on the rotating table to reflect the piece of laser light to the droplet and its laser. on the trajectory of motion.

The mirror is mounted on the rotary displacement stage.

The beam expander element is a beam expander or a lens group.

The signal acquisition and processing unit includes a field of view lens, a horizontal slit diaphragm and an area array digital camera; the scattered light emitted from the droplets enters the area array digital camera through the field of view lens and the horizontal slit diaphragm in sequence. Wherein, the field lens is a convex lens, and the convex lens, the horizontal slit diaphragm and the digital camera are sequentially arranged in the rainbow angle region of the droplet and are collinear. And, the horizontal slit diaphragm is provided on the back focal plane of the convex lens.

Among them, the rainbow signals scattered by the droplets at different heights are collected by the field lens, and the horizontal slit diaphragm located in the focal plane of the field lens allows only the rainbow signals that enter the field lens horizontally to pass through, so that the droplets of different heights can pass through. The rainbow signal is separated; the size of the field of view is controlled by adjusting the distance between the digital camera and the horizontal slit diaphragm; the height of the droplet generating unit is adjusted, so that the digital camera records the rainbow image of the droplet from oscillating to a stable spherical shape.

The width of the horizontal slit diaphragm is adjustable, with a line width of 0.5mm-5mm, and is located at the back focal plane of the field of view lens.

The signal acquisition and processing unit includes a field of view lens and a line array digital camera, and the scattered light emitted from the droplet enters the line array digital camera through the field of view lens.

Further, the device provided by the present invention also includes a linear moving and rotating device. A monodisperse droplet stream generator or single droplet generator is mounted on a displacement stage with five degrees of freedom to adjust the position and alignment of the droplet trajectory; a digital camera is mounted on a linear stage to control the collected scattering The droplet height corresponding to the signal.

The advantages of the invention are: the non-contact on-line measurement of the surface tension and viscosity of the droplet will not cause contamination to the sample; the rainbow angle of the droplet is very sensitive to its ellipsoid, so that the small deformation can be detected by the digital camera and detected. Resolution: The position information of the droplet is converted into the time information of the droplet oscillating deformation, which greatly improves the time resolution of the system.

The method and device for simultaneous online measurement of liquid surface tension and viscosity provided by the invention realizes simultaneous online measurement of liquid surface tension and viscosity; has the advantages of simple operation, short time consumption, and suitable for liquid parameter measurement in extreme conditions such as supercooling and overheating. It can quickly, accurately and effectively determine the transient surface tension and viscosity of the droplet formation process.

Description of drawings

1 is a schematic structural diagram of a simultaneous on-line measuring device for liquid surface tension and viscosity provided by the present invention;

Fig. 2 is the structural representation of another kind of liquid surface tension and viscosity on-line measuring device provided by the present invention;

Among them, 1. Laser; 2. Beam expanding element; 3. Reflector; 4. Field of view lens; 5. Horizontal slit diaphragm; 6. Area array digital camera; 7. Monodisperse droplet flow generator; 8. Syringe pump; 9. Piezoelectric driver; 10. Droplet flow; 11. Linear digital camera; 12. Single droplet generator; 13. Single droplet and its motion trajectory;

3 is a rainbow image recorded by the area array digital camera provided in Embodiment 1;

FIG. 4 is the fitting result of the rainbow image oscillation in Example 1. FIG.

Detailed ways

The specific embodiments of the present invention will be further described below through examples and in conjunction with the accompanying drawings.

Example 1

As shown in Figure 1, it is a schematic structural diagram of a device for simultaneous online measurement of liquid surface tension and viscosity provided by the present invention, including a droplet generation unit, a sheet laser beam expansion unit, and a signal acquisition and processing unit. Among them, the droplet generating unit includes a monodisperse droplet generator 7, a syringe pump 8 and a piezoelectric driver 9 for generating a stable monodisperse droplet flow 10; the sheet laser beam expanding unit includes a laser 1, a beam expanding element 2 and The mirror 3 is used to generate a sheet light source and illuminate the droplet stream; the signal acquisition and processing unit includes a field of view lens 4 , a horizontal slit diaphragm 5 and an area array digital camera 6 . In addition, the sheet laser beam expanding unit and the signal acquisition and processing unit are respectively located on the two linear guide rails.

Specifically, in this embodiment: the laser 1 adopts a semiconductor continuous laser with a wavelength of 532 nanometers; the beam expanding element 2 is a 20-fold beam expander, and the laser beam of 2 mm is expanded to 40 mm; the diameter of the field lens 4 is 100 mm. mm, the focal length is 150 mm; the slit width of the horizontal slit diaphragm 5 is 1 mm; the pixel size of the area scan digital camera is 5.86 microns, the number of pixels is 1200×1920, and the height of the effective measurement area is 11.5 cm. The method for measuring liquid surface tension and viscosity with the above-mentioned device comprises the following steps:

Step 1: Turn on the droplet generating unit: connect the syringe pump 8 and the monodisperse droplet flow generator 7 with a hose, and connect the piezoelectric driver 9 to the piezoelectric ceramic sheet of the monodisperse droplet flow generator 7 through wires. Positive and negative. After the connection is completed, the syringe pump 8 pushes the liquid to be tested into the monodisperse droplet flow generator 7, and the parameters such as the flow rate of the syringe pump 8 and the excitation frequency of the piezoelectric driver 9 are adjusted to make the monodisperse droplet flow generator 7 operate. The jet breaking process is under the Rayleigh mechanism to generate a monodisperse droplet flow 10 of second order oscillation (second order mode);

Step 2: Turn on the laser 1, so that the laser beam is expanded into a sheet laser after passing through the beam expanding element 2, and the angle and position of the mirror 3 are adjusted so that the sheet laser is irradiated on the droplet stream 10.

Step 3: Adjust the position and angle of the signal processing and acquisition unit so that it is located near the rainbow area of the droplet; at the same time, adjust the distance between the area array digital camera 6 and the horizontal slit diaphragm 5 to control the size of the recorded field of view; adjust The height of the monodisperse droplet flow generator 7 enables the area array digital camera 6 to record a rainbow image in which the monodisperse droplet flow 10 oscillates from the droplet to a stable spherical shape, as shown in FIG. 3 .

Step 4: After the recording is completed, use the laser beam expander unit, mirror and gantry system to calibrate the height of the rainbow signal and the scattering angle, and obtain the calibration curve of the pixel column and the scattering angle; the details are:

Set a mirror with a rotating displacement stage in the droplet measurement area in the extension direction of the main optical axis of the chip laser beam expanding unit; adjust the rotating displacement platform so that the light reflected by the mirror coincides with the main optical axis of the chip laser beam expanding unit , record the initial angle of the rotary stage; fine-tune the rotation angle of the rotary stage, record the rotation angle and the position of the reflected light on the digital camera, combined with the recorded initial angle of the stage, the scattering angle of the calibration point can be obtained, and then the signal processing can be obtained. and the relationship between the digital camera pixels in the acquisition unit and the scattering angle;

Synchronously adjust the upper and lower heights of the reflector and the laser beam expander unit, and record the position of the beam on the digital camera, to obtain the corresponding relationship between the measurement points of different heights on the one-dimensional line and the digital camera pixels.

Step 5: Extract the signal of every 40 pixel rows in the recorded rainbow image, correspond it to the calibration curve, and invert the rainbow image in steady state to obtain the refractive index m and radius r ₀ of the spherical droplet .

Step 6: Use the processing program to quickly analyze the surface tension and viscosity information of the liquid. The processing process includes: firstly calculating the angular offset Δθ of the oscillating droplet and the droplet rainbow image in steady state, using formula (1) to calculate the evolution of the droplet ellipsoid; using formula (5) to convert the droplet ellipsoid into Oscillation amplitude information, and use formula (6) to fit it; obtain the oscillation frequency and time constant of the damped oscillation function from the fitting, and use formula (7) and formula (8) to obtain the surface tension and viscosity of the liquid respectively. .

As shown in Figure 4, the measured oscillation frequency and time constant of an ethanol droplet with a temperature of 20.3 °C and a steady-state radius of 71.5 μm are 24840 Hz and 0.672 ms, respectively, and the corresponding surface tension and viscosity values are 73.72 mN/m, respectively. and 1.09mPa s.

Example 2

As shown in FIG. 2 , another device for simultaneous online measurement of liquid surface tension and viscosity provided by the present invention includes a droplet generation unit, a laser beam expanding unit and a signal acquisition and processing unit. The droplet generating unit includes a single droplet generator 12 , a syringe pump 8 , and a piezoelectric driver 9 for generating an oscillating single droplet 13 ; the sheet laser beam expanding unit includes a laser 1 , a beam expanding element 2 and a mirror 3 , used to generate a sheet light source and irradiate the droplet and its motion trajectory; the signal acquisition and processing unit includes a field of view lens 4 and a line array digital camera 11 . The method for measuring liquid surface tension and viscosity with the above-mentioned device comprises the following steps:

Step 1: Turn on the droplet generating unit: connect the syringe pump 8 and the single droplet generator 12 with a hose, and connect the piezoelectric driver 9 to the positive and negative poles of the piezoelectric ceramic sheet of the single droplet generator 12 through wires. After the connection is completed, the syringe pump 8 pushes the liquid to be tested into the single droplet generator 12, and the parameters such as the flow rate of the syringe pump 8 and the excitation frequency of the piezoelectric driver 9 are adjusted to make the single droplet generator 12 generate at a certain time interval. Single droplet 13 of second order oscillation.

Step 2: Turn on the laser 1, so that the laser beam is expanded into a piece of laser light through the beam expander element 2, and the angle and position of the reflector 3 are adjusted, so that the piece of laser light is irradiated on the droplet 13 and its motion trajectory;

Step 3: Adjust the position and angle of the signal processing and acquisition unit so that it is located near the rainbow area of the droplet; control the linear array digital camera 11 to record the rainbow image of the droplet oscillation of a single droplet 13;

The method for calibrating the height and angle of the rainbow signal and the data processing method using the simultaneous online measuring device of liquid surface tension and viscosity described in this embodiment is as in Embodiment 1.

A simultaneous online measurement device for liquid surface tension and viscosity provided by the present invention has been described above in detail. The description of the embodiments is only used to help understand the method of the present invention, and should not be construed as a limitation of the present invention.

Claims (10)

1. A method for simultaneously measuring the surface tension and the viscosity of a liquid on line is characterized by comprising the following steps:

(1) the liquid drop generating unit generates liquid drops oscillating in a second-order mode, and the cross section of each liquid drop is ellipsoidal;

(2) the chip laser beam expanding unit generates chip laser and irradiates the oscillated liquid drop and the motion trail thereof to generate a rainbow signal; the signal processing and collecting unit records the oscillating ellipsoid liquid drop to form a rainbow image of the spherical liquid drop in a stable state;

(3) calibrating the rainbow signal height and the scattering angle in the rainbow image to obtain a calibration curve of a pixel column and the scattering angle; extracting signals in the rainbow image, corresponding to the calibration curve, and inverting the rainbow image in a steady state to obtain the refractive index and the radius of the spherical liquid drop;

(4) combining the refractive index and the radius of the spherical liquid drop, and obtaining the evolution condition of the ellipsoid degree in the liquid drop falling process according to the rainbow angle deviation of the oscillating ellipsoid liquid drop and the spherical liquid drop rainbow image in a stable state; converting the ellipsoid degree information of the liquid drops into oscillation amplitude information, and fitting by using a damping oscillation function; and obtaining the oscillation frequency and the time constant of the damping oscillation function by fitting, and respectively obtaining the surface tension and viscosity value of the liquid.

2. The method for on-line measurement of liquid surface tension and viscosity simultaneously as claimed in claim 1, wherein the method for calibrating rainbow signal height and scattering angle in step (3) comprises:

a reflector with a rotary displacement table is arranged in a liquid drop measuring area in the extension direction of a main optical axis of a sheet laser beam expanding unit, the rotary displacement table is adjusted, light rays reflected by the reflector are overlapped with the main optical axis of an optical system unit, the initial angle of the rotary displacement table is recorded, the rotation angle of the rotary displacement table is finely adjusted, the positions of a rotation angle and reflected light on a digital camera are recorded, and the scattering angle of a calibration point can be obtained by combining the angle between a laser beam emitted by a laser in a liquid drop generating unit and the main optical axis of the optical system unit, so that the relation between the pixel of the digital camera in a signal processing and collecting unit and the scattering angle is obtained;

and (3) adjusting the vertical heights of the reflector and the laser synchronously, measuring the variation of the heights, and repeating the measuring process to obtain the corresponding relation between the measuring points with different heights on the one-dimensional line and the upward and downward directions of the pixels of the digital camera.

3. The method for the simultaneous on-line measurement of liquid surface tension and viscosity according to claim 1, characterized in that the drop oscillation process in step (4) is fitted by the following formula:

A₂(t)＝A₀exp(-t/τ)·sin[Ω·t+φ]+c

wherein A is₀Phi is the amplitude and phase of the liquid drop oscillation at 0 moment; tau and omega are time constant and frequency of oscillation; c is the offset of the asymmetric oscillation.

4. The method for on-line measurement of liquid surface tension and viscosity simultaneously as claimed in claim 1, wherein in step (4), the liquid viscosity μ and the surface tension σ are obtained by calculating the time constant and frequency of oscillation respectively according to the following formula:

wherein Ω is represented by formula

Correction, ρ is the liquid density, r₀Is the radius of the droplet at steady state.

5. A device for simultaneously measuring the surface tension and the viscosity of a liquid on line is characterized by comprising a liquid drop generating unit, a sheet laser beam expanding unit and a signal acquisition and processing unit;

the liquid drop generating unit comprises a liquid drop generator, an injection pump and a piezoelectric driver and is used for generating oscillation liquid drops of the liquid to be detected;

the chip laser beam expanding unit comprises a laser, a beam expanding element and a reflector, wherein a laser beam emitted by the laser is modulated into chip laser through the beam expanding element, and the chip laser irradiates oscillating liquid drops through the reflector to generate a rainbow signal;

and the signal acquisition and processing unit comprises a digital camera and a field lens, and is used for imaging rainbow signals of the oscillating liquid drops with different heights on different pixel lines of the digital camera through optical filtering respectively and outputting the rainbow signals in a data form.

6. The device for the simultaneous on-line measurement of liquid surface tension and viscosity according to claim 5, wherein the mirror is mounted on a rotary displacement table.

7. The device for on-line measurement of liquid surface tension and viscosity simultaneously according to claim 5, wherein the beam expanding element is a beam expander or a lens group.

8. The device for the simultaneous on-line measurement of the surface tension and the viscosity of a liquid according to claim 5, wherein the signal acquisition and processing unit comprises a field lens, a horizontal slit diaphragm and an area array digital camera; scattered light emitted from the droplet flow sequentially passes through the field lens and the horizontal slit diaphragm and then enters the area-array digital camera.

9. The device for the simultaneous on-line measurement of the surface tension and the viscosity of a liquid according to claim 8, wherein the horizontal slit diaphragm has an adjustable width, a line width of 0.5mm to 5mm, and is located in a back focal plane of the field lens.

10. The device for the simultaneous on-line measurement of the surface tension and viscosity of a liquid according to claim 5, wherein the signal acquisition and processing unit comprises a field lens and a line digital camera, and wherein scattered light emitted from the liquid drop enters the line digital camera through the field lens.

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