CN114965177B - A non-contact measuring device and method for liquid surface tension coefficient - Google Patents

Abstract

The application discloses a non-contact measuring device and a non-contact measuring method for a liquid surface tension coefficient. The measuring device excites the surface of the liquid sample to be measured through a vibrator with adjustable frequency to generate a surface wave, light emitted by a light source is obliquely incident to the liquid level, the incident light is subjected to phase modulation generated by the surface wave of the liquid sample to be measured when passing through the surface wave of the liquid sample to be measured for the first time, the light wave carries the phase information and is subjected to diffuse reflection by a diffuse reflection surface at the bottom of a sample groove, and then the light wave carries the phase information to meet the surface wave of the liquid sample to be measured again, namely, the light wave is subjected to phase modulation again by the surface wave of the liquid sample to be measured, thus the light wave is used as a phase information carrier, the phases of two opposite propagation of one surface wave are overlapped, stable phase standing waves are formed in the phase of the light wave, and stable fringes with alternate brightness are observed by CCD (charge coupled device) or human eyes, so that the surface tension coefficient of the liquid can be accurately obtained. The method can be widely used for accurately measuring the surface tension coefficient of the transparent liquid.

Description

A non-contact measuring device and method for liquid surface tension coefficient

Technical Field

The invention belongs to the field of measuring instruments and equipment, and specifically relates to a non-contact measuring device and method for liquid surface tension coefficient.

Background technique

From the perspective of molecular theory, due to the attraction between molecules, the surface of the liquid tends to shrink as much as possible. This force that shrinks the liquid surface along the surface is called surface tension. There are two types of methods for measuring the surface tension coefficient of liquid: contact method and non-contact method. Contact measurement techniques such as the pull-off method, as a mechanical balance measurement method, roughly ignore the gravity of the liquid film during calculation, and the horizontality of the hanging plate will have a greater impact on the accuracy of the measurement results. Compared with the contact method, non-contact measurement has the advantages of being fast, non-destructive, simple and practical. Non-contact measurement techniques, such as the laser diffraction method, analyze the diffraction of liquid surface waves to obtain the analytical relationship between the distribution of the diffracted light field and the surface wave, and measure the surface tension coefficient of the liquid based on this relationship; however, this method is not obvious under ordinary experimental conditions, requires a larger observation distance, and requires a high-frequency vibration source. More importantly, the diffraction fringes are easily disturbed by the external environment, difficult to maintain stability, and require relatively high experimental conditions.

Therefore, it is necessary to improve the existing measurement methods to enhance the measurement accuracy.

Summary of the invention

In order to solve the problems existing in the above background technology, the present application proposes a non-contact measuring device for liquid surface tension coefficient and a measuring method using the non-contact measuring device. The non-contact measuring device is used to accurately measure the surface tension coefficient of the liquid sample to be measured.

To achieve the above objectives, this application adopts the following technical solutions:

A non-contact measuring device for liquid surface tension coefficient, characterized in that it comprises: a light source, a sample tank, a vibration source, a vibrator, a diffuse reflection surface, an image collector and an image processor;

The light source is configured to emit incident light that is incident obliquely onto the sample slot;

A sample tank, which is used to accommodate the liquid sample to be tested, and the bottom of the sample tank is provided with a diffuse reflection surface; a vibrator, which is connected to a vibration source, and the vibrator is arranged in the sample tank, and is used to excite the liquid sample to be tested and generate surface waves on its surface;

An image collector, which is aligned with the sample slot, and is used to collect a surface image of the liquid sample to be tested and transmit the collected image to an image processor, wherein the surface image includes a stripe pattern of alternating light and dark stripes;

The incident light emitted by the light source carries the phase information of the surface wave after being phase modulated by the surface wave of the liquid sample to be tested. The incident light carrying the phase information of the surface wave is reflected by the diffuse reflection surface and meets the surface wave again. After the second phase modulation of the surface wave, a light and dark stripe pattern is generated on the surface of the liquid sample to be tested.

In one embodiment, the frequency emitted by the vibration source is higher than 24 Hz, a frequency required for the human eye to produce the persistence of vision effect.

In one embodiment, in the light and dark alternating stripe pattern, the distance d between two adjacent bright stripes and the wavelength λ of the surface wave of the liquid sample to be measured satisfy λ=2d.

In one embodiment, the relationship is based on: Obtain the surface tension coefficient σ of the liquid sample to be tested,

Where: ρ is the density of the liquid sample to be measured, f is the frequency of the vibration source, ɡ is the gravitational acceleration, and λ is the wavelength of the surface wave.

The embodiment of the present application provides a non-contact measurement method, which uses the above-mentioned non-contact measurement device, and the measurement method comprises the following steps:

Based on the oscillator generating surface waves on the surface of the liquid sample to be tested,

Based on the incident light emitted by the light source being incident obliquely on the surface of the liquid sample to be tested, a light and dark stripe pattern is generated on the surface of the liquid sample to be tested.

The fringe pattern is collected by an image collector and fed back to an image processor.

The image processor obtains the wavelength of the surface wave according to the received fringe pattern information and based on a preset model, and calculates the surface tension coefficient of the liquid sample to be tested according to the dispersion relationship between the surface tension coefficient and the surface wave.

In one embodiment, the non-contact measurement method further includes:

The incident light is modulated by the surface wave for the first time, and the incident light carrying the phase information of the surface wave is reflected by the diffuse reflection surface. After reflection, it meets the surface wave again. After the second phase modulation of the surface wave, a light and dark stripe pattern is generated on the surface of the liquid sample to be tested.

In one embodiment, in the non-contact measurement method,

The image processor obtains the spacing d between two adjacent bright stripes according to the received stripe pattern information, and calculates it based on the formula:

The wavelength λ of the surface wave is obtained.

In one embodiment, the non-contact measurement method,

Based on the calculation formula, The surface tension coefficient σ of the liquid sample to be tested is obtained, where: ρ is the density of the liquid sample to be tested, f is the frequency of the vibration source, and ɡ is the gravitational acceleration.

In one embodiment, the non-contact measurement method further includes calibrating the image collector to determine the actual size corresponding to the size of a single pixel of the image collector.

In one embodiment, the non-contact measurement method further includes:

The frequency of the vibration source is adjusted until a pattern of alternating light and dark stripes is observed on the surface of the liquid sample to be measured.

Beneficial Effects

The non-contact measuring device proposed in this application can achieve accurate measurement of the surface tension coefficient of the liquid sample to be measured, and is particularly suitable for measuring the surface tension coefficient of transparent liquids. Compared with other measurement technologies, it has the following advantages:

1. Adopt non-contact liquid surface tension coefficient measurement method, the measurement result is accurate;

2. The measuring device has a simple structure, is easy to operate, and the phenomenon is intuitive and obvious;

3. The test results are very stable and clear, with strong anti-interference ability.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG1 is a schematic structural diagram of a non-contact measuring device for liquid surface tension coefficient according to an embodiment of the present application;

Figure 2 shows the light and dark stripe pattern when the extended light source is incident;

Fig. 3. Light and dark fringe patterns at different frequencies.

Among them: 1-light source, 2-sample slot, 3-liquid sample to be tested, 4-vibration source, 5-vibrator, 6-diffuse reflection surface, 7-image collector, 8-image processor.

Detailed ways

The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention.

The present application proposes a non-contact measuring device and method for the surface tension coefficient of liquid. The measuring device excites the surface of the liquid sample to be measured to generate surface waves through a frequency-adjustable oscillator, and uses the light emitted by the light source to obliquely irradiate the liquid surface. When the incident light passes through the surface wave of the liquid sample to be measured for the first time, it is phase-modulated by the surface wave of the liquid sample to be measured. After the light wave carries the phase information and diffusely reflects through the diffuse reflection surface at the bottom of the sample tank, it carries the phase information and meets the surface wave of the liquid sample to be measured again, that is, it is phase-modulated by the surface wave of the liquid sample to be measured again. In this way, the light wave acts as a phase information carrier, superimposing the two phases of a surface wave that propagate in opposite directions, forming a stable phase standing wave in the phase of the light wave, so that the CCD or the human eye observes stable stripes of light and dark, thereby accurately obtaining the surface tension coefficient of the liquid.

Embodiment 1

As shown in FIG1 , a non-contact measuring device for the surface tension coefficient of liquid according to an embodiment of the present application is shown. The non-contact measuring device comprises: a light source 1, a sample tank 2, a vibration source 4, a vibrator 5, a diffuse reflection surface 6, an image collector 7 and an image processor 8; the sample tank is used to accommodate a liquid sample 3 to be measured; the vibrator 5 is connected to the vibration source 4 and is arranged in the sample tank 2 to excite the surface of the liquid sample to be measured to generate surface waves; a diffuse reflection surface 6 is arranged at the bottom of the sample tank 2; the image collector 7 is aligned with the sample tank 2 to collect the surface image of the liquid sample to be measured (i.e., a light and dark stripe pattern) and transmit the collected image to the image processor 8;

The incident light emitted by the light source is incident obliquely into the sample tank 2. After the incident light is phase modulated by the surface wave of the liquid sample 3 to be tested, it carries the phase information of the surface wave. The incident light carrying the phase information of the surface wave is reflected by the diffuse reflection surface 6 and meets the surface wave again. In this way, after the second phase modulation of the surface wave, a light and dark stripe pattern is generated on the surface of the liquid sample to be tested.

The fringe pattern is obtained by the image collector 7 and transmitted to the image processor 8. The image processor 8 obtains the wavelength of the surface wave by performing image processing on the received fringe pattern, and obtains the surface tension coefficient of the liquid sample to be tested based on the relationship between the surface tension coefficient and the wavelength of the surface wave. The liquid sample to be tested is preferably a transparent liquid. In this embodiment, the area ratio of the diffuse reflection surface 6 to the area ratio of the bottom of the sample tank 2 is greater than 0.6 (preferably, the area ratio of the diffuse reflection surface 6 to the area ratio of the bottom of the sample tank 2 is between 0.8 and 0.95), so that most of the incident light emitted by the light source is diffusely reflected.

The measurement principle of the non-contact measurement device for the liquid surface tension coefficient is:

When the incident light passes through the surface wave of the liquid sample to be tested for the first time, it is phase modulated by the surface wave of the liquid sample to be tested.

After the incident light carries the phase information and diffusely reflects through the diffuse reflection surface at the bottom of the sample tank (also called the tank bottom), it meets the surface wave of the liquid sample to be tested again, that is, it is phase modulated by the surface wave of the liquid sample to be tested again.

In this way, the incident light acts as a carrier of phase information, superimposing the two phases of the same surface wave that propagate in opposite directions, forming a stable phase standing wave in the phase of the light wave, so that the CCD or the human eye can observe stable stripes of alternating light and dark, and ultimately the surface tension coefficient of the liquid to be tested can be obtained more accurately.

It should be noted that the light and dark stripes mentioned above are not interference stripes between incident light and reflected light waves. The specific analysis is as follows:

In the implementation scheme proposed in the present application, the liquid surface tension coefficient can be obtained by measuring the wavelength λ of the liquid surface wave according to the liquid surface wave dispersion relation.

When only the surface tension of the liquid is considered, the dispersion relation of the surface wave is:

Among them, ω is the angular frequency of the surface wave, and k is the wave vector of the surface wave.

Will Substitute into (1). We get:

Among them, ρ and ɡ are known quantities. From formula (2), it can be seen that the surface tension coefficient σ of the liquid can be calculated by simply measuring the wavelength λ of the liquid surface wave.

The vertical plane where the vibration source is located is taken as the coordinate plane, the contact point between the vibration source and the liquid surface is taken as the coordinate origin, and the propagation to the right is the positive direction of the surface wave propagation;

The expression of liquid surface wave (mechanical wave) is:

Propagating to the right: y ₁ = Acos(ωt-kx)

Propagating to the left: ₂ =Acos(ωt+kx) (3)

Where _y1 is the displacement of the right-propagating surface wave, _y2 is the displacement of the left-propagating surface wave, A is the amplitude, t is the time, and x is the coordinate in the propagation direction of the surface wave.

The incident light is incident obliquely to induce surface waves. Since the surface wave is approximately a sine wave, the incident light beam undergoes different optical paths when entering the liquid surface, so that different positions of the light field after entering the liquid surface obtain different phases. After the first phase modulation of the sinusoidal surface wave, the phase distribution is approximately:

Among them, _k0 is the wave vector of the incident light, and n is the refractive index of the liquid to be measured.

From the phase transformation function, we can get that the light field distribution _E10 at this time is:

Among them, _E0 is the initial light field of the incident light.

When the light propagates to the bottom of the sample tank, because the light propagation path is short, the light field distribution _E1 can be approximated as:

Wherein, L is the horizontal displacement caused by the oblique incidence of light on the bottom of the sample tank.

The incident light containing the phase information of the surface wave is reflected by the diffuse reflection surface and reaches the liquid surface again. After the second phase modulation of the surface wave, the phase distribution is:

At this time, the light field distribution _E2 is:

The light field distribution _E2 after the second phase modulation of the surface wave propagates to the light field distribution _E3 at the image collector:

According to the light propagation theory, bright fringes can be observed at the antinode position of the light field phase distribution pattern, as shown in FIG2 .

It can be seen from equation (8) that after two phase modulations of the surface wave, the phase distribution of the light wave is a standing wave:

From the properties of standing waves, we know that the distance between two adjacent antinodes is half the wavelength. Since the phase distribution at this point is similar to that of a lens, a converging or diverging light field will appear. When the frequency emitted by the vibration source is higher than the frequency 24Hz required for the human eye to produce a visual persistence effect, the human eye will experience a visual persistence effect, and thus stable light and dark stripes will be observed. Therefore, the relationship between the spacing d of the bright stripes and the wavelength λ of the surface wave can be obtained as follows:

Substituting (11) into (2), we get:

The liquid density ρ, vibration source frequency f and gravitational acceleration ɡ are known. The bright fringes are accurately collected by an image collector, and then the bright fringe spacing can be measured and the liquid surface tension coefficient can be calculated through image processing.

Next, a measurement method using the non-contact measurement device is described, comprising the following steps: generating a surface wave on the surface of the liquid sample to be measured based on a vibrator,

The incident light emitted by the light source is incident obliquely on the surface of the liquid sample to be tested and meets the surface wave. The incident light carrying the phase information of the surface wave is reflected by the diffuse reflection surface and meets the surface wave again, so as to produce a light and dark stripe pattern on the surface of the liquid sample to be tested.

The fringe pattern is collected by an image collector and fed back to an image processor.

The image processor obtains the wavelength of the surface wave based on the received fringe pattern information and the preset model, and calculates the surface tension coefficient of the liquid sample to be tested based on the dispersion relationship between the surface tension coefficient and the surface wave. This method can accurately measure the surface tension coefficient of the liquid to be tested (such as a transparent liquid).

The following describes in detail a measurement method using the non-contact measurement device for the surface tension coefficient of liquid using the above-mentioned method in conjunction with the second embodiment. The measurement method includes:

1) Calibrate the image collector to determine the actual size corresponding to the size of a single pixel of the image collector;

2) Immerse the vibrator in the liquid sample to be tested and adjust the frequency of the vibration source until a pattern of alternating light and dark stripes is observed;

3) The fringe pattern is collected by an image collector, and the image processor processes the fringe pattern collected by the image collector to obtain the wavelength of the surface wave, and the surface tension coefficient of the liquid sample to be tested is obtained according to the relationship between the surface tension coefficient and the wavelength of the surface wave.

Furthermore, the calibration process of step 1) is specifically as follows:

(1) Use graph paper to assist in image acquisition device calibration and adjust the image acquisition device position so that the image acquisition device lens is horizontal and the scale line on the graph paper is parallel to the bottom line of the acquisition area of the image acquisition device;

(2) Adjust the focal length and aperture of the image collector to make the collected graph paper image clearest;

(3) Collect the graph paper image and calculate the ratio of the image collector pixel size to the actual length.

In one embodiment, the light source uses an extended light source, the image collector can use a 640*480 CCD, and the liquid sample to be measured is tap water. Before the experiment, the measuring device needs to be calibrated to determine the actual size corresponding to the size of a single pixel. In this solution, the actual length corresponding to each pixel size is 90 μm.

First, pour the liquid sample to be tested (hereinafter referred to as the liquid to be tested) into the sample tank. Take tap water as an example, the water temperature is about 25°C, change the frequency of the vibration source, and perform multiple measurements. From Table 1 and Figure 3 (a/b/c/d in Figure 3 represent the patterns of light and dark stripes at frequencies of 70Hz, 90Hz, 120Hz and 160Hz, respectively), it can be seen that the stripe spacing decreases with the increase of frequency, and the measured surface tension coefficient remains basically the same, indicating that this method can accurately measure the surface tension coefficient of liquid at different frequencies.

Table 1 Measurement results of tap water surface tension coefficient at different frequencies

The above description of the disclosed embodiments enables one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to one skilled in the art, and the general principles defined in this case may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown in this case, but will conform to the widest scope consistent with the principles and novel features disclosed in this case.

Claims (6)

1. A non-contact measuring device for liquid surface tension coefficient, comprising: Light source, sample slot, vibration source, vibrator, diffuse reflection surface, image collector and image processor; The light source is configured to emit incident light that is incident obliquely onto the sample slot; A sample tank, which is used to accommodate the liquid sample to be tested, and the bottom of the sample tank is provided with a diffuse reflection surface; a vibrator, which is connected to a vibration source, and the vibrator is arranged in the sample tank, and is used to excite the liquid sample to be tested and generate surface waves on its surface; An image collector, which is aligned with the sample slot, and is used to collect a surface image of the liquid sample to be tested and transmit the collected image to an image processor, wherein the surface image includes a stripe pattern of alternating light and dark stripes; The incident light emitted by the light source carries the phase information of the surface wave after being phase modulated by the surface wave of the liquid sample to be tested. The incident light carrying the phase information of the surface wave is reflected by the diffuse reflection surface and meets the surface wave again. After the second phase modulation of the surface wave, a light and dark stripe pattern is generated on the surface of the liquid sample to be tested. In the light and dark stripe pattern, the distance d between two adjacent bright stripes and the wavelength λ of the surface wave of the liquid sample to be tested satisfy λ＝2d, Based on the relationship: Obtain the surface tension coefficient σ of the liquid sample to be tested, Where: ρ is the density of the liquid sample to be measured, f is the frequency of the vibration source, ɡ is the gravitational acceleration, and λ is the wavelength of the surface wave. 2. The non-contact measuring device for liquid surface tension coefficient according to claim 1, characterized in that: The frequency emitted by the vibration source is higher than the frequency 24 Hz required for the human eye to produce the persistence of vision effect. 3. A non-contact measurement method, characterized in that the non-contact measurement device according to claim 1 or 2 is used, and the measurement method comprises the following steps: Based on the oscillator generating surface waves on the surface of the liquid sample to be tested, Based on the incident light emitted by the light source being incident obliquely on the surface of the liquid sample to be tested, a light and dark stripe pattern is generated on the surface of the liquid sample to be tested. The fringe pattern is collected by an image collector and fed back to an image processor. The image processor obtains the wavelength of the surface wave based on the received fringe pattern information and the preset model, and obtains the surface tension coefficient of the liquid sample to be tested based on the relationship between the surface tension coefficient and the dispersion of the surface wave. The image processor obtains the spacing d between two adjacent bright stripes according to the received stripe pattern information, and calculates it based on the formula: Get the wavelength λ of the surface wave, Based on the calculation formula, The surface tension coefficient σ of the liquid sample to be tested is obtained, where: ρ is the density of the liquid sample to be tested, f is the frequency of the vibration source, and ɡ is the gravitational acceleration. 4. The non-contact measurement method according to claim 3, further comprising: The incident light is modulated by the surface wave for the first time, and the incident light carrying the phase information of the surface wave is reflected by the diffuse reflection surface. After reflection, it meets the surface wave again. After the second phase modulation of the surface wave, a light and dark stripe pattern is generated on the surface of the liquid sample to be tested. 5. The non-contact measurement method according to claim 3, further comprising calibrating the image collector to determine the actual size corresponding to the size of a single pixel of the image collector. 6. The non-contact measurement method according to claim 3, further comprising: The frequency of the vibration source is adjusted until a pattern of alternating light and dark stripes is observed on the surface of the liquid sample to be measured.