阅读说明：本技术 一种同时测量二元系热扩散率和互扩散系数的装置及方法 (Device and method for simultaneously measuring binary system thermal diffusivity and mutual diffusivity ) 是由 张颖 何茂刚 陈俊帅 占涛涛 刘向阳 于 2019-10-25 设计创作，主要内容包括：本发明提供一种同时测量二元系热扩散率和互扩散系数的装置及方法,该装置通过偏振光路将光束扩展成直径较大的均匀平行光束,进入实验本体后可以实现全域扫描测量,通过检测分析单元即可获取透射光与散射光干涉叠加的图像,其中包含各个散射体积下对应的散射光信息。本发明提供的同时测量二元流体混合物热扩散率和互扩散系数的方法,通过图像作差分析可以得到与时间相关的散射光强度信息,本发明即可同时计算获得热扩散率和互扩散系数数据。本发明除了可以实现热扩散率和互扩散系数全域测量以及同时测量外,无需机械控制角度,即可实现大量独立散射矢量下散射光信号的同时采集,显著提高了测量精度。(The invention provides a device and a method for simultaneously measuring binary system thermal diffusivity and mutual diffusion coefficient, wherein the device expands a light beam into a uniform parallel light beam with a larger diameter through a polarization light path, can realize global scanning measurement after entering an experiment body, and can obtain an image of interference superposition of transmitted light and scattered light through a detection analysis unit, wherein the image contains corresponding scattered light information under each scattering volume. The method for simultaneously measuring the thermal diffusivity and the mutual diffusivity of the binary fluid mixture can obtain scattered light intensity information related to time through image difference analysis, and the thermal diffusivity and the mutual diffusivity data can be simultaneously calculated and obtained. The invention can realize the global measurement and the simultaneous measurement of the thermal diffusivity and the mutual diffusivity, can realize the simultaneous acquisition of scattered light signals under a large number of independent scattering vectors without mechanically controlling angles, and obviously improves the measurement precision.)

1. A device for simultaneously measuring binary system thermal diffusivity and mutual diffusivity comprises a polarized light path, an experimental unit and a detection and analysis unit, wherein the experimental unit is provided with a light-transmitting experimental body (7) and a temperature and pressure measurement and control system, and fluid to be measured can be filled in the experimental body (7); the temperature and pressure measurement and control system is used for controlling and measuring the temperature and the pressure of the fluid to be measured; the polarized light generated by the polarized light path enters the experiment body, transmits the fluid to be measured, induces to generate scattered light, and the scattered light and the transmitted light form an interference superposition image to be detected, collected and analyzed by the detection and analysis unit.

2. The device for simultaneously measuring the binary system thermal diffusivity and the mutual diffusivity according to claim 1, wherein the polarized light path comprises a laser (1), an adjustable attenuator (2), a polarizer (3), a spatial filter (4), a collimating lens (5) and a diaphragm (6) which are arranged in sequence.

3. The device for simultaneously measuring the thermal diffusivity and the mutual diffusivity of a binary system according to claim 1, wherein the detection and analysis unit comprises an analyzer (8), a CCD sensor (9) and a computer (10) which are arranged in sequence, and the computer (10) comprises an image processing program.

4. The device for simultaneously measuring the thermal diffusivity and the mutual diffusivity of a binary system according to claim 1, wherein the adjustable attenuator (2), the polarizer (3), the spatial filter (4), the collimating lens (5) and the diaphragm (6) can be fixed on the cage-shaped support rod to form a cage-shaped optical system, which is convenient for adjusting the collimation of the light path.

5. A method for simultaneously measuring binary system thermal diffusivity and interdiffusion coefficient using the device of claim 1, comprising a data acquisition process and a data processing process, wherein,

the data acquisition process comprises the steps of:

1) preparing a binary fluid mixture sample under the concentration to be measured, wherein the concentration of components is more than 0 and less than 100%, and the types of the mixture comprise a salt solution, a polymer solution, a gas-liquid mixture solution and an organic matter solution;

2) filling the fluid sample to be measured prepared in the step 1) into the experiment body;

3) adjusting the temperature and pressure in the experimental body to set values, wherein regions capable of realizing measurement comprise a supercooling region, a saturated liquid phase region, a saturated gas phase region, a near critical region and a supercritical region according to different mixtures;

4) opening a laser light source and calibrating a polarization light path;

5) the detection analysis unit collects interference images of the transmitted light beams and the scattered light beams and records the sampling time of each time;

the data processing process comprises the following steps:

the detection analysis unit selects enough images to average light intensity information of the images according to the acquired interference images through an image processing program, takes the result as a reference image at zero time, performs difference between the image at each time and the reference image, performs Fourier transform on the obtained result to obtain scattered light spectrum information, and finally fits the scattered light spectrum information into a time correlation function so as to calculate the thermal diffusivity and the mutual diffusivity of the binary fluid mixture;

the data processing process comprises the following specific steps:

1) microscopically, the intensity of scattered light continuously fluctuates along with the change of temperature fluctuation and concentration fluctuation, and the statistical average is zero macroscopically, so that enough images are selected from the acquired interference images, and the intensity of transmitted light can be obtained by averaging light intensity signals of the images, so that the intensity of the transmitted light is used as a reference image at zero time;

2) and (3) subtracting the image at each moment after the zero moment from the reference image to obtain the corresponding scattered light information under each scattering vector at each moment, and then carrying out Fourier transform on the scattered light information to obtain the corresponding scattered light spectrum information until the obtained scattered light spectrum tends to be stable, namely, the number of the processed images is enough to meet the precision requirement. Since the scattered light spectrum information in the binary fluid mixture system contains the influence of both temperature fluctuation (controlled by thermal diffusivity) and concentration fluctuation (controlled by interdiffusion coefficient), in order to solve both thermal diffusivity and interdiffusion coefficient, a time-dependent function G (q, tau) containing thermal diffusivity term and interdiffusion coefficient term is given

G(q,τ)＝2{A(q)[I_St(q)(1-f_t(q,τ))+I_Sc(q)(1-f_c(q,τ))]+B(q)} (2)

Where A (q) is a parameter related to the optical layout and the scattering vector q; i is_St(q) and I_Sc(q) is the average scattered light intensity at q due to temperature fluctuations and concentration fluctuations, respectively; f. of_t(q, τ) and f_c(q, τ) are intermediate scattering functions corresponding to temperature fluctuations and concentration fluctuations, respectively; b (q) is background noise;

3) at each scattering vector, a least squares method can be used, with A (q) I_St(q)、A(q)I_Sc(q) and B (q) fitting the scattered light intensities to a time-dependent function with respect to time τ as fitting parameters, from which an intermediate scattering function f can be obtained for each scattering vector_t(q, τ) and f_c(q, τ), both in the form of an exponential decay with respect to time τ:

f_t(q,τ)＝exp(τ/τ_Ct(q)) (3)

f_c(q,τ)＝exp(τ/τ_Cc(q)) (4)

wherein, tau_Ct(q) and τ_Cc(q) is a decay time constant which characterizes the mean time taken for the relaxation of temperature and concentration fluctuations to equilibrium, respectively, and τ can be obtained for each scattering vector by fitting the intermediate scattering function under each scattering vector_Ct(q) and τ_Cc(q), the relationship of the time constant to the scattering vector can be expressed as:

τ_Ct(q)＝1/aq²(5)

τ_Cc(q)＝1/D₁₂q²(6)

wherein a is thermal diffusivity; d₁₂For the mutual diffusion coefficient, the thermal diffusivity and the mutual diffusion coefficient can be calculated according to the fitting results of the formula (5) and the formula (6).

Technical Field

The invention belongs to the technical field of fluid thermophysical property measurement, and relates to a device and a method for simultaneously measuring binary system thermal diffusivity and mutual diffusivity.

Background

Thermal diffusivity and interdiffusion coefficient are important thermophysical properties in related fields such as scientific research and engineering practice. Thermal diffusivity is the ability to characterize the temperature of parts of an object during heating or cooling; the interdiffusion coefficient characterizes how fast the mass transfer behavior is due to concentration differences. Therefore, the method has important practical significance for experimental measurement and theoretical research of thermal diffusivity and mutual diffusivity.

The main methods for measuring thermal diffusivity are the flat plate method, the coaxial cylinder method, the transient hot wire method and the light scattering method. The basic principles of the first three methods are similar and are all established based on the Fourier heat conduction law, and a stable temperature gradient needs to be kept in the experimental process, so that the influence of convective heat transfer and radiative heat transfer is not negligible. The physical quantity directly measured by the three methods is the heat conductivity coefficient lambda, and then the density rho and the specific constant pressure heat capacity c are combined_pThe thermal diffusivity, a, is calculated by equation (1):

a＝λ/ρc_p(1)

compared with the first three methods, the light scattering method is a new method for measuring the thermal diffusivity, the thermal diffusivity can be obtained by analyzing a scattered light signal caused by temperature fluctuation in the sample under a macroscopic thermodynamic equilibrium state, the influence of convective heat exchange and radiative heat exchange can be effectively avoided, and the method is also beneficial to the measurement of certain special samples (corrosion and toxicity). Common measurement methods for the interdiffusion coefficient of binary fluid mixtures are membrane cell methods, taylor dispersion methods, optical interference methods and light scattering methods. The membrane pool method is established based on Fick's first law, and the physical quantity to be measured is concentration difference, so the method needs very accurate chemical analysis means; the Taylor dispersion method is mainly applied to modularized measurement, and batch measurement can be realized by purchasing components of corresponding models according to measurement requirements; the optical interference method has the advantages of non-contact measurement, high sensitivity and the like, is established based on the principle that the concentration difference can cause the refraction of transmitted beams, so that a diffusion liquid level with proper concentration difference is required to be established for each measurement, the working intensity is high, the influence of window heat leakage on interference fringes is avoided, and the temperature application range of the method is small; the light scattering method can also realize the measurement of the mutual diffusion coefficient, is suitable for a very wide temperature and pressure range, and in a binary system, a scattered light signal detected by the method is generated by temperature fluctuation and concentration fluctuation together, usually the scattered light signal corresponding to the temperature fluctuation with fast attenuation is ignored, and the result is only used for calculating the mutual diffusion coefficient, so certain errors exist.

It can be seen that, among the above methods, the light scattering method, which is a high-sensitivity non-contact measurement method, can achieve the measurement of thermal diffusivity and mutual diffusivity in a thermodynamic equilibrium state. The method does not need to build a temperature gradient or a concentration gradient, so that the temperature and pressure can be controlled and measured very simply and conveniently, the method has a large temperature and pressure application range, and the method is a thermal diffusivity and mutual diffusivity measurement method with great potential. However, the existing light scattering measurement methods also have some problems: (1) thermal diffusivity is usually one to two orders of magnitude larger than the mutual diffusivity, and both exist on different time scales, and the measurement of both needs a highly configured digital correlator, which means high cost. In general measurement, the arrangement of a digital correlator needs to be adjusted, and the thermal diffusivity and the mutual diffusivity of the binary system are measured separately, so that the thermal diffusivity and the mutual diffusivity cannot be measured simultaneously. (2) The traditional light scattering method is carried out under a fixed angle and a fixed scattering volume, and the requirement on the accuracy of angle control is very high. When repeated measurements are required with varying angles and scattering volumes, the entire optical path is typically recalibrated, and collimation of the optical path has a significant effect, a process that is time and effort intensive. (3) Theoretically, the smaller the set scattering angle is, the larger the measurement range is and the higher the accuracy is, but under practical conditions, because a photon counter or a photomultiplier tube is adopted in the traditional method to receive scattered light, the devices are very sensitive to light signals, and under small angles, the signal-to-noise ratio of the collected scattered light signals is lower due to the influence of stray light, dispersion effect and the like. In general, to obtain a sufficiently high signal-to-noise ratio, the angle setting is not too small.

In view of the above, the main idea of the present invention is to establish an apparatus and a method that can achieve the simultaneous measurement of the thermal diffusivity and the interdiffusion coefficient of a binary fluid mixture. The invention introduces the image acquisition technology of a pixilated sensor CCD (charge Coupled device) into a light scattering method to acquire interference images of scattered light and incident light in real time; a time correlation function containing a thermal diffusivity term and a mutual diffusion coefficient term is provided for fitting scattered light information, so that the scattered light information related to the thermal diffusivity and the mutual diffusion coefficient can be extracted at the same time, and the thermal diffusivity and the mutual diffusion coefficient can be measured at the same time. Compared with the traditional method that the angle and the scattering volume are adjusted through a mechanical device, once the device is adjusted to be aligned, the whole-domain measurement can be realized without any other adjustment, namely, any part of the transmitted light beam can be used as the scattering volume, the scattering angle can be determined according to the position relation among each pixel on a receiving plane of the CCD sensor, the scattering volume and the transmitted light beam, the scattering vector can be calculated, the mechanical control is not needed, and the precision is higher and more convenient. Under the device, because scattered light isotropy, can realize scattered light signal's while collection under the scattering vector that a large amount of moduli are equal, wherein also contained the light signal under the minimum angle, realized laser beam detection region's universe collection promptly, possessed very obvious statistical advantage, reduced error occasionally to show the promotion measurement accuracy. The data processing process is also changed into the interference image of scattered light and incident light by utilizing a computer program, and compared with an expensive hardware digital correlator in the traditional light scattering experimental device, the data processing device has a wider application range and greatly reduces the cost.

Disclosure of Invention

The invention aims to provide a device and a method for simultaneously measuring binary system thermal diffusivity and mutual diffusivity, which can simultaneously acquire scattered light signals containing thermal diffusivity and mutual diffusivity information and firstly provide a time correlation function containing a thermal diffusivity term and a mutual diffusivity term. The method adopts global measurement, can realize the simultaneous acquisition of scattered light signals under a large number of scattering vectors corresponding to each scattering volume, wherein the scattered light signals under a tiny angle are included, the result processing does not depend on the calculation of a hardware digital correlator any more, and the method is suitable for the simultaneous measurement of the thermal diffusivity and the mutual diffusion coefficient of the binary fluid mixture.

The invention is realized by the following technical scheme:

a device for simultaneously measuring binary system thermal diffusivity and mutual diffusivity comprises a polarized light path, an experimental unit and a detection and analysis unit,

the experiment unit is provided with a light-transmitting experiment body and a temperature and pressure measurement and control system, and fluid to be measured can be filled in the experiment body; the temperature and pressure measurement and control system is used for controlling and measuring the temperature and the pressure of the fluid to be measured; polarized light generated by the polarized light path enters the experiment body to be induced to generate scattered light, and the scattered light and the transmitted light form an interference superposition image which is detected, collected and analyzed by the detection and analysis unit.

Preferably, the polarized light path is composed of a laser, an adjustable attenuator, a polarizer, a spatial filter, a collimating lens and a diaphragm which are sequentially arranged, the laser emitted by the laser adjusts the light intensity through the adjustable attenuator, the adjustable attenuator is required to increase the light intensity of the laser due to weaker scattered light when the temperature is lower, and the scattered light is stronger at high temperature, so that the light intensity can be decreased to reduce the influence of stray light; then adjusting the polarization state of the laser by a polarizer and improving the polarization ratio; and finally, expanding the diameter of the laser beam through a spatial filter, a collimating lens and a diaphragm to obtain a large and uniform light spot, and then entering an experiment body to realize global scanning measurement.

Preferably, the detection and analysis unit comprises an analyzer, a CCD sensor and a computer, wherein the analyzer can reduce the influence of stray light caused by the environment, the wall surface of the body, the glass window and the like, thereby improving the signal-to-noise ratio of the acquired signal; the CCD sensor is used for receiving image information superposed by interference of scattered light and transmitted light and transmitting the image information to the computer; the computer displays the interference image information and calculates the thermal diffusivity and the interdiffusion coefficient of the binary fluid mixture.

Preferably, the adjustable attenuator, the polarizer, the spatial filter, the collimating lens and the diaphragm can be fixed on the cage-type support rod to form a cage-type optical system, so that the collimation of a light path can be conveniently adjusted.

A method for simultaneously measuring binary system thermal diffusivity and mutual diffusivity comprises a data acquisition process and a data processing process, wherein,

the data acquisition process comprises the steps of:

1) preparing a binary fluid mixture sample under the concentration to be measured, wherein the concentration of components is more than 0 and less than 100%, and the types of the mixture comprise a salt solution, a polymer solution, a gas-liquid mixture solution and an organic matter solution;

2) filling the fluid sample to be measured prepared in the step 1) into the experiment body;

3) adjusting the temperature and pressure in the experimental body to set values, wherein regions capable of realizing measurement comprise a supercooling region, a saturated liquid phase region, a saturated gas phase region, a near critical region and a supercritical region according to different mixtures;

4) opening a laser light source and calibrating a polarization light path;

5) the detection and analysis unit collects interference images of the transmitted beam and the scattered beam and records the time of each sampling.

The data processing process comprises the following steps:

the detection analysis unit selects enough images to average the light intensity information of the images according to the acquired interference images through an image processing program, takes the result as a reference image at zero time, performs difference between the image at each time and the reference image, performs Fourier transform on the obtained result to obtain scattered light spectrum information, and finally fits the scattered light spectrum information into a time correlation function, thereby calculating the thermal diffusivity and the mutual diffusivity of the binary fluid mixture.

The data processing process comprises the following specific steps:

1) microscopically, the intensity of scattered light continuously fluctuates along with the change of temperature fluctuation and concentration fluctuation, and the statistical average is zero macroscopically, so that enough images are selected from the acquired interference images, and the intensity of transmitted light can be obtained by averaging light intensity signals of the images, so that the intensity of the transmitted light is used as a reference image at zero time;

2) and (3) subtracting the image at each moment after the zero moment from the reference image to obtain the corresponding scattered light information under each scattering vector at each moment, and then carrying out Fourier transform on the scattered light information to obtain the corresponding scattered light spectrum information until the obtained scattered light spectrum tends to be stable, namely, the number of the processed images is enough to meet the precision requirement. Since the scattered light spectrum information in the binary fluid mixture system simultaneously comprises the influence of temperature fluctuation (controlled by thermal diffusivity) and concentration fluctuation (controlled by interdiffusion coefficient), in order to simultaneously solve the thermal diffusivity and the interdiffusion coefficient, the invention provides a time-dependent function G (q, tau) comprising thermal diffusivity terms and interdiffusion coefficient terms

G(q,τ)＝2{A(q)[I_St(q)(1-f_t(q,τ))+I_Sc(q)(1-f_c(q,τ))]+B(q)} (2)

Where A (q) is a parameter related to the optical layout and the scattering vector q; i is_St(q) and I_Sc(q) is the average scattered light intensity at q due to temperature fluctuations and concentration fluctuations, respectively; f. of_t(q, τ) and f_c(q, τ) are intermediate scattering functions corresponding to temperature fluctuations and concentration fluctuations, respectively; b (q) is background noise.

3) At each scattering vector, a least squares method can be used, with A (q) I_St(q)、A(q)I_Sc(q) and B (q) fitting the scattered light intensities to a time-dependent function with respect to time τ as fitting parameters, from which an intermediate scattering function f can be obtained for each scattering vector_t(q, τ) and f_c(q, τ), both in the form of an exponential decay with respect to time τ:

f_t(q,τ)＝exp(τ/τ_Ct(q)) (3)

f_c(q,τ)＝exp(τ/τ_Cc(q)) (4)

wherein, tau_Ct(q) and τ_Cc(q) is the decay time constant, which characterizes the average time taken for temperature and concentration fluctuations, respectively, to relax to equilibrium values. By fitting the intermediate scattering function under each scattering vector, τ under each scattering vector can be obtained separately_Ct(q) and τ_Cc(q), the relationship of the time constant to the scattering vector can be expressed as:

τ_Ct(q)＝1/aq²(5)

τ_Cc(q)＝1/D₁₂q²(6)

wherein a is thermal diffusivity; d₁₂Is the interdiffusion coefficient. According to the fitting results of the formula (5) and the formula (6), the thermal diffusivity and the mutual diffusivity can be calculated.

Compared with the prior art, the invention has the following beneficial technical effects:

the invention provides a device for simultaneously measuring the thermal diffusivity and the mutual diffusivity of a binary fluid mixture, which comprises a polarization light path, an experiment unit and a detection and analysis unit, wherein the polarization light path is expanded to form a uniform polarization light beam, the global scanning measurement of an experiment body is realized, the scattered light and the transmission light beam generated by the experiment body are subjected to interference superposition, the detection and analysis unit detects to obtain an image, and the thermal diffusivity and the mutual diffusivity of the binary fluid mixture to be measured can be simultaneously obtained through image processing and fitting calculation; the detection and analysis unit adopts the CCD sensor for detection, and can realize simultaneous acquisition of scattered light signals under a large number of independent scattering vectors (including minimum scattering vectors) without angle adjustment and control, thereby having very significant statistical advantages, reducing accidental errors and significantly improving precision. The processing result of the computer image processing software breaks through the limit of an expensive hardware digital correlator, the application range is wider, and the cost is greatly reduced.

The method for simultaneously measuring the thermal diffusivity and the mutual diffusivity of the binary fluid mixture firstly provides a time correlation function containing a thermal diffusivity term and a mutual diffusivity term, so that the thermal diffusivity and the mutual diffusivity are simultaneously obtained. In the data processing process, the difference is made through images, the influence of stray light can be effectively reduced, the signal to noise ratio is improved, and the scattered light intensity information under each scattering vector can be obtained through the statistical average of a large number of images, so that the measurement accuracy of the thermal diffusivity and the mutual diffusion coefficient is remarkably improved.

Drawings

FIG. 1 is a schematic diagram of an apparatus for simultaneously measuring the thermal diffusivity and the interdiffusion coefficient of a binary system according to the present invention.

Fig. 2 is a structural diagram of a temperature and pressure measurement and control system provided by the invention.

FIG. 3 is a schematic structural diagram of an experimental body according to the present invention.

FIG. 4 is a schematic plane view of the experimental structure provided by the present invention.

Fig. 5 is an image fitted to experimental data.

The device comprises a laser 1, an adjustable attenuator 2, a polarizer 3, a spatial filter 4, a collimating lens 5, a diaphragm 6, an experimental body 7, an analyzer 8, a CCD sensor 9, a computer 10, a liquid storage 11, a filter 12, a plunger pump 13, a vacuum pump 15, a hand pump 17, a heating cavity 20, a pressure transmitter 21, a heater 22, a platinum resistance thermometer 23, a temperature controller 24, a digital multimeter 25, a liquid collector 27, valves 14, 16, 18, 19 and 26, bolts 28, temperature measuring holes 29, flanges 30, a window 31 and sealing gaskets 32.

Detailed Description

The present invention will now be described in further detail with reference to specific examples, which are intended to be illustrative, but not limiting, of the invention.

Referring to fig. 1, the device for simultaneously measuring the thermal diffusivity and the mutual diffusivity of a binary fluid mixture of the present invention comprises a polarized light path, an experimental unit and a detection and analysis unit, wherein the experimental unit comprises a light-transmitting experimental body 7 and a temperature and pressure control system, and a fluid to be measured can be filled in the experimental body 7; the temperature and pressure measurement and control system is used for controlling and measuring the temperature and the pressure of the fluid to be measured; polarized light generated by the polarized light path enters the experiment body 7 to be induced to generate scattered light, and the scattered light and the transmitted light form an interference superposition image to be detected, collected and analyzed by the detection and analysis unit.

The polarized light route is by the laser 1 that sets gradually, adjustable attenuator 2, polarizer 3, spatial filter 4, collimating lens 5, diaphragm 6 is constituteed, laser 1 sends laser, adjust to suitable light intensity through adjustable attenuator 2, the laser polarization state is adjusted to rethread polarizer 3, carry out the even beam expanding to laser through spatial filter 4 and collimating lens 5 at last, adopt diaphragm 6 control to get into the facula size of experiment body 7, the laser beam gets into experiment body 7 and begins the global scanning measurement, the scattered light that produces interferes the stack with the transmitted light and gets into the detection and analysis unit, detected the analysis unit and detect, gather and analysis.

Adjustable attenuator 2, polarizer 3, spatial filter 4, collimating lens 5, diaphragm 6 are all installed on the cage bracing piece, fix respectively on adjustable elevating platform with experiment body 7 to realize the accurate regulation of light path.

The polarized light path, the experimental body 7, the polarizer 8 of the detection and analysis unit and the CCD sensor 9 are all arranged on an air cushion vibration isolation platform in a dust-free room. Therefore, the stability of the whole device can be ensured, and the influence of the environment on the experimental precision is reduced.

The detection and analysis unit mainly comprises a polarizer 8, a CCD sensor 9 and a computer 10. The CCD sensor 9 is connected with a computer 10, and transmits the acquired interference image to the computer for processing. The experiment body 7 is connected with a temperature and pressure measurement and control system, the temperature and pressure measurement and control system is used for measuring and controlling the temperature and the pressure in the experiment body 7, and a data acquisition module of the temperature and pressure measurement and control system is constructed based on a Keithley 2002 digital multimeter and is controlled by an acquisition program developed by LabVIEW voice.

Referring to fig. 2, the temperature and pressure measurement and control system mainly comprises a liquid storage 11, a filter 12, a plunger pump 13, a vacuum pump 15, a hand pump 17, a heating cavity 20, a pressure transmitter 21, a platinum resistance thermometer 23, a heater 22, a temperature controller 24, a digital multimeter 25, a liquid collector 27 and other valves. The invention adopts an electric heating mode, a temperature controller 24 is connected with a heater 22 and inserted into a heating cavity 20, an experiment body 7 is fixed in the heating cavity 20, and a PID control strategy is adopted for temperature feedback. The digital multimeter 25 is connected to the pressure transmitter 21 and the platinum resistance thermometer 23. The side end of the experiment body 7 is communicated with a temperature measuring stainless steel pipe, and a platinum resistance thermometer 23 is inserted into the temperature measuring hole 29; the pressure transmitter 21 is connected between a liquid outlet of the liquid filling device to be measured and a liquid inlet stainless steel pipe of the liquid inlet of the experiment body. The liquid filling device to be measured of the present invention includes a flow pump 13 and a vacuum pump 15; the vacuum pump 15 is used for vacuumizing the whole system and is connected into a system liquid inlet pipeline through a control valve 16; the plunger pump 13 is used for injecting liquid into a system pipeline after being vacuumized, one end of the plunger pump is connected into a system liquid inlet pipeline through a control valve 14, the other end of the plunger pump is connected with the filter 12 through a pipeline, and the pipeline is connected into the liquid storage device 11 which is to be tested. The secondary pressurizing device is a hand pump 17 and is connected into a system liquid inlet pipeline through a control valve 18.

Referring to fig. 3, the flange 10 and the body are fixed by 4 bolts 28 respectively at the front and the back of the experimental body, and 29 is a temperature measuring hole inserted with a platinum resistance thermometer 23.

Referring to fig. 4, a window glass 31 and a sealing gasket 32 are installed between the flange 10 and the body to ensure the sealing performance of the experimental body.

Referring to fig. 5, the interference image collected by the CCD sensor 9 is transmitted to a computer, and can be fitted to a time-dependent function after image processing:

G(q,τ)＝2{A(q)[I_St(q)(1-f_t(q,τ))+I_Sc(q)(1-f_c(q,τ))]+B(q)}

the use method of the optical experimental device for simultaneously measuring the thermal diffusivity and the mutual diffusivity of the binary fluid mixture comprises the following steps:

(1) a scatter light path is arranged.

Arranging optical components as shown in figure 1, coaxially fixing the experiment body 7, the cage-type support rod on which the components are installed and the detection and analysis unit, turning on the laser 1, and preheating for 30 minutes. The laser 1 is adjusted to enable the laser to pass through the central lines of the adjustable attenuator 2, the polarizer 3, the spatial filter 4, the collimating lens 5 and the diaphragm 6 to form uniform beams with proper diameters, and the beams pass through the experiment body 7, the analyzer 8 and the CCD sensor 9 to ensure that the beams are coincident with the central lines of components. The CCD sensor is turned on and the positions of the respective elements are adjusted until the computer 10 can observe a clear image and the optical path adjustment is completed.

(2) And (5) detecting the tightness of the experimental system.

Connecting the pipelines according to the figure 2, closing the valves 14 and 26, keeping the other valves fully opened, vacuumizing the whole experiment system pipeline by using a vacuum pump 15 to ensure that the internal vacuum degree reaches below 135kPa, closing the valve 16 and keeping for about 1 hour, and if the pressure is still below 135kPa, considering that the system has good sealing property. And then, carrying out pressure test on the system by using a hand pump according to the target pressure.

(3) The liquid to be measured is prepared and filled.

Preparing a binary fluid mixture with the concentration to be measured, loading the binary fluid mixture into the liquid reservoir 11, opening the valves 14, 19 and 26, closing the valve 16, filling the sample to be measured into the experimental pipeline and the hand pump through the plunger pump, entering the experimental body 7, and closing all the valves except the valves 18 and 19 after filling.

(4) Target temperature and pressure are set.

The heater 22 and the temperature controller 24 are connected and inserted into the heating cavity 20, the temperature controller 24 is opened to set a target temperature, and the experiment body 7 is heated until the temperature is stable. The test body was pressurized to a target pressure by means of a hand pump 17.

(5) And (6) data acquisition.

After the temperature and the pressure to be measured are stable, the CCD sensor 9 is used for collecting the image of interference superposition of the transmitted light and the scattered light, and the image and the collection time are recorded in the computer 10. The temperature and pressure data of the sample to be measured are collected in real time using a platinum resistance thermometer 23 and a pressure transmitter 21 in combination with a digital multimeter 25.

(6) And (5) processing the image.

6.1) selecting a time point as a reference, averaging the light intensity distribution of all images in a previous sampling time period, and taking the average as a reference image at zero moment;

6.2) the image at each moment after the zero moment is differentiated from the reference image to obtain the scattered light intensity information corresponding to each scattering vector at each moment. The invention firstly provides a time correlation function containing a thermal diffusivity term and a mutual diffusion coefficient term, and adopts a least square method to use A (q) I_St(q)、A(q)I_Sc(q) and B (q) fitting data G (q, τ) to the parameters

G(q,τ)＝2{A(q)[I_St(q)(1-f_t(q,τ))+I_Sc(q)(1-f_c(q,τ))]+B(q)} (2)

Wherein A (q) is a function with respect to q, related to the optical layout; i is_St(q) and I_Sc(q) is the average scattered light intensity at q due to temperature fluctuations and concentration fluctuations, respectively; f. of_t(q, τ) and f_c(q, τ) are intermediate scattering functions corresponding to temperature fluctuations and concentration fluctuations, respectively; b (q) is background noise.

6.3) according to the fitting result, an intermediate scattering function f under each scattering vector can be obtained_t(q, τ) and f_c(q, τ), both in exponentially decaying form with respect to time τ:

f_t(q,τ)＝exp(τ/τ_Ct(q)) (3)

f_c(q,τ)＝exp(τ/τ_Cc(q)) (4)

wherein, tau_Ct(q) and τ_Cc(q) is the decay time constant. By fitting the intermediate scattering function under each scattering vector, τ under each scattering vector can be obtained separately_Ct(q) and τ_Cc(q), the relationship of the time constant to the scattering vector can be expressed as:

τ_Ct(q)＝1/aq²(5)

τ_Cc(q)＝1/D₁₂q²(6)

wherein a is thermal diffusivity; d₁₂Is the interdiffusion coefficient. According to the fitting results of the formula (5) and the formula (6), the thermal diffusivity and the mutual diffusivity can be calculated.

The invention is characterized in that the invention can realize the global scanning measurement, any position transmitted by the laser can be selected as the scattering volume, and the thermal diffusivity and the mutual diffusivity of the binary fluid mixture to be measured can be obtained simultaneously through image processing and fitting calculation. In addition, the result of each measurement is established on the statistical average of a large amount of data, the precision is higher, the method is not limited by a hardware digital correlator any more, the experiment cost is reduced, and the application range is wider.