A method and apparatus for simultaneous measurement of fluid viscosity and density

Abstract

The application discloses a method and device suitable for simultaneously measuring fluid viscosity and density. According to a physical model of a vibrating tuning fork immersed in the fluid, a set of viscosity and density measurement equations based on a double tuning fork are established. Compared with a previously used empirical correlation formula, the density measurement formula has practical physical significance without affecting the measurement accuracy, wherein each parameter in the formula is determined by the structure, size and material of the tuning fork, and has a reference function for the design and selection of the tuning fork. Based on the proposed method, a device for simultaneously measuring fluid viscosity and density is provided, which has the advantages of small volume, convenient operation and wide application scene, and can be used for measuring the viscosity and density of high-temperature and high-pressure fluid.

Description

Technical Field

[0001] This invention relates to the field of fluid thermophysical property measurement technology, specifically to a method and apparatus for simultaneously measuring fluid viscosity and density. Background Technology

[0002] Viscosity and density are fundamental thermophysical properties of fluids. In scientific research, viscosity and density serve as the data foundation for studying thermodynamics, heat transfer, fluid mechanics, and other disciplines, as well as for developing and utilizing new energy sources and designing new materials. In engineering design and industrial production, accurate viscosity and density data are crucial for chemical equipment design, production process control, equipment safety testing, and product quality assessment, and have wide applications in petrochemicals, biomedicine, energy conservation and environmental protection, and national defense. Therefore, viscosity and density are indispensable thermophysical parameters of fluids.

[0003] Currently, there are few research reports on devices for simultaneously measuring fluid viscosity and density. Chinese patent CN112748046A provides a pipeline system integrating a capillary viscometer and a vibrating tube densitometer, using two instruments to measure the viscosity and density of the fluid separately. It offers high measurement accuracy, but the system is relatively complex, bulky, and costly. US patent US 2003041653A discloses a method for simultaneously measuring fluid viscosity and density using a piezoelectric quartz tuning fork. It extracts viscosity and density information from electrical parameters such as the tuning fork's resonant frequency, impedance, and quality factor in the fluid. However, the electrical signals are often difficult to measure accurately and stably due to factors such as electrode arrangement and impurities in the fluid environment, significantly hindering its widespread application. For example, when measuring the viscosity of lubricating oil in large machinery, impedance deviations caused by metal shavings in the oil often lead to large measurement errors. Chinese patent CN107601424A discloses a MEMS viscosity-density sensor based on in-plane resonance, which also suffers from similar problems. Chinese patent CN114594021A (application number 202210225611.0) discloses an asymmetric dual-piezoelectric tuning fork viscosity sensor. It can determine the viscosity and density of a fluid by measuring the resonant frequencies of the two tuning forks in the fluid, avoiding the measurement of electrical characteristic parameters and achieving high accuracy. The sensor measures density through a given empirical correlation formula, and the coefficients need to be calibrated experimentally. However, the use of this formula places certain requirements on the structure, size, and material parameters of the tuning forks, but it cannot provide reasonable and effective guidance for the design of these parameters. Summary of the Invention

[0004] The purpose of this invention is to provide a method suitable for the simultaneous measurement of fluid viscosity and density. Compared with the empirical correlation formulas used in the past, the method establishes a measurement equation in which each parameter is related to the physical parameters of the tuning fork, such as its structure, size, and material, without affecting the measurement accuracy. This method is of reference value for the design of tuning forks.

[0005] The present invention also aims to provide a device for simultaneously measuring fluid viscosity and density based on the proposed method. This device has the advantages of small size, convenient operation, and wide application scenarios, and can be used for measuring the viscosity and density of high-temperature and high-pressure fluids.

[0006] This invention is achieved through the following technical solution:

[0007] A method suitable for simultaneous measurement of fluid viscosity and density includes the following steps:

[0008] 1) In a vacuum, the inverse piezoelectric effect of piezoelectric materials is used to drive the vibration of a double tuning fork structure. Simultaneously, the piezoelectric effect of the other piezoelectric element in each tuning fork is used to detect the resonant frequency f of the tuning fork. 1,vac f 2,vac ;

[0009] 2) Under constant temperature and pressure conditions, two tuning forks were successively immersed in several fluids with known viscosity η and density ρ, and the tuning forks were driven to vibrate in the fluids. The resonant frequencies f of the two tuning forks were measured respectively. 1,liq f 2,liq ;

[0010] 3) Based on the measurement dataset (η,ρ,f) 1,liq ,f 2,liq And combined with the calibrated constant f 1,vac f 2,vac , with f 1,liq With ρ as the independent variable and ρ as the dependent variable, according to the formula... The calibration coefficients B1 were obtained by fitting; with f 2,liq With ρ as the independent variable and η as the dependent variable, according to the formula... The calibration coefficients A2 and B2 were obtained through fitting.

[0011] 4) When measuring an unknown fluid, immerse the two tuning forks in the fluid and measure their resonant frequency f. 1,liq and f 2,liq Substituting these values ​​into the following equations will yield the viscosity and density of the fluid:

[0012]

[0013] In the formula, the subscripts 1 and 2 correspond to the density-sensitive tuning fork and the viscosity-density-sensitive tuning fork in the double tuning fork, respectively.

[0014] Calibration coefficient Ai B i (i=1,2) are the viscosity-density sensitive characteristic parameters of each tuning fork, which can be obtained according to the formula An estimate is made and used as a reference value for experimental calibration, where ρ m t represents the density of the tuning fork material, and w and t represent the width and thickness of the tuning fork fork arms. Conversely, the material and size parameters can also be set according to the formula during the tuning fork design process.

[0015] The two equations in the measurement equation set have different applicability, so they are distinguished by subscripts 1 and 2: the density measurement equation is applicable to density-sensitive tuning forks, corresponding to parameter subscript 1, that is, the change in fluid density will cause the tuning fork's resonant frequency f. 1,liq Obvious changes; the viscosity measurement equation is applicable to viscosity-sensitive tuning forks, corresponding to parameter subscript 2, meaning that changes in fluid density and viscosity will affect the resonant frequency f of the tuning fork. 2,liq Obvious changes.

[0016] A device suitable for simultaneous measurement of fluid viscosity and density includes: an experimental body, a double tuning fork structure, a signal generation and detection unit, and a temperature and pressure control system. The experimental body is a sealed metal container that can be filled with the fluid to be measured. The double tuning fork structure consists of a density-sensitive tuning fork and a viscosity-density-sensitive tuning fork, both fixed to the same end face of a base. The base is fixed to an opening on one side of the experimental body by threads or a flange, with the tuning fork bodies facing inwards. The signal generation and detection unit is mainly an integrated circuit embedded in the tuning fork base, used to provide sweep frequency excitation signals for the two tuning forks and acquire their respective resonant frequencies in the fluid to be measured. The temperature and pressure control system consists of a metal heating rod, a pump, and temperature and pressure sensors built into both.

[0017] The heating rods of the temperature and pressure control system are arranged circumferentially inside the shell of the experimental body to control the temperature of the fluid inside the container. The pump is located outside the body and is connected to the inside of the experimental body through pipelines to control the pressure of the fluid inside the container.

[0018] The main body of the signal generation and detection unit is connected to the electrodes of the piezoelectric material in each tuning fork body via insulated wires.

[0019] The material of the experimental body is not limited to metal, but can be glass, ceramic, or plastic; it is also not limited to a closed structure, but can be an open container.

[0020] The double tuning fork structure is not limited to working in the experimental body; it can be assembled into various containers by means of threads or flanges or fixed in various open fluid environments by means of clamps.

[0021] The two tuning forks are arranged such that the center of their bottom ends coincides with the center of the base, so they do not interfere with each other. At the same time, the two electrodes on the piezoelectric material of the two tuning forks are connected in parallel with the signal generation and detection unit through wires, and they are independent of each other. Due to differences in materials, size, etc., the resonant frequencies of the two are more than ten times different, so they do not interfere with each other and will not affect the measurement.

[0022] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0023] 1. This invention provides a method for simultaneously measuring fluid viscosity and density. Based on the interaction between a vibrating tuning fork immersed in the fluid and the fluid, a set of viscosity and density measurement equations are established. Compared to the empirical correlation formulas commonly used in existing density measurements, the density measurement equations derived in this invention are simpler in form, have comparable accuracy, and all undetermined parameters are determined by the physical properties of the tuning fork. This provides guidance for the design of relevant parameters in tuning fork viscometers / density meters.

[0024] 2. The present invention also provides a device suitable for simultaneous measurement of fluid viscosity and density, which can be fixed in various fluid environments in various ways, realizing the miniaturization of the device and the diversification of the types of fluids measured. It has the characteristics of small size, convenient operation and wide application scenarios, and can be applied to the measurement of viscosity and density of high temperature and high pressure fluids. Attached Figure Description

[0025] Figure 1 A schematic diagram of the physical model of a vibrating single tuning fork immersed in a fluid;

[0026] Figure 2 This is a schematic diagram illustrating the derivation process of the method for simultaneously measuring fluid viscosity and density according to the present invention.

[0027] Figure 3 The image of function g(f) in an embodiment of the present invention;

[0028] Figure 4 This is a schematic diagram of the overall structure of the fluid viscosity and density simultaneous measurement device of the present invention;

[0029] Figure 5 This is a basic flowchart of the fluid viscosity and density simultaneous measurement device of the present invention;

[0030] Figure 6 This is a comparison of the effects of fitting experimental values ​​using different correlations in the embodiments of the present invention. Detailed Implementation

[0031] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0032] A method suitable for simultaneous measurement of fluid viscosity and density, the principle of which is derived includes the following steps:

[0033] S0: Consider a single tuning fork structure immersed in a fluid, which is made to vibrate using the inverse piezoelectric effect. Based on the analysis of the interaction model between the fluid and the tuning fork, the resonant frequency of the tuning fork in the fluid has the following basic mathematical relationship with the viscosity and density of the fluid:

[0034]

[0035] In the formula, ρ m The density of the tuning fork is expressed in kg·m³. -3 w and t represent the width and thickness of the tuning fork arm, respectively, in meters (m); η and ρ represent the dynamic viscosity and density of the fluid, respectively, in Pa·s and kg·m³. -3 ;f vac f liq These are the resonant frequencies of the tuning fork in vacuum and fluid, respectively, in Hz.

[0036] Define constants Viscosity-density sensitive characteristic parameter of a tuning fork, used to characterize the influence of fluid viscosity and density on the resonant frequency of the tuning fork. It is related to the structure, size and density of the tuning fork, and can be estimated by formula or calibrated by experiment.

[0037] S1: Rearrange equation (1) into a direct expression for viscosity:

[0038]

[0039] As can be seen from equation (2), for an unknown fluid, besides measuring the resonant frequency f of the tuning fork in the fluid... liq Furthermore, the fluid density ρ is needed to calculate the viscosity η. Therefore, we consider adding another tuning fork to the single tuning fork to measure the fluid density separately.

[0040] S2: To derive the expression for density measurement, equation (1) can be rearranged into the following quadratic equation:

[0041]

[0042] Using the quadratic formula, we can obtain: Due to the force exerted by the fluid on the tuning fork, the resonant frequency of the tuning fork in the fluid is always lower than its resonant frequency in the same vibration mode in a vacuum, i.e., f liq <f vac Furthermore, since all physical quantities in the formula are positive, we take the positive solution:

[0043]

[0044] Furthermore, considering the ratio of the two radical terms in the numerator of equation (4), and substituting the expressions for A and B, we get:

[0045]

[0046] The rightmost expression in equation (5) can be viewed as the product of four terms. The first term... It is a constant; the second term The third term η is a constant related to the material and size of the tuning fork; the fourth term is the viscosity of the fluid; For the resonant frequency f of a tuning fork in a vacuum and a fluid vac f liq The expression.

[0047] Let the function g(f) is a function with excitation frequency f as the independent variable, where g(f) = 0 and f = f. vac For the asymptote, in (0, f vac A monotonically increasing positive function within the interval. For a fork arm with a width w and thickness t both of 10... -3 ~10 -2 Tuning forks on the order of m with an aspect ratio l / w ≥ 10, and common liquids (ρ = 500–2500 kg·m). -3 For η = 0 to 2 Pa·s, g(f) ≈ 10 -6 ~10 -2 .

[0048] Substituting the values ​​of each physical quantity within the above range into equation (5), we obtain:

[0049]

[0050] and

[0051]

[0052] Furthermore, based on meeting the measurement accuracy requirements, the two relatively small quantities mentioned above can be successively omitted from the density expression (4) to gradually simplify it:

[0053]

[0054] Right now:

[0055]

[0056] In the formula, B and f vac All are constant coefficients related to the structure, size, and material of the tuning fork, f liq This is to be measured.

[0057] S3: Since the viscosity measurement equation (2) and the density measurement equation (6) have different applicability to tuning forks with different structures, sizes, materials, etc. (i.e., different viscosity-density sensitive characteristics), they are rewritten as a set of equations for two different types of tuning forks:

[0058]

[0059] In the formula, the density measurement equation is applicable to density-sensitive tuning forks, and the subscript 1 corresponds to the fluid density change, which will cause the tuning fork's resonant frequency f. 1,liq Obvious changes; the viscosity measurement equation is applicable to viscosity-sensitive tuning forks, corresponding to parameter subscript 2, meaning that changes in fluid density and viscosity will affect the resonant frequency f of the tuning fork. 2,liq Obvious changes.

[0060] The present invention also provides a device suitable for simultaneous measurement of fluid viscosity and density, comprising: an experimental body, a double tuning fork structure, a signal generation and detection unit, and a temperature and pressure control system.

[0061] The experimental body is a sealed metal container that can be filled with the fluid to be tested. The double tuning fork structure consists of a density-sensitive tuning fork and a viscosity-density-sensitive tuning fork, both fixed to the same end face of the same base. The base is fixed to an opening on one side of the experimental body by threads or flanges, with the tuning fork bodies facing inwards. The main body of the signal generation and detection unit is an integrated circuit embedded in the tuning fork base. It is connected to the electrodes of the piezoelectric material in each tuning fork body through insulated wires, and is used to provide a sweep frequency excitation signal for the tuning forks and to obtain their resonant frequency temperature in the fluid. The temperature and pressure control system includes a metal heating rod and a pump, as well as the temperature and pressure sensors built into both, to control the temperature and pressure of the fluid to be tested.

[0062] Furthermore, the material of the experimental body is not limited to metal, but can be glass, ceramic, plastic, etc.; it is also not limited to a fully enclosed structure, but can be an open container.

[0063] Furthermore, the base of the double tuning fork structure has a circumferential thread structure, which can be installed in other containers by threads or fixed in an open fluid environment by clamps.

[0064] Furthermore, both tuning forks can be made of piezoelectric materials and metal. Their working principle is as follows: piezoelectric materials are symmetrically distributed on the two fork arms of the tuning fork. One end is driven by the inverse piezoelectric effect, causing the tuning fork to vibrate and be affected by fluid forces; the other end outputs an electrical signal containing fluid viscosity information through the piezoelectric effect.

[0065] Furthermore, the two piezoelectric electrodes of the double tuning fork are connected in parallel with the signal generation and detection unit via wires, and are independent of each other. Due to differences in materials, size, etc., their resonant frequencies differ by more than ten times, and they do not interfere with each other and will not affect the measurement.

[0066] Furthermore, the density-sensitive tuning fork refers to a tuning fork that has a "density-sensitive" characteristic, meaning that changes in fluid density will cause a significant change in the resonant frequency of the tuning fork, while changes in viscosity have a very small effect on the resonant frequency and can be ignored; similarly, the viscosity-density-sensitive tuning fork refers to a tuning fork that has a "viscosity-density-sensitive" characteristic, meaning that changes in both fluid density and viscosity will cause a significant change in the resonant frequency of the tuning fork.

[0067] Furthermore, in the temperature and pressure control system, multiple electric heating rods are circumferentially distributed within the shell of the experimental body to control the temperature of the fluid; the pump is externally placed within the experimental body and connected to the interior of the experimental body through pipelines to control the pressure of the fluid inside the container.

[0068] Example 1

[0069] like Figure 1 As shown, the physical model of a vibrating single tuning fork immersed in a fluid is the basis and source of the fluid viscosity and density measurement method provided in this invention. The length, width, and thickness of the tuning fork arm are l, w, and t, respectively, and the density and viscosity of the fluid are ρ and η, respectively. Based on the interaction between the fluid and the tuning fork, the resonant frequency f of the tuning fork in the fluid is... liq The viscosity and density of a fluid have the following mathematical relationship:

[0070]

[0071] In the formula, ρ m f is the density of the tuning fork material. vac Let be the resonant frequency of the tuning fork in a vacuum. Assume constant coefficients.

[0072] Figure 2 This is a schematic diagram illustrating the derivation process of the fluid viscosity and density simultaneous measurement method of the present invention. On one hand, equation (1) can be transformed into a direct expression for viscosity:

[0073]

[0074] As can be seen from equation (2), for an unknown fluid, besides measuring the resonant frequency f of the tuning fork in the fluid... liq In addition, the fluid density ρ is also needed to determine the viscosity η. Therefore, we consider adding a second tuning fork to the single tuning fork to measure the fluid density separately.

[0075] Therefore, on the other hand, in order to obtain a direct expression for the density, equation (1) is transformed into the following quadratic equation:

[0076]

[0077] The solution yields:

[0078]

[0079] Considering the ratio of the two square root terms in the numerator of the expression, and substituting the expressions for A and B, we get:

[0080]

[0081] The right side of equation (5) can be viewed as the product of four terms. These are respectively... constant The tuning fork's material density, fork arm width, and thickness determine the fluid viscosity η; the tuning fork's resonant frequency f in vacuum and fluid, respectively. vac f liq Value:

[0082] Let the function g(f) is a function with frequency f as the variable, where g(f) = 0 and f = f. vac For the asymptote, in (0, f vac A monotonically increasing positive function within an interval, its graph is as follows: Figure 3 As shown in the figure, g(f) is a relatively small value over a large frequency range.

[0083] Taking a typical density tuning fork with the given parameter values ​​in Table 1 as an example, the resonance frequency values ​​of the tuning fork in several common liquids with known viscosity and density were measured under the conditions of pressure of 0.1 MPa and temperature of 298.15 K. The experimental results are shown in Table 2, and the corresponding values ​​of equation (5) were calculated.

[0084] Table 1

[0085]

[0086] Table 2

[0087]

[0088] Among them are:

[0089]

[0090] and

[0091]

[0092] Within the range that meets the measurement accuracy requirements (0.1% to 1%), the two relatively small quantities mentioned above are successively omitted from the density expression (4):

[0093]

[0094] The density measurement formula can then be derived:

[0095]

[0096] Because the viscosity and density measurement formulas are not applicable to tuning forks, the two equations are rewritten as follows:

[0097]

[0098] In the formula, subscript 1 corresponds to a density-sensitive tuning fork, and subscript 2 corresponds to a viscosity-density-sensitive tuning fork. B1, A2, and B2 are calibration coefficients determined by the relevant parameters of the tuning fork, and f l,liq and f 2,liq The viscosity and density can be calculated simply by measuring the resonant frequencies of the two tuning forks in the fluid.

[0099] Example 2

[0100] Figure 4 This is a schematic diagram of a device for simultaneously measuring the viscosity and density of fluids, provided by the present invention. Figure 4 As shown in (a), its overall structure mainly includes an experimental body 1, which is filled with the fluid to be tested. The double tuning fork structure 2 consists of two tuning forks fixed on the same base, which is connected to the experimental body by threads. The tuning fork base is embedded with an electronic control system 3 that integrates signal generation and detection units. The experimental body is equipped with a temperature and pressure control system 4. Figure 4 (b) Further shows a three-dimensional image of the double tuning fork structure 2, the main structure of which is a density-sensitive tuning fork 201 and a viscosity-density-sensitive tuning fork 202 fixed together on the base 203.

[0101] Preferably, the two tuning forks can be arranged in a way that the center of the bottom end of the two tuning forks coincides with the center of the base 203, or the two tuning forks are arranged in parallel, but are not limited to these arrangements.

[0102] Preferably, the double tuning fork structure is not limited to working in the experimental body, but can be assembled into other containers by threads or flanges or fixed in various fluid environments by clamps; it can also be installed as a sensor in industrial sites to realize online monitoring of fluid viscosity and density.

[0103] Figure 5The basic workflow for simultaneously measuring fluid viscosity and density using this device is demonstrated. First, the fluid to be tested is injected into the experimental body, completely submerging the two tuning forks. The temperature and pressure control system is then manipulated to maintain the set values ​​for temperature and pressure. Next, a frequency sweep excitation signal is applied to the tuning forks using a signal generation unit, and the resonant frequency f of each tuning fork in the fluid is measured using a signal detection unit. 1,liq f 2,liq Finally, the density and viscosity of the fluid to be measured are calculated based on the measurement equations, and the average value of multiple measurements is taken as the final measurement result.

[0104] Example 3

[0105] To improve measurement accuracy, the device needs to be calibrated before actual measurement. The calibration process is as follows:

[0106] (1) After evacuating the container to a vacuum state and controlling the temperature to reach the set value and maintain stability, a certain excitation frequency is applied to the two tuning forks to make them resonate in an in-plane anti-bending state. The resonance frequencies of the density-sensitive tuning fork and the viscosity-density-sensitive tuning fork in the vacuum are measured to be f0 and f1, respectively. 1,vac f 2,vac ;

[0107] (2) Several standard fluids with known viscosity η and density ρ were sequentially injected into the experimental body to completely submerge the two tuning forks. The temperature and pressure were controlled to reach the set values ​​and kept stable. The resonant frequencies f of the two tuning forks in the fluid were measured respectively. 1,liq f 2,liq ;

[0108] (3) Based on the measured dataset (η,ρ,f) 1,liq ,f 2,liq According to the expression for density and viscosity measurement and respectively and f 2,liq ρ are the independent variables, and the parameters B1, A2, and B2 are obtained by fitting using the least squares method.

[0109] To verify the fitting effect of the density measurement equation in the measurement equation established in this invention on the experimental values, it is compared with the following two commonly used empirical correlation equations:

[0110] ρ=a2f 2 +a1f+a0 (7a)

[0111]

[0112] In the formula, a i b i All are constant coefficients to be calibrated, i = 0, 1, 2.

[0113] Define root mean square error As an evaluation index for the fitting effect of the measurement equation. Where, ρ exp ρ is the known fluid density value from the experiment. cal The fluid density value is calculated using the fitting formula, where N is the number of experimental points.

[0114] The apparatus was calibrated using several fluids of known viscosity and density at a temperature of 298.15 K and a pressure of 0.1 MPa. The experimental results and fitting effects are as follows: Figure 6 As shown in the figure, the points represent experimental data points, and the lines represent the fitted curves. The temperature was 298.15 K, and the pressure was 0.1 MPa. It can be seen that the root mean square error of the density measurement formula established in this invention is very small compared to the other two formulas, indicating that the fitting effect is comparable. Furthermore, the number of parameters to be calibrated is smaller and they have physical meaning—they can be determined according to the given parameter expressions. This allows for estimations based on parameters such as the structure, size, and materials of the tuning fork, which in turn can guide the design of various parameters of the tuning fork.

[0115] The above description is merely an explanation of the principles and preferred embodiments of the present invention, and does not limit the patent scope of the present invention. Other specific technical solutions of the present invention can be conceived by those skilled in the art without any creative effort, and all fall within the protection scope of the present invention.

Claims

1. A method suitable for simultaneous measurement of fluid viscosity and density, characterized in that, Includes the following steps: 1) In a vacuum, the inverse piezoelectric effect of piezoelectric materials is used to drive the vibration of a double tuning fork structure. At the same time, the piezoelectric effect of the other piezoelectric element in each tuning fork is used to detect the resonant frequency of the tuning fork. f 1,vac , f 2,vac ; 2) Under constant temperature and pressure conditions, the double tuning forks were sequentially immersed in several known viscosities. η ,density ρ A fluid was used to drive tuning forks to vibrate within the fluid, and the resonant frequencies of the two tuning forks were measured. f 1,liq , f 2,liq ; 3) Based on the measurement dataset And combined with the calibrated constants f 1,vac , f 2,vac ,by f 1,liq As the independent variable, with ρ As the dependent variable, according to the formula The calibration coefficients are obtained by fitting. B 1; with and ρ As the independent variable, with η As the dependent variable, according to the formula The calibration coefficients were obtained by fitting. A 2. B 2, 4) When measuring an unknown fluid, immerse the two tuning forks in the fluid and measure their resonant frequencies. f 1,liq and f 2,liq Substituting these values ​​into the following equations will yield the viscosity and density of the fluid: (1) In the formula, the subscripts 1 and 2 correspond to the density-sensitive tuning fork and the viscosity-density-sensitive tuning fork in the double tuning fork, respectively; Calibration coefficient A i , B i ( i =1,2) are the viscosity-sensitive characteristic parameters of each tuning fork, according to the formula , Estimate the values ​​and use them as reference values ​​for experimental calibration. ρ m The density of the tuning fork material, w , t This refers to the width and thickness of the tuning fork fork arm; conversely, when designing the tuning fork, the material and size parameters are set accordingly according to the formula based on the requirements.

2. The method for simultaneously measuring fluid viscosity and density according to claim 1, characterized in that, The two equations in the measurement equation set have different applicability, so they are distinguished by subscripts 1 and 2: the density measurement equation is applicable to density-sensitive tuning forks, corresponding to parameter subscript 1, which indicates that changes in fluid density will cause the tuning fork to resonate at a certain frequency. f 1,liq Obvious changes; the viscosity measurement equation is applicable to viscosity-sensitive tuning forks, corresponding to parameter subscript 2, meaning that changes in fluid density and viscosity will affect the resonant frequency of the tuning fork. f 2,liq Obvious changes.

3. An apparatus based on the method for simultaneously measuring fluid viscosity and density as described in claim 1, characterized in that, include: The experiment consists of a main body, a double tuning fork structure, a signal generation and detection unit, and a temperature and pressure control system. The main body is a sealed metal container that can be filled with the fluid to be tested. The double tuning fork structure comprises a density-sensitive tuning fork and a viscosity-density-sensitive tuning fork, both fixed to the same end face of a base. The base is fixed to an opening on one side of the main body via threads or a flange, with the tuning fork bodies facing inwards. The signal generation and detection unit is an integrated circuit embedded in the tuning fork base, used to provide sweep frequency excitation signals to the two tuning forks and acquire their respective resonant frequencies in the fluid to be tested. The temperature and pressure control system consists of a metal heating rod, a pump, and temperature and pressure sensors built into both. The two tuning forks are arranged such that the center of their bottom ends coincides with the center of the base, ensuring they do not interfere with each other. Furthermore, the two electrodes on the piezoelectric material of the double tuning forks are connected in parallel to the signal generation and detection unit via wires, operating independently. Due to differences in materials and dimensions, their resonant frequencies differ by more than ten times, ensuring they do not interfere with each other and will not affect the measurement.

4. The device for simultaneously measuring fluid viscosity and density according to claim 3, characterized in that, The heating rods of the temperature and pressure control system are arranged circumferentially inside the shell of the experimental body to control the temperature of the fluid inside the container. The pump is located outside the body and is connected to the inside of the experimental body through pipelines to control the pressure of the fluid inside the container.

5. The device for simultaneously measuring fluid viscosity and density according to claim 3, characterized in that, The main body of the signal generation and detection unit is connected to the electrodes of the piezoelectric material in each tuning fork body via insulated wires.

6. The device for simultaneously measuring fluid viscosity and density according to claim 3, characterized in that, The experimental body can be made of any one of the following materials: metal, glass, ceramic, or plastic.

7. The device for simultaneously measuring fluid viscosity and density according to claim 3, characterized in that, The double tuning fork structure can be assembled into various containers by means of threads or flanges, or fixed in various open fluid environments by means of clamps.

Images