An image analysis method for yield stress viscous fluid rheological parameters
By using image analysis and modified dyes to label helical curves, the actual shear radius of the fluid was measured and the influence of slug layers was corrected, thus solving the problem of rheological parameter errors caused by slug layers and achieving higher precision in rheological parameter measurement.
Patent Information
- Application Number
- CN202310568029.9
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- Filing Date
- 2023-05-19
- Publication Date
- 2025-10-31
- Estimated Expiration
- 2043-05-19
AI Technical Summary
Existing technologies for measuring fluid rheological parameters suffer from significant errors due to the presence of slug layers, making it difficult to accurately calculate the actual shear radius of the fluid and affecting the measurement accuracy of rheological parameters.
Image analysis was used to mark straight lines on the surface of the fluid sample and form a spiral curve. Combined with a modified dye, the actual shear radius was measured using image analysis. The influence of the plug layer on the shear flow was considered, the shear deformation rate was corrected, and the Bingham or Herschel-Bulkley model was used for parameter fitting.
It improves the fitting accuracy and reliability of rheological parameters, reduces calculation errors, is easy to operate, and is applicable to a variety of rheological models, especially the Bingham and Herschel-Bulkley models.
Smart Images
Figure CN116735426B_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of concrete testing technology, specifically relating to an image analysis method for yield stress viscous fluid rheological parameters. Background Technology
[0002] Fluid materials involve multiple fields such as mechanics, physics, biology, materials science, and chemistry, and their development will directly impact application areas such as medicine, petroleum, bioengineering, civil engineering, and chemical engineering. Rheological properties are one of the most important properties of fluid materials, and accurately measuring the rheological parameters and characterizing the rheological properties of fluid materials is of paramount importance for their production, processing, and application.
[0003] Coaxial rotating rheometers are commonly used to measure the rheological properties of fluids. Typically, it is assumed that the fluid is subjected to complete shearing. The shear deformation rate of the fluid can be calculated based on the rotor's rotational speed. When measuring the rheological properties of fluid materials using a coaxial dual-cylinder rheometer, the shear stress τ of the fluid at a certain distance from the rotor axis can be calculated using the following formula. Based on the relationship between shear stress and shear deformation rate, rheological parameters such as yield stress and viscosity can be fitted.
[0004]
[0005] Because fluids possess inherent yield stress, they will not undergo shear deformation when the shear stress within the fluid is less than its yield stress. From the above equation, it can be seen that within a fluid, the shear stress experienced by the fluid material is related to r. 2 The shear stress is inversely proportional to the rotor; the closer to the rotor, the greater the shear stress within the fluid; the farther away from the rotor, the smaller the shear stress. When the shear stress at locations far from the rotor is lower than the yield stress of the fluid material itself, a stagnant region exists at these locations, known as a throttle layer. Figure 2 As shown.
[0006] The presence of a slug layer can introduce errors into the calculation of rheological parameters of fluid materials, and the larger the slug layer, the greater the error. The slug layer cannot be ignored in the calculation process; therefore, accurately measuring the actual shear radius of the fluid sample is crucial for calculating its rheological parameters. Summary of the Invention
[0007] The purpose of this invention is to overcome the shortcomings of the prior art and provide an image analysis method for the rheological parameters of viscous fluids with yield stress.
[0008] To achieve the above objectives, the present invention is implemented using the following technical solution:
[0009] This invention provides an image analysis method for the rheological parameters of viscous fluids with yield stress, comprising the following steps:
[0010] Take a certain amount of fluid sample, stir it thoroughly, and then pour it into a sample holding cylinder;
[0011] Pre-shearing of fluid samples was performed using a coaxial rotational rheometer.
[0012] After pre-shearing, let it stand for a period of time, and then use a modified dye to mark a straight marking line along the radial direction on the surface of the fluid sample;
[0013] Set the rotor speed of the rheometer to shear the fluid sample so that the straight marking lines on the surface of the fluid sample form a planar helical curve under shearing action, and use a video recording instrument to capture images of the surface of the fluid sample from directly above the sample cylinder during the shearing stabilization stage.
[0014] Image analysis and measurement are performed on the captured images of the fluid sample surface to obtain the average radius of the helical curve, which is then used as the actual shear radius of the fluid sample.
[0015] Repeat the above operation to obtain the actual shear radius of the fluid sample at different rotor speeds;
[0016] The actual shear deformation rate of the fluid sample at each rotor speed is calculated using each rotor speed and the corresponding actual shear radius.
[0017] The rheological parameters of the viscous fluid are obtained by substituting the shear stress and actual shear deformation rate given by the rheometer into the rheological model and fitting the parameters.
[0018] Furthermore, the modified dye has the same rheological properties as the test fluid sample to satisfy the coordinated movement of the dye and the test fluid sample.
[0019] Furthermore, the analytical measurement steps for obtaining the average radius of the helical curve are as follows:
[0020] On the surface image of the fluid sample, two mutually perpendicular directions are selected from the center point of the rotor, and the angle between the selected directions and the straight marking line is no greater than 60°.
[0021] Measure the outermost diameter of the spiral curve formed by the dye and the inner diameter of the sample-holding cylinder along the two selected directions respectively. Calculate the actual shear radius based on the ratio of the outermost diameter of the spiral curve to the inner diameter of the sample-holding cylinder. The calculation formula is as follows:
[0022]
[0023] In the formula, R s To determine the actual shear radius through image analysis; d s1 and d s2 The diameter of the helical curve formed by the dye in the image in two mutually perpendicular directions; d c1and d c2 R is the diameter of the sample-holding cylinder in the image in two mutually perpendicular directions; R is the inner radius of the sample-holding cylinder.
[0024] Furthermore, it also includes the following steps:
[0025] Considering the influence of the slug layer on shear flow, the shear deformation rate of the fluid on the rotor surface is calculated using the shear radius corresponding to each rotor speed. The calculation formula is as follows:
[0026]
[0027] In the formula, Represented as the corrected shear deformation rate, R1 is the rotor radius, i represents the i-th data point, R s [i] is the shear radius.
[0028] Furthermore, the rheological model adopts the Bingham model or the Herschel-Bulkley model.
[0029] Compared with the prior art, the beneficial effects achieved by the present invention are as follows:
[0030] The image analysis method for yield stress viscous fluid rheological parameters provided by this invention, based on the use of a coaxial rotating rheometer to measure fluid rheological properties, can measure rheological parameters such as the actual shear radius range and fluid shear deformation rate of viscous fluids. It also fully considers the influence of the plug layer caused by the fluid yield stress on the fluid shear flow, improving the fitting accuracy and reliability of rheological parameters. Moreover, the method has low requirements for equipment and materials, is easy to operate, and has strong versatility, which is of great significance for accurately characterizing and evaluating the rheological properties of fluids. Attached Figure Description
[0031] Figure 1 A flowchart of an image analysis method for yield stress viscous fluid rheological parameters provided in an embodiment of the present invention;
[0032] Figure 2 This is a schematic diagram of fluid shearing in a coaxial rotating rheometer.
[0033] Figure 3 This is an example of setting the rotor speed during the rheological testing process in a specific embodiment;
[0034] Figure 4 This is a schematic diagram of the marking line before and after cutting, provided in an embodiment of the present invention;
[0035] Figure 5 This is a schematic diagram of the shear radius image analysis method provided in an embodiment of the present invention;
[0036] Figure 6This is a comparison chart of fluid shear radii calculated based on ideal assumptions and the present invention in a specific embodiment;
[0037] Figure 7 This is a comparison chart of rheological curves calculated based on ideal assumptions and the present invention in a specific embodiment. Detailed Implementation
[0038] The present invention will be further described below with reference to the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present invention, and should not be used to limit the scope of protection of the present invention.
[0039] This invention provides an image analysis method for yield stress viscous fluid rheological parameters, such as... Figure 1 As shown, the operation steps are detailed below:
[0040] Step 1: After thoroughly stirring the fluid sample, pour it into the measuring cylinder and make the surface of the fluid sample flush with the sampling mark line on the measuring cylinder.
[0041] Step 2: Set the rotor speed of the coaxial rotating rheometer to pre-shear the fluid sample to eliminate experimental errors caused by initial material inhomogeneity;
[0042] Step 3: After the pre-shearing is completed, the fluid sample is left to stand for 25 seconds. During this time, a straight marking line is drawn on the surface of the fluid sample along the radial direction using a modified dye.
[0043] Step 4: Set up the video recording equipment for capturing images and start recording;
[0044] Step 5: Set the rotation speed to shear the fluid sample so that the straight marking lines on the surface of the fluid sample become a spiral curve under the shearing action;
[0045] Step 6: During the shear stabilization phase, take an image of the fluid sample surface from directly above the measuring cylinder and looking downwards.
[0046] Step 7: Measure the average radius of the helical curve based on image analysis, and use it as the actual shear radius of the fluid sample;
[0047] Step 8: Repeat steps 1-7 to obtain the actual shear radius of the rheological material at different rotor speeds. In this embodiment, the rotor should be set with no less than 5 different speeds.
[0048] Step 9: Calculate the actual shear deformation rate of the sample using the actual shear radius at each rotational speed. Obtain the rotor speed ω[i] and the shear stress τ[i] acting on the rotor side using a rheometer. Calculate the actual shear deformation rate of the fluid sample at each rotor speed using each rotor speed and the corresponding actual shear radius; substitute the shear stress and actual shear deformation rate given by the rheometer into the rheological model for parameter fitting to obtain the rheological parameters of the viscous fluid.
[0049] In this embodiment, the modified Bingham model, which is commonly used in rheological models, is selected for rheological parameter fitting. The rheological parameters of the fluid are fitted according to the rheological model.
[0050] The working principle of the image analysis method for yield stress viscous fluid rheological parameters of the present invention will be described below in conjunction with the usage of specific embodiments.
[0051] Freshly mixed cement paste was prepared as a viscous fluid to be tested, exhibiting yield stress.
[0052] Pour the prepared fresh cement paste into the sample measuring cylinder of the rheometer. Specifically, the sample measuring cylinder is 10cm in diameter, and a cross-shaped paddle rotor is selected. The rotor diameter is 3cm, and the effective shearing cylinder height is 6cm.
[0053] The rheometer performs rheological performance tests according to a predetermined rotational procedure. The preset rotational procedure uses a speed control mode, such as... Figure 3 The process is divided into three stages: pre-shearing stage, settling stage, and shearing stage.
[0054] Specifically, during the pre-shearing stage, the rotor accelerates from a standstill to 100 rpm in 10 seconds, maintains this speed for 10 seconds, and then decelerates from 100 rpm to a stop in another 10 seconds. The cement paste is allowed to stand for 25 seconds before entering the shearing stage. During the shearing stage, six speeds are set: 40 rpm, 30 rpm, 20 rpm, 15 rpm, 10 rpm, and 5 rpm, with each stage lasting 10 seconds.
[0055] During the settling stage, a modified stain is used to draw a straight line along the radial direction on the surface of the cement paste. During the shearing stage, the stain rotates with the cement paste, forming a spiral curve. The changes in the marked line before and after shearing are as follows: Figure 4 As shown, video recording equipment was used to record and capture images of the cement paste surface during the cutting stage.
[0056] In the image, select two mutually perpendicular directions passing through the rotor's center point, with the angle between each direction and the straight marking line not exceeding 60°. Measure the diameter of the helical curve formed by the dye and the inner diameter of the sample-holding cylinder along these two directions, respectively. Figure 5 As shown.
[0057] The actual shear radius is calculated by the ratio of the diameter of the helical curve formed by the dye in the image to the inner diameter of the measuring cylinder containing the sample. The formula is as follows:
[0058]
[0059] Where: R s To determine the actual shear radius through image analysis; d s1 and d s2 The diameter of the helical curve formed by the dye in the image in two mutually perpendicular directions; d c1 and d c2 R is the diameter of the sample-holding cylinder in the image in the two mutually perpendicular directions mentioned above; R is the inner radius of the sample-holding cylinder.
[0060] The actual shear radius data obtained by image analysis are shown in Table 1 below:
[0061] Table 1
[0062] i ω[i] / rpm <![CDATA[ω[i] / rad·s -1 ]]> R / mm <![CDATA[R s [i] / mm]]> 1 5 0.524 50 23.3 2 10 1.047 50 32.3 3 15 1.571 50 35.5 4 20 2.094 50 40.3 5 30 3.142 50 48.2 6 40 4.189 50 50.0
[0063] Based on the shear radius R calculated above s Meanwhile, considering the influence of the slug layer on the shear flow, the shear deformation rate of the rotor surface fluid corresponding to each rotor speed is recalculated according to the following formula, which is expressed as follows.
[0064]
[0065] The corrected data on the shear deformation rate of the rotor surface fluid corresponding to each rotor speed are shown in Table 2.
[0066] Table 2
[0067]
[0068] In this embodiment, assuming the freshly mixed cement paste is completely sheared, the ideal shear radius is 50 mm. The technical solution in this embodiment uses an image analysis method for yield stress viscous fluid rheological parameters to calculate a comparison between the actual shear radius and the ideal shear radius, such as... Figure 6 As shown in the figure, the lower the shear rate, the greater the slug layer thickness, and the smaller the true shear radius of the sample. The results calculated by this method are consistent with the actual measurement patterns. Using the method of this invention, the slug phenomenon during the testing of the rheological properties of the sample can be reflected, and the true shear radius of the sample after the influence of slug flow can be obtained.
[0069] This embodiment calculates the actual shear deformation rate of freshly mixed cement paste at various rotational speeds based on the corrected shear radius, obtaining a rheological curve that considers the influence of the plug layer. A comparison is made between the rheological curve obtained using the optimization method of this invention and the rheological curve based on ideal assumptions. Figure 7 As shown.
[0070] The two rheological curves show a significant difference at lower shear strain rates. As the shear rate decreases, the slug layer thickens, the shear radius of the sample decreases, and the influence of the slug on the calculated shear deformation rate increases. Ignoring the influence of the slug will result in an underestimation of the calculated shear deformation rate at the same rotational speed, causing the rheological curve to shift towards lower shear deformation.
[0071] Based on the modified Bingham model, the rheological curves of cement paste were fitted using existing ideal conditions and the calculation method proposed in this invention, respectively. The fitting parameters are shown in Table 3 below.
[0072] Table 3
[0073]
[0074] Since ideal assumptions are difficult to guarantee in experiments, there are errors between the rheological parameters obtained based on these assumptions and the actual rheological parameters. The error between the rheological parameters fitted based on ideal assumptions and the actual rheological parameters fitted by this invention reaches a maximum of 420.8%. Using the calculation method proposed in this invention can fully consider the influence of slug flow on rheological measurement results, significantly improving the accuracy of rheological parameters.
[0075] This case study uses the modified Bingham model, which is suitable for freshly mixed cement paste. The method of this invention is also applicable to other rheological models, such as the Bingham model and the Herschel-Bulkley model, and can significantly reduce the calculation error of rheological parameters.
[0076] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the technical principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.
Claims
1. A method for image analysis of rheological parameters of viscous fluids at yield stress, characterized in that, Includes the following steps: Take a certain amount of fluid sample, stir it thoroughly, and then pour it into a sample holding cylinder; Pre-shearing of fluid samples was performed using a coaxial rotational rheometer. After pre-shearing, let it stand for a period of time, and then use a modified dye to mark a straight marking line along the radial direction on the surface of the fluid sample; Set the rotor speed of the rheometer to shear the fluid sample so that the straight marking lines on the surface of the fluid sample form a planar helical curve under shearing action, and use a video recording instrument to capture images of the surface of the fluid sample from directly above the sample cylinder during the shearing stabilization stage. Image analysis and measurement are performed on the captured images of the fluid sample surface to obtain the average radius of the helical curve, which is then used as the actual shear radius of the fluid sample. Repeat the above operation to obtain the actual shear radius of the fluid sample at different rotor speeds; The actual shear deformation rate of the fluid sample at each rotor speed is calculated using each rotor speed and the corresponding actual shear radius. The rheological parameters of the viscous fluid are obtained by substituting the shear stress and actual shear deformation rate given by the rheometer into the rheological model and fitting the parameters.
2. The image analysis method for yield stress viscous fluid rheological parameters according to claim 1, characterized in that, The modified dye has the same rheological properties as the fluid sample to be tested, so as to satisfy the coordinated movement of the dye and the fluid sample to be tested.
3. The image analysis method for yield stress viscous fluid rheological parameters according to claim 2, characterized in that, The analytical measurement steps for obtaining the average radius of the helical curve are as follows: On the surface image of the fluid sample, two mutually perpendicular directions are selected from the center point of the rotor, and the angle between the selected directions and the straight marking line is no greater than 60°. Measure the outermost diameter of the spiral curve formed by the dye and the inner diameter of the sample-holding cylinder along the two selected directions respectively. Calculate the actual shear radius based on the ratio of the outermost diameter of the spiral curve to the inner diameter of the sample-holding cylinder. The calculation formula is as follows: In the formula, R s To determine the actual shear radius through image analysis; d s1 and d s2 The diameter of the helical curve formed by the dye in the image in two mutually perpendicular directions; d c1 and d c2 R is the diameter of the sample-holding cylinder in the image in two mutually perpendicular directions; R is the inner radius of the sample-holding cylinder.
4. The image analysis method for yield stress viscous fluid rheological parameters according to claim 3, characterized in that, It also includes the following steps: Considering the influence of the slug layer on shear flow, the shear deformation rate of the fluid on the rotor surface is calculated using the shear radius corresponding to each rotor speed. The calculation formula is as follows: In the formula, Represented as the corrected shear deformation rate, R1 is the rotor radius, i represents the i-th data point, R s [i] is the shear radius.
5. The image analysis method for yield stress viscous fluid rheological parameters according to claim 1, characterized in that, The rheological model used is either the Bingham model or the Herschel-Bulkley model.