Real-time measuring method and device for rheological characteristics of non-Newtonian fluid of bulking machine

Abstract

The invention relates to a real-time measurement method and device for rheological characteristics of a non-Newtonian fluid of a bulking machine. The method comprises the following steps that (1) on the basis of the Newton first law and a non-Newtonian fluid power law model, the quantitative relation between a rheological coefficient K and the real-time pressure difference and the quantitative relation between the rheological coefficient K and the real-time flow are established, a model for calculating the rheological coefficient of the non-Newtonian fluid in a flow channel is obtained by combining geometric parameters of the flow channel, and the flow channel comprises a round pipe flow channel and a convergence pipe flow channel; and (2) obtaining a complete rheological characteristic curve according to temperature parameters measured in real time in the flow channel and a non-Newtonian fluid rheological coefficient calculation model. According to the embodiment of the invention, a non-Newtonian fluid rheological coefficient calculation model in the flow channel is innovated, the dynamic change of the material rheological property is captured in real time, the test condition is consistent with the actual production environment, the data timeliness is improved, and the accuracy and reliability of the measurement result are remarkably improved by virtue of a dual verification mechanism of the circular tube flow channel and the convergence tube flow channel; and a solid data support is provided for the production process.

Description

Technical Field

[0001] This application relates to the technical field of fluid mechanics measurement, and particularly to a method and device for real-time measurement of the rheological properties of non-Newtonian fluids in an extruder. Background Art

[0002] As a core mechanical equipment in the industrial processing field, screw extrusion equipment has been widely used in the manufacturing processes of polymer, food, feed, and lithium batteries, etc., due to its significant advantages such as high continuous production efficiency, wide range of applicable raw materials, and simple operation and maintenance. Such equipment plays a key role in industrial production, responsible for realizing functions such as material transportation, mixing, plasticization, and forming, and is an indispensable core equipment in modern manufacturing.

[0003] During the extrusion process, the rheological behavior of the material plays a decisive role in the quality of the final product. Taking food processing as an example, the rheological properties of the material are directly related to key indicators such as the puffing degree, tissue structure, and taste of the product; while in the field of polymer material processing, the rheological properties are closely related to the mechanical properties and surface quality of the product. Therefore, accurately obtaining the rheological parameters of the fluid is of crucial guiding significance for optimizing process parameters, improving product quality, and increasing production efficiency, and is the core basis for achieving precise control of product quality.

[0004] Currently, it mainly relies on offline measurement methods, such as offline rotational rheometers or capillary rheometers. There are problems such as being unable to capture the dynamic changes of rheological properties in real time, sampling interfering with production, large differences between test conditions and actual situations, and slow response affecting real-time quality control, which restricts the development of intelligent and automated production processes. Summary of the Invention

[0005] Based on this, in view of the problem that the offline measurement method cannot capture the dynamic changes of the rheological properties of the material in real time, it is necessary to provide a method and device for real-time measurement of the rheological properties of non-Newtonian fluids in an extruder.

[0006] An embodiment of the first aspect of this application proposes a method for real-time measurement of the rheological properties of non-Newtonian fluids in an extruder, and the method includes the following steps:

[0007] (1) Based on Newton's first law and the power-law model of non-Newtonian fluids, establish a quantitative relationship between the rheological coefficient K, the real-time pressure difference, and the real-time flow rate, and combine the geometric parameters of the flow channel to obtain a calculation model for the rheological coefficient of non-Newtonian fluids in the flow channel. Specifically:

[0008] In a circular pipe flow channel, the expression of the rheological coefficient is

[0009]

[0010] Among them, K-rheological coefficient, ΔP-pressure difference, l-collection end length, Q-volume flow rate, n-rheological index, R-tube radius;

[0011] In the converging pipe flow channel, the rheological coefficient expression is

[0012]

[0013] Among them, K-rheological coefficient, ΔP-pressure difference, L-collection section length, Q-volume flow rate, n-rheological index, r0-convergent pipe flow channel inlet radius, r1-convergent pipe flow channel outlet radius;

[0014] (2) Obtaining a complete rheological characteristic curve based on the temperature parameters measured in real time in the flow channel and the rheological coefficient calculation model of the non-Newtonian fluid.

[0015] In one embodiment, in the step (1), in the circular tube flow channel, when the fluid moves at a low and uniform speed, the normal stress and the tangential stress are balanced, and the normal force equation and the tangential force equation are combined to calculate the shear stress equation;

[0016] The power law equation and the shear stress equation are combined to solve the velocity distribution of the non-Newtonian fluid and obtain the velocity distribution formula; combined with the volume flow formula, the rheological coefficient K is inferred.

[0017] In one embodiment, the velocity distribution formula is:

[0018]

[0019] Among them, u (r) is the velocity of the fluid at the radius r, n is the rheological index, ΔP is the pressure difference, K is the rheological coefficient, l is the length of the collection section, and R is the radius of the circular tube.

[0020] In one embodiment, the volume flow formula is

[0021] .

[0022] In one embodiment, in the converging pipe flow channel, the rheological coefficient model is integrated into the geometric parameters of the converging pipe flow channel 140;

[0023] When the fluid in the convergent pipe flow channel moves at a low and uniform speed, the normal stress and the tangential stress are balanced. The normal force equation and the tangential force equation are combined to calculate the shear stress equation.

[0024] The power law equation and the shear stress equation are combined to solve the pressure difference at the inlet and outlet, and the rheological coefficient K is inferred by combining the volume flow formula.

[0025] In one embodiment, when establishing the rheological coefficient expression in the convergent pipe flow channel, the geometric parameter expression of the convergent pipe flow channel is:

[0026]

[0027] Among them, θ is the convergence angle of the θ-converging pipe channel, r0 is the inlet radius of the converging pipe channel, r1 is the outlet radius of the converging pipe channel, and L is the length of the collection section.

[0028] In one embodiment, the expression of the pressure difference ΔP is:

[0029]

[0030]

[0031] Among them, ΔP is the pressure difference, K is the rheological coefficient, n is the rheological index, and Q is the volume flow rate.

[0032] In one embodiment, by changing the pressure difference and volume flow rate in the working condition channel, the same value of the rheological coefficient can be obtained, and the rheological index can be solved simultaneously. The expression of the rheological index n is

[0033]

[0034] Among them, P1 is the pressure difference in the first working condition, P2 is the pressure difference in the second working condition, Q1 is the volume flow rate in the first working condition, Q2 is the volume flow rate in the second working condition, M1 is the mass flow rate in the first working condition, and M2 is the mass flow rate in the second working condition.

[0035] In one embodiment, a temperature sensor is arranged in the channel to ensure that the temperature remains unchanged when the pressure difference and volume flow rate are finely adjusted under different working conditions.

[0036] An embodiment of the second aspect of the present application provides a real-time measurement device for the rheological properties of non-Newtonian fluids in an extruder, including:

[0037] A data acquisition module, which is used to acquire the pressure difference, flow rate, and temperature of the fluid in the channel in real time;

[0038] A model establishment module, which is communicatively connected to the data acquisition module. The model establishment module establishes a quantitative relationship between the rheological coefficient K and the pressure difference and flow rate based on Newton's first law and the power-law model of non-Newtonian fluids, and combines the geometric parameters of the channel to obtain a calculation model for the rheological coefficient of non-Newtonian fluids in the channel, specifically;

[0039] In a circular pipe channel, the expression of the rheological coefficient is

[0040]

[0041] Among them, K is the rheological coefficient, ΔP is the pressure difference, l is the length of the collection end, Q is the volume flow rate, n is the rheological index, and R is the radius of the circular pipe;

[0042] In the converging pipe flow channel, the expression of the rheological coefficient is

[0043]

[0044] where K is the rheological coefficient, ΔP is the pressure difference, L is the length of the acquisition section, Q is the volume flow rate, n is the rheological index, r0 is the inlet radius of the converging pipe flow channel, and r1 is the outlet radius of the converging pipe flow channel;

[0045] The rheological characteristic curve establishment module obtains a complete rheological characteristic curve according to the temperature parameters measured in real time in the flow channel and the corresponding non-Newtonian fluid rheological coefficient calculation model.

[0046] According to the method and device for real-time measurement of the rheological characteristics of non-Newtonian fluids in an extruder according to an embodiment of the present application, the calculation model of the rheological coefficient of non-Newtonian fluids in the flow channel is innovated, and real-time measurement can be carried out under production disclosure, dynamically capturing the dynamic changes of the rheological characteristics of the material. The test conditions are completely consistent with the actual production environment, greatly improving the timeliness of the data. With the dual verification mechanism of the circular pipe flow channel and the converging pipe flow channel, the accuracy and reliability of the measurement results are significantly improved, providing solid data support for the production process. Brief Description of the Drawings

[0047] Figure 1 It is a schematic structural diagram showing the circular pipe flow channel in an extruder according to an embodiment of the present application.

[0048] Figure 2 It is a schematic structural diagram showing the converging pipe flow channel in an extruder according to an embodiment of the present application.

[0049] Figure 3 It is a schematic structural diagram of the circular pipe flow channel in the method for real-time measurement of the rheological characteristics of non-Newtonian fluids in an extruder according to an embodiment of the present application.

[0050] Figure 4 It is a schematic structural diagram of the converging pipe flow channel in the method for real-time measurement of the rheological characteristics of non-Newtonian fluids in an extruder according to an embodiment of the present application.

[0051] Reference Signs:

[0052] 100, extruder; 110, screw; 120, feed inlet; 130, circular pipe flow channel; 140, converging pipe flow channel;

[0053] 200, pressure sensor;

[0054] 300, temperature sensor. Detailed Description of the Embodiment

[0055] To make the above objects, features, and advantages of the present application more apparent and understandable, the following provides a detailed description of the specific embodiments of the present application with reference to the accompanying drawings. Many specific details are set forth in the following description to facilitate a thorough understanding of the present application. However, the present application can be implemented in many other ways different from those described herein, and those skilled in the art can make similar improvements without departing from the spirit of the present application. Therefore, the present application is not limited by the specific embodiments disclosed below.

[0056] In the description of the present application, it should be understood that if terms such as "center", "longitudinal", "transverse", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", "axial", "radial", "circumferential", etc. appear, the orientation or positional relationship indicated by these terms is based on the orientation or positional relationship shown in the drawings. These are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and thus should not be construed as a limitation of the present application.

[0057] In addition, if terms such as "first" and "second" appear, these terms are only for descriptive purposes and should not be construed as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. Thus, features defined with "first" and "second" may explicitly or implicitly include at least one such feature. In the description of the present application, if the term "plurality" appears, the meaning of "plurality" is at least two, such as two, three, etc., unless otherwise specifically and clearly defined.

[0058] In the present application, unless otherwise clearly specified and limited, if terms such as "install", "connect", "join", "fix", etc. appear, these terms should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or integrated; it can be a mechanical connection or an electrical connection; it can be directly connected or indirectly connected through an intermediate medium, and it can be the communication inside two elements or the interaction relationship between two elements, unless otherwise clearly limited. For those of ordinary skill in the art, the specific meanings of the above terms in the present application can be understood according to specific circumstances.

[0059] In this application, unless otherwise clearly specified and defined, when a first feature is described as being "on" or "under" a second feature or the like, it may mean that the first and second features are in direct contact, or the first and second features are in indirect contact through an intermediate medium. Moreover, the first feature being "above", "over" and "on top of" the second feature may mean that the first feature is directly above or obliquely above the second feature, or simply indicates that the first feature has a higher horizontal height than the second feature. The first feature being "under", "beneath" and "underneath" the second feature may be that the first feature is directly below or obliquely below the second feature, or simply indicates that the first feature has a lower horizontal height than the second feature.

[0060] It should be noted that if an element is referred to as being "fixed to" or "disposed on" another element, it can be directly on the other element or there may also be an intermediate element. If an element is considered to be "connected to" another element, it can be directly connected to the other element or there may be an intermediate element at the same time. If present, the terms "vertical", "horizontal", "upper", "lower", "left", "right" and similar expressions used in this application are only for the purpose of illustration and do not represent the only implementation.

[0061] Currently, in the field of screw extrusion equipment, measuring the rheological properties of materials mainly relies on traditional off-line measurement methods. The inventor noticed that there are many drawbacks to this method:

[0062] Unable to capture dynamic changes in real time: During actual production, the rheological properties of materials change continuously with fluctuations in process parameters such as temperature, pressure, and shear rate. Traditional off-line measurement requires sampling from the production line and sending it to the laboratory for testing, resulting in an obvious time delay. During the period from sampling to obtaining the results, the rheological properties of the materials on the production line may have changed significantly, making the measurement results unable to accurately reflect the actual rheological properties of the materials under the current production conditions. This lag increases the difficulty of timely adjustment of process parameters and affects the quality stability of products.

[0063] Interfering with the production process: Off-line measurement requires regular sampling from the production line, which will interfere with normal production. The sampling operation may cause pressure fluctuations in the production line, affecting the continuous and stable transportation of materials; frequent sampling will cause material loss and reduce production efficiency; the sampling process may also introduce external contamination, threatening product quality. These factors together have an adverse impact on the continuity and stability of production.

[0064] Large differences between test conditions and actual ones: Off-line measurement is usually carried out in the laboratory, and there are significant differences between the test conditions and actual production. The rheological properties of samples may change due to temperature fluctuations during transportation and testing; the shear conditions applied by laboratory testing equipment are different from those in actual production; and it is difficult to simulate the pressure environment and complex flow state in actual production during off-line measurement. These differences cause deviations between the measurement results and the actual rheological properties of materials, reducing the reference value of the measurement results.

[0065] Difficult to achieve real-time quality control: Offline measurement involves multiple steps such as sampling, transportation, and testing. It takes a long time from problem discovery to obtaining test results, making it difficult to achieve real-time control of product quality. If the test results show abnormal rheological properties of the material, a large number of unqualified products may have been produced on the production line. Moreover, the long response time increases the complexity of process parameter adjustment, prone to situations of untimely adjustment or over-adjustment, affecting the stability of product quality and restricting the improvement of the intelligent and automated level of the production process.

[0066] Based on the above problems, in order to alleviate issues such as the inability to capture the dynamic changes of rheological properties in real time, sampling interfering with production, large differences between test conditions and actual conditions, and slow response affecting real-time quality control, the inventors have found through research that for the geometric characteristics of different flow channels in the extruder, corresponding online calculation methods for the rheological coefficients of non-Newtonian fluids are proposed respectively, and a real-time measurement method and device for the rheological properties of non-Newtonian fluids in an extruder are proposed.

[0067] Refer to Figure 1 and Figure 2 , the extruder 100 mainly consists of a screw 110, a feed inlet 120, and a flow channel. Its flow channel includes a circular pipe flow channel 130 and a converging pipe flow channel 140. The feed inlet 120 is used to input materials. After the materials enter, the screw 110 rotates to push the materials to move in the flow channel. In the circular pipe flow channel 130 and the converging pipe flow channel 140, the materials are subjected to different pressures, shear forces, etc. In the circular pipe flow channel 130, the flow characteristics of the materials are affected by factors such as the pipe diameter; in the converging pipe flow channel 140, since the pipe diameter gradually becomes smaller, it will change the flow rate and pressure distribution of the materials. In these flow channels, physical and chemical changes occur to the materials, such as temperature increase, plasticization, etc., and finally the materials are extruded from the extruder 100 to achieve the puffing processing of the materials.

[0068] At least one embodiment of the present application proposes a real-time measurement method for the rheological properties of non-Newtonian fluids in an extruder 100, and the method includes the following steps:

[0069] (1) Based on Newton's first law and the power-law model of non-Newtonian fluids, establish a quantitative relationship between the rheological coefficient K, the real-time pressure difference, and the real-time flow rate, and combine the geometric parameters of the flow channel to obtain a calculation model for the rheological coefficient of non-Newtonian fluids in the flow channel, specifically:

[0070] In the circular pipe flow channel 130, the expression of the rheological coefficient is

[0071]

[0072] where, K - rheological coefficient, ΔP - pressure difference, l - length of the acquisition end, Q - volume flow rate, n - rheological index, R - radius of the circular pipe;

[0073] In the converging pipe channel 140, the expression of the rheological coefficient is

[0074]

[0075] where K is the rheological coefficient, ΔP is the pressure difference, L is the length of the acquisition section, Q is the volume flow rate, n is the rheological index, r0 is the inlet radius of the converging pipe channel 140, and r1 is the outlet radius of the converging pipe channel 140;

[0076] (2) According to the temperature parameters measured in real time in the channel and the calculation model of the rheological coefficient of the non-Newtonian fluid, obtain the complete rheological characteristic curve.

[0077] For the geometric characteristics of different channels of the extruder 100, different online calculation methods for the rheological coefficient of the non-Newtonian fluid are respectively corresponding. According to the real-time measurement method of the rheological characteristics of the non-Newtonian fluid of the extruder 100 in the embodiments of the present application, the calculation model of the rheological coefficient of the non-Newtonian fluid in the channel is innovated, and real-time measurement can be carried out under production disclosure, capturing the dynamic changes of the rheological characteristics of the material in real time. The test conditions are completely consistent with the actual production environment, greatly improving the timeliness of the data. With the double verification mechanism of the circular pipe channel 130 and the converging pipe channel 140, the accuracy and reliability of the measurement results are significantly improved, providing a solid data support for the production process.

[0078] Combined with Figure 1 and Figure 3 , in some embodiments, in step (1), in the circular pipe channel 130, when the fluid moves at a low speed and uniformly, the normal stress and the shear stress are in balance. Combine the normal force equation and the shear force equation to calculate the shear stress equation;

[0079] Combine the power-law equation and the shear stress equation to solve the velocity distribution of the non-Newtonian fluid and obtain the velocity distribution formula; Combine with the volume flow rate formula and inversely deduce the rheological coefficient K.

[0080] In the present application, the principle of fluid mechanics balance is the basis of this model. In circular pipe flow, the non-Newtonian fluid is in a state of force balance. Along the flow direction, the normal force and the shear force are in balance with each other. Connecting the pressure difference with the shear stress lays the foundation for establishing the quantitative relationship between the rheological coefficient and the pressure difference and the flow rate subsequently. The power-law model is a common way to describe the characteristics of non-Newtonian fluids. In the calculation model of the rheological coefficient of the non-Newtonian fluid in the present application, the power-law model is adopted because the viscosity of the non-Newtonian fluid is not constant like that of the Newtonian fluid but is related to the velocity gradient. Through this model, the viscous change characteristics of the non-Newtonian fluid under different flow states can be described. Combine the previously obtained shear stress equation with the power-law model, and through a series of mathematical derivations, such as logarithmic and integral operations, the velocity distribution formula and the volume flow rate formula can be further obtained, and finally the quantitative relationship between the rheological coefficient and the pressure difference and the flow rate is established, and the expression of the rheological coefficient is inversely deduced.

[0081] In order to more accurately describe the rheological properties at different temperatures in the circular tube flow channel 130 of the extruder 100, the pressure sensor 200 and the temperature sensor 300 are arranged on the circular tube flow channel 130 to measure the pressure difference of the fluid in real time. By measuring the pressure difference in real time, the pressure change information of the fluid during the flow process can be obtained, providing important data for calculating the rheological coefficient. The temperature sensor 300 is used to feedback the temperature parameters because the temperature has a significant effect on the rheological properties of non-Newtonian fluids. At different temperatures, the molecular structure and interaction force of non-Newtonian fluids will change, resulting in changes in rheological properties. When establishing the model and calculating the rheological coefficient, considering the temperature factor can make the model more accurately reflect the actual situation, and then accurately describe the rheological properties of the non-Newtonian fluid in the circular tube of the extruder 100 at different temperatures.

[0082] Specifically, Newton's first law states that any object must maintain a state of uniform rectilinear motion or rest until an external force forces it to change its state of motion. In the circular tube flow channel 130, the flow of non-Newtonian fluid can be regarded as maintaining a relatively stable state under certain conditions. At this time, the viscosity can be detected based on its force balance, and then the rheological coefficient can be obtained.

[0083] Specifically, for the non-Newtonian fluid flowing in the circular tube flow channel 130, the normal force along the flow direction is:

[0084] (1)

[0086] Among them, F1 is the normal force along the flow direction, ΔP is the pressure difference of the non-Newtonian fluid in the circular tube flow channel 130, that is, the pressure difference between two points of the fluid in the flow direction, S1 is the effective force area perpendicular to the pressure difference ΔP in the circular tube flow channel 130. In the case of the circular tube flow channel 130, the cross-section perpendicular to the flow direction is a circle, and r is the radius of the circular tube.

[0087] Tangential force (internal friction)

[0088] (2)

[0090] Among them, F2 is the tangential force, τ is the shear stress, S2 is the side area of ​​the circular tube flow channel 130, r is the radius of the circular tube, and l is the length of the collection section.

[0091] According to Newton's first law, the force on the material is balanced when it moves in a straight line at a uniform speed. In engineering, it is usually judged that the normal stress and the tangential stress are balanced based on the low-speed and uniform motion conditions in the pipe, and F1=F2. So by combining equations (1) and (2), we can get the shear stress equation

[0092] (3)

[0094] Since the material in the extruder 100 exhibits non-Newtonian fluid properties in the molten state, the viscosity of the material is characterized by the non-Newtonian fluid viscosity formula in the subsequent model building. Among the many non-Newtonian fluid viscosity models, the most widely used is the power law model (see equation (4)). Generally, for the power law model, it is only necessary to determine the rheological coefficient K and the exponent n. The solution idea and control logic will be shown below.

[0095] (4)

[0097] Combining equations (3) and (4), we get

[0098] (5)

[0100] For equation (5), taking logarithm operation at the same time, we get

[0101] (6)

[0103] After finishing, we can get:

[0104] (7)

[0106] Since the velocity distribution of viscous fluid changes with the radius, the closer to the center of the pipe, the greater the flow velocity. Figure 3 As shown. Therefore, the velocity distribution of non-Newtonian fluid needs to be solved before calculating the volume flow rate. The integral calculation equation (7) can be obtained

[0107] (8)

[0109] The velocity distribution formula can be obtained by solving:

[0110] (9)

[0112] Among them, u (r) is the velocity of the fluid at the radius r, n is the rheological index, ΔP is the pressure difference, K is the rheological coefficient, l is the length of the collection section, and R is the radius of the circular tube.

[0113] The volume flow rate is calculated as follows:

[0114]

[0115]

[0116] (10)

[0118] So the rheological coefficient K can be deduced

[0119] (11)

[0121] If n=1, the non-Newtonian fluid degenerates into a Newtonian fluid. At this time, K=μ, so the famous Hagen-Poiseuille formula can be derived:

[0122] (12)

[0124] Since the value of n in equation (11) is unknown, it needs to be determined by experiments. Given that for a certain formula of expanded material, its rheological coefficient is almost unchanged under the same temperature conditions, the same rheological coefficient K can be obtained by changing the pressure difference ΔP and volume flow rate Q in the working flow channel, and the rheological index n can be solved together. Let the first pressure difference and volume flow rate be (ΔP1, Q1), and the second pressure difference and volume flow rate be (ΔP2, Q2), and the K value expression be combined to obtain

[0125] (13)

[0127] Therefore

[0128] (14)

[0130] Among them, P1 is the pressure difference of the first working condition, P2 is the pressure difference of the second working condition, Q1 is the volume flow of the first working condition, Q2 is the volume flow of the second working condition, M1 is the mass flow of the first working condition, and M2 is the mass flow of the second working condition.

[0131] See also Figure 1 When measuring the rheological properties of non-Newtonian fluids in the circular tube flow channel 130, by arranging pressure sensors 200 in front and behind the flow channel, with a distance l ≥ 10 cm between adjacent sensors, the front and rear pressure difference of the non-Newtonian fluid in the flow channel can be captured more significantly. Because when a non-Newtonian fluid flows in the flow channel, the pressure will change, and the pressure difference is an important parameter reflecting the flow resistance and energy loss of the fluid. Appropriate sensor spacing can ensure that the measured pressure difference has obvious numerical changes, which facilitates the subsequent accurate analysis of the rheological properties of the fluid. If the spacing is too small, the pressure change may not be accurately detected; if the spacing is too large, the pressure change in a certain area in the flow channel may not be accurately reflected.

[0132] The calculation of the volume flow rate in the flow channel of the extruder 100 is based on the conversion between the inherent physical density of the material and the mass flow rate. In actual production or experiments, it is first necessary to obtain the mass flow data of the material and clarify the inherent physical density of the material. The volume flow rate can be derived according to the density formula. In this way, the volume flow data for subsequent calculations can be obtained.

[0133] In some embodiments, a temperature sensor 300 is arranged in the flow channel to ensure that the temperature remains unchanged when fine-tuning the pressure difference and volume flow rate under different working conditions. Temperature has a significant effect on the rheological properties of non-Newtonian fluids. At different temperatures, the molecular structure and interaction force of non-Newtonian fluids will change, which will lead to changes in their rheological properties. When measuring the rheological index, it is necessary to ensure that the temperature is constant. Equation (14) is used to calculate the rheological index. When deriving and using the equation, it is assumed that the temperature remains unchanged so that the rheological index can be accurately calculated. If the temperature fluctuates during the measurement process, the rheological properties of the fluid will become unstable, thereby affecting the accuracy of the value.

[0134] After obtaining data such as pressure difference, volume flow rate, temperature, and known geometric parameters of the flow channel (such as the tube radius R, etc.), these parameters are substituted into equation (11) to calculate the rheological coefficient K of the non-Newtonian fluid under specific temperature conditions. The viscosity of the non-Newtonian fluid can be calculated using the following formula:

[0135] (15)

[0137] By adjusting different temperature, pressure difference and flow conditions, calculating the rheological coefficient K, rheological index n and viscosity μ for multiple times, and sorting and analyzing these data, a complete rheological characteristic curve of a certain material can be drawn. This curve can intuitively show the changing law of the rheological characteristics of the material under different conditions, providing an important basis for studying the flow characteristics of non-Newtonian fluids in the circular tube flow channel 130, and also helping to optimize the process parameters of the extruder 100 and improve product quality.

[0138] Combination Figure 2 and Figure 4 , in some embodiments, within the convergent pipe flow channel 140 , the rheological coefficient model is integrated into the geometric parameters of the convergent pipe flow channel 140 ;

[0139] When the fluid in the convergent pipe flow channel 140 moves at a low and uniform speed, the normal stress and the tangential stress are balanced, and the normal force equation and the tangential force equation are combined to calculate the shear stress equation;

[0140] The power law equation and the shear stress equation are combined to solve the pressure difference at the inlet and outlet, and the rheological coefficient K is inferred by combining the volume flow formula.

[0141] Part of the flow channel inside the extruder 100 is convergent, that is, the convergent tube flow channel 140, and the flow characteristics of the non-Newtonian fluid inside it are relatively complex. For in-depth research, this application has carried out a detailed force analysis on the convergent flow microelement. In the convergent tube flow channel 140, the fluid is subjected to normal force and tangential force. Based on Newton's first law, when the fluid flows at a uniform speed, the normal force is balanced with the tangential force. Because non-Newtonian fluids follow a power law model, and at the same time, considering the geometric relationship of the convergent tube flow channel 140, these relationships are combined, and the integration from the inlet radius of the convergent tube flow channel 140 to the outlet radius of the convergent tube flow channel 140 is performed. After a series of complex mathematical derivations, the rheological coefficient calculation formula applicable to the convergent tube flow channel 140 is finally obtained.

[0142] The unique geometric features of the convergent tube flow channel 140, such as the convergence angle, inlet radius and outlet radius, have an important influence on the flow of non-Newtonian fluids. In the process of deriving the calculation formula for the rheological coefficient, the present application fully considers these geometric parameters. By introducing the geometric relationship of the geometric parameters of the convergent tube flow channel 140, the shape information of the convergent tube flow channel 140 is integrated into the formula. These geometric parameters not only affect the velocity distribution and pressure changes of the fluid in the flow channel, but are also directly reflected in the calculation formula of the rheological coefficient, so that the formula can accurately reflect the characteristics of the convergent tube flow channel 140, thereby more accurately describing the rheological behavior of the non-Newtonian fluid in this special flow channel.

[0143] In view of the fact that there is a convergent circular tube flow channel 130 in the actual extruder 100, a modeling of the rheological coefficient of non-Newtonian fluid in the convergent circular tube flow channel 130 is developed specifically, and the value of the rheological coefficient K can be obtained with minimal changes to the original mechanical structure. Based on Newton's first law, when the fluid flows at a uniform speed, the tangential force and the normal force of the fluid in the convergent tube flow channel 140 are balanced, so the rheological coefficient and viscosity model of the non-Newtonian fluid can be constructed. The specific modeling scheme is as follows:

[0144] In some embodiments, when establishing the rheological coefficient expression in the convergent pipe flow channel 140, the geometric parameter expression of the convergent pipe flow channel 140 is:

[0145]

[0146] Wherein, θ is the convergence angle of the convergent pipe flow channel 140, r0 is the inlet radius of the convergent pipe flow channel 140, r1 is the outlet radius of the convergent pipe flow channel 140, and L is the length of the collection section.

[0147] The size of r0 and r1 and their difference determine the degree of convergence of the convergent pipe flow channel 140. When the difference is large, the convergence degree of the convergent pipe flow channel 140 is large, and when the fluid flows in the flow channel, the flow velocity and pressure change more dramatically. Since the cross-sectional area of ​​the convergent pipe flow channel 140 gradually decreases from the inlet to the outlet, according to the continuity equation Q=vA (Q is the volume flow rate, v is the flow velocity, and A is the cross-sectional area), the fluid flow velocity will gradually increase when the volume flow rate remains unchanged. At the same time, according to relevant theories such as the Bernoulli equation, when the flow velocity increases, the pressure will change accordingly, which will also change the shear stress, etc., to which the fluid is subjected during the flow process, thereby affecting the rheological properties of the non-Newtonian fluid.

[0148] For the non-Newtonian fluid flow in the convergent circular tube flow channel 130, the normal force along the flow direction is:

[0149] (16)

[0151] Among them, F1 is the normal force along the flow direction, δP is the pressure difference on both sides of the microelement, and r is the radius of the convergent pipe flow channel 140 (variable).

[0152] The tangential force (internal friction) is:

[0153] (17)

[0155] Among them, r is the radius of the tube (variable), Δl is the length perpendicular to the cross section, τ r -Unit shear stress at radius r, S2-lateral area of ​​microelement (cylindrical, not cone), 2πrΔlsecθ-lateral area of ​​cone, θ is a constant, secθ=cos -1 θ.

[0156] According to Newton's first law, the force balance of the material is balanced when it moves in a straight line at a uniform speed. In engineering, it is usually assumed that the force balance is achieved when the material moves at a low speed and at a uniform speed in the tube, and F1=F2. Therefore, by combining equations (16) and (17), we can get

[0157] (18)

[0159] According to the power law model of non-Newtonian fluid, the unit shear stress expression is:

[0160] (19)

[0162] Among them, K-rheological coefficient, n-rheological index, - Shear rate, which is expressed as:

[0163] (20)

[0165] The derivation of this expression can be obtained by back - calculating from the integral value of the volume flow rate of the circular pipe flow.

[0166] Then, by simultaneously solving equations (18), (19) and (20), we can get:

[0167] (21)

[0169] Also

[0170] (22)

[0172] Substituting equation (22) into equation (21), we can get:

[0173] (23)

[0175] Integrating δP from r1 to r2, the expression of the pressure difference ΔP can be obtained as:

[0176]

[0177] (24)

[0179] Where, ΔP - pressure difference, K - rheological coefficient, n - rheological index, Q - volume flow rate.

[0180] And

[0181] (25)

[0183] Substituting equation (25) into equation (24), ΔP can be obtained as:

[0184]

[0185] (26)

[0187] Where, ΔP is the pressure difference at the inlet and outlet. In the experimental design, its value will be obtained through the pressure sensor 200. Q is the volume flow rate, and its value will be obtained in the control panel. Then the expression of the rheological coefficient is

[0188] (27)

[0190] Given that the rheological coefficient is basically stable at the same temperature (an inherent property of the fluid physical properties), therefore, under the same temperature condition, the pressure difference and volume flow rate are adjusted twice, denoted as (ΔP1, Q1) and (ΔP2, Q2) respectively, then the rheological index n can be obtained as

[0191] (28)

[0193] where P1 is the pressure difference in the first working condition, P2 is the pressure difference in the second working condition, Q1 is the volume flow rate in the first working condition, Q2 is the volume flow rate in the second working condition, M1 is the mass flow rate in the first working condition, and M2 is the mass flow rate in the second working condition.

[0194] So far, the rheological coefficient model of the non-Newtonian fluid in the converging circular pipe flow channel 130 has been established, as shown in Equation (27). The corresponding viscosity model is:[[]]

[0195] (29)

[0197] where μ is the viscosity value of the non-Newtonian fluid.

[0198] Refer to Figure 2 , when measuring the rheological properties of the non-Newtonian fluid in the converging pipe flow channel 140, pressure sensors 200 are arranged before and after the flow channel, and the distance l between adjacent pressure sensors 200 is l≥10 cm, which can ensure that the pressure difference before and after the fluid in the flow channel can be captured more significantly.

[0199] The acquisition of the volume flow rate Q in the flow channel of the extruder 100 is based on the conversion of the inherent physical density of the material and the mass flow rate M.

[0200] The temperature sensor 300 is arranged in the converging pipe flow channel 140 to ensure that the temperature remains unchanged when the pressure difference and volume flow rate are finely adjusted, and then the rheological index n can be effectively obtained, as shown in Equation (28).

[0201] With the complete acquisition of the above parameters, combined with the geometric parameters of the converging pipe flow channel 140, substituting into Equation (27) can obtain the rheological coefficient K of the non-Newtonian fluid under specific temperature conditions, and the viscosity of the non-Newtonian fluid can be calculated through the calculation formula of Equation (29). By adjusting different temperature, pressure difference and flow rate conditions, a complete rheological property curve of a certain material can be obtained.

[0202] It can be understood that in the embodiment of the present application, the converging pipe flow channel 140 part can also be flexibly designed with a diffuser flow, however, this adjustment requires a careful re-evaluation of the comprehensive effects of the inlet effect, stretching effect and shear effect.

[0203] At least one embodiment of the present application proposes a device for real-time measurement of the rheological properties of the non-Newtonian fluid of the extruder 100. The device includes:

[0204] A data acquisition module, which is used to collect the fluid pressure difference, flow rate, and temperature in the flow channel in real time;

[0205] A model establishment module, which is communicatively connected to the data acquisition module. The model establishment module establishes a quantitative relationship between the rheological coefficient K and the pressure difference and flow rate based on Newton's first law and the non-Newtonian fluid power-law model, and combines the geometric parameters of the flow channel to obtain a calculation model for the non-Newtonian fluid rheological coefficient in the flow channel. Specifically;

[0206] In the circular pipe flow channel 130, the expression of the rheological coefficient is

[0207]

[0208] where, K - rheological coefficient, ΔP - pressure difference, l - length of the acquisition end, Q - volume flow rate, n - rheological index, R - radius of the circular pipe;

[0209] In the converging pipe flow channel 140, the expression of the rheological coefficient is

[0210]

[0211] where, K - rheological coefficient, ΔP - pressure difference, L - length of the acquisition section, Q - volume flow rate, n - rheological index, r0 - inlet radius of the converging pipe flow channel 140, r1 - outlet radius of the converging pipe flow channel 140;

[0212] A rheological characteristic curve establishment module, which obtains a complete rheological characteristic curve according to the temperature parameter measured in real time in the flow channel and the corresponding non-Newtonian fluid rheological coefficient calculation model.

[0213] Among them, in some embodiments, the fluid pressure difference in the flow channel is collected in real time by the pressure sensor 200, the real-time flow rate is obtained through the flow meter or the device panel, and the temperature is collected in real time by the temperature sensor 300.

[0214] In this application, the method and device for real-time measurement of the rheological properties of non-Newtonian fluids in the extruder 100 cover the optimized arrangement of the pressure sensor 200, the reasonable selection of the measurement interval, and the careful formulation of the dual-condition acquisition strategy. In view of the diversity of the outlet flow channels of the extruder 100, a flexible sensor arrangement scheme is formulated. This scheme can accurately capture the rheological properties of the fluid on the premise of maximizing the retention of the original extrusion process, thus significantly improving the reliability of the measurement results. This application covers two measurement modes, namely the circular pipe flow channel 130 and the converging pipe flow channel 140. These two flow channels are common in the extruder 100 and have an important impact on the processing process of the material. The circular pipe flow channel 130 measurement mode is suitable for analyzing the rheological properties of the material under relatively stable pipe diameter conditions, and its calculation model and data acquisition scheme are designed around the geometric characteristics of the circular pipe and the fluid flow characteristics. The converging pipe flow channel 140 measurement mode is aimed at the situation where the pipe diameter of the flow channel gradually changes, and fully considers the special geometric shape of the converging section and the force and flow changes of the fluid in it. The two modes complement each other, comprehensively covering the common flow channel conditions in the extruder 100, and providing a comprehensive technical means for accurately measuring the rheological properties of non-Newtonian fluids in the extruder 100.

[0215] The method and device for real-time measurement of the rheological properties of non-Newtonian fluids in the extruder 100 in the embodiments of this application have significant advantages:

[0216] Real-time measurement: By installing a pressure sensor 200 and a flowmeter on the production line and matching with an innovative calculation model, the rheological parameters of the material can be obtained online and in real time. The measurement frequency jumps from the hourly level of traditional offline measurement to the second level, and the timeliness of the data is greatly improved;

[0217] Non-interference measurement: Install the pressure sensor 200 on the outer wall of the pipeline, and combine the existing flowmeter data to avoid additional sampling operations and reduce the interference to the production process. The measurement device is integrated into the production line without affecting the material transportation, ensuring the continuous and stable production;

[0218] Reliable results: Directly measure in real time under production conditions, and the test conditions are consistent with the actual production environment. Using the dual verification mechanism of circular pipe flow and converging flow, the accuracy and reliability of the measurement results are significantly improved, providing strong data support for production;

[0219] Fast quality control: The measurement results are transmitted to the control system in real time and work together with the high-precision quality control model. The process parameters can be quickly adjusted, and the product quality fluctuation can be controlled within the allowable range. The quality control response time is shortened from the hourly level to the minute level, greatly improving the quality control efficiency.

[0220] The technical features of the above-described embodiments can be combined arbitrarily. For the sake of concise description, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, it should be considered as the scope recorded in this specification.

[0221] The above-described embodiments merely represent several implementation manners of the present application. The description is relatively specific and detailed, but it should not be construed as a limitation on the scope of the patent application. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present application, several modifications and improvements can still be made, and these all belong to the protection scope of the present application. Therefore, the protection scope of the patent of the present application shall be subject to the appended claims.

Claims

1. A real-time measurement method for rheological properties of non-Newtonian fluids in an extruder, characterized in that: The method comprises the following steps: (1) Based on Newton's first law and the power law model of non-Newtonian fluid, a quantitative relationship between the rheological coefficient K and the real-time pressure difference and real-time flow rate is established. Combined with the flow channel geometric parameters, a calculation model for the rheological coefficient of non-Newtonian fluid in the flow channel is obtained. Specifically, In the circular tube flow channel, the rheological coefficient expression is Among them, K-rheological coefficient, ΔP-pressure difference, l-collection end length, Q-volume flow rate, n-rheological index, R-tube radius; In the converging pipe flow channel, the rheological coefficient expression is Among them, K-rheological coefficient, ΔP-pressure difference, L-collection section length, Q-volume flow rate, n-rheological index, r0-convergent pipe flow channel inlet radius, r1-convergent pipe flow channel outlet radius; (2) Obtaining a complete rheological characteristic curve based on the temperature parameters measured in real time in the flow channel and the rheological coefficient calculation model of the non-Newtonian fluid.

2. The real-time measurement method of rheological properties of non-Newtonian fluids in an expander according to claim 1, characterized in that: In the step (1), when the fluid moves at a low and uniform speed in the circular tube flow channel, the normal stress and the tangential stress are balanced, and the normal force equation and the tangential force equation are combined to calculate the shear stress equation; Solve the power law equation and the shear stress equation to obtain the velocity distribution formula for the non-Newtonian fluid. Combined with the volume flow formula, the rheological coefficient K can be inferred.

3. The real-time measurement method of rheological properties of non-Newtonian fluids in an expander according to claim 2, characterized in that: The velocity distribution formula is: Among them, u (r) is the velocity of the fluid at the radius r, n is the rheological index, ΔP is the pressure difference, K is the rheological coefficient, l is the length of the collection section, and R is the radius of the circular tube.

4. The real-time measurement method of rheological properties of non-Newtonian fluids in an expander according to claim 3, characterized in that: The volume flow rate formula is 。 5. The real-time measurement method of rheological properties of non-Newtonian fluid in an expander according to claim 1, characterized in that: In the convergent pipe flow channel, the rheological coefficient model is integrated into the convergent pipe flow channel 140 geometric parameters; When the fluid in the convergent pipe flow channel moves at a low and uniform speed, the normal stress and the tangential stress are balanced. The normal force equation and the tangential force equation are combined to calculate the shear stress equation. The power law equation and the shear stress equation are combined to solve the pressure difference at the inlet and outlet, and the rheological coefficient K is inferred by combining the volume flow formula.

6. The real-time measurement method for rheological properties of non-Newtonian fluids in an expander according to claim 5, characterized in that: When establishing the rheological coefficient expression in the convergent pipe flow channel, the geometric parameter expression of the convergent pipe flow channel is: Among them, θ is the convergence angle of the convergent pipe flow channel, r0 is the inlet radius of the convergent pipe flow channel, r1 is the outlet radius of the convergent pipe flow channel, and L is the length of the collection section.

7. The real-time measurement method for rheological properties of non-Newtonian fluids in an expander according to claim 6, characterized in that: The expression of pressure difference ΔP is: Among them, ΔP-pressure difference, K-rheological coefficient, n-rheological index, Q-volume flow rate.

8. The real-time measurement method of rheological properties of non-Newtonian fluid in an expander according to claim 1, characterized in that: By changing the pressure difference and volume flow rate in the working flow channel, the same value of the rheological coefficient can be obtained, and the rheological index can be solved simultaneously. The expression of the rheological index n is: Among them, P1 is the pressure difference of the first working condition, P2 is the pressure difference of the second working condition, Q1 is the volume flow of the first working condition, Q2 is the volume flow of the second working condition, M1 is the mass flow of the first working condition, and M2 is the mass flow of the second working condition.

9. The real-time measurement method for rheological properties of non-Newtonian fluids in an expander according to claim 8, characterized in that: Temperature sensors are arranged in the flow channel to ensure that the temperature remains constant when fine-tuning the pressure difference and volume flow rate under different working conditions.

10. A real-time measurement device for rheological properties of non-Newtonian fluids in an extruder, characterized in that: include: A data acquisition module, which is used to collect the pressure difference, flow rate and temperature of the fluid in the flow channel in real time; A model building module is connected to the data acquisition module for communication. The model building module establishes a quantitative relationship between the rheological coefficient K and the pressure difference and the flow rate based on Newton's first law and the non-Newtonian fluid power law model, and combines the flow channel geometric parameters to obtain a calculation model for the rheological coefficient of the non-Newtonian fluid in the flow channel, specifically: In the circular tube flow channel, the rheological coefficient expression is Among them, K-rheological coefficient, ΔP-pressure difference, l-collection end length, Q-volume flow rate, n-rheological index, R-tube radius; In the converging pipe flow channel, the rheological coefficient expression is Among them, K-rheological coefficient, ΔP-pressure difference, L-collection section length, Q-volume flow rate, n-rheological index, r0-convergent pipe flow channel inlet radius, r1-convergent pipe flow channel outlet radius; The rheological characteristic curve establishment module obtains the complete rheological characteristic curve based on the temperature parameters measured in real time in the flow channel and the corresponding non-Newtonian fluid rheological coefficient calculation model.

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