CN112100931B - Paper absolute permeability detection method based on paper two-dimensional structure - Google Patents
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- 239000011148 porous material Substances 0.000 claims abstract description 108
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- 241000219927 Eucalyptus Species 0.000 description 11
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Abstract
The invention discloses a method for detecting absolute permeability of a paper sheet based on a two-dimensional structure of the paper sheet, which comprises the steps of scanning the paper sheet by adopting a scanning electron microscope to obtain a two-dimensional fiber-pore binary image on the surface of the paper sheet, and recording pores or fiber material properties of each pixel point in a two-dimensional array mode; counting the two-dimensional pore structure of the paper by using the function as a target value, and obtaining a three-dimensional pore structure of the paper meeting the target value of the two-dimensional pore structure of the paper based on a mode of solving the total office optimal solution by using a simulated annealing algorithm; and importing computer software Avizo as input, and performing paper sheet penetration simulation by using an absolute penetration simulation module to obtain the absolute penetration of the paper sheet. According to the method, the microstructure of the paper pore is accurately represented according to limited morphological information, a three-dimensional structure of the paper is constructed through two-dimensional structure characteristics of the paper, absolute permeability of the paper and fluid distribution in the paper pore are effectively obtained, and nondestructive detection of the paper permeability is achieved.
Description
Technical Field
The invention relates to the technical field of pulping and papermaking, in particular to a method for detecting absolute permeability of a paper sheet based on a two-dimensional structure of the paper sheet.
Background
The paper has a complex three-dimensional structure consisting of fibers and pores as a porous biological material, and the paper structure not only determines the physical properties of the paper, but also influences the permeability of the paper, and further influences the water absorption, air permeability, permeability and other paper transmission properties of the paper, so that the permeability of the paper is always a research hot spot. Absolute permeability is defined as a representation of the ability of a porous material to transport a single-phase fluid, which is the permeability measured when 100% of the pore is occupied by a fluid and is saturated, and is an inherent property of the material. At present, an experimental device full-automatic film aperture and permeability measuring instrument is adopted to measure the gas permeability and the liquid permeability of the paper sheet, and an experimental method such as a liquid permeation method, an ink scribing method and the like is adopted to measure the water absorption of the paper sheet, so that the permeability of the paper sheet is indirectly represented. The full-automatic film aperture and permeability measuring instrument is used for measuring the gas permeability of the porous material, is usually expressed by adopting a relative permeability coefficient, and can accurately measure the flow and pressure difference of the gas passing through a dried sample so as to calculate the sample permeability. The method is characterized by simple and quick measurement process, but toxic ammonium thiocyanate, irritation and larger human error.
The Chinese patent (CN 201711126813.5, a method for predicting permeability based on carbonate pore structure and a device thereof) proposes a method for predicting permeability based on carbonate pore structure, classifying pore structure by mercury intrusion curves, fitting pore structure parameters with permeability and porosity respectively, establishing a database, and further predicting permeability. The method needs a mercury-pressing method to classify pore structures, and mercury has strong volatility and can cause harm to human bodies due to improper operation; meanwhile, a large number of experiments are needed to detect the porosity, permeability and pore structure of different samples so as to construct a database, the operation is complex, the time is long, and the accuracy of the database has a large influence on the prediction result.
Disclosure of Invention
The invention aims to solve the defects in the prior art and provides a method for detecting the absolute permeability of a paper sheet based on a two-dimensional structure of the paper sheet. According to the method, the pore characteristics of the two-dimensional structure of the paper pattern are counted by utilizing the two-point correlation function and the linear correlation function, the microstructure is quantized in the probability sense by counting the occurrence probability of point pairs with different distances, and the microstructure of the paper sheet is accurately represented by utilizing that as little data as possible contains more image information of the paper sheet. The simulated annealing reconstruction is a Monte Carlo process based on an optimization method, and has the main advantages that random correlation functions can be introduced for reconstruction, energy items in the algorithm are defined as square sums of statistical structure descriptors (namely space correlation functions) and are used for representing the morphology and topology of random structures, and the three-dimensional pore structure of the paper meeting the target value of the two-dimensional pore structure of the paper can be quickly and effectively constructed; the method overcomes the limitation of acquiring the three-dimensional structure of the material by utilizing the X-ray tomography technology, and can effectively acquire the absolute permeability of the paper and the fluid distribution in the visualized paper pores based on the reconstructed three-dimensional pore structure of the paper, thereby realizing the nondestructive detection of the permeability of the paper.
The aim of the invention can be achieved by adopting the following technical scheme:
a detection method of absolute permeability of a paper sheet based on a two-dimensional structure of the paper sheet comprises the following steps:
S1, scanning a paper pattern by adopting a scanning electron microscope, and obtaining a surface two-dimensional structure diagram of the paper pattern;
S2, sequentially carrying out graying, median filtering and binarization treatment on the image by utilizing computer software Matlab to obtain a fiber-pore binary structure diagram of the paper pattern;
s3, recording the fiber or pore material properties of each pixel in a two-dimensional array mode, and counting the pore characteristics of the two-dimensional structure of the paper sample by adopting a two-point correlation function and a linear correlation function;
S4, taking the two-point correlation function value and the linear correlation function value which are obtained through statistics as target values, and obtaining a three-dimensional pore structure of the paper sample, which meets the target value of the two-dimensional pore structure of the paper sample, based on a mode of solving the total office optimal solution of a simulated annealing algorithm;
S5, importing the constructed three-dimensional pore structure diagram of the paper pattern into computer software Avizo as input, and performing paper pattern permeation simulation by using an absolute permeability simulation module to obtain the absolute permeability of the paper pattern.
Further, the two-dimensional structure diagram of the surface of the paper sample obtained by adopting the scanning electron microscope is processed, and the specific process is as follows:
Cutting a fiber pattern into squares with the size of (0.1 cm multiplied by 0.1 cm) - (0.5 cm multiplied by 0.5 cm), pasting the squares on a double-sided carbon conductive electric adhesive tape, performing metal spraying treatment, performing surface scanning by adopting a scanning electron microscope, accelerating the voltage to be 5-25kev, and amplifying the voltage to be 10-500, and storing the obtained pattern surface two-dimensional structure picture in a label image file format (TIFF).
Further, processing a paper pattern image, importing a two-dimensional structure diagram of the surface of the paper pattern into computer software Matlab, firstly carrying out graying treatment, converting a fluorescent image of the paper pattern into a gray image, smoothing the image by adopting median filtering treatment, obtaining a gray distribution histogram by counting the gray image, obtaining a threshold value by adopting a maximum inter-class method, carrying out binarization treatment according to the threshold value to obtain a binary image of the paper pattern, wherein a pixel with a value of 1 is a pore, a pixel with a value of 0 is a fiber, and recording whether material properties of pixels at different positions are fibers (I=0) or pores (I=1) by adopting a two-dimensional array I (x, y).
Further, the two-point correlation function and the linear correlation function are adopted to count the pores of the paper pattern binary diagram, so that the pore structure characteristics of the paper pattern two-dimensional diagram are obtained, and the specific process is as follows:
(1) The two-point correlation function represents the probability that any point pair with a fixed distance in the image is simultaneously located in the aperture (i=1), and the calculation formula of the two-point correlation function value S is as follows:
S＝<I(x1,y1)·I(x2,y2)>
Where < · > represents the desired operator, I is the property of the pixel point in the image, x 1 and x 2 are the abscissa of the pixel in the image, and y 1 and y 2 are the ordinate of the pixel in the image, respectively.
(2) The linear correlation function represents the probability that two pixel points r 1 and r 2 are randomly selected in the image, and the pixel point of the straight line where the two pixel points are located is completely a pore, so that the calculation formula of the linear correlation function value L is as follows:
L＝<I(r1)·I(r1+dr)·I(r1+2dr)…I(r1+ndr)·I(r2)>
Wherein I is an attribute of a pixel in the image, r 1 and r 2 are positions of the pixel in the image, ndr is a distance between straight lines where r 1 and r 2 are located, and r 1+dr,r1+2dr,……,r1 + ndr is a position of the pixel between straight lines where r 1 and r 2 are located.
(3) And sequentially counting two-point correlation function values and linear correlation function values of the two-dimensional graph of the paper pattern at different pixel distances (0-50) by adopting Matlab. When the pixel distance is 0, the two-point correlation function only considers a single point, and therefore represents the porosity of the paper pattern, denoted by P.
Further, based on a mode of solving the total optimum solution by a simulated annealing algorithm, the three-dimensional pore structure of the paper pattern meeting the target value of the two-dimensional pore structure of the paper pattern is obtained, and the specific process is as follows:
(1) According to the porosity P, a three-dimensional array R (x, y, z) of corresponding pores is randomly generated, whether the material properties of voxels at different positions are fibers (R=0) or pores (R=1) is recorded, two points of a newly generated three-dimensional structure and linear correlation function values are counted, a square difference E 1 between the function value of the newly generated structure with different pixel pitches and a target value is calculated, and a calculation formula is as follows:
E1＝(S2-S1)2+(L2-L1)2
wherein S 1 and S 2 are respectively the target and new generated two-point correlation function values, and L 1 and L 2 are respectively the target and new generated linear correlation function values.
(2) Randomly selecting a fiber voxel and a pore voxel exchange position, counting two points and linear related function values of a newly generated three-dimensional structure, calculating square differences E 2 of the function values of the newly generated structure with different intervals and a target value, if E 2<E1 is accepted by image exchange, enabling E 1＝E2 to continue to select voxel exchange, if E 2>E1 is rejected by image exchange, continuing to select voxel exchange until square differences E 1 meet a set condition (less than 10 -5), and outputting the three-dimensional structure of the generated paper sample pore.
Further, the absolute permeability simulation module of the computer software Avizo is adopted to perform the paper sample permeability simulation to obtain the absolute permeability of the paper sample, and the specific process is as follows:
And introducing Avizo the generated three-dimensional structure of the paper sample pore, adopting an absolute permeability experimental simulation module, taking the upper side of the pore in the Z direction as fluid input, taking the lower side of the pore in the Z direction as fluid output, determining a fluid circulation area, fluid viscosity, a wall interface, a flow direction, a flow pressure difference and the like, and obtaining the absolute permeability of the paper sample and the fluid distribution in the paper sample pore after the simulation is finished.
Compared with the prior art, the invention has the following advantages and effects:
1. According to the invention, an electron microscope is used for scanning to obtain a two-dimensional structure diagram of the surface of the paper, two-point and linear correlation functions are used for representing the pore characteristics of the paper, an array is used for representing an image, as little data as possible is used for containing more effective information, and the microstructure of the pore of the paper is accurately represented according to limited morphological information.
2. And extracting the pore characteristics of the paper by adopting an array, constructing a three-dimensional pore structure of the paper meeting the pore characteristics of the paper by utilizing a mode of solving an optimal solution by using a simulated annealing algorithm, and realizing the visualization of the three-dimensional structure of the paper.
3. The invention utilizes the fluid simulation technology to obtain the absolute permeability of the paper and the fluid distribution in the pores of the paper, thereby realizing the nondestructive detection of the permeability of the paper.
Drawings
FIG. 1 is an electron microscope scanning view of eucalyptus fiber patterns in an embodiment of the invention;
FIG. 2 is a binarization chart of eucalyptus fiber patterns in an embodiment of the invention;
FIG. 3 is a graph of a two-point correlation function of a eucalyptus fiber pattern in accordance with an embodiment of the present invention;
FIG. 4 is a graph of a linear correlation function of eucalyptus fiber patterns in an embodiment of the present invention;
FIG. 5 is a three-dimensional pore structure of eucalyptus fiber patterns constructed in the examples of the present invention;
FIG. 6 is a graph showing the distribution of fluid in the pores of a eucalyptus fiber pattern according to an embodiment of the present invention;
fig. 7 is a flowchart of a method for detecting absolute permeability of a sheet based on a two-dimensional structure of the sheet according to an embodiment of the present invention.
Detailed Description
For the purpose of making the objects, technical solutions and advantages of the embodiments of the present invention more apparent, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention, and it is apparent that the described embodiments are some embodiments of the present invention, but not all embodiments of the present invention. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
Examples
The embodiment discloses a detection method of absolute permeability of a paper sheet based on a two-dimensional structure of the paper sheet, scanning the paper sheet by adopting a scanning electron microscope, obtaining a two-dimensional structure diagram of the surface of the paper sheet, sequentially carrying out graying, median filtering and binarization processing on the image by utilizing computer software Matlab, obtaining a fiber-pore binary structure diagram of the paper sheet, recording fiber or pore material properties of each pixel by adopting a two-dimensional array mode, sequentially adopting a two-point correlation function and a linear correlation function to count pore characteristics of the two-dimensional structure of the paper sheet, taking the counted two-point correlation function value and the linear correlation function value as target values, and obtaining the three-dimensional pore structure of the paper sheet meeting the target value of the two-dimensional pore structure of the paper sheet by adopting a mode of solving the total office optimum solution based on a simulated annealing algorithm. And importing the constructed three-dimensional pore structure diagram of the paper pattern into computer software Avizo as input, and performing paper pattern permeation simulation by using an absolute permeability simulation module to obtain the absolute permeability of the paper pattern.
As shown in fig. 7, the detection method specifically includes the following steps:
s1, scanning a paper pattern: cutting eucalyptus fiber paper into square with the size of 0.1cm multiplied by 0.1cm, pasting the square on a double-sided carbon conductive electric adhesive tape, performing metal spraying treatment, adopting a scanning electron microscope to perform surface scanning, enabling the accelerating voltage to be 15kev and the amplification factor to be 100, and storing the obtained paper surface two-dimensional structure picture in a label image file format (TIFF), so as to obtain a eucalyptus fiber paper surface two-dimensional structure diagram, as shown in figure 1.
S2, processing the two-dimensional image of the paper pattern: the two-dimensional structure diagram of the surface of the eucalyptus fiber paper sample is imported into computer software Matlab, firstly, the gray-scale treatment is carried out, the fluorescent image of the paper sample is converted into a gray-scale image, the median filtering treatment is adopted to smooth the image, the gray-scale distribution histogram is obtained by counting the gray-scale image, the threshold value is obtained by adopting the maximum inter-class method, the binarization treatment is carried out according to the threshold value, the binary image of the eucalyptus fiber paper sample is obtained, as shown in fig. 2, the black pixel (with the value of 1) is a pore, the white pixel (with the value of 0) is a fiber, and the two-dimensional array I (x, y) is adopted to record whether the pixel materials at different positions are the fiber (I=0) or the pore (I=1).
S3, counting a two-dimensional pore structure of the paper sample: based on the two-dimensional graph of the eucalyptus fiber paper pattern shown in fig. 2, a two-dimensional array I (x, y) of the two-dimensional graph of the paper pattern is counted by adopting a two-point correlation function and a linear correlation function in sequence, so that the pore structure characteristics of the two-dimensional graph of the paper pattern are obtained.
The two-point correlation function represents the probability that any point pair with a fixed distance in the image is simultaneously located in the aperture (i=1), and the calculation formula of the two-point correlation function value S is as follows:
S＝<I(x1,y1)·I(x2,y2)>
Where < · > represents the desired operator, I is the property of the pixel point in the image, x 1 and x 2 are the abscissa of the pixel in the image, and y 1 and y 2 are the ordinate of the pixel in the image, respectively. .
The linear correlation function represents the probability that two pixel points r 1 and r 2 are randomly selected in the image, and the pixel point of the straight line where the two pixel points are located is completely a pore, so that the calculation formula of the linear correlation function value L is as follows:
L＝<I(r1)·I(r1+dr)·I(r1+2dr)…I(r1+ndr)·I(r1)>
Wherein I is an attribute of a pixel in the image, r 1 and r 2 are positions of the pixel in the image, ndr is a distance between straight lines where r 1 and r 2 are located, and r 1+dr,r1+2dr,……,r1 + ndr is a position of the pixel between straight lines where r 1 and r 2 are located.
And sequentially counting a two-point correlation function and a linear correlation function of the two-dimensional graph of the paper pattern at different pixel distances (0-50) by adopting computer software Matlab, as shown in fig. 3 and 4. When the pixel spacing is 0, the two-point correlation function only considers a single point, the porosity of the paper sample is represented at the moment and is marked as P, the two-point correlation function is stable after the two-point spacing is 20 pixels, and the average pore diameter of the paper sample is about 20 pixels, so that the two-point correlation function value of the first 20 pixels can effectively record the pore characteristics. The linear correlation function characterizes connectivity of the pores, when the distance between two points is gradually increased, the function value tends to 0, the number of the pores is reduced along with the increase of the pore volume, and the function value of the first 20 distances is used for representing the pore characteristics of the paper pattern as a target value by combining the two-point correlation function.
S4, constructing a three-dimensional pore structure of the paper sample: voxels with a three-dimensional structure of 300 x 300 are arranged, and according to the porosity p=26.27%, pores of 7092900 voxels and fibers of 19907100 voxels are randomly generated by Matlab, and a three-dimensional array R (x, y, z) recording whether the voxel material at different positions is fiber (R=0) or pore (R=1), counting two points of the newly generated three-dimensional pore structure and linear correlation functions, and calculating the square difference E 1 of the function value and the target value of the newly generated structure at different intervals, wherein the calculation formula is as follows:
E1＝(S2-S1)2+(L2-L1)2
wherein S 1 and S 2 are respectively the target and new generated two-point correlation function values, and L 1 and L 2 are respectively the target and new generated linear correlation function values.
Randomly selecting a fiber voxel and a pore voxel exchange position, counting two points and linear correlation functions of a newly generated three-dimensional pore structure, calculating square differences E 2 of function values and target values of the newly generated structure with different intervals, and if E 2<E1 shows that the characteristics of the newly generated structure are closer to the characteristics of the target structure, accepting image exchange, enabling E 1＝E2 to continue selecting voxel exchange; if E 2>E1, the characteristics of the newly generated structure deviate from the target structure characteristics, so that image exchange is refused, voxel exchange is continuously selected until the square error E 1 meets the set condition (less than 10 -5), iteration is stopped, and the generated paper pattern pore three-dimensional structure is output, as shown in fig. 5.
S5, calculating the absolute permeability of the paper sample: the three-dimensional structure of the generated paper pattern pore is imported into computer software Avizo, an absolute permeability experiment simulation module (Absolute Permeability Experiment Simulation) is adopted, the upper side of the pore in the Z direction is used as fluid input, the lower side of the pore in the Z direction is used as fluid output, and parameters are set as follows: the pore space is 1, and the fluid circulation area is determined to be an aperture and a fluid and wall interface; fluent direction is the Z axis; convergence Criterion is 0.0001,Iteration min, 500s, max is 1000000 times, when the system iteration times are more than 1000000 times or the average energy standard deviation is less than 10 -4, calculating convergence, terminating the system iteration, and outputting a calculation result; outputs are the density field and the pressure field; boundary condition was set to input pressure=1.3x 5 Pa and out pressure=10 5 Pa; water was used as the flow medium and for ease of calculation the viscosity of water at 20 ℃ was used, fluid viscosity=0.001 pa·s.
After the simulation is completed, the absolute permeability of the output paper pattern is calculated to be 0.0505 according to Darcy's law, the flow distribution of the fluid in the pores is shown as in fig. 6, and the visualization of the three-dimensional distribution of the fluid penetrating through the paper pattern is realized.
In summary, according to the method for detecting the absolute permeability of the paper based on the two-dimensional structure of the paper disclosed by the embodiment, on one hand, the absolute permeability of the paper can be obtained, the fluid distribution of the fluid in the three-dimensional pores of the paper can be visually displayed, nondestructive detection of the permeability of the paper is realized, destructive experiments are not needed, the detection cost is reduced, and the detection efficiency is improved; on the other hand, a rapid and convenient detection method is provided for the development of the functional paper, and the simulation result has guiding significance for the development of the functional paper, so that the development of the functional paper can be quickened.
The above examples are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above examples, and any other changes, modifications, substitutions, combinations, and simplifications that do not depart from the spirit and principle of the present invention should be made in the equivalent manner, and the embodiments are included in the protection scope of the present invention.
Claims (5)
1. The method for detecting the absolute permeability of the paper based on the two-dimensional structure of the paper is characterized by comprising the following steps of:
S1, scanning a paper pattern by adopting a scanning electron microscope, and obtaining a surface two-dimensional structure diagram of the paper pattern;
S2, sequentially carrying out graying, median filtering and binarization treatment on the image by utilizing computer software Matlab to obtain a fiber-pore binary structure diagram of the paper pattern;
s3, recording the fiber or pore material properties of each pixel in a two-dimensional array mode, and counting the pore characteristics of the two-dimensional structure of the paper sample by adopting a two-point correlation function and a linear correlation function;
the method comprises the following steps of sequentially adopting a two-point correlation function and a linear correlation function to count the pores of a paper pattern binary image to obtain pore structure characteristics of the paper pattern two-dimensional image, wherein the process is as follows:
S31, counting the pore characteristics of the paper pattern by adopting a two-point correlation function and a linear correlation function in sequence, wherein the two-point correlation function represents the probability that any point pair with a fixed distance in an image is simultaneously positioned in a pore I=1, and the calculation formula of the two-point correlation function value S is as follows:
S＝<I(x1,y1)·I(x2,y2)>
Wherein </cndot > represents a desired operator, I is an attribute of a pixel point in the image, x 1 and x 2 are respectively an abscissa of a pixel in the image, and y 1 and y 2 are respectively an ordinate of a pixel in the image;
the linear correlation function represents the probability that two pixel points r 1 and r 2 are randomly selected in an image, and the pixel point of a straight line where the two pixel points are located is completely a pore, so that the calculation formula of the linear correlation function value L is as follows:
L＝<I(r1)·I(r1+dr)·I(r1+2dr)…I(r1+ndr)·I(r2)>
Wherein I is an attribute of a pixel in the image, r 1 and r 2 are positions of the pixel in the image, ndr is a distance between straight lines where r 1 and r 2 are located, and r 1+dr,r1+2dr,……,r1 + ndr is a position of the pixel between straight lines where r 1 and r 2 are located;
S32, respectively counting two-point correlation function values and linear correlation function values of a two-dimensional graph of the paper sample at different pixel distances of 0-50 by adopting computer software Matlab, wherein when the pixel distance is 0, the two-point correlation function only considers a single point, so that the porosity of the paper sample is represented and is marked as P;
S4, taking the two-point correlation function value and the linear correlation function value which are obtained through statistics as target values, and obtaining a three-dimensional pore structure of the paper sample, which meets the target value of the two-dimensional pore structure of the paper sample, based on a mode of solving the total office optimal solution of a simulated annealing algorithm;
The method comprises the following steps of taking a two-point correlation function value and a linear correlation function value of a two-dimensional chart of a paper pattern as target values, and constructing a three-dimensional structure of a pore of the paper pattern by adopting a mode of solving an optimal solution by using a simulated annealing algorithm:
S41, according to the porosity P, adopting computer software Matlab to randomly generate a three-dimensional array R (x, y, z) of corresponding pores, recording whether the material properties of voxels at different positions are fiber R=0 or pore R=1, counting two points of newly generated three-dimensional pore structures and linear correlation functions, and calculating square difference E 1 of function values and target values of the newly generated structures under different pixel distances, wherein the calculation formula is as follows:
E1＝(S2-S1)2+(L2-L1)2
Wherein S 1 and S 2 are respectively the target and new generated two-point correlation function values, and L 1 and L 2 are respectively the target and new generated linear correlation function values;
S42, randomly selecting a fiber voxel and an aperture voxel exchange position, counting two points and linear correlation function values of a newly generated three-dimensional structure, calculating a square difference E 2 of the function value and a target value of the newly generated structure with different pixel pitches, if E 2<E1 shows that the characteristic of the newly generated structure is closer to the characteristic of the target structure, accepting image exchange, enabling E 1＝E2 to continue selecting voxel exchange; if E 2>E1, indicating that the characteristics of the newly generated structure deviate from the characteristics of the target structure, rejecting image exchange, continuing to select voxel exchange until the square error E 1 meets the set condition, stopping iteration, and outputting the generated paper pattern pore three-dimensional structure;
S5, importing the constructed three-dimensional pore structure diagram of the paper pattern into computer software Avizo as input, and performing paper pattern permeation simulation by using an absolute permeability simulation module to obtain the absolute permeability of the paper pattern.
2. The method for detecting the absolute permeability of a sheet based on a two-dimensional structure of a sheet according to claim 1, wherein the step S1 is as follows:
Cutting a fiber paper into squares with the size of (0.1 cm multiplied by 0.1 cm) - (0.5 cm multiplied by 0.5 cm), pasting the squares on a double-sided carbon conductive electric adhesive tape, performing metal spraying treatment, performing surface scanning by adopting a scanning electron microscope, accelerating the voltage to be 5-25kev, and amplifying the voltage to be 10-500, and storing the obtained paper sample surface two-dimensional structure picture in a label image file format.
3. The method for detecting the absolute permeability of a sheet based on a two-dimensional structure of a sheet according to claim 1, wherein the step S2 is as follows:
The method comprises the steps of importing a two-dimensional structure diagram of the surface of a paper sample into computer software Matlab, carrying out graying treatment, converting a fluorescent diagram of the paper into a gray diagram, smoothing the image by adopting median filtering treatment, counting the gray diagram, obtaining a gray distribution histogram, obtaining a threshold value by adopting a maximum inter-class method, and carrying out binarization treatment according to the threshold value to obtain a fiber-pore binary structure diagram of the paper sample, wherein the fiber-pore binary structure diagram of the paper sample is recorded as whether pixel materials at different positions are fibers or pores by adopting a two-dimensional array I (x, y), I=0 represents that the pixel materials are fibers, and I=1 represents that the pixel materials are pores.
4. The method for detecting the absolute permeability of a sheet based on a two-dimensional structure of a sheet according to claim 1, wherein the step S5 is as follows: the three-dimensional structure of the paper pattern pores is imported into computer software Avizo, the penetration of fluid in the paper pattern pores is simulated, the absolute permeability of the paper pattern is calculated, and the fluid distribution inside the three-dimensional pores of the paper pattern is visually displayed.
5. The method for detecting the absolute permeability of a sheet based on a two-dimensional structure of a sheet according to claim 4, wherein the process of calculating the absolute permeability of a sheet in step S5 is as follows: and (3) introducing the three-dimensional pore structure of the paper sample into computer software Avizo, adopting an absolute permeability experimental simulation module, taking the upper side of the Z direction of the pore as fluid input, taking the lower side of the Z direction of the pore as fluid output, determining a fluid circulation area, fluid viscosity, a wall interface, a flow direction and a flow pressure difference, and obtaining the absolute permeability of the paper sample and the fluid distribution in the pores of the paper sample after the simulation is finished.
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