Calculation method, system and equipment for flow resistance rate of kapok fiber felt material and medium

Abstract

The invention discloses a method, a system and equipment for calculating the flow resistivity of a kapok fiber felt material and a medium. The method comprises the following steps: obtaining the size of kapok fiber; obtaining the porosity of the kapok fiber felt material; establishing a dual-pore equivalent model; calculating the specific surface area; calculating the flow resistance provided between fibers in the kapok fiber felt material; calculating the flow resistance rate jointly provided by the kapok fiber hollow holes and the nano-scale small holes in the kapok fiber felt material; and calculating the total flow resistance of the kapok fiber felt material. According to the calculation result of the flow resistance rate of the kapok fiber felt material, the sound absorption coefficient and the sound reduction index of the kapok fiber felt material can be conveniently predicted subsequently, the number of experiments is effectively reduced, and a reference basis is provided for optimization design of an acoustic package; and 2) in the calculation process of the flow resistance of the kapok fiber felt material, the specific structure of the nano-scale pores on the wall of the kapok fiber is considered, so that the internal condition of the kapok fiber can be accurately calculated.

Description

Technical Field

[0001] The present invention relates to the field of acoustic optimization design of automotive acoustic packages, and particularly to a calculation method, system, device and medium for the flow resistivity of kapok fiber felt materials based on the microstructure of kapok fibers. Background Art

[0002] Controlling noise is one of the main indicators for evaluating the NVH performance of vehicles. The acoustic package is used to block external noise from entering the cab and at the same time absorb the noise inside the cab to reduce the noise level inside the cab. Porous materials are one of the common materials for making acoustic packages. The flow resistivity is one of the characteristic parameters of porous materials, and is usually used to predict the characteristic impedance and propagation function of porous materials, and then solve the sound absorption coefficient. The flow resistivity reflects the resistance of air when passing through porous materials. As the flow resistivity increases, the resistance of air passing through porous materials also increases, and more sound waves will be reflected by the material surface, resulting in difficulty for sound waves to penetrate the material. Each porous material has a suitable flow resistivity, so that more sound wave energy can be blocked and absorbed by the material, thereby achieving better sound absorption and insulation effects.

[0003] After making kapok fiber felt materials by mixing kapok fibers with other fibers, and then testing the flow resistivity of the kapok fiber felt materials through experiments after pressing them into a specified density, the workload is large and the test cost is high. Therefore, it is of great significance to obtain the flow resistivity of kapok fiber felt materials through theoretical calculation methods.

[0004] In the existing technology, the methods for calculating the flow resistivity of kapok fiber felt materials are as follows: fitting the flow resistivity circular tube superposition model of kapok fiber felt materials with a bulk density below 60 kg / m 3 and the flat superposition model of the flow resistivity of kapok fiber felt materials with a bulk density above 150 kg / m 3 through experimental data. The intermediate transition section is fitted by introducing the fiber flattening rate to obtain a complete correction model (Xie Xinxing. Research on the Sound Absorption and Insulation Characteristics of Multilayer Kapok Felt Composites [D]. South China University of Technology, 2023.). However, this method does not consider the influence of nanoscale pores in the kapok fiber wall on the flow resistivity, and this influence cannot be ignored. The accuracy of the results obtained by this method is relatively low. Summary of the Invention

[0005] In order to solve at least one of the problems existing in the prior art, starting from the microstructure of kapok and considering the slippage effect, the present invention provides a method, system, device and medium for calculating the flow resistivity of a kapok fiber felt material. According to the actually measured inner and outer diameters of kapok fibers, the length of kapok fibers, and the porosity of the kapok fiber felt material, the flow resistivity provided by the gaps between kapok fibers in the kapok fiber felt material is determined. By establishing a double-porosity equivalent model, the kapok fiber felt material is regarded as the superposition of a macropore equivalent model and a micropore equivalent model. After considering the slippage effect, the macropores and micropores are equivalent to equivalent pores, and the flow resistivity provided jointly by the mesopores and nanoscale micropores in the kapok fibers is obtained; the two are linearly superposed to obtain the flow resistivity of the kapok fiber felt material.

[0006] To achieve the object of the present invention, a method for calculating the flow resistivity of a kapok fiber felt material provided by the present invention includes the following steps: <UNK>

[0007] (1) Obtain the size of kapok fibers: Use a scanning electron microscope (Scanning Electron Microscopy) to observe kapok fibers, and measure the microscopic morphology of kapok fibers, the inner and outer short axes of kapok fibers, the ratio of the long and short axes of kapok fibers, the length of a single kapok fiber, the wall thickness of kapok fibers, and the number of pores with different diameters per gram of kapok fibers.

[0008] (2) Obtain the porosity of the kapok fiber felt material: Use an Autoneum PORPOS porosity test system to measure the porosity of the kapok fiber felt material;

[0009] (3) Establish a double-porosity equivalent model: Establish a three-dimensional rectangular coordinate system, assuming that kapok fibers are distributed parallel to the x, y, and z directions, and the number of kapok fibers in each direction is the same. When air flows through the material along the x direction, the total number of air entering the kapok fibers is 1 / 3 of the total number of kapok, and the remaining 2 / 3 of the kapok fibers have no air flowing through. Therefore, the inner surface of this part of the fibers does not generate viscous frictional force. The kapok felt material is defined as a material in three dimensions: a macroscopic kapok felt material, a macropore material equivalent material, and a micropore equivalent material. The size of the nanoscale micropores in the kapok fiber wall does not change with the bulk density of the kapok felt. The complex nanoscale micropores on the kapok fiber wall are simplified to ideal elliptical holes with a fixed ratio k of the long and short axes. Since its long and short axes are small, this material is called the micropore equivalent material. The sizes of the macropores and hollows in the kapok felt change with the bulk density of the kapok felt. The macropores and mesopores are equivalent to an ideal porous material with a single elliptical cylindrical pore, and there are no nanoscale micropores on the fiber wall. Since its size is large, this model is called the macropore equivalent material. The length of the pore diameter is much smaller than the length of the pore, so it is assumed that the pore is a narrow elliptical tube with a ratio k of the long and short axes.

[0010] (4) Calculate the specific surface area: Calculate the specific surface area of the equivalent material of the macropores of the kapok fiber felt material according to formula (1).

[0011]

[0012] Where n m-kapok is the percentage content of kapok fiber in the cotton felt, ρ wall refers to the bulk density of the kapok fiber wall, k refers to the ratio of the long axis to the short axis, and h1 and h2 respectively refer to the short axis of the outer diameter and the short axis of the inner diameter.

[0013] (5) Calculate the flow resistance rate provided by the gaps between fibers in the kapok fiber felt material: Calculate the flow resistance rate provided by the gaps between kapok fibers according to formula (2).

[0014]

[0015] Where η refers to the viscosity of air, n area refers to the percentage of the cross-sectional area of fibers in the total area within a tiny equivalent unit.

[0016] (6) Calculate the flow resistance rate jointly provided by the hollow holes and nano-scale small holes of kapok fibers in the kapok fiber felt material: Calculate the weighted average short axis of the small hole equivalent material of the kapok fiber felt material according to formula (3):

[0017]

[0018] Where N i and d i respectively refer to the average pore diameter and the average number of pores within the discrete range. Calculate the average short diameter and the number of pores of the macropore equivalent material per unit volume of the kapok fiber felt material according to formula (4) and formula (5):

[0019]

[0020] Where φ macro refers to the porosity of the kapok fiber felt material, L kapok refers to the average length of the kapok fiber. Calculate the equivalent short axis of the kapok fiber in the kapok fiber felt material according to formula (6).

[0021]

[0022] Where h porous and N porous respectively refer to the average short axis and the number of pores of the macropore equivalent material per unit volume, h micro and N micro respectively refer to the average short axis and the number of pores of the small hole equivalent material per unit volume. ε is an empirical parameter. Calculate the equivalent Knudsen number of the kapok fiber felt equivalent material according to (7).

[0023]

[0024] where l mean denotes the average molecular free path of air, and d pore denotes the hydraulic diameter of the equivalent kapok fiber.

[0025] Calculate the hydraulic diameter of the equivalent kapok fiber according to formula (8)

[0026]

[0027] where S is the cross-sectional area of the elliptical hollow hole of the equivalent kapok fiber, and C is the perimeter of the elliptical hollow hole of the equivalent kapok fiber.

[0028] Calculate the cross-sectional area of the elliptical hollow hole of the equivalent kapok fiber and the perimeter of the elliptical hollow hole of the equivalent kapok fiber according to formula (9)

[0029]

[0030] When considering the slip effect in the small hole, the velocity field formula (10) is

[0031]

[0032] where v(r) s is the velocity distribution on the cross-section of the pipe considering the slip effect; dP / dz is the pressure gradient on the axis of the circular pipe, r is the distance from the center of the pipe to the pipe wall; K n-eq is the effective pore diameter d eff corresponding Knudsen number.

[0033] The steady-state volume flow rate Q of the gas in the pipe considering the slip effect s is

[0034]

[0035] where, when it is pipe flow, b = -1, and η is the fluid viscosity of air.

[0036] According to the flow rate formula, the average velocity when the gas flows through the fiber cross-section can be obtained as

[0037]

[0038] where A is a constant coefficient, and the expression is as shown in (13)

[0039]

[0040] According to the characteristics of laminar flow, the viscous frictional resistance generated on the inner surface when the gas flows through a single fiber can be solved according to Newton's viscosity law, and the relationship between the frictional force on the inner surface of the fiber and the velocity gradient

[0041]

[0042] When the area of the kapok felt is S and the thickness is H′, the total number N of fibers in the kapok felt can be calculated by Equation (15). kapok For

[0043]

[0044] In the formula, H is the outer short axis; L is the outer long axis; h is the inner short axis; l is the inner long axis; n kapok is the mass percentage of kapok in the kapok felt.

[0045] Therefore, the total internal friction force in the kapok felt is

[0046]

[0047] According to the formula and combining with Formulas (12), (16), and (17), the flow resistance rate σ provided jointly by the hollow holes and the nano-scale small holes in the kapok fibers can be obtained by calculating Formula (18). ellipse_S :[[]]END]]

[0048]

[0049] (7) Calculate the total flow resistance rate of the kapok fiber felt material: Calculate the flow resistance rate of the kapok fiber felt material according to (19).

[0050] σ = σ Tarnow_S + σ ellipse_S (19)

[0051] The large-hole equivalent model in step (3) is an equivalent model with only hollow holes.

[0052] The small-hole equivalent model in step (3) is an equivalent model with only nano-scale small holes.

[0053] The double-porosity in step (3) is equivalent to the linear superposition of the small-hole model and the large-hole model.

[0054] The present invention also provides a calculation system for the flow resistance rate of a kapok fiber felt material.

[0055] The present invention also provides a computer device.

[0056] The present invention also provides a computer-readable storage medium.

[0057] Compared with the prior art, the present invention has the following positive effects:

[0058] 1) According to the calculation results of the flow resistivity of kapok fiber felt materials, it is convenient to predict the sound absorption coefficient and sound insulation of kapok fiber felt materials subsequently, effectively reducing the number of experiments and providing a reference basis for the optimized design of acoustic packages.

[0059] 2) In the calculation process of the flow resistivity of kapok fiber felt materials, considering the unique structure of the nanoscale pores on the kapok fiber wall can accurately reflect the internal situation of kapok fibers.

[0060] 3) In the process of calculating the flow resistivity jointly provided by the pores and nanoscale pores in kapok fiber felt materials, the slip effect that occurs when air passes through kapok fibers is considered, which can accurately reflect the situation of sound propagation in kapok fiber felt materials. Description of the Drawings

[0061] Figure 1 is a schematic diagram of kapok fiber felt materials.

[0062] Figure 2(a) is a schematic diagram of the fiber arrangement of kapok fiber felt materials.

[0063] Figure 2(b) is a cross-sectional electron micrograph of kapok fiber felt materials.

[0064] Figure 3 is a curve graph showing the relationship between the number of nanoscale pores and the pore diameter in the kapok fiber wall per unit weight.

[0065] Figure 4 is a schematic diagram of the Autoneum PORPOS porosity test system.

[0066] Figure 5 is a schematic diagram of the double-porosity equivalent model of kapok felt.

[0067] Figure 6 is a schematic diagram of the curve showing the relationship between the equivalent Knudsen number of kapok felt and the bulk density.

[0068] Figure 7 is a schematic flow chart of a method for calculating the flow resistivity of a kapok fiber felt material provided by an embodiment of the present invention. Detailed Embodiments

[0069] To make the purpose, technical solutions and advantages of the present invention clearer and more definite, the following further describes the present invention in detail.

[0070] Please refer to Figure 7 , a method for calculating the flow resistivity of a kapok fiber felt material provided by the present invention includes the following steps:

[0071] Step 1: Test the microscopic morphology and size of kapok fibers.

[0072] The kapok fiber felt material was observed using a Scanning Electron Microscopy (SEM) to directly observe the microscopic morphology of the kapok fibers. Subsequently, the inner and outer diameters of the kapok fibers, the ratio of the major axis to the minor axis of the kapok fibers, the length of a single kapok fiber, the wall thickness of the kapok fibers, and the number of pores with different pore diameters per gram of kapok fibers could be measured. In some embodiments of the present invention, the microscopic morphology of the kapok fibers is shown in FIGS. 2(a) and 2(b), and the relationship between the number of nanoscale pores in the wall of kapok fibers per unit weight and the pore diameter is as Figure 3 shown.

[0073] Step 2: Obtain the characteristic parameter of the kapok fiber felt material, i.e., the porosity of the kapok fiber felt material.

[0074] In some embodiments of the present invention, as Figure 4 shown, the porosity of the kapok fiber felt material at different bulk densities was measured using an Autoneum PORPOS porosity test system.

[0075] Microscopically, the kapok fiber felt material consists of a skeleton and air in the pores. The test specimen was placed in a closed system, and a compression-expansion process was carried out at a constant temperature. The changes in air pressure and volume during this process were measured. According to the ideal gas state equation, the cell volume and porosity in the kapok fiber felt material could be calculated.

[0076] Step 3: Establish a dual-porosity equivalent model.

[0077] As Figure 5As shown in the figure, a dual-porosity equivalent model is established. The dual-porosity equivalent model is a theoretical model of kapok fiber felt material. In the actual kapok fiber felt material, the arrangement of kapok is disorderly. A spatial rectangular coordinate system is established. The dual-porosity equivalent model assumes that kapok fibers are distributed parallel to the x, y, and z directions, and the number of kapok fibers in each direction is the same. When air flows through the kapok fiber felt material along the x direction, the total number of kapok fibers through which air enters is 1 / 3 of the total number of kapok fibers, and the remaining 2 / 3 of the kapok fibers have no air flowing through. Therefore, no viscous friction force is generated on the inner surface of the kapok fibers without air flowing through. Since the kapok fibers have a hollow structure and there are nanoscale pores on the kapok fiber walls, the kapok fiber felt material is a multi-porosity structure with three different levels of pores. The kapok fiber felt material is defined as a material in three dimensions: macroscopic kapok felt material, equivalent material of macropores, and equivalent material of small pores (the three different-dimensional materials are determined according to the order of magnitude of their pore sizes). In actual observations, the cross-sectional shapes of the hollow pores and nanoscale pores of kapok fibers are different, mostly presenting ellipses with a fixed aspect ratio k of the major and minor axes. Therefore, the dual-porosity equivalent model simplifies all pore cross-sections to ellipses with an aspect ratio of k of the major and minor axes. During the change of the bulk density of the kapok fiber felt material, the shape of the nanoscale pores does not change with the change of the bulk density, and the sizes of the macropores and hollow pores in the kapok fiber felt material will change with the change of the bulk density of the kapok fiber felt material. The complex nanoscale pores on the kapok fiber walls are simplified to ideal elliptical pores with an aspect ratio of 2:1 of the major and minor axes. Since their major and minor axes are relatively small, this material is called the equivalent material of small pores. The macropores and hollow pores are equivalent to an ideal porous material with a single elliptical cylindrical pore, and there are no nanoscale pores on the fiber walls. Since its size is relatively large, this model (the macropores and hollow pores are equivalent to a single pore equivalent model) is called the equivalent material of macropores. The lengths of the pore diameters of the equivalent material of macropores and the equivalent material of small pores are much smaller than the length of the pores. Therefore, it is assumed that the pores are narrow and elliptical tubes with an aspect ratio of k of the major and minor axes.

[0078] In this step, the macroscopic kapok felt material is an equivalent material with only pores between fibers, the equivalent material of macropores is an equivalent material with only hollow pores; the equivalent material of small pores is an equivalent material with only nanoscale pores.

[0079] In this step, the small-pore equivalent model and the large-pore equivalent model are linearly superimposed to obtain the dual-porosity equivalent model.

[0080] Step 4: Calculate the specific surface area.

[0081] According to formula (1), calculate the specific surface area S of the equivalent material of macropores of the kapok fiber felt material porous ;

[0082]

[0083] where nm-kapok is the percentage content of kapok fiber in the cotton felt, ρ wall refers to the bulk density of the kapok fiber wall, k refers to the ratio of the long axis to the short axis, and h1 and h2 respectively refer to the short axis of the outer diameter and the short axis of the inner diameter.

[0084] Step 5: Calculate the flow resistance rate provided between fibers in the kapok fiber felt material.

[0085] According to formula (2), calculate the flow resistance rate σ contributed by the large pores between kapok fibers in the kapok fiber felt material Tarnow_S :

[0086]

[0087] In the formula, a1 is the average distance between the axes of two adjacent fibers, n area is the percentage of the cross-sectional area of fibers in the total area within a small equivalent unit, η refers to the viscosity of air, D is the fiber diameter, and φ is the porosity of the cotton felt.

[0088] Step 6: Calculate the flow resistance rate jointly provided by the hollow holes and nano-scale small holes in the kapok fibers in the kapok fiber felt material.

[0089] Calculate the weighted average short axis h of the small hole equivalent material in the kapok fiber felt material according to formula (5) micro , and the distribution of nano-scale small holes in the kapok fiber felt material is as Figure 3 shown.

[0090]

[0091] In the formula, N i and d i respectively refer to the average pore diameter and the average number of pores of nano-scale small holes within the discrete range; i refers to the index variable in the pore diameter distribution of nano-scale small holes; x refers to the summation upper limit in the pore diameter distribution of nano-scale small holes;

[0092] Calculate the average short diameter and the number of pores of the large hole equivalent material per unit volume of the kapok fiber felt material according to formula (6) and formula (7):

[0093]

[0094] In the formula, h porous and N porous respectively refer to the average short axis length and the number of pores of the large hole equivalent material per unit volume, φ macro refers to the porosity of the kapok fiber felt material, L kapok refers to the average length of the kapok fiber; V macro refers to the volume of the kapok felt, taking the unit volume of 1 m 3 ;

[0095] Calculate the equivalent minor axis h of kapok fibers in the kapok fiber felt material according to formula (8). eff :

[0096]

[0097] In the formula, h micro and N micro respectively refer to the average minor axis length and the number of pores of the equivalent material of nanoscale pores per unit volume, and ε is the effective coefficient for calculating the equivalent minor axis.

[0098] Calculate the equivalent Knudsen number K of the equivalent material of the kapok fiber felt according to formula (9). n_eq ;

[0099]

[0100] In the formula, l mean refers to the average molecular free path of air, d pore refers to the hydraulic diameter of the equivalent kapok fiber. In some embodiments of the present invention, the results of the variation of the equivalent Knudsen number with density are as shown in Figure 6 shown.

[0101] Calculate the hydraulic diameter of the equivalent kapok fiber according to formula (10):

[0102]

[0103] In the formula, S is the cross-sectional area of the elliptical hollow hole of the equivalent kapok fiber, and C is the perimeter of the elliptical hollow hole of the equivalent kapok fiber.

[0104] Calculate the cross-sectional area of the elliptical hollow hole of the equivalent kapok fiber and the perimeter of the elliptical hollow hole of the equivalent kapok fiber according to formula (11).

[0105]

[0106] When considering the slip effect in the small pores, the velocity field formula (12) is:

[0107]

[0108] In the formula, v(r) s is the velocity distribution on the cross-section of the pipe considering the slip effect; dP / dz is the pressure gradient on the axis of the circular pipe, r is the distance from the center of the pipe to the pipe wall; K n-eq is the equivalent Knudsen number of the equivalent material of the kapok fiber felt.

[0109] The steady-state volume flow rate Q in the pipe considering the slip effect s is:

[0110]

[0111] Wherein, when it is a pipe flow, b = -1, and η is the fluid viscosity of air.

[0112] According to the flow rate formula, the average velocity when the air flow passes through the fiber cross-section can be obtained as:

[0113]

[0114] Wherein, A is a constant coefficient, and the expression is as shown in (15):

[0115]

[0116] According to the characteristics of laminar flow, when the gas flows through a single fiber, the viscous frictional resistance generated on its inner surface can be solved according to Newton's viscosity law. The relationship between the frictional force f on the inner surface of the fiber and the velocity gradient is:

[0117]

[0118] p1 is the air pressure when the gas flows into the surface of the kapok felt, and p2 is the air pressure when the gas flows out of the surface of the kapok felt;

[0119] When the area of the kapok felt is S and the thickness is H′, the total number N of fibers in the kapok felt can be calculated from Equation (17) kapok :

[0120]

[0121] Wherein, H is the outer minor axis; L is the outer major axis; h is the inner minor axis; l is the inner major axis; n kapok is the mass percentage of kapok in the kapok felt; ρ felt refers to the bulk density of the kapok felt.

[0122] Therefore, the total internal frictional force F in the kapok felt is:

[0123]

[0124] According to the formula and combining formulas (14), (18), and (19), the flow resistance rate σ provided jointly by the hollow holes in the kapok fiber and the nano-scale small holes in the fiber can be obtained by formula (20) ellipse_S :

[0125]

[0126] Wherein, A is a constant related to the ratio of the major axis to the minor axis; H eff is the equivalent minor axis h of the kapok fiber eff and the fiber wall thickness 2h of the kapok felt wall sum, and d eff is the effective pore diameter.

[0127] In step 6, the effective coefficient is the coefficient for calculating the equivalent pore diameter by considering the combined effects of macropores and nanoscale small pores in the dual-porosity equivalent model.

[0128] Step 7: Calculate the total flow resistivity of the kapok fiber felt material.

[0129] Linearly superimpose the flow resistivity provided between the fibers in the kapok fiber felt material and the flow resistivity jointly provided by the hollow pores and nanoscale small pores in the kapok fibers in the kapok fiber felt material, and calculate the total flow resistivity σ of the kapok fiber felt material according to formula (9):

[0130] σ = σ Tarnow_S + σ ellipse_S (9)

[0131] In some embodiments of the present invention, a calculation system for the flow resistivity of a kapok fiber felt material is provided, which is used to implement the method provided in the foregoing embodiments. The system includes the following modules:

[0132] Kapok fiber size acquisition module, used to acquire the size of kapok fibers;

[0133] Porosity acquisition module, used to acquire the porosity of the kapok fiber felt material;

[0134] Dual-porosity equivalent model establishment module, used to define the kapok fiber felt material as a material in three dimensions: macroscopic kapok felt material, macroporous material equivalent material, and small-pore equivalent material, simplify the complex nanoscale small pores on the kapok fiber wall into ideal elliptical pores with a fixed aspect ratio k of the major and minor axes to obtain a small-pore equivalent model; in the macroporous equivalent model, assume that the pores are narrow and elliptical tubes with an aspect ratio of k; linearly superimpose the small-pore equivalent model and the macroporous equivalent model to obtain a dual-porosity equivalent model;

[0135] Specific surface area acquisition module, used to calculate the specific surface area S of the macroporous equivalent material in the kapok fiber felt material porous ;

[0136] First flow resistivity acquisition module, used to calculate the flow resistivity σ provided by the gaps between the fibers in the kapok fiber felt material Tarnow_S ;

[0137] Second flow resistivity acquisition module, used to calculate the flow resistivity σ jointly provided by the hollow pores and nanoscale small pores in the kapok fibers in the kapok fiber felt material ellipse_S ;

[0138] Total flow resistivity acquisition module, used to calculate the total flow resistivity σ of the kapok fiber felt material through the formula σ = σ Tarnow_S + σ ellipse_S

[0139] In some embodiments of the present invention, a computer device is provided, including a memory, a processor, and a computer program stored in the memory and executable on the processor. It is characterized in that when the processor executes the computer program, a method for calculating the flow resistivity of kapok fiber felt material provided in the foregoing embodiments is implemented.

[0140] In some embodiments of the present invention, a computer-readable storage medium is provided. The computer-readable storage medium stores a computer program. It is characterized in that when the computer program is executed by a processor, a method for calculating the flow resistivity of kapok fiber felt material provided in the foregoing embodiments is implemented.

[0141] In the embodiments of the present invention, based on the double-porosity equivalent model of kapok fiber felt, an assumption is proposed that the flow resistivity consists of two parts, that is, the first part is the flow resistivity contributed by the large pores between fibers, and the second part is the flow resistivity contributed by the pores of the hollow structure of kapok fibers themselves and the nano-scale pores on the kapok fiber walls. The Tarnow_S model is used to calculate the flow resistivity contributed by the pores between fibers. The hollow pores of kapok fibers and the nano-scale pores on the fiber walls are simplified into an equivalent pore. Considering the slip effect, the average velocity on the cross-section of kapok fibers and the total internal friction force of kapok fibers are obtained, and further the flow resistivity of the second part is obtained. Summing the flow resistivities of the two parts gives the flow resistivity of the kapok fiber felt. The embodiments of the present invention consider the influence of nano-scale pores in the kapok fiber wall on the magnitude of the flow resistivity, making the obtained flow resistivity of the kapok fiber felt material more accurate.

[0142] The above description of the disclosed embodiments enables those skilled in the art to implement or use the present invention. Various modifications to these embodiments will be obvious to those skilled in the art, and the general principles defined in the present invention can be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to these embodiments shown in the present invention, but will conform to the widest scope consistent with the principles and novel features disclosed in the present invention.

Claims

1. A calculation method for the flow resistance rate of kapok fiber felt material, characterized in that, The steps include: Obtain the size of kapok fibers; Obtain the porosity of the kapok fiber felt material; Define the kapok fiber felt material as materials in three dimensions: macroscopic kapok felt material, equivalent material of macroporous material, and equivalent material of microporous material. Simplify the complex nanoscale micropores on the kapok fiber wall into ideal elliptical holes with a fixed aspect ratio k of the major and minor axes to obtain a micropore equivalent model. In the macropore equivalent model, assume that the pores are narrow and elliptical tubes with an aspect ratio of k. Linearly superimpose the micropore equivalent model and the macropore equivalent model to obtain a dual-porosity equivalent model; Calculate the specific surface area S of the equivalent material of macropores in kapok fiber felt material porous ; Calculating the flow resistance rate σ provided by the gap between fibers in kapok fiber felt material Tarnow_S ; Calculate the flow resistance rate σ provided jointly by the hollow pores and nano-scale pores of kapok fibers in the kapok fiber felt material ellipse_S ; Calculate the total flow resistivity σ of kapok fiber felt material through the formula σ = σ Tarnow_S + σ ellipse_S .

2. The calculation method of the flow resistivity of a kapok fiber felt material according to claim 1, wherein The obtaining of the size of kapok fibers includes: observing kapok fibers using a scanning electron microscope to observe the microscopic morphology of kapok fibers, and measuring the inner and outer diameters of kapok fibers, the aspect ratio of the major and minor axes of kapok fibers, the length of a single kapok fiber, the wall thickness of kapok fibers, and the number of pores with different diameters per gram of kapok fibers.

3. The calculation method of the flow resistance rate of a kapok fiber felt material according to claim 1, characterized in that, The calculation formula for the specific surface area of the macroporous equivalent material in the kapok fiber felt material is: where n m-kapok is the percentage content of kapok fibers in the cotton felt, ρ wall refers to the bulk density of the kapok fiber wall, k refers to the ratio of the long axis to the short axis, and h1 and h2 respectively refer to the short axis of the outer diameter and the short axis of the inner diameter.

4. The calculation method of the flow resistance rate of a kapok fiber felt material according to claim 1, characterized in that, The calculation formula for the flow resistance rate provided between fibers in the kapok fiber felt material is: where η refers to the fluid viscosity of air, and n area refers to the percentage of the cross-sectional area of fibers in a tiny equivalent unit to the total area.

5. A method for calculating the flow resistance rate of a kapok fiber felt material according to any one of claims 1-4, characterized in that, The calculation formula for the flow resistance rate jointly provided by the hollow pores and the nanoscale micropores in kapok fibers is: Where A is a constant related to the ratio of the major axis to the minor axis, h eff is the equivalent minor axis of kapok fibers in the kapok fiber felt material, K n-eq is the equivalent Knudsen number of the equivalent material of the kapok fiber felt, H eff is the equivalent minor axis h of the kapok fibers eff and the kapok felt fiber wall thickness 2h wall sum, ρ wall refers to the bulk density of the kapok fiber wall, ρ felt refers to the bulk density of the kapok felt.

6. The calculation method of the flow resistivity of a kapok fiber felt material according to claim 5, characterized in that, Equivalent Knudsen number K of equivalent material of kapok fiber felt n-eq The expression is as follows: where l mean denotes the average molecular free path of air, and d pore denotes the hydraulic diameter of the equivalent kapok fiber; The equivalent short axis h of kapok fibers in the kapok fiber felt material eff has the following expression: Where h porous and N porous respectively refer to the average minor axis and the number of pores of the equivalent material of macropores per unit volume, h micro and N micro respectively refer to the average minor axis and the number of pores of the equivalent material of micropores per unit volume, and ε is an empirical parameter.

7. A method for calculating the flow resistance rate of a kapok fiber felt material according to claim 6, characterized in that, The average minor axis h of the equivalent material of the small holes in the kapok fiber felt material micro The expression is as follows: where N i and d i refer to the average pore diameter and the average number of pores within a discrete range, respectively; The expressions for the average minor axis and the number of pores of the macroporous equivalent material per unit volume of the kapok fiber felt material are: where φ macro denotes the porosity of kapok fiber felt material, and L kapok denotes the average length of kapok fibers.

8. A calculation system for the flow resistance rate of kapok fiber felt material, characterized in that, For implementing the method according to any one of claims 1-7, the system includes the following modules: A kapok fiber size acquisition module for acquiring the size of kapok fibers; A porosity acquisition module for acquiring the porosity of the kapok fiber felt material; A dual-porosity equivalent model establishment module for defining the kapok fiber felt material as materials in three dimensions: macroscopic kapok felt material, equivalent material of macroporous material, and equivalent material of microporous material. Simplify the complex nanoscale micropores on the kapok fiber wall into ideal elliptical holes with a fixed aspect ratio k of the major and minor axes to obtain a micropore equivalent model. In the macropore equivalent model, assume that the pores are narrow and elliptical tubes with an aspect ratio of k. Linearly superimpose the micropore equivalent model and the macropore equivalent model to obtain a dual-porosity equivalent model; Specific surface area acquisition module, used to calculate the specific surface area S of the equivalent material of macropores in kapok fiber felt material porous ; The first flow resistivity acquisition module is used to calculate the flow resistivity σ provided by the gaps between fibers in the kapok fiber felt material Tarnow_S ; The second flow resistivity acquisition module is used to calculate the flow resistivity σ jointly provided by the hollow holes and nano-scale small holes of kapok fibers in the kapok fiber felt material ellipse_S ; Total flow resistivity acquisition module, which is used to calculate the total flow resistivity σ of kapok fiber felt material through the formula σ = σ Tarnow_S + σ ellipse_S .

9. A computer device, comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, characterized in that, When the processor executes the computer program, it implements the calculation method of the flow resistance rate of a kapok fiber felt material according to any one of claims 1 to 8.

10. A computer-readable storage medium storing a computer program, characterized in that, When the computer program is executed by the processor, it implements the calculation method of the flow resistance rate of a kapok fiber felt material according to any one of claims 1 to 8.

Images