A method for testing the permeability of porous media

Abstract

The present invention relates to a method for testing the permeability of a porous medium, which is characterized by comprising the following steps: sample preparation: making the porous medium into a block with a regular shape; sample testing: filling the pores of the porous medium with liquid through a liquid suction experiment, and obtaining the relationship between the mass of the liquid absorbed by the porous medium and the time, which is recorded as M(t); data processing: according to the relationship between the mass of the liquid absorbed by the porous medium and the time M(t), the permeability of the porous medium is calculated to be: #imgabs0# wherein μ is the dynamic viscosity of the absorbed liquid / Pa·s, L is the length of the porous medium / m, ε is the porosity of the porous medium, and A is the cross-sectional area of ​​the block porous medium / m 2 ρ L is the liquid density / kg·m ‑3 .

Description

Technical Field

[0001] The invention relates to the field of porous media, and in particular to a method for testing the permeability of porous media. Background Art

[0002] In recent years, porous media materials have become a hot topic in the research field. They have the advantages of good permeability, high specific surface area, good material stability, strong material processability, and good environmental adaptability. They have been widely used in filtration, catalysis, heat exchange, sensing, biology, sound absorption and even air flotation support.

[0003] Among them, the block porous media with regular shapes has rich internal void structure and high specific surface area (up to 10 3 m 2 / g level), and has important application value in the fields of heat and mass transfer, catalysis, chemical adsorption, etc. For example, the block capillary wick is the core component of the heat pipe heat exchanger.

[0004] Permeability refers to the ability of porous media to conduct liquid under a certain pressure difference. It is an important indicator for evaluating the performance of porous media. The air permeability, filtration performance, catalytic efficiency and absorption ratio of porous media are all affected by the permeability index.

[0005] Currently, there are two main methods to obtain the permeability of porous media, namely experimental method and theoretical calculation method.

[0006] The experimental method is mainly based on Darcy's formula, that is,

[0007] Where: k is permeability / m 2 ; Q is the volume flow rate of the liquid / m 3 ·s -1 ; L is the length of the porous medium / m; A is the cross-sectional area / m 2 ; ΔP is the pressure difference on both sides of the porous medium / Pa. The permeability is obtained by measuring the fluid flow and pressure difference passing through the porous medium.

[0008] The theoretical calculation method is to use the Kozeny–Carman formula, namely:

[0009] Where: d is the average particle size of the powder / m; ε is the porosity; C is the KC constant.

[0010] However, the experimental method has strict requirements on the shape and size of the porous medium, and often requires the destruction of the original sample. In addition, the measurement steps are complicated, and precision instruments are required to measure parameters such as fluid flow and pressure difference. For the theoretical calculation method, the KC constant is greatly affected by the parameters of the preparation process of the porous medium, and there is no unified standard for the selection of the value. For example, for porous media prepared by sintering metal powders, the KC constant is affected by parameters such as powder particle size, particle shape, sample preparation pressure and sintering temperature. The values ​​reported publicly at home and abroad have recommended values ​​such as 122, 150, and 180, which leads to inaccurate calculations of the actual permeability. In addition, for porous media sintered with metal powders, it is often necessary to add pore-forming agents to increase their porosity and permeability. The content and particle size of the pore-forming agent also have a significant effect on the KC constant. Summary of the invention

[0011] In view of the shortcomings of the prior art, the present invention, based on experimental and theoretical analysis, proposes to first use the Archimedean principle to measure the porosity of porous media, and then place one end of a regularly shaped block of porous media in a liquid. Under the action of capillary force, the porous media draws liquid to fill the internal pores, and obtains the relationship between the mass of liquid absorbed by the porous media and time. Through the energy conservation and force balance of the internal meniscus of the porous medium, the relationship between the suction mass and the permeability is obtained, and then the suction curve is subjected to data fitting processing, and the permeability is finally obtained by combining theoretical derivation and the slope of the fitting curve.

[0012] In order to solve the above technical problems, the present invention provides a method for testing the permeability of a porous medium, which is characterized by comprising the following steps:

[0013] Sample preparation: preparing the porous medium into a block with a regular shape;

[0014] Sampling: The pores of the porous medium are filled with liquid through the liquid suction experiment, and the relationship between the mass of liquid absorbed by the porous medium and time is obtained, which is recorded as M(t);

[0015] Data processing: According to the relationship between the mass of liquid absorbed by the porous medium and the time M(t), the permeability of the porous medium is calculated as: Wherein, μ is the dynamic viscosity of the absorbed liquid / Pa·s, L is the length of the porous medium / m, ε is the porosity of the porous medium, and A is the cross-sectional area of ​​the bulk porous medium / m 2 ρ L is the liquid density / kg·m -3 .

[0016] Furthermore, the porosity of the porous medium is, Among them, V a is the apparent volume of porous media / m 3 ;M satM is the saturated wet weight of porous media / kg; dry It is the dry weight of porous medium / kg.

[0017] Furthermore, the relationship between the permeability k and the relative permeability K is: Where K is the relative permeability / m·(Pa·s) -1 , H is the liquid climbing height / m.

[0018] Furthermore, the local relative permeability of the porous medium is equal to the overall relative permeability, that is,

[0019] Furthermore, the force balance and energy conservation equations of the internal liquid of the porous medium are: Among them, ΔP c is the capillary force / Pa, obtained according to the Laplace-Young equation; dH / dt is the liquid climbing speed / m·s -1 .

[0020] Furthermore, the liquid can be pumped to fill the entire porous medium, then ΔP c =ρ L gL.

[0021] Furthermore, in the sampling step, M(t) is measured by a sampling device; the sampling device includes a horizontal base placed horizontally, a high-precision electronic balance and a liquid pool are placed in sequence on the surface of the horizontal base, a vertical support shaft is vertically arranged on the horizontal base, a suspension parallel to the horizontal base and movable along the vertical support shaft is fixedly arranged on the vertical support shaft, a fixed bracket is fixedly arranged on the suspension, the porous medium is suspended on the fixed bracket, and the surface of the porous medium facing the liquid pool is in parallel contact with the liquid surface of the liquid pool.

[0022] Furthermore, the volume of the liquid pool is recorded as V3, and the volume of the liquid pool is V a The relationship is: V3>100V a .

[0023] Furthermore, the porous medium is any one of a porous medium sintered with pure metal powder or a porous medium sintered with a pore-forming agent added.

[0024] Furthermore, the block is any one of a cuboid or a cube.

[0025] In summary, the present invention has the following beneficial effects:

[0026] 1. The present invention proposes to first use the Archimedean principle to measure the porosity of porous media, and then place one end of a regularly shaped block of porous media in a liquid. Under the action of capillary force, the porous media draws liquid to fill the internal pores, and obtains the relationship between the mass of liquid absorbed by the porous media and time. Through the energy conservation and force balance of the internal meniscus of the porous medium, the relationship between the suction mass and the permeability is obtained, and then the suction curve is subjected to data fitting processing, and the permeability is finally obtained by combining theoretical derivation and the slope of the fitting curve.

[0027] 2. The permeability test method of the present invention can be used to quickly measure the permeability of a regularly shaped bulk porous medium. The test method is simple in form and can be applied to various situations such as loose sintering, pressure sintering and pore-forming agent sintering. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the structures shown in these drawings without paying creative work.

[0029] Figure 1 It is a schematic diagram of the permeability testing device of a regularly shaped block porous medium of the present invention.

[0030] Figure 2 This is the microscopic void structure of the bulk porous medium obtained by pressure sintering the metal powder in Example 1.

[0031] Figure 3 This is the microscopic void structure of the bulk porous medium of loosely sintered metal powder in Example 2 (the mass fraction of the pore former is 10%).

[0032] Figure 4 This is the liquid absorption performance curve of the bulk porous medium sample obtained by pressure sintering the metal powder in Example 1.

[0033] Figure 5 This is the data processing of liquid absorption of the bulk porous medium sample obtained by pressure sintering of metal powder in Example 1.

[0034] Figure 6 This is the liquid absorption performance curve of the bulk porous medium sample of loosely sintered metal powder in Example 2 (pore former mass fraction 10%).

[0035] Figure 7 This is the data processing for the liquid absorption of the bulk porous medium sample of loosely sintered metal powder in Example 2 (pore former mass fraction 10%).

[0036] Figure 8 Comparison between experimental and predicted values ​​of suction performance of bulk porous media loosely sintered with metal powder.

[0037] Fig. 9 Comparison between experimental and predicted values ​​of suction performance of bulk porous media sintered by pressure-sintering metal powder.

[0038] Among them, 1 is a horizontal base; 2 is a high-precision electronic balance; 3 is a liquid pool; 4 is a block-shaped porous medium; 5 is a suspension; 6 is a fixed bracket, and 7 is a vertical support shaft.

[0039] The realization of the purpose, functional features and advantages of the present invention will be further explained in conjunction with embodiments and with reference to the accompanying drawings. DETAILED DESCRIPTION

[0040] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0041] The experimental methods in the following examples are conventional methods unless otherwise specified. The experimental materials and reagents used in the following examples are all commercially available unless otherwise specified. The quantitative tests in the following examples were performed in triplicate, and the data are the average or average ± standard deviation of the triplicate experiments.

[0042] In addition, the "and / or" in the full text includes three solutions. Taking A and / or B as an example, it includes technical solution A, technical solution B, and a technical solution that satisfies both A and B. In addition, the technical solutions between the various embodiments can be combined with each other, but it must be based on the fact that ordinary technicians in the field can implement it. When the combination of technical solutions is contradictory or cannot be implemented, it should be deemed that such a combination of technical solutions does not exist and is not within the protection scope required by the present invention.

[0043] The present invention provides a method for testing the permeability of a porous medium, which is characterized by comprising the following steps:

[0044] Sample preparation: preparing the porous medium into a block with a regular shape;

[0045] Sampling: The pores of the porous medium are filled with liquid through the liquid suction experiment, and the relationship between the mass of liquid absorbed by the porous medium and time is obtained, which is recorded as M(t);

[0046] Data processing: According to the relationship between the mass of liquid absorbed by the porous medium and the time M(t), the permeability of the porous medium is calculated as: Wherein, μ is the dynamic viscosity of the absorbed liquid / Pa·s, L is the length of the porous medium / m, ε is the porosity of the porous medium, and A is the cross-sectional area of ​​the bulk porous medium / m 2 ρ L is the liquid density / kg·m -3 .

[0047] In some embodiments, the porosity of the porous medium is, Among them, V a is the apparent volume of porous media / m 3 ;M sat M is the saturated wet weight of porous media / kg; dry It is the dry weight of porous medium / kg.

[0048] In some embodiments, the relationship between the permeability k and the relative permeability K is: Where K is the relative permeability / m·(Pa·s) -1 , H is the liquid climbing height / m.

[0049] In some embodiments, the local relative permeability of the porous medium is equal to the overall relative permeability, that is,

[0050] In some embodiments, the force balance and energy conservation equations of the internal liquid of the porous medium are: Where ΔP c is the capillary force / Pa, obtained according to the Laplace-Young equation; dH / dt is the liquid climbing speed / m·s -1 .

[0051] In some embodiments, the liquid can be pumped to fill the entire porous medium, then ΔP c =ρ L gL.

[0052] In some embodiments, in the sampling step, M(t) is measured by a sampling device; the sampling device includes a horizontal base placed horizontally, a high-precision electronic balance and a liquid pool are placed in sequence on the surface of the horizontal base, a vertical support shaft is vertically arranged on the horizontal base, a suspension parallel to the horizontal base and movable along the vertical support shaft is fixedly arranged on the vertical support shaft, a fixed bracket is fixedly arranged on the suspension, the porous medium is suspended on the fixed bracket, and the surface of the porous medium facing the liquid pool is in parallel contact with the liquid surface of the liquid pool.

[0053] In some embodiments, the volume of the liquid pool is denoted as V3, and the volume of the liquid pool is V3 of the porous medium. a The relationship is: V3>100V a .

[0054] Through the above technical solution, it is ensured that the block-shaped porous medium will not cause obvious changes in the liquid level in the liquid pool during the liquid absorption process, thereby avoiding the influence of the test results due to the change of the liquid level in the liquid pool.

[0055] In some embodiments, the porous medium is any one of a porous medium sintered by pure metal powder or a porous medium sintered by adding a pore-forming agent.

[0056] In some embodiments, the metal powder is any one of nickel powder, copper powder, and stainless steel powder, and the average particle size of the metal powder ranges from 2 to 200 μm.

[0057] In some embodiments, the pore-forming agent is any one of alkali metal salts that are easily soluble in water, such as NaCl and Na2CO3, with a particle size of 50-150 μm.

[0058] In some embodiments, the block is any one of a cuboid or a cube.

[0059] Preferably, the block is a cuboid.

[0060] In summary, the permeability test method of the present invention can be used to quickly measure the permeability of a regularly shaped bulk porous medium. The test method is simple in form and can be applied to various situations such as loose sintering, pressure sintering and pore-forming agent sintering.

[0061] Embodiment 1

[0062] Sample preparation: The pressure-sintered rectangular nickel powder porous medium is used as the test object, the pressure is 200MPa, the powder particle size is 20μm, and the porous medium is made into a block with a regular shape. The porous medium is a block of metal powder pressure-sintered. The microscopic void structure of the block-shaped porous medium of metal powder pressure-sintered is as follows: Figure 2 As shown;

[0063] Sampling: The pores of the porous medium are filled with liquid through the liquid suction experiment, and the relationship between the mass of liquid absorbed by the porous medium and time is obtained, which is recorded as M(t);

[0064] The sample measuring device comprises a horizontal base placed horizontally, a high-precision electronic balance and a liquid pool are placed on the surface of the horizontal base in sequence, a vertical support shaft is vertically arranged on the horizontal base, a suspension parallel to the horizontal base and movable along the vertical support shaft is fixedly arranged on the vertical support shaft, a fixed bracket is fixedly arranged on the suspension, a porous medium is suspended on the fixed bracket, and a surface of the porous medium facing the liquid pool is parallel to the liquid surface of the liquid pool;

[0065] Data processing: According to the relationship between the mass of liquid absorbed by the porous medium and the time M(t), the permeability of the porous medium is calculated as: Wherein, μ is the dynamic viscosity of the absorbed liquid / Pa·s, L is the length of the porous medium / m, ε is the porosity of the porous medium, and A is the cross-sectional area of ​​the bulk porous medium / m 2 ρ L is the liquid density / kg·m -3 .

[0066] The data processing steps are as follows:

[0067] First, the porosity of porous media is measured using the Archimedes principle, namely:

[0068]

[0069]

[0070] Where: ε is the porosity of the porous medium; V L is the volume of the porous medium inside / m 3 ; V a is the apparent volume of porous media / m 3 ;M sat M is the saturated wet weight of porous media / kg; dry is the dry weight of porous medium / kg; ρ L is the liquid density / kg·m -3 .

[0071] The force balance and energy conservation equations of the liquid inside the porous medium are as follows:

[0072]

[0073] Where: ΔP c is the capillary force / Pa, which can be obtained according to the Laplace-Young equation; μ is the dynamic viscosity of the liquid / Pa·s; H is the liquid climbing height / m; dH / dt is the liquid climbing speed / m·s -1 .

[0074] Under the test conditions, the height of the porous medium is required to be less than its capillary limit height, and the liquid can be sucked to fill the entire porous medium. At this time, there are:

[0075] ΔP c =ρ L gL (4)

[0076] Where: L is the apparent length of the porous medium / m.

[0077] In practical engineering, relative permeability K is often used, and its relationship with permeability k is as follows:

[0078]

[0079] Where: K is relative permeability / m·(Pa·s) -1 ; The local relative permeability is equal to the overall relative permeability.

[0080] Substituting equation (4) and equation (5) into equation (3) to solve the differential equation, we can obtain

[0081]

[0082] Convert equation (6) into the relationship between the mass of liquid absorbed by the porous medium and the time:

[0083]

[0084] Where: A is the cross-sectional area of ​​the blocky porous medium / m 2 .

[0085] By rearranging equation (7), we can get the linear relationship between liquid absorption weight and permeability:

[0086]

[0087] Therefore, the permeability of a porous medium is:

[0088] The difference between Example 2 and Example 1 is that the porous medium is a bulk porous medium formed by loose sintering of metal powder (a pressure-sintered rectangular nickel powder porous medium is used as the test object, the pressure is 200 MPa, the powder particle size is 20 μm, the pore-forming agent is Na2CO3 particles, the particle size is 100 μm, and the mass fraction of the pore-forming agent is 10%). The microscopic void structure of the bulk porous medium formed by loose sintering of metal powder is as follows: Figure 3 shown.

[0089] The suction performance curve of M(t) measured in Example 1 and Example 2 is processed according to formula (8) and linear fitting is performed to obtain the slope of the fitting formula -Kρ L g / ε, and the relative permeability K is obtained by conversion. The suction performance curve and fitting results are shown in Figure 4-7 shown.

[0090] by Figure 4 and Figure 5 For example, a pressure-sintered rectangular nickel powder porous medium is used as the test object, the pressure is 200 MPa, the powder particle size is 20 μm, the pore-forming agent is Na2CO3 particles, the particle size is 100 μm, and the mass fraction is 0%. The porosity is determined to be 21.1% using equations (1) and (2). Then, using Figure 1The capillary suction curve test device shown in the figure fixes the pressure-sintered rectangular nickel powder porous medium on the suspension 5, and slowly adjusts the height of the suspension 5 so that the porous medium contacts the liquid level surface of the liquid pool 3, and the liquid pool 3 is filled with deionized water. Under the action of capillary force, water is sucked into the porous medium, and a high-precision electronic balance 2 is used to record the mass M(t) of the sucked water until saturation, and the obtained Figure 4 Then, the suction performance curve is processed according to formula (8) and linear fitting is performed to obtain the slope of the fitting formula -Kρ L g / ε=-0.023, such as Figure 5 As shown. Then the permeability k can be calculated to be 1.2×10 -11 m 2 .

[0091] like Figure 8 and Fig. 9 As shown, the calculated permeability k is substituted into formula (7) to obtain the predicted value of the porous medium suction curve, which is in good agreement with the experimental value, verifying the permeability test method for a regularly shaped block porous medium proposed in the present invention, which can be applied to various situations such as loose sintering, pressure sintering and pore-forming agent sintering.

[0092] The technical features of the above-described embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0093] The above-mentioned embodiments only express several implementation methods of the present invention, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.

Claims

1. A method for testing the permeability of a porous medium, characterized in that: The following steps are involved: Sample preparation: preparing the porous medium into a block with a regular shape; Sampling: The pores of the porous medium are filled with liquid through the liquid suction experiment, and the relationship between the mass of liquid absorbed by the porous medium and time is obtained, which is recorded as M(t); Data processing: According to the relationship between the mass of liquid absorbed by the porous medium and the time change M(t), the permeability of the porous medium is calculated as: Wherein, μ is the dynamic viscosity of the absorbed liquid / Pa·s, L is the length of the porous medium / m, ε is the porosity of the porous medium, and A is the cross-sectional area of ​​the bulk porous medium / m 2 ; ρ L is the liquid density / kg·m -3 .

2. A method for testing the permeability of a porous medium according to claim 1, characterized in that: The porosity of the porous medium is, Among them, V a is the apparent volume of porous media / m 3 ;M sat M is the saturated wet weight of porous media / kg; dry It is the dry weight of porous medium / kg.

3. A method for testing the permeability of a porous medium according to claim 1, characterized in that: The relationship between the permeability k and the relative permeability K is: Where K is the relative permeability / m·(Pa·s) -1 , H is the liquid climbing height / m.

4. A method for testing the permeability of a porous medium according to claim 3, characterized in that: The local relative permeability of the porous medium is equal to the overall relative permeability, that is, 5. A method for testing the permeability of a porous medium according to claim 1, characterized in that: The force balance and energy conservation equations of the internal liquid of the porous medium are: Among them, ΔP c is the capillary force / Pa, obtained according to the Laplace-Young equation; dH / dt is the liquid climbing speed / m·s -1 , k is the permeability / m 2 , H is the liquid climbing height / m, g is the gravitational acceleration / m·s -2 .

6. A method for testing the permeability of a porous medium according to claim 5, characterized in that: The liquid can be pumped to fill the entire porous medium, then ΔP c =ρ L gL.

7. A method for testing the permeability of a porous medium according to claim 1, characterized in that: In the sampling step, M(t) is measured by a sampling device; The sample measuring device includes a horizontal base placed horizontally, a high-precision electronic balance and a liquid pool are placed in sequence on the surface of the horizontal base, a vertical support shaft is vertically arranged on the horizontal base, a suspension parallel to the horizontal base and movable along the vertical support shaft is fixedly arranged on the vertical support shaft, a fixed bracket is fixedly arranged on the suspension, the porous medium is suspended on the fixed bracket, and the surface of the porous medium facing the liquid pool is in parallel contact with the liquid surface of the liquid pool.

8. A method for testing the permeability of a porous medium according to claim 7, characterized in that: The volume of the liquid pool is denoted as V3, and the apparent volume of the porous medium is denoted as V a , the relationship between the volume of the liquid pool and the apparent volume of the porous medium is: V3>100V a .

9. A method for testing the permeability of a porous medium according to claim 1, characterized in that: The porous medium is any one of a porous medium sintered by pure metal powder or a porous medium sintered by adding a pore-forming agent.

10. A method for testing the permeability of a porous medium according to claim 1, characterized in that: The block is any one of a cuboid or a cube.

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