CN103149140A - Porous media air permeability estimating device - Google Patents

Abstract

The invention discloses a porous medium gas permeability evaluation device, which includes a high-pressure gas cylinder, a specimen clamping assembly and a monitoring display; the specimen clamping assembly includes an upper clamp and a lower clamp connected to each other, and the upper clamp and the lower clamp are connected. Hollow cylinder; gaskets are provided at the junction of the upper and lower clamps; upper and lower air holes are respectively provided at the top of the upper and lower clamps, and the upper air holes pass through the first gas flow rate meter, pressure gauge and pressure reducing valve in turn. The gas cylinders are connected, and the lower gas hole is connected with the monitoring display through the second gas flow meter and the gas flow sensor in sequence. The invention provides a porous medium gas permeability evaluation device, which is easy to operate, high in testing accuracy, and good in sealing effect, and can realize the purpose of parallel testing of porous media with different gas permeability such as low permeability or high permeability, and greatly reduce the It reduces the experimental error, improves the reliability and comparability of the test results, and can also be used to qualitatively and quantitatively evaluate the air permeability of porous media.

Description

A porous medium gas permeability evaluation device

technical field

The invention relates to the technical field of porous material testing, in particular to a porous medium gas permeability evaluation device.

Background technique

The utility of porous media often involves the mass transfer and heat transfer process of fluids, such as porous ceramics with catalytic and filtering functions, foam insulation boards for thermal insulation, and cement-based materials with low permeability, etc. These materials are usually related technologies. core components of the field. So far, there have been endless theoretical studies on the conduction process in porous media. Generally, it is regarded as a continuous medium, and the transmission channel is regarded as a cylindrical capillary model. Problems such as irregular interfaces and complex boundary conditions between fluid and solid lead to large deviations from the research results of the simplified model, and currently there are relatively few devices used for testing and evaluation in this area. It is necessary to evaluate the mass transfer efficiency of porous media.

Existing evaluation methods for the air permeability of porous media are mainly divided into positive pressure and negative pressure. The former includes the Cembureau method advocated by RILEM and the method proposed by Wang Zhongping, etc., and the latter includes the test method proposed by Torrent and the Figg method. These test methods The proposal is mainly aimed at porous media with low permeability. When the input pressure and gas flow rate are relatively low during the test process, it is difficult to accurately measure the flow rate of trace gas, which often leads to distortion of test results and large errors; in addition, For porous media with good air permeability, such as porous ceramics and foam materials, the air permeability level is often several or even dozens of orders of magnitude higher. Larger, the side wall of the specimen becomes a channel for gas dissipation, which will seriously affect the test results; therefore, the design of a test device with good sealing performance and high test accuracy is the key to the evaluation of the gas permeability of porous media.

Contents of the invention

The technical problem to be solved by the present invention is that the evaluation device for porous media permeability in the prior art focuses on the evaluation of low-permeability porous media, and is rarely used in the evaluation of high-permeability porous media. The flow measurement error is large, which leads to the distortion of the test results, and the above defects such as large errors. It provides a porous medium with simple operation, high test accuracy, good sealing effect, and can achieve different air permeability such as low permeability and high permeability. The purpose of the parallel test is to greatly reduce the test error, improve the reliability and comparability of the test results, and can be used to qualitatively and quantitatively evaluate the porous medium permeability evaluation device of the porous medium.

The technical solution adopted by the present invention to solve the technical problem is: a porous medium gas permeability evaluation device, including a high-pressure gas cylinder, a pressure reducing valve, a pressure gauge, a first gas flow meter, a second gas flow meter, and a specimen holder components, gas flow sensors and monitor displays;

The specimen clamping assembly includes an upper fixture and a lower fixture connected to each other. The upper fixture and the lower fixture are both hollow cylinders, and the two are connected to each other through a hollow interior; a gasket is also provided at the connection between the upper fixture and the lower fixture;

The top of the upper fixture and the bottom of the lower fixture are respectively provided with an upper air hole and a lower air hole, wherein the upper air hole is connected to the high-pressure gas cylinder through the first gas flow meter, pressure gauge and pressure reducing valve in sequence, and the lower air hole is connected with the high-pressure gas cylinder through the second gas flow meter in turn. It is connected with the gas flow sensor and the monitoring display.

The specific operation steps and test principles of the porous medium air permeability evaluation device of the present invention are as follows:

(1) Process the test piece to the size required for the test, dry it to a constant weight, and coat the side wall of the test piece with a thin layer of epoxy resin. After the epoxy resin hardens, put the test piece into the test piece holder After confirming that the upper fixture and the lower fixture are connected firmly, open the valve of the high-pressure gas cylinder to test the tightness of the porous medium gas permeability evaluation device. If the evaluation device does not leak, start the test immediately The air permeability of the piece to be tested; the air flow output end is connected to the atmosphere, and the gas pressure at the control input end is reduced step by step from 0.4MPa to 0.15MPa, with a step difference of 0.05MPa. After the readings of the gas flow meter and the second gas flow meter are stable, read the flow velocity u _n of the gas at the input end, the pressure P _n , and the gas flow Q _n at the output end in sequence (the gas flow rate can be corrected according to the formula Q=u·A);

(2) Under a specific pressure, after the gas flow through the test piece becomes stable, read 3-5 gas flow rate, pressure and gas flow data, and average them as the characteristic value of the test piece, Therefore, the gas permeability coefficient of the high permeability test piece can be calculated by the following formula:

$\frac{\mathrm{\μ}}{K}=\frac{p_1^2-p_0^2}{2{\mathrm{LP}}_1{u}_1}-\frac{p_1{u}_1}{2L(p_1{u}_1-p_{\mathrm{no}}{u}_{\mathrm{no}})}[\frac{p_1}{u_1}-\frac{p_{\mathrm{no}}}{u_{\mathrm{no}}}+p_0^2(\frac{1}{p_{\mathrm{no}}{u}_{\mathrm{no}}}-\frac{1}{p_1{u}_1})]$ (Formula 1)

In the formula, μ—gas dynamic viscosity (Ns/m ² );

L——thickness of the piece to be tested (m);

P ₁ - air pressure at the first input port (Pa);

u ₁ ——gas flow velocity at the first input port (m/s);

P _n - air pressure at the nth input terminal (Pa);

u _n ——the gas flow rate at the input end of the nth time (m/s);

P _o - atmospheric pressure (Pa);

K——gas permeability coefficient (m ² );

When the porous medium has poor gas permeability, the gas pressure P at the input end changes little with time, and the above formula 1 can be simplified as:

$\frac{\mathrm{\μ}}{K}=\frac{p_1^2-p_0^2}{{2\mathrm{LP}}_1{u}_1}$ (Formula 2)

According to the law of mass conservation, the gas at the input end and the output end satisfies p ₁ u ₁ =P ₀ u ₀ , and the flow rate per unit time through the porous medium is Q=u·A. The calculation formula for the gas permeability coefficient of the low-permeability medium is as follows:

$K=\frac{Q}{A}\&Center\; Dot;\frac{{2\mathrm{\μLp}}_0}{(p_1^2-p_0^2)}$ (Formula 3)

Among them: A——gas transmission cross-sectional area (m ² );

Q——The gas flow through the specimen per unit time (m ³ /s).

From the description of the above specific operation steps, it can be known that the gas permeability evaluation device for porous media in the present invention takes into account the assumptions of the calculation model in the test process, and can use the same evaluation device to achieve the purpose of parallel testing of porous media with different gas permeability. This not only greatly reduces the experimental error, but also improves the reliability and comparability of the test results, and can also be used to qualitatively and quantitatively evaluate the air permeability of porous media.

In the technical solution of the present invention, the specimen holding assembly includes an upper clamp and a lower clamp connected to each other, and a gasket is provided at the connection between the upper clamp and the lower clamp, so that the porous medium is air-permeable. The evaluation device has a good sealing effect, which can prevent the gas from escaping from the side wall of the test piece when the flow rate and pressure of the transmission gas are large or the gas flow through the medium is large, thereby ensuring relatively high test accuracy.

In the technical solution of the present invention, the top of the upper clamp and the bottom of the lower clamp are respectively provided with an upper air hole and a lower air hole, wherein the upper air hole is connected to the high-pressure gas cylinder through the first gas flow rate meter, pressure gauge and pressure reducing valve in sequence, The lower air hole is connected to the monitoring display through the second gas flow meter and the gas flow sensor in turn, that is, the technical solution of the present invention adopts a high-sensitivity gas flow sensor, and is assisted by a gas flow meter for correction, which makes the porous flow meter of the present invention The medium gas permeability evaluation device can accurately measure the flow rate of trace gas, which improves the accuracy of test result measurement.

As an improvement to the technical solution of the present invention, the bottom of the upper clamp is provided with a concave, and the top of the lower clamp is provided with a convex, and the shape of the concave corresponds to the shape of the convex. In this way, the upper clamp and the lower clamp are butted together through the concave and convex anchoring between the two, and the contact surface of the two is concave-convex, which reduces the possibility of gas leakage and further strengthens the porous structure. Media Permeability Evaluates the airtightness of the device.

As an improvement to the technical solution of the present invention, the bottom of the upper clamp is provided with a convex, and the top of the lower clamp is provided with a concave, and the shape of the convex corresponds to the shape of the concave. As mentioned above, the contact surface between the upper jig and the lower jig is concave-convex, which reduces the possibility of gas leakage and also enhances the airtightness of the porous medium permeability evaluation device.

As an improvement to the technical solution of the present invention, at least 3 through holes for the upper fixture are provided on the edge of the upper fixture, and at least 3 through holes for the lower fixture are provided on the edge of the lower fixture, and the positions of the through holes of the upper fixture and the through holes of the lower fixture are Uniform one-to-one correspondence; each upper fixture through hole is provided with a screw, and the screw passes through the lower fixture through hole at the corresponding position. In this way, the upper fixture and the lower fixture can be further fixed by passing the screw rod through the through hole of the upper fixture and the lower fixture through hole, so that the connection between the upper fixture and the lower fixture is more stable, and the contact surface of the two is fitted more closely. Tightness can prevent the upper and lower clamps from separating from each other when the flow rate and pressure of the transmission gas are high or the gas flow through the medium is large, which helps to improve the airtightness of the evaluation device. Therefore, the device for evaluating the air permeability of porous media in the present invention can not only be applied to the evaluation of air permeability of porous media with low permeability, but also can be applied to the evaluation of air permeability of porous media with different air permeability such as high permeability.

As an improvement to the technical solution of the present invention, both the first gas flow meter and the second gas flow meter are Pitot tube flow meters with a measurement range of 0-60m/s and a response time of less than 1 second. A gas flow meter is used to calibrate the gas flow rate passing through the test piece, so as to ensure that the porous medium permeability evaluation device has high test accuracy and sensitivity.

As an improvement to the technical solution of the present invention, the test range of the gas flow sensor is 1ml/min-1000ml/min, and the accuracy is 0.5ml/min. As mentioned above, the use of a gas flow sensor with a test range of 1ml/min-1000ml/min and an accuracy of 0.5ml/min is helpful to improve the test accuracy of the porous medium gas permeability evaluation device.

As an improvement to the technical solution of the present invention, the material of the specimen holding assembly is A3 steel or organic plastic.

As an improvement to the technical solution of the present invention, the gasket is a rubber gasket or a silicone gasket.

In the technical scheme of the present invention, conventional high-pressure gas cylinders, pressure reducing valves, pressure gauges, gas flow meters, gas flow sensors and monitoring displays in the technical field can be used to realize the technical scheme; in addition, in the present invention, For other things that are not specifically stated, the purpose of this technical solution can be achieved by adopting conventional means in the art.

Therefore, the beneficial effect of the present invention is to provide a porous medium permeability evaluation device, the evaluation device is easy to operate, the test accuracy is high, and the sealing effect is good. Using the evaluation device can realize the evaluation of low permeability or high permeability, etc. The purpose of parallel testing of porous media with different air permeability not only greatly reduces test errors, but also improves the reliability and comparability of test results, and the evaluation device can also be used to qualitatively and quantitatively evaluate the air permeability of porous media.

Description of drawings

The present invention will be further described below in conjunction with accompanying drawing and embodiment, in the accompanying drawing:

Fig. 1 is the structural schematic diagram of porous medium gas permeability evaluation device of the present invention;

Fig. 2 is a schematic diagram of the structure after the test piece is loaded into the test piece holding assembly, wherein the black area is the contact surface between the test piece and the test piece holding assembly, and the shaded area is the concave-convex contact surface between the upper fixture and the lower fixture;

The labels in the accompanying drawings are explained as follows: 1 is a high-pressure gas cylinder, 2 is a pressure reducing valve, 3 is a pressure gauge, 4 is a first gas flow rate meter, 5 is a specimen clamping assembly, 6 is a gas flow sensor, 7 For monitoring the display, 8 is a gasket, 9 is an upper clamp, 10 is a screw rod, 11 is a lower clamp, and 12 is a second gas flow meter.

Detailed ways

In order to make the object, technical solution and advantages of the present invention clearer, the present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described here are only used to explain the present invention, not to limit the present invention.

As shown in Figure 1, the device for evaluating gas permeability of porous media includes a specimen holding assembly 5, a first gas flow meter 4, a high-pressure gas cylinder 1, a pressure reducing valve 2, a pressure gauge 3, a gas flow sensor 6, a second gas A flow meter 12, a monitoring display 7 and a plurality of conduits, wherein the specimen holding assembly 5 includes an upper clamp 9 and a lower clamp 11 which are hollow cylinders, and the hollows of the upper clamp 9 and the lower clamp 11 communicate; the bottom of the upper clamp 9 There is an inner concave, and the top of the lower fixture 11 is provided with an outer convex. The inner concave and outer convex shapes correspond, and a gasket 8 is provided at the connection between the two, and the edges of the two are respectively provided with 4 corresponding and uniform positions. The distributed upper and lower fixture through holes are provided with screw rods 10 in each pair of corresponding upper and lower fixture through holes;

The top of the upper fixture 9 and the bottom of the lower fixture 11 are respectively provided with an upper air hole and a lower air hole, wherein the upper air hole is connected with the high-pressure gas cylinder 1 through the first gas flow rate meter 4, the pressure gauge 3 and the pressure reducing valve 2 in sequence, and the lower air hole is sequentially connected to each other. It is connected with the monitoring display 7 through the second gas flow meter 12 and the gas flow sensor 6 .

In addition, the first gas flow meter 4 and the second gas flow meter 12 both use a Pitot tube flow meter with a measurement range of 0-60m/s and a response time of less than 1 second, and the test range of the gas flow sensor 6 is 1ml/min~1000ml /min, the precision is 0.5ml/min.

Example 1

The structure of the porous medium gas permeability evaluation device is shown in Figure 1. The specimen clamping component 5 is made of A3 mold steel, the outer diameter is 150mm, the inner diameter is 105mm, the height is 90mm, and the height of the concave and convex part is 10mm. The diameter of the air hole is 8mm; the thickness of the gasket 8 between the test piece and the specimen clamping assembly 5 is about 2mm, its inner diameter is 100mm, and the outer diameter is 105mm; the gasket 8 at the connection between the upper fixture 9 and the lower fixture 11 The thickness is about 3mm, the inner diameter is 105mm, and the outer diameter is 125mm.

Before the test, dry the test piece at a certain temperature to a constant weight, and then coat the side wall of the test piece with a thin layer of epoxy resin. After the epoxy resin hardens, put the test piece into the test piece holding assembly 5, and sealed with gasket 8, and then tightened with screw 10, after connecting each component with a conduit, the air permeability test can be carried out.

The test object is a highly gas-permeable PVF material. Gradually increase the gas pressure at the input end until it reaches 0.4MPa. After 5 minutes of stabilization, read the gas pressure P at the input end and the gas flow rate u _n , and decrease the pressure at the input end in turn. The second drop is about 0.05MPa. After the gas flow at the downstream output end is stable, read the gas pressure P _n and gas flow velocity u _n at the input end in sequence. The test data of gas pressure P _n and gas flow velocity u _n are shown in Table 1, and the calculation For the gas permeability coefficient, the data points with relatively large dispersion were removed to obtain the data in Table 2.

Table 1 Input gas pressure P _n and gas flow rate u _n

serial number n u _n (m/s) P _n (MPa) serial number u _n (m/s) P _n (MPa) 1 0.876 0.398 4 0.676 0.253 2 0.832 0.351 5 0.546 0.199 3 0.762 0.297 6 0.338 0.147

Table 2 Gas permeability coefficient of highly permeable porous media

It can be seen from Table 2 that the permeability of highly permeable porous media can be tested using the porous media permeability evaluation device, and the test accuracy has reached 10 ^-11 m ² , which greatly reduces the experimental error and improves the The test results are reliable and comparable, and the porous medium air permeability evaluation device is easy to operate.

Example 2

The structure of the porous medium gas permeability evaluation device is the same as that of Example 1, and the test pieces are formed according to the ingredient ratio of the porous medium in Table 3, and the size of the test pieces is carried out according to the standard 150mm×150mm×150mm, and it is to be cured to different ages Finally, according to the requirements of the device, drill the core of the size of the test piece to prepare the test piece; dry the test piece at 105°C and cool it to constant weight at room temperature, seal the side with epoxy resin, and put it into the test piece holder Tighten the specimen holding assembly 5 with the screw 10 to check the tightness of the porous medium gas permeability evaluation device. If there is no air leakage, open the air valve for the test, and control the air pressure at the input end to about 0.2MPa , after stabilizing for 10 minutes, record the gas flow Q at the output end for a certain period of time in the test, and finally calculate the gas permeability coefficient of the test piece. The measured gas permeability coefficient is shown in Table 4.

Table 3 Ingredients ratio of low-permeability porous media

water-binder ratio cement water sand pebbles Water reducing agent% 0.25 550 137.5 716 1074 1.8 0.30 550 165 687 1030 0.9 0.35 550 192.5 658 986 0.9

Table 4 Gas permeability coefficient of low permeability porous media

From the data in Table 3, it can be known that the test object is a low-permeability porous medium, and the data in Table 4 also shows that the porous medium gas permeability evaluation device can realize testing the low-permeability porous medium, and the test accuracy has reached 10 ^-17 , the test accuracy is high.

It should be understood that those skilled in the art can make improvements or changes based on the above description, and all these improvements and changes should belong to the protection scope of the appended claims of the present invention.

Claims (8)

1. porous medium gas penetration potential apparatus for evaluating, it is characterized in that, comprise gas cylinder (1), reduction valve (2), tensimeter (3), the first gas flow rate meter (4), the second gas flow rate meter (12), test specimen clamp assemblies (5), gas flow sensor (6) and monitor display (7);

Described test specimen clamp assemblies (5) comprises interconnective upper fixture (9) and lower clamp (11), and described upper fixture (9) and lower clamp (11) are hollow cylinder, and both inner hollow is connected; Described upper fixture (9) and lower clamp (11) junction also are provided with packing ring (8);

Described upper fixture (9) top and lower clamp (11) bottom are respectively equipped with pore and lower pore, wherein, described upper pore is connected with gas cylinder (1) with reduction valve (2) by the first gas flow rate meter (4), tensimeter (3) successively, and described lower pore is connected with monitor display (7) with gas flow sensor (6) by the second gas flow rate meter (12) successively.

2. porous medium gas penetration potential apparatus for evaluating according to claim 1, is characterized in that, described upper fixture (9) bottom is provided with indent, and lower clamp (11) top is provided with evagination, and the shape of described indent is corresponding with the shape of evagination.

3. porous medium gas penetration potential apparatus for evaluating according to claim 1, is characterized in that, described upper fixture (9) bottom is provided with evagination, and lower clamp (11) top is provided with indent, and the shape of described evagination is corresponding with the shape of indent.

4. according to claim 2 or 3 described porous medium gas penetration potential apparatus for evaluating, it is characterized in that, described upper fixture (9) edge is provided with at least 3 upper fixture through holes, and lower clamp (9) edge is provided with at least 3 lower clamp through holes, and upper fixture through hole is corresponding with the position homogeneous one of lower clamp through hole; Be equipped with screw rod (10) on each in the fixture through hole, and screw rod (10) passes the lower clamp through hole of correspondence position.

5. porous medium gas penetration potential apparatus for evaluating according to claim 1, is characterized in that, it is 0 ~ 60m/s, response time less than the Pitot tube velocimeter of 1 second that described the first gas flow rate meter (4) and the second gas flow rate meter (12) all adopt measurement range.

6. porous medium gas penetration potential apparatus for evaluating according to claim 1, is characterized in that, the test specification of described gas flow sensor (6) is 1ml/min ~ 1000ml/min, and precision is 0.5ml/min.

7. porous medium gas penetration potential apparatus for evaluating according to claim 1, is characterized in that, the material of described test specimen clamp assemblies (5) is A3 steel or organic plastics.

8. porous medium gas penetration potential apparatus for evaluating according to claim 1, is characterized in that, described packing ring (8) is rubber washer or silicone gasket.

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