GOST 25283-93

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  ГОСТ 25283-93

GOST 25283−93 (ISO 4022−87) Materials sintered permeable. The determination of permeability to liquids

GOST 25283−93
(ISO 4022−87)

Group B59

INTERSTATE STANDARD

THE SINTERED PERMEABLE MATERIALS

The determination of permeability to liquids

Permeable sintered metal materials. Determination of fluid permeability

OKS 77.160
AXTU 1790

Date of introduction 1997−01−01

Preface

1 DEVELOPED by the Technical Committee for standardization TC 150 «Powder metallurgy"

INTRODUCED by Gosstandart of Russia

2 ADOPTED by the Interstate Council for standardization, Metrology and certification (Protocol No. 3−93 from 17.02.93)

The adoption voted:

3 the Standard contains the full authentic text of ISO 4022−87 «Materials sintered permeable. The determination of permeability to liquids» with additional requirements that reflect the needs of the economy

4 Decree of the Russian Federation Committee on standardization, Metrology and certification dated June 19, 1996 N 382 inter-state standard GOST 25283−93 (ISO 4022−87) introduced directly as a state standard of the Russian Federation from January 1, 1997

5 REPLACE GOST 25283−82

1 PURPOSE AND SCOPE

This standard specifies a method for determining the permeability of liquids, permeable sintered metal materials open or through porosity. The test is performed under such conditions that the permeability of liquids can be expressed by the coefficients of viscous and inertial permeability (Appendix A).

Allow the definition by the method of the permeability of the gas permeable sintered metal materials.

This standard does not apply to long hollow cylindrical specimens of small diameter for which it is unacceptable to neglect the pressure drop of the fluid when passing along the cavity of the cylinder compared to the pressure drop of the fluid when passing through the wall (Appendix A).

Additional requirements that reflect the needs of the economy, in italics.

2 NORMATIVE REFERENCES

The present standard features references to the following standards:

GOST 166−89 Calipers. Specifications

GOST 6507−90 Micrometers. Specifications

GOST 17216−71* Industrial purity. Classes of clean fluids
______________
* On the territory of the Russian Federation GOST 17216−2001, here and hereafter. — Note the manufacturer’s database.

GOST 18898−89 powder Products. Methods of determination of density, oil content and porosity

3. THE ESSENCE OF THE METHOD

The transmittance of the liquid for testing with a known viscosity and density through the specimen, measurement of pressure drop and volumetric flow rate.

Determination of the coefficients of viscous and inertial permeability, which are the formula parameters that describe the relationship between pressure drop, volumetric flowrate, viscosity and density of the liquid for the test and dimensions of porous metal of the test sample impregnated with this liquid.

The coefficient of viscous permeability of materials determined in conditions of laminar flow of a liquid or gas, and the ratio of the inertial permeability — when turbulent flow.

4 SYMBOLS AND DEFINITIONS

Terms used in the standard are shown in table 1.


Table 1 — Terms and definitions

5 SAMPLING

Before the test, you must use gas to remove from the pores of the test sample of the liquid. Oil and grease should be removed with a suitable solvent extraction method. The specimen shall be dried before testing.

5.1 the Sampling carried out according to normative-technical documentation on powder products.

5.2 Tests carried out on samples in the form of a disk with a diameter of from 25 to 100 mm and a thickness of from 0.25 to 10 mm or a parallelepiped, ring, or hollow cylinder (tube) with an active surface of 5 to 100 cmwhen the ratio of height to outer diameter of not more than 2:1. It is preferable to use as the sample for testing finished products (sheets, tapes, etc.), if they satisfy the above conditions.

5.3 If products do not meet the requirements of 5.2 tests carried out on samples obtained in manufacturing technology controlled batch and close the form.

5.4 the Smallest size of the active surface of the sample for test must be greater than 100-fold, and the thickness of the sample more than 10 times the average diameter of powder particles is made of material of the sample.

5.5 allowed machining of the surfaces of the sample, which carry the sealing system, with the exception of the surface through which penetrates the gas or liquid.

5.6 Samples to be tested should be completely soaked with this fluid immediately before the test.

6 INSTRUMENTATION

6.1 Equipment

The choice of equipment depends largely on size, shape and physical characteristics of the test sample.

This standard provides for the use of two types of devices for determining the permeability of liquids porous test specimens.

6.1.1 Head with o-rings for testing flat test pieces.

This type of testing device it is recommended to perform nondestructive testing of individual sections of flat porous sheets.

Permeable metal sheet is clamped between two pairs of movable pads. The inner pair, the corresponding square tests, has average diameter . The outer pair, the average diameter of which forms a sealing ring surrounding the test area, its tightness helps to avoid lateral leakage from the area tested (figure 1). The width of the opening formed by sealing rings of the head, should be not less than the thickness of the sheet, i.e.

.

 — the average diameter of the inner seals;  — head diameter;  — volume flow rate under pressure ;  — atmospheric pressure;  — the pressure at the outlet of the sample after infiltration between the sealing rings, it is set equal to ;  — the pressure drop across the flowmeter;  — the pressure drop on porous metal

Figure 1

Lateral leakage is minimized sealing rings of the head due to equal pressures in the inner and outer chambers. This is achieved from the upper surface of the sample as large as possible to increase the passage between the upper chamber (figure 1). From the lower surface of the sample after infiltration of the inner chamber is connected with a flow meter and is usually under a small back pressure, and the outer chamber connects with the atmosphere through the valve, equalizing the pressure. This valve is intended to equalize the pressure in the inner and outer chambers. Allowed to install the restrictor between the sample and the flow meter to increase the back pressure and thus to stabilize the control valve and pressure equalization.

In the ideal case, the pressure on the lower surface of the sample should be as close as possible to atmospheric pressure, wherein the limiter is not used, except when it is necessary to adjust the differential pressure flowmeter.

For internal seals are recommended the toroidal sealing rings (O — rings).

The seals must be sufficiently flexible to cover all surface irregularities and violations of flatness of the porous metal. In some cases it may be necessary to separately load the inner and outer seals to provide a seal precluding leakage free.

Mandatory two upper and two lower seal. They must be aligned relative to each other.

6.1.2 Clamp for test specimens form hollow cylinders

The permeability of hollow cylindrical samples is conveniently measured by mounting the cylinder symmetrically between the two flat surfaces that the liquid has penetrated outwards through the wall of the cylinder. An example is shown in figure 2. A flow meter placed in front of the sample. When attaching a porous metal cylinder to be applied are flexible enough seals to cover all surface irregularities and prevent free percolation.

Note — to minimize the adjustment device, the distance should be as small as possible and the diameter should be approximately equal to the diameter .

Figure 2

6.1.3 Holders for mounting samples (products) of small dimensions.

The necessity of using holders, which are shown in figures 3 and 4, should be specified in regulatory technical standards on specific products.

1 — sample; 2 — cover; 3 — rubber gasket; 4 — seal side surface of the sample with a mixture of 60% paraffin and 40% of rosin, synthetic tar or other sealant; 5 — base; 6 — channels of diameter 1.5 to 2.0 mm for removal pressure gauge in gas or liquid; 7 — channels for supply and discharge of liquid or gas

Figure 3

1 — sample; 2 — cover; 3 — rubber sleeve; 4 — base; 5 — channels of diameter 1.5 to 2 mm for removal pressure gauge in gas or liquid; 6 — the channels for supply and discharge of gas or liquid

Figure 4

6.2 Fluid for testing

In most cases, gases are more convenient for testing than fluid (Appendix B).

Gases for testing must be clean and dry.

By agreement between the interested parties, the permeability can be determined, if necessary, through a specific fluid. The fluid should be clean and should not contain dissolved gases.

The cleanliness class of the fluid for testing (GOST 17216) needs to be specified in regulatory technical standards on material (product).

6.3 Installation to determine the coefficient of viscous permeability of liquids and gases whose schema is given in Fig 5. The installation is used only in conditions of laminar flow of liquids and gases.

1 — compressed gas cylinders; 2 — pressure reducing valve; 3 — gas filter; 4 — dehumidifier; 5 — manostat for ensuring pressure equilibrium; 6 — crane fine adjustments of the gas supply; 7, 9, 11, 13, 14, 15, 20, 21, 24, 26, 28, 29, 30 — valves supplying gas and liquid; 10 and 12 — water pressure with an upper limit of measurement of 3 kPa and an error of less than 10 PA; 22, 27 — mercury manometers with an upper limit of measurement 40 kPa (instead of water and mercury you can use model gauges); 16, 17, 18, 31, 32, 33 — rotameters or other flow meters with a measuring error of not more than 1%; 8, 25 — holders for mounting samples; 19, 34 — thermometers for measuring the temperature of a liquid or gas with an error no more than 0,5 °C; 23 — tank with the liquid for testing is free from absorption of gas bubbles and from contamination by foreign particles or other liquids

Figure 5

6.4 Caliper with measurement error not more than 0.05 mm according to GOST 166 for measurement of samples with sizes of 1 mm or more.

6.5 Micrometer according to GOST 6507 for the measurement of samples with sizes less than 1 mm.

6.6 pressure Gauge to determine atmospheric pressure with an uncertainty of measurement not more than 1%.

6.7 Thermometer to determine the ambient temperature with the measurement error not more than 0.5 °C.

7 THE TEST PROCEDURE

7.1 measuring the thickness and area of test sample

7.1.1 Flat samples for testing

The size of the jaws of the micrometer should be not more than the size of surface irregularities not less than the size of pores.

The test area determined in a direction perpendicular to the fluid flow, the pressure gradient must be constant.

7.1.2 Samples for testing hollow cylindrical shape

The thickness and area of test for hollow cylinders (figure 2) is calculated according to the formulas:

,

,

,

where .

If the wall thickness is small compared to , for example less than 0.1, the thickness and the area of the test determined by the formula:

;

.

7.2 Measurement of differential pressures

Installation (equipment) used in the test must be checked for leaks.

Installation (figure 5) check for leaks under the pressure of 7 to 8 kPa.

The differential pressure can be determined by measuring the pressure at the inlet and the outlet of the sample separately or with a differential pressure gauge.

Amendment the instrument to get when a sample is missing in the device, observing the pressure drop over the desired range of flow rates. Amendment to the instrument shall not exceed a differential pressure of more than 10% (table 1).

7.3 flow-rate Measurement

The flow rate of the fluid, it is preferable to measure the primary standard. The flow rate should be adjusted to the average pressure and temperature of the sample. More convenient to work with a standard flow meter (pre-calibrated with a primary standard).

7.4 Measurement of pressure and temperature

It is necessary to measure pressure and temperature at the flow meter and test sample to adjust the readings of the flow meter to calculate average flow velocity through the test sample, to determine the density and the viscosity of the fluid for testing.

Tests carried out at ambient temperature (22±5) °C. the Equipment must be isolated from heat sources.

7.5 the Sequence of operations for determination of permeability of gases under conditions of laminar flow.

Close the taps 2, 6, 7, 13, 14, 15, 20. Open the taps 2, 7, 13 and by adjusting the tap 6, fed gas to the holder 8 with the sample, gradually increasing the differential pressure controlled by pressure gauge 10. By selecting a certain differential pressure gauge time interval from 2 to 3 min, hold samples of the gas flow () on the rotameter 16. At the same time, record the pressure and temperature of the gas flowing through the flow meter gauge thermometer 12 and 19, respectively. When the limit of measurement of gas flow rate on the rotameter 16 is reached, open the valve 14 and close the valve 13. The measurement is performed on the rotameter 17. When switching on the flowmeter 18 to open valve 15 and close the valve 14.

Rotameters (flow meters) shall be calibrated for pressure and temperature.

Take out the sample from the holder 8 and measures the pressure drop across the sample holder without a pressure gauge 10 for values of gas flow rate () obtained during sample testing, in terms of cranes, as in the test sample. Record gas flow rate on the readings of the rotameters (), pressure drop, gas in the holder with the sample * and the differential pressure on the holder without the sample . The difference between and must meet the requirements of 7.2.
________________
* Consistent with the original. — Note the manufacturer’s database.

The differential pressure across input and output surfaces of the sample (), N/m, is calculated for each value by the formula

,

where — the differential gas pressure on the holder with the sample;

— the pressure drop of the gas in the holder without the sample, i.e. the adjustment device;

pressure of the gas flow is measured instead of pressures and in the absence of the instrument (holder) of the test sample.

7.6 the Sequence of operations in determining the permeability of fluids under conditions of laminar flow

As for gases, the test is performed on the installation (figure 5). Close the taps 2, 6, 7, 20, 24, 28, 29, 30 and set the sample in the holder 25. Then you open the valves 28, 24, 20, 2. Arbitrarily changing the system pressure tap 6, ranging from 1000 PA to a maximum value allowed by the pressure gauge 22, change the differential pressure on the holder with the sample is controlled by the pressure gauge 27. The flow rate of fluid passing through the holder with sample () at the prescribed pressure difference recorded by the flowmeter 31. When the limit of measurement of fluid flow by the flow meter 31 is reached, open the valve 29 and close the valve 28. Further, the measurement is carried out by flowmeter 32. When switching on the flowmeter 33 and open the valve 30 and close the valve 29. The differential pressure without the sample, and input and output surface is determined, as specified in 7.5.

7.7 testing in the determination of permeability of gases and liquids in conditions that differ from laminar flow must be specified in normative and technical documentation on specific product.

8 PROCESSING OF RESULTS

8.1 the Average flow rate

Readings of the flowmeter are corrected, if used uncalibrated, the values of pressure and temperature using the correction factor to the flow meter , installed by the manufacturer. Corrected the reading of the meter find from the equation

.

To bring the corrected readings of the flowmeter to the average velocity in the porous test sample is used in amendment . The amendment is calculated from the equation of the law of gas

.

Then the average flow rate will be

.

For inserting data into a table apply the generalized correction factor

to obtain the average flow velocity .

When using gases for the test of the average flow rate in m /s in the porous test sample is calculated by the formula

,

where — corrected readings of the meter, m/s;

— pressure in the outlet (figure 1 ) or input (see figures 2−4, ) surfaces of the sample, N/m;

— half of the amount of gas temperatures at the exit of the sample and its output (figures 1 to 4 );

— half of the amount of pressure at the input and output or on input and output surfaces of the test sample

(figures 1 and 7.5, ;

figures 2 to 4 ), N/m;

— gas temperature at the exit of the sample (figure 1) or at the input (figures 2−4), K.

To obtain the average velocity of the fluid flow the test sample values , it accordingly, correct temperature, equal to the half sum of the temperatures of the fluid at the inlet into the test sample and the output.

The average values of the flow velocity needs to be found for all pressure drops calculated in

7.5 and 7.6.

8.2 the Average density and viscosity

The average pressure and average absolute temperature of the test sample to allow medium density and viscosity on the basis of published data.

The value of the viscosity and density of gases and liquids take the tables of physical constants.

8.3 Calculation of results

The coefficients of the viscous and inertial permeability determined by simultaneous measurements of flow rate and differential pressure. The number of measurements of the speed of flow should not be less than five. They should be evenly distributed over the entire interval of values of flow rate, with the greatest dimension shall not be less than ten times the smallest.

Results analyzed according to the equation

(Appendix a, equation A. 2).

This equation can be rewritten in the form ,

where

;

.

The values and calculate for each level of pressure drop and flow rate. Appropriate values and is applied to the graph paper and draw a line, optimally connecting these points.

At the intersection of this line and the axis determine the inverse viscous permeability .

The tangent of the slope of this line gives the reciprocal of the inertial permeability .

In case of difficulty, a straight line should be determined by the method of least squares.

Note — When measuring the flow in a laminar condition determine only the coefficient of viscous permeability (see Appendix a).

8.4 the Representation of the result

The coefficient of viscous permeability recorded in 10m(1 micron), and the inertial permeability coefficient at 10m (1 micron) with an accuracy of ±5% with respect to their size.

The procedure for rounding results of computations of coefficients of permeability must be specified in normative and technical documentation on specific product.

Note — the Unit of measurement of the coefficient of viscous permeability (µm), sometimes called the Darcy.

9 TEST REPORT

The test report shall include the following information:

a) reference to this standard;

b) all details necessary for identification of the test sample;

C) the type of used equipment;

d) liquid used for the test;

d) the result obtained;

e) all operations not specified in this standard or regarded as optional;

g) random factors that could affect the outcome.

Annex a (mandatory). THE FLOW OF FLUID THROUGH POROUS MATERIALS

APPENDIX A
(required)

A. 1 Viscous flow

The empirical formula of flow of fluids through porous materials was derived by Darcy for the first time based on experimental data of water. It sets up a proportional relationship of pressure drop per unit thickness of the flow rate per unit area and the viscosity. It can be written in the form

, (A. 1)

in this case losses occur as a result of shear on viscosity.

A. 2 Viscous and inertial for

In fact, the liquid and gas flow through porous materials involves several mechanisms, many of which can take place simultaneously. Experience shows that in most cases during the flow of liquids and gases through porous materials are, as a rule, only three mechanisms. It is a viscous, inertial and slip flow. The inertial period is accompanied by loss of energy due to the change in direction of fluid flow when passing through the tortuous pores and the occurrence of local phenomena of turbulence in the pores. In the absence of grazing flow, the inertial losses were combined Forchheimer losses in viscous flow Darcy and represented by the equation

, (A. 2)

which is used in this standard (8.3). However, at low flow rates of viscous liquids, the inertia in equation (A. 2) are negligible compared to viscosity and can be neglected in order to simplify equation (A. 1).

A. 3 Moving within

Equation (A. 1) implies that the pore size is greater than the average free path of gas molecules for testing. It is not applicable for pore size is very small for gases at reduced pressure or high temperature. Rolling over occurs when the mean free path of the molecules and the pore sizes of the metal are the values of the same order. In the presence of grazing flow porous metal has a higher permeability than in its absence. As in the presence of grazing flow, there is usually no inertial losses, equation (A. 2) can be written in the form

, (A. 3)

where  — coefficient of permeability in the presence of grazing flow.

Find the amendment to the moving currents

, (A. 4)

where is the observed viscous permeability in the presence of the moving flow;

the true coefficient of viscous permeability;

 — the multiplier of Klinkenberg, which is constant for a given gas and porous material and has the dimension of pressure.

The relationship between and can be represented in the form

. (A. 5)

Hence, by measuring throughout the range of different pressures (i.e., and ), build dependency from and get a straight line.

The tangent of the slope of the line equal . The intersection of this line with the axis gives the viscous permeability .

The multiplier of Klinkenberg increases with decreasing pore size, a decrease in the relative molecular weight and an increase in the temperature and viscosity of the gas.

A. 4 Effects of the wall and boundary

Equation (A. 2) for the flow of fluids applicable if the porosity is homogeneous and uniform, in reality, on the surface of the test sample has heterogeneity. Consider two cases:

the effect of wall for test specimens, the edges of which are sealed in the container;

the effect on regional output and input surfaces of all test specimens.

For the material of the granules the effect of the wall, as a rule, not taken into account, if the diameter of the test sample is not less than 100 times the particle diameter of the porous metal. If the diameter of the test sample of about 40 particle diameters, the error less than 5%.

Edge effects can be neglected when the thickness of the test sample at least 10 diameters of the particles constituting the porous metal. In the same way as in the case of the effect of the wall boundary effect depends on the difference between the porosity at the surface and internal porosity.

A. 5 Long tube of porous metals

Equation (A. 2), the calculation of area and thickness (7.1.2) and the change of pressure drop (7.2) assume that the inlet pressure around the sample is the same. For long tubes with small holes possible deviations. To establish that the error caused by the pressure drop of the fluid across the length of the axis of the tube, less than 5%, you can use one of the following methods:

a) move the second removal pressure the farthest from the fluid inlet end and compare it with the reading obtained on removal of the pressure, located at the entrance of the liquid;

b) overlap with one end of the tube approximately half of the area. Measure the permeability of the closed tube, while uncovered portion of the tube is as close or as far away from the inlet end of the liquid. Comparing both indicators of permeability.

APPENDIX B (mandatory). FLUID FOR TESTING

APPENDIX B
(required)

In most cases, to use gases more convenient than liquid. Difficulties arising from the application of fluids, are as follows:

it is difficult to remove all the debris that can get into the pores of the porous metal and thus change the permeability;

dissolved gases can be released in the pores, causing the phenomenon of «blocking gas»,

the hydrostatic pressure of the fluid can cause additional difficulties in the measurement of differential pressure;

liquid is more expensive and inconvenient to work with.

some metals can react with the adsorption of some liquids, resulting in decreased pore size;

due to the effects of capillarity and surface activity of the degree of wetting of the surface of the porous material can affect the observed permeability, especially in the case of porous metals with small pore sizes.

In rare cases, use liquid, if required determination of permeability using a specific fluid. If said liquid is a liquid of Newton, you must meet the following conditions:

in the liquid should not be solid particles and dissolved gases;

all the porous metal must be soaked in liquid, not allowed the formation of gas bubbles on the surfaces and in the pores of the test sample from the porous metal.

When the pores are large, the results of determination of permeability obtained when using gases and liquids, as a rule, coincide. Therefore, gases to use better than the liquid.

In the case of the use of gas increases the likelihood of inertial losses and so it is recommended to use equation (A. 2) Appendix A.