1、BSI BSx4357 PART*2 A2 W 1b2qbb7 OLb7L)b7 T BS 4359 : Part 2 : 1982 UDC 66-492.2:531.724:539.217 of this publication may be photocopied or otherwise reproduced without the prior permission in writing of BSI. / British Standard Determination of the specific surface A area of-powders O Part 2. Recommen
2、ded air permeability methods -I Oetermination de ia surface spcifique des poudres Partie 2. Mthodes recommandes de permabilit lair Bestimmung der spezifischen Oberflche von Pulvern Teil 2. Empfohlene Verfahren zur Bestimmung der Luftdurchlssigkeit British Standards Institution COPYRIGHT British Stan
3、dards Institute on ERC Specs and StandardsLicensed by Information Handling ServicesI- BSI BS*4357 PART*2 82 - Lb24bb9 01b7470 b - BS 4359 : Part 2 : 1982 Contents Foreword Cooperating organizations Methods O. Introduction 1. Scope 2. Definitions 3. Symbols 4. Principles 5. Apparatus: general 6. Prep
4、aration of the powder bed 7. Measurement of permeability 8. Variables affecting the result 9. Reporting Page Inside front cover Back cover Appendices A. Measurement of the effective solid density of a powder B. Lea and Nurse constant flow rate method C. Fisher sub-sieve sizer constant flow rate meth
5、od 1 1 1 2 3 4 7 7 8 9 10 11 12 Foreword This British Standard, prepared under the direction of the Chemical and Petroleum Engineering Standards Committee, supersedes BS 4359 : Part 2 : 1971, which is withdrawn. This revision is based on the systematic study of the methods and the comparison of the
6、results from various sources during the last ten years. Clause O details the technical changes involved in this revision. No single method of specific surface measurement can be recommended to cover the many different types of powders encountered and the circumstances of usage, but it is possible to
7、 formulate recommended procedures that may be applied to the majority of cases. The purpose of these methods is to obtain uniformity in procedure for any one of the methods selected, in order to facilitate comparisons between determinations made in different laboratories, As with other standard meth
8、ods it is advisable to check the preliminary results using standard samples. Accurate sampling of particulate material is an essential prerequisite for the determination of the specific surface D. Rigden constant volume method E. Blaine constant volume method F. Test for bed uniformity G. Sources of
9、 reference materials for ait permeability measurements Tables 1. Variation of air viscosity with temperature 2. Density of pure water, pw 3. Indicated diameter correction factors for a sample volume v1 of 1.25 cm3 Figures 1. Permeability cells 2. Lea and Nurse apparatus with pressure drop flowmeter
10、3. Schematic diagrams of Fisher sub-sieve sizer and sample tube 4. Rigden apparatus 5. Blaine apparatus Page 15 17 18 18 9 10 15 5 11 13 15 17 of powders, especially when using methods in which the test portion may be relatively small in amount. The procedures described in BS 3406 : Part 1 have been
11、 selected to prevent any alteration to the size grading of the gross sample and to avoid segregation of different sized particles when taking increments for testing purposes. The air permeability methods described in this Part of this standard are characterized by simplicity of apparatus and rapidit
12、y of measurement. The technique may therefore be readily applied to the routine control of manufacturing and sizing processes. Measurements wholly in the molecular diffusion zone are not dealt with in this standard but are under consideration for future inclusion in the BC 4359 series. It has been a
13、ssumed in the drafting of this standard that the execution of its provisions is entrusted to appropriately qualified and experienced people, for whose guidance it has been prepared. Compliance with a British Standard does not of itself confer immunity from legal obligations. COPYRIGHT British Standa
14、rds Institute on ERC Specs and StandardsLicensed by Information Handling ServicesBSI BS*4359 PART*2 82 m 3629669 O369971 8 m BS 4359 : Part 2 : 1982 British Standard Methods for Determination of specific surface of powders Part 2. Recommended air permeability methods O. Introduction Permeability met
15、hods measure a surface area of a solid volume of powder. The result is expressed in units of m2/m3. The specific surface so obtained can be converted to a mass basis by dividing by the solid density, the result being expressed in units of m2/kg. The specific surface area measured by other methods is
16、 usually different from that obtained by permeability methods (e.g. see 4.2). Also, the latter methods use the effective solid density to calculate the solid volume of powder used for measurement (see 2.2). For these reasons the specific surface obtained from permeability measure- ments is properly
17、called the effective permeability volume specific surface. However, for convenience, this correct terminology is implied, in this Part of this standard only, by the simpler term specific surface. A technical change of the basic equation used to relate permeability data to specific surface area has b
18、een made in this revision. The original standard was based on the Kozeny-Carman equation and referred the user to other publications for procedures to follow in the transitional zone between wholly viscous flow and flow due to molecular diffusion. (The extra component of flow in this transitional zo
19、ne is known as slip flow.) This revision is based on one of the equations that takes slip flow into account and the Carman-Arne11 equation has been chosen (equation 1). For coarse powders where the effect of slip flow is small, or for some industrial purposes where the value due to viscous flow alon
20、e is sufficient for quality control, that part of the Carman-Arne11 equation giving the contribution of viscous flow is identical to the Kozeny-Carman equation. When comparing the specific surfaces of materials of different densities, the effective permeability volume specific surface, S, as used th
21、roughout this standard, gives a measure of the fineness of a powder, which is what is sometimes required. 0 1. Scope This Part of this British Standard describes recommended methods for determining the permeability surface area of powders by measuring the resistance offered to the flow of air throug
22、h a compacted bed of the powder. The methods are applicable to powders with permeability volume specific surfaces in the range 2 x 104 m2/m3 to5x7m2/m3. O Four specific methods are described in appendices B to E. Use of the permeability methods is precluded when: (a) agglomerates are not easily brok
23、en down (unless the specific surface area required is that of the agglomerated form); (b) the particles fracture or undergo deformation when the powder bed is being compacted. NOTE. The titles of the publications referred to in this standard are listed on the inside back cover. 2. Definitions For th
24、e purposes of this standard, the following definitions, together with those given in BS 2955, apply. 2.1 effective solid density (pJ. The density of powder particles as determined by a given liquid displacement met hod. NOTE. See appendix A. 2.2 effective solid volume (v). The mass of the particles
25、divided by the effective solid density. 2.3 bed porosity (e). The ratio of the volume of inter- particle voids to the total bulk volume of the bed of powder used for the determination of the effective permeability specific surface. It is calculated from the mass, bulk volume and effective solid dens
26、ity of the powders in the manner described in 6.3. NOTE. The term porosity has been retained in this context because of its wide usage. It should not be confused with the internal porosity of individual powder particles, much of which is not accessible to measurement by the methods of this standard.
27、 2.4 effective permeability volume specific surface (SV). The permeability surface area per unit effective volume of the particles. NOTE. For convenience, this term is referred to as specific surface throughout the rest of this standard (see clause O). 2.5 effective permeability mass specific surfac
28、e (Sw). The effective volume specific surface divided by the effective solid density, .e. S, = S,/p,. NOTE.Sw should not be confused with the same symbol used in methods employing other principles of measurement. 2.6 viscous flow. Airflow in which adjacent layers of air do not mix except at the mole
29、cular level and when the velocity of the air at the powder interface is zero. 2.7 slip flow. Enhanced airflow caused by the air velocity at the air/powder interface not being zero as assumed for viscous flow. It becomes significant at low pressures or for very fine powders. 1 COPYRIGHT British Stand
30、ards Institute on ERC Specs and StandardsLicensed by Information Handling ServicesBS 4359 : Part 2 : 1982 2.8 molecular (Knudsen) flow. At very low pressures the mean free path of the gas molecules, h. increases and inter-molecular collisions become increasingly rare until all collisions are between
31、 the gas molecules and the void (capillary) walls. The concept of viscosity thus breaks down and molecular transfer is governed by Ficks Law of Diffusion. This regime is called the molecular flow, Knudsen flow or diffusional flow regime. 2.9 effective permeability volume surface mean diameter t,). T
32、he diameter of an imaginary solid sphere that has the same volume specific surface as the powder to which the term is applied. If a hypothetical powder is assumed, composed entirely of spheres of this diameter, the effective volume specific surface of the whole will be equivalent to that of the powd
33、er under test. 2.10 primary standard apparatus. Apparatus for the measurement of permeability specific surface that has been calibrated by calculation from the dimensions of the system. 2.1 1 secondary standard apparatus. Apparatus for the measurement of permeability specific surface that has been c
34、alibrated by the use of a powder whose specific surface has been previously determined by using a primary standard apparatus. 3. Symbols For the purposes of this standard, the following symbols apply. Symbol A a B b C C dm dl S“ h hl hi # K Quantity cross-sectional area of a bed of powder perpendicu
35、lar to the direction of the flow of air manometric cross-sectional area of a constant volume apparatus atmospheric pressure at the time of the determination as indicated by a height of manometer liquid error in t (see 8.7) constant of a capillary flowmeter error in either pL or h (see 8.6) effective
36、 permeability volume surface mean diameter particle diameter indicated on the Fisher sub-sieve sizes chart (d, = d, when 1 cm3 of powder is used in the determination) local acceleration due to gravity pressure difference across a bed of powder as indicated by a height of manometer liquid pressure di
37、fference across a capillary flowmeter resistance as indicated by a height of mano- meter liquid manometric heights corresponding to the first and second timing Unit or value m2 m2 m % dimensionless % IJm Cim 9.8 m m m/s2 marks in a constant volume method m Kozeny constant dimensionless (see 4.1.2) Q
38、uantity apparatus constant, representing all the factors in a specific surface/permeability relationship that are derived solely from the apparatus dimensions apparatus constant for a constant volume apparatus used with a fixed volume cell and a constant bed porosity linear dimension of a bed of pow
39、der parallel to the direction of the flow of air (commonly known as the height of the powder bed) mean molecular mass of air atmospheric pressure at the time of the determination pressure of air leaving the bed of powder pressure of air entering the bed of powder water vapour pressure at the tempera
40、ture of test pressure difference across a bed of powder rate of flow of an incompressible fluid through a bed of powder rate of flow of air from a bed of powder rate of flow of air into a bed of powder universal gas constant effective permeability volume specific surface of a powder effective permea
41、bility mass specific surface of a powder effective permeability volume specific surface of a powder assuming only viscous flow occurs in the determination effective permeability volume specific surface of a powder assuming only slip-flow occurs in the determination temperature at the time of the det
42、ermination time volume of dry air passed through a constant flow rate apparatus during the determination (or during calibration of a capillary flow meter) volume of a constant volume apparatus between the manometer equilibrium level and the bottom of the powder bed effective solid volume of a powder
43、 sample Unit or value d i m ension less dimensionless m 0.029 kg Pa Pa Pa Pa Pa m3 Is m3 /s m3 Is 8.31 J/(K.mol) m2 /m3 m2 /kg m2 /m3 m2 /m3 K S m3 m3 m3 2 COPYRIGHT British Standards Institute on ERC Specs and StandardsLicensed by Information Handling ServicesSymbol Quantity Unit or value “1 effect
44、ive solid volume of a powder sample used in the Fisher sub-sieve sizer cm3 W mass of a bed of powder g Wl mass of pure water to fill a density bottle at the selected operating temperature g mass of displacement liquid to fill a density bottle at the selected operating temperature 9 W2 plus the mass
45、of the empty density bottle 9 mass of sample used to determine the effective solid density of a powder 9 W, plus the mass of the empty density bottle and the displacement liquid to fill the bottle at the selected operating temperature g X (see figure 3) m X error in A (see 8.3) % Y error in L (see 8
46、.3) % z error in ps (see 8.4) % k, constant in the Carman-Arne11 2.25 equation (comprising and k,) E porosity of a bed of powder dimensionless El porosity of a bed of powder indicated on the Fisher sub-sieve sizer dimensionless viscosity of air at its temperature at the time of the determination den
47、sity of the displacement liquid used in the measurement of effective solid density kg/m3 density of a manometer liquid during the determination at the selected operating temperature kg/m3 PS effective solid density of a powder kg/m3 pw density of pure water during the calibration of a density bottle
48、 at the selected operating temperature kg/m3 NOTE 1. All the equations given in this standard are true for SI units or any set of coherent units, except those involving vl, which is measured in cm3. If practical units are used, the appropriate correction factors should be made to the equations. NOTE
49、 2.1 Pa = 1 N/ma. W2 W3 W, W, (see 4.1.3) 1) h mean free path of gas molecules m pDL N-s/rn2 “ 4. Principles 4.1 Carmen-Arnell equation 4.1.1 Basic equation. The rate of flow of a fluid moving under the influence of a constant pressure difference through a compacted bed of powder of uniform cross-sectional area is a function of the magnitude of the surface area that the walls of the channels through the bed present to the moving fluid. Because there is normally a great variation in, and a lack of precise knowledge of, BS 4359 : Part 2 : 1982 the shape and dimensions
