ISO-4638-1984.pdf
《ISO-4638-1984.pdf》由会员分享,可在线阅读,更多相关《ISO-4638-1984.pdf(9页珍藏版)》请在三一文库上搜索。
1、International Standard 4638 0 N 4 a! INTERNATIONAL ORGANIZATION FOR STANDAROIZATIONMEYHAPOAHAR OPrAHbl3AUbiR IlO CTAHIIAPTH3AUblM.ORGANlSATlON INTERNATIONALE DE NORMALISATION Polymeric materials, cellular flexible - Determination of air flow permeability Mathriaux polym b) in ensuring product qualit
2、y (quality assurance). NOTE - Details of publications relating to flow behaviour in both laminar and turbulent conditions are given in a bibliography. 1 Scope and field of application This International Standard specifies a method for the deter- mination of the permeability of flexible cellular poly
3、meric materials to air flow. It is applicable to test pieces cut from products of cellular material. NOTE - IS0 7231, Polymeric materials, cellular flexible - Method of assessment of air flow value at constant pressure drop, ) specifies a simple quality control method which is also based on the flow
4、 of air through cellular materials. This can be used when it is not the intention to calculate the intrinsic properties of various materials in order to com- pare them, but merely to control the quality of a given cellular material. 2 References IS0 471, Rubber - Standard temperatures, humidities an
5、d times for the conditioning and testing of test pieces. IS0 845, Cellular rubbers and plastics - Determination of ap- parent density. 3 Principle Passing air under controlled conditions through a test piece in the form of a cylinder or parallelepiped. Measurement of the pressure drop between the tw
6、o free faces of the test piece. 4 Symbols and terminology 4.1 Air flow permeability, K, is given by Darcy s law (see figure I), which describes the air flow in a homogeneous and isotropic (see note I) porous medium under laminar flow condi- tions (see note 2) by the equation qv KAP u=-=- A t16 where
7、 u is the linear air flow velocity, in metres per second; qv is the volumetric air flow rate, in cubic metres per second, crossing the test piece; A is the right cross-sectional area, in square metres, of the test piece ; K is the flow permeability, in square metres, of the porous medium ; Ap is the
8、 pressure drop, in pascals, across the test piece; q is the dynamic viscosity, in Pascal seconds, of air; 6 is the thickness, in metres, of the test piece. NOTES 1 For anisotropic materials, it is necessary to define the direction of the flow. 2 For the flow of air to be laminar in the interior of t
9、he porous medium, it is necessary for the following conditions to be fulfilled : Re* = % n V where Re* is the modified Reynolds number; v is the kinematic viscosity, in square metres per second, of air; 1) At present at the stage of draft. -,-,- IS0 4538-1994 (El q is a limiting value depending on t
10、he structure of the product. In the absence of precise data on this subject, it is sufficient to use several very low air flow rates of the order of centimetres per second, on a single type of material, to verify that K does not vary or varies only slightly, with changes in u (see 9.1). 4.2 Specific
11、 air flow resistance, R, is a parameter derived from the permeability of a material, used particularly in the field of acoustics, and is derived from permeability by the equation R, =$- It is expressed in Pascal seconds per square metre (Pa.s-m-2). 4.3 Air flow resistance, R, is related to the thick
12、ness of the material 6, whether it is homogeneous or not (it may even con- sist of a skinned surface or a coating which is more or less porous, such as paint etc.). If the material is homogeneous it is proportional to the specific air flow resistance by the relation- ship R = square of side 50 or 10
13、0 mm). Then II, in metres per second, is equal to 400 qvor 100 qVdepending on whether the small or the large test piece is used. Calculations in clause 9 are facilitated if the area of the test piece is standardized at 18,5 cm2 M8,5 mm diameter; square of side 45 mm) and the thickness of the test pi
14、ece is 100 mm. Then K2K AP 5.2 Means of providing air flow 5.2.1 Source It is recommended that pressure depression systems, of the water reservoir or vacuum pump type, should be used. Alter- natively, pressurization systems (air compressor, etc.) may be used. Whatever source is used, the installatio
15、n shall permit fine control of the flow and shall ensure the stability of the flow in the lower part of the test cell. 5.2.2 Characteristics of the flow The source shall provide a volumetric air flow rate, qv, equal to uA cubic metres per second. The area chosen for the cell, A, shall be within the
16、limits in- dicated in 5.1 and the source shall permit air flow velocities up to Xl mm- to be obtained. For example, for cylindrical specimens of diameters between 50 and 120 mm, and with an air flow velocity of the order of 10m2 rnms-l, the volumetric air flow rate through the apparatus will be appr
17、oximately between 1 dm3.min - 1 and 7 dm3m min - I, The source shall have sufficient stability so that the instan- taneous volumetric air flow rate may be estimated to better than f2,5 %, and so that the change in flow rate with time does not exceed 1 % per minute. 5.3 Means of measuring volumetric
18、flow rate The instrument for measuring the volumetric air flow rate shall be placed between the source and the test piece, as close as possible to the test piece. It shall be selected from a type capable of measuring the values of flow indicated in 5.2.2. 2 -,-,- IS0 4636-1964 (El The arrangement us
19、ed shall permit measurement of the flow with an accuracy of +2 % of the full scale value. The arrangement may be, for example, an assembly of flow- meters arranged in parallel, one of which can be selected to suit the required range of measurement. By analogy, in the case of a test piece which is a
20、rectangular parallelepiped of side L, in millimetres, after cutting, the side of the right cross-section of the measurement cell being L, in millimetres, then the relationship required is L = (L, + 2) 5 1 The flowmeter used for any measurement shall allow reading of the volumetric air flow rate at a
21、 graduation between 20 and 100 % of the full scale value of the meter. Calibrated flowmeters with a scale at least 250 mm long are recommended. 6.2.2 Thickness The thickness of the test piece shall be chosen to obtain pressure drops measurable under optimum conditions (see 8.8) and to suit the usabl
22、e depth of the measurement cell (see 5.1). 5.4 Means of measuring pressure drop The apparatus used for measuring differential pressures shall permit measurements of pressure drops as small as 1 Pa. In- clined water or alcohol manometers or any other apparatus allowing readings with an accuracy of 0,
23、5 Pa may be used. If the test pieces available are not sufficientlythick to produce a suitable pressure drop, not more than five test pieces, chosen in the same way, may be superimposed. In general, thicknesses between 50 and 100 mm are sufficient. 5.3 Preparation 5.5 Means of measuring test piece t
- 配套讲稿:
如PPT文件的首页显示word图标,表示该PPT已包含配套word讲稿。双击word图标可打开word文档。
- 特殊限制:
部分文档作品中含有的国旗、国徽等图片,仅作为作品整体效果示例展示,禁止商用。设计者仅对作品中独创性部分享有著作权。
- 关 键 词:
- ISO 4638 1984
链接地址:https://www.31doc.com/p-3777859.html