1、BS ISO 3966:2008ICS 17.120.10NO COPYING WITHOUT BSI PERMISSION EXCEPT AS PERMITTED BY COPYRIGHT LAWBRITISH STANDARDMeasurement offluid flow in closedconduits Velocityarea method usingPitot static tubesThis British Standardwas published under theauthority of the StandardsPolicy and StrategyCommittee
2、on 31 August2008 BSI 2008ISBN 978 0 580 62863 4Amendments/corrigenda issued since publicationDate CommentsBS ISO 3966:2008National forewordThis British Standard is the UK implementation of ISO 3966:2008. Itsupersedes BS 1042-2.1:1983 which is withdrawn.The UK participation in its preparation was ent
3、rusted to TechnicalCommittee CPI/30/5, Velocity based methods.A list of organizations represented on this committee can be obtained onrequest to its secretary.This publication does not purport to include all the necessary provisionsof a contract. Users are responsible for its correct application.Com
4、pliance with a British Standard cannot confer immunityfrom legal obligations.BS ISO 3966:2008Reference numberISO 3966:2008(E)ISO 2008INTERNATIONAL STANDARD ISO3966Second edition2008-07-15Measurement of fluid flow in closed conduits Velocity area method using Pitot static tubes Mesurage du dbit des f
5、luides dans les conduites fermes Mthode dexploration du champ des vitesses au moyen de tubes de Pitot doubles BS ISO 3966:2008ISO 3966:2008(E) PDF disclaimer This PDF file may contain embedded typefaces. In accordance with Adobes licensing policy, this file may be printed or viewed but shall not be
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10、l copyrightiso.org Web www.iso.org Published in Switzerland ii ISO 2008 All rights reservedBS ISO 3966:2008ISO 3966:2008(E) ISO 2008 All rights reserved iiiContents Page Foreword iv 1 Scope . 1 2 Normative references . 1 3 Symbols and definitions 2 4 Principle. 4 5 Design of Pitot tubes 7 6 Requirem
11、ents for use of Pitot tubes. 8 7 Positioning of Pitot tube 11 8 Velocity computation 11 9 Determination of the discharge velocity by graphical integration of the velocity area 14 10 Determination of the discharge velocity by numerical integration of the velocity area . 17 11 Determination of the dis
12、charge velocity by arithmetical methods 19 12 Corrections of local velocity measurements . 23 13 Errors . 28 Annex A (normative) Pitot tubes 34 Annex B (normative) Correction to the measuring position of Pitot tubes used in a transverse velocity gradient . 39 Annex C (normative) Study concerning tur
13、bulence correction 41 Annex D (normative) Damping of pressure gauges . 44 Annex E (normative) Measurements with a Pitot tube in a compressible fluid. 46 Annex F (normative) Determination of coefficient m for extrapolation near the wall . 50 Annex G (normative) Example of calculation of the uncertain
14、ty on the flow-rate measurement by means of Pitot tubes. 51 Bibliography . 54 BS ISO 3966:2008ISO 3966:2008(E) iv ISO 2008 All rights reservedForeword ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies (ISO member bodies). The work of prep
15、aring International Standards is normally carried out through ISO technical committees. Each member body interested in a subject for which a technical committee has been established has the right to be represented on that committee. International organizations, governmental and non-governmental, in
16、liaison with ISO, also take part in the work. ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization. International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2. The main task
17、of technical committees is to prepare International Standards. Draft International Standards adopted by the technical committees are circulated to the member bodies for voting. Publication as an International Standard requires approval by at least 75 % of the member bodies casting a vote. Attention
18、is drawn to the possibility that some of the elements of this document may be the subject of patent rights. ISO shall not be held responsible for identifying any or all such patent rights. ISO 3966 was prepared by Technical Committee ISO/TC 30, Measurement of fluid flow in closed conduits, Subcommit
19、tee SC 5, Velocity and mass methods. This second edition results from the reinstatement of ISO 3966:1977 which was withdrawn in 2003 and with which it is technically identical. BS ISO 3966:2008INTERNATIONAL STANDARD ISO 3966:2008(E) ISO 2008 All rights reserved 1Measurement of fluid flow in closed c
20、onduits Velocity area method using Pitot static tubes 1 Scope This International Standard specifies a method for the determination in a closed conduit of the volume rate of flow of a regular flow: a) of a fluid of substantially constant density or corresponding to a Mach number not exceeding 0,25; b
21、) with substantially uniform stagnation temperature across the measuring cross-section; c) running full in the conduit; d) under steady flow conditions. In particular, it deals with the technology and maintenance of Pitot static tubes, with the calculation of local velocities from measured different
22、ial pressures and with the computation of the flow rate by velocity integration. 2 Normative references The following referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the r
23、eferenced document (including any amendments) applies. ISO 2186, Fluid flow in closed conduits Connections for pressure signal transmissions between primary and secondary elements ISO 7194, Measurement of fluid flow in closed conduits Velocity-area methods of flow measurement in swirling or asymmetr
24、ic flow conditions in circular ducts by means of current-meters or Pitot static tubes BS ISO 3966:2008ISO 3966:2008(E) 2 ISO 2008 All rights reserved3 Symbols and definitions 3.1 Symbols Symbol Quantity Dimensions SI unit A cross-sectional area of the conduit L2m2a, a distance of the extreme measuri
25、ng point to the nearest wall L m D pipe diameter L m d head diameter L m d steam diameter L m ditotal pressure tapping hole diameter L m H rectangular conduit height L m h height of a particular point above the bottom L m kbblockage coefficient of a cylindrical stem kgcoefficient depending on the no
26、se shape ktcoefficient of turbulence correction L rectangular conduit width L m l distance from a particular point to the side-wall L m M molar mass of fluid M kg/mol m roughness coefficient Ma Mach number p absolute static pressure of the fluid ML1T2Pa qVvolume flow rate L3T1m3/s Rgmolar constant o
27、f gas ML2T11J/molK R pipe radius L m r measuring circle radius L m Re Reynolds number S frontal projected area of the stem inside the conduit L2m2T absolute temperature K U discharge velocity LT1m/s u mean velocity along a circumference or a measurement line LT1m/sv local velocity of the fluid LT1m/
28、s X pipe dimension L m y distance of a measuring point to the wall L m Z gas law deviation factor calibration factor of the Pitot tube ratio of the specific heat capacities p differential pressure measured by the Pitot tube ML1T2Pa expansibility factor (1 ) compressibility correction factor universa
29、l coefficient for head loss dynamic viscosity of the fluid ML1T1Pas kvkinematic viscosity of the fluid L2T1m2/s head loss ML1T2Pa density of the fluid ML3kg/m3 Pitot tube inclination BS ISO 3966:2008ISO 3966:2008(E) ISO 2008 All rights reserved 33.2 Terms and definitions For the purposes of this doc
30、ument, the following terms and definitions apply. 3.2.1 Pitot static tube “Pitot tube” a tubular device consisting of a cylindrical head attached perpendicularly to a stem allowing measurement of a differential pressure from which the flow rate of the fluid in which it is inserted can be determined,
31、 and which is provided with static pressure tapping holes (drilled all around the circumference of the head at one or more cross-sections) and with a total pressure hole (facing the flow direction at the tip of the axially symmetrical nose of the head) 3.2.2 static pressure tapping a group of holes
32、for the measurement of fluid static pressure 3.2.3 total pressure tapping a hole for the measurement of fluid stagnation pressure (the pressure produced by bringing the fluid to rest without change in entropy) 3.2.4 differential pressure the difference between the pressures at the total and static p
33、ressure taps 3.2.5 stationary rake a set of Pitot tubes, mounted on one or several fixed supports, which explore the whole diameter or measuring section simultaneously 3.2.6 peripheral flow rate the volume flow rate in the area located between the pipe wall and the contour defined by the velocity me
34、asuring points which are the closest to the wall 3.2.7 discharge velocity the ratio of the volume rate of flow (integral of the axial component of local velocities with respect to the cross-sectional area) to the area of the measuring cross-section 3.2.8 relative velocity the ratio of the flow veloc
35、ity at the considered point to a reference velocity measured at the same time and being either the velocity at a particular point (e.g. the centre of a circular conduit) or the discharge velocity in the measuring section 3.2.9 straight length a conduit section, the axis of which is rectilinear and t
36、he surface and cross-section of which are constant NOTE The shape of this section is usually circular, but it may be rectangular or annular. 3.2.10 irregularity any element or configuration of a conduit which makes it different from a straight length NOTE For the purpose of this International Standa
37、rd, those irregularities which create the most significant disturbances are bends, valves, gates and sudden widening of the section. BS ISO 3966:2008ISO 3966:2008(E) 4 ISO 2008 All rights reserved4 Principle 4.1 General principle The principle of the method consists of: a) measuring the dimensions o
38、f the measuring section, which must be normal to the conduit axis this measurement is necessary for defining the area of the cross-section (see 4.2); b) defining the position of the measuring points in the cross-section, the number of measuring points having to be sufficient to permit adequate deter
39、mination of the velocity profile; c) measuring the differential pressure existing between the total and static pressures of the Pitot tube placed at these measuring points (see 4.3) and determining the density of the fluid in the test conditions; d) determining the local velocity of the flow, from g
40、iven formulae, on the basis of previous measurements (see Clause 8); e) determining the discharge velocity from these values; f) calculating the volume rate of flow equal to the product of the cross-sectional area and the discharge velocity. Errors in the techniques described in a) to f) contribute
41、to the error in the flow-rate measurement; other sources of error (such as the shape of the velocity distribution and the number of measuring points) are discussed in Clause 13. The method of measurement and the requirements defined in this International Standard aim at reaching, at the 95 % confide
42、nce level, an uncertainty in flow rate not greater than 2 %. To attain this result, it may be necessary, according to measurement conditions, to take into account the corrections given in Clause 12. If any of the requirements of this International Standard are not fulfilled, this method may still be
43、 applied in special cases but the uncertainty on flow rate will be larger. This International Standard presents three types of methods for determining the discharge velocity. 4.1.1 Graphical integration of the velocity area (see Clause 9) This method consists in plotting the velocity profile on a gr
44、aph and evaluating the area under the curve which is bounded by the measuring points closest to the wall. To the value thus obtained is added a calculated term which allows for the flow in the peripheral zone (the area between the wall and the curve through the measuring positions closest to the wal
45、l) on the assumption that the velocity profile in this zone satisfies a power law. For this method, the measuring points may be located at whichever positions are required in order to obtain a satisfactory knowledge of the velocity profile. 4.1.2 Numerical integration of the velocity area (see Claus
46、e 10) The difference between this method and 4.1.1 lies in the fact that the graphical velocity profile is replaced by an algebraic curve and the integration is carried out analytically. 4.1.3 Arithmetical methods (see Clause 11) The arithmetical methods assume that the velocity distribution follows
47、 a particular law and the mean velocity in the conduit is then given by a linear combination of the individual velocities measured at the locations specified by the method. For the arithmetical methods described in Clause 11, the assumption is made that in the peripheral zone the velocity distributi
48、on follows a logarithmic law as a function of the distance from the wall. BS ISO 3966:2008ISO 3966:2008(E) ISO 2008 All rights reserved 54.2 Measurement of the measuring cross-section 4.2.1 Circular cross-sections The mean diameter of the conduit is taken as equal to the arithmetic mean of measureme
49、nts carried out on at least four diameters (including the traverse diameters) at approximately equal angles to each other in the measuring section. Should the difference between the lengths of two consecutive diameters be greater than 0,5 %, the number of measured diameters shall be doubled. 4.2.2 Rectangular cross-sections The conduit width and height shall both be measured at least on each straight line (at least four) passing through th
