1、BRITISH STANDARD BS EN ISO 9300:2005 Measurement of gas flow by means of critical flow Venturi nozzles The European Standard EN ISO 9300:2005 has the status of a British Standard ICS 17.120.10 BS EN ISO 9300:2005 This British Standard was published under the authority of the Standards Policy and Str
2、ategy Committee on 21 October 2005 BSI 21 October 2005 ISBN 0 580 46705 8 National foreword This British Standard is the official English language version of EN ISO 9300:2005. It is identical with ISO 9300:2005. It supersedes BS EN ISO 9300:1995 which is withdrawn. The UK participation in its prepar
3、ation was entrusted by Technical Committee CPI/30, Measurement of fluid flow in closed conduits, to Subcommittee CPI/30/2, Differential pressure methods, which has the responsibility to: A list of organizations represented on this subcommittee can be obtained on request to its secretary. Cross-refer
4、ences The British Standards which implement international or European publications referred to in this document may be found in the BSI Catalogue under the section entitled “International Standards Correspondence Index”, or by using the “Search” facility of the BSI Electronic Catalogue or of British
5、 Standards Online. This publication does not purport to include all the necessary provisions of a contract. Users are responsible for its correct application. Compliance with a British Standard does not of itself confer immunity from legal obligations. aid enquirers to understand the text; present t
6、o the responsible international/European committee any enquiries on the interpretation, or proposals for change, and keep UK interests informed; monitor related international and European developments and promulgate them in the UK. Summary of pages This document comprises a front cover, an inside fr
7、ont cover, the EN ISO title page, the EN ISO foreword page, the ISO title page, pages ii to iv, pages 1 to 38, an inside back cover and a back cover. The BSI copyright notice displayed in this document indicates when the document was last issued. Amendments issued since publication Amd. No. Date Com
8、mentsEUROPEANSTANDARD NORMEEUROPENNE EUROPISCHENORM ENISO9300 August2005 ICS17.120.10 SupersedesENISO9300:1995 EnglishVersion MeasurementofgasflowbymeansofcriticalflowVenturi nozzles(ISO9300:2005) MesurededbitdegazaumoyendeVenturituyresen rgimecritique(ISO9300:2005) DurchflussmessungvonGasenmitVentu
9、ridsenbei kritischerStrmung(ISO9300:2005) ThisEuropeanStandardwasapprovedbyCENon15July2005. CENmembersareboundtocomplywiththeCEN/CENELECInternalRegulationswhichstipulatetheconditionsforgivingthisEurope an Standardthestatusofanationalstandardwithoutanyalteration.Uptodatelistsandbibliographicalreferen
10、cesconcernings uchnational standardsmaybeobtainedonapplicationtotheCentralSecretariatortoanyCENmember. ThisEuropeanStandardexistsinthreeofficialversions(English,French,German).Aversioninanyotherlanguagemadebytra nslation undertheresponsibilityofaCENmemberintoitsownlanguageandnotifiedtotheCentralSecr
11、etariathasthesamestatusast heofficial versions. CENmembersarethenationalstandardsbodiesofAustria,Belgium,Cyprus,CzechRepublic,Denmark,Estonia,Finland,France, Germany,Greece,Hungary,Iceland,Ireland,Italy,Latvia,Lithuania,Luxembourg,Malta,Netherlands,Norway,Poland,Portugal, Slovakia, Slovenia,Spain,Sw
12、eden,SwitzerlandandUnitedKingdom. EUROPEANCOMMITTEEFORSTANDARDIZATION COMITEUROPENDENORMALISATION EUROPISCHESKOMITEEFRNORMUNG ManagementCentre:ruedeStassart,36B1050Brussels 2005CEN Allrightsofexploitationinanyformandbyanymeansreserved worldwideforCENnationalMembers. Ref.No.ENISO9300:2005:E EN ISO 93
13、00:2005 2 Foreword This document (EN ISO 9300:2005) has been prepared by Technical Committee ISO/TC 30 “Measurement of fluid flow in closed conduits“ in collaboration with CMC. This European Standard shall be given the status of a national standard, either by publication of an identical text or by e
14、ndorsement, at the latest by February 2006, and conflicting national standards shall be withdrawn at the latest by February 2006. This document supersedes EN ISO 9300:1995. According to the CEN/CENELEC Internal Regulations, the national standards organizations of the following countries are bound to
15、 implement this European Standard: Austria, Belgium, Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Slovakia, Slovenia, Spain, Sweden, Switzerland and United Ki
16、ngdom. Endorsement notice The text of ISO 9300:2005 has been approved by CEN as EN ISO 9300:2005 without any modifications. Reference number ISO 9300:2005(E)INTERNATIONAL STANDARD ISO 9300 Second edition 2005-08-15 Measurement of gas flow by means of critical flow Venturi nozzles Mesure de dbit de g
17、az au moyen de Venturi-tuyres en rgime critique EN ISO 9300:2005 ii EN ISO 9300:2005 iii Contents Page Foreword iv 1 Scope . 1 2 Terms and definitions. 1 2.1 Pressure measurement 1 2.2 Temperature measurement 2 2.3 Venturi nozzles 2 2.4 Flow 2 3 Symbols . 5 4 Basic equations 6 4.1 State equation . 6
18、 4.2 Flow-rate under ideal conditions 6 4.3 Flow-rate under real conditions 6 4.4 Critical mass flux 7 5 Applications for which the method is suitable 7 6 Standard critical flow Venturi nozzles (CFVN). 7 6.1 General requirements. 7 6.2 Design 8 7 Installation requirements . 11 7.1 General. 11 7.2 Up
19、stream pipeline. 11 7.3 Large upstream space 12 7.4 Downstream requirements 12 7.5 Pressure measurement 12 7.6 Drain holes 13 7.7 Temperature measurement 13 7.8 Density measurement. 13 7.9 Calculated density 14 8 Calculation methods. 14 8.1 Mass flow-rate . 14 8.2 Discharge coefficient, C d 14 8.3 C
20、ritical flow function, C , and real gas critical flow coefficient, C R15 8.4 Conversion of measured pressure and temperature to stagnation conditions. 15 8.5 Maximum permissible downstream pressure 16 9 Uncertainties in the measurement of flow-rate . 17 9.1 General. 17 9.2 Practical computation of u
21、ncertainty . 18 Annex A (normative) Venturi nozzle discharge coefficients . 19 Annex B (normative) Tables of values for critical flow function C Various gases 21 Annex C (normative) Computation of critical mass flux for natural gas mixtures 28 Annex D (normative) Mass flow correction factor for atmo
22、spheric air 32 Annex E (normative) Computation of critical mass flux for critical flow nozzles with high nozzle throat to upstream pipe diameter ratio, 0,25 33 Bibliography . 36 EN ISO 9300:2005 iv Foreword ISO (the International Organization for Standardization) is a worldwide federation of nationa
23、l standards bodies (ISO member bodies). The work of preparing 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. Internation
24、al organizations, governmental and non-governmental, in 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
25、 given in the ISO/IEC Directives, Part 2. The main task 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 le
26、ast 75 % of the member bodies casting a vote. Attention 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 9300 was prepared by Technical Committee ISO/TC 30,
27、 Measurement of fluid flow in closed conduits, Subcommittee SC 2, Pressure differential devices. This second edition cancels and replaces the first edition (ISO 9300:1990), which has been technically revised. 1 Measurement of gas flow by means of critical flow Venturi nozzles 1 Scope This Internatio
28、nal Standard specifies the geometry and method of use (installation in a system and operating conditions) of critical flow Venturi nozzles (CFVN) used to determine the mass flow-rate of a gas flowing through a system. It also gives the information necessary for calculating the flow-rate and its asso
29、ciated uncertainty. It is applicable to Venturi nozzles in which the gas flow accelerates to the critical velocity at the throat (this being equal to the local sonic velocity), and only where there is steady flow of single-phase gases. At the critical velocity, the mass flow-rate of the gas flowing
30、through the Venturi nozzle is the maximum possible for the existing upstream conditions while CFVN can only be used within specified limits, e.g. Iimits for the nozzle throat to inlet diameter ratio and throat Reynolds number. This International Standard deals with CFVN for which direct calibration
31、experiments have been made in sufficient number to enable the resulting coefficients to be used with certain predictable limits of uncertainty. Information is given for cases where the pipeline upstream of the CFVN is of circular cross-section, or it can be assumed that there is a large space upstre
32、am of the CFVN or upstream of a set of CFVN mounted in a cluster. The cluster configuration offers the possibility of installing CFVN in parallel, thereby achieving high flow-rates. For high-accuracy measurement, accurately machined Venturi nozzles are described for low Reynolds number applications.
33、 2 Terms and definitions For the purposes of this document, the following terms and definitions apply. 2.1 Pressure measurement 2.1.1 wall pressure tapping hole drilled in the wall of a conduit in such a way that the edge of the hole is flush with the internal surface of the conduit NOTE The tapping
34、 is achieved such that the pressure within the hole is the static pressure at that point in the conduit. 2.1.2 static pressure of a gas actual pressure of the flowing gas which can be measured by connecting a pressure gauge to a wall pressure tapping NOTE Only the value of the absolute static pressu
35、re is used in this International Standard. 2.1.3 stagnation pressure pressure which would exist in a gas in a flowing gas stream if the stream were brought to rest by an isentropic process NOTE Only the value of the absolute stagnation pressure is used in this International Standard. EN ISO 9300:200
36、5 2 2.2 Temperature measurement 2.2.1 static temperature actual temperature of a flowing gas NOTE Only the value of the absolute static temperature is used in this International Standard. 2.2.2 stagnation temperature temperature which would exist in a gas in a flowing gas stream if the stream were b
37、rought to rest by an isentropic process NOTE Only the value of the absolute stagnation temperature is used in this International Standard. 2.3 Venturi nozzles 2.3.1 Venturi nozzle convergent/divergent restriction inserted in a system intended for the measurement of flow-rate 2.3.2 normally machined
38、Venturi nozzle Venturi nozzle machined by a lathe and surface polished to achieve the desired smoothness 2.3.3 accurately machined Venturi nozzle Venturi nozzle machined by a super-accurate lathe to achieve a mirror finish without polishing 2.3.4 throat section of minimum diameter of a Venturi nozzl
39、e 2.3.5 critical flow Venturi nozzle CFVN Venturi nozzle for which the nozzle geometrical configuration and conditions of use are such that the flow-rate is critical at the nozzle throat 2.4 Flow 2.4.1 mass flow-rate q mmass of gas per unit time passing through the CFVN NOTE In this International St
40、andard, the term flow-rate always refers to mass flow-rate. 2.4.2 throat Reynolds number Re ntdimensionless parameter calculated from the gas flow-rate and the gas dynamic viscosity at nozzle inlet stagnation conditions NOTE The characteristic dimension is taken as the throat diameter at stagnation
41、conditions. The throat Reynolds number is given by the formula: nt 0 4 m q Re d = EN ISO 9300:2005 3 2.4.3 isentropic exponent ratio of the relative variation in pressure to the corresponding relative variation in density under elementary reversible adiabatic (isentropic) transformation conditions N
42、OTE 1 The isentropic exponent is given by the formula: 2 s d d pc pp = where p is the absolute static pressure of the gas; is the density of the gas; c is the local speed of sound; s signifies “at constant entropy”. NOTE 2 For an ideal gas, is equal to the ratio of specific heat capacities and is eq
43、ual to 5/3 for monatomic gases, 7/5 for diatomic gases, 9/7 for triatomic gases, etc. NOTE 3 In real gases, the forces exerted between molecules as well as the volume occupied by the molecules have a significant effect on the gas behaviour. In an ideal gas, intermolecular forces and the volume occup
44、ied by the molecules can be neglected. 2.4.4 discharge coefficient C ddimensionless ratio of the actual flow-rate to the ideal flow-rate of non-viscous gas that would be obtained with one-dimensional isentropic flow for the same upstream stagnation conditions NOTE This coefficient corrects for visco
45、us and flow field curvature effects. For each type of nozzle design and installation conditions specified in this International Standard, it is only a function of the throat Reynolds number. 2.4.5 critical flow maximum flow-rate for a particular Venturi nozzle, which can exist for the given upstream
46、 conditions NOTE When critical flow exists, the throat velocity is equal to the local value of the speed of sound (acoustic velocity), the velocity at which small pressure disturbances propagate. 2.4.6 critical flow function C dimensionless function which characterises the thermodynamic flow propert
47、ies of an isentropic and one- dimensional flow between the inlet and the throat of a Venturi nozzle NOTE It is a function of the nature of the gas and of stagnation conditions (see 4.2). 2.4.7 real gas critical flow coefficient C Ralternative form of the critical flow function, more convenient for g
48、as mixtures NOTE It is related to the critical flow function as follows: R CCZ = EN ISO 9300:2005 4 2.4.8 critical pressure ratio r ratio of the static pressure at the nozzle throat to the stagnation pressure for which the gas mass flow-rate through the nozzle is a maximum NOTE This ratio is calculated in accordance with the equation given in 8.5. 2.4.9 back-pressure ratio ratio of the nozzle exit static pressure to the nozzle upstream stagnation pressure 2.4.10 Mach number Ma at nozzle upstream static conditions
