1、AN AMERICAN NATIONAL STANDARD ASME MFC-72016Revision and Redesignation of ASME/ANSI MFC-7M1987 (R2014)Measurement of Gas Flow by Means of Critical Flow Venturis and Critical Flow NozzlesASME MFC-72016Revision and Redesignation of ASME/ANSI MFC-7M1987 (R2014)Measurement of GasFlow by Means ofCritical
2、 Flow Venturisand Critical FlowNozzlesAN AMERICAN NATIONAL STANDARDTwo Park Avenue New York, NY 10016 USADate of Issuance: August 31, 2016This Standard will be revised when the Society approves the issuance of a new edition.ASME issues written replies to inquiries concerning interpretations of techn
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11、nd policies, which precludes the issuance of interpretations by individuals.No part of this document may be reproduced in any form,in an electronic retrieval system or otherwise,without the prior written permission of the publisher.The American Society of Mechanical EngineersTwo Park Avenue, New Yor
12、k, NY 10016-5990Copyright 2016 byTHE AMERICAN SOCIETY OF MECHANICAL ENGINEERSAll rights reservedPrinted in U.S.A.CONTENTSForeword ivStandards Committee Roster . vCommittee Correspondence vi1 Scope and Field of Application . 12 References 13 Symbols and Definitions . 14 Basic Equations . 55 Applicati
13、ons for Which the Method Is Suitable 66 Standard Critical Flow Venturis . 67 Installation Requirements 98 Calculation Methods. 129 Uncertainty of CFV Flow Measurements . 18Figures6.2.1-1 Toroidal Throat CFV Geometry . 86.2.2-1 Cylindrical Throat CFV Geometry 97.1-1 Inlet Conduit Schematic 107.5-1 Pr
14、essure Tap Schematic . 118.2-1 Percent Difference Between the Ideal Gas Critical Flow Function, Ci*, andthe Real Gas Critical Flow Function, CR*, at T0p 295K. 148.2-2 Percent Difference Between the Polytropic Gas Critical Flow Function, Cp*,and the Real Gas Critical Flow Function, CR*, at T0p 295K 1
15、58.3-1 Difference Between Static and Stagnation Pressure for Various Beta Ratiosand Isentropic Exponent Values 178.4-1 Recommended Maximum Back Pressure Ratio Versus Diffuser Area Ratiofor Various Isentropic Exponent Values . 189.2-1 Percent Uncertainty in CFV Throat Area due to Uncertainty in Throa
16、t DiameterMeasurement 20Tables3.1-1 Nomenclature Used in This Standard . 28.1-1 Coefficients for Calculating Empirical CdValues . 12Nonmandatory AppendicesA CFV Discharge Coefficients . 23B Example Flow and Uncertainty Calculations 25C CFV Mass Flow Equation and Real Gas Critical Flow Function 35D H
17、umid Air Composition . 41E CFV Unchoking Test Procedure . 47iiiFOREWORDThis Standard was prepared by Subcommittee 7 (SC 7) of the ASME Standards Committee onMeasurement of Fluid Flow in Closed Conduits; it has been revised from ASME MFC-7M1987 inits entirety.During the preparation,reference was made
18、 toolder ASME standardsand documents,including ASME MFC-3M2004 and ASME PTC 19.5-2004, and to international standards includ-ingISO9300:2005andISO/IECGuide98-3:2008.Inaddition,informationwasgatheredfrommanypublishedpapersandfromtheexperienceoftheSubcommitteemembersandotherknowledgeableengineers. Thi
19、s standard is a blend of the available technical information and best practices, andit is intended to be a practical guide to the proper use of critical flow venturis (CFV) and criticalflow nozzles (CFN).Changes made during the revision of this Standard are summarized as follows:(a) The Scope and Fi
20、eld of Application was revised to clarify usage of the terms “critical flowventuri” and “critical flow nozzle.”(b) Afewsymbolsanddefinitionshavebeenadded,andmanyhavebeenclarifiedandupdated.(c) Manufacturing tolerances have been updated to be more verifiable and to accommodatesmaller CFVs.(d) The dis
21、charge coefficient equations have been brought into alignment with extensiveresearch results and ISO 9300.(e) Recommendations for the calculation of thermophysical properties have been directedalmost entirely toward the NIST Reference Fluid Thermodynamic and Transport PropertiesDatabase (REFPROP), w
22、hich is maintained by the National Institute of Standards and Technology(NIST).(f) Uncertainty calculation methods have been extensively modified to be consistent with moremodern methods and ISO/IEC Guide 98-3:2008. A statement of uncertainty is now required inorder to be compliant with this Standar
23、d.(g) The Nonmandatory Appendices have been modified to provide two new comprehensiveexamples, including uncertainty calculation, and to derive and clarify the mass flow equation,the real gas critical flow function, other gas property calculations, and humid air considerations.(h) An “unchoking test
24、 procedure” is provided in a Nonmandatory Appendix.Critical flow venturis are especially suited as transfer standards and reference flowmeters forcalibration and testing and for precise flow control applications. CFVs provide a stable flow ofcompressible fluids, and per this Standard can and should
25、be associated with a precise statementof uncertainty for the measured flow. Although this Standard is a complete guide that providesspecific requirements and methods for the proper use of CFVs and CFNs, some latitude andvariations in application are allowed if necessary tests are performed and prope
26、r judgment isapplied.Suggestions for improvement of this Standard will be welcomed. They should be sent to TheAmerican Society of Mechanical Engineers; Attn: Secretary, MFC Main Committee;Two Park Avenue; New York, NY 10016-5990.This revision was approved as an American National Standard on January
27、6, 2016.ivASME MFC COMMITTEEMeasurement of Fluid Flow in Closed Conduits(The following is the roster of the Committee at the time of approval of this Standard.)STANDARDS COMMITTEE OFFICERSD. C. Wyatt, ChairR. J. DeBoom, Vice ChairC. J. Gomez, SecretarySTANDARDS COMMITTEE PERSONNELR. M. Bough, Rolls-
28、Royce Corp.M. S. Carter, Flow Systems, Inc.R. J. DeBoom, ConsultantC. J. Gomez, The American Society of Mechanical EngineersF. D. Goodson, Emerson Process ManagementW. M. Mattar, Invensys/Foxboro Co.G. E. Mattingly, ConsultantA. M. Quraishi, American Gas AssociationR. N. Steven, Colorado Engineering
29、 Experiment Station, Inc.D. E. Wiklund, Emerson Process Management RosemountDivisionD. C. Wyatt, Wyatt EngineeringSUBCOMMITTEE 7 CRITICAL FLOWMETERSM. S. Carter, Chair, Flow Systems, Inc.C. L. Britton, ConsultantR. W. Caron, Visteon Corp.R. J. DeBoom, ConsultantR. H. Dieck, Ron Dieck Associates, Inc
30、.A. N. Johnson, NISTvD. Faber, Contributing Member, Faber however, they should not contain proprietary names or information.viRequests that are not in the format described above may be rewritten in the appropriate formatby the Committee prior to being answered, which may inadvertently change the int
31、ent of theoriginal request.ASME procedures provide for reconsideration of any interpretation when or if additionalinformation that might affect an interpretation is available. Further, persons aggrieved by aninterpretation may appeal to the cognizant ASME Committee or Subcommittee. ASME does not“app
32、rove,” “certify,” “rate,” or “endorse” any item, construction, proprietary device, or activity.Attending Committee Meetings. The MFC Standards Committee regularly holds meetingsand/or telephone conferences that are open to the public. Persons wishing to attend any meetingand/or telephone conference
33、should contact the Secretary of the MFC Standards Committee.Future Committee meeting dates and locations can be found on the Committee Page atgo.asme.org/MFCcommittee.viiINTENTIONALLY LEFT BLANKviiiASME MFC-72016MEASUREMENT OF GAS FLOW BY MEANS OF CRITICAL FLOWVENTURIS AND CRITICAL FLOW NOZZLES1 SCO
34、PE AND FIELD OF APPLICATIONThis Standard applies only to the steady flow of single-phase gases through critical flow venturis (CFV) of shapesspecified herein also sometimes referred to as critical flow nozzles (CFN), sonic nozzles, or critical flow venturinozzles. This Standard applies to CFVs with
35、diverging sections on the downstream side of the throat. When aCFN (no diverging section) is discussed, it is explicitly noted. This Standard specifies the method of use (installationand operating conditions) of CFVs. This Standard also gives information necessary for calculating the mass flowof the
36、 gas and its associated uncertainty.This Standard applies only to CFVs and CFNs in which the flow is critical. Critical flow exists when the massflow through the CFV is the maximum possible for the existing upstream conditions. At critical flow or chokedconditions, the average gas velocity at the CF
37、V throat closely approximates the local sonic velocity.This Standard specifically applies to cases in which(a) it can be assumed that there is a large volume upstream of the CFV or upstream of a set of CFVs mountedin a parallel flow arrangement (in a common plenum), thereby achieving higher flow; or
38、(b) the pipeline upstream of the CFV is of circular cross section with throat to pipe diameter ratio equal to orless than 0.252 REFERENCESThe following publications are referenced in this Standard. The latest edition of ASME publications should be used.ASME MFC-3M, Measurement of Fluid Flow in Pipes
39、 Using Orifice, Nozzle, and VenturiASME PTC 19.5, Flow MeasurementPublisher: The American Society of Mechanical Engineers (ASME), Two Park Avenue, New York, NY 10016-5990(www.asme.org)ISO 9300:2005, Measurement of gas flow by means of critical flow Venturi nozzlesISO/IEC Guide 98-3:2008, Uncertainty
40、 of measurementPart 3: Guide to the expression of uncertainty inmeasurementPublisher: International Organization for Standardization (ISO) Central Secretariat, Chemin de Blandonnet 8, CasePostale 401, 1214 Vernier, Geneva, Switzerland (www.iso.org)NIST Standard Reference Database 23, NIST Reference
41、Fluid Thermodynamic and Transport Properties Database(REFPROP): Version 9.1Publisher: National Institute of Standards and Technology (NIST), 100 Bureau Drive, Stop 1070, Gaithersburg,MD 20899 (www.nist.gov)3 SYMBOLS AND DEFINITIONS3.1 Symbols and NomenclatureSee Table 3.1-1.3.2 Definitions3.2.1 Temp
42、erature Measurementmeasured gas temperature: temperature of the gas after being irreversibly brought to rest against the temperatureprobe.1ASME MFC-72016Table 3.1-1 Nomenclature Used in This StandardSymbol Name Dimensions SI Unit U.S. Customary UnitA* Area of CFV throat L2m2ft2A2Area of CFV exit L2m
43、2ft2b0, b1, n Coefficients for empirical Cdequation Dimensionless Dimensionless Dimensionlessc Sound speed LT1m/s ft/secCdDischarge coefficient Dimensionless Dimensionless DimensionlessC*iIdeal gas critical flow function Dimensionless Dimensionless DimensionlessC*PPolytropic gas critical flow functi
44、on Dimensionless Dimensionless DimensionlessC*RReal gas critical flow function Dimensionless Dimensionless DimensionlesscpConstant pressure specific heat L2T2H92581kJ/kg K Btu/lbm RcvConstant volume specific heat L2T2H92581kJ/kg K Btu/lbm RD Diameter of upstream conduit L m ftd Diameter of CFV throa
45、t L m fth Specific enthalpy L2T2J/kg Btu/lbmhtTotal specific enthalpy L2T2J/kg Btu/lbmk Coverage factor Dimensionless Dimensionless DimensionlessM Molar mass MM1mole1kg/kg mole lbm/lbm molem Mass flow MT1kg/s lbm/secMa Mach number: ratio of gas velocity to Dimensionless Dimensionless Dimensionlessso
46、und speedmthTheoretical mass flow for one-dimen- MT1kg/s lbm/secsional isentropic flow of a real gasP* Absolute static pressure of the gas at ML1T2Pa lbf/in.2CFV throatP*/P0Critical pressure ratio: ratio of throat Dimensionless Dimensionless Dimensionlesspressure to inlet stagnationpressureP0Absolut
47、e stagnation (or total) pres- ML1T2Pa lbf/in.2sure of the gas at CFV inletP1Absolute static pressure of the gas in ML1T2Pa lbf/in.2the upstream conduitP2Absolute static pressure of the gas at ML1T2Pa lbf/in.2CFV exitP2/P0Back pressure ratio: ratio of CFV exit Dimensionless Dimensionless Dimensionles
48、sstatic pressure to inlet stagnationpressurercRadius of curvature of CFV inlet L m ftRedCFV throat Reynolds number Dimensionless Dimensionless DimensionlessRfRecovery factor or temperature probe Dimensionless Dimensionless DimensionlessconstantRuUniversal gas constant: 8 314.4598 ML2T2H92581J/(mol K
49、) ft lbf/(mol R)J/(mol K) 1,545.3467 ft lbf/(mol R)s Specific entropy of the gas L2H92581T2J/(kg K) Btu/(lbm R)T* Absolute static temperature at CFV H9258 KRthroatT0Absolute stagnation (or total) temper- H9258ature of the gasT1Absolute static temperature of the H9258 KRgas at CFV inletTm1Measured temperature H9258U Expanded uncertainty (with specified . . . . . . . . .coverage factor, k)u Standard uncertainty (k p 1) . . .ucCombined standard uncertainty (k p 1) . . .V One-dimensional gas velocity LT1m/s ft/secV*Velocity of
