ANSI ASME MFC-13M-2006 Measurement of Fluid Flow in Closed Conduits Tracer Methods《封闭管道中流量的测量.跟踪法》.pdf

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1、AN AMERICAN NATIONAL STANDARDMeasurement of Fluid Flow in Closed Conduits: Tracer MethodsASME MFC-13M2006Intentionally left blank ASME MFC-13M2006Measurement ofFluid Flow inClosed Conduits:Tracer MethodsAN AMERICAN NATIONAL STANDARDThree Park Avenue New York, NY 10016Date of Issuance: February 12, 2

2、007This Standard will be revised when the Society approves the issuance of a new edition. There willbe no addenda issued to this edition.ASME issues written replies to inquiries concerning interpretations of technical aspects of thisStandard. Interpretations are published on the ASME Web site under

3、the Committee Pages athttp:/cstools.asme.org as they are issued.ASME is the registered trademark of The American Society of Mechanical Engineers.This code or standard was developed under procedures accredited as meeting the criteria for American NationalStandards. The Standards Committee that approv

4、ed the code or standard was balanced to assure that individuals fromcompetent and concerned interests have had an opportunity to participate. The proposed code or standard was madeavailable for public review and comment that provides an opportunity for additional public input from industry, academia

5、,regulatory agencies, and the public-at-large.ASME does not “approve,” “rate,” or “endorse” any item, construction, proprietary device, or activity.ASME does not take any position with respect to the validity of any patent rights asserted in connection with anyitems mentioned in this document, and d

6、oes not undertake to insure anyone utilizing a standard against liability forinfringement of any applicable letters patent, nor assume any such liability. Users of a code or standard are expresslyadvised that determination of the validity of any such patent rights, and the risk of infringement of su

7、ch rights, isentirely their own responsibility.Participation by federal agency representative(s) or person(s) affiliated with industry is not to be interpreted asgovernment or industry endorsement of this code or standard.ASME accepts responsibility for only those interpretations of this document is

8、sued in accordance with the establishedASME procedures and 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

9、 Society of Mechanical EngineersThree Park Avenue, New York, NY 10016-5990Copyright 2007 byTHE AMERICAN SOCIETY OF MECHANICAL ENGINEERSAll rights reservedPrinted in U.S.A.CONTENTSForeword ivCommittee Roster . vCorrespondence With the MFC Committee . vi1 Scope and Field of Application. 12 Symbols 13

10、Units . 14 Method of Use 15 Choice of Tracer. 26 Measuring Length and Adequate Mixing Distance . 27 Errors 48 Extensions of the Methods 59 Practical Application Notes 5Table1 Symbols . 2Nonmandatory AppendicesA Typical Tracer Fluids . 7B Mixing Distances 9iiiFOREWORDThis Standard defines the use of

11、tracer (dilution) methods in the measurement of single-phasefluid (gas or liquid) flows in closed conduits. This method of measurement is applicable only tosingle-phase homogeneous fluid mixtures.This Standard was developed to fill the need for a generalized reference based on fundamentalprinciples

12、to measure fluid flow using tracer methods. ISO standards issued in 1977 addressedtracer methods for gas flows; these were withdrawn in 2001, leaving a void on this subject. AnInternet search on this subject will find a large number of documents, standards, references,consultants, and manufacturers.

13、 Most of the papers, standards, and products are for very specificapplications and provide detailed guidance only for those needs. This Standard defines the termsand principles needed for intelligent consideration of tracer methods for any application.ASME MFC-13M2006 was approved by the American Na

14、tional Standards Institute onSeptember 29, 2006.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 OFFICERSR. J. DeBoom, ChairZ. D. Husain, Vice ChairA. L. Guzman, SecretarySTANDA

15、RDS COMMITTEE PERSONNELC. J. Blechinger, Member Emeritus, ConsultantR. M. Bough, Rolls-RoyceG. P. Corpron, ConsultantR. J. DeBoom, ConsultantD. Faber, Corresponding Member, Badger Meter, Inc.R. H. Fritz, Corresponding Member, Lonestar Measurement however, they shouldnot contain proprietary names or

16、information.Requests that are not in this format will be rewritten in this format by the Committee priorto being answered, which may inadvertently change the intent of the original request.ASME procedures provide for reconsideration of any interpretation when or if additionalinformation that might a

17、ffect an interpretation is available. Further, persons aggrieved by aninterpretation may appeal to the cognizant ASME Committee or Subcommittee. ASME does not“approve,” “certify,” “rate,” or “endorse” any item, construction, proprietary device, or activity.Attending Committee Meetings. The MFC Commi

18、ttee regularly holds meetings, which are opento the public. Persons wishing to attend any meeting should contact the Secretary of theMFC Standards Committee.viASME MFC-13M2006MEASUREMENT OF FLUID FLOW IN CLOSED CONDUITS:TRACER METHODS1 SCOPE AND FIELD OF APPLICATIONFor steady-state flow of fluid in

19、a closed conduit, theonly conserved parameter is the mass rate of flow, qm.If the mass density is known, the volume rate of flow,qv, can be deduced.The accuracy of flow rate measurement with the tracermethods is a function of how well the injected tracermaterial mixes with the flowing fluid. It is a

20、lso a functionof the accuracy and precision of the sensing devices,and the (tracer methods) techniques used.The following two tracer methods are used:(a) The dilution method is based on a constant rateof tracer injection, and the concentration of tracer foundin the downstream conduit is a measure of

21、 the relativeflow rates.(b) The transit time method determines the flow rateby measuring the time it takes the tracer material totravel between two detector points or between the injec-tion point and a detector point in the conduit.The advantages and disadvantages of these two meth-ods are reviewed

22、in section 4.A wide variety of tracer materials may be used radioactive or nonradioactive, mineral or organicmaterials, etc. The choice of tracer depends on the pur-pose of the measurement and environmental concerns(section 5). The uncertainty of the measurementsdepends completely on the accuracy of

23、 the methodsused (section 7). Some typical tracer fluids are listed inNonmandatory Appendix A.2 SYMBOLSSee Table 1.3 UNITSCalculations for mass and volumetric flow rates inthis document are expressed in terms of ratios of lengthsand in other nondimensional parameters, as shown inTable 1. Hence, no d

24、imensional units are defined forthose terms.4 METHOD OF USE4.1 DilutionIn the dilution method, a measured quantity of tracerfluid of known composition is injected into the flowing1stream at the injection point. At the detection location,the mixture is analyzed for composition. A simple calcu-lation

25、provides the flow of the main stream. If the massof the tracer stream is known, then the result is inmass units.4.1.1 Advantages of the Dilution Method(a) It is not necessary to know the geometrical charac-teristics of the conduit.(b) It is not necessary that the flowing conditions ofthe fluid (p, T

26、) be the same between the two measuringcross sections.(c) It is not necessary to know the time of injection.(d) It is inherently a mass flow measurement.4.2 Transit Time MethodIn the transit time method, a quantity of tracer fluidis injected into the flowing stream. Two detection pointsare commonly

27、used, with both far enough downstreamto allow adequate mixing and far enough apart toachieve adequate precision in the time measurement.The flow of the mixed fluids should be continuous fromthe time of injection until the mixed fluid is detected atthe second detection point. The time for the detecte

28、dchange in fluid properties is compared at the two pointsto provide the average velocity of the fluid mixture. Theshape of the detected rise time, the length of the pulse,and the rate of decay are all used to estimate the degreeof mixing and possible error. The cross section of theflow conduit at th

29、e detection points is used with theflow time to determine the volumetric flow rate at thesecond detection point. The time required for tracer fluidinjection is determined by the response time of the detec-tor and the system geometry.4.2.1 Advantages of the Transit Time Method(a) It is necessary only

30、 to determine the modified fluidcharacteristic time distribution at two measuring crosssections separated by a known volume of pipe orconduit.(b) It is not necessary to know the volume, mass, orflow rates of the injected tracer.(c) Transit time is inherently a volumetric method.(d) In some applicati

31、ons only one detection point isused, the injection point taking the place of the firstdetection point.ASME MFC-13M2006Table 1 SymbolsSymbol Description Dimensions SI Units U.S. Customary UnitsqvVolumetric flow rate L3T1m3/s ft3/secqmMass flow rate MT1kg/s lbm/secH9004c Variation in percent concentra

32、tion of tracer . . . % %f0Friction factor of a perfectly smooth conduit . . . . . . . . .(para. 6.2.1.1)f Friction factor coefficient of resistance (Moody . . . . . . . . .coefficient)L/D Ratio, conduit length to diameter, in the same LL1Not applicable Not applicableunits of measureRe Reynolds numbe

33、r . . . . . . . . .(e) The degree of fluid mixing is less critical in thismethod.4.2.2 Special Recommendation for the Method Basedon Transit Time Measurement. For this method, it ispreferable to have a conduit length of constant crosssection between two measuring points, so that the flowparameters a

34、re approximately constant over the measur-ing length.5 CHOICE OF TRACER5.1 General(a) Different types of tracers may be used, but forsatisfactory operation the tracer injected in the flowingfluid must satisfy the following requirements:(1) it should mix well with the fluid in the conduit(2) the quan

35、tity used should result in negligible orknown modifications of the flow rate of fluid in the flowstream(3) the instrument used to monitor the concentra-tion of the tracer must have sufficient measurement accu-racy, and be suitable for the fluids and environment(4) it should be chemically stable in t

36、he conditionsof use(5) if the tracer material used is also present in theflow prior to injection of the tracer, it must be at anegligible or constant concentration(b) For the dilution method, it is important that thetracer fluid does not react with the measured fluid, orwith the conduit wall materia

37、l, to the extent that it affectsthe measurement.(c) For transit time methods, it is recommended that(1) the tracer concentration in the measuring crosssections can be determined at any time(2) to achieve greatest precision, the detector signalshould be proportional to the tracer concentration andthe

38、 detector response time be fast enough that timeaccuracy is not lost25.2 Comparison Between the Different Tracers5.2.1 Advantages of Radioactive Tracers (SeeTable A-2)(a) If a tracer emitting gamma radiation with suffi-cient energy is permissible, the probes may be locatedoutside the conduit.(b) For

39、 tracers with a short half-life and are chemicallyacceptable, any radioactive contamination disappearsquickly.5.2.2 Advantages of Nonradioactive Tracers(a) Nonradioactive tracers do not require consider-ation of the requirements and regulations for the owner-ship and handling of radioactive material

40、s.(b) The substances generally remain stable with time.Delays between the supply and the use of the substancedo not matter.6 MEASURING LENGTH AND ADEQUATE MIXINGDISTANCE6.1 IntroductionAdequate mixing of the tracer with the flowing streamis required for accurate flow measurements. The mixingdistance

41、 is defined as the shortest distance that the maxi-mum variation, H9004c, in the mixture composition, as mea-sured over the cross section of the stream, is less thansome predetermined value.This mixing distance is not one fixed value, but willvary with the allowable concentration variations thesmall

42、er the acceptable variation (greater precision ofmeasurement), the greater the mixing distance. Thelength of the available conduit may limit reduction ofpercent variation in concentration, H9004c, below a certainvalue. This also varies with the fluid flow properties (i.e.,greater turbulence and flow

43、 disturbances aid mixing).A multipoint sampling or detection arrangementshould be used where possible, particularly when a sys-tematic variation in concentration may exist at the sam-pling cross section.ASME MFC-13M2006Depending on the tracer and the method of detectionused, the mixing requirements

44、for the transit timemethod may not be as stringent as for the dilutionmethods.Several techniques are available to improve the mixingthat can reduce the required mixing distance. Seeparas. 6.2 through 6.4.6.2 Mixing Distance6.2.1 Theoretical Derivation of Mixing Distance.The mixing length determined

45、by experiment may differconsiderably from the length predicted theoretically(para. 6.2.2). Paragraph 6.2.1.1 should be used only asa preliminary guide.6.2.1.1 Central Injection. Equations (1) through (3)relate mixing distance, L/D, to the varying concentrationof tracer across the conduit. These were

46、 developed basedon Reynolds number, Re, and pipe friction. Equation (1)is based on an assumed constant radial diffusion coeffi-cient and uniform flow velocity. Equation (2) is basedon a parabolic distribution of radial diffusion coefficientand uniform flow velocity. Equation (3) assumes a para-bolic

47、 distribution of radial diffusion coefficient and alogarithmic velocity profile.LDp1.18H209068fH208982.94 ln (H9004c)2.30H20899(1)LDpH208982.95 ln (H9004c)2.40H20899 H209068f(2)LDpH2090020.50 2.85 W ln (H9004c)H20901Re0.10H20898f0fH20899(3)where the symbols are defined in Table 1.Equations (1) throu

48、gh (3) are shown graphically inNonmandatory Appendix B, Fig. B-1, which shows theincrease in the required mixing distance for a decreasein H9004c for a Reynolds number of Rep 105and a smoothconduit. Note that Fig. B-1 is qualitative in nature andthe plot is for guidance only.The slight dependence of

49、 mixing distance on Reynoldsnumber is shown for eq. (3) in Fig. B-2 as an example.For a change in Re from 105to 106,atH9004c p 1% themixing distance increases by about 25%.6.2.1.2 Ring Injection. The mixing distances arereduced to about one-third of the values derived for acentral injection point for uniform injection using a ringwith a radius of 0.63 of the conduit radius.6.2.2 Experimental Test of Mixing Distance. Mixingdistance experimentally determined for central injectionin an unobstructed, straight, circular conduit is reportedto be about twice the values predicted