1、AN AMERICAN NATIONAL STANDARDASME MFC-21.22010Measurement of Fluid Flow by Means of Thermal Dispersion Mass FlowmetersINTENTIONALLY LEFT BLANKASME MFC-21.22010Measurement of FluidFlow by Means ofThermal DispersionMass FlowmetersAN AMERICAN NATIONAL STANDARDThree Park Avenue New York, NY 10016 USADat
2、e of Issuance: January 10, 2011This 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 thisdocument. Periodically certain actions
3、of the ASME MFC Committee may be published as Cases.Cases and interpretations are published on the ASME Web site under 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
4、under procedures accredited as meeting the criteria for American NationalStandards. The Standards Committee that approved 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 madea
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6、ith respect to the validity of any patent rights asserted in connection with anyitems mentioned in this document, and does 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 standar
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9、 form,in an electronic retrieval system or otherwise,without the prior written permission of the publisher.The American Society of Mechanical EngineersThree Park Avenue, New York, NY 10016-5990Copyright 2011 byTHE AMERICAN SOCIETY OF MECHANICAL ENGINEERSAll rights reservedPrinted in U.S.A.CONTENTSFo
10、reword ivCommittee Roster . vCorrespondence With the MFC Committee . vi1 Scope. 12 Terminology and Symbols 13 General Description 54 Principle of Operation . 85 Guidelines for Flowmeter Selection . 126 Guidelines for Installation and Applications . 147 Inspection and Compliance. 188 Safety 189 Refer
11、ences 19Figures3.1-1 The Major Components of Two Configurations of Thermal Dispersion MassFlowmeters 63.2-1 Flow Sensor of Thermal Dispersion Mass Flowmeters . 73.3-1 Two Modes of Flow Sensor Operation 94-1 Principle of Operation 9Tables2.3-1 Symbols . 22.4-1 Abbreviations 46.1.4-1 Straight Pipe Len
12、gth Requirements for an In-Line Flowmeter With a Built-InFlow Conditioner 166.1.4-2 Straight Pipe Length Requirements for Insertion Flowmeters With No FlowConditioning 16Mandatory AppendixI Flow Calibration . 21Nonmandatory AppendicesA In-Line Flowmeter Sizing and Permanent Pressure Loss . 25B Accur
13、acy and Uncertainty 27iiiFOREWORDThermal dispersion mass flowmeters comprise a family of instruments for the measurementof the total mass flow rate of a fluid, primarily gases, flowing through closed conduits.The operation of thermal dispersion mass flowmeters is attributed to L.V. King who, in 1914
14、 1,published his famous Kings Law revealing how a heated wire immersed in a fluid flow measuresthe mass velocity at a point in the flow. King called his instrument a “hot-wire anemometer.”However, it was not until the 1960s and 1970s that industrial-grade thermal dispersion massflowmeters finally em
15、erged.This Standard covers the thermal dispersion type of thermal mass flowmeter. A companionstandard, ASME MFC 21.1, Measurement of Fluid Flow by Means of Capillary Tube ThermalMass Flowmeters and Controllers, covers the other most commonly used type of thermal massflowmeter. Both types measure flu
16、id mass flow rate by means of the heat convected from a heatedsurface to the flowing fluid. In the case of the thermal dispersion, or immersible, type of flowmeter,the heat is transferred to the boundary layer of the fluid flowing over the heated surface. In thecase of the capillary tube type of flo
17、wmeter the heat is transferred to the bulk of the fluid flowingthrough a small heated capillary tube. The principles of operation of the two types are boththermal in nature, but are so substantially different that two separate standards are required.Additionally, their applications are much differen
18、t. Thermal dispersion flowmeters are commonlyused for general industrial gas-flow applications in pipes and ducts, whereas capillary tubeflowmeters are primarily used for smaller flows of clean gases in tubes.Suggestions for improvement of this Standard will be welcomed. They should be sent toThe Am
19、erican Society of Mechanical Engineers; Attn: Secretary, MFC Standards Committee;Three Park Avenue; New York, NY 10016-5990.This Standard was approved as an American National Standard on June 24, 2010.ivASME MFC COMMITTEEMeasurement of Fluid Flow in Closed Conduits(The following is the roster of the
20、 Committee at the time of approval of this Standard.)STANDARDS COMMITTEE OFFICERSR. J. DeBoom, ChairZ. D. Husain, Vice ChairD. C. Wyatt, Vice ChairC. J. Gomez, SecretarySTANDARDS COMMITTEE PERSONNELC. J. Blechinger, Honorary Member, ConsultantR. M. Bough, Rolls-Royce Motor CarsM. S. Carter, Flow Sys
21、tems, Inc.G. P. Corpron, Honorary Member, ConsultantR. J. DeBoom, ConsultantD. Faber, Contributing Member, Badger Meter, Inc.C. J. Gomez, The American Society of Mechanical EngineersF. D. Goodson, Emerson ProcessZ. D. Husain, Chevron Corp.C. G. Langford, Honorary Member, ConsultantT. O. Maginnis, Co
22、nsultantW. M. Mattar, Invensys/Foxboro Co.SUBCOMMITTEE 21 THERMAL MASS FLOWMETERSR. J. DeBoom, Chair, ConsultantT. O. Maginnis, Vice Chair, ConsultantZ. D. Husain, Chevron Corp.vG. E. Mattingly, The Catholic University of AmericaD. R. Mesnard, ConsultantR. W. Miller, Honorary Member, R. W. Miller ho
23、wever, they shouldnot contain proprietary names or information.Requests that are not in this format may be rewritten in the appropriate format by the Committeeprior to being answered, which may inadvertently change the intent of the original request.ASME procedures provide for reconsideration of any
24、 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“approve,” “certify,” “rate,” or “endorse” any item, construction, proprietary de
25、vice, or activity.Attending Committee Meetings. The MFC Standards Committee regularly holds meetings thatare open to the public. Persons wishing to attend any meeting should contact the Secretary ofthe MFC Standards Committee.viASME MFC-21.22010MEASUREMENT OF FLUID FLOW BY MEANS OF THERMALDISPERSION
26、 MASS FLOWMETERS1 SCOPEThis Standard establishes common terminology andgives guidelines for the quality, description, principleof operation, selection, installation, and flow calibrationof thermal dispersion flowmeters for the measurementof the mass flow rate, and to a lesser extent, the volumet-ric
27、 flow rate, of the flow of a fluid in a closed conduit.Multivariable versions additionally measure fluid tem-perature. Thermal dispersion mass flowmeters are appli-cable to the flow of single-phase pure gases and gasmixtures of known composition and, less commonly, tosingle-phase liquids of known co
28、mposition. Companionstandard ASME MFC-21.1 covers capillary tube typethermal mass flowmeters and controllers.2 TERMINOLOGY AND SYMBOLS(a) Paragraph 2.1 lists definitions fromASME MFC-1M used in ASME MFC-21.2.(b) Paragraph 2.2 lists definitions specific to thisStandard.(c) Paragraph 2.3 lists symbols
29、 (see Table 2.3-1) usedin this Standard (see notes and superscripts).(d) Paragraph 2.4 lists abbreviations (see Table 2.4-1)used in this Standard.2.1 Definitions Copied From ASME MFC-1Maccuracy: the degree of freedom from error; the degreeof conformity of the indicated value to the true valueof the
30、measured quantity.calibration: the experimental determination of the rela-tionship between the quantity being measured and thedevice that measures it, usually by comparison with astandard. Also, the act of adjusting the output of a deviceto bring it to a desired value, within a specified tolerance,f
31、or a particular value of the input.cavitation: the implosion of vapor bubbles formed afterflashing when the local pressure rises above the vaporpressure of a liquid. (See also flashing.)flashing: the formation of vapor bubbles in a liquid whenthe local pressure falls to or below the vapor pressureof
32、 the liquid, often due to local lowering of pressurebecause of an increase in the liquid velocity. (See alsocavitation.)1flow profile: graphic representation of the velocitydistribution.fullydevelopedvelocitydistribution: a velocity distribution,in a straight length of pipe, that has zero radial and
33、azimuthal fluid velocity components and an axisymme-tric axial velocity profile that is independent of axialposition along the pipe.rangeability (turndown): flowmeter rangeability is theratio of the maximum to minimum flow rates orReynolds number in the range over which the metermeets a specified un
34、certainty (accuracy).repeatability (qualitative): the closeness of agreementamong a series of results obtained with the same methodon identical test material, under the same conditions(same operator, same apparatus, same laboratory, andshort intervals of time). See also repeatability(quantitative).r
35、epeatability (quantitative): the value below which theabsolute difference between any two single test resultsobtained under same conditions may be expected tolie with a specified probability. In the absence of otherindications, the probability is 95%. See also repeatability(qualitative).reproducibil
36、ity (quantitative): the closeness of agreementbetween results obtained when the conditions of mea-surement differ; for example, with respect to differenttest apparatus, operators, facilities, time intervals, etc.swirling flow: flow that has axial and circumferentialvelocity components.transmitter(se
37、condarydevice): electronic system providingthe drive and transforming the signals from the flowsensor to give output(s) of measured and inferredparameters; it also provides corrections derived fromparameters such as temperature.uncertainty interval, u: an estimate of the error band,centered about th
38、e measurement, within which the truevalue must fall with a specified probability.2.2 Definitions Specific to This Documentbase conditions: the conditions of temperature and pres-sure to which measured volumes are to be corrected(same as Reference or Standard Conditions).ASME MFC-21.22010Table 2.3-1
39、SymbolsDimensions SI Units USC UnitsSymbol Description (First Use) Note (1) Note (2) Note (2)Abs ( ) Absolute value of the quantity in parentheses eq. (B-1) dim-lessAeExternal surface area of the heated section of the velocity sensor eq. (4-2) L2m2ft2, in.2AfsAccuracy of flowmeter, percent of full s
40、cale eq. (5-2) dim-less % fs % fsApipeCross-sectional area of the flow conduit or flow body eq. (4-6) L2m2ft2, in.2ArAccuracy of flowmeter, percent of reading eq. (5-1) dim-less % r % rAtOverall accuracy of flowmeter, in percent of reading eq. (5-1) dim-less % r % ratm Atmospheric pressure at base c
41、onditions, 101,325 Pa ML-1T-2Pa, bar psibiGas factors, i p 1, 2,5 eq. (4-10) dim-lessCPPressure influence coefficient (para. 5.6.1) M-1LT2% r/bar % r/psicpCoefficient of specific heat of the fluid at constant pressure eq. (4-9) L2T-2K-1J/kgK Btu/lbFCTTemperature influence coefficient (para. 5.6.1) K
42、-1% r/K % r/FD Outside diameter of the velocity sensor eq. (4-2) L m ft, in.FcConduit factor eq. (4-8) dim-lessf ( ) Function of terms in parentheses eq. (4-9) dim-lessh Film coefficient for convective heat transfer from the heated section of the MT-3K-1W/m2K Btu/velocity sensor eq. (4-3) hft2FheEqu
43、ivalent film coefficient for convective heat transfer from the heated MT-3K-1W/m2K Btu/section of the velocity sensor eq. (4-2) hft2FI Electrical current input to T1RTD in the heated section of the velocity amperes A Asensor (para. 3.5.2)kfThermal conductivity of the fluid eq. (4-9) MLT-3K-1W/mK Btu
44、/hftFL Length of the heated section of the velocity sensor eq. (4-2) L m ft, in.M Molecular weight of the gas eq. (4-21) - kg/kgmole lb/lbmoleN Number of equal areas in the cross-sectional area Apipeof a flow conduit dim-lesseq. (4-20)Nu Nusselt number eq. (4-9) dim-lessn Number of input variables e
45、q. (B-2) dim-lessP Static pressure of the flowing fluid eq. (4-21) ML-1T-2Pa, bar psiPbBase static pressure of the flowing fluid (para. 4.7.3) ML-1T-2Pa, bar psi “normal” base conditions: Pbp Pnp 101,325 Pa (1 atm) “standard” base conditions: Pbp Psp 101,325 Pa (1 atm)PLThe upper or lower limit of t
46、he pressure flow calibration reference condition ML-1T-2Pa, bar psirange eq. (B-1)Pr Prandtl number eq. (4-9) dim-lessQ Heat convected away from the heated section of the velocity sensor by the ML2T-3W Btu/hfluid eq. (4-1)QLStem conduction heat loss eq. (4-1) ML2T-3W Btu/hqmMass flow rate of the flu
47、id (para. 3.2) MT-1kg/s lb/s,lb/minqm,fsFull scale mass flow rate of the flowmeter eq. (5-2) MT-1kg/s lb/s,lb/minqm,iMass flow rate of the fluid measured by flow sensor i eq. (4-20) MT-1kg/s lb/s,lb/minqvVolumetric flow rate of the fluid eq. (4-16) L3T-1m3/s ft3/minqv,bVolumetric flow rate of the fl
48、uid referenced to base (“b”) conditions L3T-1bm3/s bft3/mineq. (4-17)R Universal gas constant eq. (4-21) - m3bar/(kg ftlbf/moleK) (lbmoleR)Re Reynolds number of the velocity sensor eq. (4-9) dim-lessRepipeReynolds number of the flow conduit, pipe, or flow body eq. (4-8) dim-lessRsSkin thermal resist
49、ance eq. (4-5) M-1L-2T3K K/W F/(Btu/h)R1Electrical resistance of the T1RTD eq. (4-1) ohms ohms ohmsSiSensitivity coefficient of qmto input variable xieq. (B-3) variesT Temperature of a gas in the absolute scale eq. (4-21) K K R2ASME MFC-21.22010Table 2.3-1 Symbols (Contd)Dimensions SI Units USC UnitsSymbol Description (First Use) Note (1) Note (2) Note (2)TbBase temperature of the flowing fluid (para. 4.7.3) K K, C F “normal” base conditions: Tbp Tnp 0C
