1、AN AMERICAN NATIONAL STANDARDMeasurement ofFluid Flow in Closed Conduits Using Multiport Averaging Pitot Primary ElementsASME MFC-12M2006Intentionally left blank ASME MFC-12M2006Measurement ofFluid Flow in ClosedConduits UsingMultiport AveragingPitot PrimaryElementsAN AMERICAN NATIONAL STANDARDThree
2、 Park Avenue New York, NY 10016Date of Issuance: October 9, 2006This 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 thisStanda
3、rd. Interpretations are published on the ASME website under the Committee Pages athttp:/www.asme.org/codes/ 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
4、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 madeavailable for public review and comment that provides an
5、opportunity for additional public input from industry, academia,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 asserte
6、d 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 standard are expresslyadvised that determination of the validit
7、y of any such patent rights, and the risk of infringement of such 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 re
8、sponsibility for only those interpretations of this document issued 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,wit
9、hout the prior written permission of the publisher.The American Society of Mechanical EngineersThree Park Avenue, New York, NY 10016-5990Copyright 2006 byTHE AMERICAN SOCIETY OF MECHANICAL ENGINEERSAll rights reservedPrinted in U.S.A.CONTENTSForeword ivCommittee Roster . vCorrespondence With the MFC
10、 Committee . vi1 Scope 12 Terms and Definitions . 13 References 24 Operating Principles 35 Flow Equations 56 Unit Construction Considerations. 57 Installation Effects 68 Operation 79 Flow Coefficient . 710 Flow Rate Measurement Uncertainty 7Figures1 APT Showing Total and Reference Pressure Sensed on
11、 the Strut . 42 APT Showing Total Pressure Sensed on the Strut and Reference Pressure Sensedat the Pipe Wall . 4Tables1 Symbols . 2Nonmandatory AppendicesA Typical Cross Sections of Multiport Averaging Pitot Primary Elements 9B Multiport Averaging Pitot Primary Element Flow Theory . 10iiiFOREWORDMul
12、tiport averaging pitot primary elements cover a family of head-class devices that makeuse of the Bernoulli principal to measure the flow of liquids and gases. This Standard tries toclarify differences between the construction and operation of these devices and other head-classdevices, such as orific
13、e meters, Venturi meters, and nozzles.Due to differences in the design of multiport averaging pitot primary elements, this Standardcannot address detailed performance characteristics in specific applications. It does cover issuesthat are common to such devices.Suggestions for improvements to this St
14、andard are encouraged and should be sent to: Secretary,ASME MFC Committee, the American Society of Mechanical Engineers, Three Park Avenue, NewYork, NY 10016-5990.ASME MFC-12M2006 was approved by the American National Standard Institute onMarch 21, 2006.ivASME MFC COMMITTEEMeasurement of Fluid Flow
15、in Closed Conduits(The following is the roster of the Committee at the time of approval of this Standard.)STANDARDS COMMITTEE OFFICERSZ. D. Husain, ChairR. J. DeBoom, Vice ChairA. L. Guzman, SecretarySTANDARDS COMMITTEE PERSONNELC. J. Blechinger, Member Emeritus, ConsultantR. M. Bough, Rolls-RoyceG.
16、 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 information.Requests that are not in this format will be rewritten in this format by the Commi
17、ttee 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 affect an interpretation is available. Further, persons aggrieved by aninterpretation may appea
18、l 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 Committee regularly holds meetings, which are opento the public. Persons wishing to attend any meet
19、ing should contact the Secretary of the MFCStandards Committee.viASME MFC-12M2006MEASUREMENT OF FLUID FLOW IN CLOSED CONDUITS USINGMULTIPORT AVERAGING PITOT PRIMARY ELEMENTS1 SCOPEThis Standard, provides information on the use ofmultiport averaging Pitot head-type devices used tomeasure liquids and
20、gases. The Standard applies whenthe conduits are full and the flow(a) has a fully developed profile(b) remains subsonic throughout the measurementsection(c) is steady or varies only slowly with time(d) is considered single-phaseA differential pressure transmitter or other pressuremeasuring device, k
21、nown as a secondary element, mustbe used with a multiport averaging Pitot primary ele-ment to produce a flow rate measurement.Although multiport averaging Pitot primary elementsare sometimes used in noncircular conduits, such appli-cations are beyond the scope of this Standard.2 TERMS AND DEFINITION
22、SThe terminology and symbols (Table 1) used in thisStandard are in accordance with ASME MFC-1M. Someitems from ASME MFC-1M are listed in para. 2.2.1 foreasier reference.Terminology not defined in ASME MFC-1M, but usedin this Standard, are defined in para. 2.2.2.2.1 SymbolsSee Table 1.2.2 Definitions
23、2.2.1 Definitions Found in ASME MFC-1Mcavitation: the implosion of vapor bubbles formed afterflashing when the local pressure rises above the vaporpressure of the liquid. See also flashing.differential pressure device: device inserted in a pipe tocreate a pressure differential whose measurement,toge
24、ther with a knowledge of the fluid conditions andof the geometry of the device and the pipe, enables theflow rate to be calculated.1flashing: the formation of vapor bubbles in a liquid whenthe local pressure falls to or below the vapor pressureof the liquid, often due to local lowering of pressurebe
25、cause of an increase in the liquid velocity. See alsocavitation.primary device (of a differential pressure device): differentialpressure device with its pressure tappings.rangeability: flowmeter rangeability is the ratio of themaximum to minimum flowrates or Reynolds numberin the range over which th
26、e primary element meets aspecified uncertainty (accuracy).reproducibility: the closeness of agreement betweenresults obtained when the conditions of measurementdiffer; for example, with respect to different test appara-tus, operators, facilities, time intervals, etc.Reynolds number: a dimensionless
27、parameter expressingthe ratio between inertia and viscous forces. It is givenby the formulaRe pVlv(1)whereV p average spatial fluid velocityl p characteristic dimension of the system in whichthe flow occursv p kinematic viscosity of the fluidNOTE: When specifying a Reynolds number, one should indica
28、tethe characteristic dimension on which it has been based (e.g., diam-eter of the pipe or width of the multiport averaging Pitot primaryelement).total pressure (or total head): also known as stagnationpressure; sum of the static pressure and the dynamicpressure. It characterizes the state of the flu
29、id when itskinetic energy is completely transformed into potentialenergy.2.2.2 Definitions for MFC-12MAPT or averaging Pitot tube: common abbreviation formultiport averaging Pitot primary element.ASME MFC-12M2006 MEASUREMENT OF FLUID FLOW IN CLOSED CONDUITS USINGMULTIPORT AVERAGING PITOT PRIMARY ELE
30、MENTSTable 1 SymbolsDimensions SISymbol Quantity Note (1) UnitsD Diameter of the conduit Note (2) L mg Local acceleration of gravity Note (2) LT2m/s2P Absolute pressure Note (2) ML1T2PaH9004p Differential pressure Note (2) ML1T2PaqmMass flow rate Note (2) MT1kg/sqvVolume flow rate Note (2) L3T1m3/sR
31、e Reynolds number Note (2) . . . . . .T Absolute temperature Note (2) H9258 KU Mean axial velocity Note (2) LT1m/sH9255 Expansibility Note (2) . . . . . .H9267 Density Note (2) ML3kg/m3A Area of conduit at measurement conditions Note (3) L2m2K Flow coefficient Note (3) . . . . . .PgGage pressure Not
32、e (3) ML1T2PaPtTotal pressure Note (3) ML1T2PaPsLocal static pressure Note (3) ML1T2Paz Vertical elevation Note (3) L mqbVolume flow at base conditions Notes (3) and (4) L3T1m3/sH9262 Absolute viscosity Note (3) ML1T1Pa.sNOTES:(1) Dimensions: M p mass, H9258 p temperature, L p length, T p time.(2) S
33、ymbols identical to ASME MFC-1M.(3) Symbols defined specifically for this Standard, ASME MFC-12M.(4) Subscript b is for base conditions.expansibility(expansionfactor)H9255: dimensionless coefficientgiven by the formulaH9255 pqmH92664KD2H209062H9004pH9267f(2)where K is the flow coefficient of the APT
34、 and D is thepipe diameter.NOTES:(1) This definition is similar to that given in MFC-1M. It has beenmodified to make it apply for APT applications.(2) Subscript f is for flowing conditions.in-situ: the primary element is installed in the actualconfiguration and under actual flowing conditions inthe
35、conduit where it is to be used.linearity: linearity refers to the constancy of the flowcoefficient, K, over a range of Reynolds numbers or flowrates. This value is usually specified by maximum andminimum values of K defined over the range. The upperand lower limits of this range can be specified by
36、themanufacturer as either a maximum and minimum Reyn-olds number range, flow rate range of a specified fluid,2or other meter design limitations such as pressure, tem-perature, or installation effects.NOTE: This definition is similar to that given in MFC-1M. It hasbeen modified to make it apply for A
37、PT applications.secondary device: a device that receives a signal from theprimary device and displays, records, and/or transmitsit as a measure of the flow rate.velocity profiles: distribution of axial vectors of the localfluid velocities over a cross-section of a conduit.3 REFERENCESUnless otherwis
38、e noted all references are to the latestpublished edition of these standards. The following isa list of publications referenced in this Standard.ASME MFC-1M, Glossary of Terms Used in the Measure-ment of Fluid Flow in PipesASME MFC-2M, Measurement Uncertainty for FluidFlow in Closed ConduitsASME MFC
39、-7M, Measurement of Gas Flow by Meansof Critical Flow Venturi NozzlesMEASUREMENT OF FLUID FLOW IN CLOSED CONDUITS USING ASME MFC-12M2006MULTIPORT AVERAGING PITOT PRIMARY ELEMENTSASME MFC-8M, Connections for Pressure Signal Trans-missions Between Primary and Secondary DevicesASME MFC-9M, Measurement
40、of Liquid Flow in ClosedConduits by Weighing MethodASME MFC-10M, Method for Establishing InstallationEffects on FlowmetersPublisher: The American Society of MechanicalEngineers (ASME), Three Park Avenue, New York,NY 10016-5990; Order Department: 22 Law Drive,P.O. Box 2300, Fairfield, NJ 07007-2300IS
41、O 4185, Measurement of Liquid Flow in ClosedConduits Weighing MethodISO 5168, Measurement of Fluid Flow Evaluation ofUncertaintiesISO 8316, Measurement of Liquid Flow in ClosedConduits Method by Collection of the Liquid in aVolumetric TankPublisher: International Organization for Standardiza-tion (I
42、SO), 1 rue de Varembe, Case Postale 56, CH-1211,Geneve 20, Switzerland/Suisse4 OPERATING PRINCIPLES4.1 Description of OperationThe multiport averaging Pitot primary flow elementor averaging Pitot tube (APT) is similar to the conven-tional single point Pitot tube in operation, but differs inconstruct
43、ion. It is typically designed as a strut, or cylin-der (the cross section of the cylinder is not necessarilycircular), that is inserted across the circular pipe or con-duit on a diameter. Some APT designs have more thanone strut to achieve a more representative sample of thefluid velocity in the pip
44、e or conduit (see NonmandatoryAppendix A). The strut has ports that sense the totalvelocity head (total pressure), and a reference, or lowpressure. In some APT designs the reference pressureis measured at the pipe wall. Figures 1 and 2 show twocommonly used methods for sensing the total pressureand
45、reference pressure. The sensed pressure(s) are con-veyed through isolated passages, or chambers in thecylinder to the exterior of the assembly, where there areconnections to the secondary device. By combining theindividually sensed pressures from its sensing ports, theAPT produces a differential pre
46、ssure that can be relatedto the average fluid velocity in the pipe or conduit.4.2 Bernoullis EquationAs with other differential pressure-based flow pri-mary elements, the underlying principle for the APTsensor is the application of the momentum equationfrom basic fluid theory. Using the assumptions
47、forsteady state, inviscid, and incompressible flow along astreamline, the equation reduces to the Bernoulli equa-tion (see Nonmandatory Appendix B)3Ps+H9267 U22+ H9267gz p Pt(3)whereg p local acceleration of gravityPsp fluid static pressurePtp fluid total pressureU p fluid velocityz p vertical dista
48、nce from a datum reference to thepoint of measurementH9267 p fluid densityFor a horizontal pipe, the vertical distance for the twopoints of measurement are the same, and H9267gz is droppedfrom eq. (3). If a standard Pitot tube is inserted intothe flow stream, the flowing fluid will come to rest, ors
49、tagnate, isentropically at the Pitot tip. The pressure atthis point will be equal to the sum of the fluid staticpressure and the dynamic head, also called the totalhead or total pressure. If the static pressure at the Pitottube is known, or measured, the velocity can be calcu-lated fromPtp Ps+H9267 U22(4)orU pH209062(Pt Ps)H9267(5)wherePsp local static pressurePtp total pressureU p fluid velocity sensed at the Pitots tip4.3 Total PressureThe multiport averaging Pitot primary element mea-sures the total pressure by
