ASME MFC-21 1-2015 Measurement of Gas Flow by Means of Capillary Tube Thermal Mass Flowmeters and Mass Flow Controllers.pdf

1、AN AMERICAN NATIONAL STANDARD ASME MFC-21.12015Measurement of Gas Flow by Means of Capillary Tube Thermal Mass Flowmetersand Mass Flow ControllersASME MFC-21.12015Measurement of GasFlow by Means ofCapillary Tube ThermalMass Flowmetersand Mass FlowControllersAN AMERICAN NATIONAL STANDARDTwo Park Aven

2、ue New York, NY 10016 USADate of Issuance: October 16, 2015This Standard will be revised when the Society approves the issuance of a new edition.ASME issues written replies to inquiries concerning interpretations of technical aspects of thisStandard. Interpretations are published on the Committee We

3、b page and under go.asme.org/InterpsDatabase. Periodically certain actions of the ASME MFC Committee may be published asCases. Cases are published on the ASME Web site under the MFC Committee Page at go.asme.org/MFCcommittee as they are issued.Errata to codes and standards may be posted on the ASME

4、Web site under the Committee Pages toprovide corrections to incorrectly published items, or to correct typographical or grammatical errorsin codes and standards. Such errata shall be used on the date posted.The MFC Committee Page can be found at go.asme.org/MFCcommittee. There is an option available

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8、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 does not undertake to insure anyone utilizing a standard against liability forinfringement of any applicable letters patent, nor assume a

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11、art 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 York, NY 10016-5990Copyright 2015 byTHE AMERICAN SOCIETY OF MECHANICAL ENGINEERSAll

12、 rights reservedPrinted in U.S.A.CONTENTSForeword ivCommittee Roster vCorrespondence With the MFC Committee vi1 Scope 12 Terminology, Symbols, and References . 13 General Description . 44 Performance and Operating Specifications 135 Principle of Operation . 156 Standard Volumetric Flow Rate 187 Conv

13、ersion From One Gas to Another 208 Best Practices 21Figures3.2-1 Typical General Purpose Mass Flow Controller (MFC) . 73.2-2 Typical Semiconductor Mass Flow Controller (MFC) . 83.5-1 Flow Paths in Mass Flowmeters (MFMs) 85.2-1 Sensor Tube and Temperature Distributions . 165.4-1 Instrument Outputs Ve

14、rsus the Mass Flow Rate, qm, Through theSensor Tube for Four Different Gases . 195.4-2 Instrument Outputs Versus Heat Capacity Rate, qmcp, for the SameFour Gases in Fig. 5.4-1 19Tables2.3-1 Symbols . 52.4-1 Abbreviations 64.2-1 Flow Ranges . 13Mandatory AppendixI Gas Flow Calibration . 23Nonmandator

15、y AppendicesA Energy Equation for the Gas Flowing in the Sensor Tube 25B Bibliography . 27iiiFOREWORDCapillary tube thermal mass flowmeters (MFMs) and mass flow controllers (MFCs) comprisea family of instruments for the measurement and control of the mass flow rate of gases flowingthrough closed con

16、duits.This Standard covers the capillary tube type of thermal MFM. A companion standard, ASMEMFC-21.2, Measurement of Fluid Flow by Means of Thermal Dispersion Mass Flowmeters, coversthe other most commonly used type of thermal MFM. Both types of instruments measure themass flow rate of gases by mea

17、ns of a heated element in contact with the flowing gas, and inboth types, the composition of the gas must be known.In the case of the thermal dispersion, or immersible, type of MFM, heat is transferred to theboundary layer of the gas flowing over a heated sensor immersed in the main flow stream. The

18、heat carried away by the gas provides the measurement of mass flow rate. Thermal dispersionMFMs are used for general industrial gas flow applications in ducts and pipes.In the case of the capillary tube type of MFM described in this Standard, the flowing gas entersthe flowmeter and passes through a

19、laminar flow element, or bypass. This creates a pressuredrop that forces a small, but proportional, fraction of the total mass flow rate through an adjacentcapillary sensor tube. The capillary sensor tube measures its internal mass flow rate by meansof the heat capacity of the gas that carries heat

20、from an upstream resistance-temperature-detectorwinding to a downstream winding, both on the outside of the sensor tube. The difference in theelectrical resistances of the two windings provides the output signal proportional to the totalmass flow rate in the process.A capillary tube thermal MFC is a

21、 capillary tube thermal MFM with an integral control valvemounted on the same flow body. The MFM portion measures the mass flow rate in the processline, the electronics compares this measurement with a set-point value, and the control valveregulates the flow to equal the set-point value. Capillary t

22、ube thermal MFMs and MFCs are usedfor smaller flows of clean gases flowing in tubes.In this Standard, the term mass flow controller is abbreviated MFC and should not be confusedwith the name of the cognizant ASME Standards Committee, MFC, Measurement of Fluid Flowin Closed Conduits.Suggestions for i

23、mprovements in this Standard are welcome. They should be sent to theSecretary, ASME MFC Standards Committee, Two Park Avenue, New York, NY 10016-5990.This Standard was approved as an American National Standard on May 19, 2015.ivASME MFC COMMITTEEMeasurement of Fluid Flow in Closed Conduits(The follo

24、wing is the roster of the Committee at the time of approval of this Standard.)STANDARDS COMMITTEE OFFICERSR. J. DeBoom, ChairD. C. Wyatt, Vice ChairC. J. Gomez, SecretarySTANDARDS COMMITTEE PERSONNELC. J. Blechinger, Honorary Member, ConsultantR. M. Bough, Rolls-Royce Corp.M. S. Carter, Flow Systems

25、, Inc.R. J. DeBoom, ConsultantD. Faber, Contributing Member, Faber however, they shouldnot contain proprietary names or information.Request 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

26、 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 appeal to the cognizant ASME Committee or Subcommittee. ASME does not“approve,” “c

27、ertify,” “rate,” or “endorse” any item, construction, proprietary device, or activity.Attending Committee Meetings. The MFC Standards Committee regularly holds meetings and/or telephone conferences that are open to the public. Persons wishing to attend any meetingand/or telephone conference should c

28、ontact the Secretary of the MFC Standards Committee.Future Committee meeting dates and locations can be found on the Committee Page atgo.asme.org/MFCcommittee.viASME MFC-21.12015MEASUREMENT OF GAS FLOW BY MEANS OF CAPILLARY TUBETHERMAL MASS FLOWMETERS AND MASS FLOWCONTROLLERS1 SCOPEThis Standard est

29、ablishes common terminology andprovides guidelines for the quality, description, princi-ple of operation, selection, operation, installation, andflow calibration of capillary tube thermal mass flow-meters and mass flow controllers for the measurementand control of the mass flow rate of gases. The co

30、ntentof this Standard applies to single-phase flows of puregases and gas mixtures of known composition.2 TERMINOLOGY, SYMBOLS, AND REFERENCES2.1 Definitions From MFC-1Maccuracy (of measurement): the extent to which a givenmeasurement agrees with a reference for that measure-ment, often used by manuf

31、acturers to express the per-formance characteristics of a device.NOTE: Accuracy is not the same as uncertainty see uncertainty (ofmeasurement).bell prover: volumetric gaging device used for gases thatconsists of a stationary tank containing a sealing liquidinto which is inserted a coaxial movable ta

32、nk (the bell),the position of which may be determined. The volumeof the gas-tight cavity produced between the movabletank and the sealing liquid may be deduced from theposition of the movable tank.calibration: the experimental determination of the rela-tionship between the quantity being measured an

33、d thedevice that measures it, usually by comparison with astandard, then (typically) adjustment of the output of adevice to bring it to a desired value, within a specifiedtolerance, for a particular value of the input.critical flow devices: a flowmeter in which a critical flowis created through a pr

34、imary differential pressure device(fluid at sonic velocity in the throat). A knowledge ofthe fluid conditions upstream of the primary device andof the geometric characteristics of the device and thepipe suffice for the calculation of the flow rate.flow conditioner: general term used to describe any

35、oneof a variety of devices intended to reduce swirl and/orregulate the velocity profile.1flow rate: the quantity of fluid flowing through a crosssection of a pipe per unit of time.fullydevelopedvelocitydistribution: a velocity distribution,in a straight length of pipe that has zero radial andazimuth

36、al fluid velocity components and an axisymme-tric axial velocity profile that is independent of the axialposition along the pipe.laminar flow: flow under conditions where forces due toviscosity are more significant than forces due to inertia,and where adjacent fluid particles move in essentiallypara

37、llel paths.NOTES:(1) Laminar flow may be unsteady but is completely free fromturbulent mixing.(2) Laminar flow in a pipe follows the Poiseuille law.Mach number: the ratio of the mean axial fluid velocityto the velocity of sound in the fluid at the consideredtemperature and pressure.mass flow rate: m

38、ass of fluid-per-unit-time flowingthrough a cross section of a pipe.piston prover: volumetric gaging device consisting of astraight section of pipe with a constant cross section andof known volume. The flow rate is derived from thetime taken by a piston, with free or forced displacement,to travel th

39、rough this section.rangeability: the rangeability of a flowmeter is the ratioof the maximum to minimum flow rates (Reynolds num-bers, velocities, etc.) in the range over which the metermeets a specified and acceptable uncertainty, also calledturndown.repeatability (qualitative): closeness of agreeme

40、nt amonga series of results obtained with the same method onidentical test material, under the same conditions (sameoperator, same apparatus, same laboratory, and shortintervals of time).NOTE: The representative parameters of the dispersion of thepopulation that may be associated with the results ar

41、e qualifiedby the term repeatability. Examples are standard deviation of repeat-ability and variance of repeatability.repeatability (quantitative): closeness of the agreementbetween the results of successive measurements of theASME MFC-21.12015same measurand carried out under the same conditionsof m

42、easurement.NOTES:(1) These conditions are called repeatability conditions.(2) Repeatability conditions include the same measurement proce-dure, using the same measuring instrument under the sameconditions with the same observer in the same location,repeated over a short period of time.(3) Repeatabil

43、ity may be expressed quantitatively in terms of thedispersion characteristics of the results.reproducibility (quantitative): closeness of agreementbetween results obtained when the conditions of mea-surement differ, e.g., with respect to different test appa-ratus, operators, facilities, time interva

44、ls, etc. A completestatement of reproducibility should include a descrip-tion of the conditions of measurement.response time: the time interval between a specified pro-cess change and the instant when the response of theinstrumentation reaches and remains within specifiedlimits around its final stea

45、dy value.EXAMPLE: 0.5 s (0.5 sec) to reach and remain within 1% of thesteady value following an abrupt change from 90% of full scale to10% of full scale.NOTE: The time constant is a special case of response time thatindicates the dynamic behavior is completely described by a first-order differential

46、 equation in time.Reynolds number: a dimensionless parameter expressingthe ratio between the inertia forces and viscous forcesand referenced to some pertinent characteristic dimen-sion, e.g., diameter of the pipe, diameter of the bore ofa differential pressure device, diameter of the Pitot tubeshaft

47、, etc. The Reynolds number is determined by veloc-ity, density, and viscosity of the flowing fluid at thecharacteristic dimension of the device. It is given by thegeneral formulaRe p Vl/vwherel p characteristic dimension of the system in whichthe flow occurs;V p average spatial fluid velocity; andv

48、p kinematic viscosity of the fluiduncertainty (of measurement): parameter, associated withthe result of a measurement that characterizes the dis-persion of the values that could reasonably be attributedto the measurand.NOTES:(1) The parameter may be, for example, a standard deviation (ora given mult

49、iple of it) or the half-width of an interval havinga stated level of confidence.(2) Uncertainty of measurement comprises, in general, any compo-nents. Some of these components may be evaluated from thestatistical distribution of the results of series of measurementsand can be characterized by experimental standard deviations.2The other components that can also be characterized by stan-dard deviations are evaluated from assumed probability distri-butions based on experience or other information.(3) It is understood that the result of the measurement is the bestestimate of the value