ASME MFC-21.1 pdf download Measurement of Gas Flow by Means of Capillary Tube Thermal Mass Flowmeters and Mass Flow Controllers
This Standard establishes common terminology andprovides guidelines for the quality, description, principle 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 contentof this Standard applies to single-phase flows of puregases and gas mixtures of known composition.
2 TERMINOLOGY,SYMBOLS，AND REFERENCES
2.1 Definitions From MFC-1M
accuracy (of measurement): the extent to which a givenmeasurement agrees with a reference for that measurement, often used by manufacturers to express the performance characteristics of a device.
NOTE: Accuracy is not the same as uncertainfy [see uncerfainty (ofmeasurerent)
bell prover: volumetric gaging device used for gases thatconsists of a stationary tank containing a sealing liquicinto which is inserted a coaxial movable tank (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 relationship between the quantity being measured and 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 primary 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 oneof a variety of devices intended to reduce swirl and/orregulate the velocity profile.
flow rate: the quantity of fluid flowing through a crosssection of a pipe per unit of time.
full developed velocitu distribution: a velocity distributionin a straight length of pipe that has zero radial andazimuthal fluid velocity components and an axisymmetric 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 inertiaand where adjacent fluid particles move in essentiallyparallel paths.
(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: mass 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 displacementto travel through this section.
rangeability: the rangeability of a flowmeter is the ratioof the maximum to minimum flow rates (Revnolds numbers, velocities etc.) in the range over which the metermeets a specified and acceptable uncertainty, also calledturndown
repeafability (gualitative): closeness of agreement 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 are qualifiedby the term repeatability Examples are standard deviation ofrepeatability and variance of repeatability.
repeatability (quantitative): closeness of the agreementbetween the results of successive measurements of the