ASME MFC-18M:2001 pdf download MEASUREMENT OF FLUID FLOW USING VARIABLE AREA METERS
1 SCOPE
This Standard describes the common variable areaflowmeter.This Standard does not attempt to standardizedimensions because the commercial products differ toowidely.
The variable area meter is manufactured in a varietyof designs. This Standard addresses only those metersbased on a vertical tapered tube of round or a modifiedround cross section. Specifically not addressed are thevarious vane type meters, meters with horizontal flowor meters which use a spring deflection to oppose flowforces.
2 REFERENCES AND RELATED DOCUMENTSASME MFC-1M Glossary of Terms Used in the Measurement of Fluid Flow in PipesASME MFC-2M Measurement Uncertainty for FluidFlow in Closed ConduitsASME Fluid Meters,6 EdPublisher: The American Society of Mechanical Engineers (ASME)Three Park Avenue.New York.NY10016; Order Department: 22 Law Drive，Box 2300Fairfield，NJ 07007-2300
3 SYMBOLS AND DEFINITIONSFor symbols and their definitions,see Table 1.
4 FLOW RATE EQUATIONS
The variable area flowmeter is composed of a bodycontaining the fuid and a “foat,”” which is free tomove in the body to a position related to the flowrate. The balance of forces positions the float. Gravitypulls the float downward. The buoyancy of the floatplus the velocity related dynamic fluid forces lift thefloat. The float rises to increase the flow area until thefluid forces lifting the float match the downward forceThe meter must be oriented with fow vertically upfor the analysis to be correct. Orientation substantially
off the vertical will cause errors or a failure to respond.(See ASME Fluid Meters for more complete analysisof the variable area meter).
It is not practical to calculate meter capacity fromphysical principles for commercial variable area meters.The manufacturer’s catalogs do not list the tube crosssection areasor foat volumes or weights, or inletand exit pressure drops; all of this information isproprietary. The manufacturer supplies all of the capac-ity data in the form of tables. This reduces the equationfor each meter fow to:
Q= C*%Scale/100
The full scale meter flow, C, is defined and tabulatedin the manufacturer’s catalogs for each specific meteringtube and float. Separate tables are used for liquids andcompressible fluids. The industry often uses the term“normal”[typical 1.013 bar and 20°C (14.7 psia and70°F)] conditions for compressible fluid sizing ratherthan “standard”. The user is cautioned to define thereference conditions used.(See the manufacturer’s litera-ture for guidance on sizing and calibration.) Equation2 shows how to correct for a foat material densitydiffering from the basis density and for a flowing fluiddensity differing from the basis density:
5 VISCOSITY EFFECTS
For variable area meters, a fluid viscosity exceeding the limit value or “viscosity ceiling”, or “viscosity immunity ceiling” as listed in the catalog tables for that specific tube and float, will affect the meter calibra- tion. In general, float designs with a sharp edge on the maximum diameter part of the float will be less sensitive to viscosity (See the manufacturer’s literature for guidance). In general, viscosity effects occur with fluids more viscous than water.
ASME MFC-18M:2001 pdf download
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