ASME MFC-6:2013 pdf download

ASME MFC-6:2013 pdf download.Measurement of Fluid Flow in Pipes Using Vortex Flowmeters
1 SCOPE
This Standard (a) describes the use of vortex fowmeters, including their physical components, principle of operation, instal- lation, performance, infuence factors, and calibration in a closed conduit running full for the measurement of volu- metric fow rate and volume fow total of single-phase liquids or gases, including vapors such as steam (b) describes the use of vortex fowmeters in combi- nation with one or more other process measurements for the inferential measurement of mass fow rate, mass fow total, base volumetric fow rate, base volume total, and heat fow metering (c) is limited to full-bore fowmeters and does not include the special case of insertion-type fowmeters
3 TERMINOLOGY AND SYMBOLS
3.1 defnitions from asMe MfC-1M used in this standard For the purposes of this Standard, the following def- nitions are particularly useful in describing the charac- teristics of vortex shedding fowmeters. ASME MFC-1M provides a more extensive collection of defnitions and symbols pertaining to the measurement of fuid fow in closed conduits.cavitation: the implosion of vapor bubbles formed after fashing when the local pressure rises above the vapor pressure of the liquid. fashing: the formation of vapor bubbles in a liquid when the local pressure falls to or below the vapor pressure of the liquid, often due to local lowering of pressure because of an increase in the liquid velocity. K factor: in pulses per unit volume, the ratio of the meter output in number of pulses to the corresponding total volume of fuid passing through the meter during a measured period. Variations in the K factor may be pre- sented as a function of either the meter bore Reynolds number or the fow rate of a specifc fuid at a specifc set of thermodynamic conditions (see Fig. 9.2-1). lowest local pressure: the lowest pressure found in the meter. This is the pressure of concern regarding fashing and cavitation. Some of the pressure is recovered down- stream of the meter.meter factor: the reciprocal of the mean K factor. pressure loss: the difference between the upstream pres- sure and the pressure downstream of the meter after recovery. random error: a component of the error of measurement that, in the course of a number of measurements of the same measurand, varies in an unpredictable way. NOTE: It is not possible to correct for random error. random uncertainty: a component of uncertainty associ- ated with a random error. Its effect on mean values can be reduced by taking many measurements. rangeability: fowmeter rangeability is the ratio of the maxi- mum to minimum fow rates or Reynolds number in the range over which the meter meets a specifed uncertainty. response time: for a step change in fow rate, response time is the time needed for the indicated fow rate to differ from the true fow rate by a prescribed amount (e.g., 10%). systematic error: a component of the error of measure- ment that, in the course of a number of measurements of the same measurand, remains constant or varies in a predictable way. NOTE: Systematic errors and their causes may be known or unknown. systematic uncertainty: the error associated with sys- tematic error, i.e., the error that cannot be reduced by increasing the number of measurements under identical conditions. Also known as bias.
Sensors are used to detect shedding vortices, i.e., to convert the pressure or velocity variations associated with the vortices to electrical signals. One cycle of the shedding frequency corresponds to the generation of two vortices, one from one side of the bluff body, fol- lowed by another from the bluff body’s other side. The electrical signal generated by a fowmeter’s vortex sen- sor varies at the shedding frequency, f, one cycle of which corresponds to the shedding of a pair of vortices.