ASME MFC-14M:2003 pdf download MEASUREMENT 0F FLUID FLOW USING SMALL BORE PRECISION ORIFICE METERS MEASUREMENT 0F FLUID FLOW USING SMALL BORE PRECISION ORIFICE METERS
3.2 Definitions
3.21 Pressure Measurement
differential presstre: difference between the static pressuremeasured on the upstream side and on the downstreamside of the primary device. For installations other tharhorizontal the lead lines must be installed in accordancewith ASME MFC-8M (see also ISO 2186) to eliminaterrors due to elevation differences between the taps. Theterm differenfial pressure is applicable only if the pressuretaps are in the positions specified by this Standard foreach standard primary device.
pressifre mtio: the absolute static pressure at the downstream pressure tap, divided by the pressure at theupstream pressure tap,P2/p
pressifre tap: hole or annular slot in a flange, fitting, othe wall of a pipe of a primary device that is flush withthe inside surface.
static pressure of a fluid flowing through a primary devicepressure measured by connecting a pressure measuringdevice to a pressure tap in the plane of the differentia.pressure taps. Absolute static pressure is used in theequations presented in this Standard.
3.2.2 Primary Devices
diameter rafio of a primary elemenf in a given pipe: thediameter of the orifice divided by the internal diameterof the measuring pipe upstream of the primary elementorifice: opening of minimum cross-sectional area in aprimary element, Standard primary element orifices arecircular and coaxial with the pipe line.
orifice plafe: thin plate in which a circular concentric holehas been machined. A standard orifice plate is describedas a thin plate and with a sharp edee. The thickness ofthe plate is small compared with the hole diameter(bore), and the upstream edge of the orifice is sharp andsquare.
small bore integral orifice fittings: the primary elementdesign used with precision bore orifice flowmeters hav-ing integral fittings may not conform to the designsspecified in this Standard, Users of this Standard aretherefore directed to consult manufacturers for desigrand performance limitations of these flowmeters
3.2.3 Flow
discharge coefficients: calibration of standard primarydevices by means of nominally incompressible fluids(liquids) shows that the discharge coefficient, C,a dimensionless number defined by the following relation in agiven installation, is dependent only on the Reynoldsnumber for a given primary device. The discharge coefficient is given by the following:
The numerical value of C is the same for differentinstallations whenever such installations are geometri-cally similar and flows are characterized by identicalReynolds numbers.[See Eqs.(3.13) and (3.14).] For liquids, Pr = pf = P. Empirical equations for the dischargecoefficient, C, of this Standard were based on data estab-lished experimentally (see para. 7). In these equations,the temperature of the orifice and the pipe is at theflowing fluid temperature.
expansion factor (or expansibility): calibration of a givenprimary device by means of a compressible fluid (gas),shows that the ratio is dependent on the value of theReynolds number, as well as on the values of the differ-ential pressure and variations in the isentropic exponentof the gas.
The method adopted for representing these variationsconsists in multiplying the discharge coefficient of theprimary device as determined by direct liquid calibra-tion for the same value of Reynolds number, by theexpansion factor defined by the following relationship: