Orifice meter expansion factor

Rate of discbarge through an orifice meter is given by Eq. (10-8) for either hquids or gases. For the case of subsonic flow of a gas (/ < / < 1.0), the expansion factor Y for orifices is approximated by... 

Figure 2-38B. Net expansion factor, Y, for compressible flow through nozzles and orifices. By permission, Crane Co., Technical Paper 410, Engineering Div., 1957. Also see 1976 edition and Fluid Meters, Their Theory and Application, Part 1, 5th Ed., 1959 and R. G. Cunningham, Paper 50-A-45, American Society of Mechanical Engineers.

Figure 10-11 Expansion factor for orifice, nozzle, and venturi meter, (a) k = 1.3 (b) k = 1.4. (From Crane Co., 1978.)...

The flow through the orifice/Venturi meter also depends on the thermal expansion of the flow meter and pipe (FJ, and the expansion factor (Y). With those corrections the final equation will be ... 

Temperature Correction. A temperature correction factor, must be used to account for any change of the area of section A 2 of the primary element when the operating temperature differs appreciably from the ambient temperature at which the device was manufactured and measured. If the meter is to be used under temperature conditions within the range of ordinary atmospheric temperatures, any difference between the thermal expansion of the pipe and the primary element may be ignored and the diameter ratio, p, may be considered to be unaffected by temperature. At cryogenic temperatures, the material for the throat liner of a Venturi tube, a flow nozzle, or an orifice plate should have a coefficient of thermal expansion as close as possible to that of the pipe. 

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