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How to use it
Enter the inside diameter of the pipe, the bore diameter, the tapping position, the differential pressure read and the properties of the liquid. The tool calculates by iteration the discharge coefficient, which depends on the Reynolds number, and returns flow rate, velocity in the pipe and the pressure loss that remains downstream of the orifice plate.
Formulas used
Limits
The calculation applies to liquids, that is, with an expansibility factor equal to 1: for gases and steam the expansibility factor is also needed. The standard applies with a bore of at least 12.5 mm, a pipe between 50 and 1000 mm, β between 0.10 and 0.75 and turbulent flow, and requires straight lengths upstream and downstream that depend on the fittings present. For sizing the meter and calculating the uncertainty there is the service orifice plate flow meter.
FAQ
What is the discharge coefficient?
It is the ratio between the real flow rate and the theoretical one without losses. For a sharp-edged orifice plate it is about 0.60 and changes little with β and with the Reynolds number: the standard gives it by a formula, with no need for calibration.
How much pressure is lost?
Part of the differential pressure is recovered downstream, the rest is lost. With β = 0.6 the permanent loss is about 60% of the differential pressure; it decreases as β increases.
Which tapping position should I choose?
Flange tappings are the most common because they are machined in the orifice flanges. Corner tappings are used on small pipes. The formula changes little, but the value of C must be calculated for the real configuration.