ABSTRACT
This chapter illustrates and analyzes some of the more common methods for measuring flow rate in conduits, including the pitot tube, venturi, nozzle, and orifice meters. Most meters assume that the flow profile across the tube is symmetrical. This generally requires that the meter be installed at least 10 pipe diameters downstream and 5 diameters upstream of any flow disturbance elements, such as elbows, valves, bends, contractions/expansions, etc. The pitot tube is a relatively complex device and requires considerable effort and time to obtain an adequate number of velocity data points, especially close to the wall of the conduit, and to integrate these over the cross section to determine the total flow rate. Because the discharge coefficient accounts for the non-idealities in the system such as the friction loss, deviations from plug flow, etc., one would expect it to decrease with increasing Reynolds number, similar to the friction factor in pipe flow, although this is contrary to the trend.
