On the Theory of Discharge Coefficients for Rounded-Entrance Flowmeters and Venturis

Abstract
A theory of rounded-entrance flowmeters, based on a consideration of the potential and boundary-layer flows in a converging nozzle, is constructed. Curves are presented showing the discharge coefficient as a function of diameter Reynolds number, with the “total equivalent length-diameter ratio” of the nozzle as a parameter. The equivalent frictional length-diameter ratio of the contraction section of the ASME long-radius nozzle is presented. The theoretical curves of discharge coefficient versus diameter Reynolds number are in good agreement with experiment over a range of Reynolds number from 1 to 106. The theory provides a rational framework for correlating and extrapolating experimental results; it shows the effects of contraction shape and location of pressure taps; it furnishes values of discharge coefficient for untested designs; and it suggests precautions to be taken in design, installation, and operation.

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