文档介绍：FENOMENOS DE TRANSPORTE Y MECANICA DE FLUIDOS – ASPECTOS TEORICOS 96
Capítulo tomado del libro clásico de Mecánica de Fluidos “Fluid Mechanics and Hydraulics” de
Ranald V. Giles publicado en el año 1962 en N. York por Schaum Publishing Co.
MEASUREMENT OF FLOW OF FLUIDS
INTRODUCTION
Numerous devices are used in engincering practice to measure the flow of fluids. Velocity
measurements are made with Pitot tubes, current meters, and rotating and hotwire anemometem. In model
studies, photographic methods are often used. Quantity measurements are plished by means of orifices,
tubes, nozzles, Venturi meters and flumes, elbow meters, weirs, numerous modifications of the foregoing and
various patented meters. In order to apply the hydraulic devices intelligently, use of the Bernoulli equation and
additional knowledge of the characteristics and coefficients of each device are imperative. In the absence of
reliable values of coefficients, a device should be calibrated for the expected operating conditions.
Formulas developed for pressible fluids may be used pressibIe fluids where the
pressure differential is small relative to the total pressure. In many practical cases such small differentials
occur. However, pressibility must be considered, special formulas will be developed and used.
PITOT TUBE
The pitot tube measures the velocity at a point by virtue of the fact that the tube measures the
stagnation pressure, which exceeds the local static pressure by w(V2/2g) psf. In an open stream of fluid, since
the local pressure is zero gage, the height to which the liquid rises in the tube measures the velocity head.
COEFFICIENT of DISCHARGE
The coefficient of discharge (c) is the ratio of the actual discharge through the device
to the ideal discharge. This coefficient may be expresaed as
actual flow Q in cfs Q
c = = 2 2 gH (1)
ideal flow Q in cfs
More practically, when the coefficient of di