Flow Rate

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flow rate

[′flō ‚rāt]
(fluid mechanics)
Also known as rate of flow.
Time required for a given quantity of flowable material to flow a measured distance.
Weight or volume of flowable material flowing per unit time.

Flow Rate


in hydraulics, the volume of fluid flowing through a cross section of a stream per unit time. The flow rate Q of a fluid for a given cross section ω is determined by the formula

Q = ∫ωu dω

where u is the flow velocity within the limits of d, an elementary segment of the cross section. In steady flow, the flow rate of a dropping liquid is constant along a given stream. The average flow velocity of the fluid can be determined from the known values of the flow rate and cross-sectional area: v = Q/ω. The mass of fluid flowing per unit time through a cross section of the stream is called the mass flow rate M. This rate is related with the volume flow rate by the equation M = ρ Q, where ρ is the density of the fluid. The flow rate of a fluid is measured with water meters, measuring spillways, hydrometers, rate-of-flow meters, and other instruments.


Al’tshul’, A. D., and P. G. Kiselev. Gidravlika i aerodinamika. Moscow, 1965.
Chugaev, R. R. Gidravlika, 2nd ed. Leningrad, 1970.
References in periodicals archive ?
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