Sharp engineering calculator2/3/2024 ![]() After the metering device the velocity will decrease to the same level as before the obstruction. The viscous effect is usually expressed in terms of the non-dimensional parameter Reynolds Number - Re.ĭue to the Benoulli and the Continuity Equation the velocity of the fluid will be at it's highest and the pressure at the lowest in " Vena Contracta". " Vena Contracta" is the minimum jet area that appears just downstream of the restriction. The discharge coefficient c d is a function of the jet size - or orifice opening - theĪ vc = area in "vena contracta" (m 2, ft 2) The ideal equation (3) can be modified with a discharge coefficient: ![]() The theoretical flow rate q will in practice be smaller ( 2 - 40%) due to geometrical conditions. Q = A 2 1/2 (3)įor a given geometry (A), the flow rate can be determined by measuring the pressure difference p 1 - p 2. ![]() Γ = specific weight of fluid (kg/m 3, slugs/ft 3)Īssuming uniform velocity profiles in the upstream and downstream flow - the Continuity Equation can be expressed asĬombining (1) and (2), assuming A 2 < A 1, gives the "ideal" equation: The equation can be adapted to vertical flow by adding elevation heights : The Bernoulli EquationĪssuming a horizontal flow (neglecting the minor elevation difference between the measuring points) the Bernoulli Equation can be modified to: To understand orifice, nozzle and venturi meters it is necessary to explore the Bernoulli Equation. In a flow metering device based on the Bernoulli Equation the downstream pressure after an obstruction will be lower than the upstream pressure before.
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