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Orifice meter is type of variable head meter. In this meter the
obstruction to the flowconsist of an engineering constriction in
the metered fluid which causes a reductionin the flow pressure. An
orifice meter is a conduit and a restriction to create apressure
drop. It uses the same principle as a Venturinozzle, namely
Bernoulli'sprinciplewhich states that there is a relationship
between the pressure of the fluid
and the velocity of the fluid. hen the velocity increases, the
pressure decreasesand vice versa.
An orifice plate is a thin plate with a hole in the center of
the plate. It is usually placed
in a pipe in such a way that fluid passed through the hole. hen
the fluid reaches
the orifice plate, with the hole in the middle, the fluid is
forced to converge to go
through the small hole! the point of ma"imum convergence
actually occurs shortly
downstream of the physical orifice, at the so#called vena
contracta. Vena contracta
is a point where the velocityand the pressurechanges. Beyond the
vena contracta,
the fluid e"pands and the velocity and pressure change once
again. By measuring
the difference in fluid pressure between the normal pipe section
and at the vena
contracta, the volumetric and mass flow rates can be obtained
from Bernoulli's
e$uation.%here are different types of orifice plate that are
namely&oncentric,
egmental, (ccentric and )uadrant (dge and &onic (dge.
http://en.wikipedia.org/wiki/Venturi_effecthttp://en.wikipedia.org/wiki/Bernoulli's_principlehttp://en.wikipedia.org/wiki/Bernoulli's_principlehttp://en.wikipedia.org/wiki/Vena_contractahttp://en.wikipedia.org/wiki/Velocityhttp://en.wikipedia.org/wiki/Pressurehttp://en.wikipedia.org/wiki/Bernoulli's_equationhttp://en.wikipedia.org/wiki/Bernoulli's_equationhttp://en.wikipedia.org/wiki/Bernoulli's_principlehttp://en.wikipedia.org/wiki/Bernoulli's_principlehttp://en.wikipedia.org/wiki/Vena_contractahttp://en.wikipedia.org/wiki/Velocityhttp://en.wikipedia.org/wiki/Pressurehttp://en.wikipedia.org/wiki/Bernoulli's_equationhttp://en.wikipedia.org/wiki/Bernoulli's_equationhttp://en.wikipedia.org/wiki/Venturi_effect
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In order to use any of these devices for measurement it is
necessary to
empirically calibrate them. %hat is, pass a *nown volume through
the meter and note
the reading in order to provide a standard for measuring other
$uantities. +ue to the
ease of duplicating and the simple construction, the thin sharp
edged orifice has
been adopted as a standard and e"tensive calibration wor* has
been done so that it
is widely accepted as a standard means of measuring fluids.
rovided the standard
mechanics of construction are followed no further calibration is
re$uired. An orifice in
a pipeline with a manometer for measuring the drop in pressure
-differential as the
fluid passes through the orifice. %he minimum cross sectional
area of the /et is
*nown as the 0vena contracta1 where the velocity is ma"imum and
static pressure is
minimum. It is observed at some distance from orifice because of
inertia effects
persisting in flow direction. 2aterials used for orifice plate
are mild steel, stainless
steel, phosphor bronze and gun metal.
A fluid passing though an orifice constriction will experience a
drop in pressure acrossthe orifice. This change can be used to
measure the flowrate of the fluid.
To calculate the flowrate of a fluid passing through an orifice
plate, enter the parameters
below. (The default calculation involves air passing through a
medium-sized orifice in a
4" pipe, with answers rounded to significant figures.!
