This document describes the operation and use of an orifice meter for measuring fluid flow rates. It discusses how an orifice plate placed in a pipe creates a pressure drop that can be used to calculate flow rate based on Bernoulli's equation. Specifically, it introduces orifice meters and their basic components, explains how they work using principles of fluid dynamics and continuity, provides equations to calculate flow rates, and describes common applications like measuring gas and liquid flows in pipes.

1. G.H.PATEL COLLEGE OF ENGINEERING AND TECHNOLOGY
CHEMICAL DEPARTMENT
TOPIC NAME: ORIFICE METER
SUBJECT: FLUID FLOW OPERATION(2130502)
NAME:
VYOM PATODIYA (150110105033)
KRISHNA PESHIVADIYA (150110105034)
HARDIK PIPALIYA (150110105035)
BHAVIN POSHIYA (150110105036).
FACULTY NAME:
PROF. VINAY B. PATEL

2. INTRODUCTION
 An orifice plate is a device used for measuring flow rate, for reducing pressure or for restricting flow. An orifice
plate is a thin plate with a hole in it, which is usually placed in a pipe. When a fluid (whether liquid or gaseous)
passes through the orifice, its pressure builds up slightly upstream of the orifice. but as the fluid is forced to
converge to pass through the hole, the velocity increases and the fluid pressure decreases.
 A little downstream of the orifice the flow reaches its point of maximum convergence, the vena contracta (see
drawing to the right) where the velocity reaches its maximum and the pressure reaches its minimum. Beyond that,
the flow expands, the velocity falls and the pressure increases. By measuring the difference in fluid pressure across
tappings upstream and downstream of the plate, the flow rate can be obtained from Bernoulli's equation using
coefficients established from extensive research.

3. PRINCIPAL OF ORIFIC METER
 The principle of the orifice meter is identical with that of the venturi meter. The reduction of the cross section of
the flowing stream in passing through the orifice increases the velocity head at the expense of the pressure head,
and the reduction in pressure between the taps is measured by a manometer. Bernoulli's equation provides a
basis for correlating the increase in velocity head with the decrease in pressure head.
 One important complication appears in the orifice meter that is not found in the venturi. Because of the sharpness
of the orifice, the fluid stream separates from the downstream side of the orifice plate and forms a free-flowing jet
in the downstream fluid. A vena contracta forms, as shown in figure.

5.  The jet is not under the control of solid walls, as is the case in the venture and the area of the jet varies from that
of the opening in the orifice to that of the vena contracta. The area at any given point, for example at the
downstream tap, is not easily determinable and the velocity of the jet at the downstream tap is not easily related
to the diameter of the orifice. Orifice coefficients are smaller and more variable than those for the venturi and
the quantitative treatment of the orifice meter is modified accordingly.
 The basic equation for the orifice meter is obtained by writing the Bernouli equation for the incompressible
fluids across the upstream cone. Va and Vb are the average upstream and downstream velocities respectively
and ρ is the density of the fluid.
ὰbVb
2 - ὰaVa
2 =
𝟐(𝐏𝐚− 𝐏𝐛)
𝛒
--------------(1)
 The continuity relation can be written,
Va = (
𝐷𝑏
𝐷𝑎
)2Vb ----------------(2)
Where Da=diameter of pipe, Db=diameter of throat of meter, β4=diameter ratio Db/Da

6.  If Va is eliminated from Eq.(1) and (2), the result is Vb = (
𝟏
ὰ 𝐛
−
𝛃 𝟒
ὰ 𝐚
)
𝟐(𝑷𝒂−𝑷𝒃)
𝛒
-------------------------(3)
 Eq.(3) applies strictly to the frictionless flow of noncompressible fluids. To account for the small friction loss
between location a and b, Eq.(3) is corrected by introducing an empirical factor Co and writing
Vb = (
𝑪𝒐
𝟏−𝛃 𝟒)
𝟐(𝑷𝒂−𝑷𝒃)
𝛒
-------------------------(4)
 The small effect of the kinetic energy factors ὰa and ὰb are also taken into account in the definition of Co. The
coefficient Co is determined experimentally. It is called the venturi coefficient, velocity of approach not included.
 The volumetric flow rate is calculated by using below equation,
q = Vb * Sb Where q=Volumetric flow rate, Sb=area of throat

7. IT’S DESIGN
 Orifice meter is type of variable head meter. In this meter the obstruction to the flow consist of an engineering
constriction in the metered fluid which causes a reduction in the flow pressure. An orifice meter is a conduit and
a restriction to create a pressure drop.
 It uses the same principle as a Venturi nozzle, namely Bernoulli's principle which states that there is a
relationship between the pressure of the fluid and the velocity of the fluid. When the velocity increases, the
pressure decreases and 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. When 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 maximum convergence actually occurs shortly
downstream of the physical orifice, at the so-called vena contracta .

8.  Vena contracta is a point where the velocity and the pressure changes. Beyond the vena contracta, the fluid
expands 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 equation. There are different types of orifice plate that are namely Concentric, Segmental,
Eccentric and Quadrant Edge and Conic Edge.
 In order to use any of these devices for measurement it is necessary to empirically calibrate them. That is, pass a
known volume through the meter and note the reading in order to provide a standard for measuring other
quantities. Due to the ease of duplicating and the simple construction, the thin sharp edged orifice has been
adopted as a standard and extensive calibration work has been done so that it is widely accepted as a standard
means of measuring fluids. Provided the standard mechanics of construction are followed no further calibration is
required. An orifice in a pipeline with a manometer for measuring the drop in pressure (differential) as the fluid
passes through the orifice. The minimum cross sectional area of the jet is known as the “vena contracta” where the
velocity is maximum and static pressure is minimum. It is observed at some distance from orifice because of inertia
effects persisting in flow direction. Materials used for orifice plate are mild steel, stainless steel, phosphor bronze
and gun metal.

10.  Orifice plates can be a surprisingly good way of measuring small gas flows. To be able to use orifice plates of
very small orifice diameter in an existing installation in a declining gas field may be much more economical than
to replace the metering or shut the field.
 From the beginning of the flow measurement to its conclusion a 4″ orifice meter with different orifice plates
(including those described in this appendix) might measure a range of around 3000:1 in terms of mass flow rate.
 The orifice fitting, which enables the operator to change or remove an orifice plate easily.

11. APPLICATION
 Orifice plates are most commonly used to measure flow rates in pipes, when the fluid is single-phase (rather than
being a mixture of gases and liquids, or of liquids and solids) and well-mixed, the flow is continuous rather than
pulsating, the fluid occupies the entire pipe (precluding silt or trapped gas), the flow profile is even and well-
developed and the fluid and flow rate meet certain other conditions.
 Under these circumstances and when the orifice plate is constructed and installed according to appropriate
standards, the flow rate can easily be determined using published formulae based on substantial research and
published in industry, national and international standards.
 Plates are commonly made with sharp-edged circular orifices and installed concentric with the pipe and with
pressure tappings at one of three standard pairs of distances upstream and downstream of the plate; these types
are covered by ISO 5167 and other major standards. There are many other possibilities

12.  The edges may be rounded or conical, the plate may have an orifice the same size as the pipe except for a
segment at top or bottom which is obstructed, the orifice may be installed eccentric to the pipe, and the pressure
tappings may be at other positions. Variations on these possibilities are covered in various standards and
handbooks. Each combination gives rise to different coefficients of discharge which can be predicted so long as
various conditions are met, conditions which differ from one type to another.
 Once the orifice plate is designed and installed, the flow rate can often be indicated with an acceptably low
uncertainty simply by taking the square root of the differential pressure across the orifice's pressure tappings and
applying an appropriate constant. Even compressible flows of gases that vary in pressure and temperature may
be measured with acceptable uncertainty by merely taking the square roots of the absolute pressure and/or
temperature, depending on the purpose of the measurement and the costs of ancillary instrumentation.
 Orifice plates are also used to reduce pressure or restrict flow, in which case they are often called restriction
plates.

13. REFERENCES
 McCABE SMITH HARRIOTT (McGraw- HILL )
 Wikipedia