Flow-Measurement- it's definition , types, example ppt.ppt

Flow Meter Selection Criteria
 The phase of the fluid-like gas, liquid, steam
 Flow conditions and flow range, flow conditions
like clean, dirty, abrasive, viscous will affect
 Process conditions like pressure and temperature
 Preferred material mostly in case of corrosive
fluid
 Pipe size and accuracy
 Repeatability and cost

Variable Head Flow Meters
1) Orifice Plate

 As the fluid approaches the orifice the pressure
increases slightly and then drops suddenly as the
orifice is passed.
 The decrease in pressure as the fluid passes through
the orifice is a result of the increased velocity of the
gas passing thru the reduced area of the orifice.
 Materials for orifice plates are stainless steel ,brass,
gun metal and bronze.
 Types of Orifice plate:
 1) Concentric type
 2) Eccentric orifice plate
 3) Segmental plate

Application
 It is used to measure the flow rate of fluids in
their single state (i.e. gaseous state or liquid
state).
 It can also be used to measure the flow rate of
fluids in a mixed state (both gaseous and liquid
states) such as, wet steam, or natural gas with
water.

Main parts of Venturimeter:-
1) Converging part:-It is starting section of
venturimeter which attached at inlet pipe.
2) Throat:-Throat is middle portion of venturimeter
and its cross sectional area is too small. At this point
pressure is decreases and velocity is increases. One
end is connected with converging part and other
end is attached with diverging part
3) Diverging part :- Diverging part is last part of
venturimeter and its cross sectional area is increases
continually. Angle of diverging part is 5 to 15 degree.
Its cross sectional area continuously increases. The
main reason behind the low diverging angle is to
avoid the formation of which will results in large
amount of loss in energy

Applications
 1) It is not affected by wear and abrasion.
 2) High pressure recovery is attainable.
 3) Less chances to clogged with sediments.
 4) Co efficient of discharge is high.
 5) Venturi meters are used where pressure
recovery is important .
 6) It can be used for slurries and dirty liquids, if the
pressure taps are protected from plugging.
 7) They are widely used for high flow rates.

 The basic system consist of tube or pipe cylindrical
pressure vessel into which a construction wedge is
fabricated leaving an open segment of known height.
 A wedge acts as a restrictor in the pipe reduces available
flow area due to which fluid velocity increases and static
pressure decrease.
 The pressure taps on either side of wedges gives
differential pressure which is used to directly calculate
flow rate.
 Application:-
 Pressure drop is about half of conventional orifice flow
meter.
 Ability to measure low Reynolds flows.
 Useful for measuring highly viscous fluids, slurries, and
dirty fluids.
 Can be used for bi-directional flow.

Construction And Working
 The pitot tube is a differential pressure
measurement device used for flow measurement of
liquid and gases.
 It is right angled glass tube placed in the pipe such
that one end of the tube faces the flow and other
end open to atmosphere.
 The point at the tube opening where velocity of
fluid become zero is called stagnation pressure.
 Velocity of fluid V= C 2gh (P1-P2)
√

Applications of Pitot Tube
 It is used to measure speed of an aircraft
 It is used to measure speed of a boat
 It is used to measure fluid flows in different
industries
 It is used where very high accuracy is not required
 It is used to measure flow profile in a duct or
channel


Dall tube
 The dall tube is a shortened version of a Venturi
meter, with a lower pressure drop than an orifice
plate.
 As with these flow meters the flow rate in a Dall tube
is determined by measuring the pressure drop
caused by conical reducers in fluid carrying pipe.
 The two cones are separated by a slot or gap
between two cones. The low pressure is measured at
slotted throat.


 Applications :
 Flow measurement in gas transmission pipelines
 Flow metering of clean gasses
 Single phase flow measurement of hydrocarbon gas
 Flow measurement in circular pipes

Constant head variable area meter
1) Rotameter

Construction
 TRANSPARENT TUBE: This Tube Is In A Conical Shape Which
Has A Measurement Scale And Floats Inside It, This Transparent Tube
Helps To See The Measurements Directly.
 FLOAT: Float is small equipment with accurate dimensions placed
inside the tube to indicate the flow rate in the tube. This can be which
helps made with glass, metals or plastic.
 SCALE: Scale shows the measurements of flow by indicating with
float.

Working
 The fluid in rotameter used to flow from downwards to
up and in the middle of the device there is a scale which
used to given an output flow rate.
 when the fluid flow takes place there is an increase or
decrease in flow by this flow the float used to move up
and down according to the flow in it .
 Due to the presence of float in the tube, there is a head
loss occurs, this loss is equal to the weight of the float.
 APPLICATIONS :
 Highly used in industries.
 It used where there is a quality supply of air is needed.
 This is used at low pressure is required eg: gases.


Hot Wire Anemometer
 Hot Wire Anemometer works When an electrically
heated wire is placed in a flowing gas stream, heat is
transferred from the wire to the gas and hence the
temperature of the wire reduces, and due to this, the
resistance of the wire also changes. This change in
resistance of the wire becomes a measure of flow rate.
 Conducting wires placed in a ceramic body.
 Leads are taken from the conducting wires and they are
connected to one of the limbs of the wheat stone bridge
to enable the measurement of change in resistance of the
wire.
 There are two types
1) Constant current method 2) Constant temperature
method


 A constant current is passed through the sensing
wire. That is, the voltage across the bridge circuit is
kept constant.
 Due to the gas flow, heat transfer takes place from
the sensing wire to the flowing gas and hence the
temperature of the sensing wire reduces causing a
change in the resistance of the sensing wire.
 The galvanometer which was initially at zero
position deflects and this deflection of the
galvanometer becomes a measure of flow rate of
the gas.

 A current is initially passed through the wire.
 Due to the gas flow, heat transfer takes place from
the sensing wire to the flowing gas and this tends to
change the temperature and hence the resistance of
the wire.
 he principle in this method is to maintain the
temperature and resistance of the sensing wire at a
constant level. Therefore, the current through the
sensing wire is increased to bring the sensing wire
to have its initial resistance and temperature.
 The electrical current required in bringing back the
resistance and hence the temperature of the wire to
its initial condition becomes a measure of flow rate
of the gas.

Positive Displacement Flow Meter
1) Coriolis flow meter

Construction and Working
 It consist of pair of parallel vibrating tubes.
 The tube ends anchor to a stationary manifold.
 A force acting on a tube due to a fluid flowing through
a pipe. This force deforms the tube and the
deformation depends on mass flow rate through pipe.
 The tube moves from and back towards the axis of
oscillation resulting in changing angular momentum
of the fluid.
 The output from pick up sensor are sine waves
showing oscillation frequency. Which measure
magnitude of deformation and the mass floe rate can
be determined.

 Advantages
 True mass flow measurement
 Very high accuracy for mass flow measurements
 Unaffected by pressure, temperature and viscosity
 No inlet and outlet sections required
 Operates in both flow directions (forward and
reverse)
 Disadvantages
 Affected by gas inclusions
 Vibration sensitive when improperly installed
 Limited choice of materials

Oscillating piston flow meters
 It is one of the oldest type of positive displacement meter.
 It is a precision-machined chamber containing a
cylindrical piston that oscillates as liquid flows.
 The liquid enters and exits compartments machined into
the underside of the piston.
 The position of the piston divides the chamber into
compartments containing an exact volume. Liquid
pressure drives the piston to oscillate and rotate on its
center hub.
 The movements of the hub are sensed through the flow
meter wall by a follower magnet.
 Each revolution of the piston hub is equivalent to a fixed
volume of fluid, which is indicated as flow by an
indicator.

 Advantages
 High accuracy and repeatability.
 Only one moving part to cause wear.
 It can be made of materials to ensure sanitary
needs of food and beverage processing.
 Disadvantages
 It can only be used with relatively clean liquids.
 It is relatively expensive , large and Heavier.

 It is a positive displacement meter in which fluid
passes through a rotating set of vanes.
 Each set of vanes delivers a specific volume of
fluid and the flow rate can be determined by
revolutions of rotor.
 The rate of rotation of vane is proportional to
mean flow velocity.
 The total no of revolutions used to indicate total
volume of fluid pass through system.
 The more vanes in a rotor higher the accuracy of
rotary vane .

 If a sound wave is aimed at a moving object, and the
echo’s frequency is compared to the transmitted
(incident) frequency.
 If the reflected wave returns from a bubble advancing
toward the ultrasonic transducer, the reflected
frequency will be greater than the incident frequency.
 A bubble traveling away from the transducer, the
reflected frequency will be less than the incident
frequency.
 A Doppler flow meter bounces sound waves off of
bubbles or particulate material in the flow stream,
measuring the frequency shift and inferring fluid
velocity from the magnitude of that shift.

Construction and working
 The velocity of propagation of sound waves changes
with the change in velocity of fluid flow.
 In this system the flow velocity can be measured by
sending pulses of ultrasound signal between two sensors
i.e. upstream sensor and downstream sensor.
 When there is no liquid in pipe the travel time of signal
in both direction is same.
 If the liquid inside the pipe is moving the sound will
travel faster when it is sent in same direction of flow and
it will travel slower when it is sent against liquid flow.
 Liquid velocity is proportional to the difference in time
between upstream and downstream time
measurements.


Thank
You !!!!!!!!!!!!!!!!!!!!!!!!
!!!!!!!!!

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