2. Introduction
• The measurement of fluid flow is important in applications ranging from
measurements of blood-flow rates in human artery to the measurement
of liquid oxygen in a rocket.
• The selection of the proper instrument for a particular application is
governed by many variables, including cost.
• Flow-rate-measurement devices frequently require accurate pressure and
temperature measurements in order to calculate the output of the
instrument.
• The most widely used flow metering principle involves placing a fixed area
flow restriction of some type in the pipe or duct carrying the fluid. This
flow restriction causes a pressure drop that varies with the flow rate.
• Thus, measurement of the pressure drop by means of a suitable
differential-pressure pick up allows flow rate measurement.
3. Flowmeters
• Devices used to measure flow rate:
– Venturi meter (based on pressure difference)
– Orifice meter (based on pressure difference)
– Rotameter (based on drag forces)
– Pitot tube
– Magnetic (magnetic field is used to measure flow rate)
– Ultrasonic (ultrasonic waves are used to measure flow
rate)
– Turbine flow meter
5. Continued…
• The venturi flow meter is an obstruction flow meter due to which pressure
drop occurs
• Pressure drop is given by :
• Discharge is given by:
• C discharge co-efficient
8. Rotameter
• Rotameters are devices for direct measuring of the flow of moving
fluid
• The main elements of its construction are a transparent conic pipe
1 and a float , made of a conic tip 2, a cylindrical body 3 and a board
4
• The value of the quantity measured is defined by the height of float
going up.
• The rotameters have found wide application in practice due to their
simple construction, distinct indications along a linear scale,
possibility to measure small flows of fluids and gases,including
aggressive ones, sufficiently wide range of measuring, etc
9.
10. Pitot tube
• The Pitot tube is a simple device that allows for the
measurement of the flow pressure in a moving fluid
• It also works on Bernoulli’s principle
11. • Applying Bernoulli's equation we get:
• Now from above equation we get,
• We can calculate the velocity and multiplying it with the area
will give the flow rate
13. • It is based on Faraday’s law of electromagnetic induction
• An electrical current (I) is applied to a coil package inside the flowmeter
• As a result, a magnetic field (B) is created across the metering pipe
• When a conductive liquid flows through the magnetic field, a small voltage
(u) is induced
• This voltage is proportional to the velocity of the flow and is accurately
measured by two stainless steel electrodes mounted opposite each other
inside the metering pipe
• The two electrodes are connected to an advanced electronic input
circuitry which processes the signal and in turn feeds it to the a
microprocessor inside the electronics module
• The microprocessor then calculates the volumetric flow and controls the
various outputs on the terminal board
