Flow measurement

Manojkumar MauryaME – 13906Heat power engg.

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.

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

Venturimeter

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

Orifice Meter• Using bernoullis principle we have,

• Volume flowrate is given as:

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

• The discharge is given by α is a discharge coefficient of the fluid flow through the conic pipe – the least surface of the annular orifice of the fluid flow, corresponding to the height of the float H with respect to the initial section of the conic pipe, g – acceleration of the float mass Lf – float length

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

• 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

Magnetic flow-meter

• 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

Thank you