The objective of our presentation is comparisons of different flow measuring devices

Objective

Orifice meter

Venturi meter

Rota meter

Pitot tube

Contents

The most diverse substances are transported and distributed in piping system in every single day they may include solvents , chemicals oil&gas , drinking water , fruit juices , slurries etc

The fluid flowing through pipe often have completely different properties consequintly there are different principles and different flow measuring devices

Why we use different flow meters.

A simple instrument made by inserting drilled orifice plate between two pipe flanges and arranging suitable pressure connection.

An orifice plate is thin plate with a hole in middle which helps to measure flow rate.

Orifice Meter

Some three years ago swiss mathematician and physicsts danel bernulli discover direct relationship between pressure and speed of fluid flowing in a pipe. italian physicsts batista venturi also perform experiment on flow and in 1797 he build first flow meter known venturi tube

Venturi Meter

A meter consist of short converging pipe relatively longer pipe diverging with suitable pressure differential measurement.

When fluid passes through converging side its velocity increases maximum at throat and and become same after passing throat

What Is Venturi Meter…??

Rotameter consist of tapered tube made by glass or plastic with a float inside that is free to move A rotameter is device measure flow rate of liquid and gas in a closed tube

It belongs to class of meters called variable flow meter in which pressure drop remain constant and flow varies directly with cross sectional area

Rotameter

When fluid enter from bottom it exert force on float and float move up when gravitational and force exerted by liquid become equal equlibrium exist and float becomes stationary then flow rate measure by graduation scale on float

Principle and Working

Pitot tube is pressure measure instrument used to measure fluid flow velocity.

Pitot tube measure local velocity at given point in stream not average velocity in pipe.

Pitot tube

When pitot tube placed in a pipe from which fluid is flowing as pitot tube has two tubes one with large diameter having holes which measure static pressure . while fluid entering small tube on striking become rest kinetic energy converted into pressure energy exerted a pressure called impact pressure the difference in total pressure minus static pressure give pressure difference which give velocity of fluid by bernoullis equation.

Principle

ComparisonType Viscous

liquidSlurry Gas Pressure

lossAccuracy% full scale

Orifice Limited Poor   Good High ±0.5to ±2%

Venturi Limited Limited Good Minimal ±0.5to ±3%

Variable area meter

Limited Limited Good Average ±0.5%

Pitot tube Poor Poor Good Poor ±5to ±10%

Inference…• There are many types of flowing fluids having

different properties and nature so different measuring instruments require

• So flow meters as we discuss in this presentation their accuracy and effeciency depend on nature of flowing fluid

• But most comman flow meter used in chemical industries is orifice meter which mainly measure flow of liquids and gases

Khalid Nawaz

cell no:+923007024407

institute of chemical engineering and technology Punjab university Lahore

Pakistan