Fluid Flow Measurement
FLUID FLOW MEASUREMENT
By N. Asyiddin
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TABLE OF CONTENTS
FLUID FLOW MEASUREMENT ...... 1 WHAT IS FLOW?...... 1 UNDERSTANDING FLOW...... 3 The Flow Law ...... 3 Energy Balance in Flow...... 4 Physical Nature of Flow...... 7 Minimum and Maximum Volumetric Flow (Qmin/Qmax) Calculation ...... 8
UNITS OF FLOW ...... 9 Conversions between Units...... 9
MEASURING THE FLOW...... 10 A. Head Type, or Differential Meter ...... 11 Orifice Plates ...... 12 Venturi Tube...... 14 Pitot tubes ...... 15 Flow Nozzle...... 16 Special DP meter - Rosemount’s Probar® ...... 17
B. Turbine Meters ...... 19 C. Positive Displacement Meter (PD) ...... 20 i. Rotating or sliding vane meter...... 20 ii. Rotating impeller meter...... 21 iii. Rotating piston meter...... 21 iv. Nutating-disk meter...... 21
D. Magnetic Flowmeter ...... 22 E. Ultra-Sonic Flowmeter...... 23 F. Vortex Flowmeter ...... 27 G. Coriolis-Effect meter ...... 29 H. Rotameter (Variable Area Flow Meter)...... 36
COMPARISON OF METER CLASSES...... 37
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FLUID FLOW MEASUREMENT
Flow measurement has a history of about 3000 years. It has been studied only in the last 200 years and in the last 30 years all the new techniques have evolved. There is now a wide variety of methods available to measure the flow of liquids, solids, gases and vapours. From the flow of a cupful of liquid to the equivalent to a large river, can be measured. The cost to measure flow can be from a hundred, up to a million Malaysian Ringgit.
There are three different flow quantities to be measured :- i. The actual velocity of the fluid at a given point (measured in metres per second). ii. The volume rate of flow (measured in metres cubed per minute). iii. The mass flow rate (measured in kilograms per second).
It is also possible to measure total flow which is the total volume or mass which has flowed in a set time period.
Fluid flow metering systems provide vital information for the following purpose :-