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Flow Measurement methods | Flow measuring instruments, devices

This page describes flow measurement basics including methods,instruments and devices. It covers flow measurement methods, flow measuring instruments or flow measuring devices.

Introduction:
The flow of material in a process can be measured by variety of methods which depends on its condition and material, the type of flow, volume, range and rangeability, pressure, temperature, accuracy and control needed.

The characteristics of flow can be determined based on Reynold's number as expressed below.

Flow Measurement Methods

Reynolds number equation

Following are the flow measurement methods commonly used for flow related measurements.
• Variable head flow meters: These meters use obstruction in the fluid path. This creates differential pressure across it which is used as measure of fluid flow. It includes venturimeter, Orifice meter, Flow nozzle, Pitot tube
• Variable area and variable head flow meters: Weirs, Flumes
• Variable area type flowmeters: Rotameter, Turbine flowmeter, Ultrasonic flowmeter, Laser Doppler Aneamometer (LDA)

Flow Measuring Instruments | Flow Measuring Devices

Following table mentions flow measuring instruments or flow measuring devices with description.

flow measuring instruments or flow measuring devices Description
Venturimeter It is used for measurement of discharge through the pipe. It works based on Bernoull's principle. It has higher sensitivity and can be used in any position. It is used for measurement of water, gases, liquids, slurries etc.
Orifice meter It is used for measuement of volumetric flow rate. It also works on Bernoull's principle. Different types of orifice plates are used in these meters for various applications.
Flow Nozzle It is similar to venturimeter but does not have diverging zone. It uses lesser jet contraction unlike Orifice meter.
Pitot tube It works on principle of "Transformation of kinetic energy of liquid into its potential in the form of static head". It consists of two concentric tubes.
Weirs These are devices which are commonly used for flow measurement of open channel or open stream. There are different types of weirs based on their notches viz. rectangular, V-type, trapezoidal etc. They are used in water works, waste & sewage systems. They can measure flow ranging from flow litres/minute to millions of liters/day.
Flumes Its sizes are arranged to form inlet and throat in which throat is thinner in size compare to inlet. This create shape similar to venturi. Hence it is known as venturi-flume.
Rotameter It is constant pressure drop type variable area flowmeter. In this flowmeter, fluid flows from bottom to top part.
Electromagnetic flowmeter It is non-obstruction type flowmeter. It is used to measure flow of slurries and electrically conductive liquid. It consists of non-conducting and non-magnetic pipe which is surrounded by electromagnet. The magnet produces magnetic field.
Turbine flowmeter It is volumetric flowmeter. In this meter, small turbine wheel is placed in the pipe along the path of the fluid flow.
Ultrasonic flowmeter It uses ultrasonic transducer or piezo-electric crystal. It measures average velocity along the path of emitted beam of ultrasonic waves. The crystal is placed in various arrangements in the tube.
Laser Doppler Aneamometer (LDA) It uses laser beam. The beam is focused at a point where velocity of flow is to be measured.


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What is difference between or comparison between

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