Post on 19-Oct-2015
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5/28/2018 A Hot Wire Anemometer
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HOT WIRE ANEMOMETER
A hot-wire anemometer measures local instantaneous velocity based on
principles of heat transfer. A hot-wire probe is used in gas flows, while a
hot-film is used for liquid flow. The hot-wire has a limitation that it is
insensitive to the flow direction. Further, it has a non-linear input-output
relationship which makes its sensitivity non-uniform over any velocityrange. In particular, the sensitivity decreases with increasing velocity. The
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hot-wire probe is a platinum-coated tungsten wire, typically of diameter and
about 5 m length, supported between highly conducting prongs. Tungsten
has high temperature coefficient of resistance (i.e., resistance increases
rapidly with temperature) and the platinum coating affords strength as well
as protection against corrosion of the thin wire.
Constant Temperature Type Anemometer
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Constant Current Type Anemometer
Current across the wire exposed to flow is kept constant. Variation in
resistance of wire caused by fluid flow is measured by monitoring the voltagedrop across filament. Figure below shows the basic circuitry of constant
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current anemometer. It has few disadvantages such as it is difficult to use,
its output decreases with velocity, there is very high exist risk of probe
burnout.
The calibration curve for the constant current type anemometer is shown
below.