
Experimental Techniques and Thermal Design 411
used for measuring aircraft air speed but used only for the calibration of the other
velocity measurement probes that are used in the electronic equipment.
A device that is often used to measure velocity in electronic equipment is hot-wire
anemometer. It is usually made of a platinum or tungsten wire that is about 5–10
micrometers in diameter and about 1 mm in length. If such a wire is heated electri-
cally and exposed to a ow, the heat transfer rate from it is given by
(15.13)
where T
w
and T
∞
are the wire and uid temperatures, U is the uid velocity, and a and
b are constants ...