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hot-wire anemometer[′hät ¦wīr ‚an·ə′mäm·əd·ər]
an instrument for measuring liquid or gas flow velocities of at least 0.1 m/sec. The operation of the instrument is based on the relationship between the flow velocity v and the heat emission of a thin wire placed in the flow and heated by an electric current.
The main part of a hot-wire anemometer is a Wheatstone bridge, with a sensitive nickel, tungsten, or plastinum wire 3–12 mm long and 0.005–0.15 mm in diameter connected to one arm of the bridge and mounted on thin conductive pins. The quantity of heat imparted by the hot wire to the flow of liquid or gas depends on the physical characteristics of the moving medium and the geometry and orientation of the wire. The sensitivity of the instrument increases with increasing wire temperatures.
Because of their rapid action and high sensitivity, accuracy, and compactness, hot-wire anemometers are commonly used in the study of unsteady motions and boundary-layer flows near walls. They are used to determine the direction of flow (two-wire and three-wire anemometers) and, more generally, to determine the turbulence of airflows. They are also used for probing flows both under ordinary pressures and at great rarefactions.
REFERENCESGorlin, S. M., and I. I. Slezinger. Aeromekhanicheskie izmereniia. Moscow, 1964.
Popov, S. G. Izmerenie vozdushnykh potokov. Moscow-Leningrad, 1947.