Measurement of velocity in high-temperature liquid metals
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I. V E L O C I T Y M E A S U R E M E N T M E T H O D S IN L I Q U I D M E T A L S AND T H E I R L I M I T A T I O N S K N O W L E D G E of flow velocities in liquid metal systems is important in the design and control of hightemperature processes from laboratory up to actual industrial scale setups. Some examples of processes where metal flows occur include aluminum reduction cells and continuous casting equipment from the aluminum industry, while from the steel industry, representative examples are flows in tundishes, stirred ladles, induction furnaces, and continuous casting processes. Velocities averaged over a small region are measured in common fluids based on several different physical principles. They include the following: (a) flow visualization by direct injection-photographic methods, (b) measurement of velocities with differential pressure, (c) electromagnetic velocity measurement, (d) hot wire and hot film anemometry, and (d) Laser-Doppler velocimetry, For the case of liquid metals, opacity rules out flow visualization techniques and photographic methods, except for measurements at free surfaces. [L2,3] LaserDoppler velocimetry is also excluded for the same reason. The pitot tube suffers from the difficulty of coupling it to the pressure sensor without freezing liquid in the lines or overheating the sensor. Hot wire and hot film anemometers are also unable to withstand temperatures in excess of approximately 100 ~ so the application of A.C. MIKROVAS, formerly Graduate Student, Department of Metallurgy and Materials Science, University of Toronto, is Research E n g i n e e r , C o m i n c o Ltd., Trail, BC, C a n a d a . S.A, ARGYROPOULOS, Associate Professor, is with the Department of Metallurgy and Materials Science, University of Toronto, Toronto, ON, Canada M5S IA4. e-mail address: argyro~ecf.utoronto.coc. Manuscript submitted July 16, 1992. METALLURGICAL TRANSACTIONS B
these sensors has been restricted mostly to mercury [4 131 and Wood's metal flows. 1~41 In addition to photographic methods and hot wire-film anemometry, the following probe-velocity measurement techniques have been applied in liquid metals: (a) reaction probes, (b) tracer techniques, (c) electromagnetic probes, (d) velocity measurements from dissolution studies, and (e) fiber optic velocity sensor. The principle of operation of the reaction probe is based on measuring the force exerted on a submerged body by the flowing fluid. Reaction probes have been used in a variety of configurations, depending on the type of submerged body and its positioning: they include horizontal tm or vertical [16,~71 discs or plates and porous spheres.t~8 -~2~The most sophisticated probe of this type is the one by Moros et a1.,[22] since it can simultaneously measure two-dimensional velocities. However, this probe has been used only in low-temperature studies (mercury pools). The other reaction probes have the following limitations: (a) they measure only one velocity component, t~5"16"~71(b) they have been used only in lowtemperature studies, t~s.~s-2~ (c
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