Measurement of magnitude and direction of velocity in high-temperature liquid metals. Part I: Mathematical modeling
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I. METHODS OF VELOCITY MEASUREMENT: A REVIEW
FLUID flow phenomena in the reactors of various materials processes at very high temperatures play an essential role in the efficiency of these processes. The great majority of fluid mechanics problems in engineering are associated with some form of fluid flow measurement. The need for such measurements has increased exponentially with the development of models aimed at predicting fluid flow characteristics, since these measurements provide the necessary validation and tuning for model predictions. In measuring fluid velocity, it is necessary to be able to measure localized velocity over a short period of time, if possible without contaminating the bath. The term “common fluids” will be used to describe fluids that are transparent at low temperatures and do not possess corrosive properties. A thorough description of various velocity techniques for common fluids is given in a review book edited by Goldstein.[1] The problem faced by a liquid metal practitioner when attempts are made to measure velocity in liquid metals or liquid slags is that these fluids are very hostile and, as such, cannot be classified as common fluids. For example, the opacity of the liquid metals rules out most flow visualization techniques and photographic methods, except for measurements at free surfaces. Laser-doppler velocimetry is also excluded for the same reason, except for the rare case of molten transparent salts. The Pitot tube suffers from the difficulty of being coupled to the pressure sensor without either freezing the liquid in the lines or overheating the sensor. Hot wire and hot film anemometers are also unable to withstand high temperBLAS MELISSARI, Ph.D., formerly a Graduate Student with the Materials Science and Engineering Department, University of Toronto, Toronto, ON, Canada, is now an Engineer with HATCH and Associates, Mississauga, ON, Canada. STAVROS A. ARGYROPOULOS, Professor, is with the Materials Science and Engineering Department, University of Toronto, Toronto, ON, Canada M5S 3E4. Contact e-mail: [email protected] Manuscript submitted July 9, 2004. METALLURGICAL AND MATERIALS TRANSACTIONS B
atures. Another problem that complicates the measurement of velocity is the corrosive properties of most liquids encountered in high-temperature liquid metal operations. In the temperature range below 100 °C, hot wires and hot films can be used quite effectively to measure velocity. These probes have been used extensively for studying flows in mercury (Hg) and the low melting point alloy named Wood’s metal (50 pct Bi, 25 pct Pb, 12.5 pct Sn, and 12.5 pct Cd).[2,3] For the temperature range of up to 720°C, the electromagnetic probe developed by Vives and Ricou is the only sensor that can measure simultaneously two-dimensional (2-D) velocities in liquid metals, and can also give information about the turbulent characteristics of the flow. However, this probe also has some disadvantages when it is used in liquid metals. The probe’s duration in liquid aluminum is rather lim
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