The measurement and prediction of the melt velocities in aturbulent,electromagnetically driven recirculating low melting
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him so that a direct comparison between these data and any theoretical models is not feasible. The work to be described in this paper was undertaken with the objective of carrying out systematic velocity measurements in an induction stirred melt of a low melting alloy for a known electromagnetic f o r c e field, so as to allow the critical assessment of the predictive methods. The main motivation for the work is to provide a better understanding of e l e c tromagnetically driven circulatory flows as applied t o continuous casting problems. In the following Section 2 w e s h a l l describe the a p paratus and the experimental procedure; in Section 3 we shall briefly review the modeling equations used while the comparison between measurements and predictions will be given in Section 4. 2. APPARATUS AND EXPERIMENTAL PROCEDURE The apparatus was constructed so as t o allow the measurement of melt velocities in an inductively stirred melt of a low melting point alloy. In o r d e r to accomplish this, molten Woods m e t a l was s t i r r e d in a stainless steel container of 250 mm diam positioned inside a stirring coil with an inside diam of 317.5 mm. The s t i r r i n g coil consisted of t h r e e individual phase coils of 30 turns each. The stirring power was electrically phased t o stir metal in the upward direction on the outside radius with the return flow downward in the center. The phase coils had a power capability of 600 A with a maximum field strength of 350 Gauss (0.035 Wb/m 2) at the wall of the container. A f o r c e reaction probe was used to m e a s u r e the m e t a l velocity a l o n g the vertical a x i s . A 19 mm diam non-ferromagnetic stainless s t e e l disc was fastened t o the end of a spring loaded rod. The disc edge was bevelled to reduce the effect of r a d i a l flow components. The end of the rod was connected to a Hewlett-Packard m o d e l 7DC-3000 L i n e a r Voltage Differential Transformer. The electrical VOLUME 8B,JUNE 1977-333
output of the LVDT, which t r a c e d the f o r c e on the disc, was displayed on a graphic recorder. The probe was calibrated by deflecting the r e c o r d e r pen a fixed number of l i n e s by preloading the disc on a Mettler K-7 balance. The pressure on the disc was converted t o the (stagnation) velocity by the following formula: Vo = V2gAh
The quantities J and B may be obtained from the solution of Maxwell's equations, the MHD approximation of which may be written in the following f o r m :8
~/--
[1]
I[ewlett-Packard 7 3000 LVDT
DC -
Recorder
and Vo = m e t a l velocity, g = acceleration due to gravity, and Ah = net pressure head.
Spring Loaded Rod
The field strength readings were made simultaneously with the velocity readings by inserting a t r a n s v e r s e Hall Effect probe into the m e t a l adjacent to the velocity probe. The Hall Effect probe was protected by b e i n g located inside an air cooled stainless steel tube, which was not ferromagnetic. The g e n e r a l layout of the apparatus is sketched in Fig. 1. A typical r e c o r d of the
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