Fluid velocities in induction melting furnaces: Part I. Theory and laboratory experiments
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A N D J A M E S W. E V A N S
F l u i d flow in an induction f u r n a c e due to e l e c t r o m a g n e t i c s t i r r i n g f o r c e s i s p r e d i c t e d t h e o r e t i c a l l y f r o m f u r n a c e d e s i g n p a r a m e t e r s by the s i m u l t a n e o u s s o l u t i o n of the M a x w e l l and N a v i e r S t o k e s e q u a t i o n s . S t r e a m l i n e p l o t s and v e l o c i t y p r o f i l e s a r e o b t a i n e d and c o m p a r e d with s u r f a c e v e l o c i t i e s m e a s u r e d e x p e r i m e n t a l l y . T h e m e a s u r e m e n t s w e r e m a d e on a m e r c u r y p o o l s t i r r e d i n d u c t i v e l y by a T o c c o 30 kW 3 kHz i n d u c t i o n m e l t i n g unit. T h e a g r e e m e n t b e t w e e n the e x p e r i m e n t a l m e a s u r e m e n t s and t h e o r e t i c a l p r e d i c t i o n s w a s good c o n s i d e r i n g t h a t no c u r v e f i t t i n g b y m a n i p u l a t i o n of a d j u s t a b l e p a r a m e t e r s w a s i n v o l v e d . It i s b e l i e v e d t h a t s u c h a m o d e l would be of v a l u e in the d e s i g n and d e v e l o p m e n t of i n d u c t i o n f u r n a c e s .
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induction m e l t i n g f u r n a c e s the m e l t i s h e a t e d by e l e c t r i c c u r r e n t s i n d u c e d by a f l u c t u a t i n g m a g n e t i c f i e l d . T h e f l u c t u a t i n g m a g n e t i c f i e l d a r i s e s f r o m an a l t e r n a t i n g c u r r e n t p a s s e d t h r o u g h a c o i l e x t e r n a l to t h e m e l t by a g e n e r a t o r . The i n t e r a c t i o n b e t w e e n the i n d u c e d c u r r e n t s and the m a g n e t i c f i e l d r e s u l t s in e l e c t r o m a g n e t i c f o r c e s within t h e f l u i d . T h e s e f o r c e s , in t u r n , r e s u l t in a v i g o r o u s s t i r r i n g of the bath. The stirring has three important consequences: i) i m p r o v e d h o m o g e n i z a t i o n of t h e m e l t (following t h e a d d i t i o n of a l l o y i n g a g e n t s , etc.), ii) m a s s t r a n s f e r t h r o u g h the top s u r f a c e of the m e l t (e.g. into a v a c u u m o r r e f i n i n g s l a g ) i s p r o m o t e d , and i i i ) t h e l i f e t i m e of the r e f r a c t o r i e s c o n t a i n i n g t h e m e l t i s s h o r t e n e d , due to e r o s i o n and e n h a n c e d m a s s transfer. D e s p i t e the i m p o r t a n c e of t h i s e l e c t r o m a g n e t i c s t i r r i n g it has r e c e i v e d v e r y l i t t l e i n v e s t i g a t i o n by p r o c e s s m e t a l l u r g i s t s and until now no m e t h o d of p r e d i c t i n g m e l t v e l o c i t i e s and r e f i n i n g r a t e s h a s b e e n available, except via empirical or semiempirical m e t h o d s . One s u c h s e m i e m p i r i c a l m e t h o d w a s p r o v i d e d by M a c h l i n 1 who u s e d a H i g b i e p e n e t r a t i o n m o d e l 2 to p r e d i c t the r a t e s of m a s s t r a n s f e r t h r o u g h the top s u r f a c e of a m e l t in an i n d u c t i o n m e l t i n
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