The physical and mathematical modeling of the flow field in the mold region in continuous casting systems: Part I. model
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I N r e c e n t y e a r s c o n s i d e r a b l e i n t e r e s t h a s been e x p r e s s e d in p r o b l e m s r e l a t i n g to the q u a l i t y and in p a r t i c u l a r the s u r f a c e q u a l i t y of c o n t i n u o u s l y c a s t s t e e l . Since the s u r f a c e quality of b i l l e t s and s l a b s d e p e n d s on the n a t u r e of the i n i t i a l l y s o l i d i f i e d l a y e r , t h i s c o n c e r n s t i m u l a t e d n u m e r o u s s t u d i e s into the b e h a v i o r of the u p p e r p o r t i o n of the m o l d . The w o r k that h a s been done in t h i s a r e a m a y be c l a s s i f i e d into t h r e e g r o u p s , n a m e l y m a t h e m a t i c a l m o d e l l i n g , r a d i o a c t i v e t r a c e r s t u d i e s on full s c a l e s y s t e m s , and w a t e r m o d e l l i n g s t u d i e s . The p u r e l y m a t h e m a t i c a l w o r k c o n c e r n e d with flow p a t t e r n s 1'2 r e l i e d l a r g e l y on d i s p e r s i o n m o d e l s and in the a b s e n c e of e x p e r i m e n t a l i n f o r m a t i o n could not p r o v i d e a much i m p r o v e d i n s i g h t into the flow f i e l d in the m o d e l r e g i o n , although the use of the d i s p e r s i o n m o d e l could be helpful for the i n t e r p r e t a t i o n of e x p e r i m e n t a l data. The r a d i o a c t i v e t r a c e r t e s t s r e p o r t e d on o p e r a t i n g s y s t e m s by K r a i n e r et al. 3 c o n t r i b u t e d c o n s i d e r a b l y to the u n d e r s t a n d i n g of the g e n e r a l n a t u r e of the flow p a t t e r n within the liquid pool. A s a r e s u l t of t h e s e s t u d i e s it w a s g e n e r a l l y a g r e e d that (for s t r a i g h t n o z z l e s ) the l i q u i d pool m a y b e d i v i d e d into t h r e e r e g i o n s : the u p p e r part, where there exists turbulent recirculatory motion d r i v e n by the i n c o m i n g m e t a l s t r e a m , an i n t e r m e d i a t e zone w h e r e the l i q u i d flow is d r i v e n by n a t u r a l c o n v e c tion, and f i n a l l y a lower p a r t w h e r e fluid m o t i o n is n e g l i g i b l e b e c a u s e of the confined n a t u r e of the s p a c e s a v a i l a b l e for flow. The a c t u a l d i m e n s i o n of the u p p e r zone would, of c o u r s e , depend on the g e o m e t r y and on the c a s t i n g s p e e d ; the d a t a in R e f s . 3 and 4 i n d i c a t e , h o w e v e r , that for s t r a i g h t n o z z l e s the r e g i o n w h e r e the j e t i m p a c t i s s i g n i f i c a n t e x t e n d s to a length of about 4 to 6 m o l d w i d t h s . In c o n t r a s t to the s m a l l n u m b e r of r e p o r t e d i n v e s t i g a t i o n s c o n c e r n e d with r a d i o a c t i v e t r a c e r t e s t s , the literature describing water model studies is far more e x t e n s i v e . 5-16 The m a j o r i t y of t h e s e i n v e s t i g a t o r s quoted above m o d e l l e d the u p p e r p o r t i o n of the inlet J. SZEKELY is Professor of Chemical Engineering and Director
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