On convection in aluminum reduction cells
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The convection p a t t e r n in the b a t h e l e c t r o l y t e and the cathode m e t a l of 150 k a m p p r e b a k e d anode a l u m i n u m r e d u c t i o n c e l l s has b e e n s t u d i e d by m e a n s of r a d i o a c t i v e t r a c e r s . The i n i t i a l d i s t r i bution of the t r a c e r s - - Z 4 N a for the bath and 198Au for the m e t a l p h a s e - - i n d i c a t e s a f a s t c i r c u l a t i n g m o v e m e n t with v o r t i c e s at the ends in both p h a s e s . C i r c u l a t i o n r a t e s up to 100 cm p e r s e c w e r e o b s e r v e d , and an a v e r a g e v a l u e s e e m e d to be 10 c m p e r s e c . The i m p l i c a t i o n s of the c o n v e c t i o n on the m e c h a n i s m of the s e c o n d a r y r e a c t i o n s , the d i s s o l u t i o n of a l u m i n a in the bath e l e c t r o l y t e and the d i s t r i b u t i o n of c a r b o n p a r t i c l e s in the c e i l a r e d i s c u s s e d . O N E c h a r a c t e r i s t i c f e a t u r e of c o m m e r c i a l a l u m i n u m e l e c t r o l y s i s c e l l s is the f a i r l y v i o l e n t c o n v e c t i o n t h a t t a k e s p l a c e in the i n t e r p o l a r s p a c e . T h i s c o n v e c t i o n i s i m p e r a t i v e to m a s s and h e a t t r a n s p o r t in the c e l l , and k n o w l e d g e of the c o n v e c t i o n p a t t e r n and r a t e s i s an i m p o r t a n t p r e r e q u i s i t e f o r i m p r o v e d c e l l c o n s t r u c tion. V e r y few e x p e r i m e n t a l s t u d i e s of c o n v e c t i o n in a l u m i n u m r e d u c t i o n c e l l s have a p p e a r e d in the l i t e r a t u r e . An a t t e m p t to study the c o n v e c t i o n p a t t e r n in the m e t a l p h a s e w a s m a d e b y W i n k h a u s , ~ who c o n s i d e r s his r e s u l t s i n c o n c l u s i v e a s to any p r e f e r r e d p a t t e r n f o r the c o n v e c t i o n . Dell, P e t e r s o n , and R u m b l e , 2 on the o t h e r hand, found in an e x p e r i m e n t a l study of c o n v e c t i o n i n d i c a t i o n of a f i g u r e eight flow in the m e t a l p h a s e , with an a p p a r e n t p o o r m i x i n g b e t w e e n the r i n g s . M e a d and Roy s h a v e p e r f o r m e d m o d e l s t u d i e s of the c o n v e c t i o n in a l u m i n u m c e l l s . T h e i r r e s u l t s d e m o n s t r a t e d t h a t the c o n v e c t i o n p a t t e r n would d e p e n d on the way the c u r r e n t w a s fed to the c e l l . G i v r y 4 h a s m a d e c o m p u t e r c a l c u l a t i o n of the m a g n e t i c e f f e c t s in the b a t h of a l u m i n u m r e d u c t i o n c e l l s , and p r e d i c t e d the c o n v e c t i o n p a t t e r n at the m e t a l / b a t h i n t e r f a c e u n d e r s i m p l i f i e d c o n d i t i o n s . The c o n v e c t i o n in a l u m i n u m c e i l s i s due to the f o l lowing d r i v i n g f o r c e s : a) I n t e r a c t i o n b e t w e e n c u r r e n t and m a g n e t i c f i e l d b) G a s evolution at the a n o d e c) T e m p e r a
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