The influence of gas phase resistance on mass transfer to a liquid metal
- PDF / 562,866 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 42 Downloads / 225 Views
key {qf~b
--
Cb}
and equations a r e d e v e l o p e d r e l a t i n g t h i s to the v a r i a b l e s m e n t i o n e d . E x p e r i m e n t a l w o r k has been c a r r i e d out with dilute oxygen j e t s (p(O2) = 0.1 and 0.2 a t m ) blowing onto m o l t e n s i l v e r , and the r e s u l t s have c o n f i r m e d that the r e s i s t a n c e in the g a s p h a s e c o n t r i b u t e s to the o v e r a l l r e s i s t a n c e . F r o m t h e s e r e s u l t s it has b e e n p o s s i b l e to e s t i m a t e gas p h a s e m a s s t r a n s f e r c o e f f i c i e n t s which r a n g e f r o m 1.4 c m / s for a j e t m o m e n t u m of 8000 dyne and l a n c e height of 18.5 c m to 4.8 c m / s for a j e t m o m e n t u m of 56,000 d y n e s and l a n c e height of 10.5 c m .
W H E N a g a s e o u s o r v o l a t i l e c o n s t i t u e n t is a b s o r b e d in a l i q u i d , the r e l a t i v e r e s i s t a n c e s to m a s s t r a n s f e r in the g a s and liquid p h a s e s w i l l be" i n f l u e n c e d b y the s o l u b i l i t y of the c o n s t i t u e n t in the liquid. In c e r t a i n m e t a l l u r g i c a l p r o c e s s e s such a s i n e r t g a s p u r g i n g for the r e m o v a l of d i s s o l v e d g a s e s , the r e s i s t a n c e within the g a s p h a s e m a y b e c o m e s i g n i f i c a n t o r even p r e d o m i n a n t . In an a t t e m p t to i n v e s t i g a t e t h i s a s P e c t of m a s s t r a n s f e r , p r e v i o u s w o r k x in which p u r e oxygen j e t s w e r e d i r e c t e d on the s u r f a c e of m o l t e n s i l v e r h a s b e e n e x t e n d e d to include gas m i x t u r e s of oxygen and n i t r o g e n . THEORETICAL DEVELOPMENTS Solutions Which Follow H e n r y ' s Law When the s o l u b i l i t y of a s p e c i e s in a liquid is d i r e c t l y p r o p o r t i o n a l to its p a r t i a l p r e s s u r e in the gas (c = Hp), the r a t e of m a s s t r a n s f e r f r o m the g a s to the liquid is given b y 2
7l" = .~bov{YPb
-
Cb}
[1]
"biii,-ov
Solutions Which Follow S i e v e r t ' s Law In m a n y s y s t e m s the r e l a t i o n s h i p b e t w e e n c o n c e n t r a tion in the liquid and the p a r t i a l p r e s s u r e is n o n l i n e a r . F a m i l i a r e x a m p l e s a r e s y s t e m s in which d i a t o m i c g a s e s a r e d i s s o l v e d in liquid m e t a l s . T h e s e s y s t e m s u s u a l l y o b e y Si e v e r t ' s law. (X~)g-
:
_1
kl
+
-
2[Xk; c =q~-
= kz
- cb}
H
kg
The m a s s t r a n s f e r c o e f f i c i e n t s p r e d i c t e d by the v a r i ous t h e o r i e s such a s the p e n e t r a t i o n t h e o r y a o r the f i l m t h e o r y 4 a r e p r o p o r t i o n a l to the d i f f u s i o n c o e f f i c i e n t s r a i s e d to p o w e r s of b e t w e e n one half and unity. Since t y p i c a l r a t i o s of the diffusion c o e f f i c i e n t s in the g a s to t h o s e in the liquid a r e of the o r d e r of 10 4 to l 0 s , the value of kg i s u s u a l l y g r e a t e r than k l
Data Loading...
