CHEMICAL ENGINEERING

MASS TRANSFER 261

If: ADMVC BDLVC,then:

(^9) AD 1. (^59) B
N^0 A (^9) ADN^0 B (^9) B
and: N^0 BDN^0 A,
(^9) A
(^9) B

D 1. 5 N^0 A

N^0 ADDCT

dxA

dy

CuFCA (from equations 10.46aand 10.19)

DDCT

dxA

dy

C

N^0 ACN^0 B

CT

CA

DDCT

dxA

dy

CN^0 A 1. 5 N^0 A

xA

N^0 A 1 C 0. 5 xA DDCT

dxA

dy

i

N^0 A

∫ 5 ð 10  4

0

dyDDCT

∫ 0. 5

0. 7

dxA

1 C 0. 5 xA

N^0 Að 5 ð 10 ^4 DDCT 2

[

ln 1 C 0. 5 xA

] 0. 5

0. 7

N^0 AD 2 DCTln

1. 25

1. 35

ð

1

5 ð 10 ^4

D 1. 41 ð 10 ^4 kmol/m^2 s

and: N^0 BD
2. 11 ð 10 ^4 kmol/m^2 s

At the mid-point:yD 2. 5 ð 10 ^4 m

N^0 Að 2. 5 ð 10 ^4 D 2 ð 10 ^5 ð 0. 0229 ð 2

[

ln 1 C 0. 5 xA

]xA

0. 7

ln

1 C 0. 5 xA

1. 35

D

1. 41 ð 10 ^4 ð 2. 5 ð 10 ^4

2 ð 10 ^5 ð 0. 0229 ð 2

ln

1. 35

1 C 0. 5 xA

D 0. 0384

and: xAD 0. 598

The concentration gradient is given by equation (i) or:

dxA

dy

D

N^0 A 1 C 0. 5 xA

DCT

WhenxAis 0.598, then:

dxA

dy

D

1. 41 ð 10 ^4  1 C 0. 5 ð 0. 598



 2 ð 10 ^5 ð 0. 0229

D400 m^1 D 0 .4mm^1