CHEMICAL ENGINEERING

284 CHEMICAL ENGINEERING VOLUME 1 SOLUTIONS

CTD

P

RT

D

 0. 760 ð 13 , 600 ð 9. 81



 8314 ð 349



D 0 .0350 kmol/m^3

For air: CB 1 DCTCA 1 D 0. 0350  0. 0138

D 0 .0212 kmol/m^3

and: CB 2 DCTD 0 .0350 kmol/m^3.

The evaporation rate of water is: N^0 AD

26 ð 10 ^6

y 2 y 1

ð 0 .0350 ln

(

0. 0350

0. 0212

)

D

0. 456 ð 10 ^6

y 2 y 1

kmol/m^2 s

But: N^0 AD 4. 11 ð 10 ^3 kg/m^2 sD 0. 228 ð 10 ^3 kmol/m^2 s.

giving a film thickness of:y 2 Dy 12
ð 10 ^3 mD2mm

For ethanol:Vapour pressureD541 mm Hg at 343 K.

At 343 K: CA 1 D

PA 1

RT

D

 0. 541 ð 13 , 600 ð 9. 81



 8314 ð 343



D 0 .0253 kmol/m^3

CTD

P

RT

D

 0. 760 ð 13 , 600 ð 9. 81



 8314 ð 343



D 0 .0356 kmol/m^3

CB 1 DCTCA 1

 D 0 .0103 kmol/m^3

and: CB 2 DCTD 0 .0356 kmol/m^3

The evaporation rate of ethanol,N^0 AD

(

12 ð 10 ^6

0. 002

)

ð 0. 0356 ðln

(

0. 0356

0. 0103

)

D 0. 265 ð 10 ^3 kmol/m^2 s

D 12. 2 ð 10 ^3 kg/m^2 s

The total flux at any locationDdiffusional fluxCbulk flow

bulk flow

total flux

D 1 

diffusional flux

total flux

D 1 

CB

CT

At the ethanol surface, the proportion of flux due to bulk flow is:

1 

0. 0103

0. 0356

D 0. 71