Tutorial/HW Week #8
WRF Chapter 23; WWWR Chapters 25-26
ID Chapter 14
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Tutorial #8
WWWR #25.6, #25.11, # 25.13, #26.4.
To be discussed during the week 16-20 March, 2015.
By either volunteer or class list.
Special Forms
• Combining the flux equation with the
continuity equation,
n A   DAB A   A n A  n B 
 A
   DAB A     A v 
 rA  0
t
N A  cDABy A  cAV
c A
   cD ABy A    c A V 
 RA  0
t
• Assuming constant  and DAB, we get
c A
2
v  c A 
 DAB c A  RA
t
• Additionally, if there are no reactions, then
c A
 v  c A  DAB 2 c A
t
or
Dc A
2
 D AB c A
Dt
• And if there is also no fluid motion, v = 0,
c A
2
 DAB c A
t
Which is Fick’s second law of diffusion
• For steady state process, constant  and
DAB,
v  cA  DAB cA  RA
2
With no chemical reaction and no fluid
flow, becomes
 cA  0
2
which is the Laplace equation for molar
concentration.
Initial and Boundary Conditions
• Initial condition: e.g. t = 0, CA=CA0.
• Boundary condition:
• (a) The concentration of the transferring
species A at a boundary is specified.
• (b) A reacting surface boundary is specified.
Example 1
Example 2
Example 3
R2
R2
R1
Review #2:
Convective Heat Transfer & Mass
Transfer Fundamentals
• Please Refer to Appendix 8.