Continuity Eqn. of species A mole balance
General form :
Cartesian :
Cylinder :
Sphere :
(for mass transfer)

C A
 N A  RA  0
t
C A N Ax N Ay N Az



 RA  0
t
x
y
z
C A 1  rN Ar  1 N A N Az



 RA  0
t
r
z
r
r 
2
C A 1  r N Ar 
1   N A sin  
1 N A
 2


 RA  0
t
r
r sin 

r sin  
r