Advanced Transport Phenomena Module 6 Lecture 29. Mass Transport: Illustrative Problems. Dr. R. Nagarajan Professor Dept of Chemical Engineering IIT Madras. Mass Transport: Illustrative Problems. SOLUTION TO THE PROBLEM. SOLUTION. Catalytic Converter. SOLUTION.
Module 6 Lecture 29
Mass Transport: Illustrative Problems
Dr. R. Nagarajan
Dept of Chemical Engineering
If Re < 2100 (see below),transport to the wall is by Fick diffusion of CO(g) through the prevailing mixture.
Analogous heat transfer diffusivity is for gas
b. Discuss whether the Mass transfer Analogy Conditions(M A C) and Heat transfer Analogy Conditions (H A C) are met; implications ?
c. Sc for the mixture :
d. L=? We will need Re
therefore (laminar-flow regime)
For a square channel
and (used below).
If then the mass-transfer analogy is:
We estimate at which
Tentatively, assume F (entrance =1).Then:
(at which F (entrance) is indeed ). Solving for L gives: L =8.3 cm ( needed to give 95 % CO-Conversion).
e. Discuss underlying assumptions, e.g.,
fully developed flow?
nearly constant thermo physical properties?
no homogeneous chemical reaction?
“ diffusion-controlled” surface reaction?
f. If the catalyst were “ poisoned,” it would not be able to maintain . This would cause to exceed 8.3 cm. If catalyst were completely deactivated, then and, of course,
g. If the heat of combustion is 67.8 kcal/mole CO, how much heat is delivered to the catalyst channel per unit time? Overall CO balance gives the CO-consumption rate/channel:
Mixing cup avg temp at duct outlet ?
Again, we see that
h. “Quasi-Steady” Application of These Results?
hence, if the characteristic period of the unsteadiness >> 8.2 ms, the previous results can be used at each flow condition.
From overall momentum balance: