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CE 561 Homework 11:
Assigned 11/16/09,
due 11/30/09
(1)
Shetty et al. (1992) studied gasphase backmixing for the airwater system in bubblecolumn
reactors by measuring RTDs of a pulseinjected helium tracer.
The results of one particular
experiment were as follows:
Dimensionless
Time
0.1
0.2
0.4
0.6
0.7
0.9
1.3
1.9
2.8
3.4
Normalized
Concentration
0.00
0.01
0.56
0.97
1.00
0.88
0.48
0.17
0.02
0.00
Using the above data,
(a)
Determine the normalized variance of the RTD.
(b)
Find,
N
, the number of tanks in a tanksinseries model that best matches the variance.
(c)
Find the Peclet number for a plugflowwithdispersion model that best matches this
variance.
(d)
Plot the experimental RTD along with the tanksinseries RTD using the
N
found in part
(b) and the plugflowwithdispersion RTD using the Peclet number found in (c).
Which
gives the better fit?
(e)
For either model, can the fit be improved by fitting directly to the data rather than just
matching the experimental variance?
(2) A tracer study was conducted on a flow reactor, and it was found that the RTD was
consistent with the tanksinseries model, with
N
= 5.
The mean total residence time in the
system was 8 minutes.
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 Fall '09

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