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CHBE 470 – Process Dynamics and Control – Fall 2007
Homework Set 4
Assigned:
Wednesday, September 26
Due:
Wednesday, October 3
Note:
Please staple your papers and include your name in the first page
Use table 7.1 from textbook wherever you find appropriate
Problem 1:
Consider
the 2tank
liquid level system where the outlet from the first tank is
the inlet to the second tank. Assume linear resistances and that the system operates at
steady state when a unitstep change is made in the flow rate entering tank 1. The
transient response is critically damped and it takes 1 min for the change in level of the
second tank to reach 50 percent of the total change. If the ratio of the crosssectional
areas of the tanks is A
1
/A
2
=2,
a)
Calculate the ratio R
1
/R
2
, where R
1
, R
2
are the resistances in the 2 tanks.
b)
Calculate the time constant for each tank.
c)
How long does it take for the change in the level of the first tank to reach 90
percent of the total change?
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 Spring '09
 Smith

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