ENVE 331, Winter 2009
Homework #2
Due on February 4
th
2009
Mass Balance Problems:
Problem 1:
Alcohol
containing 15% salt is fed at a rate of 10 kg/min in a mixer (CSTR) that initially holds 100 L
of
5% salt in alcohol.
The exit solution leaves the mixer at a rate of 10 kg/min.
Determine the exit
concentration after 30 minutes in
ppm
and assume complete mixing.
The density of alcohol is 0.8 g/mL
and can be assumed constant due to low salt concentration.
Problem 2:
A CSTR is running at steady state with a flowrate of 50 mL/min.
At any instant of time you started
injecting a dye (2 mL/min with a dye concentration of 100 g/L) in the inlet line and continued to do so.
The inlet flow rate
turned to (50+2) 52ml/min and the volume of the CSTR is 2500 ml.
No reaction occurs
in the reactor.
Find the concentration of the dye after 15 and 30
minutes.
Problem 3:
A lake with a surface area of 1.13 mi
2
, is fed by a river with a flow rate of 5000 cfs.
The flow
rate in the river exiting the lake is 6000 cfs.
A wastewater treatment plant discharges into the lake at the
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 Winter '08
 VIGIL
 Environmental Engineering

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