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Mtg) 4L [awed— = MUD—t JD Fmd*_ awe l\_\ ’2 (pm) Water Balance on a C ity Reservoir The water level in a municipal reservoir has been decreasing steadilyr during a dry spell, and there
is concern that the drought could continue for another 60 days. The local water company estimates
that the consumption rate in the city is approximately 10T Liday. The State Conservation Service
estimates that rainfall and stream drainage into the reservoir coupled with evaporation from the
reservoir should yield a net water input rate of 105 eel}! —r,«i 100) leay, where I is the time in days from the beginning of the drought, at which time the reservoir contained an estimated '109 liters of water. 1. Write a differential balance on the water in the reservoir.
2. Integrate the balance to calculate the reservoir volume at the end of the 60 days of continued drought. Wig l\.L\.—l (9w) Transient Balances on :3 Sent thatch Reactor
chm An aqueous solution containing ML of species A is fed into a holding tank that initially contains 75 lit re water. The reactant decomposes at a rate r
g 3 a, 03/13 3" VC” “VII “‘13 =° r[mol Anon] = 0.03750A A 5
\___—_’__J ———9
where Cannot AtL) is the concentration of A in the tank The volumetric feed rate of the solu—
tion, Mt], increases linearly over a 10second period from U to 25 Us and stays constant at that rate thereafter until the tank is ﬁlled to the desired level. The density of the feed stream is constant.
’——a 1. Write transient balances for the total mass of the tank contents and the mass of A in the tank.
Convert the equations to differential equations for VG) (the volume of the tank contents) and CAU) (the concentration of A in the tank) that have the form of Equations 11.4—1 and 11.42.
and provide initial conditions. ; 2. Sketch the shapes of the plots you would expect for the volume ofthe tank contents. I" ['L L and
the concentration of A in the tank, Cﬁ[1noltL). versus time. 3. Outtine how the equations woan be suited to derive an expression for (24 (t) for the period
from t = til to i — 5th s. ...
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 Spring '08
 SEONGKIM
 Mass Balance

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