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Mixing Problems Exercises: A Guide to Compartmental Systems, Exercises of Mathematics

A comprehensive guide to solving mixing problems, a common type of compartmental system in engineering and related fields. It explores the concept of compartmental systems, their graphical representation using block diagrams, and the derivation of differential equations to model the mixing process. Detailed examples and step-by-step solutions to illustrate the application of these principles. It is particularly useful for students studying chemical engineering, environmental engineering, or other disciplines involving mass transfer and material balance.

Typology: Exercises

2020/2021

Uploaded on 12/11/2024

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1TMixing Problems
Exercises 1.7 13
Many complicated processes can be
broken down into distinct stages and the
entire system modeled by describing interactions
between the various stages
Such systems are called compartmental
and are graphically depicted by block diagrams
Input Xlt
rate Output
rate
It represents the amount of a
substance at time t
The substance enters the compartment
at an input rate and exits at an
output rate
The rate of change in Xlt is
given by
dog input rate output rate
pf3
pf4
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pf9
pfa

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(^1) T

Mixing

Problems Exercises 1.7^1

Many complicated processes can^ be

broken (^) down into distinct

stages and^ the

entire system modeled

by describing

interactions between (^) the various

stages

Such

systems

are called compartmental

and (^) are graphically depicted^ by^ block (^) diagrams

Input Xlt

rate

Output

rate It (^) represents the (^) amount of^ a substance at^ time t The (^) substance enters^ the (^) compartment

at an input rate^ and^ exits at^ an

output rate The rate of^

change

in (^) Xlt is given (^) by dog input rate^ output rate

Mixing

Problem

Example consider^ a

large

tank

holding 1000L of^ pure water into which a^ brine solution of salt

salt water begins to^ flow^ at

a constant^ rate^

of (^6) 4m The solution^ inside (^) the tank

is kept well^ stirred and^ is

flowing

out of^ the^ tank^ at^ 64min

If (^) the concentration of salt in^ the brine^ entering

the

tank is^ at^ kg L^ determine when^ the

concentration of^ salt in^ the will

reach 0.05^ kg L

64min Is

O I^ kg L

X It^ kg 1000 L 101 0

kg

E (^6) 4min Solution 8 rate (^) in rate^ out

rate in^ Concentration^ Flow^ in

in

Cool kg^ L^ 64min

X t^006 x 6 multiply by^

I e

e 00Gt x t^006 e^ 00Gt

x 6

00Gt e out x 6 e 00Gt

e

tx f (^600006) tdt (^) t

c

e 00Gt

X

gl qje^

006ttC

Aside

fektdt fekttcx E.at gge

oobttc

x ogE 00bte out

e

oobt

Xlt

t Ce

00Gt

Xlt 100 CE^

0067 We know that^ x^07 0 so (^) c

O X O 100 C

E O 100 C C 100 X

100 100 E

00Gt J t what (^) happens to (^) x as t (^) becomes large Find 7

lim 100 100 e

(^006) t 100 too Iott O

Example For (^) the mixing problem from the last^ example assume that the brine^ leaves^ the^ tank^ at^ a^ rate

of 54min instead of 64min with

all else^

being

the same Determine

the amount of^ salt^ at^ time t and the^ concentration^ at^ time^ t 64min (^) so

0.1kg L^

X It^ kg o 1000L^ 54min X IO O Kg Solution

Let's find a formula for volume

Rate

ofchange^

in volume^ dot 64min^ 54min V tt^ C We (^) have Vio^ 7000kg a (^) volume at (^) to 1000 0 C^1000 t 1000

Let's develop a differential

equation to (^) find X

X rate^ in^ rate^ out

x 64min

1kg L

Xlt

115 4min t t^1000 T (^) T concentration

in the tank^ flow^

out at time^ t It

x 6

IW X

t so^

of

9

t

X t^ 5

Solve

Integrating

factor

I (^) e Spit^

dt

I e

Sfo d (^) t I e^ stilettos S (^) Edu

5 lml ul t

e

en Ctt 1000 5

It 1000

5 I

x III I ooo^ s Concentration Cit II tT^ Etops of t 11ft kg L A s^ t^ o we (^) have l im^ cuts^ II to so YES to to kg L I kg L