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Unformatted text preview: ChE 210: Meeting 28 March 28, 2011 Outline (F&R Sections 8.08.2) Homework Due Friday 04/01/2011
 Questions from Example 7.19, 7.29, 7.42, 7.51 a&b
Problem  Hypothetical Process Paths
 Sensible Heat and Heat
Capacity Example Problem 100 mol/h of a liquid mixture of 25 mol% toluene (T) in acetone (A) at
atmospheric temperature and pressure (T = 25 C and Pabs = 1 atm) is fed to
an evaporator that operates at 120 C and 1 atm. All of the liquid is
vaporized. Heat is provided to the evaporator by condensing saturated
steam at 10 bar. Calculate the amount of heat that must be supplied to the
evaporator and the mass flow rate of saturated steam. nin = 100 mol/h nout =
XAJn = 0.75 mol A/mol xA1out =
xTJn = 0.25 mol A/mol xT’out = Out Saturated Steam Water (L)
Pabs = 10 bar P = 10 bar Reference T, P and A A
hase Hin kJ/mol) Hout (kJ/mol) Given: 1/6 ChE 210: Meeting 28 March 28, 2011 2/6 ChE 210: Meeting 28 March 28, 2011 Hypothetical Process Paths A A U and H are state properties, which means that they only depend on the T,
P and phase and not how the species arrived at that state. A A 9 Can calculate U and H relative to any convenient reference state using
a hypothetical process path. These calculations combine 5 basic
processes: 1. AP at constant T and ¢ (Section 8.2)
2. AT at constant P and (1) (Section 8.3)
3. A4) at constant P and T (Section 8.4) 4. Mixing of two liquids or dissolution of a gas or solid in a liquid at
constant T and P (Section 8.5) 5. Chemical reaction at constant T and P (Chapter 9) These steps can be combined in any logical order to move from the
reference state to the actual state. In general, AP at constant T and q) is easier to calculate for a liquid or solid
than a gas. Liquids and solids at fixed T and q): A A A A A A AV~Oand AU~O,so AH=AU+APVzVAP Ideal gases near and 1 atm: , A Nonideal gases require thermodynamic relationships that are beyond
the scope of this course. 3/6 ChE 210: Meeting 28 March 28, 2011 Examples of Hypothetical Process Paths Component: Chloroform ;_ ,1 7 , 5 , ,
Reference: P = 1 atm, T = 25 C, q) = liquid
Actual: P = 10 atm, T = 200 C, 4) = vapor (P =1 atm, T = 25 C, q; = liquid) (P =10 atm, T = 200 C, (l) = vapor) Component: Methanol ‘5 ~ v v <7, ; a ,
Reference: P = 3 atm, T = 100 C, q) = vapor
Actual: P = 3 atm, T = 20 C, (i) = liquid (P = 3 atm, T = 100 C, q) = vapor) (P = 3 atm, T = 20 C, q) = liquid) 4/6 ChE 210: Meeting 28 March 28, 2011 Sensible Heat and Heat Capacity Sensible heat is the amount of heat need to raise or lower the temperature
of a substance at constant pressure without a phase change A Closed system: AU = Q and U =f A T,V o o A A A _/\
Open system: AH=Q and HEU+ PV=f T,P,V h w x k W At constantV in a closed system: \ _ m V x i"
AU 8U
Cv(T) E “m  AU = fCV(T)dT
T1 5/6 ChE 210: Meeting 28 March 28, 2011 At constant P in an open system: A A _ AH_ w
CP(T)EA!IIT>OE_ 6T P A T2
AH = pr(T)dT
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This note was uploaded on 07/31/2011 for the course CHEM E 210 taught by Professor Shanks during the Spring '02 term at Iowa State.
 Spring '02
 Shanks

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