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THERMODYNAMICS II [MECH 351]
Lectures: Dr. Lyes KADEM
Office: EV 4.207
Office hours: M-W: 11:00 to 12:00 am
Course notes and assignments solutions will be available [temporarily] on the web site: edzm.f2g.net Textbook: Thermodynamics an Engineering Approach [by Cengel and Boles] I find it very expensive: so READ IT “The person who does read good books has no advantages over the person who can’t read them” [Mark Twain (1835-1910)]
Recommended reference: Fundamental of Thermodynamics [by Sonntag; Borgakke and Van Wylen]
MECH 351 Lyes KADEM Fall 2006
The French translation of the most important terms will be available on the web site.
MECH 351 Lyes KADEM Fall 2006
MECH 351: Revision
MAIN TOPICS
- Vapor and combined power cycles Chap.9
- Gas power cycles Chap.8
- Refrigeration cycles Chap.10
- Thermodynamic property relations Chap. 11 & 12
- Gas-vapor mixtures and air conditioning Chap.13
- Chemical reactions and phase equilibrium Chap.14
MECH 351 Lyes KADEM Fall 2006
MECH 351: Revision
LABORATORY
- Laboratory instructor: Marco Antonitti
- The lab will start the second week #18/09.
- Lab manuals should be available at the bookstore.
- Be sure to attend the correct lab section at the designed week.
- There will be no Lab exam this year. You will be graded on your reports.
MECH 351 Lyes KADEM Fall 2006
MECH 351: Revision
ASSIGNMENTS
- Problem assignments are given in your course outline.- You must do your assignments at the end of each chapter.
- Doing the assignments will be the most important point for this course.
- Tutors: XA (Benjamin Preece); XB (Philippe Sejean)
MECH 351 Lyes KADEM Fall 2006
MECH 351
GRADING
Quizzes 15% 100% from assigned problems
Laboratory 15%
Midterm 20%
Final Exam 50% You must have more than 50% to pass the course.
Rate your Professor at: www.ratemyprofessors.com
MECH 351 Lyes KADEM Fall 2006
MECH 351: Revision
Definition of Thermodynamics:
“Thermodynamics is the Science of Energy and Entropy”
MECH 351 Lyes KADEM Fall 2006
MECH 351: Revision
- Some definitions.
- Properties of pure substances.
- Ideal gas law.
- The zeroth law.
- Entropy and the second law.
MECH 351 Lyes KADEM Fall 2006
MECH 351: RevisionSome definitions
Intensive properties: independent of the size of the system [T, P]
Extensive properties: dependent of the size of the system [V]
Specific extensive properties per unit mass [υ]
Quasi-static process
A process in which the system remains infinitesimally close to an equilibrium state at all times.
gas
MECH 351 Lyes KADEM Fall 2006
MECH 351: Revision
The Zeroth law of thermodynamics0th
Thermal equilibrium: two states are said in thermal equilibrium if, when they are brought into thermal contact with one another, their states do not change.
0th law of thermodynamics: if A is in thermal equilibrium with B and B is in thermal equilibrium with C the; A is in thermal equilibrium with C.
& ⇒
A B B C A CThis “obvious” law is the basis for the validity of temperature measurement.
The 0th cannot be concluded from the other laws of thermodynamics.
MECH 351 Lyes KADEM Fall 2006
MECH 351: Revision
Properties of pure substances.
Definition: a pure substance is a substance with fixed and stable chemical composition
Properties of pure substances.
MECH 351 Lyes KADEM Fall 2006
MECH 351: Revision
Quality
Properties of pure substances.
massTotalmassVaporx =
The state of a pure substance is completely determined knowing two independent thermodynamic properties.
Steam tables
MECH 351 Lyes KADEM Fall 2006
MECH 351: Revision
Engineering Equation Solver (EES)
Result from table: U=546.02 kJ/kg
P1=PRESSURE(Steam, T=T1, v=v1) P2=PRESSURE(Steam, u=u1, v=v1) X1=QUALITY(Steam, S=S2, P=P1) TA=TEMPERATURE(Prpoane, h=h1, P=P1) S1=ENTROPY(Propane, T=TP, H=HP)
EES ⇒ gain of TIME & ACCURACY
MECH 351 Lyes KADEM Fall 2006
MECH 351: Revision
The ideal-gas equation of state
General formulation:
ZRTPv =Temperature
Gas constantCompressibility factor
Pressure
Specific volume
Ideal gas
Z=1
Real gas
Z<1 Z=1 Z>1
A gas behaves like an ideal gas if:- The pressure is very low.
- The temperature is very high (T> 2 Tc), regardless of pressure.
MECH 351 Lyes KADEM Fall 2006
MECH 351: Revision
Specific heats
At constant volume:
ctevv T
uC=
⎟⎠⎞
⎜⎝⎛∂∂
=
At constant pressure:
ctepp T
hC=
⎟⎠⎞
⎜⎝⎛∂∂
=
Gives you an idea on the energy that you must spend to rise the temperature of 1 kg of a substance by 1 degree.
Cp – Cv=R
MECH 351 Lyes KADEM Fall 2006
MECH 351: Revision
First law of Thermodynamics
Clausius statement:
The variation of energy during a process is equal to the sum work and heat exchanged with the environment during the same process.
E W QΔ = +Variation in internal energy Work Heat
First law of Thermodynamics
MECH 351 Lyes KADEM Fall 2006
MECH 351: RevisionFirst law of Thermodynamics
EΔ
Internal energy variation Kinetic energy variation Potential energy variation
2 1( )m u u− 2 22 1
1 ( )2
m V V− 2 1( )mg z z−
Steady flow process
2 2
2 2
i e
e ie e e i i i
m m
V VQ W m h gz m h gz
⎧ =⎪⎨ ⎛ ⎞ ⎛ ⎞
− = + + − + +⎜ ⎟ ⎜ ⎟⎪⎝ ⎠ ⎝ ⎠⎩
∑ ∑
∑ ∑
& &
& & & &
exits inlets
MECH 351 Lyes KADEM Fall 2006
MECH 351: Revision
Second law of Thermodynamics
MECH 351 Lyes KADEM Fall 2006
MECH 351: Revision
Second law of Thermodynamics
A process is realizable only if the 1st and 2nd laws for thermodynamics are fulfilled.
The second law states that processes occur in a certain direction.
MECH 351 Lyes KADEM Fall 2006
MECH 351: RevisionSecond law of Thermodynamics
Heat engine
Heat Work
1net out Lth
H H
W QQ Q
η = = −
Wnet out net work output
QH heat supplied to the engine
QL heat rejected by the engine
High temperature reservoir
Low temperature reservoir
QH
QL
Wnet out
MECH 351 Lyes KADEM Fall 2006
MECH 351: RevisionSecond law of Thermodynamics
Refrigeration and Heat Pump
Work Heat
1
1
1
1
LR
Hnet in
L
HHP
Lnet in
H
QCOP QWQ
QCOP QWQ
= =−
= =−
MECH 351 Lyes KADEM Fall 2006
MECH 351: Revision
Carnot cycle
A-B: Reversible isothermal expansion B-C: Reversible adiabatic expansion C-D: Reversible isothermal compression D-A: Reversible adiabatic compression
1 Lth
H
TT
η = −
Example:
TL=430 C
TH=1870 C67.2thη =
MECH 351 Lyes KADEM Fall 2006
MECH 351: Revision
Increase in entropy principle:
0genS ≥
MECH 351 Lyes KADEM Fall 2006
MECH 351: Revision
Entropy relationsT ds du P dvT ds dh v dP
= += −
Ideal gases 1
2 1
1 2
( 1) /
2 2
1 1
2 1
1 2
k
s ctek k
s cte
k
s cte
T vT v
T PT P
P vP v
−
=
−
=
=
⎛ ⎞ ⎛ ⎞=⎜ ⎟ ⎜ ⎟
⎝ ⎠ ⎝ ⎠
⎛ ⎞ ⎛ ⎞=⎜ ⎟ ⎜ ⎟
⎝ ⎠ ⎝ ⎠
⎛ ⎞ ⎛ ⎞=⎜ ⎟ ⎜ ⎟
⎝ ⎠ ⎝ ⎠
MECH 351 Lyes KADEM Fall 2006
MECH 351: Revision
Ideal process for steady flow devices is the isentropic process (adiabatic and reversible), isentropic efficiency is:
Turbine 1 2
1 2
2 1
2 1
1 2
1 2
aT
s
sC
a
aN
s
h hActual turbine workIsentropic turbine work h h
h hIsentropic compressor workActual compressor work h h
h hActual KE at nozzle exitIsentropic KE at nozzle exit h h
η
η
η
−= =
−
−= =
−
−= =
−
Compressors
Nozzles
(a) actual; (s) isentropic
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