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.

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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

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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.

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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

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Definition of Thermodynamics:

“Thermodynamics is the Science of Energy and Entropy”

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- Some definitions.

- Properties of pure substances.

- Ideal gas law.

- The zeroth law.

- Entropy and the second law.

MECH 351 Lyes KADEM Fall 2006

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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

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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.

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Properties of pure substances.

Definition: a pure substance is a substance with fixed and stable chemical composition

Properties of pure substances.

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Quality

Properties of pure substances.

massTotalmassVaporx =

The state of a pure substance is completely determined knowing two independent thermodynamic properties.

Steam tables

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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

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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.

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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

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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

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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

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Second law of Thermodynamics

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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.

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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

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Refrigeration and Heat Pump

Work Heat

1

1

1

1

LR

Hnet in

L

HHP

Lnet in

H

QCOP QWQ

QCOP QWQ

= =−

= =−

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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 =

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Increase in entropy principle:

0genS ≥

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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

−

=

−

=

=

⎛ ⎞ ⎛ ⎞=⎜ ⎟ ⎜ ⎟

⎝ ⎠ ⎝ ⎠

⎛ ⎞ ⎛ ⎞=⎜ ⎟ ⎜ ⎟

⎝ ⎠ ⎝ ⎠

⎛ ⎞ ⎛ ⎞=⎜ ⎟ ⎜ ⎟

⎝ ⎠ ⎝ ⎠

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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