ENGR 224 Thermodynamics

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Oct 27, 2013 (3 years and 9 months ago)

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ENGR 224



Thermodynamics


Test #1


Outline

Spring 2011


Chapter 1


Introduction: Basic Concepts of Thermodynamics



1
st

& 2
nd

Laws of Thermodynamics



Internal, kinetic and potential energies



Dimensions and Units: SI & AE



g
c

F = m a



Nomenclature

o

Systems: Op
en vs. Closed

o

Properties



Intensive vs. Extensive



Molar and Specific Properties

o

State of a system

o

Processes and Process Paths



Isobaric, Isothermal & Isochoric



Thermodynamic Cycles

o

Equilibrium: Thermal, Chemical, Phase and Mechanical

o

Quasi
-
Equilibrium Proces
s



Pressure: Absolute, Gauge and Vacuum

o

Barometer, Manometer and Differential Manometer Equations



Temperature Scales:
o
C, K,
o
R,
o
F

o

Converting between T scales

o

Changes in temperature


Chapter 2


Properties of Pure Substances



Pure Substances



Phases and Phas
e Changes

o

Vaporization/Condensation, Melting/Freezing, Sublimation/Desublimation



Phase Diagrams: PV, TV & PT

o

Subcooled Liquid, Saturated Liquid, Saturated Mixture, Saturated Vapor,
Superheated Vapor

o

T
sat

and P
sat

= P*

o

Saturated Liquid Curve, Saturated Vapo
r Curve, Two
-
Phase Envelope, Critical Point

o

Isotherms and Isobars

o

Triple Point



Thermodynamic Data Tables

o

Saturation Temperature Tables and Saturation Pressure Tables

o

Superheated Vapor Tables and Subcooled Liquid Tables

o

Linear Interpolation

o

Double Interpola
tion



Vapor
-
Liquid Equilibrium

o

Partial Pressure, Vapor Pressure, Total Pressure,
and
Mole Fraction

o

Relative and Absolute Humidity

o

Boiling vs. Evaporation



Equations of State (EOS’s)

o

The Ideal Gas EOS: Always test its validity

o

Compressibility Factor EOS

o

Advan
ce
d

EOS’s: Virial, Van der Waals, RK, and SRK

Chapter 3


Heat Effects



U(T,P) and H(T,P): Real Substances, Incompressible Liquids and Ideal Gases



Using the NIST Webbook



Heat Capacities: Constant Volume and Constant Pressure

o

Integrate C
V

to determine

U.
Integrate C
P

to determine

H.

o

IG

C
P

polynomial = Shomate Equation

(NIST Webbook)

o

IG
: C
P

= C
V

+ R

o

Solids & Incompressible Liquids:
C
P

=
C
V

and

U =

H.



Hypothetical Process Paths (HPP’s)

o

Break a complicated process into steps in which just one property cha
nges

o

Change in any property for the entire HPP is the sum of the changes in that property
for the steps that make up the HPP.

o

Latent Heats: Vaporization, Fusion and Sublimation



Clapeyron equation



H
vap

= fxn(dP*/dT)



Clausius
-
Clapeyron Equation



Assumes I
G and V
sat vap

>> V
sat liq




H
vap

from slope of LnP* vs. 1/T(K)



Antoine Equation


P* = fxn(T)



Chapter 4


The First Law of Thermodynamics


Closed Systems



Work

o

Path variable, inexact differential

o

Integral of F dx

o

Boundary Work: W
b

=


P dV

o

Sign Conventio
n
:
W > 0

for work done
BY

the system
ON

the surroundings

o

Quasi
-
Equilibrium Process: Slow, No Unbalanced Forces





P dV is easy to evaluate because the restraining force is just P
bulk

x A
cross

of
the piston.

o

Special Processes: Isothermal, Isochoric and Isob
aric



Easier to evaluate W
b
.

o

Shaft Work


very important for open systems, see chapter 5.

o

Other kinds of work



Gravitational and Acceleration Work



It is more convenient to express these in terms of change in kinetic and
potential energies



Spring Work



We will

usually consider this just another form of boundary work.



Heat

o

Energy that moves across the boundary of the system because of a difference in
temperature.

o

Moves spontaneously from hot to cold things.

o

Sign Convention
:
Q > 0

when heat is transferred
from

th
e
surroundings

into

the
system
.

o

Adiabatic Processes: Q
net

= 0

o

Path variable, inexact differential

o

Mechanisms for Heat Transfer



Conduction: Fourier’s Law



Convection: Newton’s Law of Cooling



Radiation: Stephan
-
Boltzmann Law



The 1
st

law of Thermodynamics

o

Ener
gy cannot be created or destroyed, it can only change form

o

Integral Form: Q


W =

E
sys

= {

U +

E
kin

+

E
pot

}
sys

o

Differential or Rate Form is more useful for open systems (see chapter 5)



Problem Solving Procedure

o

Read Carefully, Draw a Diagram, List Giv
en Info & List Assumptions

o

Write Equations and Lookup Data then Solve Equations

o

Verify Assumptions & Answer Questions !!



Special Cases of the 1
st

law

o

Isobaric Processes: Q =

H

o

Isochoric Processes: Q =

U



Thermodynamic Cycles

o

1
st

Law: Q
cycle

= W
cycle

o

Types

of Cycles



Heat Engines: Purpose is to convert heat into work



Thermal efficiency:

th

= fxn(Q
C
, Q
H
)



Refrigeration Cycles: Use work input to remove heat from a cold object (and
incidentally reject heat to a hot object)



Coefficient of Performance: COP
R

= fxn
(Q
C
, Q
H
)



Heat Pump: Use work input to add heat to a hot object (and incidentally
absorb heat from a cold object)



Coefficient of Performance: COP
HP

= fxn(Q
C
, Q
H
)


Chapter
5



1
st

law Open Systems



Mass & Energy Balances on Steady
-
State Processes

o

Flow work

o

Tu
rbines, nozzles, diffusers, compressors, throttling devices, pumps, heat exchangers,
mixers, splitters

o

SISO & MIMO



Transient Mass & Energy Balances

o

Uniform flow & uniform state assumptions

o

SISO and MIMO