2 005 Thermal Fluids Engineering I Lecture Notes
Lecture 1 Basic Principles of Energy
Thermodynamics Basic concepts
System objectof our analysis In practice it's a region of spacedelimitedby a
boundary and typicallycontaining some matter
Boundary closed surface defining the system ndany
Environment universe minus the system f you
State condition of the system at a given time environ men
state is defined bythe numerical values of a set of
properties I
Property observable or measurable quantity
that is independent of the systemhistory
examples E M T P Emv V P S entropy charge a p
color position J
examplesof non properties distance travelled cashflow
heat transfer work transfer
Properties can beextensive property of the system is the sum of the properties
of the subsystems
e
g I m E V S charge
Properties can beintensive not additive
e
g T
PP J
Process a systemundergoes a process when its statechangesfrom state 1 to stat
2 Examplesinclude a material point from ri to ri a blockof hot
moving
material cooling downfrom T to Ta and an electric capacitorcharged from
Q 0 to Q2 O
Processes can be represented on thermodynamic planes
I it S V
ft T
A process that starts and ends at the same state is called a cycle
pa in
anygiven state a system can store or process or
contain mass entropy momentum
energy
Energy is the property that satisfies the 1stLaw of
Thermodynamics At the microscopic level all materials
aremadeof molecules andatoms within whichelectron
u
and protons within whichthere are neutrons and protons
At a fundamental level there are only twotypes of energy kinetic and
potential describing an interaction
, i
molecules withinatoms protons centralfields gratify
E É'Émiv y
t
energy of the system
Introducethe center of mass Miti
jam ti E ti't Jem
Mi relative velocity with
to com
Vi Ji Ji Ti't Tom ti't Van Vi Vent 2Vivomrespect
Miri Miri t Mvim Van
Pimiti
E
E f mi vie Mvc'm Vij Vij t.JO ijt Yi
Now let's transition to macroscopic description materials are continuous
media with effective properties Modesofenergystorage
ctypes
E Ekinetic Egrant Echemical t Enuclear't
Yitngmqctrict
I energyof
thesystem energy
How do I calculate theseenergystoragemodes in practice
kinetic energy
M s E kinetic MV
Gravitational energy
Egrave Mgh IFgravl Mg
M
j
h
Elastic energy rigidityconstant Mlm
u
reece m Felastic f
t E elastic thx
elongation of the spring wrt a
zero force condition
Internal energy for solids and incompressible fluids
To No are irrelevant reference values
u mo ITI Immirature
tass's specific
heat
Slug c
, During a process a system can transfer or exchange mass energy entropy
and momentum with the environment
A system is called
Isolated it it experiences no mass and no energy transfer
Closed it it experiences
energy transfer but no mass transfer
Open it it experiences bothenergy and mass transfer
Energy transfer can beof twotypes
Heat transfer energy transfer driven by a temperaturedifferencebetween th
system and environment
Use symbol Q Q 0 it heat transfer into the system
Q c O it heat transfer outof thesystem
Q O process is called adiabatic
Work transfer energy transfer driven a force x displacement or a torque
x motion or a
by
charge x voltage
Usesymbol W W O if work transfer out ofthesystem
W c o it work transfer into the system
Wi z S E dr Wi 2 Si T d0 Wi z fEv dg
displacementof the
et
fore exerted internalpointof
by
the environment applicationofforce
on the
system
external
iii
a op
Wi z 0
i
me
Examples Foreach of thefollowingsystems processes determine it open closed
isolated and of Q and W
sign
o o w
mama em butsealedtight
QED
gigitiisigitem
piston moves upward so
dosedsystem Q O
W O space Heater
41 closedsystem Q O W C O
son
1st PVpanel so
, Internal Combustion Engine
F opensystem Q O W O
fuel I Tf
air d shaft
Lecture 2 First Second Law of Thermodynamics
Review Thermodynamics Basic Concepts
System Boundary environment state property extensive us intensive
process cycle
E imgur.EE
Eg
Emin EIIEE
Emre high MELT Tolthottlex
for solidsand
incompressiblefluids Environment
A system can be isolated dosedoropen
Modes of energy transfer wine di fie W
eternal a
force from
environment
Examples
insulated
not.it ghnd
IM if hot Cublock
mm
111 Block dosed Wco
2 Person Block isolated
1 System Waterton isolated
2
System Arblock closed Q O
3 System water closed Q O
Asystemissaidtobeinanequilibrium state it left to its own devices i.e
rendered isolated the state does not change In other words fora system in a
state of equilibrium di properties o rigidamen insulated
at
a not an equilibrium state
state my equilibrium
no m
signs
I frictionless
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