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8/20/2019 Thermodynamics Notes 1
1/15
Source URL: http://me.queensu.ca/Courses/230/LectureNotes.htmlSaylor URL: http://www.saylor.org/
© Ciccarcelli/Queens University (www.queens.ca) Saylor.orgUsed by permission. Page 1 of 15
Introduct ion to Thermodyn amics, Lecture 1-2 Prof. G. Ciccarelli (2012)
Why do we need to study thermodynamics?
Knowledge of thermodynamics is required to design any
device involving the interchange between heat and work,
or the conversion of material to produce heat
(combustion).
Examples of practical thermodynamic devices:
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Source URL: http://me.queensu.ca/Courses/230/LectureNotes.htmlSaylor URL: http://www.saylor.org/
© Ciccarcelli/Queens University (www.queens.ca) Saylor.orgUsed by permission. Page 2 of 15
What is thermodynamics?
The study of the relationship between work,
heat, and energy.
Deals with the conversion of energy from oneform to another.
Deals with the interaction of a system and it
surroundings.
System - identifies the subject of the analysis by defining
a boundary
Surroundings - everything outside the system boundary.
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As an example, consider an Internal Combustion (IC)
Engine
EXHAUST GAS
WORK(drive shaft)
HEAT
(hot engine block)
FUEL
AIR
SYSTEM
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Closed System - fixed non-changing mass of fluidwithin the system, i.e., no mass transfer across thesystem boundary but can have energy exchange
with the surroundings. Example: piston-cylinderassembly
Isolated System - a system that does not interact at
all with the surroundings, e.g., no heat transferacross system boundary
CYLINDER
GAS
PISTON
ENERGY
INSULATED WALLS
ENERGY
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Open System (Control Volume) - fixed volume inspace, mass and energy exchange permitted acrossthe system boundary. Example: jet engine
As far as the surroundings are concerned the control
volume is:
C T Air
Fuel
CombustionProducts
Air
Fuel
CombustionProducts
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System Properties – macroscopic characteristics ofa system to which a numerical value can beassigned at a given time without knowledge of the
history of the system, e.g., mass, volume, pressure
There are two types of properties:
Extensive – the property value for the system isthe sum of the values of the parts into which thesystem is divided (depends on the system size) e.g.,mass, volume, energy
Intensive – the property is independent of systemsize(value may vary throughout the system), e.g., pressure,
temperature
VS = VA + VB extensive
Vs, Ts, Ms V A T A M A
VB TB MB
System
SystemSystem
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MS = MA + MB extensive
TS TA + TB intensive
Units – SI used exclusively
Fundamental units:
Mass kilograms kg
Length meter m
Time seconds s
Temperature Celcius/Kelvin oC/oK
Derived units:
Force (F) Newton N
Pressure (P) Pascal Pa
Energy (E) Joule J
Newton’s Law states: Force = mass x acceleration
F = m a
[N] = [kg] [m/s2] 1 N = 1 kgm/s2
P = F / A
[Pa] [kgm/s2] [m2] 1 Pa = 1 kg/ms2
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E = F x
[J] = [kgm/s2] [m] 1 J = 1 kgm2/s2
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Property Definitions
In order to speak of an intrinsic property “at a point” we
must treat matter as a continuum, i.e., matter is distributedcontinuously in space
In classical thermodynamics a point represents thesmallest volume V’ for which matter can be
considered a continuum.
The value of the property represents an average overthis volume V’.
At any instant the density, ρ, at a point is defined as
lim
V V
M
V units: kg/m3
Mass, M , of the system with volume, V , is
V dV dM M dV
dM
Note: if is uniform over the volume M= V
Specific volume, , defined as
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1 units: m3/kg
Consider a small area A passing through a point in a fluid
at rest. Fluid on one side of the area exerts a compressiveforce F normal to the area
The pressure, P , at a point is defined as
P F
A A A
lim
units: 1 Pa = 1 N/m2
1 standard atmosphere = 101,325 Pa
1 bar = 100,000 Pa = 100 kPa = 0.1 MPa
Absolute pressure , P abs, measured relative to a perfect
vacuum
F
A
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Gauge pressure , P g , measured relative to the local
atmospheric pressure, P atm.
Note: P* g = P*abs - P atm
Gauge pressure measurement via a manometer
P* g = P*abs – P atm = gL g= 9.81 m/s2
Gas atP*abs
Patm
L
Mercury/water
Local atmosphericpressure, P atm
0 kPa perfect vacuum
P= P*
P* g
P* abs
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The density of mercury is 13.5 times the density of water
Note: 1 standard atmosphere = 760 mm (29.9 in.) mercury= 10,260 mm water
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Temperature, T , in units of degrees celcius, oC, is a
measure of “hotness” relative to the freezing and boiling
point of water
A thermometer is based on the thermal expansion of
mercury
Microscopic point of view:
Temperature is a measure of the internal molecularmotion, e.g., average molecule kinetic energy
At a temperature of – 273.15oC molecular motion ceases
Temperature in units of degrees kelvin, oK, is measured
relative to this absolute zero temperature, so
0oK = -273oC
ICE BATH BOILINGWATER
0oC
100oC
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in general, T in oK = T in oC + 273.13
System state – condition of the thermodynamic system as
described by its properties (P1,T1,….)
A system is at steady-state if none of the system
properties change with time
A system is in equilibrium if when the system is isolated
from its surroundings there are no changes in its
properties
Example: thermal equilibrium
TH TC
TH TC TE TE
Non-Equilibrium EquilibriumTC
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A process is the transformation of a system from one
state to another state.
A cycle is a sequence of processes that begins and ends atthe same state.
Example showing a cycle consisting of two processes
P1,T1 P1,T1 P2,T2
STATE 1P1, T1
STATE 2P2, T2
Process 1 Process 2
1
2
CYCLE