introduction - Faculty of Mechanical Engineering

Transcription

PHILOSOPHY
Thermodynamics is a funny subject
The first time you go through it, you don’t
understand it at all
The second time you go through it, you think
you understand it, except for one or two small
points
The third time you go through it, you know you
don’t understand, but by that time you’re so
used to it, it doesn’t bother you any more
By Arnold Sommerfield
DESIGNED AND PREPARED BY : MOHD KAMAL ARIFFIN/2003
BAB 1 : DEFINISI DAN KONSEP ASAS
INTRODUCTION
The Word `THERMODYNAMICS’ comes from the
combination of two Greek words
THERME
Hot/Heat
+
DYNAMIS
Motion/Work
THERMODYNAMICS
• the branch of physics concerned with the conversion of different
forms of energy
or
• the study of the conversion of energy into work and heat and its
relation to macroscopic variables such as temperature and
pressure
1
MY BUSSINESS CARD
MOHD KAMAL ARIFFIN
B.Eng. (Mech), UTM,
MSc Building Services Engineering, (Heriot-Watt, UK)
LECTURER/AUTOCAD INSTRUCTOR
Office: C25-325
Faculty of Mechanical Engineering
Universiti Teknologi Malaysia
81310 Skudai
Johor, Malaysia
Tel: 07-5534738 (office)
H/P : 019-7255525
Email : [email protected]
Telefax: 07-5566159
Telex : MA 60205
Cable : UTEKMA
COURSE INFO
COURSE : THERMODYNAMICS 1
COURSE CODE : SME 1413
NO. OF CREDITS : 3
NO OF MEETING HOURS : 42 hrs
PRE-REQUISITE : NONE
PRE-REQUISITE TO :
SME 2423, SME 4912, SME 4924
PASSING MARK : 50/100
MINIMUM ATTENDANCE : 34 hrs (80%)
Student with an attendance less than 80% (36 hrs) (without
specific reason) will be banned from taking final exam
2
COURSE LEARNING OUTCOME
At the end of the course, students should be able to::
explain the basic concepts of thermodynamics such as system, state,
state postulate, equilibrium, process and cycle
explain the concept of energy and forms of energy transfer such as
work and heat
describe the state and phase change process of pure substances on
property diagrams based on the property tables, state equations and
charts
analyze closed systems involving heat and work interactions for pure
substances and ideal gases using the 1st law of Thermodynamics
analyze common steady flow devices and uniform flow processes
using the principles of mass conservation and the 1st law of
thermodynamics
analyze performance of reversible and actual heat engines,
refrigerator and heat pump cycles based on the first law and Carnot
principles
analyze the entropy changes during thermodynamic processes
determine isentropic efficiencies of various steady-flow devices
COURSE CONTENTS
• Intoduction & Basic Concepts (3 hrs)
Units, Pressure, Temperature, Systems, Surroundings, Boundary,
Properties, Cycle, Equilibrium, Property Diagram, State Postulate
• Properties of Pure Substance (9 hrs)
Phase change Processes of Pure Substance, Pressure-VolumeTemperature Relationships, Property Tables, Ideal Gas Equation of
State, Property Diagram for Ideal Gases, Compressibility factor,
Principle of Corresponding States, Other Equations of State.
• Energy, Heat and Work (3 hrs)
Kinetic, Potential & Internal Energy, Heat Transfer, Boundary work,
Shaft Work, Spring Work, Electrical Work, Enthalpy, Specific Heats of
Ideal Gases
• First Law of Thermodynamics for Closed System
(3 hrs)
Conservation of Energy for Closed System, Heat Transfer for Closed
System
3
COURSE CONTENTS
• First Law of Thermodynamics for Open System
(9 hrs)
Flow Work, Conservation of Mass and Energy for Open Systems,
General Conservation Energy Equations, Unsteady (Transient) Flow
Process, Steady State Energy Equations, Applications of Steady
State Equations : Turbines, Pumps, Nozzle, Diffusers, Throttling
Valve, Mixing Chambers, Heat Exchanger.
• Second Law of Thermodynamics (6 hrs)
Heat Reservoirs, Heat Engines, Reversible and Irreversible
Processes, Efficiency, Kelvin-Planck Statement, Reversed Heat
Engines, Coefficient of Performance, Clausius Statement, Carnot
Principles, Kelvin Temperature Scale, Max Performance of Heat
Engine & Reversed Heat Engines, Carnot and Reversed Carnot
Cycles
• Entropy (9 hrs)
Clausius Inequality, Definition of Entropy, Entropy change of Pure
Substances, TdS Relations, Isentropic Processes, Increase of
Entropy Principle, Entropy Generation of Closed System, Entropy
Generation of Open, Isentropic Efficiency.
CHAPTER 1 : DEFINITION AND BASIC CONCEPT
BIRTH OF THERMODYNAMICS AS A
MODERN SCIENCE
At its origins, thermodynamics known as the study of engines
In 1650 Otto Von Guericke built and designed the world's first vacuum
pump and created the world's first ever vacuum known as the
Magdeburg Hemispheres
Shortly thereafter, Irish physicist and chemist Robert Boyle with
English scientist Robert Hooke had built an air pump. They noticed the
pressure-volume correlation: PV=constant
In 1697, an engineer Thomas Savery built the world first engine.
Although these early engines were crude and inefficient, they attracted
the attention of the leading scientists of the time
Scientist, Sadi Carnot, the “father of thermodynamics”, in 1824
published “Reflections on the Motive Power of Fire”, a discourse on
heat, power, and engine efficiency. This marks the start of
thermodynamics as a modern science
NEXT
4
MODERN SCIENCE
The 1698 Savery Engine - the
world's first engine built by
Thomas Severy based on the
designs of Denis Papin
BACK
MODERN SCIENCE
In the years to follow, more variations of steam engines were built,
such as the Newcomen, and later the Watt Engine
In 1849, the British mathematician and physicist William Thomson
(Lord Kelvin) coined the term thermodynamics in a paper on the
efficiency of steam engines.
In 1850, the famed mathematical physicist Rudolf Clausius originated
and defined the term enthalpy H to be the total heat content of the
system, stemming from the Greek word enthalpein meaning to warm,
and defined the term entropy S to be the heat lost or turned into waste,
stemming from the Greek word entrepein meaning to turn.
First Thermodynamics book was published in 1859 by Prof. W.Rankine,
Glasgow University
NEXT
5
MODERN SCIENCE
A Watt steam engine, that propelled the Industrial Revolution
in Britain and the world
BACK
APPLICATIONS OF THERMODYNAMICS
PRINCIPLE
Refrigerator
Car Engine
Jet Engine
Power Plant
6
THERMODYNAMICS SYSTEM
Definition : A quantity of matter or a region in space chosen for study
Closed System
System
Energy
Boundary
Energy
Fixed mass (mass
cannot cross the
boundary)
Example
Gas in cylinder
Air in a balloon
Open System
System
Mass
enters
System
Surrounding
Energy
Mass
exits
Mass can cross the
boundary
Example
House hold water tank
Water pump
Air Compressor
Car Engine
THERMODYNAMICS SYSTEM
7
THERMODYNAMICS PROPERTIES
ion
Definit
Type 1
Ty
pe
11
te
g
Ca
Measurable
m, V, T, p
Specific
Properties
1
11
ry
go
te
a
C
Type 111
PROPERTIES
or
y
Characteristic of
System
Not depending on
system history
Extensive
Properties
Extensive
properties perunit
mass
υ = V/m m3/kg
Intensive
Properties
Immeasurable
U, H, S, ρ
Depend on system size and
can be mixed, m, V, U
1 kg + 2 kg = 3 kg
Define using
mathematical equation
based on measurable
properties
The State Postulate
The state of simple system is
completely specified by two
independent, intensive properties
Independent of system
size and cannot be mixed
T, p, ρ
50 oC + 70 oC ≠ 120 oC
THERMODYNAMICS PROCESS
DEFINITION
Any change that a system undergoes from one equilibrium state to another
state is called PROCESS
During a process, properties maybe change or constant
A series of states through which a system passes during a process is called
PATH
CONSTANT PROPERTIES PROCESS
p
A name given to any process according to
any properties that is constant during a
process
Isothermal (T-Constant)
Isobar (p-Constant)
Isometric (V-Constant)
Isentropic (S-Constant)
Isenthalpic (H-Constant)
Final State
p2
2
Direction
Process Path
Initial State
p1
1
v2
v1
v
QUASI-STATIC PROCESS
A sufficiently slow process that
allows the system to adjust itself
internally so that properties do
not change any faster than those
other parts of system
8
QUASI-STATIC PROCESS
THERMODYNAMICS CYCLE
A system is said to have undergone a cycle if it returns to its initial state at
the end of the process after going through a series of processes.
The initial and final states are identical.
P
R
o
p
4
3
I
2
1
Prop II
The total of property change = 0
Example
Total pressure change = (p1-p2) + (p3-p2) + (p4-p3) + (p1-p4)
=0
9
DIMENSIONS AND UNITS
UNITS
Primary Dimensions & Units
SI
kg m sec K
Imperial Ibm ft sec R
Force
F = mass x acceleration = ma
1 N = 1 kgm/s2
1 Ibf = 32.174 Ibm.ka/s2
Standard Prefix
Prefix
Syimbol
Tera
Giga
Mega
Kilo
Hekto
Deka
Deci
Centi
Mili
Mikro
Nano
Pico
T
G
M
k
H
da
d
c
m
µ
n
p
Multiple
1012
109
106
103
102
101
10-1
10-2
10-3
10-6
10-9
10-12
Example
1 TW =102 TW
1 Gpa = 109 pa
1 MW = 106 W
1 kN = 103 N
1 HI = 102 I
1 daA = 101 A
1 dl = 10-1 l
1 cm = 10-2 m
1 mm = 10-3 m
1 µm = 10-6 m
1 nm = 10-9 m
1 pF = 10-12 F
WORK
W = Force x Distance
= F x l (Nm)
1 Nm = 1 Joule
WEIGHT
(Gravity Force)
w = mg (N)
PRESSURE
DEFINITION
Pressure, p =
Force acting to a rod
Normal Force
Area
=
F
normal
A
Force exerted by Fluid
Force, F
Area, A
Force, F
Fluid
Area, A
UNIT
Rod
N/m2
Pa
kPa
Bar
MPa
1 kPa = 103 N/m2
1 Bar = 105 N/m2
1 MPa = 106 N/m2
10
TYPES OF PRESSURE
PRESSURE
Gage
Pressure
psistem > patm
pabs = pgage + patm
Vacuum Pressure
psystem < patm
pabs = patm - pvac
Absolute, Gage and Vacuum Pressure Relations
Pressure above
Atmospheric Pressure
pgage
Pressure Measurement Using
Manometer
Atmospheric
Pressure
pvac
pabs
patm
pabs
Manometric
Liquid
Gas at
Pressure
p
Pressure below
Atmospheric
Pressure
h
P =ρgh + patm
Absolute Vacuum
PRESSURE MEASURMENT
Bourdon Gage
To measure pressure in
closed container
Atmospheric Pressure Measurement
h
Simple
Barometer
Mercury
p = ρgh
Analog
Barometer
Digital
Barometer
11
TEMPERATURE
Comparison of Various Temp Scales
Definition
oC
65
80oC
90oC
Thermal Equilibrium
HeatHeat
TEMP SCALE
CELCIUS
FAHRENHEIT
KELVIN
RANKINE
70oC
70oC
oF
R
373.15
212.00
671.67
0.01
273.16
32.02
419.69
A physical properties
used to indicate the
thermal equilibrium
of a system
50oC
65
K
100.00
Water
Boiling
Point
Water
Three
phase
point
70oC
Zeroth Law of Thermodinamics
Formulated by R.H. Fowler
(1931)
-273.15
Inventor
Freezing
A.Celcius
0 oC
G.Fahrenheit
32 oF
Lord Kelvin
273 K
WJM Rankine
420 R
Boiling
100 oC
212 oF
373 K
672 R
0
-459.67
0 Abbsolute
Zero
• T(oC) = T(K) - 273
• T(R) = 1.8T(K)
• T(oF) = T(R) - 460
• T(oF) = 1.8T(oC) + 32
PROBLEM SOLVING TECHNIQUE
State the problem, the key information given and the quantities to be found
Sketch the physical system involved and list the relevant information on the
sketch, indicate any energy and mass interactions with the surroundings. Listing
the given information and check for properties that remain constant during a
process indicate them on the sketch.
State any appropriate assumptions and approximations made to simplify the
problem to make it possible to obtain a solution
Apply all the relevant basic physical law and principles and reduce them to their
simplest form by utilizing the assumptions made
Determine the unknown properties at known states necessary to solve the
problem from property relations or tables
Substitute the known quantities into the simplified relations and perform the
calculations to determine the unknowns. Pay particular attention to the units and
round the results to an appropriate number of significant digits.
Check to make sure the results obtained are reasonable and intuitive.
12

introduction - Faculty of Mechanical Engineering

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