Download basic concept of thermodynamics

BASIC COCEPT OF
THERMODYNAMICS
Prof. kiran gore
Thermodynamics
Greek word
Theme – Heat
Dynamics – Motion
Thermo” refers to released heat during
combustion
“ Dynamics” refers to mechanical action for
doing work
“
Definition
“Thermodynamics is the science
which deals with energy transfer & effect of
energy transfer on the properties of substance.”
Thermodynamic system, boundary
,surrounding
Thermodynamic system
Types of system
1. Closed system
2. Open system
3. Isolated system
Closed system (Control mass)
Example of closed system
Food items in pressure cooker
Example of closed system
• Gas trapped within a piston & cylinder device
stopper
P
I
S
T
O
N
C
Y
L
I
N
D
E
R
Example of closed system
• Hot coffee in a cup
Heat flows in the direction
of decreasing temperature.
Example of closed system
• Bulbs & lamp
Open system (control volume)
Example of open system
WATER BOILER
Example of open system
Nozzle
Example of open system
Reciprocating air comp
Example of open system
Internal combustion engine
Adiabatic system
Example of isolated system
Thermos
Units & Dimension
 Mass –
The basic unit of mass is Kg. for larger
masses units of mass is Tone.
1 Tone = 1000 Kg. or 103 Kg.
 Volume The space occupied by the matter is called
as volume.
Unit = m3 or Liter
1 Liter= 10-3 m3
Units & Dimension
 Weight –
Weight of the body is the force exerted on
it’s mass due to gravity.
Weight (W) = m . g
Where
m= mass of the body in Kg.
g= acceleration due to gravity.
Units & Dimension
 ForceThe product of mass & acceleration is
called as force .
Force = mass X acceleration
= Kg X m/s2
=N
Units & Dimension
 Density
-mass per unit volume of a substance.
Specific volume
-volume per unit mass of a substance.
Units & Dimension
 Specific gravity
The ratio of the density of a
substance to the density of water.
Units & Dimension
force
pressure 
area
Which shoes create the most pressure?
Units of Pressure
The most
common unit for
pressure is bar
1 bar = 105pa
= 105 N/ m2
= 102 KN/ m2
= 102 K pa
Force
Pressure = Area
m2
= Pascal
= N/
N
Pa  2
m
Atmospheric pressure, absolute, gauge
Units & Dimension
Temperature –
Temperature can be define as measure of
hotness or coldness.
The temperature of a body is measured in
Celsius (o c), Kelvin (K), Fahrenheit (o f).
Their relation is
1 o c = 273 K
Energy
• Energy is defined as capacity to do work.
• Any one form of energy can be converted into
another form.
• Energy can be stored in different forms.
• The different forms are as
1. Potential energy
2. Kinetic energy
3. Internal energy
Potential energy
Potential energy of the system is the
energy stored in the system due to its position
in a gravitational field.
d(P.E.) = m . g . (Z2 –Z1)
Kinetic energy
Kinetic energy of a system is the
energy which arises from the motion of a mass.
d(K.E.) = 1/2 . m . (V2 2 –V1 2 )
Internal energy (U)
It is the energy arising in the form
motions of molecules & atoms.
Total energy
The total energy of the system is the
summation of potential energy, kinetic
energy, & internal energy.
Total energy (E) = P.E.+ K.E.+U
Heat
• It is the transfer form of energy that flows
between two system (or a system & its
surrounding ) by virtue of the temperature
difference between them.
Surroundings
System
Heat
Heat transfer rate (Q)
The quantity of heat transfer in unit time
is called as heat transfer rate.
Q = Q/ dt KJ/s or KW
Heat transfer (q)
The heat transfer per unit mass of the system
is denoted by q & it is expressed as
q = Q/ m kJ/ kg
Relation between Q & q
Q = 30kJ
m = 2kg
t = 5s
Q = 6kW
q = 15kJ/kg
Specific heat (C)
• The specific heat of a substance is define as
the quantity of heat required to raise the
temperature of unit mass of substance
through unit degree temperature difference.
C = 1/m (dQ/dT)
kJ/kg.K
Liquids & solids have only one specific heat.
Gases have two specific heat (Cp or Cv).
Cp = specific heat at constant pressure
Cv = specific heat at constant volume
Work
The work like heat is also form energy in
transit. It is defined as the energy transfer
associated with force acting through a distance.
Surroundings
System
Work
Mechanical work –
Work done = Force X displacement
=NXm
= Joule
Heat
Moving boundary work
Pext
work  force  distance
V2
Pint
V1
w  ( Pext  A)  L
w   Pext  V
Sign Conventions
U = q - w
+w
System
-w
+q
-q
engineering
Units & Dimension
 PowerThe rate of doing of work is called as
power.
workdone
power 
time
= N.m/
s
= J/s
=Watt (W)
Enthalpy (H)
• The sum of internal energy (U )& the product
of pressure (P) & volume (V) appears
frequently in many thermodynamic analyses.
Enthalpy (H) = U + p V
• It is measured in units of Kj.
• The enthalpy per unit mass system is referred
as specific enthalpy & is denoted by h (Kj/Kg).
Entropy
Equality of temperature
Hot
system
TRANSFER
OF HEAT
Cold
system
Example of Equality of temperature
Zeroth low of thermodynamics
“It states that when two system are in thermal
equilibrium with third system then they are thermal
equilibrium with each other”.
System
(s1)
A
D
I
A
B
T
I
C
W
A
L
L
System
(s3)
System
(s2)
Thermodynamic Properties
• Any measurable & observable characteristics
of a system is called as “thermodynamics
property”.
Properties:
•Temperature
•Pressure
•Volume
•Internal energy
•Entropy
System
Classes of properties
• Intensive
– TEMPERATURE
– PRESSURE
– DENSITY
NOT ADDITIVE OVER
THE SYSTEM.
Intensive properties: Those
that are independent of the
mass of a system, such as
temperature, pressure, and
density.
• Extensive
– MASS
– VOLUME
– ENERGY
ADDITIVE OVER
THE SYSTEM.
Extensive properties: Those
whose values depend on the
size—or extent—of the
system.
Criterion to differentiate intensive
and extensive properties.
Thermodynamics State,
path, process & cycle
Thermodynamics State
The thermodynamic state is the condition of the
system as characterized by certain thermodynamic
properties like pressure, temperature specific volume
etc.
Thermodynamic process
• The transformation of the system from
one fixed stats to another state is called
as a process.
Thermodynamic path
• A locus of series of state thorough which a
system passes between initial state and final
states is called path.
Thermodynamic cycle
A thermodynamic cycle is a
sequence of processes that begins &
ends at the same state.
Point function
When
a
system
undergoes a change from
one state to another, the
properties of the system
also change, which depends
only on the end states & not
on the path followed
between these two stats.
Therefore, these properties
are called state function /
point function.
E.g. Temperature, pressure,
volume.
Path function
A quantity whose value
depends upon on the
particular path followed
during the process is
called as
a
path
function.
It requires a particular
path & direction to
represent the quantity
on any plot.
E.g. heat , work.
Types of process
Process- The transformation of the system
from one fixed stats to another state is
called as a process.
• Types of process
1.
2.
3.
4.
5.
Isobaric process
Isochoric process
Isothermal process
Adiabatic process
Polytrophic process
Isobaric process (constant=P)
The process in which
pressure
of
the
system is kept remain
constant is called as
isobaric process.
Isochoric process (const=V)
The process in which
volume of the system
is kept remain constant
is called as isochoric
process
Isothermal process (const =T)
The process in which
Temperature of the
system is kept remain
constant is called as
Isothermal process.
Adiabatic process (pv√)
The
process
in
which entropy is kept
constant
during
a
process is called as
adiabatic process.
in these process
heat neither leave nor
enters the system.
Gas Laws
BOYLES
CHARLES
GAY-LUSSAC’s
Boyle’s Law
It states that if unit mass of
gas is maintained at constant
temperature, then the volume of
gas is inversely proportional to the
absolute pressure of gas.
Robert Boyle
P
V ά1/P
PV = k
V
Boyle’s Law
Charles’ Law
It states that if unit mass of
gas is maintained at constant
pressure, then the volume of gas is
directly proportional to the absolute
temperature of gas.
Jacques Charles
V
T
V T
V
k
T
Charles’ Law
Gay-Lussac’s Law
It sates that, the absolute
pressure of unit mass of gas varies with
it’s absolute temperature, when the
volume of gas is kept constant.
Gay-Lussac’s
P
T
P T
P
k
T
D. Combined Gas Law
P
V
PV
PV = k
T
P 1V 1 P 2V 2
=
T1
T2
P 1 V 1T 2 = P 2V 2 T 1
Ideal gas equation
pV = mRT
• Where,
P = pressure in N/m2 or pa,
V = Volume in m3,
m = Mass of gas in kg,
T = absolute temperature in K &
R = Gas constant in J/kg.K
= 0.287 kJ/kg.K
Low of conservation of energy
It states that the “ the
energy can neither created
nor be destroyed, but
whenever there is change
in the state of a system
there is only transformation
of one form of energy in to
another.
First law of thermodynamics
The statement of first low of thermodynamics
in different forms can be stated as
When system undergoes in cyclic change, then
the algebric sum of work delivered to the
surrounding is directly proportional to the
algebric sum of heat taken from the surrounding.
i.e. Ф dw α
THERMODYNAMICS AND ENERGY
• Thermodynamics: The science of
energy.
• Energy: The ability to cause changes.
• The name thermodynamics stems from
the Greek words therme (heat) and
dynamis (power).
• Conservation of energy principle:
During an interaction, energy can change
from one form to another but the total
amount of energy remains constant.
• Energy cannot be created or destroyed.
• The first law of thermodynamics: An
expression of the conservation of energy
principle.
• The first law asserts that energy is a
thermodynamic property.
Energy cannot be
created or destroyed; it
can only change forms 75
(the first law).
Example
• Imagine a brick resting on window ledge 3
meters high. As the brick rests on the ledge
it has potential energy.
• If you knock the brick out of the ledge, the
potential energy is converted to kinetic
energy( the brick accelerated towards the
ground).
• When the brick hits the ground the kinetic
energy converted to light energy (sparks),
Sound energy and chemical energy (the
brick breaks).
1-12
Bomb Calorimeter Used to
Determine Energy Content of
Food
(Fig. 1-53)
E. Pressure
• Barometer
– measures atmospheric pressure
Aneroid Barometer
Mercury Barometer
E. Pressure
• Manometer
– measures contained gas pressure
U-tube Manometer
Bourdon-tube gauge
B. Charles’ Law
V
T
Volume
(mL)
Temperature
(K)
V/T
(mL/K)
40.0
44.0
47.7
51.3
273.2
298.2
323.2
348.2
0.146
0.148
0.148
0.147
V
k
T
10 miles
4 miles
Sea level
0.2 atm
0.5 atm
1 atm
As P (h) increases
V decreases
1-7
Compressed Process P-V Diagram
(Fig. 1-31)
1-8
Absolute, Gage, and Vacuum
Pressures
(Fig. 1-36)
1-9
The Basic Manometer
1-10
Temperature Scales Comparison
(Fig. 1-48)
1-27
Chapter Summary
• The absolute temperature scale in the SI is the
Kelvin scale, which is related to the Celsius scale
by
1-28
Chapter Summary
• In the English system, the absolute temperature
scale is the Rankine scale, which is related to the
Fahrenheit scale by
1-29
Chapter Summary
• The magnitudes of each division of 1 K and
1 0C are identical, and so are the magnitude of
each division of 1 R and 10F. Therefore,
and
• The second law of thermodynamics:
It asserts that energy has quality as
well as quantity, and actual processes
occur in the direction of decreasing
quality of energy.
• Classical thermodynamics: A
macroscopic approach to the study of
thermodynamics that does not require
a knowledge of the behavior of
individual particles.
• It provides a direct and easy way to the
solution of engineering problems and it
is used in this text.
• Statistical thermodynamics: A
microscopic approach, based on the
average behavior of large groups of
individual particles.
• It is used in this text only in the
supporting role.
Conservation of energy
principle for the human
body.
Heat flows in the
direction of decreasing
92
Application Areas of Thermodynamics
93
IMPORTANCE OF DIMENSIONS AND UNITS
• Any physical quantity can be characterized by
dimensions.
• The magnitudes assigned to the dimensions
are called units.
• Some basic dimensions such as mass m,
length L, time t, and temperature T are
selected as primary or fundamental
dimensions, while others such as velocity V,
energy E, and volume V are expressed in
terms of the primary dimensions and are
called secondary dimensions, or derived
dimensions.
• Metric SI system: A simple and logical
system based on a decimal relationship
between the various units.
• English system: It has no apparent
systematic numerical base, and various units
in this system are related to each other rather
arbitrarily.
94
• Open system (control volume): A properly
selected region in space.
• It usually encloses a device that involves
mass flow such as a compressor, turbine, or
nozzle.
• Both mass and energy can cross the
boundary of a control volume.
• Control surface: The boundaries of a control
volume. It can be real or imaginary.
An open system (a
control volume) with
95
PROPERTIES OF A
SYSTEM
• Property: Any characteristic of a
system.
• Some familiar properties are
pressure P, temperature T, volume
V, and mass m.
• Properties are considered to be
either intensive or extensive.
• Intensive properties: Those that
are independent of the mass of a
system, such as temperature,
pressure, and density.
• Extensive properties: Those
whose values depend on the size—
or extent—of the system.
• Specific properties: Extensive
Criterion to differentiate
properties per unit mass.
intensive and extensive
properties.
96
Thermodynamic Systems
Air
Water
Water
Water
Sediment
Types of Systems
Isolated
System
Closed
System
Open
System
Terms
Phases
Surroundings
System
quartz
Water
CaO•CO2
Components
SiO2
H2O
Calcite
wollastonite
CaO•SiO2
Equation of State
PV  nRT
Intensive Variables
P = Pressure
T = Temperature
Extensive Variables
V = Volume
n = moles
First Law
U  q  w
work
Internal
Energy
heat
Entropy
~
dq
dS  rev
T
Second Law
S°ice < S°water < S°steam
Measure of disorder of a phase
S° of a pure crystalline solid = 0 at 0 K
Third Law
Enthalpy
Heat content of a substance at constant pressure
H  U  PV
dH  dq p  VdP
dH  TdS  VdP
Heat Capacity
q
H
Cp 

TP TP
c
C p  a  bT 

T
1-1
Applications of Thermodynamics
The human body
Air-conditioning
systems
Car radiators
Airplanes
Power plants
Refrigeration systems
Isolated System
•
Closed system where no heat or work (energy) may cross the system boundary
– typically a collection of the a main system (or several systems) and its
surroundings is considered an isolated system
Isolated system boundary
work
Surr 1
system
heat
Surr 2
mass
Surr 3
Total Energy of a System
• Sum of all forms of energy (i.e., thermal, mechanical, kinetic,
potential, electrical, magnetic, chemical, and nuclear) that can exist
in a system
• For systems we typically deal with in this course, sum of internal,
kinetic, and potential energies
E = U + KE + PE
E = Total energy of system
U = internal energy
KE = kinetic energy = mV2/2
PE = potential energy = mgz
Properties
• Any characteristic of a system in equilibrium is
called a property.
• Types of properties
– Extensive properties - vary directly with the size
of the system
Examples: volume, mass, total energy
– Intensive properties - are independent of the size
of the system
Examples: temperature, pressure, color
• Extensive properties per unit mass are intensive properties.
specific volume
density
v = Volume/Mass = V/m
r = Mass/Volume = m/V
State & Equilibrium
• State of a system
– system that is not undergoing any change
– all properties of system are known & are not
changing
– if one property changes then the state of the
system changes
• Thermodynamic equilibrium
– “equilibrium” - state of balance
– A system is in equilibrium if it maintains thermal
(uniform temperature), mechanical (uniform
pressure), phase (mass of two phases), and
chemical equilibrium
Processes & Paths
• Process
– when a system changes from one equilibrium state to
another one
– some special processes:
• isobaric process
- constant pressure process
• isothermal process
- constant temperature process
• isochoric process
- constant volume process
• isentropic process
- constant entropy (Chap. 6)
process
• Path
– series of states which a system passes through during a
process
1-7
Compression Process
1-6
Quasi-Equilibrium Processes
• System remains practically in
equilibrium at all times
• Easier to analyze (equations of state
can apply)
• Work-producing devices deliver the
most work
• Work-consuming devices consume
the least amount of work
State Postulate & Cycles
•
State Postulate
– The thermodynamic state of a simple compressible substance is
completely specified by two independent intensive properties.
•
Cycles
– A process (or a series of connected processes) with identical end
states
P
2
Process
B
1
Process
A
V