Details of basic law's of thermodynamics and definition

1. Aircraft Propulsion
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5. Basic concepts of
Thermodynamics
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7. WHY TO STUDY THERMODYNAMICS
• Energy propels the society
• Economic & technological advances of the civilized
world is directly proportional to the energy available &
used.
• It is the science which is strongly related to man’s
societal needs because of increase in consumption of
energy for producing energy & services.
• So future hangs on energy conversation &
THERMODYNAMICS provide tools to do it.

8. Scope of Thermodynamics
Energy
transformation

9. Application

10. • A Thermodynamic system is defined as
a quantity of matter or a region in space
upon which attention is concentrated in
the analysis of a problem.
• Everything external to the system is
called the surroundings.
• The real or imaginary surface that
separates the system from its surroundings
is called the boundary.
• The boundary of a system can be fixed or
movable.
• The boundary is the contact surface shared
by both the system and the surroundings.
• The boundary has zero thickness, and thus
it can neither contain any mass nor occupy
any volume in space.
BASIC DEFINITIONS
Universe = Systems
+Surroundings

11. The behaviour of a matter can be studied at two
levels:
a) Macroscopic. b) Microscopic.
Macroscopic (or classical thermodynamics):
• In this approach, a certain quantity of matter is
considered, without taking into account the
events occurring at the molecular level.
• This macroscopic approach to the study of
thermodynamics that does not require
knowledge of the behaviour of individual
particles.
• Macroscopic thermodynamics is only concerned
with the effects of the action of many molecules,
and these effects can be perceived by human
senses.
• The macroscopic observations are completely
independent of the assumptions regarding the
nature of matter.
• Example: A moving car, a falling stone from a
cliff, etc.

12. Microscopic(statistical thermodynamics)
• From the microscopic viewpoint, matter
is composed of a large number of small
molecules and atoms.
• This microscopic approach to the study
of thermodynamics that require
knowledge of the behaviour of
individual particles.
• Microscopic thermodynamics is
concerned with the effects of the action
of many molecules, and these effects
cannot be perceived by human senses.
• The microscopic observations are
completely dependent on the
assumptions regarding the nature of
matter.
• Example: Individual molecules present
in air, etc.

13. TYPES OF SYSTEMS
• A closed system (also known as a
control mass) consists of a fixed
amount of mass, and no mass can cross
its boundary. That is, no mass can enter
or leave a closed system. But energy, in
the form of heat or work, can cross the
boundary; and the volume of a closed
system does not have to be fixed.
• If, as a special case, even energy is not
allowed to cross the boundary, that
system is called an isolated system.
• An open system, or a control volume,
as it is often called, is one in which
mass and energy transfer takes place. It
usually encloses a device that involves
mass flow such as a compressor,
turbine, or nozzle.

14. SYSTE
M

15. Homogeneous & Hetrogeneous
system
► A system consisting of single phase is called homogeneous
system
► System consisting more than one phase is known as a
heterogeneous system

16. PROPERTIES OF A SYSTEM
• Any characteristic of a system by which it’s physical condition may
be described is called a property.
• Pressure, temperature, volume, mass, viscosity, thermal conductivity,
modulus of elasticity, thermal expansion coefficient, electric
resistivity, velocity, elevation, etc.
• Properties are considered to be either intensive or extensive.
• Intensive properties are those that are independent of the mass of a
system, such as temperature, pressure, and density.
• Extensive properties are those whose values depend on the size—or
extent—of the system. Total mass, total volume, and total momentum
are some examples of extensive properties.
• Extensive properties per unit mass are called specific properties.
Some examples of specific properties are specific volume (v=V/m)
and specific total energy (e =E/m).

17. STATE POSTULATE(TWO PROPERTY RULE)
• The number of properties required to fix the state of a system is given by the state
postulate
• The state of a simple compressible system is completely specified by two
independent, intensive properties
• Simple compressible system:
• Absence of electrical, magnetic, gravitational,
motion and surface tension effects.
• Independent if one property can be held constant
while another is varied.
The state of nitrogen is
fixed by two
independent,
intensive properties

18. STATE AND EQUILIBRIUM
• Consider a system not undergoing any change. At this point, all the
properties can be measured or calculated throughout the entire system, which
gives us a set of properties that completely describes the condition, or the
state, of the system.
• At a given state, all the properties of a system have fixed values. If the value
of even one property changes, the state will change to a different one.
• Properties are the coordinates to describe
the state of a system.Any operation in
which one or more properties of a system
changes is called a change of state.
• Thermodynamics deals with equilibrium states. The word equilibrium
implies a state of balance.
• In an equilibrium state there are no unbalanced potentials (or driving forces)
within the system.
• A system in equilibrium experiences no changes when it is isolated from its
surroundings.

19. THERMODYNAMIC EQUILIBRIUM
A system is sais to exist in a state of Thermodynamic equilibrium when no
change in any macroscopic property is registered,if the system is isolated
from surroundings
Thermal equilibrium- Temperature should be same throughout the system.
Mechanical equilibrium-Unbalanced forces should be absent,
eg, change in pressure
Chemical equilibrium –No chemical reaction and mass transfer .
Diathermic wall-Allows heat to flow

20. PROCESSES AND CYCLES
• Any change that a system undergoes from one equilibrium state to another is
called a process, and the series of states through which a system passes during a
process is called the path of the process.
• To describe a process completely, one should specify the initial and final states
of the process, as well as the path it follows, and the interactions with the
surroundings.
• A system is said to have undergone a cycle if it returns to its initial state at the
end of the process. That is, for a cycle the initial and final states are identical
• In a cyclic process, the system starts and returns to the same thermodynamic
state. The net work involved is the enclosed area on the P-V diagram. If the
cycle goes clockwise, the system does work. In a non-cyclic process, the series
of changes involved do not return the system back to its initial state

21. The prefix iso- is often used to designate a process for which a particular
property remains constant.
• An isothermal process, for example, is a process during which the
temperature T remains constant.
• An isobaric process is a process during which the pressure P remains
constant.
• An isochoric (or isometric) process is a process during which the specific
volume v remains constant.
• Adiabatic process:
❑ A process during which there is no heat transfer is called an adiabatic
process .
❑ The word adiabatic comes from the Greek word adiabatos, which
means not to be passed.
❑ For a adiabatic process, the system is well insulated so that no or only
a negligible amount of heat can pass through the boundary.
❑ A wall which is impermeable to the flow of heat is an adiabatic wall.
❑ A wall which permits the flow of heat is a diathermic wall.

22. QUASI-STATIC PROCESSES
• When a process proceeds in such a manner that the system remains
infinitesimally close to an equilibrium state at all times, it is called a
quasistatic, or quasi-equilibrium, process.
• A quasi-equilibrium process can be viewed as a sufficiently slow process that
allows the system to adjust itself internally so that properties in one part of
the system do not change any faster than those at other parts.

23. CONTINUUM
• The mean distance that a molecule travels between collisions with
neighboring molecules is defined as the mean-free path λ.
• If λ is orders of magnitude smaller than the scale of the body measured by d,
then the flow appears to the body as a continuous substance. The molecules
impact the body surface so frequently that the body cannot distinguish the
individual molecular collisions, and the surface feels the fluid as a
continuous medium. Such flow is called continuum flow.

24. ZEROTH LAW OF THERMODYNAMICS
When a body A is in thermal equilibrium with a body B, and also separately with a
body C, then B and C will be in thermal equilibrium with each other. This is the zeroth
law of thermodynamics.

25. IMPORTANCE OF ZEROTH LAW
OF THERMODYNAMICS:
It is the basis of temperature
measurement. In order to obtain a
quantitative measure of temperature, a
reference body is used, and a certain
physical characteristic of this body which
changes with temperature is selected. The
change in the selected characteristic may
be taken as an indication of change in
temperature. The selected characteristic is
called the thermometric property, and the
reference body which is used in the
determination of temperature is called the
thermometer. A very common
thermometer consists of a small amount of
mercury in an evacuated capillary tube. In
this case, the extension of the mercury in
the tube is used as the thermometric

26. TEMPERATURE
▪ Is a measure of how hot or cold an object is compared to
another object
▪ When two systems are in contact with each other are in thermal
equilibrium one property common to both system has the same
value is called Temperature
▪ Indicates that heat flows from the object with a higher
temperature to the object with a lower temperature
▪ Is measured using a thermometer
⮚ A thermometer is any of class of instrument that
measures the temperature. Temperature is the physical
magnitude that is measured by thermometers.
⮚ A physical property that changes with the temperature is
called a thermometric property
- most solids an liquids expand when they are heated
- electrical resistance change when is heated
- in a gas pressure and volume change when it is heated
- radiation from the surface of a body

27. TEMPERATURE SCALES
Absolute Scales Relative Scales
Rankine Scale (°R) Fahrenheit Scale(°F)
Kelvin Scale (K) Celsius Scale (°C)

28. REMEMBER !!!
(°F) = 9/5*(°C) +32
(°C) = 5/9*[(°F) –32]
(°F) = (°R) – 459.67
(°C) = (K) – 273.15
TEMPERATURE RELATIONSHIPS

30. SFEE

48. Discussion & Questions