Lecture 2

1. APPLIED THERMODYNAMICS
EL 325 (3+0)

2. ADIABATIC PROCESSES
If a process is carried out in a system such that there
is no heat transferred into or out of the system (i.e.
Q=0) then the process is said to be adiabatic.

6. Liquefaction of gases is the process by which substances in their
gaseous state are converted to the liquid state. When pressure on a gas is
increased, its molecules closer together, and its temperature is reduced, which
removes enough energy to make it change from the gaseous to the liquid state.
A combustion engine is an engine which generates mechanical power by
combustion of a fuel. Combustion engines are of two general types

7. External combustion engine
(EC engine) is a heat engine where a working fluid,
contained internally, is heated by combustion in an
external source, through the engine wall or a heat
exchanger. The fluid then, by expanding and acting
on the mechanism of the engine, produces motion
and usable work.
an engine which generates motive power by
the burning of petrol, oil, or other fuel with
air inside the engine, the hot gases
produced being used to drive a piston or do
other work as they expand.
Internal combustion engine

10. isochoric /

15. Systems

16. ENERGY:
It is that capacity a body or substance possess which
can result in the performance of work.
The presence of energy can only be observed by its
effects and these can appear in many different forms.

17. ENERGY FORMS IN THERMODYNAMICS
SYSTEMS:

18. Kinetic Energy:
If the fluid is in motion then it possesses Kinetic Energy. For a unit
mass:
Internal Energy:
The energy associated with the disordered, random motion of
molecules is called Internal Energy. It is separated in scale from the
macroscopic ordered energy associated with moving objects; it
refers to the invisible microscopic energy on the atomic and
molecular scale. Internal energy is independent of the path.

19. Kinetic Energy Potential Energy
The energy of a body or a system with respect to
the motion of the body or of the particles in the
system.
Potential Energy is the stored energy in an
object or system because of its position or
configuration.
Kinetic energy of an object is relative to other
moving and stationary objects in its immediate
environment.
Potential energy is not relative to the
environment of an object.
Kinetic energy can be transferred from one
moving object to another.
Potential energy cannot be transferred.
Flowing water, such as when falling from a
waterfall.
Water at the top of a waterfall, before the
precipice.
Joule (J) Joule (J)
Speed/velocity and mass Height or distance and mass

25. The calorific value can be determined using the
heat balance.
Heat given by the fuel is equal to the heat gained
by the water.
Mass of fuel × calorific value.

34. Flow or Displacement Energy:
Any volume of fluid entering or leaving a system must
displace an equal volume ahead of itself in order to
enter or leave the system.
The displacing mass must do a work on the mass being
displaced.
Since the movement of any mass can only be achieved
at the expense of work.

35. This is called flow or displacement work
At entry it is energy received by the system.
At exit it is energy lost by the system.
W o r k d o n e f
F o r c e P A
W P A l
A l v
W P v
 
 




36. Heat Received or rejected:
In any system:
If heat is received Q is +ve.
If heat is rejected Q is –ve.
If heat is neither received nor rejected then Q=0.
External work done:
If the external work is done by the fluid then W is
positive.
If the external wok is done on the fluid then W is
negative.
If no external work is done on or by the fluid then W=0.

37. THE CONSERVATION OF ENERGY
One form of energy can be transformed into another.
E.g.
 A battery converts stored chemical energy to electrical
energy

38. Principle:
This states that energy can neither be created nor
destroyed; it can only changed in form.
In an Equation:
Initial energy + Energy entering = Final energy of + Energy leaving
of the system the system the system the system

39. ENTHALPY
Enthalpy is a measure of the total energy of a system. It
includes the system's internal energy, as well as its volume
and pressure.
It is denoted by the symbol ‘H’.
Its unit is J (joules).
H = U + PV

40. Types of Thermodynamic systems
Closed systems are able to
exchange energy (heat and
work) but not matter with
their environment.

41. If a process is carried on a closed system then by the principle
of conservation of energy:
Initial energy + Energy entering = Final energy of + Energy leaving
of the system the system the system the system
Q is assumed positive means it is transferred into the system.
W is taken positive means work done by the system.
is the change in the total energy.

42. E1=initial total energy of the contained substance
E2=final total energy of the contained substance
Q=heat transferred to or from the substance in the system
W=work transferred to or from the substance in the system
E1+Q=E2+W
Q=(E2-E1)+W
Q-W=E2-E1

45. The non-flow energy equation:
For a closed system at rest, the contained energy will be only the
internal energy U.
There is no flow of substance into or out of the system.
Process is called a non-flow process
1 2
2 1
2 1
U Q U W
U U Q W
U U U
  
  
  

49. Open systems may
exchange any form of
energy as well as matter
with their environment.
A boundary allowing
matter exchange is called
permeable. The ocean
would be an example of
an open system.
 Eg: Pump, compressor,
turbine.

50. Two flow energy equation:
It is an open system in which an equal mass of fluid per
unit time is both entering and leaving the system. Also
called continuity of mass flow.
The form of energy associated with moving fluid entering
the system will be:
Internal Energy = U1
Displacement or flow energy = P1V1
Kinetic energy=KE1
Gravitational potential energy=PE1
As the fluid enters the system, let the total energy of the
fluid mass actually in the system = ES1

51. The form of energy associated with the fluid mass leaving the
system will be:
Internal Energy = U2
Displacement or flow energy = P2V2
Kinetic energy=KE2
Gravitational potential energy=PE2
After passing through the system, as the fluid leaves the
system, let the total energy of the fluid mass remaining in the
system = ES2
ES1+U1+P1V1+KE1+PE1+Q = ES2+ U2+P2V2+ KE2+PE2+ W

52. U+PV=H=Enthalpy
ES1+H1+KE1+PE1+Q = ES2+ H2+ KE2+PE2+ W
Q - W= (ES2 - ES1) + (H2 - H1) + (KE2 - KE1) +(PE2 - PE1)

53. The steady – flow energy equation:
Steady flow system, it is considered that the mass flow
rate of the fluid or substance through out the system is
constant.
Also, the total energy of the fluid mass in the system
remains constant.
So,
ES2 =ES1
ES2 - ES1=0

54. From the open system:
Q - W= (ES2 - ES1) + (H2 - H1) + (KE2 - KE1)+(PE2 - PE1)
Q - W= (H2 - H1) + (KE2 - KE1)+(PE2 - PE1)
This is known as the steady –flow energy equation
More:
ES1+U1+P1V1+KE1+PE1+Q = ES1+U2+P2V2+ KE2+PE2+ W
ES2 - ES1=0
U1+P1V1+KE1+PE1+Q = U2+P2V2+ KE2+PE2+ W
This is for any mass flow rate.
For unit mass through system, specific quantities are used.
U1+P1V1+KE1+PE1+Q = U2+P2V2+ KE2+PE2+ W
Replace the values of KE and PE values .

57. Continuity of mass flow rate:
For a fluid substance flowing through a steady flow open
system, the mass flow rate through any section in the system
must be constant.
At any section in the system,

63. Isolated systems are
completely isolated from their
environment.
They do not exchange heat,
work or matter with their
environment.
 An example of an isolated
system is a completely
insulated rigid container,
such as a completely
insulated gas cylinder.

64. THANK YOU