Thermodynamics is defined as the science of energy. It studies the transformation of heat into mechanical work and vice versa. Thermodynamics has applications in systems like the human body, refrigerators, engines, turbines, heaters, and solar collectors. A system is defined as the quantity of matter under study, surrounded by its surroundings. A boundary separates the system and surroundings. Closed systems do not allow mass transfer while open systems do. Equilibrium exists when properties do not vary within a system. State refers to the condition defined by properties like temperature, pressure and volume. Quasi-static processes are reversible while non-quasi-static processes are irreversible. Cycles occur when a system returns to its original state.

2. Thermodynamics can be defined as the science of
energy.
Thermodynamics = Therme + Dynamis
(Heat) (Power)
Thermodynamics

3. Conservation of energy principle

4. Application of thermodynamics
Human Body
Refrigeration and Air conditioners
IC Engines
Gas Turbines
Water Heater
Solar Collectors
Pressure cooker ….

5. System, Surroundings & Boundary
 System
 A system is defined as a quantity of matter or a region in space chosen for study.
 Surroundings
 The mass or region outside the system is called the surroundings.
 Boundary
 The real or imaginary surface that separates the system from its surroundings is
called the boundary.

6. System, Surroundings & Boundary

7. Closed System/Control Mass
 A closed system consists of a fixed amount of mass, and no
mass can cross its boundary. 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.
 In some special case, even energy is not allowed to cross
the boundary, that system is called an isolated system.

8. Close system with fixed and moving boundary

9. Isolated System
ISOLATED
System
m = const.
E = const.
Mass NO
Energy NO

10. Open System/Control Volume
 An open system, or a control volume is a properly selected region in space. It
usually encloses a device that involves mass flow such as a compressor, turbine, or
nozzle.
 Any arbitrary region in space can be selected as a control volume.
 The boundaries of a control volume are called a control surface, and they can be
real or imaginary.
 A control volume can be fixed in size and shape, or it may involve a moving
boundary, most control volumes, however, have fixed boundaries and thus do not
involve any moving boundaries.
 e.g. Water Heater, Car Radiator, Turbine, Compressor

11. A control volume can involve fixed, moving, real, and imaginary boundaries.

12. An open system (a control volume) with one inlet and one exit.

13. Properties of a system
 Intensive Properties
• Intensive properties are those that are independent of the mass of a system, such
as temperature, pressure, and density.
 Extensive Properties
• 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
 Specific 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).

14. Criterion to differentiate intensive and
extensive properties.

15. Density & Specific Gravity
 Density is defined as mass per unit volume.
 The reciprocal of density is the specific volume v, which is
defined as volume per unit mass.
 The ratio of the density of a substance to the density of
some standard substance at a specified temperature .

16. State & Equilibrium
 Set of properties to completely describe the condition of the system
is known as its STATE
m = 2 kg
T1 = 25 ºC
V1 = 1 m3
STATE 1
m = 2 kg
T1 = 25 ºC
V1 = 3 m3
STATE 2

17. State & Equilibrium
Thermal Equilibrium :
- NO Temperature Gradient throughout the system.
Mechanical Equilibrium :
- NO Pressure Gradient throughout the system.
Phase Equilibrium :
- System having more than 1 phase.
- Mass of each phase is in equilibrium.
Chemical Equilibrium :
- Chemical composition is constant
- NO reaction occurs.
EQUILIBRIUM : State of Balance

18. Path & Process
t=0t=t1
t=0t=t2t
t2 < t1
Quasi-Static
Non-Quasi-Static
Process proceeds in such a manner that
system remains infinitesimally close to
equilibrium conditions at all times. It is
known as QUASI-STATIC or QUASI-
EQUILIBRIUM Process.

19. Path & Process
State 1 State 2
Pressure
Quasi-Static
Process Path
Volume
NOTE : Process Path is a
CONTINUOUS line only if it is
having Quasi-Static Process.
Non-Quasi-Static Process is
denoted by a DASHED line.
State 1 State 2
Pressure
Volume
Non-Quasi-Static
Process Path

20. Path & Process
Pressure(P)
Volume (V)
V=Const
Isochoric
P=Const
Isobaric
Temperature(T)
Enthalpy (h)/ Entropy (s)
T=Const
Isothermal
h=Const
Isenthalpic
s=Const
Isentropic

21. Cycle
CYCLE :
A system is said to have undergone a
cycle if it returns to its ORIGINAL
state at the end of the process.
Hence, for a CYCLE, the INITIAL and
the FINAL states are identical.
Property A
State 1
State 2
PropertyB

22. The End