TO KNOW BASIC CONCEPS & FIRST LAW OF THERMODYNAMICS

1. Unit 1 : Basic concepts and first law
out line
 Basic concepts
 Classical and statistical approaches
 Thermodynamic systems
 Zeroth law of thermodynamics
 1st law of thermodynamics applied to closed and
open systems
 Steady flow process with reference to various engg
applications

2. Thermodynamics
 The term thermodynamics derived from Greek
words.
 Therme Heat.
 Dynamics power.
 Thermodynamics can be defined as the study of
relationship between work, heat and energy.

3. “Thermodynamics is the science of energy
transfer and its effect on the physical properties
of substances”.
Thermodynamic laws and principles are found in
all fields of energy technology, notably
 Steam and nuclear power plant
 Internal combustion engines
 Gas turbines
 Air conditioning & refrigeration
 Gas dynamics & jet propulsion
 Compressors
 Chemical process plants
 Direct energy conversion devices.

4. Thermodynamic system and control volume
• Thermodynamic system: a quantity of fixed mass
under investigation,
system → fixed mass, closed
• Surroundings: everything external to the system,
• System boundary: interface separating system and
surroundings, and
• Universe: combination of system and surroundings.

5. Control volume
out
Control Volume:
fixed volume over which mass can pass
in and out of its boundary.
Control Surface:
boundary of the control volume.

6. Types of system

8. Properties of a system
 Any measurable or observable characteristics are
called property of a system
 Types:
 1.Intensive property: Independent of the mass
of the system.
 Ex: pressure, temp, volume
 2.Extensive property: dependent of the mass of
the system.
 EX: mass, energy

9. State of a system
 State is the condition of the system at any particular
moment or time the state is identified by the
properties of the system such as p , v, temp etc.
 Change of a state:
even if the values of one property
change the state will change to diff state, is called
change of a system

10. Thermodynamic process
1.quasi-static process:
A system passes through an
infinite number of continuous equilibrium state and
attains the original state when the process is reversed.
 It is an very slow process

11. Reversible process
 The reversible process also known as equilibrium
process.
 A system passes through an infinite number of
continuous equilibrium states , and it traces the
same path when the process is reversed
 Ex: constant volume, constant pressure, isothermal,
adiabatic & isentropic process.

12. Non-reversible process
 A system passes through an infinite number of
continuous non-equilibrium states, and it does not
trace the same path when the process is reversed.
 Ex:1. mixing of two different substances
2.when we are driving the car uphill, it consumes
a lot of fuel and this fuel is not returned when we are
driving down hill.

13. Flow and non flow process
 In a flow process, the working fluid enters the
system and leaves it to atmosphere after doing work.
 Ex: steady flow process applied to various systems
such as compressors.
 In non-flow process, the same working fluid
recirculated again and again , does not leave the
system after doing work
 Ex: constant volume & pressure process,etc.

14. Thermodynamic equilibrium
1.mechanical equilibrium:
A system is said to be in mechanical
equilibrium, when there are no unbalanced forces
acting 0n it.
characterized by equal pressure,
2.Thermal equilibrium:
A system is said to be in thermal
equilibrium, when there is no temperature difference
throughout the system
characterized by equal temperature

15. Cont,…
 Chemical equilibrium:
A system is said to be in
chemical equilibrium, when there is no chemical
reaction throughout the system
characterized by equal chemical potentials.

16. Thermodynamic cycle
 A thermodynamic cycle is a series of
thermodynamic processes which returns a system
to its initial state.
Initial to final=cycle
There are two types
1. open cycle.
2.closed cycle.

17. Cont,..
 Closed cycle:
The working substance is recirculated again and
again within the system without taking any mass
transfer. Energy transfer takes place

18. Cont,..
 Open cycle
The working substance is exhausted to
atmosphere after completing the process.
So, here both mass and energy transfer
take place.

19. Point and path function
 When a gas undergoes a process from initial state to
final state, the thermodynamic properties will
change.
 Point: P,V,T are dependent.
 Path: heat and work transfer are dependent

20. Zeroth law of thermodynamics

21. Concept of continuum
 A continuous homogeneous medium is called as
continuum.
 Continuum is based on the macroscopic approach.
 From the macroscopic perspective, the description of
matter is simplified by considering it to be
distributed continuously throughout a region.

22. Energy
Energy is the ability to do work.
Energy cannot be created or destroyed , it can only be
stored or transferred
Types:
1.Potential energy=stored energy
P.E=m g z
2.Kinetic energy= energy of motion or speed.
K.E=1/2 mv2

23. Work transfer
 Work is an energy interaction b/w system and
surroundings.
 Usually , the energy can cross the boundary of any
system in the form of either heat or work.
 Work=force x distance moved.
 W=F x X
 Work is expressed in terms of N-m or J or kJ.
 Power: work done per unit time is called power
unit: kJ/s or kW.

24. Heat transfer
 Heat is defined as the energy crossing the boundary
of a system due to the temperature difference
between system and surroundings.
 It is usually expressed in joule or kJ.

25. Sign conversion for heat and work

26. FIRST LAW OF THERMODYNAMICS
“When a system undergoes a thermodynamic cyclic
Process, the cyclic integral of heat energy is equal to
the cyclic integral of Work energy”.
𝑑𝑄 = 𝑑𝑊
dQ= dW + dU
Q1-2= W1-2+ U1-2

27. ENTHALPY
 Enthalpy (h) is the sum of internal energy (u) and
product of pressure and volume (pv).
h = u + pv

28. INTERNAL ENERGY
 According to First law of Thermodynamics, Internal
energy is the difference between the heat and useful
work.
U = Q-W

29. SPECIFIC HEAT CAPACITIES
 The specific heat is defined as the heat required to
raise unit mass through one degree temperature rise.
dQ = mCdT
 where, m = mass,
 C = specific heat, and
 dT = temperature rise
 There are two specific heats for gas,
 Cv - Specific heat at constant volume
 Cp - Specific heat at constant pressure

32. FOR AIR
CP = 1.005 kJ/kg K
Cv = 0.718 kJ/kg K
Gas constant,R= CP - Cv
R= 1.005-0.718 kJ/kg K
γ = CP / CV = 1.4