2. Thermodynamics
• Thermodynamics= therme + dynamis
• Latin word therme means = heat
• Dynamis means = power or forces causing motion
so, overall meaning of thermodynamics is heat–power or force
interaction between system and surrounding.
for example
It is based upon general observation and those may be formulated
in form of thermodynamic law as –
• Zeroth law of thermodynamics
• First law of thermodynamics
• Second law of thermodynamics
3. • Application areas of thermodynamics
• Steam power plant
• I.C.Engine
• Refrigerator and air conditioning
• Gas turbine
• Compressor etc.
7. • Microscopic and macroscopic view of thermodynamics
• Macro- Large scale
• Micro – small scale
Macroscopic Microscopic
Attention is focused on certain quantity of Matter consituting the system is
matter without considering the activity considered to comprise a large no. of
occurred at molecular level discrete particles called molecules.
A few properties are required to describe the Large no. of variables are required to
system such as P,V ,T etc and these can be describe the system such as position, KE,
perceived by senses and measured by Velocity, P,V, T etc. It is very difficult to
available instruments. Example Expansion of measure these quantities with help of
gases in a I.C. engine available instruments.Example KTG
Requires Simple mathematical formulae to Requires Advanced statistical and
mathematical formulae to analyse the
analyse the system system
Known as statistical thermodynamics Known as Classical thermodynamics
8. SYSTEM- Definite region in space on which attention is
concentrated for investigation of the thermodynamic
problems i.e. heat, work transfer, etc. It may be classified on
the basis of transfer of mass & energy as indicated in table-
TYPES OF THERMODYNAMIC SYSTEM
System Mass Energy Example
Closed System × √ gas filled in a cylinder
Open System √ √ compressor, turbine, or nozzle
gas filled in a cylinder but with
Isolated System × × insulation
9.
10. • Homogeneous System
• Quantity of matter is homogeneous throughout in
chemical and physical structure i.e. system in a
single phase
• Pure substance
• Substance that is homogeneous and invariable in
chemical composition i.e. combustion product,
atmospheric air
11. Thermodynamic Properties, Processes and Cycles
• Properties
• Characteristics by which physical condition of any system
can easily be defined , is known as property.
• Two types-
• Intensive ( Independent of mass example pressure,
temperature, density, composition, viscosity, thermal
conductivity)
• Extensive ( depends on mass examples- energy, enthalpy ,
entropy, volume etc.)
• Check for a property-
dP= Mdx + Ndy would be a thermodynamic property if its
differential is exact i.e.
• Specific quantity = Absolute / Mass and denoted by small
letters.Applicable for quantities depending upon the mass
like, internal energy, enthalpy, heat, work, volume etc.
12. • State
• If any system have definite values of properties , it is known as
definite state . Properties are the state variables of any system
• Change in state
• Any change in property will lead to change in state.
• Path
• Locus of all change of states is known as path.
• Process
• When path is completely defined , it becomes one process
• Process may be reversible or irreversible in nature.
• Reversible: it is possible to attain the initial states by eliminating the
effects. For example quasi static process ( reversible process)
• Cycle
• Final state of any process is identical with the initial state , it
becomes one cycle.
• State, change in states, path, process, and cycles can be described
on a diagram that is drawn between property vs property as shown
13.
14. Quasi Static Vs Non Quasi Static
Quasi- Almost slow, or infinitely slow
Quasi static Non Quasi Static
1. Infinitely slowness is the characteristic 1. Nature of process is very fast and
of process and all the intermediate
there is no equilibrium with intermediate
change in states are equilibrium with each
other. change of states.
2. Path (1-2) of process can easily be 2. Path of process (1-2) can not be
defined due to all the change in states easily defined due to existence of non
equilibrium change in states, hence can
are in equilibrium , hence process can be drawn on graph paper with dotted
be drawn on graph paper with firm line. line.
3. Processes are reversible in nature. It 3. Processes are irreversible in natute.
means it is possible to attain the initial It means it is not possible to attain the
states by eliminating the effect. initial states by eliminating the effect
4. Example: Expansion of gases behind 4. Example: Expansion of gases
the pistion against infinitely small behind the pistion against a single
weigthts. weigtht.
19. Reversible & Irreversible process
Reversible Process Irreversible Process
1. It is possible to attain the initial states 1. It is not possible to attain the initial
after eliminating the effects introduced to states after eliminating the effects
obtain the final state. introduced to obtain the final state.
Initial state will always be different in
reverse process
2. All the quasi static processes are 2. All the non quasi static processes
reversible in nature . are reversible in nature .
3.Process will become reversible by 3. Causes of irrversibility: (a) Internal
eliminating the causes of irrversibility i.e. friction between molecules (b) Free
resisted expansion of gases, no internal expansion of gases ( c) Paddle wheel
molecular friction or external friction work- Braking action causing the
conversion of mechanical work in form
of heat., it is not possible to aobtain the
∮ motion of wheel by supplying the same
∮
amount of heat to wheel.
4. Clausius inequality dQ/T=0 for cyclic 4. Clausius inequality dQ/T< 0 for
process or no change in entropy for cyclic process or change in entropy for
reversible process( ds =0) irreversible process( ds ≠0)
20.
21. Thermodynamics Equilibrium
• No spontaneous change in macroscopic property (
i.e. isolated system)
• Conditions for thermodynamic equilibrium
• Mechanical equilibrium ( No pressure gradient within
the system and also between system & surroundings
i.e.δΡ=0, or no unbalance force)
• Chemical equilibrium (No transfer of mass by any
chemical process across the boundary of system i.e.
diffusion and no unbalanced chemical reaction within
the system)
• Thermal equilibrium ( No transfer of heat across the
boundary of system when it is separated from universe
by means of Diathermic wall- that allows the heat or
δT=0)
22. Concept of Continuum
• In concept of continuum matter within the system is
assumed to be continuous and distributed uniformly.
• Importance- Used for defining the pressure and density
23. Pressure
• Definition : P = Normal Force / Cross sectional area
• Units: Height of liquid ( 760 mm of Hg), N/m2, Pascal, Bar, Torr etc.
• One atmospheric pressure= 1.01325 N/m2
24. Pascal’s Law
The pressure is the same at all points on a horizontal plane in a given fluid
regardless of geometry, provided that the points are interconnected by the
same fluid. (see figure below)
25. Measurement- Pressure
• U tube manometer- Used for measurement of pressure.
• For same liquid equation of pressure can be written very
easily as: take +ve sign if it is desired to obtain the
pressure at lower level as shown in diagram below.
28. Review Questions & Problems
• Book Engineering thermodynamics by P K Nag , (Ed.
Third )P. No. 15 Review questions section Q. No.1.1 ,
1.4 to 1.17
• Problems( P.No. 16, Q.No. 1.5, 1.6, 1.8, 1.9)
• Questions/ Problems given in assignment no. 1
