Thermodynamics part 1.pptx

By
Padmini K.Sawant
BVCOE, Navi Mumbai

1. Introduction
Thermodynamics deals with study of
energy possessed by gases and vapours
and conversion of these energies in form of
heat into mechanical work.

2. Application
House hold equipment,
Pressure cooker, refrigerators, A.C.,
Heaters, etc.
Main Application
1) I.C.Engine(Internal Combustion Engine)
2) E.C.Engine (External Combustion
Engine) e.g. Steam power plant, gas
power plant, Thermal power plant etc.

3) Thermodynamic Approach
Macroscopic
(Classical
thermodynamics)
Concerned with
overall behaviour
of matter
Microscopic
(Statistical
thermodynamics
Concerned with
behaviour of
every particle or
atom

Unit
Fundamental unit Derived unit
Systems of unit
C.G.S. F.P.S. M.K.S. S.I.
S.I. units : Length(m), Mass (kg), Time(s) , Temp(K),
angle (rad), Force(N)
Mass(kg) and Weight(N): 1 kgf = 9.81 N

4) Terms related to thermodynamic
i) Working substance:
Ability to receive, store and give out energy
E.g.- Steam , water, fuel , refrigerant
Pure substance:
Homogeneous and invariable chemical
composition, even if the substance changes its
phase.
E.g.- Steam , refrigerant

II) Thermodynamic system
Definite area where some thermodynamics
process is taking place or

Example
Piston cylinder arrangement
Fixedboundary
Movable boundary

III) Properties Of system
State described with quantity/characteristics
that quantity becomes property of system

Specific Property: -
Extensive Properties per unit mass
E.g. Sp. Volume(V/m), Sp. Enthalpy(h/m)
etc..

?
The following are examples of some intensive and
extensive properties: 1. Pressure 2. Temperature 3.
Volume 4. Velocity 5. Electric charge 6. Magnetisation
7. Viscosity 8. Potential energy .
Identify Intensive and extensive properties.

IV) State of system
1. Exact condition of system is called
state of system.
2. Assume system not undergoing any
change.
3. State is described with set of
properties.

Quasi-static process
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

Example of non quasi process- Free expansion process, throttling process
Quasi process – Frictionless adiabatic expansion and compression process

Processes named by their constant property

Why reversible process are considered only?
1. Easy to analyse as system passes through
series of equilibrium.
2. Serves as idealised model for actual
process to be compared for analysis
3. Viewed as theoretical limit for
corresponding limit.

VII) Thermodynamic cycle
a
b
1-a-2 and 2-b-1 are processes.
1-a-2-b-1 is thermodynamic cycle

Type of cycle
Open cycle – Working substance is used again and
again for new cycle.
E.g. steam power plant
Closed cycle- Working substance is used once in time.
For nest cycle new working substance required.
E.g. I.C. Engine

VIII) Point function and Path function
Point Function:
When two properties locate a point on the graph,
then those properties are called Point function. E.g.
Pressure, Volume

Path Function:
The quantities which are can not located on graph by
a point, but are given by area or so, on that graph.
Such area is function of path or process. Such
quantities are called Path function. E.g. Heat , Work.
Heat and work are inexact differential.

VIII) Important Properties
•Intensive property which determines the degree of
hotness or the level of heat intensity of body.
•Measured with help of Thermometer, Pyrometers.
•Temp scale:
TEMPRATURE

Absolute Temperature
It is the temperature below which the temp of any
substance can not fall. Or
It is the temp at which all vibratory, translatory and
rotational motions of molecules of a substance is
supposed to have seased i.e. internal energy
becomes zero.
Absolute temp= - 273 degree C
= - 460 degree F

Std. atm pressure = 760 mm of Hg
Low pressures are often expressed I term of mm of water or Hg.

?
1) Convert 745.0 mmHg to atm.
Solution: divide the mmHg value by 760.0 mmHg / atm
2) Convert 0.955 atm to kPa.
Solution: multiply the atm value by 101.325 kPa / atm.

Ans:
1) 745.0 mmHg
––––––––––––––– = 0.980 atm
760.0 mmHg / atm
2) 101.325 kPa
0.955 atm x –––––––––– =
96.8 atm (to
three sig
figs)
1 atm

Volume
Volume of gas is defines as the space
which the gas occupies. Which is
measured in meter cubic.
I litre = 10 cubic meter.

•Capacity to do work
•Two types- Stored energy and transit energy
•Total Energy of a system = K.E.+P.E.+I.E.
ENERGY
Stored energy (Energy
Possessed by a system within
its boundary)
Kinetic energy,
Potential energy,
Internal Energy
Transit energy
(Energy Possessed by a
system which has capability
of crossing boundaries)
Heat
Work

•Energy possessed by a system due to its molecular
arrangement and motion of molecules.
•Denoted by letter ‘U’
•Joules Low of Internal Energy- “ it states that internal
energy of a perfect gas is a function of temperature
only.”
•Cant measure internal energy but change in internal
energy can be measured.
INTERNAL ENERGY

HEAT
Sign Convention
+Q
System
- Q
System

WORK
Sign Convention
+Q
System
+W
- Q
System
-W

Heat And work are Path function
Work= Pdv
Area under the curve (1-B-2)
And area under the curve (1-A-2)
Are different.
Initial and final states are same. But
Path are different , so work done are
different.
Work is path function and same for heat energy.
HEAT AND WORK

IX) Ideal Gas/Perfect Gas
P
V
T
Combined Low/ General gas equation:
Gay Lussac Low

Avogadro's Low
“Equal volumes of all gases at the same pressure and
temp contain equal no. of molecules.”
O2 H2
P1,T1, V1
No. of
molecules
are same
V / n = constant Or V1 / n1 = V2 / n2
Where V is the volume of an ideal gas and n in the above
equation represent the number of gas molecules.

Characteristic Gas Equation =
Universal gas constant=
=8314 J/kg-mole K

Universal gas constant and gas constant
•Universal gas constant is same for all gases.
And it is product of gas constant(R) and
molecular mass of an ideal gas(M). Also
called molar constant.
• = R1M1=R2M2=R3M3
•Gas constant is different for every gas.

?
1) A tank has a volume of 5 m3 and contain 20 kg of an
ideal gas having a molecular mass of 25 mole kg. temp is
15 degree C. what is pressure?
Ans:- V=5 m3
m= 20 kg
M= 25 mole kg
T= 15+273=288K
R= Universal gas constant/M =
8.314 kj/kg-mole-K/25 mole =0.33 KJ/kgK
PV=m RT
P= 383 KN/m2

Specific heat of gas
•Quantity of heat required to raise the
temp of unit mass of the substance by
one degree.
•Gases has 2 sp. Heat (Cp and Cv)
•According to the definition-
Q = m C dT
Cp Cv

Thermodynamics part 1.pptx

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Thermodynamics part 1.pptx