G.K. BHARAD INSTITUTE OF
ENGINEERING
GUJARAT TECHNOLOGICAL
UNIVERSITY
Subject: ETD(2131905)
Guided By: H.H.Suchak & B.D.Lathigara
Chapter-1 : Basic Concepts of
Thermodynamics
Devmurari Akash M
130590119020
Introduction
Basis is experimental observations written down as
laws. e.g.
1st law of thermodynamics:
Energy can change from one form to another but
the total amount remains
constant.
2nd law of thermodynamics:
Energy has quality (more or less useful) and
quantity. Real changes occur only
in a direction of decreasing quality of energy.
General overview

Mechanical
Engineering
 Mechanics
 Energy
 Systems
 Design
The over arching goal
is design of products
to meet societal
needs.

Thermodynamics
A
part of the Energy
component of
mechanical
engineering.
 Governs
all energy
consuming and
transforming devices
and system.
Macroscopic vs. Microscopic
viewpoints.
A collection of atoms within a container, each
with a unique velocity.
Energy in a microscopic
description
1
Energy of each atom = e  m V
2
2
Number of atoms = N
N
mV
Total Energy = eN 
2
2
N
  ke1
i 1
The Macroscopic description
The energy in both cases
is the same, E. In the
macroscopic description,
atomistic concepts are
disregarded.
How we describe the
system chosen for study
requires careful selection of
properties that are based
on observable, measurable
quantities.
Energetic interactions
System Boundary
Surroundings
Energy
Flow
System
Closed
System
Mass Flow
dm
dt
0
Open
System
Mass Flow
System and surroundings
Universe = Systems +Surroundings
Surrounding
s
Closed System
System Boundary
Systems and Control Volume
Thermodynamic System:
A quantity of matter or a
region in space chosen for
study.
Surroundings:
Everything external to the
system.
Boundary:
Surface that separates the
system from the
surrounding. It may be
fixed ormovable
Closed and Open Systems
Closed system (Control mass)
A fixed amount of mass chosen for study
(nomass can cross its boundary). Heat and
work can cross the boundary, volume may
also change.
e.g. piston cylinder.
Open system (Control volume)
A selected region chosen for study. Mass,
heat and work can cross its boundary,
volume may also change.
e.g. water heater, car radiator, turbine,
nozzle.
Isolated system
A system closed to mass, heat and work
flows. It is not affected by the
surroundings.
Open system
Surroundings
Mass Flow
Heat
System
Power
Mass
Flow
Example: The gas turbine engine an open system
Fuel Flow In
Combustor
Air Flow In
Shaft Work Output
Compressor Work Out
Exhaust Gases Out
State and Equilibrium
A substance can be at various
pressures & temperatures or in
various states
State
Condition of a system identified by properties (e.g. T, P, v).
In a given state each property has 1 value.
Properties are defined when the system is in
Equilibrium
No unbalance exist in the system, and values of properties (T, P etc.)
remain the
same when it is isolated from the surroundings.
Thermal equilibrium: temperature of system does not change when it is
isolated from
surroundings
Mechanical equilibrium: pressure of system does not change when it is
isolated from
surroundings
Chemical equilibrium: chemical composition does not change when it is
isolated from
surroundings
Processes and Cycles

Any change from one equilibrium
state to another is called a process.

Process diagrams are very useful in
visualizing the processes.

The series of states through which a
system passes during a process is
called a path

To describe a process completely
initial and final states as well as the
path it follows, and the interactions
with the surrounding should be
specified

A process with identical end states is
called a cycle

Process diagrams plotted by
employing thermodynamic properties
as coordinates are very useful in
visualizing the processes.
Quasi-Equilibrium process

During a quasi-static or quasiequilibrium process, the system
remains infinitesimally close to an
equilibrium state at all times.

A sufficiently slow process that allow
the system to adjust itself internally
so that properties in one part of the
system do not change any faster than
those at other parts.


Compression is very slow and thus
equilibrium is attained at any
intermediate state. Therefore, the
intermediate states can be determined
and process path can be drawn.
It is an idealized process but many
process closely approximate it with
negligible error
State 2
P
Process path
Intermediate
states
State 1
20
V
20 pa
20 pa
20 pa
20 pa
20 pa
(a) Slow compression (quasi-equilibrium)
Non-Quasi-Equilibrium
process


Compression process is
fast and thus equilibrium
can not be attained.
Intermediate states can
not be determined and the
process path can not be
defined. Instead we
represent it as dashed
line.
State 2
P
Non-equilibruim
process
90
?
20
State 1
V
20 pa
90 pa
20 pa
(b) Fast compression (non quasiequilibrium)