MODULE 1
INTRODUCTION
Lesson 1: Fundamental Concepts and
Definitions
Lesson 2: Units and Dimensions
Lesson 3: Thermodynamic Properties
Lesson 4: Law of Conservation of Mass
Module 1
Basic Principles, Concepts and
Definitions
Introduction
Thermodynamics is a branch of physics and an engineering science that is very
important in this field. The study and understanding of the fundamental principles,
concepts and definition of thermodynamics which includes the physical and chemical
behavior of matter and energy and extends to the study of systems in which how these
quantities interact with their surrounding are basic in the study of this science.
Mechanical engineers use thermodynamics to study the flow of energy in systems
such as automotive engines, turbines, heat exchangers, bearings, gearboxes, air
conditioners, refrigerators, nozzles and diffusers.
Electrical engineers use thermodynamics to deal with electronic cooling
problems, increasing the energy efficiency of large-scale power generation, and the
development of new electrical energy conversion technologies such as fuel cells.
All engineering fields utilize the conversion and use of energy to improve human
condition.
This module will introduce the basic principles, concepts and definitions of terms that
will be very important in the study of thermodynamics
Learning Outcomes
After completion of this module, you should be able to:
1.
2.
3.
4.
5.
6.
7.
Define thermodynamics and its branches.
Define system and its types.
Differentiate phase and pure substance
Identify the different systems of units used.
Define the different thermodynamic properties.
Understand the Law of conservation of mass
Solve problems involving the above basic concepts
Lesson 1 – Fundamental Concepts and Definitions
Thermodynamics
Thermodynamics is the branch of science that deals with the relationship of
various forms of energy and matter. The word thermodynamics comes from the
Greek words “therme”, meaning heat and “dynamis”, meaning power. The term
“thermodynamics” was coined by James Joule in 1849.
Thermodynamics is also that branch of physical sciences that treats of
various phenomena of energy and the related properties of matter, especially of
the laws of transformation of heat into other forms of energy and vice versa.
Branches of Thermodynamics:
Classical Thermodynamics is the branch of thermodynamics that concern
with the states and properties of energy and with the laws of thermodynamics
without the atomic interpretation.
Statistical Thermodynamics is the classical thermodynamics considering
the atomic and molecular interpretation of the states and properties of energy.
Chemical Thermodynamics is concern with the interpretation of the
states and properties of energy with chemical reactions.
Systems
Thermodynamic System (or simply a system) refers to the quantity of
matter or anybody or region of space which is to be considered and analyzed.
This may be in a form of a simple body or as combinations of a body that is
enclosed within a defined volume. In our study of thermodynamics, we will
choose a small part of the universe to which we will apply the laws of
thermodynamics. We call this subset a SYSTEM. The thermodynamic system is
analogous to the free body diagram to which we apply the laws of mechanics,
(i.e. Newton’s Laws of Motion). The system is a macroscopically identifiable
collection of matter on which we focus our attention (eg: the water kettle or the
aircraft engine).
Everything that is external to the system is defined as the surrounding.
The rest of the universe outside the system close enough to the system to have
some perceptible effect on the system is called the surroundings.
The system and the surrounding is distinguished by a boundary that serves
as the borderline between the two.
Types of Thermodynamic Systems:
An isolated system is any system in which neither mass nor energy crosses
the system boundary. An isolated system obeys the conservation law that its
total energy–mass stays constant. Most often, in thermodynamics, mass and
energy are treated as separately conserved.
A closed system is defined as a system in which the particular amount of
matter is under study. The system contains that amount of matter and there is
no transfer of mass across the system’s boundary. This is also called as control
mass. A closed thermodynamic system is confined by walls that are impermeable
to matter, but, by thermodynamic operations, alternately can be made
permeable (described as 'diathermal') or impermeable ('adiabatic') to heat, and
that, for thermodynamic processes (initiated and terminated by thermodynamic
operations), alternately can be allowed or not allowed to move, with system
volume change or agitation with internal friction in system contents, as in Joule's
original demonstration of the mechanical equivalent of heat, and alternately can
be made rough or smooth, so as to allow or not allow heating of the system by
friction on its surface.
An open system is defined as a system in which mass flows through the
system across its boundary. In an open system, heat, work and matter may cross
the boundary. This is also called as control volume. An open thermodynamic
system has at least one wall that separates it from another thermodynamic
system, which for this purpose is counted as part of the surroundings of the open
system, the wall being permeable to at least one chemical substance, as well as
to radiation; such a wall, when the open system is in thermodynamic equilibrium,
does not sustain a temperature difference across itself.
Lesson 2 – Units and Dimensions
Units and Dimensions
In thermodynamics, you determine the energy of a system in its many
forms and master the mechanism by which the energy can be converted from
one form to another. A key element in this process is the use of consistent set of
dimensions and units. A calculated engineering quantity always has two parts,
the numerical value and the associated units. The result of analysis must be
correct in both categories: It must have the correct numerical value and it must
have the correct units.
Units provide us with the numerical scale whereby we can carry out a
measurement of a quantity. Units are used in measurements that indicate
specified magnitudes of dimensions. This gives number a particular meaning
We call each measurable characteristic of a quantity a dimension of that
quantity. If the quantity exists in the material world, then it automatically has
three spatial dimensions (length, width and height), all of which are called
length (L) dimensions. If the quantity changes in time, then it also has a temporal
dimension called time (t).
There are two common systems of units that are used: the SI abbreviation
for Systeme International d’Unites (International System of Units) and the English
Engineering System.
The SI is the legally accepted systems used in many countries. The SI base
units are the following:
The English Engineering System is also used. The English base units are
the following:
Also listed are the names arbitrarily given to the various derived units.
1 Newton = 1 kg-m/s2
1 dyne = 1 g-cm/s2
1 poundal = 1 lbm-ft/s2
1 lbf = 1 slug-ft/s2
Below are some common conversions
SAMPLE PROBLEMS
Example 1:
Convert 340 cm2 to m2
Solution:
1𝑚
340 cm2 x (100 𝑐𝑚)2 = 0.034m2
Example 2:
Convert 980m to ft.
Solution:
980 m x
3.281 ft
1𝑚
= 3215.38 ft
Example 3:
Convert 65 mi/hr to m/s
Solution:
65
mi
hr
x(
1.609 km
1 mi
)x (
1000 m
1 km
) x(
1 hr
3600 s
) = 29.05 m/s
Example 4:
Convert 50 ft3 to m3
Solution:
1𝑚3
50 ft3 x ((35.31)𝑓𝑡 3) = 1.42 m3
Example 5:
Convert 30 lb to slugs
Solution:
1 𝑘𝑔
1 𝑠𝑙𝑢𝑔
30 lb x (2.205 𝑙𝑏)x(14.59 𝑘𝑔) = 0.93 slug