Thermodynamics: An Engineering Approach
8th Edition
Yunus A. Çengel, Michael A. Boles
McGraw-Hill, 2015
CHAPTER 1
INTRODUCTION AND
BASIC CONCEPTS
Adapted from the lecture slides by Mehmet Kanoglu Copyright © The McGraw-Hill Education.
Permission required for reproduction or display.
Objectives
• Identify the unique vocabulary associated with
thermodynamics through the precise definition of
basic concepts to form a sound foundation for the
development of the principles of thermodynamics.
• Review the metric SI and the English unit systems.
• Explain the basic concepts of thermodynamics such
as system, state, state postulate, equilibrium,
process, and cycle.
• Review concepts of temperature, temperature scales,
pressure, and absolute and gage pressure.
• Introduce an intuitive systematic problem-solving
technique.
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THERMODYNAMICS AND ENERGY
• Thermodynamics: The science of
energy.
• Energy: The ability to cause changes.
• The name thermodynamics stems from
the Greek words therme (heat) and
dynamis (power).
• Conservation of energy principle:
During an interaction, energy can change
from one form to another but the total
amount of energy remains constant.
• Energy cannot be created or destroyed.
• The first law of thermodynamics: An
expression of the conservation of energy
principle.
• The first law asserts that energy is a
thermodynamic property.
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• The second law of thermodynamics:
It asserts that energy has quality as
well as quantity, and actual processes
occur in the direction of decreasing
quality of energy.
• Classical thermodynamics: A
macroscopic approach to the study of
thermodynamics that does not require
a knowledge of the behavior of
individual particles.
• It provides a direct and easy way to the
solution of engineering problems and it
is used in this text.
• Statistical thermodynamics: A
microscopic approach, based on the
average behavior of large groups of
individual particles.
• It is used in this text only in the
supporting role. 4
Application Areas of Thermodynamics
All activities in nature involve some interaction between
energy and matter; thus, it is hard to imagine an area
that does not relate to thermodynamics in some manner. 5
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IMPORTANCE OF DIMENSIONS AND UNITS
• Any physical quantity can be characterized by dimensions.
• The magnitudes assigned to the dimensions are called
units.
• Some basic dimensions such as mass m, length L, time t,
and temperature T are selected as primary or fundamental
dimensions, while others such as velocity V, energy E, and
volume V are expressed in terms of the primary dimensions
and are called secondary dimensions, or derived
dimensions.
• Metric SI system: A simple and logical system based on a
decimal relationship between the various units.
• English system: It has no apparent systematic numerical
base, and various units in this system are related to each
other rather arbitrarily.
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Some SI and
English Units
Work = Force Distance
1 J = 1 N∙m
1 cal = 4.1868 J
1 Btu = 1.0551 kJ
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W weight
m mass
g gravitational
acceleration
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Specific weight : The weight of
a unit volume of a substance.
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Dimensional homogeneity
All equations must be dimensionally homogeneous.
Unity Conversion Ratios
All nonprimary units (secondary units) can be
formed by combinations of primary units.
Force units, for example, can be expressed as
They can also be expressed more conveniently
as unity conversion ratios as
Unity conversion ratios are identically equal to 1 and are unitless,
and thus such ratios (or their inverses) can be inserted conveniently
into any calculation to properly convert units. 12
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SYSTEMS AND CONTROL VOLUMES
• System: A quantity of matter or a region in space chosen for study.
• Surroundings: The mass or region outside the system
• Boundary: The real or imaginary surface that separates the system
from its surroundings.
• The boundary of a system can be fixed or movable.
• Systems may be considered to be closed or open.
• Closed system (Control mass): A fixed amount of mass, and no
mass can cross its boundary
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• Open system (control volume): A properly selected
region in space.
• It usually encloses a device that involves mass flow
such as a compressor, turbine, or nozzle.
• Both mass and energy can cross the boundary of a
control volume.
• Control surface: The boundaries of a control
volume. It can be real or imaginary.
A control volume can involve
fixed, moving, real, and imaginary
boundaries.
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PROPERTIES OF A SYSTEM
• Property: Any characteristic of a
system.
• Some familiar properties are
pressure P, temperature T, volume
V, and mass m.
• Properties are considered to be
either intensive or extensive.
• Intensive properties: Those that
are independent of the mass of a
system, such as temperature,
pressure, and density.
• Extensive properties: Those
whose values depend on the size—
or extent—of the system.
• Specific properties: Extensive
properties per unit mass.
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