Modern Engineering Thermodynamics

CHAPTER 3
Thermodynamic Properties
CONTENTS
3.1 The Trees and The Forest . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57
3.2 Why are Thermodynamic Property Values Important? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58
3.3 Fun with Mathematics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58
3.4 Some Exciting New Thermodynamic Properties. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60
3.5 System Energy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62
3.6 Enthalpy. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63
3.7 Phase Diagrams . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65
3.8 Quality . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72
3.9 Thermodynamic Equations of State . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76
3.9.1 Incompressible Materials . ...................................................... 77
3.9.2 Ideal Gases .................................................................. 79
3.9.3 Variable Specific Heats . . . ...................................................... 80
3.9.4 Real Gases .................................................................. 83
3.10 Thermodynamic Tables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84
3.11 How Do You Determine the “Thermodynamic State”?..................................86
3.12 Thermodynamic Charts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87
3.13 Thermodynamic Property Software . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89
Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90
3.1 THE TREES AND THE FOREST
Thermodynamics is like a forest. The tall trees in the center of the forest are the laws of thermodynamics. They
are surrounded by a thick underbrush of thorny bushes. These bushes are the thermodynamic properties. Some
are known by their common names, such as pressure, temperature, andvolume. Others have Latin and Greek
names, like energy, enthalpy, entropy, and exergy. Before you can climb the tall trees of the thermodynamic laws to
look out over your energetic future, you must find your way through the thermodynamic underbrush that surrounds
them.
From the edge of the forest are barely visible paths that lead inward, but they intersect with other paths marked
with obscure signs like “This Way to Adiabatic Heat Engines” and “This Way to the Isotropic Pumps.” To survive
in this wilderness, you need to understand the symbiotic relationships between the bushes and the trees—that
is, the properties and the laws—and how to use them to solve engineering problems that enhance humankind.
This chapter gives you the tools to clear the paths toward the thermodynamic laws of the next chapter.
Modern Engineering Thermodynamics. DOI: 10.1016/B978-0-12-374996-3.00003-8
© 2011 Elsevier Inc. All rights reserved. 57