Modern Engineering Thermodynamics

34 CHAPTER 2: Thermodynamic Concepts
2.2 THE LANGUAGE OF THERMODYNAMICS 1
This section deals with a series of definitions and technical terms fundamental to understanding the language of
thermodynamics. Some of these terms are already in our everyday vocabulary as a result of the broad-based use
of thermodynamics concepts in everyday life. It was popular among the 19th century scientists to coin technical
terms using Greek or Latin words instead of English. Consequently, many of the key terms (words) in thermodynamics
are really Greek or Latin words, which, in the 21st century, are probably foreign to you. But when these
terms are translated into English, you will find that their English meaning is identical to their thermodynamic
use. For example, the English translation of the term isothermal is simply constant temperature, which is the physical
meaning of what the term isothermal is meant to imply. Consequently, when Greek or Latin terms are introduced
in this text, their equivalent English translations also are given at that point. Appendix B at the end of this book
gives a more comprehensive analysis of the Greek and Latin origins of scientific and engineering terms. Though
this may seem like a small point to you at this stage, your understanding and ease with this subject are greatly
enhanced if you pay particular attention to the English meanings of these otherwise meaningless technical terms.
The name thermodynamics itself is an example of a Greek technical term. Basically, it means the process of
converting heat (thermo) into mechanical power (dynamics). Modern thermodynamics deals with more than just
thermal energy. It is more appropriately defined today as in the following box titled “Thermodynamics.”
There are four basic laws of thermodynamics: the zeroth, first, second, and third laws. Like all of the other basic
laws of physics, each of these laws is a generalization of observed events in the real world, and their “discovery”
was the result of an individual’s perception of how nature functions. Curiously, the order in which the thermodynamic
laws are named does not correspond to the order of their discovery. The zeroth law is attributed to
Fowler and Guggenheim in 1939; the first law to Joule, Mayer, and Colding in about 1845; the second law to
Carnot in 1824; and the third law to Nerst in 1907. The first and second laws are the most pragmatic and consequently
the most important to engineers. A thermodynamic analysis involves applying the laws of thermodynamics
to a thermodynamic system.
A thermodynamic system often is referred to as just a system. Its boundary is defined simply as its surface.
The system and its boundary are always chosen by the analyst (i.e., you); they are almost never specified in a
problem statement. It should be clear that, if different systems are used to analyze the same quantity, they
should produce the same results in each case. A system does not have to be fixed in space. It can move, deform,
and increase or decrease in size with time. Basically, there are three types of systems: isolated, closed, and open.
Figure 2.1 illustrates each of these types of systems. In Figure 2.1a, a pan of water is in a mass and energy
impervious insulated box, thus forming an isolated system. In Figure 2.1b, we have a closed system, wherein the
contents of the pan are closed by an airtight lid, but heat energy enters the pan from the burner. In Figure 2.1c,
water (mass) enters the pan by crossing the system boundary, so here the pan is an open system.
Notice that whether a system is open or closed depends on how the analyst views the system. Figure 2.1c could be
made into a closed system if the system boundary is extended to include the faucet, all the water pipe going back
THERMODYNAMICS
Thermodynamics deals with the laws that govern the transformation of energy from one form to another.
THERMODYNAMIC SYSTEM
The thermodynamic system is a volume of space containing the item chosen for thermodynamic analysis.
THERMODYNAMIC SYSTEM BOUNDARY
The surface of a thermodynamic system forms its boundary.
1 Feel free to turn on your babble fish here, but do not put it in your ear just yet.