Modern Engineering Thermodynamics

13.2 Part I. Engines and Vapor Power Cycles 449
13.2.3 What Is an Engineer?
In English, the –er ending to a word often means someone who does something. For example, someone who
sings is a singer, someone who builds is a builder, and someone who writes is a writer. So, naturally, someone
who creates ingenious things is called an engineer. That is where the name of our profession comes from. In
French and German, the word engineer is translated as ingenieur, and in Italian, it is ingegnere. So, engineers are
the people who create ingenious solutions to society’s problems. We are the engineers.
13.2.4 What Is a Heat Engine?
The vast number of different engines (or machines) developed over time are usually classified either generally
according to their source of power (animal, wind, water, etc.) or specifically according to their function. For
example, beginning in the medieval period, an ingenious machine (an ingen or engine) was simply called a gin
(a contraction applicable to either ingen or engine). 2 So when, in 1793, Eli Whitney (1765–1825) built an
ingenious engine (or machine) for removing the seeds from raw cotton, his “cotton engine” became known as a
cotton gin. A calculating engine is a machine whose function is to make calculations (e.g., an adding machine),
whereas a pneumatic engine is an engine whose source of power is air pressure.
A heat engine is any machine whose source of power is heat (fire, steam, solar, etc.), and whose specific function
is undefined (i.e., it simply produces work, which can be mechanical, electrical, chemical, etc., in nature).
Initially, heat engines simply produced mechanical work that was used directly (e.g., in manufacturing) or else
they were connected to other engines. For example, they were often connected to pumping engines (pumps) to
move water and later to electrical engines (generators) to generate electricity. Most heat engines use either a
vapor or a gas as the internal energy transfer medium (even a thermoelectric device can be thought of as transporting
energy via an internal electron gas). Typical heat engine characteristics are shown in Table 13.1.
We call the device that actually produces the heat engine’s outputworktheprime mover. A prime mover can be a reciprocating
piston-cylinder steam engine, a steam turbine, an internal combustion engine, and so forth. Figure 13.1
illustrates these terms.
It is common to use the words engine and prime mover interchangeably when referring to reciprocating pistoncylinder
devices. We follow this custom in this textbook when no confusion is likely to occur.
The reason heat engines are so important to the study of thermodynamics is that the history of heat engine technology
is essentially the history of the Industrial Revolution. The heat engine whose prime mover was the reciprocating
piston steam engine was the first large-scale source of portable mechanical power. It was a source of power
that did not depend on wind or river and could therefore be located anywhere. The heat engine is still the primary
source of power for travel and electricity today, and it is likely to remain so for the foreseeable future.
Table 13.1 Some Typical Heat Engine Characteristics
Heat Sources
Heat Sinks
Working
Fluid
Work Output
Prime Movers Cycle Types Uses
Combustion Atmosphere Gas Engine Power Transportation
Nuclear Oceans, lakes Vapor Turbine Refrigeration Generate electricity
Atmosphere Rivers Vapor Reversed engine Heat pump Heating and cooling
Ocean Groundwater Vapor Solid state (e.g.,
thermoelectric)
Power
Generate electricity
W out
Heat source
Q H
Prime mover
Q L
Heat sink
Heat engine
FIGURE 13.1
Heat engine terminology.
2 The alcoholic beverage gin (a spirit distilled from grain and originally flavored with the juice of juniper berries) is a contraction of
the word geneva, which comes from the Latin juniperus.