Environmental Engineering Reference
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modern science had very faulty concepts of energy. To
Galileo Galilei (1564-1642) heat was an illusion of the
senses and the outcome of mental alchemies. Francis
Bacon (1561-1626) thought heat could not generate
motion, and vice versa. And the fundamental ideas of
mass, momentum, and force used by Isaac Newton
(1643-1727) had initially little relevance for men build-
ing better steam engines or pondering the energetic basis
of living organisms. But these mental and manual experi-
ments laid down the foundations of energetics as a
systematic science. Scientific understanding was first
sharpened on the basis of particularistic definitions and
quantitative assessments. Only later came laws and
theories as the burgeoning nineteenth-century science
pursued its inquiries into fuels, engines, heat, motion, ra-
diation, electricity, nutrition, metabolism, work, photo-
synthesis, and evolution.
The practical roots of this new knowledge are self-
evident in contributions made by James Watt (fig. 1.1).
His steam engine revolutionized industrial production,
and his invention of a simple indicator, a miniature
recording steam gauge, opened the way for detailed
studies of engine cycles, which contributed immeasurably
to the emergence of thermodynamics during the follow-
ing century. In contrast, Sadi Carnot (1796-1832) pur-
sued a purely abstract approach to the understanding of
working engines, and this explains why his contributions
were fully appreciated only decades later (Truesdell and
Bharatha 1977). In order to explain production of ki-
netic energy from heat, Carnot (1824) set down the
principles applicable to any imaginable heat engine, re-
gardless of its working substance.
Carnot defined the maximum efficiency (e) of an ideal
(reversible) heat engine as equal to 1 minus the quotient
1.1
James Watt (1736-1819).
of the machine's lowest (T l ) and highest (T h ) operating
temperatures (expressed in degrees Kelvin):
e ΒΌ 1 T l
T h :
Consequently, a 100% efficient engine could be realized
only if its cold end were at absolute zero, a practical
impossibility. After Carnot's death, Emile Clapeyron
(1799-1864) presented the ideal engine cycle in terms
of Watt's indicator diagram, and this usage remains the
standard in all thermodynamic studies (fig. 1.2). Antoine
Lavoisier's (1743-1794) suggested equivalence between
the heat output of animals and humans and their feed
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