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22 Entropy Analysis in Thermal Engineering Systems

electrolysis of water, combustion of metals, by an iron bar rotating under
magnetic effect, agitation of liquids, and friction of fluids. Some of the
experimental efforts of Joule on the generation of heat by the friction of fluid
will be described in Chapter 4.

After years of labor, in a letter communicated to the editors of Philosoph-
ical Magazine in 1862, Joule wrote “I do not wish to claim any monopoly of
merit. Even if Rumford, Mayer, and Seguin had not produced their works,
justice would still compel me to share with Thomson, Rankine, Helmholtz,
Holtzman, Clausius, and others, whose labours have not only given devel-
opments and applications of the dynamical theory which entitle them to
merit as well as their predecessors in these inquiries, but who have contrib-
uted most essentially in supporting it by new proofs” [20]. It is evident that
not only was Joule a highly skilled scientist and the experimental demonstra-
tor of the first law, but also a humble man who freely admired the effort and
contribution of other fellow philosophers, at home and foreign countries, to
the development of the science of thermodynamics.

2.3.5 Absolute temperature scale
In a paper published in 1848 [20], William Thomson (Lord Kelvin) begins
with a statement that the theory of thermometry is far from a satisfactory
state and urges the need for a principle to serve as a foundation for absolute
temperature scale. At the time, air thermometer was employed as a standard
scale for measuring temperature. Despite the sufficient accuracy of the ther-
mometers constructed with air or other gases, he argued that “Although we
have thus a strict principle for constructing a definite system for the estima-
tion of temperature, yet as reference is essentially made to a specific body as
the standard thermometric substance, we cannot consider that we have
arrived at an absolute scale.”
Thomson then proposes Carnot’s theory as a foundation for the absolute
temperature scale as the ratio of work-to-heat in Carnot cycle depends on
temperature, which was shown by Carnot and later by Clapeyron; see
Sections 2.3.1 and 2.3.2. In describing the new scale, Thomson wrote:
“The characteristic property of the scale which I now propose is, that all degrees have
the same value; that is, that a unit of heat descending from a body A at the temperature
T° of this scale, to a body B at the temperature (T-l)°, would give out the same mechan-
ical effect, whatever be the number T. This may justly be termed an absolute scale, since
its characteristic is quite independent of the physical properties of any specific substance.”