Page 30 - Entrophy Analysis in Thermal Engineering Systems

Birth and evolution of thermodynamics 21

Poisson derived the two equations by assuming γ as a constant parameter,
and by using the combined gas laws of Boyle-Dalton or Mariotte-Gay
Lussac, which he expressed as

p ¼ kρ 1+ αtÞ (2.10)
ð
He noted that α and k are independent of density and temperature, where
α¼0.00376 being the same for all gases, but k to be given for a particular gas.

2.3.4 Experiments of Joule

By the end of the first half of the 19th century, the immateriality of heat had
already faded away and the principle of the equivalence of heat and work as a
fundamental thermodynamic law had been accepted by the scientific com-
munity. Numerous investigators contributed to the realization of and prov-
ing the truth of this law of nature. After the pioneering experiments of
Rumford and Davy (see Section 2.2.3), it was enunciated by Davy in
1812 that “The immediate cause of the phenomenon of heat, then, is
motion, and the laws of its communication are precisely the same as the laws
of the communication of motion” [16]. The merit of discovery and foun-
dation of the first law should also be credited to several other ingenious men
like Marc Seguin, Julius Robert von Mayer, James Prescott Joule, and
Ludwig Colding who had independently realized and expressed the truth
of the equivalence of work and heat.
It is however Joule who deserves an extra credit and recognition. He con-
ducted numberless experiments with a great caution that provided a solid
foundation to support the validity of the equivalence of heat and work as a

general natural law. For this, Tyndall has recognized Joule as the “experimental
demonstrator of the equivalence of heat and work” [17]. In describing Joule’s work,
Youmans writes: “Mr. Joule’s experiments are of extreme delicacy—he tabulates to
the thousandth part of a degree of Fahrenheit, and a large number of his thermometric
data are comprehended within the limits of a single degree. Other experimenters have
given very different numerical results, but the general opinion seems to be that the num-
bers given by Mr. Joule are the nearest approximation to the truth yet obtained” [18].
Before enunciating his early findings on the mechanical equivalent of
heat in 1843, Joule had conducted experiments on electromagnetic forces
and voltaic electricity, which led him to establish the law of heat production
by electricity. Subsequently, an abstract of his work was published in the
Proceedings of the Royal Society in December 1840 [19]. He designed
apparatuses to experiment the quantity of heat evolved during the