Page 23 - Entrophy Analysis in Thermal Engineering Systems

14 Entropy Analysis in Thermal Engineering Systems

fundamental thermodynamic laws, especially the second law, were discov-
ered and formulated analytically. For this, we will only point out those who
substantially contributed to the foundation and development of the Mechan-
ical Theory of Heat.

2.2 Before 1800

The science of thermodynamics as we know today was undiscovered
during the industrial revolution and throughout the 18th century. Steam
engines were in use in England, which were then spread out to other European
countries, but their theory was not understood well. The birth of modern ther-
modynamics is attributed to the work of Sadi Carnot although his investigation
was based upon the caloric theory according to which heat was treated as a mat-
ter. But what made Carnot’s theory plausible was the empirical laws governing
the relation between the pressure, volume, and temperature of gases, which
were referred to by Carnot as the laws of Mariotte and Gay-Lussac.

2.2.1 Boyle’s law

Boyle’s law, sometimes also referred to as the law of Boyle-Mariotte, states
that the pressure and volume of a given amount of (perfect) gas at constant
temperature are inversely related. The law may analytically be expressed as
1
p∝ (2.1)
V
The law given by Eq. (2.1) was first published in 1662 by Robert Boyle who

through a series of experiments with air led to conclude that “as common air
when reduced to half its wonted extent, obtained near about twice forcible a spring as it
had before; so this thus compressed air being further thrust into half this narrow room,
obtained thereby a spring about as strong again as that it last had, and consequently
four times as strong as that of the common air” [2]. Boyle also acknowledged that
this law had also been noticed by Richard Townley. Edme Mariotte discov-
ered independently Boyle’s law in 1679 [3]. In Carnot’s essay, the law given
by Eq. (2.1) has been referred to as Mariotte’ law.

2.2.2 Charles’ law
Charles’ law states that the volume of a given quantity of (perfect) gas is pro-
portional to its absolute temperature at constant pressure. In analytical form,
the law may be expressed as
(2.2)
V∝T