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Introduction
Thermodynamics is an experimental science based on a small number of principles that are generalizations made from experience. It is concerned only with macroscopic or large-scale properties of matter and it makes no hypotheses about the small-scale or microscopic structure of matter. From the principles of thermodynamics one can derive general relations between such quantities as coefficients of expansion, compressibilities, specific heat capacities, heats of transformation, and magnetic and dielectric coefficients, especially as these are affected by temperature. The principles of thermodynamics also tell us which of these relations must be determined experimentally in order to completely specify all the properties of the system...
Thermodynamics is complementary to kinetic theory and statistical thermodynamics. Thermodynamics provides relationships between physical properties of any system once certain measurements are made. Kinetic theory and statistical thermodynamics enable one to calculate the mangitudes of these properties for those systems whose energy states can be determined.
There are three principal laws of thermodynamics. Each law leads to the definition of thermodynamic properties which help us to understand and predict the operation of a physical system. Here you can find some simple examples of these laws and properties for a variety of physical systems, although, as aerodynamicists, we are most interested in thermodynamics in the study of propulsion systems and high speed flows. Fortunately, many of the classical examples of thermodynamics involve gas dynamics. Unfortunately, the numbering system for the three laws of thermodynamics is a bit confusing.
The zeroth law of thermodynamics involves some simple definitions of thermodynamic
equilibrium. Thermodynamic equilibrium leads to the large scale definition of temperature,
as opposed to the small scale definition related to the kinetic energy of the molecules.
The first law of thermodynamics relates the various forms of kinetic
and potential energy in a system to the work which a system can perform and to the transfer of
heat. This law is sometimes taken as the definition of internal energy, and
introduces an additional state variable, enthalpy. The first law of thermodynamics
allows for many possible states of a system to exist. But experience indicates that only
certain states occur. This leads to the second law of
thermodynamics and the definition of another state variable called entropy.
The second law stipulates that the total entropy of a system plus its environment can
not decrease; it can remain constant for a reversible process but must always increase
for an irreversible process. |