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9.1.- FONDEMENTS ET CONCEPTS FONDAMENTAUX DE LA THERMODYNAMIQUE
Thermodynamics is a branch of physics that belongs to the phenomenological science that studies real systems, not modeled, and follows an experimental method. As a consequence, those systems are experimentally defined by approximations and measurement of variables.Voir plus
Macroscopically, thermodynamic systems are defined by variables. A large number of thermodynamic variables can be measured, but only one number is needed to determine unequivocally the system, the state functions. Pressure, volume, temperature, entropy and enthalpy are some of the most important state variables.
Changes in the states of matter take place with the modification of the thermodynamic variables. The fundamental states of matter are solid, liquid and gas. There are certain pressure and temperature conditions for each element or compound at which changes of state occur.
The concept of ideal gas has been introduced to simplify real thermodynamic systems and the changes of state generated. They are defined by the ideal gas equation PV = nRT. An ideal incompressible liquid is approximated in the same way.
In a closed system with liquid, there is a thermodynamic equilibrium between the liquid and its vapor phase. The evolution of the pressure and temperature of the system in equilibrium define the pressure curve of the vapor and the existing state is called saturation state. From that evolution, the temperature-pressure diagram is represented.
The study of these concepts is of great importance in practice, essentially applied to water. For example, the specification of moisture, contraction and expansion levels of the ideal matter is then applied in actual thermal machines, such as turbines, nozzles, steam engines for the evaluation of operation schemes.Voir les produits