2. Definitions and main relationships between basic quantities

In the case of a pure fluid, the thermodynamic state is entirely characterized by the knowledge of two quantities, e.g. temperature and pressure, or pressure and volume, etc. In the case of a mixture, the presence of several constituents requires the knowledge of a third quantity to characterize the thermodynamic state. In the case of moist air, this third quantity may be one of the many commonly used to define "humidity": mixing ratio, relative humidity, dew point temperature, wet bulb temperature, etc.

Once we know the temperature, pressure and any one of these quantities, we can determine all the others, as well as the various quantities such as density, mass volume, enthalpy, etc. The aim of this para-graph is to give the main definitions and the relationships we need to know in order to carry out calculations from one quantity to another. The aim of this para-graph...