Thermodynamics in CEDRE

The CEDRE thermophysics model combines all the data and procedures that allow the calculation of the thermodynamic properties and transport coefficients of the material media that make up the multi-physics system to be analyzed. This document is more specifically concerned with the thermodynamics of compressible fluids and is limited to the study of homogenous mixtures of chemical species. Starting from the different forms of the fundamental equation of thermodynamics, it involves some useful concepts: state variables and functions, extensive and intensive properties, specific (or molar) properties of the mixture, partial properties of species in the mixture and properties of pure substances. It is shown that, in the pressure-temperature-composition variable system, the free enthalpy is a potential that all the other properties are derived from (volume, entropy, enthalpy, etc.), from which arises a set of general relations between calorific and thermoelastic coefficients. Then, different models for the calculation of the properties of pure substances are presented, from the “perfect gas” limit through real gases, to compressible liquids. These are then reused in the section that covers the way in which the properties of the mixture are calculated from those of its components. Finally, the document briefly describes how the computer data management and the thermophysics computing service are organized in an independent library called ThermoLib.