4. Specific correlations

Taking into account spatial and temporal variations in the parameters of interest does not necessarily require recourse to local models, and these variations can be evaluated macroscopically through empirical correlations that allow us to relate average equilibrium quantities (titre, quality, temperature, enthalpy...) to each other. This is the purpose of the relationships proposed in this section, which enable orders of magnitude to be estimated. The aim here is not to review the state of the art in terms of the models and correlations that can be used, but rather to propose relationships that are simple to implement. However, these relationships are subject to considerable uncertainties (of the order of 20%, but which can reach 50% or even 100%). It is therefore advisable to carefully check the field of application (validity) of these relationships and the associated uncertainties....