Adaptive modeling: An intuitive approach for the application of irreversible thermodynamics to multiphase flow simulation

The second law of thermodynamics states that the combined entropy of the system and the environment must increase if a physical process is irreversible. Irreversible thermodynamics describes how this entropy is produced. If applied to multiphase flow simulation, irreversible thermodynamics governs the modeling of interphase mass and heat transfer and the boiling process. In this article the fundament of application is described. The presentation is restricted to one-component systems, and the significance of Onsager's law is emphasized. Adaptive modeling allows the evaluation of kinetic coefficients based on existing constitutive relations. The approach is demonstrated using RELAP5-3D. Effects of the application are discussed by analysis of the flooding experiment FLECHT-SEASET Test 31504.