NUMERICAL STUDY OF PHASE-CHANGE PHENOMENA: A CONSERVATIVE LINEARIZED ENTHALPY APPROACH

Solid-liquid phase-change phenomena play a key role in the thermal hydraulics of Molten Salt Reactors (MSR’s). Amongst key areas of interest are the design of the freeze plug and the analysis of accident scenarios where solidification of the fuel salt might pose a risk. As such, accurate numerical models coupling the solid-liquid phase transition with fluid flow and thermal effects are highly desired for a safe and efficient design of the MSR’s. Nowadays, the most widely used models for modelling macroscopic phase change are the apparent heat capacity method and the source-based enthalpy approach. However, these models suffer from low accuracy in the limit of large time-steps and a small mushy zone and slow convergence respectively. In addition, smearing the latent heat-peak through the introduction of
the so-called ’mushy-zone’ does not reflect the physics of isothermal phase-change and may introduce an additional source of error. For this reason, we model melting/solidification phase-change through the so-called linearized enthalpy approach, where the energy equation is linearized around a previously known value of the volumetric enthalpy. This approach is inherently energy-conservative, without the need for a mushy zone. Both the classical Stefan problem and gallium melting in a rectangular enclosure with heated side walls are considered as numerical benchmarking cases. For the latter, the linearized enthalpy method is validated using both available experimental data and a previous numerical campaign with the source-based enthalpy approach, and the accuracy of both approaches is compared. As such, this study contributes to the continuous advancement of melting and solidification modelling capabilities.