In the one-fluid approach, heat and mass source terms are added to the conservation equations to model the phase change phenomena. The activation of the mass source at the thin interfacial region, its strong coupling with the heat source, and its explicit formulation have proven to cause instability in numerical simulations. These instabilities can prevent any pseudo-transient scheme from converging. The present study proposes a fully implicit approach that lifts the related time step limitations, while preserving the most important thermofluid characteristics on a sharp or diffuse interface. The technique involves decoupling the heat and mass source terms by shifting the mass source from the interface to the wall. The new implicit and algebraic method for the evaluation of the interfacial temperature gradient does not require costly geometric calculations and is much easier to tune compared to the Lee model. The method is verified against the analytical solutions and experimental data of various test cases. The robustness and fast convergence of the present model allow industrial simulations of film condensation and boiling to be performed with one to three orders of magnitude larger timesteps and more than 10 times smaller CPU time compared to the conventional coupled approach.
Ekrani et al. (Fri,) studied this question.