Troubleshooting Fluid Film Boiling Simulations

The boiling model is formulated for sub-critical conditions and expects the latent heat, such as the enthalpy difference of gas and liquid phase at saturation, to be strictly positive.

The following warning messages signal a violation of this precondition:
[PhaseInteraction]: Boiling:… Negative latent heat encountered, and set to zero...
This warning indicates that for the number of given sites, enthalpy is specified inconsistently for the gas and liquid species. For troubleshooting, you can evaluate the enthalpy of the film and gas phase with a contour plot to check for errors. In most cases, this error message occurs when you have incorrectly defined the heat of formation, standard state temperature or specific heat material properties for the film or gas phases.
[PhaseInteraction]: Boiling: Temperature beyond critical point for some components. Latent heat contribution zeroed for these...

The boiling model in Simcenter STAR-CCM+ is not formulated to predict the flow behavior at supercritical conditions. This warning indicates that for the number of given sites, the boiling temperature exceeds the critical temperature of some participating components. Therefore, the latent heat contribution of affected component pairs is presumed to be zero. For troubleshooting, you can evaluate the severity of the violation by checking the mass fraction of the affected components. A negligible mass fraction indicate a less severe impact on the simulation results. 

[PhaseInteraction]: Boiling:… Evaluated latent heat is not strictly positive; phase change disabled...

This warning indicates that for the number of given sites, one of the two violations above has been encountered for every participating component pair. For these cases, since the simulation conditions fall outside of the modeling assumptions, the boiling model is disabled at these locations.

If a fluid film boiling simulation shows solution divergence, consider the following factors:
  • If the initial temperature for the fluid film is higher that the saturation temperature, flash boiling can occur at the start of the simulation. You are advised to prescribe gradually increasing fluid film temperatures for improved stability.
  • Excessively high boiling rates and vapor transfers suggest that the time-step is too high.
  • Very high initial wall temperatures can lead to rapid boiling and convergence issues. You are advised to prescribe gradually increasing fluid wall temperatures for improved stability.