Negative droplet growth rate in Fluent wet steam model

[James411project]

Hello everyone!

I am currently using the Wet Steam Model in ANSYS Fluent. In this model, the mass source term for the vapor phase is defined by two components: droplet nucleation and droplet growth, as shown in the equations below:

Based on my research into non-equilibrium condensation flows, both droplet condensation (growth) and evaporation should occur. This implies that the droplet growth rate can be either positive or negative.

However, according to the definitions provided in the Fluent documentation, it appears that the droplet growth term is treated as positive only. I am curious: How does the Wet Steam Model account for the droplet evaporation process?

Thanks for any insights you can provide.

[Rob]

Have a look here https://ansyshelp.ansys.com/public/account/Secured?returnurl=/Views/Secured/corp/v252/en/flu_th/flu_th_sec_wet_steam_phase_change.html    If T>T0 and (or?) r*>r then the growth terms will be negative. 

[James411project]

Thank you for your professional reply. In my calculations, I have encountered another issue: if the droplet evaporation rate is too high, it means that the already condensed liquid phase will be depleted. If the evaporation source term is too large, could this result in a negative liquid phase mass fraction (meaning the liquid in the grid is completely exhausted, even turning negative)? Does this imply that we should consider imposing a limit on the droplet evaporation rate?

[Rob]

If you're converging the solution I doubt liquid fraction could become negative.