[shuuyaan]

Hi all,

I am modeling a 2D evaporation-condensation, pool boiling case, with 2 phases (water and vapor). I am trying to only patch water during initialization. However, I noticed that the vapor phase gets patched into the other regions, excluding the water region.

A contour of the vapor fraction is attached. As you can see, it takes up the other regions where water is not patched. How should I go about patching a vacuum space in the region where the vapor is currently inhabiting?


Thanks and regards,
Shu Yan

[vinerm]

In multiphase simulations, conservation equations for the volume fractions are solved only for the secondary phases since the sum of the volume fractions should add up to 1. So, if the water is secondary phase and you patch water in one region, automatically the other region will have vapor.

In reality, there is nothing called vacuum, just low pressure. So, if the system is closed and the space above water has very very small amount of vapor, that means the pressure is very low. So, you have to model the vapor as ideal gas and initialize the vapor region (the region supposed to have vacuum) with a very low pressure. Do note that it should not be 0 Pa. Furthermore, Evaporation-Condensation model requires some amount of both phases to be present, else, there will not be a phase change.