[HHOS]

hello,


I am trying to understand how the species transport is working. I understand what the mass fraction is, but it is hard for me to grasp what its evolution show.


I have created a test case in which I have a closed domain in 2D with an air-vapor mixture. I have initialized the case with the mass fraction corresponding to the 80% RH (Relative Humidity) and set at a wall a mass fraction corresponding to the 20% RH as boundary condition. See the first image showing the mass fraction at the start.


As you can see in the second picture, after running for some time, the mass fraction of water vapor in the domain is tending towards the set 20%RH, and in the end it gets that 20%RH everywhere in the domain.


I thought, OK, that is a ratio, so maybe there is something I don't get. I checked then the evolution of the molar concentration, which is the particles I have per volume unit, and it shows the same trend, less and less particles on the left side. From the air, however, more and more particles were coming in.


And there are some things I don't understand/know how to do.

The mass in the system raises (makes sense, because air is heavier than water vapor), but I don't know how to monitor that other than controling the whole volume, because the massflow at every boundary, which are walls, is always zero. I actually will have two possible sources of species, and don't know how to monitor what comes from/goes to where.


Any clarification would be appreciated


Thanks