[hunger]

Hi everybody!

I want to simulate humidification of dry air with water vapour. The geometry can more or less be seen as some kind of T-junction, but the water inlet is very small compared to the air inlet.

First, I run a steady state simulation with simpleFoam to calculate the flow field. Here I make sure to get a converged solution and mass is conserved.
When I run scalarTransportFoam (also in steady state), mass conservation of the passive scalar is not given anymore.

I have tried different OpenFOAM versions (of4x, of240), the results are the same.
I found out that the diffusion coefficient has an influence on the result, i.e. the bigger "DT", the bigger is the difference between inlet and outlet massflow of the passive scalar. The result also gets better when I increase the inlet massflow with which the passive scalar is transported into the domain.
Therefore I thought that the difference might be due to diffusion of the passive scalar at the inlet (I am using a fixedValue BC at the inlet and a inletOutlet BC at the outlet). I know that in FLUENT one can switch off inlet diffusion at the inlet when calculating multispecies flow.

Has anybody made the same experience using scalarTransportFoam and can give me any hint? E.g. are there more suitable BC to use? Or does scalarTransportFoam in general run into problems, if the massflow of the passive scalar is very small compared to the main fluid flow?

Best regards
Harald