Hi, Does anybody know how to work out the equivalent source term, in the conservation of species equation, that models a surface reaction. I can not define a surface reaction because I want to model a permeable wall ie. blood flow through the wall with a surface reaction occuring. So I think I can define a source term, in a cell thread above an interior face, which is equivalent to a surface reaction if the interior face was a wall.

Cheers,

Andrew

Not sure if this is what you need, but there is a variable C_STORAGE(cell,thread,species) that tracks species exchange (in kg/s) for each cell. In theory, you could calculate the magnitude (and sign) of this term for the species of interest.

I use these terms for species exchange with a particulate phase. But, it does take a fair amount of work to make sure other variables, like mass and energy balances, are not comprimised. If you don't have a few weeks of time to play with this, I would recommend using built in Fluent surface reaction, if it doesn't do exactly what you want.

Hi Allan,

Thanks for your reply. Do you have more information about C_STORAGE, I can not find any information about it in the UDF manual. There is a variable C_STORAGE_R but I understand this would just return the mass fraction of species in the cells adjacent to the wall.

Andrew.

You are right - I should have typed in the variable name C_STORAGE_R(c,t,species). In my application this works for any cell in any thread, and the units are kg/s.

The variable for mass fraction of a species is C_YI(c,t,species), which again seems to work for any cell in any thread. (The species ID number of course can be determined from the list of species in your mixture with the first being 0).

At one time there was a list of user posted UDF's on the FTP section of this site (cfd-online). Some of this code had useful stuff not available in the UDF manual. I haven't looked lately to see if it is still here.