flux boundary condition as source

hello...

I have a problem in hand where i have a volume source within the aquifer at the center and the source strength is in mg/sec.  I am trying to put source in the form of flux boundary to the source emitting from all sides into the aquifer. Can you please tell whether the flux put on source boundaries should be given negative sign or positive sign?

Thanks.

Manish Chopra

For all boundary conditions, fluxes into the model are negative. For a mass source as a second kind boundary condition, you have to be careful with the form of the transport equation used: The default 'convective' form will only be OK if you do not have a flow boundary condition on the same nodes!