Thanks for replying SD. I do not know exactly how to communicate the objective in Fluent terms, but I'm basically just trying to change the concentration of a component as a function of its position. This doesn't sound like a profile to me, since to my understanding profiles refer to the concentration across the area, not along the reactor's length. My professor instructed us to use a UDF, but it does seem weird to me since the reaction can be adjusted in fluent itself.