Estimate convection and diffusion terms in transport equation
 

I have an additional variable that is transported through the domain (using the normal transport equation, third eqn. at http://www.cfd-online.com/Wiki/Gener...sport_equation).

Im am trying to estimate where and when the transport is dominated by diffusion and when it is dominated by convection. So I thought that I could compute each of the terms in the transport equation to see which term is larger than the other. To do so I need to estimate div(rho*u*scalar) and div(Gamma*grad(scalar)) in cfd-post. Is there a way to that or should I take another approach?