[mech_engg_swag]

Hi all,
I am solving a problem involving porous media, using the solver rhoPorousSimpleFoam. The equations to be solved are NS-equations with porous resistance tern, Continuity Equation and Diffusion Equation. I am trying to modify the code of rhoPorousSimpleFoam to my problem's needs.
First, I am thinking of introducing a gravity term in the NS-equations. Second, I want to modify the Energy Equation such that solving it becomes equivalent to solving the Diffusion Equation.
I have the following queries :
1) Is my plan the most optimal one, or is there a more optimal way to go about this? Please suggest improvements. Btw, Time does not permit me to design my own solver.
2) How do I add a gravity term to the NS equations for compressible flow?
3) I am planning to erase the Mechanical Energy Terms in the Energy Equation and to turn it into a Heat Diffusion Equation for Fluids, which can then be solved like a Mass Diffusion Equation. How do I do so? If there is an easier way to solve this problem, please suggest so.
4) Heat Transfer and Mass Transfer are analogous to each other. Is there a Mass Transfer Analogue for Enthalpy? What is it?
Thanks in advance.