Discussion Forum

Dear all,

I try to make a particle conversion model to simulate the conversion of a biomass particle during pyrolysis. Mathematically seen, it is just a system of coupled PDE's and ODE's. I assumed that my problem spherically symmetric resulting in a 1D problem only.

I am using the same approach as described in the Comsol tutorial 'Spherically Symmetric Transport'. Instead of the heat-conduction equation I would like to model the mass conservation equation that models: the accumlative term, convective transport and difussive transport.

The convective term of the equation requires the Darcy velocity. I have problems how to implement the Darcy equation to calculate the darcy velocity. My first solutation was:

• make a variable P: P = ctot * R * T.
• make a new varible u: u = -k/mu * d(P,x)

But this gives very strange results and i think this is due to the fact that I am missing some initial and boundary conditions. For example: at the beginning the porous particle is filled with nitrogen, hence corresponds with a certain initial pressure. At the center of the particle there is no pressure gradient and at the particle surface the pressure should be equal to the atmospheric pressure.

What is the right approach to implement the Darcy equation inside Comsol?

Kind regards,

Daan