convection and diffusion" module

I have an example to be tested in Featool,  regarding the transport a solute by bulk water flow downstream through a 2D x-y plane, where the diffusion will be taken into account. The inlet water flow rate along the X-direction is known.

I checked modules in Featool. The "convection and diffusion" module seems to be appropriate for this test.

I set up the "Convection velocity in x-direction" as the water flow rate.

There are four boundary choices for the "convection and diffusion" module. I set the "concentration" boundary at the flow-in interface with the constant bulk concentration, and I set the "convective flow/outflow" boundary at the flow-out interface.

By this setup, I found that the water flow rate actually did not have significant effect on the concentration profile over the 2D test domain.

I am wondering if there are other setup in Featool that can describe and predict this scenario?

Also, can the "convection and diffusion" module be applied to the test domain with porosity?

Thank you for your time and consideration.

James wrote

There are four boundary choices for the "convection and diffusion" module. I set the "concentration" boundary at the flow-in interface with the constant bulk concentration, and I set the "convective flow/outflow" boundary at the flow-out interface.

This seems like the correct choice.

James wrote

By this setup, I found that the water flow rate actually did not have significant effect on the concentration profile over the 2D test domain.

Without knowing anything about your particular model and parameters it is hard to say anything, but in general this would depend on the ratio of the diffusion coefficient to velocity. To get a feel for how the convection and diffusion model works you can try and play around with the Heat Exchanger quickstart model:

https://www.featool.com/doc/multiphysics_00_heat_exchanger1

as the convection and diffusion and convection and conduction equations are mathematically identical, just with different names for the dependent variable and coefficients. There are also a number of m-file script models for convection and diffusion that might be worth to look at (ex_convdiff1-6):

https://github.com/precise-simulation/featool-multiphysics/blob/master/examples/ex_convdiff5.m

James wrote

Also, can the "convection and diffusion" module be applied to the test domain with porosity?

Typically one would use the Darcy's Law or Brinkman equations to model porous flow. See the porous flow model example.