[garcijon]

Hi,

I am completely new to Comsol and modelling. I am trying to recreate a published model that uses convective diffusive transport of a molecule that binds to different surface receptors. I am following the Transport and Adsorption Tutorial.

www.comsol.com/model/transport-and-adsorption-5

I want to expand this so that there are multiple distinct active sites where the reactive species can bind to on the surface. These are represented as ODEs

There is also no diffusion through the boundary surface only binding at the surface.

[EDIT]
I tried to create the model but I get an error telling me that h is not defined but h is defined under one of the ODEs.

[niklas.rom]

Hello,
there is surface diffusion in the "Transport and Adsorption" example. It is governed by the parameter "Ds".

There is also a more elegant example available that I made:

https://www.comsol.com/model/biosensor-design-10428


It uses the "Surface Reactions" interface with which you can easily add more species and sites.

This is an app, but you can open it in COMSOL Multiphysics and click the big button "Model Builder" at the top left to review the physics implementation.

regards
Niklas Rom, COMSOL, Inc.

[garcijon]

Hi Niklas,

Thanks for the response. I'm confused about a few things. In the reacting_pillars_variables files the reaction rates are defined differently than in the pdf:

r_ads k_ads*c_P*sr.theta_free Adsorption rate
r_des k_des*sr.theta_i_cs_P Desorption rate
r_quench kf*sr.theta_i_cs_P-kr*sr.theta_i_cs_Q Quench rate

What does sr.theta_free Adsorption rate and the other sr.* terms mean?

Also, How can I specify the density of a given active site. If the inlet is bringing in a constant concentration of P and there is a finite density for S and the other species I want to add then it should saturate at some point?

Thanks