Hi everyone, I'm trying to design a simple model by using Comsol Multiphysics. I set an inlet concentration of a species "cp" that will be adsorbed to a circular surface located at the center of the microfluidic cell (I named the concentration of adsorbed protein "cpl" ). I used laminar flow, transport of diluted species and surface reaction nodes. When I run the simulation with the Surface Reaction node and the Flux section of the Transport of Diluted Species disabled, I get logical values for cp. When I run the simulation with all the sections enabled, the concentrations of cp at the 5 probes I created no longer make much sense and I get a decrease of the cp concentration on the left probe ( red line in Proble Plot 3) at, approximately, 35 seconds of simulation. This will obviously affect my cpl concentration (Probe Plot 8). I've tried different meshes and different solvers and I have no idea why this is happening, have been stuck with this problem for two months now so any help would be greatly appreciated. P.S.: It wont let me attach the file so I posted the link to where it is, if that's not ok I'll delete it. http://www.comsol.com/community/forums/general/thread/33120/ Thanks in advance.