Hi all - I have a problem that I'm probably going to model in COMSOL and would love to hear some ideas on how to get the proper BCs. Attached is the picture from Truskey. Essentially, the problem consists of removing waste (water) from the membrane tube at a rate of ~ 1 mL/min with a pressure driven flow ~ 80 mm Hg inlet and ~ 40 mm Hg at the outlet. The radius of the tube should be around ~ 8-10 mm, and length, thickness, and porosity of the membrane to be chosen for optimal and desired waste removal. I'm using COMSOL's convection and diffusion modeling. The inlet is a known concentration of waste and velocity profile. The outlet BC I use is convective flux resultant from flow out of the pores. The membrane BC is where I'm not sure what to use. Right now, It's a partition coefficient problem with a flux concentration difference (something like K*(C_inside-C_outside)). I haven't gone into the full problem really, but I was just wanted some feedback on how to set up my BCs properly to capture the waste removal at the membrane of ~ 1ml/min... Another attached picture is the actual modeling domain used. So basically, how can I capture the removal of ~ 1ml/min of waste (water) from the permeate side in COMSOL???? Is there a better way to set this problem up using incompressible Navier Stokes in COMSOL to use Brinkman's Equations for the membrane part? If so, how would I go about it given the general problem I've described as far as BC implementation. Thanks for any feedback.