I am modelling flow of water through porous cylindrical polypropylene fibers. The fiber is enclosed in a closed cylindrical cylinder again filled with water.The fiber has an inner diameter of 220 micrometres and the thickness of the porous wall is 40 micrometre thus giving an outer diameter of 300 micrometre. I am looking at two flow rates 1 ml/min and 10 microliters/min(along the tube). The respective mean velocities and reynolds number are .44 m/s(Re 48) and .0004m/s(Re .048).

Now I am interested in the diffusion of the water through the porous wall.Should i use darcy's equation(with just the linear term) or the darcy Forchheimer equation with both the linear and nonlinear terms. Also are there any formulas for the permeability and loss coefficients for such thin fibers

Take the time to try several models. Compare the results to whatever data you have available. You'll probably answer your own question.