Viscous resistance coefficients in porous medium

fpingqian

Fluent manual tell us that, for laminar flow through a fibrous mat, we can calculate the viscous resistance coefficients using Blake-Kozeny equation, and ignore the inertial resistance. In my question, the dimension of the geometry is micro scale, so the viscous resistance coefficient is up to e-10. In this condition, I can't obtain the good result compared with the experimental one. However, when I change the the viscous resistance coefficient to a higher value, for example, e10, the results can be well agreement with the experimental one. Hope someone can tell me what leads to this, and how to calculate the viscous resistance coefficient in porous medium. Thanks in advance.