Flow trough air filter

Dragan Petrovic

I would like to understand why very slow (v=1E-4 m/s) airflow seem to be stopped by a filter with, say 75% surface area opened to flow at atmospheric pressures when the center-to-center pore distance is about 0.5 mm?

Some theoretic/empirical formula predicting the conditions of blocking the airflow as a function of impinging air velocity, pore size and pore spacing would be appreciated. I feel that this may be a textbook example. If so, show me the way!

Layman's interpretations will be treatred with a great deal of gratitude.

-dragan