Air Permeability Fisher Method Specific Surface

  • The Sub-Sieve Sizer operates on the air-permeability principle for measuring the average particle size of powders. The principle is based upon the fact that particles in the path of a regulated airflow will affect that airflow in relationship to their size. More specifically, however, the principle finds its basis in the fact that a current of air flows more readily through a bed of coarse powder than through an otherwise equal bed of fine powder that is equal in shape of bed, apparent volume, and percentage of voids; but by reason of difference in general coarseness of material (differing in average pore diameter and in total interstitial surface), measurements of average particle sizes are obtained.