THEORETICAL-ANALYSIS OF SIZE DISTRIBUTIONS DETERMINED WITH SCREENS AND FILTERS

Nets, screens, and filters are used to sieve out particles larger than the pore sizes. However, during separation a significant fraction of particles smaller than the pore diameters will also be removed by coll ision and adhesion to the mesh fibers. Two filtration models were used to predict the size and mass distributions of particles during size s eparation. A capillary tube model was used to calculate particle remov al by different screens, and a fibrous filter model was used for glass -fiber filters. The extent of particle removal was modeled assuming a size distribution of 3,100 particles evenly distributed at logarithmic intervals over 31 size classes ranging from 0.1 to 100 mum. As many a s 8% of the particles and 50% of the total particle mass could be reta ined by a 210-mum (pore diam) mesh even though all particles were < 10 0 mum. This high retention of particles implies that when size distrib utions are prepared with screens and filters, the mass concentration i n smaller size fractions will be considerably underestimated.