This prolongs their intrapore residence times,increasing thereby the probability of pore wall encounters [18].There are other capture mechanisms as well for the removal of particlesby filters; direct particle depositions take place on filter surfaces;inertial impactions of particles whose mass and velocity in thefluid stream keep them on path to collide with a filter surface even asthe conveying fluid flow diverts to avoid the same; diffusive encountersbetween particles and pore surfaces resulting from the molecularcollisions caused by Brownian motion, ongoing as a consequence oftemperature. Inertial impactions favor heavier particles with highervelocities. The vector imparted to a particle by Brownian motion hasa greater moment when occasioned by the particle being light, small,and easier to move. The higher viscosities of the liquid state attenuateboth the inertial impacts and the particle movements that dependupon molecular collisions. Both of these mechanisms are more effectivein the filtration of air and gases with their lower viscosities.While all the capture mechanisms reflect, at least to some degree,the diameters of the pores relative to the size of the particles, sieveretention alone defines the “pore size,” the dimension that presumablyis the size of the smallest particle unable to penetrate the filterbecause of geometrical restraints.