Aerosols
“Technically, an aerosol is a suspension of fine solid particles or liquid droplets in a gas. Examples are smoke, oceanic haze, air pollution, smog and CS gas. In general conversation, aerosol usually refers to an aerosol spray can or the output of such a can. The word aerosol derives from the fact that matter "floating" in air is a suspension (a mixture in which solid or liquid or combined solid-liquid particles are suspended in a fluid). To differentiate suspensions from true solutions, the term sol evolved—originally meant to cover dispersions of tiny (sub-microscopic) particles in a liquid. With studies of dispersions in air, the term aerosol evolved and now embraces both liquid droplets, solid particles, and combinations of these.” (Wikipedia, Aerosol, 8/5/2011)
Recent Journal Articles
Efficiency of inertial deposition of aerosol particles in fibrous filters with regard to particle rebounds from fibers
(389-393) Colloid Journal 73 #3 (2011)
Chernyakov, Kirsh and Kirsh of the Russian Academy of Sciences, Russia, showd that there is critical filtration velocity U* below which the energy loss upon collisions has no influence on the filtration efficiency. Above this critical velocity, the filtration efficiency depends on the mechanism of the inelastic energy loss and can be noticeably lower than the result of its estimation with no allowance for the particle rebound. For a rather dense fibrous medium, when not all particles that have rebounded from a fiber have time to attain the flow velocity before the next collision with another fiber, the filtration efficiency depends on the velocity distribution of the rebounding particles. It is shown that, in this case, the filtration efficiency must increase with the packing density of a filter. (RDC 8/2/201
Stokes flow and deposition of aerosol nanoparticles in model filters composed of elliptic fibers
(345-351) Colloid Journal 73 #3 (2011)
Kirsh of the Russian Academy of Science, Russia, calculated the fiber collection efficiencies due to diffusion of nanoparticles in model filters, i.e., separate rows of fibers with an elliptic cross section located normal to the flow at different orientations of the ellipse axes with respect to the flow. The Stokes flow field in the system of the fibers is found by the method of fundamental solutions. The concentration field of Brownian particles and the efficiency of their deposition onto the fibers are determined from the numerical solution of the equation for the convective diffusion. The dependence of the capture coefficient on the Peclet number for elliptic fibers is shown to have the form η = APe−m, where exponent m changes from 2/3 to 3/4 at the parallel and normal orientation of the major axes of the ellipses with respect to the flow, respectively. It is shown that, from the viewpoint of aerosol nanoparticle capture, the best filters are those in which the fibers have a maximum midsection at the same cross-sectional area. (RDC 8/2/2011)