The deposition of aerosol particles from a Stokes flow in filters composed of nanofibers has been considered at Knudsen numbers Kn ∼ 1. The efficiency of particle collection by model filters with 2D and 3D structures has been determined by numerical simulation as depending on particle radius r_p , filter parameters (nanofiber radius a , packing density α , and filter thickness), and filtration conditions taking into account the gas slip at the fibers. It has been shown that the efficiencies of particle collection by nanofibers in model 2D and 3D filters are almost equal at the same low packing density α < 0.02. It has been found that the dependence of the penetration of particles on their radius at a constant velocity on the order of several centimeters per second and at Kn ∼ 1 passes through a maximum, which corresponds to particle radius r_p∼ a . The calculated sizes of the most penetrating particles agree with experimental data. The results obtained will be used when selecting aerosols for testing nanofibrous filters.

A hypothesis has been proposed according to which the preserved traces of the impact on the nature caused by the explosion of the Tunguska meteorite are the result of electrical discharges in a cloud of solid particles, which, when moving at the space velocity in the upper atmosphere, were heated up to a high temperature and, due to thermionic emission, acquired large positive charges. The released thermo-electrons attached to air molecules and lagged behind the charged particles. The separation of the charges in the cloud caused powerful discharges similar to horizontal lightnings in clouds. The consequences of the discharges in the cloud of highly charged solid particles, which gave rise to the generation of hard ionizing radiation, are discussed.

Previously discovered properties of an ensemble of highly charged droplets obtained by electrostatic dispersing of liquids have been discussed. It has been shown that the mechanical strength, glow, and other properties of the ensemble of such droplets are also inherent in ball lightnings. The properties of solid particles, the limiting charges of which exceed the Rayleigh charges of droplets by several orders of magnitude, have also been considered, and the hypothesis of that ball lightnings are of the aerosol nature has been substantiated.

The deposition of aerosol particles in a filter composed of fibers coated with highly porous layers of radially oriented needles and the deposition of needle-coated particles onto smooth fibers have been studied. The Stokes flow fields in a model row of parallel fibers and near an individual needle-coated spherical particle have been calculated. A correction to the Stokes force for the drag of the layer of needles covering the particle has been found. The forces of the van der Waals interaction of the needles with the particle and the fiber have been calculated within the framework of the additive approximation, and the conditions have been determined under which the needles hinder particle deposition onto the fibers.

The influence of gravity on the deposition of high-density submicron aerosol particles in fibrous filters from vertical and horizontal (relative to the gravity vector direction) gas flows has been studied at small Reynolds numbers, $$\operatorname{Re} \ll 1.$$ Numerical solutions of the Stokes equation and the equation for convective diffusion have been employed to calculate the efficiency of collection of spherical finite-size particles by model filters with two- and three-dimensional flow fields and real filters as depending on the particle size and density and flow velocity direction and taking into account particle deposition on the rear sides of fibers in ascending flows. The calculation results have been confirmed by experimental data on the deposition of submicron spherical silver particles in screens and fibrous filters.

The deposition of aerosol nanoparticles has been studied in a model granular filter composed of parallel monolayers of contacting spherical granules with a square packing, where each even monolayer is shifted in its plane relative to an odd layer by the granule radius in two directions normal to one another. The monolayers of the granules are oriented normal to an incident flow. The efficiencies of diffusion collection of point particles by the granules have been calculated as depending on the distance between the layers in the regime of a three-dimensional gas flow at small Reynolds numbers $$\operatorname{Re} $$ $$ \ll $$ 1 within a Peclet number range of $${\text{Pe}}$$ = 102−104. The calculation results have agreed with the published data and the results of measuring the deposition of monodisperse nanoparticles from nitrogen and helium upon filtration through layers of monodisperse metal spheres. The possibility of using a layer of granules as a diffusion battery for measuring the sizes of aerosol particles has been discussed.

The deposition of aerosol particles in diffusion batteries composed of model screens oriented perpendicularly to a Stokes flow has been considered. The particle collection efficiencies have been calculated as depending on screens parameters and the Peclet diffusion number. It has been shown that, at large Peclet numbers, the particle penetration through dense screens is independent of the interscreen distance and coincides with the penetration calculated by the empirical equation used for screen diffusion batteries.

Исследовано диффузионное осаждение субмикронных аэрозольных частиц в модельных фильтрах, состоящих из волокон, покрытых пористыми проницаемыми оболочками. В качестве модельного фильтра использована упорядоченная система параллельных цилиндров, расположенных перпендикулярно направлению потока. Приведены результаты расчетов зависимости коэффициента захвата от радиуса оболочек, их проницаемости, плотности упаковки фильтров, а также от радиуса частиц и скорости потока. Расчеты проведены в широком диапазоне чисел Пекле Pe. Показано, что с увеличением диффузионной подвижности частиц и ростом проницаемости оболочек коэффициент захвата и критерий качества фильтра растут, при этом зависимость критерия от радиуса проницаемых оболочек имеет максимум. Показано также, что коэффициенты захвата волокон с пористыми оболочками, рассчитанные с использованием ячеечной модели и для изолированного ряда волокон, практически совпадают.

The deposition of submicron aerosol particles in model fibrous filters consisting of composite fibers coated with coaxial porous permeable shells composed of thin whiskers directed perpendicularly to the fiber surface has been considered. The viscous drag of the composite fibers and the efficiency of the diffusion collection of nanosized (point) and submicron particles from a three-dimensional flow have been calculated taking into account the finite sizes of the latter particles at small Reynolds numbers and Peclet diffusion numbers Pe = 1–106. Filter quality criterion γ, i.e., the ratio between the logarithmic penetration of the particles and the pressure drop across the filter, has been calculated as depending on the particle size and the parameters of the composite fibers. It has been shown that, when filtering aerosols of submicron particles, the γ value of the filters consisting of the composite fibers increases with Pe, markedly exceeds the γ values for point nanoparticles, and may be several times higher than the quality criterion of filters composed of fibers without porous shells.

The viscous drag of bimodal fibrous materials and the efficiency of gas filtration through them have been studied as depending on the volume fraction of thin fibers. The dependence of the Brinkman constant on the content of fibers with a lower diameter has been calculated for the equations describing the hydrodynamics of a gas in a porous medium composed of fibers having two different diameters. The penetration of aerosol particles has been calculated as depending on their diameter for different bimodal filters. The calculated and experimental data have been compared.

Filtration of fine aerosols with model filters formed from composite fibers coated with porous permeable shells (layers) of a discrete structure consisting of finer parallel fibers has been considered. Drag forces and efficiencies of diffusion collection of submicron particles have been calculated as depending on the porosity of the filters, parameters of the shells, and the Peclet diffusion numbers at which the filter performance is substantially increased.

The diffusion deposition of point particles from a Stokes–Brinkman transverse stationary flow in a model monolayer membrane composed of contacting spherical hollow grains (capsules) with porous permeable shells formed from nanoparticles, is calculated. Monolayers with square and hexagonal packings of the grains are considered. Approximation equations are constructed for the dependences of grain drag force on shell thickness, Brinkman permeability parameter S, and internal shell radius ξ. Efficiencies of point particle collection on the grains are calculated as depending on the Peclet number, S, and ξ, and it is shown that layers of hollow permeable grains possess the highest filtration performance criterion among layers of impermeable and permeable uniform porous grains provided that the zero-concentration boundary condition is fulfilled at the outer radius of the grain.