M. V. Protasov

About choice of particle parameters for visualization and diagnostics of free concentrated air vortices

The problem of the choice of parameters (density, size) of particle inertia for visualization and diagnostics of free vortices of various intensities (characteristic velocity, vortex funnel diameter) is considered. The dimensionless criterion (Stokes number) is used, which determines the peculiarities of solid particles behavior in concentrated vortex structures. An example of the choice of particle parameters for visualization of a laboratory-simulated air vortex funnel and debris cloud is described.

Generation of free concentrated fire vortices under laboratory conditions

The possibility of the principle of physical simulation of free concentrated fire vortices without using a forced twist is demonstrated. Vortex structures were generated during combustion of urotropine (hexamethylenetetramine) pellets placed on the underlying surface (aluminum sheet). The first data on the features of the occurrence of fire vortices were obtained by photographs. Estimates of some integral parameters of the generated fire vortex structures (lifetime, height, and diameter) are carried out.

An experimental investigation of the behavior of solid particles during their motion in smooth and dimpled pipes

Results are given of LDA measurements of averaged and fluctuation velocities of glass particles during their deposition in smooth and dimpled narrow pipes. Experiments reveal a decrease in the axial component of averaged velocity of particles and a significant increase in fluctuation velocities of particles during their motion in a pipe with dimples.

Convective Heat Transfer in Combustors with a Circulating Fluidized Bed

Experimental data on heat transfer in full-scale and model combustors with a circulating fluidized bed are reviewed. A physical scheme and an algorithm are suggested for the calculation of the intensity of heat transfer to a vertical wall subjected to a dust-laden flow.

Analysis of collisions of solid bidispersed particles during their gravitational sedimentation

The process of the collision of bidispersed particles having different sizes and (or) densities during their motion in the field of the gravity force has been analyzed. A dimensionless criterion (the collision Stokes number) has been proposed that accounts for the presence and intensity of the particle-particle collisions. This criterion has been experimentally tested for the case of the sedimentation of a bidispersed mixture of iron and glass particles in the motionless air in a pipe.

The effect of gas injection on the protection of body surfaces streamlined by a two-phase flow

The first results of physical simulation of the effect of gas injection on the characteristics of gas stream with solid particles at flow around bodies are presented. The possibility of ensuring an effective protection of the body surface from the negative effects of particles (droplets) is demonstrated. A dimensionless criterion (the Stokes number) is proposed that characterizes the inertia of particles near the critical point of the body and the intensity of their deposition on the surface under injection conditions.

Composition, morphology characteristics, and optical properties of molybdenum oxide nanostructures synthesized by the laser ablation method in liquid

We present experimental data on composition, morphology, and certain optical properties of nanostructures of molybdenum oxides (MoOx). We show that, upon ablation in water, molybdenum oxides are predominantly synthesized as amorphous masses containing particles (clusters), below 1–2 nm in size, and foam-like structures. We note that the gas bubbles (occurring in the liquid during ablation) might serve as templates for hollow quasi-spherical formations observed in the experiment.

On effect of gas flow turbulence on the efficiency of particle collection in a Venturi scrubber

A general mathematical model of the evolution of the state of a three-phase polydisperse system is developed as applied to the process of the purification of gases from solid particles in a Venturi scrubber. Special attention is paid to the study of the effect of gas turbulence on the frequency of collisions of particles with drops and on the efficiency of purification.

Analysis of the deposition processes of solid particles onto channel walls

Analysis of the main forces leading to the lateral movement and eventual deposition of particles onto the wall of a tube when moving in heterogeneous flows, namely the force of gravity, fluctuational aerodynamic force, and Saffman’s force, is carried out. Simple expressions are obtained in the case of particle movement in horizontal and vertical channels, which allows one to estimate the contribution of different forces on the process of deposition in a wide range of parameters of a heterogeneous flow (velocity, size of the channel, inertia properties of particles, etc.).

Generalized Law of Hydrodynamic Drag of a Permeable Layer

Layers with random packing are employed much more frequently: in the cases of adsorption, catalysis, combustion, filtering, separation, and in numerous other cases in which it is necessary to realize a volume contact between the liquid or gas phases and the solid phase. Such layers are formed when a volume is arbitrarily filled with particles, and their properties largely depend on the technology of compaction or sintering. Strictly speaking, only layers of infinite size may be regarded as randomly packed layers. Nevertheless, if the container diameter and length exceed the size of structure-forming particles by more than an order of magnitude, such a layer may well be treated as infinite. Layers with random packing are simple and inexpensive to prepare. If all structure-forming particles are of the same shape and size d p , the properties of the permeable medium prepared from these particles may be described by a single parameter, namely, porosity Π . We will assume that all particles are spheres of diameter d p . Then, the specific area of the inner surface of the permeable medium, S p , Σ , is determined as