B. G. Pokusaev

Interfacial Mass Transfer in the Liquid–Gas System: An Optical Study

Mass transfer across the liquid–gas interface was studied by a number of optical methods: holographic interferometry in real time, polarization microscopy, shadow imaging, and modified surface-fluctuation spectroscopy. These methods visualize the evolution of the surface layer, the in-depth profile of density, and mass fluxes. Absorption and desorption of various gases by perfluorodecalin is discussed. The origination and development of irregularities in the diffusion–reaction zone were observed during chemical absorption of carbon dioxide by monoethanolamine and KOH solutions.

Modeling of boiling of subcooled water and ethanol under conditions of pulsed heat generation in a wall

Results of experimental investigation and mathematical modeling of boiling of subcooled water and ethanol under pulsed heat generation in a heater wall are presented. The defining steps of boiling, i.e., warming-up of the wall area, development of the vapor phase, and formation of the pressure wave, are considered. Beginning from some values of surface warming rates (∼3000 K/s) and underheating (∼20 K), the mechanisms of boiling of water and alcohol are demonstrated to be different.

Motion of a gas slug in inclined tubes

The velocities of a freely rising gas slug and a phase boundary (gas-liquid) under conditions of liquid discharge in tubes of various diameters are experimentally studied. It is shown that the nonmonotonic character of the dependence of measured velocities on the angle of inclination is determined only by the curvature in the vicinity of the critical point of the head of the slug or the phase boundary during liquid discharge. Experimental results are obtained by measuring the profiles of curvature of the bubble head in mutually perpendicular planes. For these purposes, an appropriate computer program was developed, and an immersion optical procedure was used that made it possible to eliminate optical “noises” associated with the thickness of a tube wall.

Peculiarities of diffusion in gels

An optical method was applied to study the peculiarities of diffusion in gel: this method provides real-time visualization of spreading of solutes brought into the gel. It was shown that spectral characteristics of reflected light give additional information about nature of diffusive spreading of solutes and about state of the gel. Gels with different densities and lifetime were studied. These parameters have strong influence on the velocity of diffusion. The study demonstrated critical differences for diffusion process in gels with true solutions and with solutions with nanoparticles. Experiments discovered the anisotropy in 3D diffusion of solutes in gels; physical explanation of this phenomenon was proposed.

Development of convection in near-wall granular bed during nonstationary heating

Based on the developed and realized optical method of the polarization of temperature fields, the results of experiments on the visualization of temperature fields and the development of convective flows during the nonstationary conductive heating of the cell wall involving a layer of pebble beds placed in liquid are presented. Upon variations in the heat physical properties of liquid and particles (pebbles) of the granular bed, as well as the value of the supplied heat flow, the mechanism of the pebble-bed effect on the time and character of the formation of free convection close to the wall heated from below has been studied. The calculation model of the process has been suggested.

Transfer processes in a multiphase medium

A study is made of the role of suspended or immobile solid particles in interfacial heat-and mass-transfer processes in gas (vapor)—liquid media under slug and bubble flow conditions under the action of acoustic and wave perturbations. New results of measuring the velocity fields of gas inclusions in water-saturated granular beds are presented that demonstrate the capabilities of visualization of opaque three-phase media by immersion tomography.

Vapor–liquid critical flow through a layer of spherical particles

Vapor–liquid flow in a cylindrical channel through fillings of spherical particles is studied experimentally. Data on the critical flow of a vapor–water mixture with various vapor contents through densely packed layers of spherical particles from stainless steel with diameters of 2 and 4 mm for a filling column height of 250 and 355 mm are obtained. Experimental data demonstrate the influence of pressure, the vapor content of the mixture at the input, and the geometric parameters of the filling on the critical mass velocity. The linear dependence of the critical mass velocity on the geometric factor

Peculiarities of unsteady mass transfer in flat channels with liquid and gel

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Some modern optical methods for the diagnostics of processes in multiphase granular media

. The possibility of generalizing the experimental results based on the gas dynamic model for the flow of a homogeneous medium is considered.

Experimental and numerical simulation of interphase mass transfer of gas bubble in granular backfill and gel

The rate of the unsteady mass-transfer process in horizontal flat channels filled with viscous liquid (water) and in channels filled with gel has been measured experimentally. It has been established that the rate of propagation of a substance through a channel under the unsteady one-dimensional mass transfer conditions depends on its width and exceeds the value corresponding to the rate of diffusion. The measured mass transport rate in an open channel is less than in a closed channel. The reason for the increased mass-transfer rate with regard to the diffusion mechanism is the slow convective flow of liquid caused by the difference between the densities of a diffusing substance and water. The presence of the surface concentration gradient of liquid gives rise to the appearance of surface forces that significantly affect the mass transport rate. The similarity of the mass-transfer behavior in channels filled with pure liquid and gels is found experimentally, which allows one to talk about their presence, as well as of convective transport in them.