V.V. Levdansky

THEORETICAL INVESTIGATION OF VAPOUR TRANSFER THROUGH A CAPILLARY-POROUS BODY

Abstract In the first part of the paper an investigation is made of the capillary evaporation under free molecular conditions for a nonisothermal case with assumption made of the evaporation occurring both on a lateral surface and at the bottom. Two modes of reflection from the surface, diffuse and specular, are considered. In both cases approximate expressions are derived for the fluxes of molecules at the capillary exit. In the case of diffuse reflection, the flow of molecules leaving the unit lateral surface and the net surface flow are obtained as well. This expression allowed investigation of the phase transition at the wall depending on the dimensionless length and temperature drop. In the second part it is shown that the effect of surface diffusion on the capillary conductivity is determined by the dimensionless parameter G L equal to the squared ratio of the square mean displacement of a molecule over the surface to the capillary length, and preceding the senior derivative in the initial integro-differential equation. In the third part, based on the approximate theory of the mean free molecular path length, an expression is found for a vapour flow through a high-dispersed porous body when the capillary model is an inexact one.

Trapping of impurity molecules in condensation from mixtures of gases

The problems of trapping of impurity molecules in deposition of substance from a mixture of gases are investigated. Both internal and external problems are considered. The influence of the condensation rate of basic substance on the concentration of impurity molecules in a condensed phase is analyzed.

Effect of electromagnetic fields on transfer processes in heterogeneous systems

Some effects are analyzed which are related to the influence of electromagnetic radiation on transfer processes in heterogeneous systems. The influence exerted by the excitation of internal degrees of freedom of molecules in a field of the resonance laser radiation is considered, as well as the effect of volumetric heating of a porous catalyst particle in the field of microwave radiation. It is shown that on exposure to microwave radiation heterogeneous reaction in a particle of the porous catalyst can occur more uniformly over the particle volume. An expression is found for temperature distribution in a spherical particle of the porous catalyst resulting in a uniform course of chemical reaction over the particle volume.

Growth and evaporation of aerosol particles in the presence of adsorbable gases

Abstract Influence of adsorption of noncondensable molecules on the surface of phase transition on the rate of growth (evaporation) of aerosol particles (drops) is investigated theoretically. Combined manifestation of the effects that influence the rate of the growth of particles in the opposite directions is considered: decrease in surface tension on adsorption of a foreign gas and blocking of the surface of phase transition by the molecules adsorbed. The effect of the adsorption of the molecules of a noncondensable (in particular, buffer) gas on the rate of homogeneous nucleation and also on the growth of particles in chemical deposition is discussed.

Chemical deposition of substance from gas phase in nonisothermal channels

The possibility of using nonisothermality effect in filling semi-closed channels by means of deposition of gas molecules on the inner channel surface is analyzed. The case of chemical deposition is investigated for free-molecular gas flow in the cylindrical channel with the temperature-dependent coefficient which characterizes the efficiency of collisions of molecules with the surface. It is shown that decrease in the surface temperature from the bottom to the open end of the channel enables one to obtain both the substance film which is sufficiently uniform in thickness and the film with monotonous decrease in the thickness towards the exit from the channel. The last factor is important for the problem of filling the channel by the substance without formation of cavities. The possibility of realization of the above temperature distribution along the channel by means of the microwave radiation is considered.

Direct statistical simulation of gas mixture mass transfer in a porous layer with condensation of one of the components and absorption of another

Abstract Based on the method of direct statistical simulation, a physical–mathematical model has been developed for gas mixture mass transfer in a highly porous body under the conditions of condensation of one of the components and trapping of a non-condensable admixture. Distributions of gas velocities and densities in a porous layer and in the space above it are found, as well as distributions of flows of a condensable component and absorbable admixture along the depth of the porous layer. The efficiencies of the absorption of the admixture in a porous layer and on a plane surface are compared.

Gas pressure on the surface of condensed phase in a resonance radiation field

Abstract The influence of resonance radiation on the pressure exerted by gas on the surface of a condensed phase is studied. The effects, which are associated with a change in the recoil pressure of molecules escaping from the surface in a radiation field, are considered. Combined manifestation of thermal and resonance effects is analyzed, as well as the influence of a change in the indicatrix of scattering of the molecules leaving a surface in a radiation field. It is shown that new components of a photophoretic force, that acts on an aerosol particle, can appear in the field of resonance radiation. In such a situation there is a resultant force even in the case of uniform heating of the particle when classical photophoresis does not occur.

Trapping of molecules by aerosol particles in physical and chemical deposition

The problem of the molecule trapping by aerosol particle is considered both for condensation growth of the particle and for heterogeneous chemical reaction on the particle surface. The equations for resultant flux of molecules into the particle and for the trapping coefficient are obtained. The temperature dependence of the trapping coefficient in the cases of the physical and chemical deposition is discussed.