Alexei Kryukov

Condensation from a vapor-gas mixture on a plane surface

An approach is developed, which was previously suggested for the investigation of intensive condensation of pure vapor in application to a one-dimensional steady-state problem of condensation in the presence of a noncondensable component. Results are obtained, which make possible the estimation of the parameters of the limiting modes of condensation from a vapor-gas binary mixture.

Selective water vapor cryopumping through argon

A selective cryopumping process for water vapor control takes place in vacuum systems for web coating or plasma operations, such as sputter deposition, etching, etc. Excessive water vapor content will affect the quality of the processes and final products. These vacuum systems typically operate at pressures corresponding to transitional or viscous flow regimes, and water vapor cryopumping is highly limited by diffusion of water vapor molecules through a noncondensable process gas (argon, air). An analytical model was created to describe water vapor condensing process through a noncondensable gas diffusion barrier. The model accounts for the collisions of different molecules by means of Boltzmann kinetic equations for two-component rarefied gas. It was assumed that water vapor content is about three orders of magnitude lower than that of the noncondensable gas (argon). Cryopumping process was analyzed for two simplified cases when water vapor source and cryosurface are parallel plates and coaxial cylinders...

Mass and heat transfer between evaporation and condensation surfaces: Atomistic simulation and solution of Boltzmann kinetic equation

Boundary conditions required for numerical solution of the Boltzmann kinetic equation (BKE) for mass/heat transfer between evaporation and condensation surfaces are analyzed by comparison of BKE results with molecular dynamics (MD) simulations. Lennard–Jones potential with parameters corresponding to solid argon is used to simulate evaporation from the hot side, nonequilibrium vapor flow with a Knudsen number of about 0.02, and condensation on the cold side of the condensed phase. The equilibrium density of vapor obtained in MD simulation of phase coexistence is used in BKE calculations for consistency of BKE results with MD data. The collision cross-section is also adjusted to provide a thermal flux in vapor identical to that in MD. Our MD simulations of evaporation toward a nonreflective absorbing boundary show that the velocity distribution function (VDF) of evaporated atoms has the nearly semi-Maxwellian shape because the binding energy of atoms evaporated from the interphase layer between bulk phase and vapor is much smaller than the cohesive energy in the condensed phase. Indeed, the calculated temperature and density profiles within the interphase layer indicate that the averaged kinetic energy of atoms remains near-constant with decreasing density almost until the interphase edge. Using consistent BKE and MD methods, the profiles of gas density, mass velocity, and temperatures together with VDFs in a gap of many mean free paths between the evaporation and condensation surfaces are obtained and compared. We demonstrate that the best fit of BKE results with MD simulations can be achieved with the evaporation and condensation coefficients both close to unity.

Numerical simulation of water droplet evaporation into vapor–gas medium

Numerical simulation has been employed to consider water droplet evaporation into a vapor–gas medium. An approximate approach has been proposed that makes it possible to take into account the effect of a noncondensable component on the character of variations in the droplet temperature during evaporation. The results of the calculations have been compared with the published experimental data.

Non-Equilibrium Boundary Effects Influence on the Interface Surface Formation

A film boiling model on a hemispherical heater in subcooled water is presented based on convection heat transport in liquid, thermal conduction in the vapor film, radiation heat transport. The numerical solution of the model has been obtained. Different cases are then analyzed with this model. The calculation results have predicted good-enough agreement with experimental data for lower part of liquid–vapor interface but significantly under-predicted the data for the part near free surface of liquid.Copyright

Boiling of He II in a porous structure in microgravity: a model representation

The results of a modeling of the boiling of superfluid helium in a microgravity environment are presented. The evolution of the vapor film on the surface of a cylindrical heater placed inside a thick-walled cylinder with porous walls is analyzed. The methods of molecular kinetic theory are used to describe the heat and mass transfer on the interphase surface. The equation of motion of the vapor–liquid interphase surface is solved. The influence of the parameters of the experiment on the characteristics of the vapor film is studied. The results of the calculation for microgravity and terrestrial environments are compared.

A NEW CONCEPT OF A SOLAR PROBE SHIELDING FROM INTENSE THERMAL RADIATION OF THE SUN

An effect of shielding of an intense solar radiation towards a solar probe with the use of micron-sized particles generated during ablation of a special composite thermal protection material is estimated on the basis of an approximate solution to a conjugate heat transfer problem. The spectral radiative properties of particles are calculated using the Mie theory, and the two-flux model is used for the radiative transfer calculations in the particle cloud. A computational model for the dynamics, heating, and evaporation/sublimation of small particles takes into account the drag force from a rarefied gas moving from the sublimating composite material, the light pressure effect and the radiative heating/cooling of absorbing and scattering particles. A preliminary numerical heat transfer analysis indicates that implementation of silicon carbide or similar particles into a thermal protection and the resulting generation of a rarefied particle cloud can be considered as a promising way to protect the solar probe from the intense thermal irradiation. This shielding effect is expected to be important to decrease the minimum working distance of the space vehicle from the solar photosphere.

Investigation the evaporation-condensation problem by means of the joint numerical solution of the Boltzmann kinetic equation and interface modelling

The paper is devoted to research of the heat and mass transfer processes in liquid and vapor phase on the basis of the uniform approach assuming the through description of liquid, interface and vapor. Multiparticles interactions in liquid will be taken into account. The problem is studied when temperature in the depth of liquid differs from temperature in the vapor region. In this case there are both mass flux and heat flux. The study of influence of the correlations resulting from interactions of molecules set in thin near-surface liquid layers and an interface on intensity of evaporation is made. As a result of calculations the equilibrium line of the liquid-vapor saturation is obtained, which corresponds good enough with experimental data. Distributions of density, temperature, pressure, heat and mass fluxes, both in a liquid and in vapor are also presented.

Motion of Vapor–Liquid Interfaces

There are many researches that concentrated on the evaporation and dynamics of liquid—vapour interface during boiling. Among them as experimental results and as theoretical model with numerical simulation are presented. For example the transient film boiling in the vicinity of a stagnation point on the frontal surface of a very hot blunt body which moves with a constant velocity in an incompressible viscous fluid in the presence of a vapour layer near the body surface is studied in [1]. Within the unsteady two-phase boundary layer approximation, the equations of motion of the liquid and vapour phases are formulated with taking into account the conservation of mass, momentum, and energy on the a priori unknown phase interface. In the vicinity of the stagnation point on the body surface, the solution of the boundary layer equations is sought. At this a parabolic system of partial differential equations is obtained, which is solved numerically. The similarity parameters controlling the film boiling process are determined. On the basis of parametric numerical calculations, the dynamics of the vapour layer are investigated for the case of a plane hot body moving in water with the room pressure and temperature. In the space of governing parameters, the limits of the existence of steady and unsteady film boiling regimes are found.

Background for Pure (One Component) Substance

One way to develop accurate boundary conditions is the application of molecular-kinetic theory to creation of these conditions. From point of this theory view intensity of evaporation and condensation processes (mass flux density j) can be defined. Brief history of study development about mass flux density j determination at evaporation and condensation of pure vapor is following.