Bulletin of Perm University. Physics

Evaporation of liquid components of a binder used for space composite materials into vacuum

Виктор Терпугов — 2024-04-12

Currently, technologies are being developed for the creation of large space constructions by curing a prepreg of a composite material with a liquid binder directly in outer space. This raises the problem of evaporation of the active components of the binder into the vacuum of outer space. We study the evaporation of individual liquid components of binding agents that bond composite materials and are intended for use or have already been tested in space structures in orbit. The rates of evaporation into vacuum are determined in the working temperature range. It is shown that the outgassing test certified in space agencies cannot be applied to assess the possibility of using these components in the vacuum of outer space.

The ionic boundary layer relaxation in the problem of proton exchange

Maxim Petukhov — 2024-04-12

The article is devoted to the study of the behavior of proton exchange reaction products in a benzoic acid melt during its interaction with a lithium niobate crystal. During protonation, positively charged lithium ions and negatively charged benzoate ions got into the acid. After recombination, these ions formed lithium benzoate molecules. The diffusion and recombination processes were described using the equations of continuum mechanics: the Navier-Stokes equation for an incompressible fluid, the equations of electrostatics, and transport equations. The numerical solution of this system of equations shows that near the interphase, benzoate ions form a stationary boundary layer supported by the flux of ions from the side of the crystal. Lithium ions, due to greater mobility, filled the entire computational region. Due to differences in ion concentration distributions within the boundary layer, an electric field formed. However, the emerging inhomogeneities were not sufficient for the occurrence of large-scale convective transfer, therefore all fields were uniform along the interphase. The study simulates a situation in which, at a certain moment of time, the conditions promoting proton exchange cease to be met, and the indicated flow of ions from the crystal ceases, as a result of which a gradual disappearance of the boundary layer is observed. The article provides time evolutions of the concentration profiles of ions and lithium benzoate molecules and of the electric potential during this relaxation. The ions, like the electric field, disappear over time, while the lithium benzoate molecules tend to uniformly fill the entire region. The influence of the intensity of the initial ion flow on relaxation processes is shown.

A mathematical model of optical breakdown of an optical fiber core

Виктория Старикова — 2024-04-12

This article describes a mathematical model of an optical fiber core breakdown based on the thermal conductivity equation. The problem is solved in an axisymmetric formulation. The computational domain consists of four elements with different thermophysical properties at the boundaries of which conjugation conditions are fulfilled. The term describing a heat source in the model is defined by a radiation wavelength and refraction indexes of the core and the shell. It also includes absorption coefficient showing the absorption of radiation resulting from electron release due to the thermal ionization of a Ge-doped silica core. The distributions of temperature fields in optical fiber are obtained. The temperature field propagation velocity is estimated. Based on the calculations, it is possible to estimate the time of occurrence of optical breakdown for different wavelengths of radiation introduced into the fiber.

An Optimization of the basic design of a water jet pump for geothermal water extraction

Sergey Peshcherenko — 2024-04-12

During the extraction of geothermal waters, their high temperature and depth of occurrence limit the use of submersible electric pumps. As an alternative, we propose the use of the basic design of water jet pumps with flow channels having conical or cylindrical surfaces, which allows their mass production at machine-building enterprises without expensive equipment. So far, the dependence of efficiency of such pumps on the design has been studied by alternately varying the geometrical dimensions, i.e., without taking into account their mutual influence. Many mutually inconsistent optimal designs have been proposed. We solved the optimization problem by means of computational fluid dynamics. When varying the geometric dimensions of the pump, a full factor experiment plan was applied. It is shown that all possible water jet pumps are geometrically similar. It is proposed to use the nozzle diameter as a natural scale. Expressions of the main geometrical dimensions of the pumps through the nozzle diameter were obtained. It is shown that the maximum efficiency of the pumps is ∼40%, and the liquid velocity at the nozzle outlet practically does not change in scaled models of the pump at fixed boundary conditions (pressures). Viscous losses grow inversely proportional to the nozzle diameter.

Hyperthermic effect in magnetic nanoparticles in the presence of weak orientation fluctuations

Victor Stepanov — 2024-04-12

The problem of steady-state oscillation of a magnetically rigid particle in an AC field of arbitrary amplitude and frequency in the presence of weak orientation fluctuations (at zero temperature or for a large particle volume) has been solved. From the condition of solvability of the Fokker-Planck equation at low temperatures, a correct solution for the magnetization of the particle has been obtained. It is shown that the energy absorption over one period of the field (the area of the dynamic hysteresis loop of magnetization) in this case is always higher than for a loop with finite temperature. In other words, for magnetically rigid particles, thermal fluctuations always reduce their heat generation. This conclusion is important for the method of magnetic hyperthermia.

Determination of the MHD channel parameters for improving the homogeneity of electric current

Gennadiy Losev — 2024-04-12

The problem of electric current flow in a conductor enclosed in a channel of arbitrary conductivity is solved numerically to estimate the conditions for obtaining a homogeneous electric field. The length of the section at which the value of the radial component of the electric current density does not exceed 1% of the maximum along the channel axis was chosen as a numerical criterion for the homogeneity of the flow. We detected the nonlinear character of the dependence of the length of the section of homogeneous current flow on the aspect ratio of the channel and on the wall thickness. By increasing the channel length at a fixed diameter, it is possible to achieve uniform current flow along more than 80% of the channel length with an aspect ratio greater than 10. The dependence of the length of the homogeneous spreading section on wall thick-ness has a local extremum at wall thickness less than 0.4 of the pipe radius. Depending on the ratio of conductivities of the wall and the medium, the extreme point can be either a local minimum (a well conducting wall) or a local maximum (a poorly conducting wall). The dependence of the length of the section of homogeneous current flow on the length of current conduits is linear, but the slope is determined by the ratio of conductivities of the medium and the wall.

The study of the kinetics of thin-film lithium niobate reactive ion etching in a fluorine-containing plasma

Andrey Kozlov — 2024-04-12

The present paper aims to investigate the kinetics of reactive ion etching (RIE) of thin-film lithium niobate (TFLN, X-cut) in a mixture of SF₆/Ar with an ICP/CCP plasma without taking into account the real structure of TFLN. The paper provides a description of the RIE mechanism, including as of a topochemical reaction of TFLN etching with the formation of non-volatile etching products (LiF). Series of kinetic curves were plotted. To study the TFLN RIE kinetics, we used the methods of optical spectral reflectometry, X-ray energy dispersive spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM). It is shown that the TFLN RIE rate is inversely proportional to the pressure during the process and drops by an order of magnitude as the pressure increases from 0.005 mbar to 0.1 mbar. This study is the first to reveal that at pressures below 0.08 mbar, the RIE rate reaches the maximum at a percentage of SF₆≈ 5%. An explanation for the presence of an extremum at given percentage is proposed based on Langmuir adsorption kinetics theory. The linear dependences of the TFLN RIE rate on the powers at the ICP and CCP sources are shown. It is for the first time that the time dependences of RIE at different stages of the topochemical reaction are demonstrated. Differences in the LiF growth mechanisms on the TFLN surface are shown using XPS and EDS analysis. This study is the first to demonstrate the effect of plasma heating of TFLN on the transition between the induction period and the stage of etch rate growth during the topochemical reaction.