卷 61, 编号 5 (2023)

In this study the applicability of the binary mixture model utilizing the first-order gas-kinetic Chapman–Enskog theory is substantiated for describing diffusion processes at different degrees of ionization of a single-temperature simple gas plasma consisting of three components: atoms, ions and electrons. On the same bases, the obtained expressions for a trinary mixture are applicable to a plasma with a fourth component that is difficult to ionize. The thermal diffusion relations of a trinary mixture are derived, whose peculiarity is the electronic component, which does not affect the diffusion flows of atoms and ions. It is shown that in a highly ionized He arc plasma with developed diffusion and ionization nonequilibrium, thermal diffusion is insignificant. It is noted that when thermodynamic equilibrium is violated, the diffusion coefficients may not change at all or decrease by half at most.

This paper studies the development of approaches to expand the method for calculating the properties of liquid sodium in the region of overheating and at high temperatures. The expansion is carried out using the hypothesis of the linearity of isochores and interpolation of the properties of sodium on the saturation line using the theory of critical exponents. Using modified techniques, the position of the spinodal is calculated and an expression is given to estimate its position. A comparison is made with the available published data. Satisfactory agreement is obtained.

The relations of the model of a two-phase local equilibrium region are used to calculate the temperature dependences of the heat capacities and coefficients of thermal linear expansion of the palladium triad (Ru, Rh, Pd) and platinum triad (Os, Ir, Pt) in the presence (absence) of an aggregate transition in the studied temperature range. In contrast to the approximation functions used in the scientific literature in individual temperature intervals (using, in particular, the Einstein function), the proposed formulas are simple, universal, and adequately describe the experimental data in the temperature range from 0 K to high temperatures. They can be used to create computer programs for calculating the specified characteristics of various solids, for example, when developing technologies for the rational use of noble metals.

The influence of porosity and pressure on the parameters of the equation of state of a porous material is studied. The model takes into account the presence of gas in the pores. The equations of state of the mixture and its components, both solid and gaseous, are presented uniformly (in the form of the Mie–Grüneisen equation with the Grüneisen coefficient depending on density). To describe the Grüneisen coefficient, a logarithmic dependence on density is used. Numerical calculations of shock-wave loading and isentropic unloading of copper samples of various porosities are carried out. It is shown that the parameters of the equation of state obtained under normal conditions adequately describe the behavior of the substance both under loading and unloading.

The paper studies the thermal conductivity and specific heat capacity of carbon fiber reinforced plastic (CFRP) with various reinforcements using the methods of a stationary heat flow (SHF) and differential scanning calorimetry with temperature modulation. The values of the thermal conductivity and heat capacity, as well as their dependence on temperature, are established in the temperature range from –20 to 100°C. The changes in the thermal conductivity range from 0.400 to 0.515 W/(m K); and the specific heat capacity coefficient, from 923 to 984 J/(kg K). The results obtained can be used to calculate and design systems and installations using PCMs as structural materials and to calculate the parameters of the technological process for the production of these materials.

Mathematical model representations of the temperature effect in regions with a thermally insulated moving boundary are developed. The boundary conditions for thermal insulation of a moving boundary are formulated both for locally equilibrium heat transfer processes within the classical Fourier phenomenology and for more complex locally nonequilibrium processes within the Maxwell–Cattaneo–Lykov–Vernott phenomenology, taking into account the finite speed of heat propagation. The applied problem of heat conductance and the theory of thermal shock for a region with a moving thermally insulated boundary, free from external and internal influences, is considered. An exact analytical solution of the formulated mathematical models for equations of the hyperbolic type is obtained. Methods and theorems of operational calculus and Riemann–Mellin contour integrals are used to calculate the originals of complex images with two branch points. A mathematical apparatus for the equivalence of functional structures for the originals of the obtained operational solutions is proposed. It is shown that the presence of a thermally insulated moving boundary leads to the appearance of a temperature gradient in the region and, consequently, to the appearance in the region of a temperature field and corresponding thermoelastic stresses of a wave nature. A numerical experiment is presented and the possibility of transition from one form of analytical solution of the temperature problem to another equivalent form is shown. The described effect manifests itself both for equations of the parabolic type based on classical Fourier phenomenology and for equations of hyperbolic type based on the generalized phenomenology of Maxwell–Cattaneo–Lykov–Vernott.

The capabilities of flow visualization and gradient heatmetry are combined for the first time in studying heat transfer during condensation. The local heat flux per unit area during drop-stream condensation of water steam on the surface of a vertical plate was measured. In the drop-stream condensation mode, the average value of a significantly unsteady heat flux was about 31.2 kW/m2. The heat flux unsteady shows a complex physical picture of condensation. The results of the experiment revealed the possibility of using gradient heatmetry as a method for monitoring heat transfer during condensation.

The response of gas (air) bubbles in a spherical cluster to an increase in the pressure of the surrounding liquid (water) is considered. Consideration is carried out only until a bubble in the cluster disintegrates or collides with another bubble. The influence of the amplitude of the increase in the liquid pressure, as well as the position of the bubbles in the cluster and the interaction between the bubbles, is studied. The centers of the cluster bubbles are located at the nodes of a cubic grid, one of which is in the center of the cluster. The effect of the interaction of bubbles is assessed by comparison with the response of a single bubble. The cluster consists of 123 bubbles, the liquid pressure is 1 bar. Initially, the bubbles are spherical with a radius of 0.1 mm, the cluster radius is about 3 mm. A discrete model is used, in which, together with the radial oscilations of bubbles, their movements in the liquid and their small deformations are also modeled. It is established that the maximum pressure in the bubbles, reached before the destruction or collision of any of them, is realized when the liquid pressure increases by 10 bar and turns out to be approximately 6500 times greater than their initial pressure and approximately 30 times greater than the response of a single bubble.

The paper presents the results of a study of the evolution of a wave signal when reflected from a rigid wall with a vapor-gas bubble “curtain” located in front of it in a liquid, which takes into account the heat and mass transfer on the interphase surface in the acoustic approximation. Based on the numerical calculations, using the fast Fourier transform method, wave patterns for the evolution of pressure pulses are obtained and the influence of various parameters of the state of a liquid with vapor-gas bubbles on the reflection and passage of acoustic waves through the curtain in front of the solid wall is analyzed.

The thermodynamic characteristics of the electrochemical process in a solid oxide fuel cell (SOFC) are determined using a physical model that takes into account the internal reforming of methane. These characteristics can be a useful tool for studying the thermodynamic cycles of power plants without calculating the physical processes in the fuel cell. The initial data when using them are the load factor and the specific surface resistance of the membrane-electrode assembly.

This paper describes the thermodynamic properties of zirconium in a high-pressure region. The available experimental data on isothermal and shock compression of this metal are summarized in the form of a simple model that specifies a pressure function of the specific volume and specific internal energy. The results of calculations of the thermodynamic characteristics of the body-centered cubic crystalline phase and zirconium melt are presented in comparison with the available experimental data in the studied range of thermodynamic parameters. The resulting equation of state can be used in the numerical modeling of adiabatic processes at high energy concentrations.

The behavior of molybdenum under the action of load pulses of picosecond duration is studied in an experiment. Using the method of spectral interferometry in the single-exposure mode in the picosecond range, changes in the phase and amplitude of the diagnostic pulse reflected from the free surface of the sample are recorded. In a film sample of molybdenum of submicron thickness, compressive stresses reaching 89 GPa are realized and are accompanied by a significant increase in the surface reflectance.

The separation of water–oil emulsions differing in the content and ratio of asphalt-resinous substances, as well as dielectric properties when exposed to a high-frequency (HF) electromagnetic field is investigated. The results of experimental studies are presented, showing the correlation between the degree of phase separation from dielectric parameters and the ratio of asphaltenes and resins in oils. It is shown that when water–oil emulsions are exposed to an HF electromagnetic field, the degree of heating and the efficiency of phase separation of the emulsion depend on the total content of asphaltenes and resins, their ratio, and whether the operating frequency of the generator falls within the region of resonant frequencies of the emulsions.