卷 61, 编号 1 (2023)

The parameters of a radio-frequency capacitive discharge confined in a closed electron drift accelerator with an extended acceleration zone have been studied for different discharge circuits, namely, with dc-closed and dc-open electrodes and with additional dc biasing of the active electrode. In the open circuit, the plasma concentration is minimal and the ion energy in the jet at the exit from the prototype is about 25 eV. The dc closing of the active electrode increases both the plasma density and the ion energy to 250 eV. A further increase or decrease in these parameters is possible by applying a positive or negative dc bias, respectively, to the active electrode.

The dynamics of thermal fields of dielectric surfaces heated as a result of initiation of a pulsed high-current surface discharge (plasma sheet) was studied. A pulsed surface discharge sliding along the surface of a dielectric was generated on the upper (flat) and lower (with a ledge) walls of the discharge chamber with quartz windows. Sequential images of optical (nanosecond range) and infrared (millisecond range) radiation were obtained near a dielectric ledge in the shape of a rectangular parallelepiped with a size of 6 × 2 × 48 mm3. The time evolution of thermal radiation from surfaces was recorded with time-lapse photography in the infrared range at pressures from 65 to 290 Torr. It is shown that the cooling time of a plasma-heated region localized near the dielectric ledge can last up to 30 ms and significantly exceeds the cooling time of a flat upper wall heated by a discharge fairly uniformly distributed over the surface of the dielectric.

A method for determining the formation energy of vacancies in phlogopite is proposed, based on an analysis of how elementary defects in its crystal lattice, associated into complexes, influence the temperature dependence of its electric conductivity. The existence of a linear relationship between the melting temperature and vacancy formation energy for the studied phlogopite samples with different impurity contents was shown. The author calculated the dependence of the obtained melting temperatures on the content of the Al, Mg, and F components in phlogopite samples, which, when associated into complexes, activate the formation of elementary lattice defects.

In cooling mode, the temperature dependence of the specific heat and changes in the thermodynamic functions of alloys of the Mg–La system in the temperature range of 300–700 K were studied. It has been shown that with increasing lanthanum concentration, the specific heat of magnesium, especially with the addition of lanthanum from 5 to 10%, noticeably decreases, and increases with increasing temperature. It has been established that with increasing temperature, the enthalpy and entropy of the alloys increase, and the values of the Gibbs energy decrease. The dependence of these functions on the lanthanum content in magnesium is inverse.

Taking into account the large volume of new data, the calculation of the melting curve of osmium, together with determination of its heat of fusion, has been revised. The new results agree noticeably better with quantum mechanical calculation data. It is significant that the slope parameter for the melting curve is compatible with the new estimate of the heat of fusion, which was approximately half the value accepted in the reference literature. It is shown that a detailed analysis of periodic table confirms the choice of entropy and heat of fusion.

As a soot particle grows, it undergoes a number of significant morphological changes (called aging), which lead to a decrease in reactivity of the particle surface. This work uses reactive molecular dynamics to study the interaction between acetylene molecules in the gas phase and the surface of soot particles of varying degrees of maturity. It is demonstrated that the branched morphology of “young” soot particles and the presence of nanosized voids on their surface can be another effect that has a significant impact on the higher reactivity of soot particles.

The article presents a refined mathematical model of thermochemical destruction of a multilayer composite material, which was developed on the basis of theoretical and known experimental results. The consideration of heat overflow across a body allows the state of a protected wood structure has under fire conditions to be predicted in a more accurate manner. The numerical computation results are compared with the known data.

The paper studies the response of gas (air) bubbles in a spherical cluster to a single pulsed cosine-shaped decrease and subsequent recovery of the pressure of the surrounding liquid (water–glycerin mixture) with a pulse duration in the vicinity of the period of natural oscillations of the cluster. It is assumed that, during the response, all bubbles remain weakly nonspherical. The effect of the duration and amplitude of the excitation pulse, the position of bubbles in the cluster, the distance between bubbles, and the number of bubbles in the cluster is studied. Cubic clusters in which the centers of the bubbles are located at the nodes of a cubic grid, as well as clusters with a random arrangement of bubbles and with bubbles located at the center and vertices of a number of regular polyhedra nested in each other are considered. To estimate the effect of the interaction between bubbles, comparison with the response of a single bubble is made. One of the variants of discrete models of the dynamics of bubbles in a cluster is used, in which, along with radial oscillations, their spatial displacements and small nonspherical deformations are simulated. It has been established that, if the nonspherical deformations of the bubbles during the response are small, the maximum increase in pressure in the bubbles relative to its initial value is at most several-fold. If this assumption is ignored, significantly higher degrees of bubble compression can be obtained. The reason is that, when the condition of smallness of deformations is violated, the ranges of the parameters under consideration expand significantly.

The problem of heat conduction is studied for a point nonstationary heat source located inside or outside a plane-layered medium. A solution is found for a harmonic heat source, followed by a solution for an arbitrary time dependence of point heat release. The harmonic solution to the problem for arbitrary plane-layered media is obtained in the form of a one-dimensional integral.

A mathematical model is proposed for a metal hydride plant, which can be used to utilize low-grade heat. As an example, the study considers a low-grade heat source, an HT PEMFC fuel cell with a high-temperature proton exchange membrane based on polybenzimidazole doped with phosphoric acid, with an operating temperature range 120–200°C. At temperatures near the lower limit of the operating range, the metal hydride utilization cycle appears preferable to the traditional Rankine cycle.

Gas oscillations and aerosol dynamics at a resonance frequency in an open pipe with a changing cross section have been studied. The dependences of the amplitude of gas pressure oscillations and the time of aerosol deposition were obtained for different amplitudes of piston displacement at resonance. The presence of a changing cross section made it possible to obtain more intense oscillations as compared to a homogeneous pipe, while the shape of the pressure wave remained continuous and close to harmonic for all considered excitation amplitudes. A decrease in the concentration of aerosol droplets over time was revealed, accelerating with increasing amplitude of piston displacement.