Technical Physics Letters最新文献

Concepts regarding the mechanisms of defect formation in material structures are examined. Problems of the kinetic theory of strength and the impact of thermal fluctuations on the initiation of microcracks and the accumulation of irreversible damage in materials are analyzed. An approach to constructing mathematical models of the damage accumulation kinetics using hypothetical schemes of quasi-chemical reaction is proposed.

The results of modeling the working processes in the combustion chamber of a gas turbine engine operating with gaseous fuel are given. Two modifications of the combustion chamber—the one equipped with a nozzle that has a jet gas supply and the other one equipped with a nozzle that has a swirling gas supply—are considered. The intrachamber processes are calculated using the EddyDissipationConcept, FiniteRate/ EddyDissipation, and NonPremixed_flamelet combustion models. As determined from the calculation results, the arrangement of a jet fuel supply enables the most efficient combustion of gaseous fuel. The EddyDissipationConcept model is a combustion model that has shown the CO and NO_x emission values closest to the experimental data.

Optimization parameters of a cyclic thermal de-icing system (DIS) are formulated. A method of optimization multiparametric calculation has been developed. The use of this technique is proposed in the conditions of the most intense icing of the structure in question to determine the best operating parameters of the de-icing system. The use of the obtained parameters reduces the DIS’ energy consumption, which can reduce the weight of the batteries powering it and increase the efficiency of both aircraft and wind turbines in icing conditions.

It has been shown that a material based on sodium ferrate NaFeO₂ can be obtained by synthesis from a melt in a solar furnace. The crystal structure is tetragonal with the lattice parameters of a = 5.638 Å, b = 5.672 Å, and c = 7.279 Å. The average particle size of the material is 1.2 μm. It has been found that the NaFeO₂ material sample provides the oxidation–reduction activity of Na⁺/Na and the oxidation–reduction activity of Fe²⁺/Fe³⁺. Therefore, NaFeO₂ can be a potential material for the cathode of a sodium-ion battery with a specific capacity of 110 mAh/g. It has been found that sodium ferrate NaFeO₂ exhibits sufficiently good resistance to water. That is, sodium ferrate does not decompose in water at 80–100°C.

The work is aimed at creating new scientifically proven technical and technological solutions for the development and implementation of additive manufacturing of products from heat-resistant reinforced composites allowing samples to be created of new equipment and structural products for the aerospace industry surpassing existing analogues in their properties. Samples of the binder used to obtain composites were studied. Studies were carried out using IR spectroscopy with Fourier transform, and a comparison of the bands of stretching and deformation vibrations of the studied sample and classical polydimethylsiloxane was carried out. The dry residue after combustion of the sample was studied using transmission electron microscopy. It was shown that the sample is polydimethylsiloxane filled with silicon dioxide. Chromatograms and molecular-weight characteristics of polydimethylsiloxane were obtained. The soluble part of the sample was no more than 35% in the case of using benzene and tetrahydrofuran as solvents.

Background. The inverse problems of electromagnetic sensing that are aimed at determining the internal parameters of an object from external measurements of an electromagnetic field are incorrectly formulated and computationally complex. The nonlinearity and instability of solutions require special regularization methods. The development of effective non-iterative methods for solving such problems, especially for three-dimensional objects, remains an urgent task for various fields, including medical imaging, geophysics, and nondestructive testing. The aim of this study is to develop and analyze a non-iterative method for solving the inverse electromagnetic scattering problem for determining the permittivity of a limited three-dimensional object by measuring a near field. Materials and methods. This study is based on solving the direct problem of diffraction of a monochromatic electromagnetic wave on a limited bulk scatterer using a singular integro-differential equation of an electric field. A two-step non-iterative method is proposed to solve the inverse problem. The method is based on the measurement of the near field scattered by an object and can be used for solutions in finite-dimensional spaces of piecewise constant functions. Results. A method for solving the inverse problem of electromagnetic scattering is implemented. The results of solving the direct and inverse problems are reported. The transmittance values for several experiments are compared. Conclusions. The developed non-iterative method for solving the inverse problem of electromagnetic scattering provides determination of the permittivity of a limited three-dimensional object on the basis of the near-field measurements. The method is efficient and can find application in various fields requiring noninvasive determination of parameters of objects.

The study is aimed at describing the processes of transport in polar media within the molecular kinetic theory. In the course of the study, the potential of interaction of molecules has been built, which is a superposition of the model developed by the authors previously and the Stockmayer potential. Based on the introduced potential for polar media, the method of contraction operators has been substantiated and adapted to search for the point of the maximum approach of molecules. In addition, test calculations have been performed to search for coordinates of the point of the maximum approach of molecules for a polar medium—water. In the future, the results will be used in computational technologies for determining the transport characteristics of polar media within the kinetic theory of gases, i.e., the Boltzmann equation.

The possibility of synthesizing nanodiamonds in an electric arc discharge between graphite electrodes has been studied. The effect of germanium atoms on the nucleation and formation of nanodiamonds has been analyzed. It has been established that nanodiamonds are nucleated and formed in an argon electric arc discharge between graphite electrodes with a small germanium‒graphite additive. It has been shown that germanium atoms play the role of a diamond structure nucleus and serve as catalysts for the formation and growth of crystals.

This paper presents an analysis of the effect of the original dryness degree on the operating parameters and performance of an oil-free refrigerating rotary-vane compressor operating in a wet steam environment using various approaches in determining the discharge factor through the ends. The calculation is based on the equation of the first law of thermodynamics for an open system, the Clapeyron–Clausius equation, and the equation of state of a real gas. When determining the discharge factor of a two-phase flow through the ends, two approaches were considered: the approach proposed by V.I. Alyoshin, taking into account the coefficient of sealing the gap by a liquid, and that proposed by M.E. Deutsch, which takes into account the theoretical and actual steam flow factors through the nozzle. The analysis of the results showed that the discrepancy in the performances of the refrigerating rotary-vane compressor operating in the wet-steam region, such as indicator power and feed ratio, calculated using two approaches, ranges from 1 to 15%. Based on the analysis, it is recommended, with allowance for the accepted assumptions, to use V.I. Alyoshin’s approach to study the characteristics of a rotary-vane refrigerating compressor operating in a wet steam environment.

In the paper, process booster piston compressors based on low-speed long-stroke machines with a linear drive have been discussed. The peculiarity of booster machines is that gas is supplied to the suction with some pressure and temperature that is most often higher than the ambient temperature. Currently, booster machines are most often multistage piston compressors, which complicate the process flow diagram due to interstage communications and heat exchange equipment. An alternative to existing designs of booster compressors can be a low-speed stage, which allows for an increased pressure ratio (up to 120) under acceptable temperature conditions due to minimizing the effect of a dead volume on productivity and a reduced piston speed to improve heat removal from the compressed gas. Based on the generalized model previously developed by the author for calculating low-speed compressors, which underwent comprehensive testing through experiments, the operation of low-speed compressors as boosters has been analyzed. Studies have shown that at an elevated temperature at the compressor inlet up to 400 K, the low-speed stage is capable of reducing the gas temperature during the compression-chamber filling process by 70 K, playing the role of a kind of heat exchanger in this process, which will accordingly allow obtaining an acceptable gas temperature at the compressor outlet up to 430–450 K. Using the example of such gases as methane, air, and carbon dioxide, it has been shown that, in the considered ranges of operating parameters, most of the studied low-speed booster compressor stages correspond to existing standards and trends both in temperature conditions and in the efficiency of the operating process. It should be noted that the experimental studies confirmed a decrease in gas temperature during the suction process.