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The results of experimental and computational studies of the processes of hydrodynamics and heat transfer of a swirling flow, heated by the counter coolant flow in the heat exchange channel under standard technological parameters of a nuclear power plant are presented in this paper. The temperature field of the heat exchange channel as a whole and the coefficient of hydraulic resistance of channels with twisted tapes of a constant swirl pitch were obtained in experiments. The numerical study was carried out using the domestic software package LOGOS and the Ansys CFX complex. The simulations were performed using the k-ω SST turbulence model, corrected for streamline curvature and rotation. Two versions of the calculation grid were developed. A comparative analysis of the calculated and experimental values of the hydraulic friction coefficient, the swirling flow temperature, and the heat transfer coefficients from the wall to the swirling flow was carried out. The analysis allowed identification of the strengths and weaknesses of the calculation methodology implemented in the domestic package. Deviations of the obtained values were compared. There is good agreement between the calculated and experimental data, as well as with the data based on generalized dependences. One of the most important conclusions of the study is the need to modernize the process of solving the coupled heat transfer problem in the LOGOS package to expand the range of problems to be solved

This paper presents the results of a chromatographic analysis of gaseous products formed during the laser synthesis of catalytic Cr/Al₂O₃ nanoparticles in a methane-argon environment. The main difficulties of such studies are noted. Methods for solving this problem and ways to optimize the methane pyrolysis accompanying the laser synthesis of nanoparticles are proposed. The fundamental possibility of simultaneous synthesis of catalytic nanoparticles and their use for methane pyrolysis is demonstrated. The main products of pyrolysis in this process are hydrogen and amorphous carbon. The maximum hydrogen yield is 4% (vol.). It is shown how the process can be optimized to increase the yield of hydrogen and expand the range of reaction products for unsaturated hydrocarbons.

The rheological characteristics of struvite-based fire-extinguishing powder mixtures are comparatively analyzed when using hydrophobic silicon dioxide as a functional filler, obtained during a single-stage synthesis by various methods. Infrared spectroscopy, scanning electron microscopy, low-temperature nitrogen sorption-desorption, and other methods are used to investigate the influence of the synthesis method on the textural and structural properties of hydrophobic functional fillers of fire-extinguishing powder mixtures. It is revealed that the key factor affecting the rheological properties of such mixtures is the uniform distribution of the functional filler over the surface of the particles of a fire extinguishing component (struvite). It is proven that the struvite-based powder composition and the developed functional filler are highly effective for fire extinguishment.

Due to the total lack of reliable experimental data on the kinetics of solid-phase transformations at high temperatures, adequate estimates of the ignition and combustion characteristics of real energetic materials are currently unavailable. In combustion theory, balance relations in the form of ignition criteria and in the form of the equivalence principle of the increase in burning rate under the action of a radiation flux corresponding to an increase in initial temperature are used in most cases without sufficient theoretical justification, what can lead to incorrect results. Numerical simulation of the ignition and combustion of model energetic materials can provide the basis to determine the conditions for the correct use of balance relations. In this work, ignition and combustion under the action of a radiant flux have been numerically studied using a model of unsteady combustion of melting energetic materials and the matching coefficients in the balance relations were obtained. It is shown that the values of these coefficients depend on the kinetic parameters of solid-phase transformations and the intensity of the external heating source. It is concluded that it is necessary to continue the theoretical research aimed at developing valid approaches to determining the parameters of global reactions in the condensed phase using data on ignition delay by heat flux and to determining the correct matching coefficients when using the equivalence principle.

A tetrahedral structure model has been proposed to estimate the size of metal agglomerates during combustion of a composite solid propellant. According to this model, oxidizing particles are located at the vertices of a regular tetrahedron, and the internal volume of the pyramid is occupied by a mixture of binder fuel and metal - the so-called pocket. Experimental data are compared with the results of calculations using the tetrahedral model, the Cohen model and the empirical correlations of Hermsen, Salita, Beckstead, Grigoriev, and Duterque. The comparison was carried out for a composite propellants containing ammonium perchlorate, binder and aluminum as an example. It has been shown that in some cases the tetrahedral model predicts the diameter of agglomerates better than the other models.

An attempt to understand the relation between the burning characteristics and thermal decomposition in a wide range of pressure is made in the present investigation based on solid propellants with ammonium perchlorate as an oxidizer and 3,3-diazomethylepoxybutane and tetrahydrofuran as a fuel binder. The burning rate measurement is carried out in a wide range of pressure: 1.0, 3.0, 7.0, 13.8, 15.0, and 20.0 MPa. The inflection point of the pressure exponent for ammonium perchlorate with and without oxalate and the flame extinguishing point both appear at 13.8 MPa. Various mechanisms of burning rate reduction by the quaternary ammonium salt and oxalate are analyzed by theoretical analysis, thermogravimetric analysis, and differential scanning calorimetry analysis. The burning rate and decomposition of the oxidizer and fuel binder with combustion modifiers and their overall impact on propellant combustion are studied. Due to modifiers, a transition between kinetically controlled combustion and diffusion controlled combustion is found to occur.

This study describes a model for initiating an explosive decomposition of composite materials based on high explosives that weakly absorb radiation and ultradisperse metal inclusions under the influence of nanosecond laser pulses. The model is based on experimental results obtained from studying the explosive decomposition of PETN with inclusions of ultrafine metal particles (Al, Ni, Fe). The model serves as a basis for constructing a scientifically grounded algorithm for determining the composition of a material with minimal thresholds for laser initiation of explosive decomposition, which makes it possible to replace most experiments with theoretical calculations and optical-acoustic measurements. The algorithm is verified using data from laser initiation of RDX with inclusions of ultrafine iron particles.

This paper describes a study of explosive parameters of a Bi₂O₃/Al nanothermite mixture with the addition of 1-methyl-3-nitro-1,2,4-triazole (1Me-3H) depending on the content of the latter and the component ratio of a Bi₂O₃/Al basic nanothermite pair. Adding 1Me-3H to the mixture increases the explosive force, but it begins to decrease as soon as the additive content reaches over a certain limit. Depending on the mixture formulation, it is possible to increase the explosive force by 22-29% relative to Bi₂O₃/Al nanothermite. Changing the mixture composition makes it possible to vary the burning rate of Bi₂O₃/Al/1Me-3H within a range of 400-690 m/s in charges 2 mm in diameter and within a range of 120-430 m/s in a 0.1-mm thick layer.

Formal transposition of kinetic data obtained in studying the processes of ignition and low-velocity combustion to supersonic detonation processes most often leads to noticeable underestimation of the critical initiation energy, detonation cell size, and other dimensional parameters of detonation as compared to experimental data. Thus, numerical predictions of the combustible system behavior become less reliable. However, because of the instability-induced non-one-dimensional, nonhomogeneous, and oscillating character of the multifront detonation wave, it is next to impossible to perform reliable experimental measurements of the kinetic parameters of combustible mixtures under the detonation conditions. In the present paper, we propose and approve a method that allows one to get over the above-mentioned limitations by using a technique as close to the detonation conditions as possible. The technique is based on using a decaying shock wave for combustible mixture initiation instead of the classical steady shock wave. Such a decaying wave is formed in the case of reaction failure behind a steadily propagating detonation wave due to its propagation in a channel with sudden expansion (so-called detonation wave diffraction). The basic issues of the technique are discussed, required estimates are made, experimental verification is performed, and results obtained are reported.

Measurements of the electrical resistance of shock-compressed aluminum is used in the present study to estimate the concentration of point defects generated by the shock wave front. The parameters of the physical state of a thin metal sample are found by means of modeling the shock wave processes in the measurement cell. Experimental values of the specific electrical resistance of aluminum are compared with predictions of the equilibrium electrical resistance model. The proposed model ensures an adequate description of currently available reference data on equilibrium isothermal compression and isobaric heating of aluminum. At the same time, the shock wave experiment yields a higher specific electrical resistance than that predicted by the model of the electrical resistance of an equilibrium defectless crystal. The detected difference in the specific electrical resistances testifies to generation of defects of the crystal structure of the metal subjected to dynamic compression. Under the assumption of predominant formation of vacancies, the concentration of defects in aluminum is estimated as a function of the shock wave pressure. The number of defects in the metal increases with an increase in the shock wave pressure. The data obtained are qualitatively consistent with available results for copper and silver, which allows one to claim that generation of defects under shock compression has common specific features for these metals. The physical state of shock-compressed aluminum is thermodynamically nonequilibrium and includes numerous defects.