High Temperature

The results of an experimental study of the effect of integral electrical and acoustic action on flame stabilization during combustion of a homogeneous air-methane mixture are presented. The experiments were carried out for fuel-rich lean mixtures. The effect of an external AC electric field in the combustion zone on flame stabilization is studied with and without external acoustic impact. The most effective relative position of the electrodes for flame stabilization was identified. Extended limits of steady-state combustion of air-methane mixture were achieved. The analysis of flame structure and shape as well as the spectral characteristics of the flame front pulsation under electrical and acoustic action were carried out.

The vortex-induced intensification of the laminar (at Re = 308) flow of transformer oil and heat transfer in a microtube with an in-line package of dimples with a depth of 0.26 of the tube diameter is calculated based on the Navier–Stokes equations and the energy equation. The heat-transfer increased by nearly 20 times for eight inclined oval-trench dimples spaced around the circumference and by 13 times for spherical dimples equal in area in comparison with that for a smooth tube; moreover, the relative hydraulic losses grow by approximately 30 and 60%, respectively.

In this paper, we compare the results of numerical calculations of the passage of a direct shock wave from pure gas into aerosol obtained with and without the effects of droplet breakup. The effect of the fragmentation of aerosol droplets on the profile and velocity of a compression wave propagating in a two-phase medium is determined. The droplet sizes at which the breakup of dispersed inclusions affects the process of the movement of a shock wave along aerosol are obtained.

In this study, in order to obtain more comprehensive characteristics of the magnesium alloys, rheological measurements were performed for the liquid and semi-solid state, taking into account the effect of thixotropy of the magnesium alloys tested. The hysteresis loop plotted shows the thixotropy of two examined alloys.

Analyses of PVT data (with a constant-volume piezometer) and the phase equilibria of an n-hexane–ionic liquid (10%) binary system have been performed in the temperature range of 300–575 K at pressures up to 16 MPa. The liquid–liquid and liquid–gas phase-equilibrium lines and critical parameters of the studied system are obtained.

A scheme is proposed for the incorporation of a screened Coulomb interaction into an embedded-atom model, which allows one to describe two- and multicomponent solutions with strong component interaction by the molecular dynamics method. The effective particle charges satisfy the electroneutrality condition and are determined via minimization of the total energy. The potentials of the pure components and fitted cross pair potentials are used in the calculations, with allowance for the electronic contributions to energy and pressure. For pairs of 1–2 in Li–Pb solutions (1 is for Li, and 2 is for Pb), a pair potential of the form 8–4 is proposed. Calculations were performed for several Li–Pb melts at zero pressure and temperatures up to 1000 K, as well as for a Li₁₇Pb₈₃ solution under shock compression at temperatures up to 25 000 K and pressures up to 470 MPa. The thermodynamic properties of the Li₁₇Pb₈₃ solution are presented in tabular form. The diffusion and structural properties of this and other solutions, the Grüneisen coefficients, and the Hugoniot adiabat are also calculated.

In this research, TGA technique was used for determining thermal and gravimetrical stability of Al/Sn/La₂O₃ nanostructures prepared by sol-gel and spin-coating methods. Structural properties and surface morphology of the films were investigated by different analysis methods. Energy dispersive X-ray spectroscopy and a map were used to make a quantitative chemical analysis of unknown materials. Electrical properties of the samples were measured by metal-dielectric-semiconductor through capacitance–voltage and current rate–voltage. The conduction mechanism in the electrical field below 0.12 MV/cm and in the temperature range of 335 K < T < 420 K was found to be ohmic emission. A model of thermal excitation is proposed to explain the mechanism of ohmic conduction current. The highest value of dielectric constant (k) was ~32 at T₁ = 200°C with almost amorphous structure. The results showed that at T₁ = 200°C the Al/Sn/La₂O₃ nanostructure has lower leakage current rate and higher capacitance than those for other samples because of almost amorphous structure.

It is shown that the electric domains in plasma are generated due to the inequality of the fluxes of the directed drift of charged particles. The time of their nucleation is approximately equal to the Maxwellian relaxation time of the space charge. It has been theoretically obtained that the frequency of space-charge waves and the time constant of the rise (decay) of oscillations during the domain instability are determined by the differential conductivity of the plasma. There are modes of electric domains generation in a gas-discharge plasma that are characteristic of a semiconductor plasma.

The properties of cylindrical and spherical modified ion-acoustic waves in a strongly coupled plasma (containing strongly correlated non-relativistic ions, weakly correlated relativistic (both non-relativistic and ultra-relativistic) electron and positron fluids, and positively charged static heavy ions) are investigated theoretically. The restoring force is provided by the degenerate pressure of the electron and positron fluids, whereas the inertia is provided by the mass of ions. The positively charged static heavy ions participate only in maintaining the quasi-neutrality condition at equilibrium. By using reductive perturbation method, we have derived modified Burgers and Korteweg–de Vries equations. Their shock and solitary wave solutions are also numerically analyzed to understand the localized electrostatic disturbances. The basic features of modified ion-acoustic shock and solitary waves are found to be significantly modified by the effects of degenerate pressure of electrons, positrons, and ion fluids, their number densities, and various charge states of heavy ions. It is also observed that the amplitude of these shock and solitary profiles are maximum for spherical geometry, intermediate for cylindrical geometry, and minimum for planar geometry. The present analysis can be helpful for understanding different degenerate and relativistic phenomena in dense astrophysical environments as well as laboratory plasma systems.

The thermal processes arising upon the implementation of the additive technologies of selective laser melting and the fusion of metals and alloys are analyzed. An adequate description of the heat transfer upon the implementation of additive technological processes associated with high-intensity local heating by a moving laser beam and the phase transitions generated by a semifinished powder product, crystallization, and the concomitant effects in the growing element is the key to gaining insight into the microstructure and the efficient properties of the obtained material and the prevention of residual deformation (shrinkage) of the item. Currently, the main causes of unpredictable production defects are deviations of the shape of the final item from the preset geometry and high-amplitude residual stresses, which can initiate destruction of the item under loads significantly lower than those calculated, as well as the occurrence of the microscopic defects (pores, layer interfaces, etc.) are. The development of mathematical models that, on the one hand, are sufficiently accurate to predict the listed phenomena and, on the other hand, allow practical implementation in engineering calculations is the basis for the further development of the laser-melting and fusion of metal materials. At the same time, analysis of the current state of the problem shows that development of efficient numerical methods providing acceptable computational costs while maintaining accuracy is the key element in the practical implementation of the models. A method based on multiscale, interconnected modeling of the mechanical and the thermal state of the growing body—at the local level in the melt pool domain, at the intermediate level in the vicinity of the melt pool and the adjacent layers, and at the level of the entire product as a whole—seems to be efficient; here, the computing process at the global level can be based on a combination of the finite-element method (indisputable in practice) and analytical calculations providing local refinement of the solution.

The results of an experimental study on the high-frequency (f = 40 MHz) barrier discharge between a dielectric and a liquid electrode (process water) at atmospheric pressure are presented. The formation of a high-frequency barrier discharge covering a dielectric tube is established. The current–voltage characteristics of a barrier discharge with a liquid electrode are presented. The heating temperature of the surface of the dielectric tube and electrolyte was measured.