Vol 55, No 5 (2017)

Allowance for nonlinearity leads to the appearance of the longitudinal electric current directed along a wave vector. This longitudinal current is orthogonal to the known transverse classical current at linear analysis. The kinetic Vlasov equation for collisional Maxwellian plasma is used upon the determination of the longitudinal electric current. The Bhatnagar–Gross–Krook collision integral is applied. The electron distribution function is taken from the Vlasov equation in the approximation quadratic over an electromagnetic field. The formula for the calculation of the electric current is derived. When the collision frequency tends to zero, all results for collisional plasma transfer into a corresponding known formula for collisionless plasma. The case of small wave numbers is considered. The value of the longitudinal current when the collision frequency tends to zero also transfers into the known expression for the current in collisionless plasma. The dependence of the dimensionless current on the wave number, frequency of electromagnetic field oscillations, and the collision frequency of electrons with plasma particles is studied.

The characteristics of an electric arc of a direct current, burning in a cylindrical channel in a uniform external axial field, are numerically computed within a nonstationary three-dimensional mathematical model at partial local thermodynamic equilibrium. A method for the numeric modeling of the screw shape of an arc in this field is suggested. This approach is in addition to the “network” analogue of fluctuations for the temperature of electrons, which increases weak numeric asymmetry of electron temperature distribution that occurs randomly during computation. This asymmetry can be “picked up” by an external magnetic field and continue to increase up to a certain value, which is enough to form an arc column screw structure. If there are no fluctuations in the computation algorithm of fluctuations, the arc column in an external axial magnetic field maintains cylindrical axial symmetry and the arc screw shape is not observed.

To determine the energetic efficiency of the formation of the run-away electron beam in a highvoltage glow discharge, we measure the temperature of the electron beam generator. According to the measurements, the energetic efficiency (the part of the input discharge power carried away by the beam) was 50–70% at the generator supply voltage of 4.4 kV and it increased up to ~85% at ~8 kV. The measurements were performed for the discharge in helium with copper, steel, molybdenum, and lanthanum hexaboride cathodes.

We present the results of numerical experiments considering the physical processes specific to the laser based on self-terminating atomic transitions of copper and study of the output characteristics of this laser numerically. The laser is pumped by trains of high-frequency (10−70 MHz) current oscillations with the repetition rate of 2−30 kHz. Inductive-type electrodeless discharge pumping is regarded. The calculations were carried out for a small set of the specified basic parameters providing a way to partially optimize the performance of the laser over its basic output characteristics and to reveal its features. The feasibility of efficient laser pumping by high-frequency discharge is demonstrated. In our numerical experiments the maximum value of the physical efficiency was about 6% and the maximum average laser output power was as high as 174 W. These values were obtained for a discharge chamber with a volume of 1.7 L.

The speed of sound in a binary liquid cyclohexane + n-hexadecane mixture is investigated by direct measurement of the pulse propagation time at ranges of temperature of 298–433 K and pressure of 0.1–100.1 MPa. The maximum measurement uncertainty is 0.1%. The density, isobaric expansion coefficient, isobaric and isochoric heat capacity, and isothermal compressibility of the mixture of three compositions are determined at 298–348 K and 0.1–80 MPa based on the data on speed of sound. The excess molar volume and coefficients of the Tait equation are calculated in the stated ranges. Thermodynamic properties of the mixture are presented in the tabular form.

Specific heats C_v and C_p, entropy S, enthalpy H, and speed of sound W have been calculated using a new thermal equation of state with a small number of variable constants, which includes regular and scale contributions with a new transition function. The calculation results correspond to the accuracy level of the modern reference equations of state with a large number of determined parameters in the regular behavioral region of SF₆ properties; in the critical region, these results make it possible to supplement the existing reference data with the related tables, taking into account the scaling-theory advances. The experimental and tabular data on C_v, C_p, S, H, and W have not been used to determine the constants of the calculation equations (except for isochoric specific heat, C_v, in the ideal-gas state). These data have been applied only for comparison of the calculated values with the experimental and tabular values. To calculate the behavior of thermal properties in the critical region, universal critical indices α, β, and γ have been used according to the threedimensional Ising model. The mean error in describing thermal properties of SF₆ does not exceed the error of the existing experimental data. The calculated values coincide with the modern reference data in the regular region in the entire range of gas and liquid states. The discrepancies in the critical region are due to the application of the scale equation of state (in contrast to the regular equations used previously in this region for composing reference tables).

We present the numerical modeling results of an experiment where the self-heating process was observed. The results confirm the supposition (put forward earlier) that self-heating occurs during the transmission of an electric current through a graphite specimen at temperatures above 3000 K and is the consequence of a combination of low thermal conductivity values and strong temperature dependence of specific electrical resistivity.

The temperature distribution during selective laser sintering of a thin vertical stainless-steel wall has been simulated. The object is grown by successive deposition and laser melting of powder layers. An adjoint problem, including calculation of temperature in the part and the surrounding operating region, has been solved for different manufacturingprocess parameters within the plane statement based on two different approaches. The first approach considers transient heat conduction problem for a layer-by-layer grown body. The height of the calculation domain increases at each calculation step due to the addition of a new powder layer and a short-term laser treatment is applied to the layer region. The duration of one calculation step is determined by the time between two laser passes. The temperature distribution found at each step is used as the initial conditions for calculations at the next step. The thermal state achieved by the object under consideration after 500 calculation steps (i.e., after deposition and melting of 500 layers) is compared with a corresponding solution to the quasi-steady-state problem, which is found for a final geometry of the part, provided that a constant time-averaged heat flux is set to be supplied to the synthesis region. By example of the simple geometry under consideration, a quasi-steady-state solution can provide a fairly good estimate of the macroscopic thermal state of the synthesized part.

The absolute instability of a Rankine vortex with an axial flow and paraxial heat source is investigated. The dispersion relation for vortex modes is derived analytically. The dependence of dispersion properties of the media on control parameters such as swirl parameter S, velocity a, and heat source power (density parameter Q) is studied. The frequency of helical waves increases and the increment decreases with increasing heat source power, accompanied by a decrease in the width of the neutral stability region. Numerical analysis also suggests that one of the dispersion curve branches could include an instability region of a parametric nature.

An analytical solution to the problem of the theory of heat conduction in an anisotropic band under the pulsed (point) action of heat sources has been obtained for the first time by constructing the boundary influence function from using the Fourier and Laplace integral transforms. An arbitrary orientation of the principal axes of the thermal conductivity tensor and arbitrary (including negative) values of the off-diagonal components of the thermal conductivity tensor are taken into account. The found solution is extended to piecewise continuous densities of heat fluxes at the free boundaries of an anisotropic plate. The influences of the principal components and the orientation of the principal axes of the thermal conductivity tensor on time-dependent temperature fields in the anisotropic plate are determined. It is established that there are saddle points and separatrices dividing the temperature field into regions of influence of the boundary heat fluxes. The results are used to solve problems involving the thermal state of thermal protection made of anisotropic materials.

This work considers issues related to the numeric simulation of high-speed combustion and detonation of mixtures of carbonic fuel with air. Model problems are used to study the applicability of global kinetic mechanisms to describe the detonation of a propane-air fuel mixture. Problems of finding equilibrium adiabatic lines, determining Chapman-Jouguet detonation parameters, and the simulation of the structure of a stationary detonation wave were considered. Applying global kinetic mechanisms with irreversible chemical reactions may lead to overestimation of the detonation velocity and temperature of combustion products.

Using atomic resonance absorption spectroscopy, we measure the temporal profiles of Cl atom concentration at interaction with acetylene behind shock waves. We used CCl4 thermal decay as the chlorine atom source. We used a 30 ppm of CCl₄ and 300 ppm of C₂H₂ in argon mixture for the experiments, at 1400–2300 K and pressures of about 2 bar. For experimental results, we determine the rate constant of the chlorine atom consumption in the Cl + C₂H₂ = C₂H + HCl reaction. The experimental data show essentially lower activation energy than the results of the theoretical calculations performed earlier, possibly due to the acetylene molecule vibrational energy contributing to overcoming the reaction barrier.

The reduction procedure to the linear form of a nonlinear regression model describing the results of measurement of the radiation intensity by polychromatic pyrometer are presented. The procedure is based on the replacement of the Planck function by the modified Vine function and is applicable to special dependence of emissivity ε on the wavelength. In particular, it can be used when ε is constant or weakly linear in the spectral interval of measurements. The obtained linear problem of estimating parameters is solved by the method of least squares, taking into account the unequal precision of measurements and the possible correlation of random errors at different wavelengths. Using a random number generator, the output random signal of multiwavelength pyrometer is simulated and the influence of the number of wavelengths (channels) of the photodiode line on the accuracy of estimated parameters is investigated.

This paper presents the feasibility of using electrophysical methods to diagnose and tune the propulsion systems of rocket and space technology items by analyzing published experimental and theoretical results on the electrophysical characteristics of combustion processes and combustor discharge of liquid- and solid-propellant rocket and air-breathing jet engines. Data on the development of emergency protection systems for propulsion engines, based on monitoring the electrophysical characteristics of the propellant, are presented.

The study of the high-temperature properties of a complex composition (Ni–Cr–Al–Re–Hf–Y) alloy was performed under the rapid heating of the foil by a single pulse current during a few microseconds. The alloy melted in the temperature range of 1670 to 2050 K and heated in a liquid state up to 4000 K. There were measured thermal properties (energy Joule heating, electrical resistance, and specific heat) of the alloy in the area of melting and in the liquid phase. Temperature was determined by a pyrometry system based on Thorlabs’ highspeed photodetector PDA-10A (with prior calibration of the optical path using a temperature lamp).

Specific features of secondary flows in horizontal heated pipes of a single-phase fluid under high thermal loads are studied. The analysis performed in this work shows that the reasons for the development of secondary flows in this case are the same as for the development of secondary flows in turbulent flows in pipes with a noncircular cross section.