Vol 55, No 6 (2017)

This paper reports on establishing the electron energy distribution function and electron impact excitation and ionization rates in noble gases and liquids in strong electric fields. The method of the unsteady electron kinetic Boltzmann equation is used allowing for all the dense effects typical of the electron scattering at spatially correlated heavy particles. Account is also taken of the influence of the electron number density growth on the relaxation process. Some special features of the excitation and ionization processes in noble media are revealed. The respective electron impact rates have been calculated and the delay times for each the process determined. A paradoxical conclusion has been drawn about the electron multiplication rates in the media with extremely sharp increase in the momentum transfer frequency.

The copper wire vaporization method is applied to obtain porous copper film on a silicon surface. We determine the distribution of the surface clusters over the sizes and the density. The average size of the clusters under optimal conditions (at a distance of 2 mm from the discharge) is about 0.5 μm, and the deposition density is 3–5 clusters per squared μm.

Abstract—The method for determining time dependences of the entropy-production density, force, and heat flux are presented. This method is based on processing the experimental thermogram at electrostatic levitation during spontaneous cooling of a solid molybdenum sphere. The results of numerical simulation of cooling a spherical sample from melting temperature T_m ≈ 2880 K showed that the isothermal approximation for the temperature field in the sphere is valid, which made it possible to pass to the entropy density and calculate its production density. It is shown that heat flux in the time-dependent thermal problem under consideration determines the time dependence of the entropy production (it tends to the minimum zero value while approaching ambient temperature) and, therefore, is responsible for the validity of the extremum principle.

The method, procedure, and results of the investigation of a high-speed air plasma flow effect on the structure of an ultrahigh-temperature coating made for a composite silicon carbide material are considered. The coating is based on hafnium diboride, silicon carbide, and oxides of hafnium, yttrium, and zirconium. The effect of a high-speed plasma flow on the samples was studied in a VAT-104 wind tunnel (Central Aerohydrodynamic Institute); this facility enables simulation of the conditions of high-velocity flight in the upper atmosphere. During the tests, the main parameters of the plasma flow were recorded, and the temperature distribution of the sample was measured. The weight loss of the samples was determined. Using the results of numerical parametric simulation of flow past and heat transfer of the samples, the catalytic activity of the coating was determined. After testing in a high-enthalpy flow, X-ray diffraction analysis and X-ray phase analysis of the samples were performed, and their surface microstructure was analyzed.

Characteristics of the process and heat transfer of subcooled water boiling on mesostructured surfaces obtained by microarc oxidation of titanium foil with formation of a TiO₂ layer and deposition of Al₂O₃ particles from boiling nanofluid have been experimentally investigated. The experiments have been carried out in the forced flow of deaerated water in a vertical rectangular channel, 21 × 5 mm in size. The ranges of regime parameters are as follows: water mass velocity is up to 650 kg/(m2 s), subcooling is 30–75°C, pressure is ~10⁵ Pa, and heat flux rate is 0.7–5.0 MW/m². It is established that the number of active nucleation sites is (70–80) × 105 1/(m² s) at the heat flux of 1.5–2.0 MW/m². Significant subcooling of the liquid and good wettability of the structured surface provide intense deactivation and lead to random spatial distribution of the nucleation sites. The characteristic size of vapor bubbles is about 200–250 μm and the bubble lifetime is 200–500 μs. Application of the coating prepared by microarc oxidation enhances heat transfer by 20–30%. At high subcoolings of liquid, the characteristics of boiling on smooth surfaces and surfaces with the coating were fairly close.

This paper continues the studies cycle of flow management simulation methods in boundary layers of compressible gas. The influence of distributed heat and mass transfer on the stability characteristics of supersonic boundary layers is considered at Mach numbers M = 2.0 and 5.35. At high Mach numbers, waves of vortex nature and unstable acoustic oscillations emerge. Resistance to both types of disturbances is studied. Both normal injection, with normal mean velocity, V, being the only nonzero component, and injection at other angles, including tangential with the longitudinal component of mean velocity, U, being the only nonzero component on the wall, are simulated. It is shown that a tangential streamwise injection causes significant flow stabilization in relation to vortex and acoustic modes. This mode management provides thermal protection of the streamlined surface under aerodynamic heating, and is able to expand the laminar flow mode region. Cooled gas injection suppresses vortex disturbances and amplifies acoustic waves, while injected heated gas influences boundary layer stability in the opposite way. The performed studies anticipate that an injection of homogeneous cold gas would be similar to an extraneous heavy gas injection, and that injected heated gas would behave similarly to injected light gas.

The reflooding investigations of large-scale model fuel assemblies and sphere beds under Design Basis Accident and Beyond Design Accident of Light Water Reactors WWER and PWR are presented. The generalizing correlation on the quench front velocity for model fuel rod assemblies and sphere beds was developed on the base of heat balance and Leidenfrost temperature correlation. It is shown that reflooding duration calculation results of model fuel assemblies and sphere beds are in good agreement with the experimental data.

An overview of the main methods of terahertz spectroscopy used for the detection of gases and gas mixtures is presented. Special attention is given to the methods and equipment used for remote express sensing of gases in the atmosphere to ensure a quick and high-precision identification of gases which is a relevant task important both from fundamental and applied points of view. The developed to date methods are analyzed and their parameters, which are largely determined by the available equipment, are discussed. The techniques and equipment used for generation and detection of terahertz radiation are considered including new trends in terahertz technology, emergence of new types of radiation sources, and upgrading of existing ones. Data on the use of the terahertz spectroscopy for the detection of gases in the laboratory and in open air are summarized. Key challenges and prospects for further application of the terahertz spectroscopy are outlined.

We present the results of a DC electric discharge experimental study between a jet anode and copper cathode at atmospheric pressure. We found the essential influence of the jet anode flow nonuniform character on the discharge development for different power supply regimes. Discharge burning peculiarities are revealed in the jet regime at different power supply voltages with small fluctuation in the milli-, micro-, and nanosecond ranges of the time sweep. We also determined temperatures at the copper cathode surface and its atomization. By means of the Fourier transformation, we reveal the frequency spectrum of the discharge current oscillations.

Results from the experimental investigation of the relative lengthening and mean thermal coefficient of the linear expansion of zirconium dioxide in the 1200–2700 K range are presented.