卷 56, 编号 4 (2018)

The effects of direct femtosecond laser processing of a polycrystalline graphite surface are experimentally investigated. The functional graphite surfaces are fabricated at laser intensity of ~10¹⁷ W/cm² in vacuum and then thoroughly analyzed by means of Raman spectroscopy and nanoindentation test. The measured Raman spectra at 257 nm show presence of an amorphous carbon phase containing sp³ hybridized carbon atoms and a discontinuous nanocrystalline diamond film, while the results of microhardness measurements demonstrate a sixteen-fold increase in microhardness as compared to the unirradiated graphite surface. The modulus of elasticity is found to increase nearly by 3.4 times.

It is shown that deviations from the Wiedemann‒Franz law in partially ionized metal plasma are caused by the electron scattering from atoms. Tantalum plasma, for which the thermal conductivity and Lorentz number at the isochore 3 g/cm³ are calculated, is considered as an example.

There are several mechanisms associated with the thermal, kinetic, and electromechanical influence of electrical fields on burning of mixes. Here, it is shown that the burning processes in the presence of the electrical fields involve, along with the known criteria, an additional criterion that is describing the processes arisen from affecting of the electrical discharges on mix, ignition and flame propagation. The role of D or A electrical fields and/or their influence on the induction time of combustion, temperature of ignition, the borders of a steady burning area, the laminar and turbulent flames propagation, and the flame flat front stability are shortly examined. Specially, affecting the combustion by an external electric field through the overheating turbulence and streamer branching is discussed. Problems of low-temperature plasma instabilities and plasma turbulence are shortly studied. The effects of the overheating instability development and generating a specific kind of turbulence during the electrical discharge burning are discussed. The modified Karlovitz Λ_K, Damköler Λ_D criteria and the generalized Borghi diagram that divides the space of non-dimensional parameters into branches of different flame behavior are presented.

The dependence of the drag coefficient of a “magnetized” (with a self-generated magnetic field) sphere on the ratio of the magnetic pressure to the gas dynamic pressure in a hypersonic rarefied plasma flow is determined experimentally. The dependences are obtained for a wide range of angles between the vectors of the incident flow velocity and the magnetic field, as well as between the velocity vectors of the incident hypersonic plasma flow and a subsonic plasma jet injected from the surface of the sphere. It is shown that the injection of a subsonic plasma jet from the surface of a “magnetized” sphere in a hypersonic rarefied plasma flow increases its drag coefficient by several times in comparison with an “unmagnetized” sphere.

The results of a study on aluminum welding by direct-current straight polarity arc in a protective gas environment (argon, helium) are presented. The welding arc burns in aluminum vapor; the condensation products consequently lower the temperature of the welding column in the anode region. The condensation products of aluminum are formed by the cluster mechanism with the formation of fractal thread-like structures. The clustering mechanism is characterized by the release of nondissociated molecular blocks of aluminum into the vapor state. They form a morphologically complex composition of the alumina film on the surface of the weld pool during condensation.

Detailed experimental data are presented on the n-heptane isobaric heat capacity obtained by a modernized adiabatic running calorimeter with the calorimetric measurement of the flow rate in the liquid, gaseous, and supercritical domains, within a temperature range of 300–620 K and a pressure range of 0.5–60 MPa. A thorough consideration of errors made it possible to obtain an error of 0.4% within a wide range of the state parameters. According to the experimental data on the heat capacity, using the known thermodynamics relations, the tables of the n-heptane enthalpy, entropy, and Gibbs energy were calculated (estimated against the accuracy) on the basis of the reliable state equations and the available literature data. The obtained results can be applied directly in the design of chemical processes and the processes in the bedded systems of the hydrocarbon deposits and for development and testing of the equations of state and the methods of the thermodynamic similarity.

With the mathematical tool of pseudo-regular solutions, we calculated the solubility of Fe, Cr, Ni, V, Mn, and Mo in eutectic Na–K melt and compared the calculation results with the available experimental data in the literature on the mass transfer of austenitic chrome-nickel steel components in a sodium-potassium loop in nonisothermal conditions. We show that the Wagner parameters of the interaction between oxygen and transition metal might be applied to predict the corrosion behavior of the construction materials in sodium-potassium melt under the presence of oxygen impurity. We present the calculation results of the threshold oxygen concentration required to form ternary sodium oxides with transition metals (Fe, Cr, Ni, V, Mn, Mo) in conditions in which the pure metal is in contact with eutectic Na–K melt.

The thermodynamic equilibria of the “Fermi–Dirac gas–Maxwell gas–Boltzmann gas” and “metal–saturated vapor” systems are considered (with allowance for charged particles). It is shown that the work function of a metal at 0 K is equal to the Mulliken electronegativity of its atoms. For the latter case, it is proposed to take into account the relationship between the work-function thermal coefficient and the thermodynamic functions of positive and negative metal ions.

The results of an experimental study of the dynamics of local heat transfer at nucleate pool boiling of liquids are presented. Experimental data on the nucleation site density and the evolution of the temperature field underneath individual vapor bubbles were obtained by high-speed infrared thermography with high spatial and temporal resolutions. Deionized water and ethanol at the saturation line under atmospheric pressure were used as working liquids. Evolution of the distribution of the local heat flux rate in the region of an individual nucleation site has been constructed based on numerical simulation. It has been shown that the maximum rate of the local heat flux is observed in the region of the liquid microlayer during the period of vapor bubble growth and reaches a value exceeding the average heat flux rate by 15–20 times. Based on the results, the thickness of the microlayer underneath the vapor bubble during the period of the bubble growth was estimated. The estimates satisfactorily agree with experimental literature data obtained with the use of laser interferometry.

The article discusses a method to solve a field-matching problem that describes a nonstationary heat exchange between an upward flow of fluid in a pipe and an ambient medium with allowance for the variability of the coefficients due to the turbulence of a multiphase flow and the nonlinear dependence of the oil heat capacity on temperature and precipitation of paraffins. The method combines asymptotic methods of small and formal parameters. Analysis of the experimental data on the dependence of heat capacity on the temperature makes it possible to approximate it by a linear function that contains a small parameter in the form of the first terms of the Taylor series. Expansion of the problem by the small parameter in the zeroth approximation leads to a linear problem that is solved by the asymptotic method for a formal parameter for uncoupling of the first coefficient of the expansion. Expressions determining the temperature field in the well and surrounding rocks that take into account the orthotropy of the thermophysical properties of the media are obtained.

The possibility of heat transfer enhancement in a plane separation-free diffuser with different expansion ratios for several Reynolds and Prandtl numbers is studied. Numerical simulation of the heat transfer is carried out using the three-parameter differential turbulence model supplemented with the transport equation for turbulent heat flux.

We consider the possible technical solutions for the treatment moisture fuel from the standpoint of such general problems as a reduction in greenhouse gas emissions and lowering fuel costs with increased energy generation. The use of the biofuels, which is almost always highly wet, does solve these problems in perspective, but it results in an urgent problem regarding an increase of the energy efficiency of the suitable technologies. The practice shows that a reduction in the costs of fuel and energy production currently takes place with generation based on the cheap brown coal (lignite); however, it is necessary to increase qualitatively the efficiency of power plants in order to reduce fuel consumption, as well as atmospheric emissions. We consider the use of complex technologies of moisture fuel preparation for its efficient application via intensive drying with subsequent gasification in order to pass to the combined cycles with the gas turbines. A new technology for intensive energy-saving drying using superheated pressurized steam is presented. We present an analysis and comparison of the means of such approach to implementation and substantiate the selection of the optimal solutions, which are applicable not only to power engineering but also elsewhere in the utilization of moisture combustible materials and waste products.

Information on the rapidly increasing use of modification of solid-state materials surfaces by femtosecond laser pulses at moderate intensities (around 0.1–10 TW/cm²) is presented as applied to creation of functional surfaces with tailored thermophysical, hydrodynamic, and mechanical properties and in application to selective modification and removal of nanoscale (1–100 nm) layers of bulk and thin-film multilayer materials. The problems in obtaining functional surfaces with the externally controllable wetting behavior of superhydrophobic surfaces showing a self-cleaning effect and superhydrophilic surfaces with a controlled Leidenfrost temperature, critical heat flux, and heat transfer coefficient are considered for heat-transfer enhancement during the evaporation and boiling of the working fluid. Data on the hardening of the surface layer of structural materials and the synthesis of diamond-like films are given. The methods for the precision selective removal of nanoscale films and surface modification with the formation of subnanoscale structures are considered.