Vol 57, No 4 (2019)

This paper simulates wave heat transfer based on an analysis of the dynamics of an isolated heat wave (thermal soliton). An isolated thermal wave arises under the action of a thermal impulse that acts for a short time and moves along a cold region. Unlike a continuous thermal process in a nonequilibrium state, when the moving front of a traveling heat wave occurs in a semi-infinite body, a thermal soliton has two fronts, anterior and posterior. There is a temperature distribution noted between them over the spatial variable. First-order gaps in the temperature distribution are observed on these fronts with decreasing amplitude due to the dissipation of thermal energy. Reaching the opposite boundary, the soliton is not reflected in the same way as a mechanical wave. At first, the vicinity of the opposite boundary heats up to a certain level, and the soliton then moves along cold space in the opposite direction with decreasing amplitude. The results of an analytical solution of the wave heat transfer problem on the basis of the hyperbolic-type heat conduction equation with allowance for relaxation phenomena are presented.

A physical and mathematical model that makes it possible to describe the processes of the self-ignition, combustion, and detonation of combustible metal-gas mixtures is given. A simplified physical and mathematical model of the process has been developed. Dispersed particles are considered to be multicomponent, and the processes of the melting and evaporation of the particle material, as well as surface reactions (in which both liquid and gaseous components can participate) are taken into account. The carrier gas is considered multicomponent with the possibility of an arbitrary number of chemical reactions. The case in which the combustion products are in a state of thermodynamic equilibrium is considered, and the presence of fine particles of metals, oxides, and metal nitrides are taken into account. The structure and minimum propagation velocity of a stationary detonation wave are determined by calculation. It is shown that the parameters calculated in waves asymptotically tend to their equilibrium values. The developed physical and mathematical model and computational algorithms can be used to create methods to model the combustion and detonation of metal-gas mixtures in a multidimensional formulation.

Laser-induced boiling and the associated foaming of biological fluids (aqueous solutions of surfactants, proteins, fluids containing dispersed phase) on laser heaters that convert near-IR laser radiation (0.97 μm, 1.47 μm) into heat are considered. The objects of study were model fluids and biological fluids, sera, as well as recorded ultrasound images of boiling human endocystosis fluid and blood obtained in the process of laser treatment of cysts and veins under ultrasound guidance. In the proposed approach, the modification and destruction of biotissue does not occur via direct laser heating but due to rapid heat delivery by two-phase jet streams that form during bubble boiling of the liquid, on the one hand, and, on the other hand, as a result of the cessation of blood flow caused by occlusion (closing) of vessel foam. During laser surgery in the veins, the blood, in addition to boiling, simultaneously foams under the action of laser heating. There is a previously undescribed effect in which a solution of denatured blood proteins foams upon boiling. The foam that has arisen in the vessel lumen causes a vein occlusion, which leads to the cessation of bleeding (hemostasis).

The stationary concentration method is used to study the mechanism of population of the hydrogen \({{{\text{H}}}_{2}}\left( {{{d}^{3}}{{\Pi }_{u}}} \right)\) state in a low-pressure nonequilibrium plasma in a DC glow discharge and a microwave discharge. This state is used in plasma diagnostics based on the emission of Fulcher system bands. The limits of the applicability of the coronal model for the population of this state are considered.

An experimental study of the heat transfer in a 100 kW high-frequency plasmatron was performed for three configurations of a discharge channel with a conical, water-cooled nozzle with exit diameters of 30 mm, 40 mm, and 50 mm. The dynamic pressures and heat fluxes to a water-cooled copper model with a 20-mm front flat face were measured in high-enthalpy subsonic air jets in a generator power range between 20 and 75 kW. The flow in the discharge channel and the subsonic dissociated air jet flow over the model were numerically studied under the experimental conditions in a high-frequency plasmatron with the Navier-Stokes and the Maxwell equations. Based on a comparison of the experimental and calculated data on heat transfer, the enthalpy at the outer edge of the boundary layer and velocity on the flow axis in front of the model were recovered. With the local heat transfer simulation theory, the numerical results for a flow over the model were used to establish the correspondence between the parameters of the plasma flow in a high-frequency plasmatron and the conditions of the entry of a blunt-nosed body with a hypersonic velocity into the atmosphere; the altitude, velocity, and the radius of curvature of the body nose with respect to the operating conditions of a high-frequency generator were calculated.

A quantum-statistical model of the thermodynamic properties of an ordered bundle of the single-walled carbon nanotubes is proposed. Generalization of the Debye heat capacity theory for the d dimensional phonon continuum is used to calculate the heat capacity. A formula for isochoric heat capacity is obtained; it contains two characteristic temperatures related to the macro- and the microstructural vibrational contributions. The calculations are in good agreement with the experimental data.

The interaction of a flow of argon atoms at a temperature of 300 K with clusters of iron atoms is studied at a cluster temperature of 500 to 2500 K. The amount of energy acquired by the argon atom increases, and the thermal-accommodation coefficient decreases according to the Arrhenius law with increasing cluster temperature. The relationship between the coefficient of thermal accommodation and the time of interaction of the incident atom with the cluster is revealed. The heat-transfer coefficient is calculated. The dependences of the thermal-accommodation coefficient and the amount of energy received by an atom on the number of atoms N in the cluster turned out to be linear along N^–1/3. The method of molecular dynamics is applied. The model consists of a cluster and one incident atom; the trajectories of the incident atom are calculated. The amount of energy produced by an atom and the coefficient of thermal accommodation are found from a comparison of the initial and final velocities of the incident atom. To simulate the flow, 10 to 300 000 trajectories of the incident atom are averaged with respect to the cluster size.

A review of the processes in the Earth’s atmosphere that affect its energetics is presented. The energetics balance of the Earth and its atmosphere as a whole is considered, and the results of NASA programs for the monitoring of the global temperature and concentration of carbon dioxide and water in the atmosphere are presented. The spectra of the optically active components of the atmosphere in the infrared region are analyzed on the basis of classical methods of molecular spectroscopy. Spectroscopic data from the HITRAN databank facilitate the analysis and lead to a simple scheme whereby the three main greenhouse components—carbon dioxide, water vapor in the form of free water molecules, and a water droplet—create an infrared radiation flux directed toward the Earth’s surface. This radiation is created by water molecules in the range of 0–580 cm^–1, the atmospheric radiation in the range of 580–780 cm^–1 is determined by the molecules of water and carbon dioxide. At frequencies above 780 cm^–1, the contribution to atmospheric radiation due to water molecules is approximately 5%, and the other is determined by the emission of water microdroplets, which partially form clouds. According to this model, at the present atmospheric composition, 52% of the radiation flux to the Earth’s surface is created by atmospheric water vapor, and 32% is due to microdroplets of water in the atmosphere, which include about 0.4% of atmospheric water and 14% of the radiation flux is determined by carbon dioxide molecules. Doubling the mass of atmospheric carbon dioxide, which will occur in about 120 years at the current rate of growth of atmospheric carbon dioxide, will lead to an increase in the atmospheric radiation flux towards the Earth by 0.7 W/m², and a 10% increase in the atmospheric concentration of water molecules increases this radiation flux by 0.3 W/m². Doubling of the mass of atmospheric carbon dioxide in a real atmosphere leads to an increase in the global temperature of 2.0 ± 0.3 K in a real atmosphere, according to NASA data analysis. If the concentration of other components does not change, then the change in global temperature will be 0.4 ± 0.2 K, and the contribution to this change due to industrial emissions of carbon dioxide into the atmosphere is 0.02 K.

The propagation of plane, spherical, and cylindrical waves in multifraction gas mixtures with polydisperse inclusions has been studied. We have taken into account that the fractions in a mixture differ in their thermophysical properties, inclusion size, and size-distribution functions. A unified dispersion relation is obtained. The evolution of the pressure pulse perturbation in a studied medium is calculated. We show the effect of heat exchange on the attenuation of a pulse perturbation of the pressure in a polydisperse gas suspension.