Thermophysics and Aeromechanics最新文献

The processes of heat transfer and phase transformations in a freshwater reservoir during the cold season are considered. A non-stationary computational model applied for determining the thermal behavior of a reservoir and the ice cover dynamics is based on the numerical solution of the Stefan problem in a generalized formulation. Climatic conditions are considered in the form of dependences of the average daily values of air temperature, wind velocity, humidity and solar radiation flux. The influence of heat fluxes and snow cover height on the reservoir temperature and ice growth dynamics is analyzed.

It is demonstrated in the paper that the range of an equilibrium SF₆ jet normalized to the nozzle diameter is independent of the dimensional stagnation temperature if the values of four dimensionless parameters (jet pressure ratio, Reynolds number based on the nozzle diameter, and two temperature factors) remain unchanged. In contrast to the equilibrium case, the range of a vibrationally excited SF₆ microjet is an essentially nonmonotonic function of the dimensional stagnation temperature.

The characteristics of three-component slurry fuels, including coal, water and pyrogenetic liquid (a by-product of thermal processing of wood waste) have been experimentally studied, and the dispersion of the obtained slurries has been investigated as applied to the technology of their combustion in energy boilers. Samples of slurries for the study were obtained using a technology that includes coal mass grinding in a ball drum mill, metered mixing of components and processing of the resulting mixture on a rotary hydrodynamic cavitation generator, ensuring additional grinding of the coal mass, slurry homogenization, and mechanochemical activation of the fuel. The slurries were dispersed using a pneumatic injector with an external mixing of the slurry and the spraying agent. The average slurry droplet size in the jet after spraying was determined using the Interferometric Particle Imaging (IPI) method. The droplet velocity was recorded using Particle Image Velocimetry (PIV). The characteristics of the gas-liquid flow created by the nozzle have been obtained from the initial breakup of the liquid jet to the final state of the spray.

The present study investigated the phenomenon of heat transfer when a liquid droplet evaporated on a heated structured surface made of black silicon and smooth glass with a graphite coating. Water and volatile dielectric liquid HFE-7100 were used as the working fluids. The temperature fields were studied when shooting with a thermal imager from the top and from the side. A convective flow inside the droplet caused by the Marangoni effect was also investigated. The structures formed inside the heated liquid droplet were analyzed depending on the type of liquid. In particular, for HFE-7100 droplets, the evolution of the flower-shaped convective cells was studied in detail, and the contact line movement velocities were measured during evaporation of microdroplets.

This study demonstrates a process of nanoparticle crystallization in an expanding jet of high-enthalpy inequilibrium plasma carrying the titanium particles flow (as an example) and their deposition on a substrate. The plasma source is a disk-type MHD accelerator. The transport gas with a gaseous precursor is fed to the plasma accelerator input. The flow from this MHD accelerator gains the velocity about several km per second and emerges into vacuum chamber. The generated plasma jet flows around the substrate. When the substrate is placed at the distance from the MHD exit equal to the channel width size, this arrangement produces a smooth coating on a substrate. For one order higher distance to the sample, this gas-particle flow creates a coating of nanosized crystals.

The density of a liquid mixture of lithium, sodium and potassium fluorides of eutectic composition (FLiNaK) was measured using gamma-ray attenuation technique over the temperature range from liquidus to 1010 K. Based on experimental data, an equation for the temperature dependence of density has been proposed. The obtained results on the volumetric properties of the FLiNaK melt have been compared with literature data. Using the approximation of an ideal solution, the temperature dependence of the FLiNaK density in the solid state has been calculated and the density jump during melting has been estimated.

The paper presents the contribution of Academician S.S. Kutateladze to the substantiation and development of engineering methods for calculating electric-arc plasmatorches based on the approaches of the similarity theory and dimensional analysis. Generalized volt-ampere and thermal characteristics of a single-chamber plasmatorch with both conventional water and porous anode cooling are presented, as well as some investigation results on high-temperature, underexpanded supersonic low-density jets, including the plasma ones.

The existence of a reverse flow behind the Mach disk in the first shock cell of a supersonic underexpanded jet is numerically studied by solving the Navier–Stokes equations. It is shown that the reverse flow existence depends on the Reynolds number: it emerges at low Reynolds numbers and vanishes when the Reynolds number exceeds a certain value. Thus, for experimental observations of this paradoxical phenomenon, it is necessary to perform experiments with sufficiently rarefied gaseous jets.

The paper investigates the geometry and droplet size distribution of a fuel spray produced by an injection system with air-assisted (pneumatic) atomizer. Two optical research methods, based on the processing of images obtained through shadow photography, were employed. The evolution of a pulsed spray was studied using a high-speed video camera with a macro lens. Droplet size distributions were studied using a camera equipped with a long-distance microscope and backlighting comprising a luminescent background screen and a pulse laser. The study was conducted for air-to-fuel mass flow rate ratios (ALR) of 1 and 0.16. The Sauter mean diameter for atomized droplets was 13 and 18 microns for the ratio values of 1.0 and 0.16, respectively.

The influence of the change in the velocity profile on stability of the Tollmien-Schlichting waves in the Blasius boundary layer is studied experimentally. The experiment is performed with a flat plate model in a low-turbulence wind tunnel T-324 at the freestream velocity U_∞ = 9 m/s. Hot-wire anemometry is applied for measurements. The results show that a distributed action on the Blasius boundary layer through a hydrodynamically smooth surface leads to attenuation of the amplitude of the naturally excited Tollmien–Schlichting wave almost by two orders of magnitude. This distributed action leads to changes in flow stability. The experimental results reveal that the distributed action is more effective than the action onto the flow through a slot, other conditions being identical.