Thermophysics and Aeromechanics最新文献

Laminar flows of a gas-dust medium with chemical reactions in an axisymmetric tube are studied in detail through numerical experiments. The study focuses on non-oxidative reactions of catalytic synthesis of hydrocarbons from methane. The hot walls of the tube warm up a two-phase flow of methane and catalytic nanoparticles. Heating of this flow enables endothermic conversion of methane into hydrocarbons and hydrogen. The presence of catalytic nanoparticles in the tube, which activate heterogeneous-homogeneous reactions, causes a significant deviation of the two-phase medium flow from the Poiseuille flow profile known for a single-component gas due to changes in the medium volume and viscosity. The change in the heat regime along the tube with variation in thermal conductivity of the reactive medium is investigated. Calculations are conducted for various values of the wall temperature, particle concentration, laminar flow velocity, and other parameters. It is discovered that the medium velocity and the gas component distributions in the tube volume and at the tube outlet are strongly affected by the methane activation energy on the catalytic nanoparticle surface, particle diameter, and particle concentration.

The results of correlating the emissivity of pure metals in the liquid phase with the atomic number of the element in the periodic system and the properties, which include the coefficients of thermal expansion and surface tension, are presented. The results obtained fit the Periodic law. The emissivity has a periodicity with traceable translational properties.

A pioneering study of the influence of streamwise slots (grooves) of various depths h (corresponding to the Reynolds numbers Re_h = 900 and 1300) on the stability of a supersonic (Mach number M = 2) boundary layer on a flat plate with respect to controlled disturbances of the first (vorticity) mode of instability determining the laminar-turbulent transition at M = 2 is performed. At Reynolds numbers Re_h = 900 and 1300, the growth rates of three-dimensional disturbances at frequency f = 14 kHz are found to be smaller than the corresponding value for the smooth plate. Thus, it is shown that controlled disturbances of the first mode can be stabilized by streamwise aligned slots of a small depth (Re_h < 1500).

In a bubble flow, both inherent liquid turbulence and pseudo turbulence induced by the bubbles are present. Total two-phase turbulence of the flow is determined by the interaction of these two components. The experimental values of the average wall shear stress and its pulsations obtained by eight double electrodiffusional probes located uniformly in one section along the pipe perimeter are presented. The gas phase is represented by monodisperse bubble mixtures with average diameters of 1 and 2 mm and a volumetric gas content of up to 20%. To modify the bubble Reynolds numbers, two working solutions with different viscosities were used. The superficial liquid velocity did not exceed 1 m/s. Flow regimes with deviations from the Sato hypothesis on the additivity of pseudo turbulence and inherent liquid turbulence were detected. At transitional liquid Reynolds numbers and small bubble Reynolds numbers, total two-phase turbulence is determined by pseudo turbulence, and there is no the influence of inherent liquid turbulence.

The effect of light gas injection on the linear stage of development in a compressible boundary layer was studied. The problem is solved in the framework of linear stability theory and using the direct numerical simulation for Navier–Stokes equations. The data on the Görtler vortices growth rate and profiles are in agreement for these two methods. It was demonstrated that helium injection into a compressible boundary layer upon a concave surface can reduce the Görtler vortices growth rate.

The density and thermal expansion coefficients of the Li₂Ca intermetallic alloy were measured in the temperature range of 284 – 906 K for the solid and liquid states by gamma-ray attenuation technique. The density jump of the Li₂Ca intermetallic alloy was also measured during the solid – liquid phase transition. Data on the volumetric properties of the alloy at above room temperature were apparently obtained for the first time. A table of recommended values of the volumetric properties of the Li₂Ca alloy over the entire measurement range is presented and their errors are estimated. It is confirmed that the Li – Ca melt with a calcium content of 33.33 at. % is an almost ideal solution.

The results of an experimental study of the rising process of a cluster of monodispersed drops of isoparaffin oil in a water-glycerol solution in the presence and absence of surfactant at the interface are presented. The cluster flow for the Reynolds numbers Re = 0.01–1 was studied. The effect of initial volume concentration of drops in a cluster on the rising dynamics was evaluated. New experimental data on drag coefficient for a cluster of monodispersed drops rising in a liquid with/without surfactant at the interface were obtained.

The direct simulation Monte Carlo method was applied for calculation of dynamics of the gas-dust particle system within a problem of the near-nucleus gas-dust atmosphere of a comet. The study considers a gas-dynamic mechanism of dust particle ejection from the comet nucleus. This assumes existence of a dust-plugged cavity filled by sublimation products of icy content. Calculation offers the data on dust particle velocity as a function of key parameters. It is shown that the ejection velocity for a dust particle is described by one generalized parameter.

The introduction of three-dimensional integrated circuit (3D IC) technology is expected to break the limitations of Moore’s law. In response to the increasingly severe thermal management problem of multi-core 3D ICs, this paper developed a 3D IC model with double-layers and microchannels to analyze the temperature and pressure drop distribution inside the model. The effects of micro-pin fin arrangement, upper microchannel structure, coolant flow direction, and different regions on the cooling performance of the model were studied. The results show that compared to in-lined and staggered arrangement of the same proportion, the non-same proportion in-lined and staggered arrangement proposed in this paper can reduce the pressure drop by at least 31 % without increasing the maximum processor temperature. For the three structures of cuboid, cuboid (in-lined), and cylinder (in-lined), the use of cylinder (in-lined) structure in the upper microchannel can achieve better cooling performance. For counter flow and parallel flow, using counter flow can lower the maximum temperature and pressure drop; using parallel flow can reduce the average temperature and temperature gradient. In addition, compared with increasing Reynolds number of the upper microchannel, increasing Reynolds number of the bottom microchannel can achieve lower maximum temperature and pressure drop.

The paper presents a method and simulation results for turbulent airflow and heat transfer in a U-shaped square duct with straight sections and with two ribbed opposite sides. For a flow with Reynolds number of 6·10⁴ and Prandtl number of 2.5, the numerical solution method was validated by comparing the simulated and experimental data on local heat and mass transfer in geometrically identical U-ducts; the ribs inclined to the duct axis by 45 and 60 deg. For one of these ducts with the rib inclination angle of 45 deg (at the same Reynolds number and Prandtl number of 0.71), the flow patterns and heat transfer were calculated for a stationary state and for a mode with rotation (with the rotation parameter values of 0.1 and 0.25). The rotation axis is perpendicular to the duct axis and parallel to the duct bending plane. The numerical data for the U-shaped duct are compared with the data for a fully developed (periodic) flow and heat transfer for a straight duct with ribbing. It is shown that for a U-duct, the effect of rotation has a positive influence on heat transfer enhancement.