High Temperature最新文献

Abstract

The work presents an example of a passive solar heating system, which utilizes direct solar energy to heat the water for domestic use. A passive thermosyphon heating system was designed, fabricated, and tested for its thermal performance in the semi-arid and four-season climate of the Faisalabad district of Pakistan. The heating system design was based on two-stage storage and natural thermosyphon circulation of water. An enhancement of the thermal performance of the thermosyphon systems by using a semicircular steel pot collector (covered with water carrying copper coil), two-step water storage, and side mirror reflectors was investigated. The experiments were conducted from April to July, 2014 when the ambient temperature was reported approximately between 30 to 45°C. For the cited time duration, the cold-water temperature remained in the range of 18 to 25°C. The maximum water temperature, during the intermittent flow mode operation of the system, remained between 48 and 88°C. In continuous flow mode operation, the hot water temperature remained between 46 and 78°C. Since water temperature in the range of 45 to 50°C is considered suitable for domestic use, the presented design is acceptable for domestic use.

Abstract

We consider the effect of concentric pulse impact (an abrupt increase in liquid pressure at some distance from a collapsing bubble surface) on the collapse of a spherical cavitation bubble in water. The vapor dynamics within the bubble and movement of the surrounding liquid are described by gasdynamic equations, closed by wide-range state equations. The thermal conductivity of both phases and heat and mass transfer on the surface of the bubble are taken into account. The calculation technique involves moving grids converging toward the bubble’s explicitly defined surface. The modified high-accuracy Godunov method is used. It has been found that the pulse impact accelerates the bubble collapse, and the bubble’s radius and pressure within its cavity increase at the end of the collapse. Under pulse impact, collapse of the bubble is accompanied by the periodic focusing of radially converging compression waves in the center of the bubble. At moments of focusing, the pressure in the small vicinity of the bubble center significantly increases. These noted features intensify with an increase in the amplitude of the impulse impact.

Abstract

The study examines local structural features, microscopic dynamics, and transport properties of an equilibrium and supercooled nickel melt. A comprehensive study of the corresponding physical properties of the nickel melt was carried out with large-scale molecular dynamics studies, X-ray diffraction experiments, and torsional vibration viscometry. Good agreement was obtained between the results of X-ray diffraction analysis of an equilibrium nickel melt and the results of molecular dynamics simulation for various EAM potentials and experimental neutron diffraction data. It has been established that in liquid nickel, the contribution of pair correlation entropy to the excess configuration entropy is (sim )60% in the high temperature region and (sim )80% near and below the melting point. Good agreement was found between the simulation results for the transport characteristics (self-diffusion and viscosity coefficients) of the nickel melt in a wide temperature range and the available experimental data and viscometry results. It is shown that the simulation results obtained with all considered interatomic interaction potentials are correctly reproduced by the modified Stokes–Einstein relation obtained using Rosenfeld scale transformations.

Abstract

The dependences between thermal conductivity and the maximum volume fraction of the filler in heat sink compound on the size, morphology, specific surface area, and particle porosity, as well as the contact angle with silicone, of various materials such as aluminum oxides, silicon, magnesium, aluminum and boron nitrides, silicon carbide, metals (aluminum, copper, nickel), and carbon materials (graphite and diamond) is presented. The quality of the produced heat sink compound is not governed by any single property listed, but rather by the combination of properties such as morphology and specific surface area (or porosity) of the particles. For each type of filler particle shape, an inversely proportional relationship exists between the specific surface area and the maximum volume fraction of the polymer. Specific aspects were discussed regarding the effect of the material’s phase and chemical composition on the angle of wettability by polydimethylsiloxane.

Abstract

A mathematical model of the combustion process of methane hydrate in a closed volume is presented, taking into account the kinetics of its decomposition (nonequilibrium), as well as absorption of thermal radiation energy. Based on the numerical solution by the large particle method, the distributions of the main parameters of the system were constructed. The authors compare the specific features of hydrate combustion for cases corresponding to different values of the fraction of evaporated water released during hydrate dissociation. It is shown that partial evaporation of water formed during decomposition of the hydrate leads to an increase in the combustion temperature of the gas mixture and to more intense decomposition of the hydrate compared to the case of complete evaporation of all released water. The dependences of the flame temperature, the maximum pressure of the gas mixture, and the law of motion of the phase transition front on the degree of evaporation of the released water are constructed and analyzed.

FA two-component electroneutral system consisting of classical macroions with finite sizes and charge numbers Z ( gg ) 1 and oppositely charged point microions with the unit charge numbers has been considered. The nonlinear screening of macroions by microions has been taken into account in the Poisson–Boltzmann plus hole approximation. The interaction energy of all particles in the system has been calculated and has appeared to be much higher than values obtained by some other authors.

Abstract

The interaction of meteoroids with Earth’s atmosphere is studied. Based on the physical theory of meteors, a mathematical model of the trajectories of celestial bodies that have invaded Earth’s atmosphere has been constructed. This model considers rarely observed cases of a change in the mode of the descending movement of meteoric bodies to ascending with their possible return back into outer space. The kinematic conditions and physical characteristics that these bodies must satisfy in order to achieve such extraordinary behavior are determined.

Abstract

The structure and electrical resistance of the alloy Ni₄₅Mn₄₆In₉ were studied. At room temperature, Ni₄₅Mn₄₆In₉ is ordered into the cubic structure L2₁, characteristic of Heusler alloys. Throughout the entire temperature range from 77 to 1100 K, a large specific resistance and negative temperature coefficient of resistance are observed. Conductivity obeys Mott’s law T^–1/4 with the addition of a metal contribution. The specific features observed in the temperature dependence of the electrical resistance curve suggest that in this alloy the phase transition between the cubic austenitic phase and martensitic phase with lower symmetry, characteristic of ferromagnetic nonstoichiometric Heusler alloys, occurs at an unusually high temperature.

Abstract

A solution was obtained to the nonstationary problem of heat transfer of counterflows that occur when a liquid flows through a loop. At the far end of the loop, temperature equality is specified and the temperature difference at the inlet and outlet is determined based on calculations at a given temperature of the incoming transfer fluid. It is shown that the formation of thermophysical processes in the heat transfer system under consideration is governed by the dimensionless convective–conductive parameter (Pnu ,) which is the ratio of the contributions of convection and heat transfer to the heat exchange of the system. The solution is represented in the Laplace–Carson integral transform space. The originals were constructed using the den Iseger numerical inversion algorithm, since it is difficult to obtain them by analytical methods. The spatiotemporal dependences of temperature changes in the downstream and upstream flows are presented, which make it possible to broaden the existing understanding of physical processes for different values of the dimensionless convective–conductive parameter. It is shown that with increasing (Pnu ), the contribution of convection, as well as that of kinematic temperature waves, increases.

Abstract

The optical properties of a nonideal fully ionized plasma are discussed using kinetic theory. It is shown that plasma conductivity in a moderately nonideal case in general requires accounting for the arbitrary degeneracy of the electron component of the plasma. The analytical results obtained generalize the recently developed consideration of the optical properties of plasma for nondegenerate electrons. Calculations were carried out for the static conductivity of plasma.