Volume 61, Nº 2 (2023)

FA two-component electroneutral system consisting of classical macroions with finite sizes and charge numbers Z @ 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.

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.

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.

The study examines the behavior of a binary mixture in the vicinity of the liquid–vapor critical point. It is shown that the pressure dependence on density along the critical isotherm, predicted within the framework of the existing theory of critical phenomena, does not match the shape of the dew-bubble curves. The problem is analyzed with the equation of state for a multicomponent near-critical mixture, adapted to describe thermophysical properties of a binary mixture. To eliminate the problem it is proposed to impose an additional condition on the equation of state coefficient. Possible consequences of imposing such a condition are considered.

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 
60% in the high temperature region and 
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.

Local heat transfer in an synthetic impact jet on a flat plate has been experimentally and numerically studied with a varying Reynolds number and pulse frequency. The thermal characteristics at the stagnation point on the surface of an obstacle have been studied: instantaneous and fluctuation values of the heat flux rate and the spectrum of heat flux fluctuations. Measurements and numerical calculations of the local heat transfer coefficient are carried out under varying the distance to the plate and the amplitude and frequency of synthetic jet fluctuations. Regions with maximum instantaneous values of the heat flux and heat transfer coefficient are determined for local heat transfer values. The maximum value of the time-averaged Nusselt number is observed at the stagnation point of the synthetic impact jet for all considered distances to the obstacle surface. A qualitatively similar distribution of the Nusselt number over the radial coordinate corresponds to those for nonsteady and steady impact jets. The largest and smallest values of the averaged heat flux at the stagnation point were obtained at H/d = 4 and 1, respectively.

We present new experimental data on the cooling of nickel and duralumin spheres in subcooled water and ethanol, along with a review of our comprehensive experimental investigations from 2015 to 2022. The hypothesis on the vapor film destabilization mechanism during unsteady cooling of high-temperature bodies is elucidated. Additionally, new correlations are proposed for estimating the temperature head at the cessation of film boiling in both saturated and subcooled liquids. The derived equations are validated against an extensive body of proprietary experimental data as well as data from other researchers, exhibiting strong qualitative and quantitative agreement with experimental outcomes.

The results of experimental and computational studies of the processes accompanying the melting of metal samples heated in air using induced currents are presented. The materials used for the experimental models—spheres and cylinders with a characteristic size of 10 mm—were pure iron, nonferrous metals, and various grades of steel. An unusual physical effect observed in experiments with iron and steels and associated with the intense release of sparks from the samples was studied: small brightly glowing metal droplets. A possible thermomechanical mechanism for the emission of droplets is proposed, based on the occurrence of excess melt pressure during metal melting inside the volume of the sample, limited by the resulting solid shell consisting of iron oxides. Numerical calculations were carried out, the results of which generally confirm the hypothesis presented.

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.

The effects of single-phase nanofluid flow in mini-/microchannels have been investigated both experimentally and numerically in the literature during the last decade. Almost all the studies show a similar trend by which the engagement of single-phase nanofluids to mini-/microchannels provides significant improvements in the thermal performance. However, there are only limited number of publications in the literature, which have experimentally focused on the heat transfer performance of nanofluids for two-phase flow boiling in mini-/microchannels. Moreover, there are some noticeably conflicting trends concluded by these experimental studies, particularly for the boiling heat transfer coefficient. In the present review, the key clue to figure out the contradictions reflected in the literature on the experimental measurements of boiling heat transfer coefficient is traced to the various deposition patterns of nanoparticles of different sizes on the boiling surface and subsequent changes in the morphology and boiling behavior as well. In addition, the crucial parameters of nanofluids in mini-/microchannels during flow boiling are identified and the effects of the parameters on the boiling heat transfer performance are comprehensively reviewed. The agreements and inconsistencies reported in the literature are also identified and discussed. Finally, a series of suggestions are provided for future experimental studies of nanofluids flow boiling to minimize the contradictory reports.

A method for investigating characteristic equations is proposed, and analytical formulas are obtained for determining the roots of the characteristic equation in the problem of nonstationary heat conduction of a spherical body. These formulas make it possible to determine any required number of roots with high accuracy, which is especially important when solving heat conduction problems at the initial moment of time. The proposed method can be used to study more complex characteristic equations arising in other heat transfer problems.