High Temperature最新文献

Abstract

Within the framework of the Gibbs statistical theory, the issue of the size distribution of particles forming a statistical system and the moments of this distribution are considered. The size distribution of particles and the moments of this distribution are determined from probabilistic considerations. The particle size depends on the interactions in the system, the compressibility factor, the number of interacting particles, and the volume of the system. The relations for the average particle size are substituted into expressions for the intrinsic volume of particles in the equations of state written using excluded volume theory for various expressions for the exclusion factor. The equations of state obtained in this way can be considered as a refinement of the equation of state for dense systems, that is, as a transition to a higher level of description.

Abstract

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.

Abstract

A numerical study has been carried out to investigate the forced convective flow around a trapezoidal cylinder exposed to a uniform stream of nanofluid. Water-based nanofluid containing various types of nanoparticles (Al₂O₃, Cu, and CuO) with the solid volume fraction φ varying from 0 to 8% were used to examine the fluid flow and potential heat transfer enhancement from the heated cylinder. Computations based on the finite volume method with SIMPLE algorithm have been carried out at the steady laminar flow regime with a Peclet number range of 25 ≤ Pe ≤ 150. Nanofluids flow and heat transfer characteristics are found to be highly dependent on solid volume fraction, Peclet number, and nanoparticles shapes. Enhanced wake lengths and surface vorticity, reduced drag and higher heat transfer rates are seen in nanofluids. Furthermore, the results reveal that one type of nanoparticle is a key factor for improving some engineering parameters. In particular, the height values of the average Nusselt number Nu_av, the maximal surface vorticity ω_s, _max, and the dimensionless wake length L_r are obtained while using Cu nanoparticles. However, the values of the drag coefficient ({{C}_{D}}) are higher for Al₂O₃ nanoparticles. Eventually, reliable correlations for ({{omega }_{{smax }}}), ({{C}_{D}})_, and Nu_av in terms of φ and Pe have been developed throughout this study.

Abstract

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.

Abstract

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.

Abstract

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.

Abstract

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.

Abstract

The thermophysical properties of shock-compressed porous iron oxide at pressures up to 1 TPa were determined for the first time. The results agree well with earlier static and dynamic measurements in the pressure range up to 0.2 TPa. An equation of state for the high-pressure phase of iron oxide was constructed and compared with data at high pressures and temperatures.

Abstract

In cooling mode, the temperature dependence of the specific heat and changes in the thermodynamic functions of alloys of the Mg–La system in the temperature range of 300–700 K were studied. It has been shown that with increasing lanthanum concentration, the specific heat of magnesium, especially with the addition of lanthanum from 5 to 10%, noticeably decreases, and increases with increasing temperature. It has been established that with increasing temperature, the enthalpy and entropy of the alloys increase, and the values of the Gibbs energy decrease. The dependence of these functions on the lanthanum content in magnesium is inverse.

An Erratum to this paper has been published: https://doi.org/10.1134/S0018151X23010224