Investigation of the evaporation process and sonic limits in sodium heat pipes

The maximum heat fluxes in the heating zone and the sonic limits of power transfer in sodium heat pipes and vapor chambers with composite (channel) wicks are investigated experimentally.Notation P vapor pressure - T temperature - density - molecular weight - L latent heat of vaporization - q specific heat flux in heating zone - Q specific heat transfer along heat pipe - G mass flow of vapor in pipe cross section - W average vapor flow velocity in pipe - surface porosity of wick - R universal gas constant - f coefficient of evaporation - momentum-flux coefficient - coefficient of friction - d_v diameter of heat pipe vapor channel Indices 0 liquid surface - v vapor at liquid surface - w wall surface - in entrance to heating zone - so critical cross section Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 33, No. 5, pp. 832–837, November, 1977.     

Calculation of the Electronic and Thermal Properties of C/BN Nanotubular Heterostructures

Modeling results are presented on the electronic, structural, and thermal properties of a (5,5)C@(17,0)BN-NT tubular heterostructure (a metal-like carbon nanotube inside a dielectric boron nitride nanotube) regarded as a prototype of nanocables. It is shown that the electronic properties of the nanocable remain unchanged up to about 3500 K. The properties of the nanocable are analyzed in comparison with those of a [C₆₀]_∞@(17,0)BN-NT peapod, a potential precursor to C/BN nanocables.__________Translated from Neorganicheskie Materialy, Vol. 41, No. 6, 2005, pp. 687–695.Original Russian Text Copyright © 2005 by Enyashin, Seifert, Ivanovskii.     

Deformation mechanisms for carbon and boron nitride nanotubes

Molecular dynamics simulation in the density functional tight-binding approximation is used to assess the energetics and atomic mechanisms of the bending and twisting of carbon and boron nitride nanotubes.     

Thermal conductivity of beryllium oxide ceramic

Prospects are discussed for the use of BeO-ceramic in electronic and other fields of technology and special instrument building. With use of BeO-ceramic in electronic technology one of the main parameters is its high thermal conductivity. Analysis of publications shows that BeO-ceramic in the range 300 – 500 K exhibits the highest thermal conductivity among all ceramic materials used in electronic technology. Results are provided for a study of the thermal conductivity of 170 ceramic specimens made from BeO-ceramic with an identical configuration and dimensions prepared from one batch of BeO starting powder. It is established that the average size of microcrystals and the density of specimens have a defining effect on thermal conductivity.     

Prototype periodic-pressure test installation GPD-1000N

Translated from Izmeritel'naya Tekhnika, No. 8, pp. 31–32, August, 1989.     

The Permeability and Solubility of Hydrogen in a Lead-Bismuth Melt of Eutectic Composition

The permeability of hydrogen through a lead-bismuth melt of eutectic composition is investigated, as well as the solubility of hydrogen in this melt in the ranges of temperature from 425 to 810°C and of hydrogen pressure from 1 to 3 kg/cm². The experimental setup and procedure are described. The calculated value of the coefficient of hydrogen diffusion in the melt is used to estimate the solubility of hydrogen in the melt.     

Problems in building vertical high-temperature heat pipes

This paper examines problems arising in building vertical high-temperature heat pipes with simple and composite wicks. The author's test results with gas-free and gas-controlled sodium heat pipes are presented.Deceased.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 38, No. 3, pp. 389–395, March, 1980.     

Photoluminescence in Beryllium Ceramics

The photoluminescence properties of beryllium ceramic obtained by semidry molding with and without deliberately introduced alkali metal impurities are considered. It is assumed that heat treatment of samples in hydrogen and the introduction of lithium and sodium impurities in small quantities lead to the formation of additional luminescent centers increasing the intensity of photoluminescence. In contrast, large concentrations of the impurity phase suppress photoluminescence. In heterovalent replacement of Be²⁺ with Li⁺ or Na⁺ ions, additional oxygen vacancies are formed, in which electrons can be localized under radiation and F⁺ centers can be formed.     

The influence of oxygen deficiency on structural and electronic properties of layered superconductor (Fe2As2)(Sr4V2O6?x)

By means of the first-principles FLAPW-GGA approach, we studied the influence of oxygen deficiency on the structural and electronic properties of the superconducting phase (Fe₂As₂)(Sr₄V₂O_6−x ). We find that the formation of vacancies in 2c sites of oxygen sublattice [when the initial tetragonal structure of the stoichiometric crystal (Fe₂As₂)(Sr₄V₂O₆) is kept] is energetically more preferable than in 4f sites, when orthorhombic distortions arise. The influence of oxygen vacancies on the structure of (Fe₂As₂) blocks is very insignificant; thus, using the known structural indicators, it is impossible to explain the observed drop of transition temperature T _C for oxygen-deficient systems by structural factors. On the other hand, the results of the band structure calculations allow us to assert that the vacancy-induced drop of T _C may be caused by the electronic factor, i.e., by the established decrease in N^tot(E _F) for the oxygen-deficient system.