The work presents calculation of Ag2 dimers emission from the substrate into the vapor medium in case of joint deposition of silver and water vapors on ideal substrate formally modeling the crystal of water ice in terms of energy properties. It is assumed that the dimers are formed on the condensation surface as a result of random collisions of atoms at their surface migration, and the dimers emission is conditioned by thermal fluctuations of crystal lattice of water ice. The calculations based on the modified Langmuir adsorption model allowed concluding that emission of silver and water dimers takes place in the entire range of the studied water vapor pressure, binding energy of silver-water, and crystal temperature. Dynamics of emission from the beginning of deposition and dependence of dimers emission on micro-roughness of the condensate surface have been investigated. Statistical processing of results has shown that the probability of dimers emission from the condensate surface is determined not only by the value of the binding energy between the dimer and condensate but by configuration of the nearest dimer environment on the condensation surface. It has been found that there is a certain value of micro-roughness of condensation surface providing the maximal intensity of dimer emission. Dimers emission from the surfaces bordering on the flows of vapor mixtures contaminates the flows with unsuspected admixtures. The latter one makes investigation of this phenomenon important for aeromechanics of vapor and gas mixtures.
Results on conjugate convective heat transfer in a system geometrically similar to the system crystal-gas-growing vessel shell of a growing vessel obtained by the Czochralski method are presented. Equations of thermal gravitation convection in Boussinesq approximation are solved by the finite element method in the following variables: temperature, stream function, and vorticity in cylindrical coordinates. Heat transfer from the crystal was studied within the range of Grashof number 100 ≤ Gr ≤ 104 for the fixed configuration of calculation domain. Dependence of the temperature field in the silicon crystal on convection intensity in gas (argon) was examined.
S.V. Stankus1, O.S. Yatsuk1, E.I. Zhmurikov2, L. Tecchio3 1 Kutateladze Institute of Thermophysics SB RAS 2 Budker Institute of Nuclear Physics SB RAS 3 Istituto Nazionale di Fisica Nucleare stankus@itp.nsc.ru
Keywords: coefficient of thermal expansion, graphite, solid state, high temperatures
Pages: 463-468
The article presents the results of studying the thermal expansion of MPG-6 and AXF-5Q graphites and graphite compositebased on 13С isotope in the temperature range 293−1650 K. Measurements were performed with dilatometric method in DIL-402C unit manufactured by NETZSCH (Germany), with the accuracy of (1÷4)×10−7 K−1. Approximation dependences of average integral coefficient of linear expansion on temperature have been obtained and reference tables calculated. It is shown that the coefficient of thermal expansion of 13С composite is much lesser than for MPG-6 and AXF-5Q. The explanation of this phenomenon is provided in the paper.
Results of computer simulation of reflective properties of the oxide film-metal system in the process of oxidation in the air environment are presented. The complex refractive indices for oxide film and metal were used as the initial data. Thin films (the thickness is comparable with the wavelength of incident radiation) and thick films (thickness is much larger than the wavelength of incident radiation) are considered. The parameter characterizing the cyclic character of system reflectivity during the growth of film thickness was derived for the thin film. It is shown that the cyclic parameter does not depend on optical properties of a metal substrate. In the air environment, this parameter is determined by a complex refractive index of the film, its thickness, and direction of incident radiation. Relationships for the estimate of system reflectivity in the process of oxide film growth are presented for the thick film.
M. Torabi1, A. Aziz2, S. Saedodin3 1 City University of Hong Kong 2 Gonzaga University 3 Semnan University Torabi_mech@yahoo.com
Keywords: concentric hemispherical system, radiation shields, temperature-dependent surface emissivities, locations of shields, radiation network method
Pages: 481-488
The radiation network method has been applied to calculate the net radiation heat transfer between two concentric hemispheres separated by two hemispherical radiation shields with temperature-dependent surface emissivities. Three different materials are chosen for radiation shields: aluminum oxide, silicon carbide, and tungsten. The reduction in heat transfer with shields depends not only on the surface characteristics of the two shields, but also on the locations of the shields. Three illustrative examples are presented to illustrate the effects of temperature dependent emissivities and shield locations on the percentage heat transfer reduction. The analysis can be used to study other cases as warranted.
In the present analysis, a numerical study is performed to examine the heat transfer characteristics of a convective flow over a vertical plate under the combined effects of magnetic field and thermal radiation in the presence of heat source/sink. The surface of the plate is subjected to a variable surface temperature. The boundary layer equations governing the flow are reduced to non-dimensional equations valid in the free convection regime using the suitable non-dimensional parameters. The dimensionless governing equations are solved by an implicit finite difference method of Crank-Nicolson type which is fast convergent, more accurate and unconditionally stable. Numerical results are obtained and presented for velocity, temperature, local and average wall shear stress, local and average Nusselt number in air. The present results are compared with the results available in the literature and are found to be in a excellent agreement.
The furnace processes of the combustion of poly-fraction high-ashes Ekibastuz coal in the furnace chamber of the boiler aggregate PK-39 and of the combustion of highly humid brown Berezov's coal in the furnace of the BKZ-210-140 boiler are investigated by mathematical modeling using the package of applied programs FIRE 3D [1-3]. Results of the numerical modeling of the processes of aerodynamics, heat exchange, and combustion in the furnace volume and their comparison with the results of nature tests are presented.
