Investigation of regimes of thermogravitational convection of a fluid between coaxial semicylinders with a heat-conducting shell in the presence of a local energy source

A numerical analysis has been made of the thermodynamic regimes of natural convection of a Newtonian fluid satisfying the Boussinesq approximation in the gap between coaxial semicylinders with finitely-thick walls in the presence of the heat-release source under the conditions of convective heat exchange with the environment. A mathematical model has been formulated in the dimensionless variables current function–velocity vorticity vector–temperature in polar coordinates. Streamlines and velocity and temperature fields reflecting the influence of the Prandtl number Pr = 0.7 and 7.0, the nonstationarity factor 0 < τ ≤ 300, the dimensions of the energy source, and of the relative thermal conductivity on the flow regimes and heat transfer have been obtained.     

Influence of Optical and Thermophysical Characteristics of Biological Tissue on Its Thermal Conditions Under Laser Irradiation

On the basis of the developed analytical method of solving the heat conduction equation in a multicomponent biological tissue, its thermal conditions under laser irradiation have been investigated. Quantitative data on the temperature fields under a wide variation of the optical and thermophysical parameters in the tissue in the 400– 700-nm range of wavelengths are given. The steady-state regime of the field in the tissue at various depths has been investigated. Estimates of the possible use of the time dependence of temperature under tissue cooling to solve the inverse problem — determine the heat-conductivity coefficient, the parameter of heat exchange with the medium, and the depth attenuation coefficient of light — are given. __________ Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 78, No. 3, pp. 15–21, May–June, 2005.     

Thermal-Conductivity Measurements and Predictions for Ni–Cr Solid Solution Alloys

Thermal conductivities of Ni–Cr solid solution alloys have been measured to develop a prediction equation for thermal conductivities as functions of temperature and chemical composition. Samples used were Ni–x at% Cr (0 ≤ x ≤ 22) and commercial alloys of Nichrome Nos. 1 and 2. Thermal conductivity measurements were carried out using the transient hot-strip method over a temperature range from 293 K to 1273 K. The thermal conductivities of the alloys increased with increasing temperature and decreased with increasing Cr concentration at constant temperature. The Smith–Palmer equation has been examined to relate the thermal conductivities of the alloys to the electrical resistivities. The thermal conductivity and electrical-resistivity data, respectively, in the present work and in the literature have confirmed that the Smith–Palmer equation applies to Ni–Cr solid solutions and Nichrome alloys. On the basis of this equation, the thermal conductivity of Ni–Cr solid solution alloys has been expressed as a function of temperature and chemical composition. This analysis has also been applied to Ni–Fe and Cu–Ni solid solution alloys.     

Dynamics of heating a solid body with thermal destruction of its surface

Based on the laws governing thermal destruction and on differential transformations, a solution of the equation of heat conduction with mass entraintment has been obtained. Analytical expressions accounting for wave disturbance of the temperature field are suggested. Using an alloyed quartz glazed ceramics as an example, a good agreement between the predicted and experimental temperature fields in a wide range of mass entrainment velocities and times of heating is shown. __________ Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 80, No. 6, pp. 30–43, November–December, 2007.     

Mathematical modeling of the process compaction of wood

Within the framework of the mechanics of heterophase systems a mathematical model for the process of pressing wood has been offered; this model takes account of the influence of its complex rheological properties and surface phenomena in thin interlayers of water on the change in a porous structure. With numerical methods, a study has been made of the influence of the sample’s humidity and temperature fields on the strength and quality of the material obtained. __________ Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 78, No. 5, pp. 62–69, September–October, 2005.     

Temperature field near the singular line of the interface of anisotropic media

A representation of the temperature fields and the components of the vector of heat-flux density in both the base material (matrix) and the conjugate medium (inclusion) has been found for anisotropic media in the case of the interface with a singular line on condition of ideal thermal contact. It has been shown that the anisotropy of thermal properties makes it possible to do away with the singularity of the components of the heatflux-density vector. Particular cases of isotropy of the media and of heat-insulated and isothermal inclusions have been investigated. The results obtained are applicable for studying the nonstationary heat conduction of an anisotropic body with an uneven anisotropic inclusion. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 82, No. 1, pp. 157–162, January–February, 2009.     

Mathematical model of heating a prism with boundary conditions of the 3rd kind

This paper describes the procedure of computational determination of the temperature field of a prismatic workpiece heated in a continuous furnace with account for the temperature dependence of the thermal diffusivity. For a numerical solution of the two-dimensional heat conduction equation with boundary conditions of the 3rd kind, an implicit scheme has been used. The calculated time dependences of the temperature for three characteristic points of the cross-section of the prismatic steel workpiece have been compared to the experimental data. The heat transfer coefficients at which the experimental data and the calculated values have a minimum discrepancy have been determined. __________ Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 80, No. 6, pp. 3–8, November–December, 2007.     

Heat and mass transfer in the heterogeneous system matrix-inclusions under pulse electron-beam processing

A mathematical model of pulse electron-beam processing of a heterogeneous material with allowance for the fact that each phase (particles and the matrix) possess its own properties and thus is characterized by its own concentration and temperature has been proposed. The processes of transfer of heat and mass in particles and the matrix and exchange processes between the phases have been taken into account. An example of a partial problem enabling one to calculate the coefficients of heat and mass exchange between the phases as functions of the temperature and the particle size has been given. The influence of the character of the external heat flux on the temperature and concentration fields in particles and the matrix has been illustrated. __________ Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 81, No. 1, pp. 147–156, January–February, 2008.     

Effect of the interrelationship of thermal and mechanical fields on the propagation of wave motions in cubically anisotropic thermoelastic materials

A characteristic equation for a system of equations of motion of a cubically anisotropic medium with allowance for the relaxation time of thermal disturbances has been obtained, and expressions for the velocities of propagation of modified elastic and thermal waves have been found. The surfaces of inverse velocities have been constructed and the influence of the effect of interrelationship of thermal and mechanical fields on the change in the phase velocities of propagation of a quasilongitudinal elastic wave and a thermal wave in different planes of a cubically anisotropic material has been analyzed. __________ Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 81, No. 2, pp. 384–388, March–April, 2008.     

Thermal Expansion of Ni–W,Ni–Cr,and Ni–Cr–W Alloys Between Room Temperature and 800 °C

The thermal expansion of Ni–W, Ni–Cr, and Ni–Cr–W alloys has been measured by quartz dilatometry for the 20 °C to 800 °C temperature range. It is found that substitution of nickel by tungsten leads to a considerable decrease of the thermal expansion coefficient (TEC), while chromium has only a small influence on the TEC of the alloy.     

Fundamental solutions of thermoelasticity equations for a semimoment isotropic medium

The Kupradze matrix of fundamental solution of the system of thermoelasticity equations for a semimoment isotropic medium with account for the relaxation time of thermal perturbations in it has been obtained. __________ Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 80, No. 2, pp. 193–196, March–April, 2007.     

Thermophysical Properties of Sn–Ag–Cu Based Pb-Free Solders

Lead–tin (Pb–Sn) alloys are the dominant solders used for electronic packaging because of their low cost and superior properties required for interconnecting electronic components. However, increasing environmental and health concerns over the toxicity of lead, combined with global legislation to limit the use of Pb in manufactured products, have led to extensive research and development studies of lead-free solders. The Sn–Ag–Cu ternary eutectic alloy is considered to be one of the promising alternatives. Except for thermal properties, much research on several properties of Sn–Ag–Cu alloy has been performed. In this study, five Sn–xAg–0.5Cu alloys with variations of Ag content x of 1.0 mass%, 2.5 mass%, 3.0 mass%, 3.5 mass%, and 4.0 mass% were prepared, and their thermal diffusivity and specific heat were measured from room temperature to 150 °C, and the thermal conductivity was calculated using the measured thermal diffusivity, specific heat, and density values. Also, the linear thermal expansion was measured from room temperature to 170 °C. The results show that Sn–3.5Ag–0.5Cu is the best candidate because it has a maximum thermal conductivity and a low thermal expansion, which are the ideal conditions to be a proper packaging alloy for effective cooling and thermostability.     

Experimental investigation of the special features of heat transfer through glass packets

We consider experimental procedures for determining the thermal resistances of certain types of commercial glass packets based on investigation of thermal and temperature fields on the outer packet surfaces at a stationary temperature head (∼40°C), which corresponds to extreme climatic conditions of the middle belt. We evaluate the inhomogeneity of thermal losses over the glass-packet area coused by edge effects. The error in measuring the thermophysical parameters does not exceed ±3%. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 73, No. 2, pp. 209–213, March–April, 2000.     

Unsteady heat transfer in wooden cylindrical sets

A mathematical model and a numerical technique have been proposed for calculating the thermal state of a fragment of the outside log wall of a building. Temperature fields in homogeneous and inhomogeneous (filled with a warmth-keeping agent) wooden cylindrical sets at a variable heat load on the surface have been established and their comparative analysis has been performed. __________ Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 79, No. 5, pp. 74–79, September–October, 2006.     

Use of the integro-interpolation method for construction of difference equations for determination of thermal properties and unsteady-state heat fluxes

Theoretical methods are considered for determination of temperature-dependent thermal properties and unsteady-state heat fluxes. The methods are based on difference equations of heat conduction obtained by the integro-interpolation method for plane, cylindrical, and spherical variants of one-dimensional temperature fields. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 71, No. 5, pp. 811–818, September–October, 1998.     

Influence of Radiation Losses on Thermal Conductivity Determination at Low Temperatures

The thermal conductivity of electrolytic iron has been measured in the temperature range from 100 to 390 K. Electrolytic iron is a standard material for the measurement of thermal conductivity. The thermal conductivity was measured on a commercial device Thermal Transport Option (TTO) of a Physical Properties Measurement System (PPMS) produced by the Quantum Design company. The temperature gradient on the sample was determined using small highly accurate Cernox chip thermometers. The thermal conductivity of the standard material showed higher values than those cited by NIST for the temperature range from 100 to 390 K (NIST’s “Report of Investigation” for SRM 8420). The maximum deviation reached 30% at 390 K. Detailed analyses of the measured data and of the commercial software of the measuring device revealed that the large differences resulted from radiative losses of the interior parts of the device. The determination of the radiative losses takes into account the sample geometry, contacts, and cooling part of the device, and these differences in the thermal conductivity values were substantially reduced after accounting for these losses.Paper presented at the Seventeenth European Conference on Thermophysical Properties, September 5–8, 2005, Bratislava, Slovak Republic.     

Numerical estimation of the efficiency of thermal insulation for the main elements of an aerospace vehicle

We present results of a numerical analysis of the fields of temperature and thermal stresses in a multilayer wall of the fuel tank of an aerospace vehicle. Research Institute of Applied Mathematics and Mechanics, Tomsk, Russia. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 69, No. 2, pp. 324–330, March–April, 1996.     

Structural and electrical studies of Cd<Subscript>1−x</Subscript>Zn<Subscript>x</Subscript> Te thin film by vacuum evaporation technique

Cd_1−xZn_xTe (where x = 0.02, 0.04, 0.06, 0.08) thin film have been deposited on glass substrate at room temperature by thermal evaporation technique in a vacuum at 2 × 10⁻⁵ torr. The structural analysis of the films has been investigated using X-ray diffraction technique. The scanning electron microscopy has been employed to know the morphology behaviour of the thin films. The temperature dependence of DC electrical conductivity has been studied. In low temperature range the thermal activation energy corresponding to the grain boundary—limited conduction are found to be in the range of 38–48 μeV, but in the high temperature range the activation energy varies between 86 and 1.01 meV. The built in voltage, the width of the depletion region and the operating conduction mechanism have been determined from dark current voltage (I–V) and capacitor-voltage (C–V) characteristics of Cd_1−xZn_xTe thin films.     

On the Applicability of the Magnetic Susceptibility Models for the Magnetic Superconductor Ru-1212

The applicability of theoretical models for the ac susceptibility measurements of polycrystalline RuSr₂GdCu₂O₈ superconductor has been examined within the temperature range between 8–50 K, ac magnetic field 0.5–25 G, and frequency 20–12500 Hz. In general, a reasonable qualitative agreement between theory and experiment was attained. An evident and detectable asymmetry was observed within the Cole–Cole polar plots with a peak enhancement for both theoretical and experimental data. The modified critical state models are found to generate much better explanation of the ac susceptibility measured data than Bean’s model. For fields above 20 G, the results are agreed roughly with the Bean critical state model, while below 20 G, the Kim–Anderson model is more suitable to account of the magnetic performance. The temperature and field amplitude dependencies of the flux-creep exponent, n, were extracted from the real part of susceptibility, χ′, dependence on frequency. The flux-creep exponent was found to decrease with both temperature and ac field amplitude in accordance to a power-law of the form: n(T,H)=n ₀(H)T ^−s(H). Such dependence might be an indication of a crossover to flux-creep bundles regime.