Gas flow through a porous heat-releasing medium with allowance for the temperature dependence of gas viscosity

The gas flow through a porous heat-releasing medium is considered. It has been noted that account for the temperature dependence of the gas viscosity strongly influences the solution: the gas flow rate markedly decreases and a stronger heating occurs. Analysis of the flow of a gas with a temperature-dependent viscosity by the Sutherland formula has revealed two steady-state cooling regimes — stable and unstable ones. It has been shown that the possibility of the steady-state regime is determined not only by the problem parameters but by the initial conditions as well. The transient process from the state of rest in the absence of heat release to the state of the regime of induced filtration upon instantaneous switching-on of heat input is described. __________ Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 79, No. 1, pp. 35–40, January–February, 2006.     

Thermoelastic state of a thermosensitive hollow sphere under the conditions of convective-radiant heat exchange with the environment

The solution of the nonstationary problem of heat conduction is constructed for a thermosensitive hollow sphere in the process of convective-radiant heat exchange with media kept at constant temperatures. In this case, it is assumed that the heat-transfer and emissivity coefficients of the surfaces are functions of temperature. We study the influence of the thermal sensitivity of the material of the sphere on the intensity and character of distribution of temperature and the components of the stress-strain state. __________ Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 42, No. 6, pp. 39–48, November–December, 2006.     

Analytical solutions of the problems of heat transfer during liquid flow in plane-parallel channels by determining the temperature perturbation front

Based on the integral method of heat balance, an analytical solution of the problem of heat transfer in stabilized liquid flow in a plane tube is obtained. To increase the accuracy of solution, the approximation of the temperature function is made by polynomials of higher degrees. To determine their coefficients, supplementary boundary conditions are introduced that are found from the basic differential equation and given boundary conditions including conditions at the temperature perturbation front. In the second approximation the obtained analytical solution in the range of the longitudinal coordinate 10⁻⁶ ≤ x ≤ ∞ already virtually coincides with the exact one. __________ Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 80, No. 5, pp. 176–186, September–October, 2007.     

Computer thermal model for hardening grinding

A mathematical model of heat transfer in steel parts under force grinding is considered that allows one to determine the grinding parameters at which a steel layer of prescribed thickness is heated up to hardening temperatures. Results of numerical simulation of the process of hardening grinding are compared with experimental data. The internal structure of the material after hardening grinding is analyzed. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 73, No. 2, pp. 430–438, March–April, 2000.     

Vapor Pressure, Speed of Sound, and PVT-Properties of R-404a in the Vapor Phase

The density (300–363 K, up to 3.5 MPa) and speed of sound (293–373 K, 7.5–480 kPa) in gaseous R-404a have been studied by an isochoric piezometer method and an ultrasonic interferometer, respectively. The pressures of the saturated vapor along the dew line were measured from 298 to 330 K. The experimental uncertainties of the temperature, pressure, density, and speed-of-sound measurements were estimated to be within ±20 mK, ±1.5 kPa, ±0.15%, and ±(0.1–0.2)%, respectively. On the basis of the obtained data, the isobaric molar heat capacity of R-404a was calculated for the ideal-gas state. An eight-coefficient Benedict–Webb–Rubin equation of state has been developed for the gaseous phase of R-404a.     

Improvement of the performance of working surfaces of materials susceptible to cracking

We study thermomechanical stresses in components of steels and alloys that are caused by finishing and lead to defects such as high-temperature-induced structural transformations (called “burnings”) and cracking. In doing so, we apply phenomenological theories based on a set of equations that represent the thermal and stress-strain state of a workpiece surface as a thermoelastic body given by a sectionally homogeneous half-plane. We accounted for local physical and mechanical properties of the workpiece material by means of the respective boundary conditions. This allows us to use criteria of fracture mechanics to study the mechanism of crack nucleation at the sites of accumulated process-induced discontinuities in the surface layer. We determine the critical values of heat flows in a machining zone whereby the process-induced discontinuities are kept at equilibrium and thus the workpiece surface remains free from crack-type defects. We consider the influence of cutting forces on the process of cracking. Taking advantage of the capabilities of a stochastic model of workpiece materials, we clarify the causes for cracking in grinding. We suggest technological methods to reduce the intensity of cracking in finishing operations, in particular, in grinding, of steels and alloys. Odessa Polytechnic University, Odessa, Ukraine. Translated from Problemy Prochnosti, No. 4, pp. 93–105. July–August, 1998.     

Combined DSC and Pulse-Heating Measurements of Electrical Resistivity and Enthalpy of Tungsten,Niobium, and Titanium

Measurements of thermophysical properties such as enthalpy, electrical resistivity, and specific heat capacity as a function of temperature starting from the solid state into the liquid phase for W, Nb, and Ti are presented in this work. An ohmic pulse-heating technique allows measurements of enthalpy and electrical resistivity from room temperature to the end of the stable liquid phase within 60 μ s. The simultaneous optical measurement of temperature is limited by the fast pyrometers with an onset temperature of T_min = 1200–1500 K; below these temperatures, the fast pyrometers are not sensitive. A differential scanning calorimeter (DSC) is used for determination of the specific heat capacity, and also to obtain enthalpy values in the temperature range of 600–1700 K. Combining the two methods entends the range of values of electrical resistivity and enthalpy versus temperature down to 600 K. Results on the metals W, Nb, and Ti are reported and compared to literature values. This paper is a continuation of earlier work. Paper presented at the Seventh International Workshop on Subsecond Thermophysics, October 6–8, 2004, Orléans, France.     

Temperature and stresses in the vicinity of friction contacts of microasperities in the process of braking

We develop an approach to the solution of heat problems of friction simulating the operation of brake systems. The thermal and stressed state of an element of the friction pair is estimated by using the criterion of octahedral tangential stresses. Franko L'viv State University, L'viv State Agricultural University, State University “L'vivs'ka Politekhnika,” L'viv. Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 32, No. 6, pp. 72–80, November–December, 1996.     

Optimization of composition and heat treatment design of Mg–Sn–Zn alloys via the CALPHAD method

This work is focused on the application of the calculation of phase diagrams method for alloy and heat treatment design. We analyzed the influence of Zn content on the precipitation of Mg₂Sn in Mg–Sn–Zn alloys. A comparison with previous studies in the Mg–Sn–Zn system was made according to the published results and computational thermochemistry simulations. The phase evolution in the Mg–Sn–Zn system was evaluated for the different compositions, and the simulations were used for precise alloy and heat treatment design. The composition of the ternary alloy was set as Mg–8wt%Sn–1.25wt%Zn. The Sn and Zn content was designed and confirmed to be within the α-Mg solubility limit at the solution treatment temperature. The addition of Zn and the heat treatment applied resulted in the enhancement and refinement of the Mg₂Sn precipitation. Three Vickers micro-hardness maxima were detected: precipitation of metastable Mg–Zn phases, heterogeneous precipitation of Mg₂Sn on the Mg–Zn precipitates, and Mg₂Sn precipitation in the α-Mg matrix. The CT simulations were found to be a valuable alloy design tool.     

Measurement of the In-plane Thermal Diffusivity and Temperature-Dependent Convection Coefficient Using a Transient Fin Model and Infrared Thermography

The transient fin model introduced recently for determination of the in-plane thermal diffusivity of planar samples with the help of infrared thermography was modified so as to be applicable to poor heat conductors. The new model now includes a temperature-dependent heat loss by convective heat transfer, suitable for an experimental setup in which the sample is aligned parallel to a weak, forced air flow stabilizing otherwise the convective heat transfer. The temperature field in the sample was measured with an infrared camera while the sample was heated at one edge. The symmetric temperature field created was averaged over the central fifth of the sample to obtain one-dimensional temperature profiles, both transient and stationary, which were fitted by a numerical solution of the fin model. One of the fitting parameters was the thermal diffusivity, and with a known density and specific heat capacity, the thermal conductivity was thus determined. The test measurements with tantalum samples gave the result (57.5 ± 0.2) W · m⁻¹ · K⁻¹ in excellent agreement with the known value. The other fitting parameter was a temperature-dependent heat loss coefficient from which the lower limit for the temperature-dependent convection coefficient was determined. For the stationary state the result was (1.0 ± 0.2) W · m⁻² · K⁻¹ at the temperature of the flowing air, and its temperature dependence was found to be (0.22 ± 0.01) W ·m⁻² · K⁻².     

Devices for monitoring the thermal state of the object “enclosure”

The design of heat flow and temperature metering equipment used at the Chernobyl Atomic Power Station for heat and temperature diagnosis of the state of the damaged reactor is described. Deceased. Institute for Problems of Energy Conservation, Academy of Sciences of Ukraine, Kiev. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 69, No. 2, pp. 255–260, March–April, 1996.     

Numerical Analysis of Heat Transport Behavior in the Ferromagnetic Metallic State of La0.80Ca0.20MnO3 Manganites

The lattice contribution to the thermal conductivity (κ_ph) in La_0.80Ca_0.20 MnO₃ manganites is discussed within the Debye-type relaxation rate approximation in terms of the acoustic phonon frequency and relaxation time. The theory is formulated when heat transfer is limited by the scattering of phonons from defects, grain boundaries, charge carriers, and phonons. The lattice thermal conductivity dominates in La–Ca–MnO manganites and is an artifact of strong phonon-impurity and -phonon scattering mechanisms in the ferromagnetic metallic state. The electronic contribution to the thermal conductivity (κ_e) is estimated following the Wiedemann–Franz law. This estimate sets an upper bound on κ_e, and in the vicinity of the Curie temperature (240 K) κ_e is about 1% of total heat transfer of manganites. Another important contribution in the metallic phase should come from spin waves (κ_m). It is noticed that κ_m increases with a T² dependence on the temperature. These channels for heat transfer are algebraically added and κ_tot develops a broad peak at about 55 K, before falling off at lower temperatures. The behavior of the thermal conductivity in manganites is determined by competition among the several operating scattering mechanisms for the heat carriers and a balance between electron, magnon, and phonon contributions. The numerical analysis of heat transfer in the ferromagnetic metallic phase of manganites shows similar results as those revealed from experiments.      

Heat and mass transfer in condensation of water vapor from moist air

Results of an analysis of heat and mass transfer in condensation of vapor from moist air are presented. The computational model is based on the solution of integral relations of boundary-layer energy and diffusion using the analogy of heat- and mass-transfer processes. The effect of the temperature and concentration boundary conditions on the relation of the components of the heat flux on the wall is analyzed. Results of calculations are compared to available experimental data. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 71, No. 5, pp. 788–794, September–October, 1998.     

Thermoactive coating as a means for controlled action on the temperature field of an infinite solid body with a spherical heating source

A mathematical model of the process of formation of a temperature field in an infinite isotropic solid body containing a spherical heating source with a thermally thin thermoactive coating of its surface has been proposed. The obtained analytical solution of the corresponding problem of nonstationary heat conduction has been used for substantiation of the possibility of acting on the temperature field of the system under study in a controlled manner. __________ Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 79, No. 3, pp. 12–19, May–June, 2006.     

Friction-induced formation of heat with account for heat transfer through the contact surface between homogeneous and piecewise-homogeneous semispaces

An analytical solution of the boundary-value heat conduction problem is obtained for a tribosystem consisting of a homogeneous semispace sliding with a constant velocity along the surface of a plane-parallel strip applied to a semi-infinite foundation. The tribosystem is heated as a result of the frictional heat formation on the sliding surface. It is assumed that the thermal contact of the semispace with the strip is not full. With the aid of the Duhamel theorem, a solution for the considered tribosystem, with sliding at a constant deceleration, is also constructed that models heat formation from friction in disk brakes. For the materials of the friction pair "pig iron semispace (disk)–metal-ceramic strip (lining)–steel foundation (frame)," the influence of the coefficient of thermal conductivity of the contact (Biot number) on the temperature distribution was investigated.     

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.     

Possible Fulde–Ferrel–Larkin–Ovchinnikov Inhomogeneous Superconducting State in CeCoIn5: Cd- and Hg-doping Studies

CeCoIn₅ undergoes a phase transition within the superconducting (SC) state. A new superconducting state occupies a high field–low temperature (HFLT) corner of the SC state in the H–T plane, and is a strong candidate for realization of the spatially inhomogeneous Fulde–Ferrell–Larkin–Ovchinnikov (FFLO) superconducting state predicted theoretically in 1960s. We present specific heat data on Cd- and Hg-doped CeCoIn₅ that shows that the HFLT phase is suppressed by minute amount of impurities, few hundred parts per million. At this concentration, the average distance between impurities is close to twice the superconducting coherence length ξ, suggesting that ξ is the characteristic length of the HFLT state. We conclude that our investigations support the superconducting, posibly FFLO, origin of the HFLT state.      

Characteristic features of the boiling of emulsions having a low-boiling dispersed phase

The results of investigation of heat transfer from thin wires to a boiling emulsion, the dispersed phase of which is formed from a liquid with a boiling temperature much lower than the boiling temperature of the dispersion medium, are presented. Two variants of boiling of such an emulsion are possible: boiling of the dispersed phase alone and simultaneous boiling of the dispersed phase and dispersion medium. In the present work, only the first variant has been studied; it is distinguished by the following most important features: high superheat of the dispersed-phase droplets ΔT_sup of the emulsion and a wide temperature range of bubble boiling (50–200°C). For conventional heat carriers (pure liquids and solutions), the value of ΔT_sup does not exceed 1–10°C, with the bubble-boiling interval lying within the range from 5 to 20°C. __________ Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 79, No. 6, pp. 81–84, November–December, 2006.     

Temperature shock waves in a moving medium with allowance for the relaxation of the heat flux

The solution of the gasdynamic equation with allowance for the heat transfer in the relaxation of the heat flux is analyzed. The relations expressing the laws of conservation on the front of strong discontinuity of the quantities sought, including the discontinuity of the temperature and the heat-flux density, are discussed. The possibility of existence of two shock waves with fixed initial data is shown using the self-similar solution of the problem on gas motion ahead of the piston. The occurrence of two strong discontinuities is due to the presence of different velocities of propagation of gasdynamic and thermal disturbances — the velocity of sound and the finite rate of heat transfer at a nonzero time of relaxation of the heat flux. __________ Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 79, No. 4, pp. 57–68, July–August, 2006.     

Thermal field on the surface of a material heated by a laser pulse in a narrow ring of illumination

Based on a solution of the problem of the temperature effect of instantaneous heat sources uniformly distributed in a thin plane ring on the boundary of a semünfinite body and different approximations of that solution, we constructed a dynamic model of a thermal field on the surface of a material heated by a laser pulse in a narrow ring of illumination. Scientific Center for Opticophysical Investigations Moscow. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 69, No. 1, pp. 55–64, January–February, 1996.