Use of Watson operations in the solution of some problems in the theory of thermal conductivity

The Watson transform method is used to obtain analytical solutiops of certain nonstationary problems in the theory of thermal conductivity for variable regions with a specified law of boundary motion.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 37, No. 3, pp. 503–507, September, 1979.     

陶瓷热障涂层的热导率和热扩散率测量

提出了应用3ω法进行等离子喷涂热障涂层材料的热导率和热扩散率测量的方法。测试了室温下2种典型的热障涂层材料Y2SiO5和La2Zr2O7的热导率和热扩散率,测试结果与文献中的结果吻合良好。实验中对不同孔隙率的样品的热导率在室温附近的温度区间内进行测试,结果表明,孔隙率的变化对热导率有明显的影响。另外,孔隙率对热扩散率有双向的影响,即存在某一孔隙率值使得涂层样品的热扩散率最大。     

On a certain application of the theory of two-dimensional potential flow to problems on the theory of plates and shells

A new approach based on the use of properties of spherical representation of a surface is proposed for solving a series of problems on the theory of plates and shells. This facilitated another approach to formulation of a resolving equation after having obtained it in a form invariant to the transformation of coordinates. Complex potentials for various flows of the stress-strain state (SSS) are given, i.e., uniform, shear and dipole. Specific applications are presented via a series of results of determination of the basic SSS in plates and shells. Stress concentration factors around holes of complex peripheral form in plates and shells in tension, shear, and torsion are also presented in a physically linear and nonlinear statement. All problems are solved in analytical form and reduced to a quantity.Translated from Problemy Prochnosti, No. 10, pp. 81–85, October, 1990.     

On the thermal conductivity of nanofluids

The dependence of the effective thermal conductivity λ of nanofluids on the properties of dispersed nanoparticles has been studied by the molecular dynamics method. It is established that the thermal conductivity of a nanofluid always exceeds that of the carrier medium, the excess depending on the volume fraction of nanoparticles, their masses, and sizes. An increase in the nanoparticle mass at a constant size leads to a more pronounced increase in λ than does the growth in size at a constant mass, which implies that the density of dispersed nanoparticles is an important factor that determines the thermal conductivity of nanofluids.     

On the thermal conductivity of a blown granular bed

Dependences for calculation of the effective thermal-conductivity coefficients of a granular bed and its constituent phases have been obtained by analogy with the processes of convective heat and mass transfer. The dependences involve simple and quite reliable formulas for calculation of the conductive thermal conductivity of an unblown bed and the radiative thermal conductivity of the skeleton of solid particles. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 81, No. 5, pp. 956–962, September–October, 2008.     

Effect of thermometer thermal conductivity and dimensions on accuracy of thermal flux measurements

Expressions are presented for evaluating errors in steady-state thermal flux measurements within massive objects with consideration of the effect of thermal conductivity and size of the active thermometer zone.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 55, No. 5, pp. 847–853, November, 1988.     

Simultaneous measurements of thermal conductivity and thermal diffusivity of liquids under microgravity conditions

A transient short-hot-wire technique is proposed and used to measure the thermal conductivity and thermal diffusivity of liquids simultaneously. The method is based on the numerical evaluation of unsteady heat conduction from a wire with the same length diameter ratio and boundary conditions as those in the experiments. To confirm the applicability and accuracy of this method. Measurements were made for five sample liquids with known thermophysical properties and were performed under both normal gravity and microgravity conditions. The results reveal that the present method determines both the thermal conductivity and the diffusivity within 2 and 5%. respectively. The microgravity experiments clearly indicate that even under normal gravity conditions, natural-convection effects are negligible for at least l s after the start of heating. This method would be particularly suitable for a valuable and expensive liquid, and has a potential for application to electrically conducting and or corrosive liquids when the probe is effectively coated with an insulating and anticorrosive material. Paper presented at the Fourth Asian Thermophysical Properties Conference, September 5–8, 1995, Tokyo, Japan.     

Converse thermal conductivity problems and calorimetry of transparent bodies

The problem of measuring temperature of transparent bodies can be solved by use of transparent thin film resistance thermometers. Such sensors have been developed using tin and indium oxide. They are used to perform calorimetry of the properties of partially transparent bodies and laser radiation.Notation T temperature - E₀ radiant flux density on plate - R plate thickness - , ,a absorption, thermal conductivity, thermal diffusivity Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 56, No. 5, pp. 811–814, May, 1989.     

Radiative heat transfer in transient hot-wire measurements of thermal conductivity

New measurements of the thermal conductivity of liquid toluene between 300 and 550 K have been used to study the importance of radiative heat transfer when using the transient hot-wire technique. The experimental data were used to obtain the radiation correction to the hot-wire temperature rises. Radiationcorrected values of thermal conductivity are reported. This study shows that the transient hot-wire method is much less affected by radiation than steady-state techniques.     

On the thermal conductivity of two-phase systems

Relationships are obtained which yield the upper and lower bounds of the coefficient of thermal conductivity for statistically homogeneous two-phase systems that have an arbitrary structure.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 18, No. 2, pp. 247–252, February, 1970.     

Effective medium theory and the thermal conductivity of plasma-sprayed ceramic coatings

The thermal diffusivity of plasma-sprayed zirconium oxide-7% yttrium oxide and aluminium oxide-3% titanium oxide ceramic coatings was measured by using a periodic heat-flow method. Samples were prepared with different porosities thus allowing the thermal diffusivity as function of porosity to be determined. The samples were also impregnated with silicone oil so that the effect on the thermal diffusivity by replacing air with silicone oil in the pores could be determined. The experimental results were compared with effective medium theories representing three different microstructures: (1) a continuous ceramic matrix with dispersed pores, (2) a continuous ceramic matrix with continuously interconnected pores, (3) dispersed ceramic particles loosely bonded together. The latter two microstructures gave the best agreement between the experimental data and the theory.     

An analytical treatment of a class of plane plastic strain problems

Conclusion In the foregoing sections a series of solutions of the problem of plastic plane strain have been found, all of which are of the following form: the Cartesian coordinates x and y of the physical plane are trigonometrical functions of , the direction of the major principal stress, multiplied by a power of s, a quantity directly connected with the isotropic stress. If the boundary condition can be described in the same form, the boundary value problem can be solved. In sec. 4 this was done for a special sort of boundary condition. There the shape of the boundary was arbitrary, but the surface traction was a constant normal pressure.The analytical method seems very suitable for the determination of the stresses in the plastic region around a hole. The method may also be applicable to other sorts of plasticity problems, but this is beyond the scope of the present paper.The possibilities are limited in the first place by the requirement that along the boundary the functions and s are continuous and further that there exists a one-to-one relation between the points (, s) and (x, y) of the boundary.One conclusion of practical importance to be drawn from sec. 3 is that the plastic stress distribution around a hole of general shape, and loaded by an arbitrary surface traction, will tend to circular symmetry at a great distance from the hole. An example of this behaviour is shown in fig. 8.     

Determination of thermal conductivity from specific heat and thermal diffusivity measurements of plasma-sprayed cermets

The thermal conductivities of three plasma-sprayed cermets have been determined over the temperature range 23–630°C from the measurement of the specific heat, thermal diffusivity, and density. These cermets are mixtures of Al and SiC prepared by plasma spray deposition and are being considered for various applications in magnetic confinement fusion devices. The samples consisted of three compositions: 61 vol% Al/39 vol% SiC, 74vol% Al/26vol% SiC, and 83 vol% Al/17 vol% SiC. The specific heat was determined by differential scanning calorimetry through the Al melt transition up to 720°C, while the thermal diffusivity was determined using the laser flash technique up to 630°C. The linear thermal expansion was measured and used to correct the diffusivity and density values. The thermal diffusivity showed a significant increase after thermal cycling due to a reduction in the intergrain contact resistance, increasing from 0.4 to 0.6 cm²·^–1 at 160°C. However, effective medium theory calculations indicated that the thermal conductivities of both the Al and the SiC were below the ideal defect-free limit even after high-temperature cycling. The specific heat measurements showed suppressed melting points in the plasmasprayed cermets. The 39 vol% SiC began a melt endotherm at 577°C, which peaked in the 640–650°C range depending on the sample thermal history. Chemical and X-ray diffraction analysis indicated the presence of free silicon in the cermet and in the SiC powder, which resulted in a eutectic Al/Si alloy.Paper presented at the Ninth Symposium on Thermophysical Properties, June 24–27, 1985, Boulder, Colorado, U.S.A.     

Uniqueness in certain inverse problems of the theory of heat conduction

Uniqueness theorems are proved for inverse two-dimensional problems of the theory of heat conduction in two different formulations.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 45, No. 2, pp. 305–309, August, 1983.     

Determination of thermal conductivity and diffusivity from measurements of unsteady temperatures

Explicit formulas are presented for determining the thermal conductivity and diffusivity from measurements of unsteady temperatures in various shaped samples.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 35, No. 2, pp. 250–256, August, 1978.     

On the effective thermal conductivity of a random suspension of spheres

We consider the effective thermal conductivity, λ¹, of a random suspension of spheres in the limit of small concentrations. The results are also directly applicable to a variety of other transport properties, e.g. electrical or magnetic. We study the problem using an iterative procedure and introduce nearest neighbor probability density functions. To lowest order we find the expression for a well separated geometric arrangement. To next order we obtain the effects of sphere interaction. We treat a number of probability density functions and consider the effect of clustering. The results are then studied in relation to the bounds for λ¹ which have been found previously.     

Low temperature thermal conductivity measurements on longitudinal and transverse sections of a superconducting coil

Thermal conductivity measurements have been performed on longitudinal and transverse sections of a superconducting coil at 5, 79, 196, and 276 K. The composite coil sections are composed of copper-stabilized niobium—titanium wire embedded in epoxy. Tabular and graphical data are presented. These data are compared to values calculated on the bases of components of the coil sections. Reasonably good agreement is obtained.     

On prediction of the thermal conductivity of liquids

Based on the Predvoditelev-Vargaftik formula, which relates uniquely thermal conductivity with density, a method is developed to predict the thermal conductivity of organic liquids, their mixtures, as well as petroleum products over a wide range of state parameters. The method employs a three-constant equation of state of a cellular model. The method is distinguished by the small amount of initial information required and an acceptable prediction accuracy.     

Comments on the measurement of thermal conductivity and presentation of a thermal conductivity integral method

A discussion is presented regarding the significance of the spatial temperature gradient approximation normally used in thermal conductivity measurement. Examples are presented illustrating the magnitude of temperature differences allowed for conductivity integral (TCI) method of analysis is presented as an alternative method which totally eliminates the need to impose temperature difference restrictions on the measurement process, so long as other errors, such as radiative heat losses, do not become excessive.