Showing papers on "Thermal contact conductance published in 1980"
TL;DR: In this article, the thermal conductivity of ice, the low-pressure phase of N${\mathrm{I}h$ phase of O$O, is reviewed and good agreement is found with the theoretical calculations of its absolute value and temperature dependence.
Abstract: The thermal conductivity of ice, the low-pressure $\mathrm{I}h$ phase of ${\mathrm{H}}_{2}$O, is reviewed and good agreement is found with the theoretical calculations of its absolute value and temperature dependence. Measurements under pressure show an anomalous decrease in conductivity with decreasing molar volume. This is explained by the negative Gr\"uneisen parameter for the transverse acoustic modes which dominate the heat transport. The conductivity behaves predominantly like that of a wurtzite lattice of rigid mass points with an atomic mass of 18. Some traces of the interaction of the lattice phonons with the higher-lying librational modes can be seen. The volume dependence of the conductivity of the higher-pressure phases of ice and of N${\mathrm{H}}_{4}$F is related to that of $\mathrm{I}h$ ice.
122 citations
TL;DR: In this article, useful expressions to describe the thermal sputtering for materials having a temperature dependent thermal diffusivity, using a heat capacity and thermal conductivity which vary as C = C 0 T n−1 and K = K 0 m−1, respectively, and assigning a width to the initial temperature distribution.
Abstract: Recent experiments on the erosion of condensed gases and alkali halides by incident ions have renewed interest in the description of thermal spikes. In such spikes a localized, transiently heated region produced by incident radiation may induce activated processes like evaporation of atoms or molecules from a surface. In this paper are presented useful expressions to describe the thermal sputtering for materials having a temperature dependent thermal diffusivity, using a heat capacity and thermal conductivity which vary as C = C 0 T n–1 and K = K 0 m–1, respectively, and assigning a width to the initial temperature distribution.
88 citations
41 citations
35 citations
TL;DR: In this article, an analytical approach is presented for the modeling of the thermomechanical interactions which occur in high speed sliding situations, which are characterized by active and interrelated thermal and mechanical phenomena called "rub energetics" problems.
32 citations
TL;DR: The thermal status of an animal is the result of a combination of physical and physiological factors as discussed by the authors, and it may be possible to separate these more easily than in homeotherms, where the presence of control mechanisms can mask the processes occurring.
Abstract: The thermal status of an animal is the result of a combination of physical and physiological factors. In poikilotherms, it may be possible to separate these more easily than in homeotherms, where the presence of control mechanisms can mask the processes occurring. The thermal time constant of a poikilotherm has been shown to be a useful measure of its thermal behaviour, and to vary with the physiological status of the animal. A simple model is developed to show how the thermal time constant is related to the physics of heat exchange. The derived thermal time constant is shown to scale as body mass raised to the power 2/3, and this is compared with results on lizards heating and cooling in water, taken from the literature. When heat exchange in air is considered, the concept of boundary layer resistance leads to a useful simplification. The thermal time constants in air taken from the literature show that the boundary layer resistance is approximately constant.
32 citations
30 citations
TL;DR: In this article, a transient heat probe method is proposed to predict thermal instability in cable backfills, which is a direct result of net moisture migration away from the heat source below a critical moisture level.
Abstract: Thermal instability, in the context of heat dissipation from buried cables, refers to the condition tion in which the thermal resistivity of the soil continuously increases with time to a value close to that of its dry state. This "thermal runaway" condition leads to a large increase in cable temperature. The thermal instability in cable backfills is a direct result of net moisture migration away from the heat source below a critical moisture level. Moisture migration in cable backfills can be caused by either a natural drying process resulting from evapotranspiration or by the thermal gradient from the heat source. This paper deals with the latter case, for which a theoretical prediction and experimental verification are provided. A transient heat probe method of predicting thermal instability in cable backfills is discussed.
30 citations
01 Jan 1980
19 citations
18 citations
TL;DR: In this paper, the concept of waviness number is recommended for use at the design stage of many engineering systems involving heat transfer across pressed contacts, in order to reduce plant capital costs and improve overall thermal efficiencies.
TL;DR: In this article, the authors measured thermal conductivity or thermal diffusivity for some rock samples using a modified Angstroem or an impulse method up to 8 kbar, the investigations were performed under hydrostatic conditions.
TL;DR: Thermal conduction is an efficient form of heating for certain tissue sizes: guidelines have been given indicating this for various tissues and tissue geometries, however, over only limited distances.
Abstract: The role of thermal conduction in hyperthermia has been studied by developing mathematical models that were based on a numerical solution of the partial differential heat conduction equation. Models were developed to study (a) the efficiency of thermal conduction as a heating modality, (b) the effect of heat conduction out of the heated region, and (c) the effect of conduction in equalizing the temperature distribution produced by a non-uniform heating source. Thermal conduction is an efficient form of heating for certain tissue sizes: guidelines have been given indicating this for various tissues and tissue geometries. Conduction of heat out of a uniformly heated region reduces the effective treatment volume. In addition, if the temperature monitoring device (used as a feedback control of power input) is in a position which is influenced by thermal conduction, the temperature within the tissue may rise above the desired value. Non-uniformities in temperature distribution are smoothed out by thermal conduction, however, over only limited distances.
TL;DR: In this article, the effect of a spatial variation of the thermal conductivity on the magnitude of the maximum tensile thermal stress in a solid circular cylinder subjected to sudden convective heating was calculated by finite element methods.
Abstract: The effect of a spatial variation of the thermal conductivity on the magnitude of the maximum tensile thermal stress in a solid circular cylinder subjected to sudden convective heating was calculated by finite element methods. The general results show that by lowering the thermal conductivity in the surface region of the cylinder, the magnitude of the maximum tensile thermal stress at the center of the cylinder is reduced significantly. The negative temperature dependence of the thermal conductivity in dielectric materials, which indirectly creates a spatial variation in thermal conductivity, also causes a significant decrease in the magnitude of the tensile thermal stresses, as demonstrated by a numerical example for aluminum oxide. It is also shown that a spatial variation in thermal conductivity can significantly affect the time to maximum tensile stress as well.
TL;DR: In this paper, the effect of a diurnally varying flux on a solid surface is analyzed in terms of thermal admittance, the reciprocal of complex thermal conductance, which can significantly affect the phase and amplitude of the temperature wave of the exposed surface.
TL;DR: In this paper, an approximate model is developed to predict the onset of instability when one elastic body slides in contact with another body, and the results show that, at a low number of waves, ring deflection predominate and greatly increase the speed at which instability begins.
TL;DR: In this paper, a three-layer model consisting of two surface layers and a core is developed to explain the effect of specimen thickness on the thermal properties of thick insulation, and a relationship between the apparent thermal resistivity and the increase in resistance per unit thickness is derived.
Abstract: A three-layer model comprising two surface layers and a core is developed to explain the effect of specimen thickness on the thermal properties of thick insulation. The model explains the effect of boundary emittance and specimen density on the measurements. A relationship between the apparent thermal resistivity and the increase in resistance per unit thickness is derived. Equations are given for the densities at which the maximum thermal resistance of the core of the specimen and whole specimen occurs and for the variation of thermal conductivities of the core and the specimen with the ratio of density to density at which the minimum conductivity occurs. The densities at which the extremes occur are almost independent of specimen thickness. A V-shape and not the customary nonsymmetrical U-shape is suggested for the variation of thermal conductivity. Equations for use in curve fitting that introduce curvature at the apex and shift the position of the minimum are suggested.
TL;DR: In this paper, the importance of thermal contact resistance between layers in heat transfer through two layer, plasma sprayed, thermal barrier coatings applied to turbine vanes was investigated with a system of NiCrAlY bond and yttria stabilized zirconia ceramic.
TL;DR: In this article, a method and an instrument for the measurement of a number of the thermophysical properties (thermal conductivity, thermal activity, volumetric specific heat, thermal diffusivity) are described.
Abstract: A method and an instrument for the measurement of a number of the thermophysical properties (thermal conductivity, thermal activity, volumetric specific heat, thermal diffusivity) are described. The results obtained for thermal conductivity and specific heat of toluene, over a temperature range 30–350°C and pressures of up to 30 MPa, are presented.
01 Jan 1980
TL;DR: In this article, it was shown that there is no direct relationship between the measured specific heat and the thermal conductivity of extruded semicrystalline polyethylene and that two-level resonance theory can explain the specific heat, but it does not explain thermal conductivities.
Abstract: Measurements of thermal conductivity and specific heat carried out on the same samples of extruded semicrystalline polyethylene show that there is no direct relationship between the measured specific heat and the thermal conductivity Although two-level resonance theory can explain the specific heat it does not explain the thermal conductivity measurements of such semicrystalline materials Preliminary calculations show good agreement with experiment using the structure scattering theory of Morgan and Smith (1974)
TL;DR: In this article, the Peltier coefficient and the contact resistance of a metal-semiconductor contact were determined for GaAs and showed that Au:Ge:Ni alloy contacts are effective in minimizing the contact resistances.
Abstract: The maximum heat that can be pumped by a metal-semiconductor thermoelectric cooling stage depends strongly on the dopant concentration in the semiconductor and on contact resistance at the metal-semiconductor interface which is cooled. A comparison is made between theoretical models describing these effects and experimental data for GaAs, both taken from original measurements and compiled from the literature. A convenient, new technique for determining the Peltier coefficient and the contact resistance of a metal-semiconductor contact is described. The results indicate that, in the case of GaAs, Au:Ge:Ni alloy contacts are effective in minimizing the contact resistance.
TL;DR: Some thermal properties of A-150 tissue-equivalent plastic have been determined and the significance of the measurements for the design of a calorimeter core calibration heater is briefly described.
Abstract: Some thermal properties of A-150 tissue-equivalent plastic have been determined The results are: thermal diffusivity, 272*10-3 cm2 s-1+or-04%; specific heat, 172 J g-1 K-1+or-13%; and thermal conductivity, 53*10-3 W K-1 cm-1+or-14% The significance of the measurements for the design of a calorimeter core calibration heater is briefly described
01 Jan 1980
TL;DR: The thermal conductivity of amorphous materials has a characteristic temperature dependence quite unlike that of crystalline solids as mentioned in this paper, and it varies roughly as T 2 below 1 K, shows little temperature dependence in a 'plateau' region between 1 and 10 K and increases again at higher temperatures.
Abstract: The thermal conductivity k of amorphous materials has a characteristic temperature dependence quite unlike that of crystalline solids k varies roughly as T2 below 1 K, shows little temperature dependence in a ‘plateau’ region between 1 and 10 K and increases again at higher temperatures 1 This behaviour is illustrated for vitreous silica in the figure The low temperature behaviour is well understood, and is the result of scattering from two-level systems
TL;DR: In this article, the dependence of the heat transfer coefficient between metal-metal interfaces on the temperature and an external magnetic field has been measured by a steady-state measuring method, and the results showed that the thermal conductance at the interface is mainly determined by the electron scattering on lattice irregularities in the diffusion layer.
Abstract: In the present work the dependence of the heat transfer coefficient between Cu and Sn, Cu and Pb, and Cu and W on the temperature and an external magnetic field has been measured. The preparation of the metal-metal junctions has been performed by melting so that a close contact at the interface was guaranteed. The heat transfer coefficient has been found by a steady-state measuring method. In the case of the Cu-Pb junction the heat transfer coefficient could be measured both in the superconducting and normal states. For all the metal—metal junctions in the normal state a linear temperature dependence of the heat transfer coefficients on the temperature has been found. In the superconducting state a strong reduction of the heat transfer coefficient has been observed. In addition, a theoretical calculation of the heat transfer coefficient on metal-metal interfaces is given. First we consider the scattering of electrons on a steplike potential barrier between two gases of free electrons. Then the thermal conductance due to scattering in an alloy layer is calculated. Such an alloy layer may arise from diffusion during the contact preparation. Comparison of these two cases with the experiments shows the thermal conductance at the interface is mainly determined by the electron scattering on lattice irregularities in the diffusion layer.
TL;DR: An apparatus for measuring the thermal conductance of insulating mechanical supports under compression is described in this paper, which requires no installation of thermometers on the sample and can be used to measure contact resistance.