Showing papers on "Thermal contact conductance published in 1987"
TL;DR: In this paper, the authors measured the thermal conductivity of polymethylmethacrylate (PMMA), amorphous polymorphous polyamide, Ca-K nitrate glass, three polyamide-based glasses, and glycerol in the temperature range 30-300 K using an ac technique that eliminates errors from blackbody radiation.
Abstract: We have measured the thermal conductivity of polymethylmethacrylate (PMMA), amorphous ${\mathrm{As}}_{2}$${\mathrm{S}}_{3}$, Ca-K nitrate glass, three ${\mathrm{SiO}}_{2}$-based glasses, and glycerol in the temperature range 30--300 K, using an ac technique that eliminates errors from blackbody radiation. This technique and the problems of blackbody radiation in thermal measurements are discussed in detail. Our data do not support a recent prediction of heat transport by fractons. Instead, we find that the thermal conductivity of these glasses above \ensuremath{\sim}50 K is well described by the minimum thermal conductivity suggested by Slack.
726 citations
TL;DR: In this paper, the effective thermal conductivity of a particulate composite exhibiting a thermal contact resistance at interphase boundaries is considered, and two micromechanical models, the generalized selfconsistent scheme and the Mori-Tanaka theory [Acta Metall. 21, 571 (1973)] previously used in composite media with perfect interfaces, are generalized to allow for the phenomenon of thermal contact resistances between the constituents.
Abstract: The effective thermal conductivity of a particulate composite exhibiting a thermal contact resistance at interphase boundaries is considered. Two micromechanical models, the generalized self‐consistent scheme, and the Mori–Tanaka theory [Acta Metall. 21, 571 (1973)] previously used in composite media with perfect interfaces, are generalized to allow for the phenomenon of thermal contact resistance between the constituents. Spherical inclusions are considered and their interaction is approximately taken into account, so that the presented treatment is valid at nondilute concentrations. Both methods, distinctly different in their approach, result in the same closed‐form simple expression for the effective thermal conductivity.
317 citations
44 citations
TL;DR: In this paper, a nonsteady state cooling method was used to measure the thermal diffusivity (α) of nonwovens, which is relatively simple and requires a minimum of coarse-grained equipment.
Abstract: A nonsteady-state cooling method has been used to measure the thermal diffusivity (α) of nonwovens. The method is relatively simple and requires a minimum of spe cialized equipment. The calculation...
40 citations
01 Mar 1987
TL;DR: In this article, an expression for nonzero thermal stress in a nonhomogeneous flat plate with arbitrary variation in mechanical properties is presented under a transient temperature distribution, and its numerical calculation is given for the case of an exponentially varying thermal conductivity and Young's modulus, but for a homogeneous Poisson's ratio and coefficient of linear thermal expansion.
Abstract: An expression for nonzero thermal stress in a nonhomogeneous flat plate with arbitrary variation in mechanical properties is presented under a transient temperature distribution. Especially an equation for nonzero thermal stress and its numerical calculation showing the effect of nonhomogeneous thermal and mechanical properties on temperature and thermal stress distribution, is given for the case of an exponentially varying thermal conductivity and Young's modulus, but for a homogeneous Poisson's ratio and coefficient of linear thermal expansion.
39 citations
TL;DR: In this article, a study of the thermal diffusivity' specific heat and thermal conductivity of a uniaxially carbon-fibre-reinforced lithia-alumino-silicate glass-ceramic was conducted.
Abstract: A study was conducted of the thermal diffusivity' specific heat and thermal conductivity of a uniaxially carbon-fibre-reinforced lithia-alumino-silicate glass-ceramic. The thermal diffusivity and conductivity parallel to the fibre direction was found to be independent of thermal history and more than an order of magnitude higher than in the transverse directions. During the first thermal cycle, the thermal diffusivi1y transverse to the fibre direction was found to exhibit a decrease attributed to crack formation under the influence of internal stresses. The transverse thermal diffusively on thermal cycling to 1000° C exhibited lower values during heating than during subsequent cooling. This hysteresis was attributed to a thermal history-dependent barrier to heat flow at the matrix-fibre interface. The thermal conductivity of the fibres along their length inferred from composite theory was found to be much lower than the corresponding value for pyrolytic graphite, attributed to less than complete graphitization and associated high density of lattice defects which act as phonon scatterers.
28 citations
TL;DR: In this paper, a new thermal conductance correlation based on improved metal, gap, and joint contact models is presented for determining the thermal inlerfacial resistance in compound cylinders.
Abstract: New thermal conductance correlations based on improved metal, gap. and joint contact models are presented for determining the thermal inlerfacial resistance in compound cylinders. The new theory utilizes models involving measured surface parameters, material hardness, thermophysical properties, and ileratively evaluated contact stresses. The predictions of previous and proposed models are compared to recently published experimental investigations on compound cylinders. Accuracy to within 5% of experimental data is obtained by means of the proposed models. It was found that the alternative models grossly overestimated the thermal contact resistance in compound cylinders, with error ranges from 25 to 100% (Ross and Stoute, Shlykov and Ganin) and 100 to 200% (Veziroglu) of the experimental results. The experimental verifications thereby support the new models in the analysis of compound cylinders, with direct applications in analyzing the performance of finned-tube heal exchangers.
25 citations
TL;DR: In this paper, the influence of contact resistance on the measurement of thermal conductivity of polystyrene using a steady-state device is examined and it is shown that although this influence can perhaps be minimized, it cannot be eliminated as an experimental complication.
Abstract: Several studies of the influence of contact resistance on the measurement of thermal conductivity of polystyrene using a steady-state device are presented. In each case it is seen that, although this influence can perhaps be minimized, it cannot be eliminated as an experimental complication. A novel technique is then described which does eliminate entirely contact resistance as a variable, and this technique is shown to yield an unequivocal value of thermal conductivity.
23 citations
22 citations
Journal Article•
22 citations
TL;DR: In this article, a critical review of existing thermal interfacial conductance correlations and their applicability to this problem was carried out and experiments were also carried out to obtain detailed temperature distribution in the walls of typical pressure and calandria tubes in contact under simulated operating conditions.
TL;DR: In this article, a study has been performed for the development of limiter and divertor plates, and their thermal and thermomechanical behavior were examined in heat load experiments with an electron beam facility, and were compared with analysis results.
TL;DR: In this article, the effect of finite boundary conductance on the magnitude of the thermal stresses in a flat plate subjected to symmetric and asymmetric conductive heat transfer from an infinite, mechanically noninteracting medium is analyzed.
Abstract: An analysis is presented of the effect of a finite boundary conductance on the magnitude of the thermal stresses in a flat plate subjected to symmetric and asymmetric conductive heat transfer from an infinite, mechanically noninteracting medium.
01 Jan 1987
TL;DR: A suite of interactive computer codes has been composed to enable design engineers to predict the thermal resistance that a large heat flux encounters as a result of passing across the pressed contact between abutting surfaces as discussed by the authors.
Abstract: A suite of interactive computer codes has been composed to enable design engineers to predict the thermal resistance that a large heat flux encounters as a result of passing across the pressed contact between abutting surfaces. These surfaces are nominally flat when isothermal at normal ambient temperatures but distort under a thermal stress, arising due to the applied temperature gradient in a direction orthogonal to the interface, so that true contact occurs only over a disc rather than over the whole nominal contact area. The predictions have been corroborated by comparisons with previous experimental measurements. The evolved codes are capable of execution on commonly available desk-top computers.
TL;DR: In this paper, the results of thermal conductivity measurements of glass-fabric base laminates CKT-5KT, CT0φ-1, CT 0φ -1 and CT 0 φ-HT within the 4-80 K temperature range are presented.
TL;DR: The thermal diffusivity of a solid material can be determined using pairs of identi cal specimens prepared for a thermal conductivity determination in a Guarded Hot Plate apparatus (ASTM C-177) as discussed by the authors.
Abstract: The thermal diffusivity of a solid material can be determined using pairs of identi cal specimens prepared for a thermal conductivity determination in a Guarded Hot Plate apparatus (ASTM C-177). Sp...
08 Jun 1987
TL;DR: In this paper, the development described in this paper were made on one of the four Infrared Space Observatory experiments and the developments described here were made during the four IROSA experiments.
TL;DR: In this paper, the authors present a review of thermal conductivity measurement at various conditions under which the lattice vibration is the principal mode of thermal conduction, and describe techniques suitable for this purpose.
Abstract: Publisher Summary This chapter reviews methods of thermal conductivity measurement at various conditions under which the lattice vibration is the principal mode of thermal conduction. Thermal conductivity measurements at zero pressure are essential to the study of terrestrial heat flow. To determine heat flow from underground temperature profiles, the thermal conductivity representative of rock samples obtained along the temperature profile must be measured at pressures at or only slightly above ordinary (atmospheric) pressure of 1.03 bars. The chapter describes techniques suitable for this purpose. Divided-bar method is a standard technique for thermal conductivity measurement. The basis of this measure is the continuity of a steady linear flow of heat through a bar. A rock sample is cut into a flat circular cylinder and sandwiched between metal cylindrical bars of the same diameter. The divided-bar method can also be used to measure thermal conductivity of soft sediment samples. Thermal stack method is another successfully applied method at higher temperatures. In the divided-bar and thermal stack methods, a steady-state temperature distribution is employed to obtain thermal conductivity. However, time-varying temperatures are also useful for determining thermal properties.
TL;DR: In this paper, the authors extended Landau's thermal stability analysis to a slab material whose thermal conductivity varies linearly across the slab thickness, and two simple combinations of boundary conditions were applied, and appropriate critical parameters were determined, thus ascertaining the effect of varying thermal conductivities of the slab material.
Abstract: Landau's thermal stability analysis is extended to a slab material whose thermal conductivity varies linearly across the slab thickness. Two simple combinations of boundary conditions are applied, and appropriate critical parameters are determined, thus ascertaining the effect of varying thermal conductivity of the slab material. The critical solutions obtained in this study can be shown to closely approach, but not be exactly reducible to, Landau's solution for constant thermal conductivity. The knowledge of a Landau solution, however, gives credence to the present results selected from a multitude of critical solutions.
TL;DR: In this paper, thermal conductivity and capacity of halogenated niobium tetraselenide (NbSe 4 ) 3 I were measured and the structural phase transition at 274K was clearly marked in both measurements.
TL;DR: In this paper, thermal conductivity measurements of the pseudobinary (Ce x La 1− x )Cu 6 system are reported, and the analysis of the results takes account of a large phonon contribution to the heat transport below 20 K. This series is characterized by unusual large Lorenz numbers.
08 Jun 1987
TL;DR: In this article, the authors investigated the pressure dependence of the thermal conductivity with respect to volume in mixed insulating crystals, assuming the presence of phonon-phonon, Umklapp and simple mass defect scattering processes alone.
Abstract: The pressure dependence of the thermal conductivity with respect to volume in mixed insulating crystals is investigated. The logarithmic derivative of the thermal conductivity with respect to volume is calculated assuming the presence of phonon-phonon, Umklapp and simple mass defect scattering processes alone, this quantity being expressed in terms of the elastic, thermal and structural parameters of the material. Results are compared with the experimental data for the mixed-crystal system AgCl-AgBr.
TL;DR: In this article, the TSPN-4 platinum thermometers were calibrated on IPTS-68 and the germanium TSG-2 ones on the VNIIFTRI scale.
Abstract: The thermal conductivity I for the material is determined in two stages on specimens of cross section S and thickness s (as is the thermal resistance of the contact R): first one measures the temperatures and derives the difference AT I from the readings with the heater switched off, and then the difference AT and the heater power Q are measured with the heater on. The sink temperature was the same in both cases (difference not more than 0.05~ The conductivity is l ~= S[(AT--AT~)/Q-RI The TSPN-4 platinum thermometers were calibrated on IPTS-68, while the germanium TSG-2 ones were calibrated on the VNIIFTRI scale. Maker's error for the thermometers 0.01~ The discrepancies between the readings during calibration did not exceed 5 mK, and the values were reproduced with an error of !0.2 mK on all the specimens. The temperature drift did not exceed 2-3 mK/h, while AT in most of the experiments was I~ There is a difficulty in implementing our method at cryogenic temperatures on account of providing reliable thermal contact between the specimens and the sink or body of the heater. In the plane-layer method, the contact resistance enters into the measured thermal resistance and distorts the result considerably (particularly under vacuum conditions). The contact resistance may be reduced and stabilized at room temperature by liquid contact media, which also somewhat eases the specifications for finish in the contacting surface and eliminates the condition for a high compressive force. However, the usual liquids (vacuum oil or organosilicon liquids) solidify at cryogenic temperatures and become brittle, and the contact layer is disrupted by the temperature-depe ndent stresses and strains. Consequently, the contact resistance increases by several orders of magnitude. It is therefore necessary
TL;DR: In this article, a mean-gap-conductance model was proposed to evaluate the effects of the mesh geometry, and with the addition of a correction term to account for three-dimensional effects and layer-to-layer contact, the effective conductivity can be accurately predicted.
Abstract: Heat conduction through a metal cloth wick saturated with a fluid has been investigated. An apparatus used to measure thermal conductivity, in which the condition of wick packing geometry is carefully controlled, and the basic experimental procedure are described. Experimental results are presented and compared to a new mean-gap-conductance model based upon the wick geometry, and to the simple series model. The mean-gap-conductance model evaluates the effects of the mesh geometry, and with the addition of a correction term to account for three-dimensional effects and layer-to-layer contact, the effective conductivity can be accurately predicted. In addition, a correlation of the mean gap which directly includes three-dimensional and contact conductance effects is presented. The correlation predicts the data within 10 percent whereas the series model may be more than 40 percent in error. From a parametric study using the new model, theoretical limits on the maximum and minimum conductivity enhancement have been determined as a function of geometric parameters. The implications of the research on heat pipe wick design are discussed.