Showing papers on "Thermal contact conductance published in 1984"

Determining specific contact resistivity from contact end resistance measurements

Abstract: A method is described to determine specific contact resistivity from contact end resistance measurements using a transmission line model. A test pattern is described which minimizes the effect of current fringing around contact corners and yields an accurate determination of contact width. With this pattern, the specific contact resistivities measured on 1.3 wt % Si/Al contacts to n+ silicon junctions with different dopings show very consistent values and are independent of contact geometries. The dependence of measured specific contact resistivities on doping concentration is also in good agreement with the predictions of tunneling theory. Surprisingly, the dependence on surface concentration extends well beyond the usual range of electrically active solid solubility.

Role of Material Properties in the Thermal‐Stress Fracture of Brittle Ceramics Subjected to Conductive Heat Transfer

Abstract: An analysis is presented of the thermal stresses in brittle ceramics subjected to thermal shock by quenching into a liquid medium in which conduction is the primary mechanism of heat transfer. The magnitude of maximum stress was shown to be a function of the coefficient of thermal expansion, Young's modulus, and Poisson's ratio of the ceramic, as well as the values of the thermal conductivity, specific heat, and density of the ceramic and quenching medium. The magnitude of thermal stress was shown to be independent of specimen size and, on cooling, to occur at the instant of cooling (t=0). Appropriate thermal-stress resistance parameters were derived.

Thermal conductance of pressed copper contacts at liquid helium temperatures

Abstract: Etude experimentale de la resistance thermique de contact de surfaces de cuivre avec un fini de surface de 0,4 micron entre 1,6 et 4,2°K pour des forces de pression allant jusqu'a 670 N. Etablissement d'une correlation

Heat flow model of rapid solidification with nonhomogeneous thermal contact

Abstract: A heat flow model is presented of the solidification process of a thin melt layer on a heat conducting substrate. The model is based on the two-dimensional heat conduction equation, which was solved numerically. The effect of coexisting regions of good and bad thermal contact between foil and substrate is considered. The numerical results for thermal parameters of the Al-Cu eutectic alloy show considerable deviations from one-dimensional solidification models. Except for drastic differences in the magnitude of the solidification rate near the foil-substrate interface, the solidification direction deviates from being perpendicular to the substrate and large lateral temperature gradients occur. Interruption of the thermal contact may lead to back-melting effects. A new quantity, the effective diffusion length, is introduced which allows some conclusions to be drawn concerning the behaviour of the frozen microstructure during subsequent cooling.

Mathematical description and calculation of contact melting

Abstract: Heat- and mass-transfer processes are investigated in the contact melting of solids with large specific loads and energy rates appropriate to conditions of thermal drilling.

Heat Transport of Powder as the Subject of Cryogenic Insulation : 1st Report, Effective Thermal Conductivity at Atmospheric and Low Pressures

Abstract: As thermal insulation powder usually contains numerous voids in each particle of the powder, the previous theoretical equations on its effective thermal conductivity do not agree with experiments if the equations are employed without modification. In the present study, the thermal conductivity of a particle is firstly estimated by a simple cell model, then the effective thermal conductivity of the powder is calculated on the assumption that the powder consists of particles with the above estimated thermal conductivity. On the other hand, the effective thermal conductivities of the powder of perlite and hollow glass microsphere are measured at low temperatures, and are compared with the calculated values. The result shows that at a given temperature and gas pressure the experimental values agree well with the calculated values.

Deriving the thermal contact resistance from the solution of the inverse heat-conduction problem

Abstract: The construction of an iterative computational algorithm is considered, and results of mathematical modeling of the solution of the coefficient inverse problem of heat conduction by deriving the dependence of the thermal contact resistance on the temperature are given.

Study on contact mechanism and electric resistance characteristics of twisted conductors

Abstract: This paper analyzes the mechanical and electrical characteristics of the hand-twisted conductor splices in communication cables. the validity of the analysis is verified by experiment. Concerning the mechanical characteristics, it is shown that in the physical contact of the conductors the central axis is twisted with an arbitrary pitch angle on a quasi-cylinder with the radius equal to that of the conductor. Based on such representation of the contact mechanism, the contact pressure and contact width of the twisted conductors are calculated. Concerning the electrical characteristics, it is assumed that there is a similarity between the current distribution through the twisted conductor contact and the electric lines of force produced by the charge on the surface of contact. Based on such assumption, the constriction resistance of the twisted contact is calculated with consideration of the contact pressure and contact width. Estimation is also made on the growth process of the film resistance and the boundary film thickness due to the chemical substances formed on the conductors in contact. the electrical equivalent circuit for the twisted conductor contact is derived, including the constriction resistance, film resistance and conductor resistance. Using the derived equivalent circuit, an expression is derived for estimation of the contact resistance of the twisted conductors.

Non-steady-state thermal diffusion and thermal conductivity in gas mixtures

Abstract: Expressions are obtained which characterize effective thermal conductivity coefficients of gas mixtures, as measured by various experimental methods.

Thermal explosion in a layer of reactive liquid bounded by large masses with different thermal conductivity

Abstract: In this paper the well-known results obtained by Frank-Kamenetskii on a thermal explosion in a layer of reagent bounded by ideally heat-conducting surfaces [i] are generalized to a layer confined between solid large masses, whose thermal conductivities differ from the thermal conductivity of the chemically active material. In this case, the heat liberated by the reaction penetrates into the large masses. In solving the problem, it is necessary to start from the conditions of continuity of temperature and heat flux at the boundaries of the layer. The general case when the large masses have different thicknesses and thermal conductivities is investigated.

Low temperature thermal conduction in solids

Abstract: The two major carriers of heat in solids are phonons and free electrons. Lattice waves or phonons carry heat in all solids, electrons in metals and alloys. In the case of highly conducting or pure metals, the electronic component is often so large as to dominate the conduction process. In alloys and in metals of lower conductivity, the lattice component is usually an appreciable fraction of the total. In insulators (which at low temperatures include semiconductors) the thermal conductivity is entirely due to lattice waves. There are, in principle, other carriers of heat, such as mobile magnetic excitations and internal electromagnetic radiation. Radiation is usually negligible at low temperatures, but can be important at high temperatures.

High specific heat dielectrics and Kapitza resistance at dielectric boundaries

Abstract: : This program has two efforts: Kapitza and thermal properties studies. Two separate Kapitza conductance test facilities have been designed and fabricated for both solid solid and for solid liquid HE II measurements. Preliminary data has been obtained for copper to T lambda C lambda interface conductance and also for KBr and LiF thermal conductance to Helium II. For the latter two materials, the test dewars were designed to allow cleaving of the samples under liquid helium. The Kapitza conductance of both samples was very near the phonon radiation limit providing strong evidence that the anomalous Kapitza conductance is not the result of surface contamination. Thermal properties work has included the measurement of the specific heat and thermal conductivity of the CdCr2O4 spinels and of several CsC lambda structure heavy metal halides in the temperature range of 1.5 to 35K. The specific heat data for the spinels was analyzed in terms of both lattice phonons and magnetic contributions. The dependence of the spinel's thermal conductivity on magnetic fields up to 15T was studied and magnetocaloric data has been obtained. For both the Zn and Cd spinels, the lattter results showed a paramagnetic behavior with demagnetization cooling and magnetization heating. Theory has been developed to explain some of the magnetocaloric effects in the new spinels, CdCr2O4 and ZnCr2O4.