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  • 1
    ISSN: 1572-9567
    Keywords: heat radiation ; hot wire ; thermal conductivity ; semitransparent material
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract A new simple analytic model applicable to the measurement system of a hot wire and a semitransparent solid material is developed. An experimental study is carried out on a special glass sample, glass K9, in the temperature range of 297 to 1230 K, and the radiation-free thermal conductivity is reported.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1572-9567
    Keywords: anisotropic materials ; pyrolytic graphite ; pyrolytic boron nitride ; thermal conductivity ; thermal diffusivity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The laser pulse method can be successfully applied to the measurement of thermal diffusivity of isotropic materials subject to some assumptions. For anisotropic materials, this method is applicable to the measurement of principal thermal diffusivity only on the condition that there is no difference in direction between the principal axis and that of the temperature gradient. After analyzing the heat conduction process in an anisotropic solid, it has been shown that large errors in the measurement of thermal diffusivity would exist if the direction of the principal axis deviates inconspicuously from that of the temperature gradient. The experimental results of thermal diffusivity of highly oriented pyrolytic graphite (HOPG) samples with various deviation angles have been compared with the analytical results. The laser pulse method is not applicable to measurements on semitransparent pyrolytic boron nitride (PBN). We adopted a two-layer composite sample to measure the thermal diffusivity of PBN in the c direction and a particular graphite-PBN composite sample has been prepared which has a very low thermal resistance at the interface. The thermal diffusivity and thermal conductivity of PG (below 2300°C) and PBN (below 1000°C) are given.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1572-9567
    Keywords: molten carbonates ; molten nitrate ; thermal conductivity ; thermal diffusivity ; transient short-hot-wire technique
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract A transient short-hot-wire technique has been successfully used to measure the thermal conductivity and thermal diffusivity of molten salts (NaNO3, Li2CO3/K2CO3, and Li2CO3/Na2CO3) which are highly corrosive. This method was developed from the hot-wire technique and is based on two-dimensional numerical solutions of unsteady heat conduction from a short wire with the same length-to-diameter ratio and boundary conditions as those used in the actual experiments. In the present study, the wires are coated with a pure Al2O3 thin film by using a sputtering apparatus. The length and radius of the hot wire and the resistance ratio of the lead terminals and the entire probe are calibrated using water and toluene with known thermophysical properties. Using such a calibrated probe, the thermal conductivity and thermal diffusivity of molten nitrate are measured within errors of 3 and 20%, respectively. Also, the thermal conductivity of the molten carbonates can be measured within an error of 5%, although the thermal diffusivity can be measured within an error of 50%.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1572-9567
    Keywords: electrical conductivity ; microstructure ; pin fin ; single carbon fiber ; steady-state short-hot-wire method ; thermal conductivity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract In this paper, the thermal conductivity of a single carbon fiber under different manufacturing conditions is measured using the steady-state short-hot-wire method. This method is based on the heat transfer phenomena of a pin fin attached to a short hot wire. The short hot wire is supplied with a constant direct current to generate a uniform heat flux, and both its ends are connected to lead wires and maintained at the initial temperature. The test fiber is attached as a pin fin to the center position of the hot wire at one end and the other end is connected to a heat sink. One-dimensional steady-state heat conduction along the hot wire and test fiber is assumed, and the basic equations are analytically solved. From the solutions, the relations among the average temperature rise of the hot wire, the heat generation rate, the temperature at the attached end of the fiber, and the heat flux from the hot wire to the fiber are accurately obtained. Based on the relations, the thermal conductivity of the single carbon fiber can be easily estimated when the average temperature rise and the heat generation rate of the hot wire are measured for the same system. Further, the electrical conductivity of the single carbon fiber is measured under the same conditions as for the thermal conductivity using a four-point contact method. The relation between the thermal conductivity and electrical conductivity is further discussed, based on the crystal microstructure.
    Type of Medium: Electronic Resource
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