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  • Articles  (92)
  • Articles: DFG German National Licenses  (92)
  • thermal conductivity  (92)
  • 2020-2024
  • 1985-1989  (92)
  • Physics  (92)
  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Journal of statistical physics 57 (1989), S. 595-629 
    ISSN: 1572-9613
    Keywords: Neutron scattering function ; shear viscosity ; bulk viscosity ; thermal conductivity ; Green-Kubo integrand ; hard-sphere fluid ; short-time expansion
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The short-time behavior of the coherent intermediate scattering function for a fluid of hard-sphere particles is calculated exactly through ordert 4, and the other hydrodynamic correlation functions are calculated exactly through ordert 2. It is shown that for all of the correlation functions considered the Enskog theory gives a fair approximation. Also, the initial time behavior of various Green-Kubo integrands is studied. For the shear-viscosity integrand it is found that at densitynσ3=0.837 the prediction of the Enskog theory is 32% too low. The initial value of the bulk viscosity integrand is nonzero, in contrast to the Enskog result. The initial value of the thermal conductivity integrand at high densities is predicted well by Enskog theory.
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    International journal of thermophysics 10 (1989), S. 409-415 
    ISSN: 1572-9567
    Keywords: critical region ; ethane ; thermal conductivity ; thermal diffusivity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The thermal conductivity of ethane in the critical region has been measured isochorically at densities up to 1.76 times the critical density and at temperatures down to 0.13 K above the critical temperature. The measurements were performed with a thermal conductivity apparatus based on the parallelplate method. The experimental accuracy was 0.5 to 5%, depending on the distance to the critical point. The experimental results agree well with a recently developed crossover theory for the thermal diffusivity of fluids in the critical region.
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    International journal of thermophysics 10 (1989), S. 673-686 
    ISSN: 1572-9567
    Keywords: chlorofluorocarbons ; fluorocarbons ; nitrogen ; thermal conductivity ; toluene ; transient hot-wire method
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract In this paper we describe a version of a transient hot-wire apparatus which employs an integrating digital voltmeter to measure the bridge out-of-balance signal. The integrating period of the voltmeter is variable and is routinely set equal to one 60-Hz power-line cycle, 16.67 ms. Use of measurement or integration periods less than an integral multiple of the power-line period results in substantially more electronic noise and a significant degradation in experimental precision. A correction to the working equation which accounts for the integration of the out-of-balance signal is also presented. The precision of the digital voltmeter used with the apparatus is ±0.1 μV, which translates into an ultimate precision of ±0.03 mK in the measured temperature rise. In practice the precision in the temperature rise is typically ±0.3 mK, which represents a moderate improvement over the precision generally obtained with transient techniques employing automatic bridge balancing schemes. Although the current apparatus is designed principally for measurements of the thermal conductivity of liquids, it can been used for gas-phase measurements, with some decrease in accuracy due to the somewhat larger heat capacity correction which must be applied to the temperature rise measurements. The operation of the instrument was verified by measuring the thermal conductivities of toluene and nitrogen. Preliminary data are presented for the new environmentally acceptable fluorocarbons such as R-134a (CF3CH2F), R-123 (CHCl2CF3), and R-141b (CCl2FCH3).
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    International journal of thermophysics 10 (1989), S. 417-426 
    ISSN: 1572-9567
    Keywords: carbon dioxide ; critical phenomena ; ethane ; methane ; thermal conductivity ; thermal diffusivity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract A practical representation for the critical thermal conductivity enhancement is developed by incorporating a finite cutoff into the asymptotic mode-coupling integrals for the diffusivity associated with the critical fluctuations. This procedure yields a simplified approximation to a more complete nonasymptotic solution of the mode-coupling integrals obtained by us earlier. A comparison is made with thermal conductivity data for carbon dioxide, ethane, and methane.
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  • 5
    Electronic Resource
    Electronic Resource
    Springer
    International journal of thermophysics 10 (1989), S. 1013-1027 
    ISSN: 1572-9567
    Keywords: high pressure ; propane ; thermal conductivity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract This paper presents thermal conductivity measurements of propane over the temperature range of 192–320 K, at pressures to 70 MPa, and densities to 15 mol · L−1, using a transient line-source instrument. The precision and reproducibility of the instrument are within ±0.5%. The measurements are estimated to be accurate to ±1.5%. A correlation of the present data, together with other available data in the range 110–580 K up to 70 MPa, including the anomalous critical region, is presented. This correlation of the over 800 data points is estimated to be accurate within ±7.5%.
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  • 6
    Electronic Resource
    Electronic Resource
    Springer
    International journal of thermophysics 6 (1985), S. 267-273 
    ISSN: 1572-9567
    Keywords: high pressure ; thermal conductivity ; vitreous boron trioxide
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The thermal conductivity, λ, of vitreous boron trioxide was measured, using a hot-wire procedure, from 170 to 570 K and under pressures of up to 1.7 GPa. The thermal conductivity at room temperature and zero pressure was found to be 0.52 W · m−1 · K−1. The values of the logarithmic pressure derivative, g = d(ln λ)/d(ln ρ), where ρ is the density, were found to be 1.1 for uncompacted glass and 0.7 for glass compacted to 1.2 GPa. The variation of λ with temperature at constant density was approximately linear, with a positive slope of 1.38×10−3W·m−1·K−2.
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  • 7
    Electronic Resource
    Electronic Resource
    Springer
    International journal of thermophysics 7 (1986), S. 455-466 
    ISSN: 1572-9567
    Keywords: aluminium/silicon carbide cermet ; aluminum/silicon eutectic ; plasma spray ; specific heat ; thermal conductivity ; thermal diffusivity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract 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.
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  • 8
    Electronic Resource
    Electronic Resource
    Springer
    International journal of thermophysics 7 (1986), S. 663-673 
    ISSN: 1572-9567
    Keywords: corresponding states ; heavy water ; thermal conductivity ; water
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract New measurements of the thermal conductivity of H2O and D2O have been performed from critical temperature up to 510°C and from atmospheric pressure up to 100 MPA. As these measurements have been made with the same cell, a precise analysis of the isotopic effect as a function of temperature and density is possible. Our analysis is presented in terms of corresponding states. It is shown that the critical thermal conductivity excesses for H2O and D2O reduced by their respective background thermal conductivity terms are represented by single reduced isotherms.
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  • 9
    Electronic Resource
    Electronic Resource
    Springer
    International journal of thermophysics 7 (1986), S. 731-742 
    ISSN: 1572-9567
    Keywords: specific heat ; thermal conductivity ; thermal diffusivity ; thermal emissivity ; thermophysical properties
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Various aspects of the importance of thermophysical property (TPP) studies to science and technology in China are discussed. Several stages of the development of experimental principles and equipment are described. Some examples of TPP applications in economic practice are presented. Theoretical and methodological studies in this field are summarized. The presentations are limited mostly to work on solids.
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  • 10
    Electronic Resource
    Electronic Resource
    Springer
    International journal of thermophysics 7 (1986), S. 273-284 
    ISSN: 1572-9567
    Keywords: alkanes ; hard-sphere theory ; hydrocarbons ; thermal conductivity ; viscosity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The paper presents the results of a preliminary attempt to represent both the viscosity and the thermal conductivity of normal alkanes in the liquid phase by means of a mutually consistent scheme. The correlation method proposed is based upon the general results of the hard-sphere theory of dense fluids, although it does not make use of the detailed predictions of that model. It is shown that the viscosity of the alkanes, ethane, propane, n-butane, n-hexane, and n-octane may be represented by a single, universal function of reduced volume if each species is assigned a characteristic molar volume which is but weakly temperature dependent. Using the same values of molar volume the thermal conductivity of the same fluids can be represented by a further universal function of reduced volume by means of the choice of a second, temperatureindependent parameter.
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