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  • Articles  (22)
  • Articles: DFG German National Licenses  (22)
  • thermal conductivity  (22)
  • 2025-2025
  • 2005-2009
  • 1985-1989  (22)
  • 1989  (22)
  • Physics  (22)
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  • Articles  (22)
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  • Articles: DFG German National Licenses  (22)
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  • 2025-2025
  • 2005-2009
  • 1985-1989  (22)
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  • Physics  (22)
  • 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 10 (1989), S. 133-144 
    ISSN: 1572-9567
    Keywords: Enskog theory ; equation of state ; fluids (dense) ; thermal conductivity ; viscosity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract An attempt is made in this work to combine the Enskog theory of transport properties with the simple cubic Peng-Robinson (PR) equation of state. The PR equation of state provides the density dependence of the equilibrium radial distribution function. A slight empirical modification of the Enskog equation is proposed to improve the accuracy of correlation of thermal conductivity and viscosity coefficient for dense gases and liquids. Extensive comparisons with experimental data of pure fluids are made for a wide range of fluid states with temperatures from 90 to 500 K and pressures from 1 to 740 atm. The total average absolute deviations are 2.67% and 2.02% for viscosity and thermal conductivity predictions, respectively. The proposed procedure for predicting viscosity and thermal conductivity is simple and straightforward. It requires only critical parameters and acentric factors for the fluids.
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  • 7
    Electronic Resource
    Electronic Resource
    Springer
    International journal of thermophysics 10 (1989), S. 1041-1051 
    ISSN: 1572-9567
    Keywords: alkanes ; mixtures ; thermal conductivity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract This paper reports new, absolute measurements of the thermal conductivity of liquid mixtures of n-heptane and isooctane in the pressure range 0.1 to 430 MPa for temperatures of 307.85 and 337.15 K. The results represent a preliminary investigation of the advantages of attempting to describe the isothermal composition dependence of the thermal conductivity of liquid mixtures along isochores, rather than isobars as has been traditional. However, no significant differences were found between the composition dependences in the two circumstances, possibly due to the lack of experimental data on the density of these mixtures. The availability of a theoretical description of the isochoric composition dependence suggests that this is the most appropriate description which reinforces the need for further high-pressure measurements of the thermal conductivity and density.
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  • 8
    Electronic Resource
    Electronic Resource
    Springer
    International journal of thermophysics 10 (1989), S. 1075-1084 
    ISSN: 1572-9567
    Keywords: aluminum nitride ; heat capacity ; substrate ; thermal conductivity ; thermal diffusivity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The thermal transport properties of four commercially available AlN substrates have been investigated using a combination of steady-state and transient techniques. Measurements of thermal conductivity using a guarded longitudinal heat flow apparatus are in good agreement with published room temperature data (in the range 130–170 W · m−1 · K−1). Laser flash diffusivity measurements combined with heat capacity data yielded anomalously low results. This was determined to be an experimental effect for which a method of correction is presented. Low-temperature measurements of thermal conductivity and heat capacity are used to probe the mechanisms that limit the thermal conductivity in AlN.
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  • 9
    Electronic Resource
    Electronic Resource
    Springer
    International journal of thermophysics 10 (1989), S. 1005-1011 
    ISSN: 1572-9567
    Keywords: benzene ; thermal conductivity ; toluene ; transient hot-wire method
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The thermal conductivity of liquid toluene and benzene was measured in the temperature range 298 to 370 K, near the saturation line, using an absolute transient hot-wire technique. The measurements were made in a modified version of an existing instrument, equipped with a new automatic Wheatstone bridge, computer controlled. The bridge measures the time that the resistance of a 7-μm-diameter platinum wire takes to reach predetermined values, programmed by the computer. The computer can generate up to 1024 analog voltages, via a 12-bit D/A converter. The accuracy of the measurements with this new arrangement was assessed by measuring the thermal conductivity of a primary standard, toluene, at several temperatures and was found to be of the order of 0.3%. Benzene was chosen because it is under study as a possible secondary standard for liquid thermal conductivity by the Subcommittee on Transport Properties of IUPAC.
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  • 10
    Electronic Resource
    Electronic Resource
    Springer
    International journal of thermophysics 10 (1989), S. 1053-1062 
    ISSN: 1572-9567
    Keywords: alumina ; composites ; glass ; porosity ; thermal conductivity ; thermal diffusivity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The thermal diffusivity of five groups of alumina/glass composite systems has been measured at room temperature using a laser flash system. These data have been used, in conjunction with specific heat and density measurements, to calculate the effective thermal conductivity of these composites. In each of the five groups a systematic variation in glass concentration was made, and each group represents systematic variations in glass and alumina particle sizes. The thermal conductivities calculated are compared with those predicted by four models. It is apparent from these comparisons that the geometry and orientation of porosity within the sample measured are a key factor in determining which of these models (if any) is appropriate for describing the thermal conductivity of these composites.
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