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  • 1
    Language: English
    In: International Journal of Thermophysics, 2012, Vol.33(5), pp.741-757
    Description: An all-quartz oscillating-disk viscometer of very high precision was used to determine the temperature dependence of the viscosities of carbon monoxide and nitrogen at low densities. The measurements were based on a single calibration at room temperature with a value theoretically calculated on the basis of an accurate ab initio pair potential for helium and the kinetic theory of dilute monatomic gases. The uncertainty of the experimental data is conservatively estimated to be ±0.15% at room temperature increasing to ±0.20% at the highest temperature of 682 K. The new data are compared with values recommended by the National Institute of Standards and Technology in the framework of its Standard Reference Data Program REFPROP as well as with experimental data from the literature. Whereas the REFPROP values for nitrogen can be considered as reference values, the new experimental data for carbon monoxide are up to 2% higher than the REFPROP values and should be taken into consideration for a new correlation. The temperature dependence of the viscosities calculated theoretically using ab initio intermolecular potential energy hypersurfaces for carbon monoxide and nitrogen and the kinetic theory of dilute molecular gases should be used for extrapolating the viscosity correlations of both gases to low and high temperatures. In addition, the viscosity ratio of carbon monoxide to nitrogen is investigated with the purpose to establish an improved correlation for carbon monoxide.
    Keywords: Carbon monoxide ; Measurement ; Nitrogen ; Oscillating-disk viscometer ; Reference values ; Viscosity
    ISSN: 0195-928X
    E-ISSN: 1572-9567
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  • 2
    In: Physical Chemistry Chemical Physics, 2011, Vol.13(30), pp.13749-13758
    Description: A six-dimensional potential energy hypersurface (PES) for two interacting rigid hydrogen sulfide molecules was determined from high-level quantum-mechanical ab initio computations. A total of 4016 points for 405 different angular orientations of two molecules were calculated utilizing the counterpoise-corrected supermolecular approach at the CCSD(T) level of theory and extrapolating the calculated interaction energies to the complete basis set limit. An analytical site–site potential function with eleven sites per hydrogen sulfide molecule was fitted to the interaction energies. The PES has been validated by computing the second pressure virial coefficient, shear viscosity, thermal conductivity and comparing with the available experimental data. The calculated values of volume viscosity were not used to validate the potential as the low accuracy of the available data precluded such an approach. The second pressure virial coefficient was evaluated by means of the Takahashi and Imada approach, while the transport properties, in the dilute limit, were evaluated by utilizing the classical trajectory method. In general, the agreement with the primary experimental data is within the experimental error for temperatures higher than 300 K. For lower temperatures the lack of reliable data indicates that the values of the second pressure virial coefficient and of the transport properties calculated in this work are currently the most accurate estimates for the thermophysical properties of hydrogen sulfide.
    ISSN: 1463-9076
    E-ISSN: 1463-9084
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  • 3
    Language: English
    In: The Journal of Chemical Physics, 14 December 2014, Vol.141(22)
    Description: A five-dimensional potential energy surface (PES) for the interaction of a rigid methane molecule with a rigid nitrogen molecule was determined from quantum-chemical ab initio calculations. The counterpoise-corrected supermolecular approach at the CCSD(T) level of theory was utilized to compute a total of 743 points on the PES. The interaction energies were calculated using basis sets of up to quadruple-zeta quality with bond functions and were extrapolated to the complete basis set limit. An analytical site-site potential function with nine sites for methane and five sites for nitrogen was fitted to the interaction energies. The PES was validated by calculating the cross second virial coefficient as well as the shear viscosity and binary diffusion coefficient in the dilute-gas limit for CH 4 –N 2 mixtures. An improved PES was obtained by adjusting a single parameter of the analytical potential function in such a way that quantitative agreement with the most accurate experimental values of the cross second virial coefficient was achieved. The transport property values obtained with the adjusted PES are in good agreement with the best experimental data.
    Keywords: Articles
    ISSN: 0021-9606
    E-ISSN: 1089-7690
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  • 4
    Language: English
    In: International Journal of Thermophysics, 2016, Vol.37(6), pp.1-20
    Description: Previously reported, but also unpublished experimental data of our group for the viscosities of dilute krypton, xenon, and carbon dioxide, obtained in the range from 295 K to a maximum of 690 K using oscillating-disk viscometers, were re-evaluated and corrected or extrapolated to the limit of zero density ( $$\eta _0$$ η 0 ). The combined standard uncertainty of the data is 0.1 % at room temperature and 0.2 % at higher temperatures. For krypton and carbon dioxide, our $$\eta _0$$ η 0 data were compared with $$\eta _0$$ η 0 values theoretically calculated using the kinetic theory and highly accurate ab initio potentials for the krypton atom pair and the CO $$_2$$ 2 molecule pair, but also with recent experimental $$\eta _0$$ η 0 data from the literature. Our data for krypton differ up to 690 K from the theoretical values by $$-0.10\,\%$$ - 0.10 % to $$+0.28\,\%$$ + 0.28 % , whereas that of Lin et al. (Fluid Phase Equilib. 418:198, 2016) show deviations of +(0.04 to 0.20) % at temperatures from 243 K to 393 K, in each case proving that experiment and theory are in consistent agreement. The re-evaluated $$\eta _0$$ η 0 data for xenon were compared with recent data from the literature and with calculated values resulting from the HFD-B potential for xenon via the corresponding-states principle to verify that they are reference values. For carbon dioxide, $$\eta _0$$ η 0 values obtained from 26 re-evaluated isotherms and from eight isotherms of Schäfer et al. (J Chem Thermodyn 89:7, 2015) between 253 K and 473 K are mutually consistent with ab initio calculated and subsequently scaled viscosity values of Hellmann (Chem Phys Lett 613:633, 2014). The isotherms of Schäfer et al. are especially suitable for determining the initial density dependence of the viscosity. Concomitantly inferred reduced second viscosity virial coefficients were checked against two theoretical approaches of the Rainwater–Friend theory.
    Keywords: Carbon dioxide ; Dilute gas ; Krypton ; Reference data ; Viscosity ; Xenon ; Zero-density limit
    ISSN: 0195-928X
    E-ISSN: 1572-9567
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  • 5
    Language: English
    In: The Journal of chemical physics, 28 August 2011, Vol.135(8), pp.084308
    Description: An ab initio nonadditive three-body potential for argon has been developed using quantum-chemical calculations at the CCSD(T) and CCSDT levels of theory. Applying this potential together with a recent ab initio pair potential from the literature, the third and fourth to seventh pressure virial coefficients of argon were computed by standard numerical integration and the Mayer-sampling Monte Carlo method, respectively, for a wide temperature range. All calculated virial coefficients were fitted separately as polynomials in temperature. The results for the third virial coefficient agree with values evaluated directly from experimental data and with those computed for other nonadditive three-body potentials. We also redetermined the second and third virial coefficients from the best experimental pρT data utilizing the computed higher virial coefficients as constraints. Thus, a significantly closer agreement of the calculated third virial coefficients with the experimental data was achieved. For different orders of the virial expansion, pρT data have been calculated and compared with results from high quality measurements in the gaseous and supercritical region. The theoretically predicted pressures are within the very small experimental errors of ±0.02% for p ≤ 12 MPa in the supercritical region near room temperature, whereas for subcritical temperatures the deviations increase up to +0.3%. The computed pressure at the critical density and temperature is about 1.3% below the experimental value. At pressures between 200 MPa and 1000 MPa and at 373 K, the calculated values deviate by 1% to 9% from the experimental results.
    Keywords: Articles;
    ISSN: 00219606
    E-ISSN: 1089-7690
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  • 6
    Language: English
    In: The Journal of Chemical Physics, 21 March 2016, Vol.144(11)
    Description: A new reference krypton-krypton interatomic potential energy curve was developed by means of quantum-chemical ab initio calculations for 36 interatomic separations. Highly accurate values for the interaction energies at the complete basis set limit were obtained using the coupled-cluster method with single, double, and perturbative triple excitations as well as t-aug-cc-pV5Z and t-aug-cc-pV6Z basis sets including mid-bond functions, with the 6Z basis set being newly constructed for this study. Higher orders of coupled-cluster terms were considered in a successive scheme up to full quadruple excitations. Core-core and core-valence correlation effects were included. Furthermore, relativistic effects were studied not only at a scalar relativistic level using second-order direct perturbation theory, but also utilizing full four-component and Gaunt-effect computations. An analytical pair potential function was fitted to the interaction energies, which is characterized by a depth of 200.88 K with an estimated standard uncertainty of 0.51 K. Thermophysical properties of low-density krypton were calculated for temperatures up to 5000 K. Second and third virial coefficients were obtained from statistical thermodynamics. Viscosity and thermal conductivity as well as the self-diffusion coefficient were computed using the kinetic theory of gases. The theoretical results are compared with experimental data and with results for other pair potential functions from the literature, especially with those calculated from the recently developed ab initio potential of Waldrop et al. [J. Chem. Phys. 142 , 204307 (2015)]. Highly accurate experimental viscosity data indicate that both the present ab initio pair potential and the one of Waldrop et al. can be regarded as reference potentials, even though the quantum-chemical methods and basis sets differ. However, the uncertainties of the present potential and of the derived properties are estimated to be considerably lower.
    Keywords: Articles
    ISSN: 0021-9606
    E-ISSN: 1089-7690
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  • 7
    Language: English
    In: Journal of Chemical & Engineering Data, 07/14/2011, Vol.56(7), pp.3265-3272
    Description: An all-quartz oscillating disk viscometer of very high precision was used to measure the temperature dependence of the viscosities of methane and hydrogen sulfide at low densities. The measurements were based on a single calibration at room temperature with a value theoretically calculated using an accurate ab initio pair potential for helium and the kinetic theory of dilute monatomic gases. The uncertainty of the experimental data is conservatively estimated to be ±0.15 % at room temperature increasing to ±0.20 % at the highest temperature of 682 K. The new data are compared with experimental data from the literature as well as with values obtained from the Quinones-Cisneros correlation for methane (2010) and the Schmidt correlation for hydrogen sulfide (2008) both implemented in the REFPROP computer program of the National Institute of Standards and Technology (NIST). The comparison shows, that the low-density values of the Quiniones-Cisneros correlation for methane, primarily based on measurements in the range from (211 to 392) K performed at NIST in 2007, can be considered as reference values. On the contrary, the new experimental data for hydrogen sulfide are (2 to 6) % lower than the low-density values of the Schmidt correlation and should be taken into account for an improvement of the viscosity correlation for hydrogen sulphide. Furthermore, the temperature dependence of the viscosities calculated theoretically using ab initio intermolecular potential energy hypersurfaces for methane and hydrogen sulfide and the extended kinetic theory of dilute molecular gases should be used to extrapolate the viscosity correlations to low and high temperatures.
    Keywords: Hydrogen-Sulfide ; Methane ; Experimental-Data ; Kinetic-Theory ; Computer-Program ; Temperature-Influence ; Rheometers ; Normalised-Value ; Potential-Energy ; Density ; Viscosity ; Schwefelwasserstoff ; Methan ; Experimentelle Daten ; Kinetische Theorie ; Computer-Programm ; Temperaturabhängigkeit ; Viskometer ; Bezugswert ; Potenzielle Energie ; Dichte ; Viskosität ; Engineering ; Chemistry;
    ISSN: 0021-9568
    E-ISSN: 1520-5134
    Source: American Chemical Society (via CrossRef)
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  • 8
    Language: English
    In: Journal of Physical and Chemical Reference Data, December 2018, Vol.47(4)
    Description: A new viscosity formulation for isobutane, valid in the fluid region from the triple point to 650 K and to 100 MPa, is presented. It employs the reference equation of state by Bücker and Wagner [J. Phys. Chem. Ref. Data 35 , 929 (2006)] and uses the residual quantity concept, in which the contributions for the zero-density viscosity and for the initial-density dependence were separately generated, while those for the critical enhancement and for the higher-density terms were pretreated. The contributions are formulated as a function of the reciprocal reduced temperature τ and the reduced density δ . The primary datasets used when developing the individual contributions were carefully evaluated. The final formulation includes 16 coefficients fitted with a state-of-the-art linear optimization algorithm. The expanded uncertainty (coverage factor k = 2) is estimated to be 0.5% at low pressures p ≤ 0.2 MPa and at temperatures 298 ≤ T ∕K ≤ 627. In the vapor phase at subcritical temperatures T ≥ 298 K as well as in the supercritical region T ≤ 498 K at pressures p ≤ 30 MPa, the expanded uncertainty is given as 1.5%. It is increased to 4.0% and 6.0%, respectively, in regions where less reliable primary data exist. Moreover, it is assumed to amount to 6.0% in ranges in which primary viscosity datasets are not available, but the equation of state is valid. In the near-critical region, a value of the expanded uncertainty was not given because of a weakness of the reference equation of state and due to a possibly too small result for the critical enhancement of the viscosity experimentally found. Viscosity tables for the new formulation are given for the single-phase region, for the vapor-liquid phase boundary, and for the near-critical region.
    Keywords: Regular Articles
    ISSN: 0047-2689
    E-ISSN: 1529-7845
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  • 9
    Article
    Article
    Oldenbourg Wissenschaftsverlag GmbH
    In: Zeitschrift für Physikalische Chemie, 2013, Vol.227(2), 2013, Vol.227(2), pp.315-332
    Description: Results of new relative measurements on the vapor of acetic acid are reported. The measurements were based on a single calibration at room temperature with a theoretically calculated viscosity value of argon. Nineteen isochoric series, differing in density, were performed in an all-quartz oscillating-disk viscometer from 298 to 598 K and for densities between 0.5 and 61 mol m -3 . The uncertainty of the experimental data is ±0.5% at low densities and ±(0.3−0.4)% at high densities increasing with temperature. This is inferior compared with measurements on simple gases due to adsorption effects on quartz at low temperatures and to thermal decomposition at high temperatures. Isotherms recalculated from the original isochoric data show with decreasing density a strong curvature with negative slope, particularly at low temperatures. The further evaluation accounts for the fact that a strong dimerization depending on temperature occurs in acetic acid vapor. The isotherms, resulting from an association model which considers additional interactions between monomers and dimers, show a smaller curvature in terms of the mole fraction of monomers. Viscosity values for monomers and dimers were deduced using a simplified equation for the viscosity of a gas mixture. These values are restricted to 570 K due to thermal decomposition and low mole fractions of the dimers at high temperature. Furthermore, viscosity values for the saturated vapor could be determined at low temperatures.
    Keywords: Acetic Acid Vapor ; Dimerization ; Measurement ; Viscosity Coefficient
    ISSN: 0942-9352
    E-ISSN: 21967156
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  • 10
    Language: English
    In: Journal of Chemical & Engineering Data, 04/14/2011, Vol.56(4), pp.1730-1737
    ISSN: 0021-9568
    E-ISSN: 1520-5134
    Source: American Chemical Society (via CrossRef)
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