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  • 1
    Online Resource
    Online Resource
    Springer Science and Business Media LLC ; 2019
    In:  Scientific Reports Vol. 9, No. 1 ( 2019-06-11)
    In: Scientific Reports, Springer Science and Business Media LLC, Vol. 9, No. 1 ( 2019-06-11)
    Abstract: Diffusion of methane diluted in supercritical carbon dioxide is studied by experiment and molecular simulation in the temperature range from 292.55 to 332.85 K along the isobars 9.0, 12.5 and 14.7 MPa. Measurements of the Fick diffusion coefficient are carried out with the Taylor dispersion technique. Molecular dynamics simulation and the Green-Kubo formalism are employed to obtain Fick, Maxwell-Stefan and intradiffusion coefficients as well as shear viscosity. The obtained diffusion coefficients are on the order of 10 −8 m 2 /s. The composition, temperature and density dependence of diffusion is analyzed. The Fick diffusion coefficient of methane in carbon dioxide shows an anomaly in the near-critical region. This behavior can be attributed to the crossing of the so-called Widom line, where the supercritical fluid goes through a transition between liquid-like and gas-like states. Further, several classical equations are tested on their ability to predict this behavior and it is found that equations that explicitly include the density are better suited to predict the sharp variation of the diffusion coefficient near the critical region predicted by molecular simulation.
    Type of Medium: Online Resource
    ISSN: 2045-2322
    Language: English
    Publisher: Springer Science and Business Media LLC
    Publication Date: 2019
    detail.hit.zdb_id: 2615211-3
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  • 2
    Online Resource
    Online Resource
    Springer Science and Business Media LLC ; 2023
    In:  International Journal of Thermophysics Vol. 44, No. 7 ( 2023-07)
    In: International Journal of Thermophysics, Springer Science and Business Media LLC, Vol. 44, No. 7 ( 2023-07)
    Abstract: A multitude of industries, including energy and process engineering, as well as academia are researching and utilizing new fluid substances to further the aim of sustainability. Knowledge of the thermodynamic properties of these substances is a prerequisite, if they are to be utilized to their fullest potential. To date, the way to acquire reliable knowledge of the thermodynamic behavior is through measurements. The ensuing experimental data are then used to develop equations of state, which efficiently embody the gained knowledge of the behavior of the fluid substance, allow for interpolation and, to some extent, extrapolation. However, the acquisition of low-uncertainty experimental data, and thus the development of accurate equations of state, is often time-consuming and expensive. For substances for which suitable force field models exist, molecular modeling and simulation are well-suited to generate thermodynamic data or to augment experimental data, however, at the expense of larger uncertainties. The major goal of this work is to present a new approach for the development of equations of state using (1) symbolic regression, which is a machine learning based model development approach, (2) optimal experimental design, and (3) efficient data acquisition. We demonstrate this approach using the example of density data of an air-like binary mixture ( $$0.2094\,\hbox {O}_{2}\,+\,0.7906\,\hbox {N}_{2}$$ 0.2094 O 2 + 0.7906 N 2 ) over the temperature range from $${100}\,{\textrm{K}}$$ 100 K to $${300}\,{\textrm{K}}$$ 300 K at pressures of up to $${8}\,{\textrm{MPa}}$$ 8 MPa , which covers the gaseous, liquid, and supercritical regions. For this purpose, an experimental data set published by von Preetzmann et al. (Int. J. Thermophys. 42, 2021) and molecular simulation data sampled in this work are used. The two data sets are compared in terms of acquisition time, cost, and uncertainty, showing that an optimized combination of experimental and simulation data leads to lower cost while maintaining low uncertainties.
    Type of Medium: Online Resource
    ISSN: 0195-928X , 1572-9567
    Language: English
    Publisher: Springer Science and Business Media LLC
    Publication Date: 2023
    detail.hit.zdb_id: 2016169-4
    detail.hit.zdb_id: 764389-5
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  • 3
    Online Resource
    Online Resource
    Springer Science and Business Media LLC ; 2022
    In:  International Journal of Thermophysics Vol. 43, No. 1 ( 2022-01)
    In: International Journal of Thermophysics, Springer Science and Business Media LLC, Vol. 43, No. 1 ( 2022-01)
    Abstract: The homogeneous density of the liquid phase is experimentally investigated for methyl diethanolamine. Data are obtained along five isotherms in a temperature range between 300 K and 360 K for pressures up to 95 MPa. Two different apparatuses are used to measure the speed of sound for the temperatures between 322 K and 450 K with a maximum pressure of 95 MPa. These measurements and literature data are used to develop a fundamental equation of state for methyl diethanolamine. The model is formulated in terms of the Helmholtz energy and allows for the calculation of all thermodynamic properties in gaseous, liquid, supercritical, and saturation states. The experimental data are represented within their uncertainties. The physical and extrapolation behavior is validated qualitatively to ensure reasonable calculations outside of the range of validity. Based on the experimental datasets, the equation of state is valid for temperatures from 250 K to 750 K and pressures up to 100 MPa.
    Type of Medium: Online Resource
    ISSN: 0195-928X , 1572-9567
    Language: English
    Publisher: Springer Science and Business Media LLC
    Publication Date: 2022
    detail.hit.zdb_id: 2016169-4
    detail.hit.zdb_id: 764389-5
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  • 4
    Online Resource
    Online Resource
    Springer Science and Business Media LLC ; 2023
    In:  Scientific Reports Vol. 13, No. 1 ( 2023-09-26)
    In: Scientific Reports, Springer Science and Business Media LLC, Vol. 13, No. 1 ( 2023-09-26)
    Abstract: Mutual diffusion of six hydrocarbons (methane, ethane, isobutane, benzene, toluene or naphthalene) diluted in supercritical carbon dioxide ( $${\hbox {CO}}_{2}$$ CO 2 ) is studied by molecular dynamics simulation near the Widom line, i.e., in the temperature range from 290 to 345 K along the isobar 9 MPa. The $${\hbox {CO}}_{2}$$ CO 2  + aromatics mixtures are additionally sampled at 10 and 12 MPa and an experimental database with Fick diffusion coefficient data for those systems is provided. Taylor dispersion experiments of $${\hbox {CO}}_{2}$$ CO 2 with benzene, toluene, n-dodecane and 1,2,3,4-tetrahydronaphthalene are conducted along the $$p =$$ p =  10 MPa isobar. Maxwell–Stefan and Fick diffusion coefficients are analyzed, together with the thermodynamic factor that relates them. It is found that the peculiar behavior of the Fick diffusion coefficient of some $${\hbox {CO}}_{2}$$ CO 2 mixtures in the extended critical region is a consequence of the thermodynamic factor minimum due to pronounced clustering on the molecular scale. Further, the strong dependence of the Fick diffusion coefficient on the molecular mass of the solute as well as the breakdown of the Stokes–Einstein relation near the Widom line are confirmed. Eleven correlations for the prediction of the Fick diffusion coefficient of $${\hbox {CO}}_{2}$$ CO 2 mixtures are assessed. An alternative two-step approach for the prediction of the infinite dilution Fick diffusion coefficient of supercritical $${\hbox {CO}}_{2}$$ CO 2 mixtures is proposed. It requires only the state point in terms of temperature and pressure (or density) as well as the molecular solute mass as input parameters. First, entropy scaling is applied to estimate the self-diffusion coefficient of $${\hbox {CO}}_{2}$$ CO 2 . Subsequently, this coefficient is used to determine the infinite dilution Fick diffusion coefficient of the mixture, based on the finding that these two diffusion coefficients exhibit a linear relationship, where the slope depends only on the molecular solute mass.
    Type of Medium: Online Resource
    ISSN: 2045-2322
    Language: English
    Publisher: Springer Science and Business Media LLC
    Publication Date: 2023
    detail.hit.zdb_id: 2615211-3
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  • 5
    Online Resource
    Online Resource
    Springer Science and Business Media LLC ; 2023
    In:  Journal of Thermal Analysis and Calorimetry Vol. 148, No. 12 ( 2023-06), p. 5687-5694
    In: Journal of Thermal Analysis and Calorimetry, Springer Science and Business Media LLC, Vol. 148, No. 12 ( 2023-06), p. 5687-5694
    Abstract: The technical importance of paraffins as phase change materials (PCM) in heat storage systems increases. Knowledge on the thermal conductivity of paraffins is necessary for the design and optimization of heat storage systems. However, for most paraffins solely the thermal conductivity of the liquid state has been sufficiently investigated. For the solid state, precise thermal conductivity data are only known for a few paraffins, while only generalized values are available for the remainder, some of which contradict each other. In this study, a measurement setup based on the modified guarded hot plate method is developed. It is used to investigate the thermal conductivity of several paraffines in the solid state, including pure n-docosane and its compounds with different types and concentrations of graphite. For n-docosane in the solid state, the thermal conductivity is determined to be 0.49 W m −1 K −1 . A particle size of 200 μm with a spherical shape turns out to be optimal to increase the thermal conductivity. This allows the thermal conductivity of a compound with 10% graphite to increase by a factor of three compared to the pure paraffin. Furthermore, significant differences to thermal conductivity data from the literature are found.
    Type of Medium: Online Resource
    ISSN: 1388-6150 , 1588-2926
    Language: English
    Publisher: Springer Science and Business Media LLC
    Publication Date: 2023
    detail.hit.zdb_id: 2017304-0
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  • 6
    Online Resource
    Online Resource
    Springer Science and Business Media LLC ; 2012
    In:  International Journal of Thermophysics Vol. 33, No. 3 ( 2012-3), p. 449-468
    In: International Journal of Thermophysics, Springer Science and Business Media LLC, Vol. 33, No. 3 ( 2012-3), p. 449-468
    Type of Medium: Online Resource
    ISSN: 0195-928X , 1572-9567
    Language: English
    Publisher: Springer Science and Business Media LLC
    Publication Date: 2012
    detail.hit.zdb_id: 2016169-4
    detail.hit.zdb_id: 764389-5
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  • 7
    Online Resource
    Online Resource
    Springer Science and Business Media LLC ; 2009
    In:  International Journal of Thermophysics Vol. 30, No. 6 ( 2009-12), p. 1791-1810
    In: International Journal of Thermophysics, Springer Science and Business Media LLC, Vol. 30, No. 6 ( 2009-12), p. 1791-1810
    Type of Medium: Online Resource
    ISSN: 0195-928X , 1572-9567
    Language: English
    Publisher: Springer Science and Business Media LLC
    Publication Date: 2009
    detail.hit.zdb_id: 2016169-4
    detail.hit.zdb_id: 764389-5
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  • 8
    Online Resource
    Online Resource
    Springer Science and Business Media LLC ; 2015
    In:  International Journal of Thermophysics Vol. 36, No. 1 ( 2015-1), p. 25-43
    In: International Journal of Thermophysics, Springer Science and Business Media LLC, Vol. 36, No. 1 ( 2015-1), p. 25-43
    Type of Medium: Online Resource
    ISSN: 0195-928X , 1572-9567
    Language: English
    Publisher: Springer Science and Business Media LLC
    Publication Date: 2015
    detail.hit.zdb_id: 2016169-4
    detail.hit.zdb_id: 764389-5
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  • 9
    Online Resource
    Online Resource
    Springer Science and Business Media LLC ; 2021
    In:  Scientific Reports Vol. 11, No. 1 ( 2021-06-10)
    In: Scientific Reports, Springer Science and Business Media LLC, Vol. 11, No. 1 ( 2021-06-10)
    Abstract: The Fick diffusion coefficient matrix of the highly associating quaternary mixture water + methanol + ethanol + 2-propanol as well as its ternary and binary subsystems is analyzed with molecular dynamics simulation techniques. Three of the ternary subsystems are studied in this sense for the first time. The predictive capability of the employed force fields, which were sampled with the Green–Kubo formalism and Kirkwood–Buff integration, is confirmed by comparison with experimental literature data on vapor-liquid equilibrium, shear viscosity and Fick diffusion coefficient, wherever possible. A thorough analysis of the finite size effects on the simulative calculation of diffusion coefficients of multicomponent systems is carried out. Moreover, the dependence of the Fick diffusion coefficient matrix on the velocity reference frame and component order is analyzed. Their influence is found to be less significant for the main matrix elements, reaching a maximum variation of 19%. The large differences found for the cross elements upon variation of the reference frame hinder a straightforward interpretation of the Fick diffusion coefficient matrix with respect to the presence of diffusive coupling effects.
    Type of Medium: Online Resource
    ISSN: 2045-2322
    Language: English
    Publisher: Springer Science and Business Media LLC
    Publication Date: 2021
    detail.hit.zdb_id: 2615211-3
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