Journal: International journal of thermophysics

Abbreviation

Int. j. thermophys.

Publisher

Springer

Journal Volumes

ISSN

0195-928X
1572-9567

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2013 - 201952020 - 20231
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Publications 1 - 6 of 6
  • Open Quantum Systems Coupled to Time-Dependent Classical Environments
    Item type: Journal Article
    Osmanov, Maksym; Öttinger, Hans Christian (2013)
    International journal of thermophysics
  • Concentration-Dependent Diffusion Coefficients of Binary Gas Mixtures Using a Loschmidt Cell with Holographic Interferometry : Part II: Single Experiment
    Item type: Journal Article
    Wolff, Ludger Wolfgang Michael; Zangi, Pouria; Brands, Thorsten; et al. (2018)
    International journal of thermophysics
    A model-based experimental approach is presented to measure concentration-dependent diffusion coefficients of binary gases from a single experimental run. The diffusion experiments are performed with a Loschmidt cell combined with holographic interferometry that has been improved in Part I of this paper (Wolff et al. in Int. J. Thermophys. 2018, https://doi.org/10.1007/s10765-018-2450-8). Measurements are taken with the system helium–krypton. Besides highly accurate measurements, a highly accurate diffusion model is required to retrieve the weak concentration dependence of the diffusion coefficient. We derive a consistent diffusion model considering real gas effects and the concentration dependence of the diffusion coefficient. The model describes the experimental fringe data with deviations of less than 0.2 interference fringe orders, which corresponds to a relative deviation of 0.17 % indicating high quality of both the experimental data and the employed model. Therefore, the concentration dependence of the helium–krypton diffusion coefficient could be successfully retrieved from a single experiment of mixing pure gases. Thus, the presented approach allows for the efficient characterization of diffusion in gases. © 2018, Springer Science+Business Media, LLC, part of Springer Nature.
  • Concentration-Dependent Diffusion Coefficients of Binary Gas Mixtures Using a Loschmidt Cell with Holographic Interferometry
    Item type: Journal Article
    Wolff, Ludger Wolfgang Michael; Zangi, Pouria; Brands, Thorsten; et al. (2018)
    International journal of thermophysics
    An improved experimental setup and data evaluation procedure are presented for a Loschmidt cell combined with interferometry to measure concentration-dependent binary diffusion coefficients. We overcome long-standing discrepancies about the concentration dependence found in the literature. The systematic analysis of the residuals from parameter estimation enabled the improvement of the experimental setup and the identification of relevant fitting parameters. In particular, we found that it is crucial to account for uncertainties (1) in the initial conditions, (2) in the thermal stability of the optical setup, and (3) in camera calibration. The improved experimental setup and data evaluation procedure are validated with diffusion measurements of the system helium–krypton. The concentration dependence of the diffusion coefficient is successfully determined from multiple experiments with gas mixtures of various initial compositions in the half-cells of the Loschmidt cell. The agreement with literature data and the excellent quality of fit allow for high confidence in the results. In Part II of this paper (Wolff et al., in Int J Thermophys, 2018, https://doi.org/10.1007/s10765-018-2451-7), the improved measurement setup is combined with a refined diffusion model to determine concentration-dependent diffusion coefficients from single measurements of mixing pure gases. © 2018, Springer Science+Business Media, LLC, part of Springer Nature.
  • Uncertainty Analysis for Emissivity Measurement at Elevated Temperatures with an Infrared Camera
    Item type: Journal Article
    Höser, Dragana; Wallimann, Roger; Rudolf von Rohr, Philipp (2016)
    International journal of thermophysics
    The current work describes the measurement of emissivity of rock samples and black paint Pyromark 2500 within the temperature range between 230∘ C and 650∘ C together with its detailed uncertainty analysis. The infrared camera Optris PI450 was used to obtain the surface temperature of the samples. The described method is based on adjusting the emissivity of the rock sample until the temperature of the rock surface detected by the IR camera matches the temperature of a reference body. The reference body represented the tested rock sample partially coated with Pyromark 2500. The emissivity of the paint was previously determined with a technique described in this work: Pyromark 2500 was applied on a ceramic heater and heated up to a certain temperature that was calculated from measured electrical resistance of the ceramic heater (previously calibrated as a resistance thermometer). The emissivity measurement of rock samples is flexible concerning the type of sample, its size, position relative to the IR camera (distance, observation angle), and environmental conditions. Emissivities of Gotthard granite and Paradiso migmatite are reported, and they are in an agreement with emissivities of some granite samples from literature. The uncertainty of the rock sample emissivity reaches the value of 10% and the main contribution to it is related to the electrical resistance measurement of the ceramic heater.
  • Diffusion Coefficients from Molecular Dynamics Simulations in Binary and Ternary Mixtures
    Item type: Journal Article
    Liu, Xin; Schnell, Sondre K.; Simon, Jean-Marc; et al. (2013)
    International journal of thermophysics
    Multicomponent diffusion in liquids is ubiquitous in (bio)chemical processes. It has gained considerable and increasing interest as it is often the rate limiting step in a process. In this paper, we review methods for calculating diffusion coefficients from molecular simulation and predictive engineering models. The main achievements of our research during the past years can be summarized as follows: (1) we introduced a consistent method for computing Fick diffusion coefficients using equilibrium molecular dynamics simulations; (2) we developed a multicomponent Darken equation for the description of the concentration dependence of Maxwell–Stefan diffusivities. In the case of infinite dilution, the multicomponent Darken equation provides an expression for which can be used to parametrize the generalized Vignes equation; and (3) a predictive model for self-diffusivities was proposed for the parametrization of the multicomponent Darken equation. This equation accurately describes the concentration dependence of self-diffusivities in weakly associating systems. With these methods, a sound framework for the prediction of mutual diffusion in liquids is achieved.
  • Modeling Mixtures with PCP-SAFT: Insights from Large-Scale Parametrization and Group-Contribution Method for Binary Interaction Parameters
    Item type: Journal Article
    Rehner, Philipp; Bardow, André; Gross, Joachim (2023)
    International journal of thermophysics
    Vapor/liquid equilibria of mixtures are of utmost importance in the design of chemical processes. Because of the combinatorial complexity of mixtures, the available experimental data are small when considering the large molecular space. To fill this knowledge gap, molecular equations of state like PCP-SAFT show promise due to their explicit consideration of intermolecular interactions that can be transferred to mixtures. In this work, we comprehensively assess and exploit PCP-SAFT for modeling phase equilibria of mixtures. First, we provide binary interaction parameters for 7861 binary systems for which pure-component parameters and experimental data are available. Bubble and dew point pressures are described with a median deviation of 2.3 %. Secondly, we adjust a matrix of binary group/group interaction parameters for the homosegmented and heterosegmented group-contribution (GC) methods for PCP-SAFT. Among 1389 mixtures that can be described with the GC methods, the median deviation in bubble and dew point pressures are 6.4 % for the homosegmented approach and 5.1 % for the heterosegmented approach. The detailed analysis shows the importance of hydrogen bonds in mixtures of non-self-associating components with self-associating components. The parametrization is only possible by introducing a fast numerical method to calculate the derivative of bubble and dew point pressures with respect to arbitrarily many model parameters. The approach leverages reverse mode automatic differentiation (backpropagation), the same method used in machine learning to regress millions of model parameters to large datasets.
Publications 1 - 6 of 6