The Experts below are selected from a list of 285 Experts worldwide ranked by ideXlab platform
Olaf Kolditz - One of the best experts on this subject based on the ideXlab platform.
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Assessment of adsorbate density models for numerical simulations of zeolite-based heat storage applications
Applied Energy, 2017Co-Authors: Christoph Lehmann, Olaf Kolditz, Steffen Beckert, Roger Gläser, Thomas NagelAbstract:The study of water sorption in microporous materials is of increasing interest, particularly in the context of heat storage applications. The potential-theory of micropore volume filling pioneered by Polanyi and Dubinin is a useful tool for the description of adsorption equilibria. Based on one single characteristic curve, the system can be extensively characterised in terms of isotherms, isobars, isosteres, enthalpies etc. However, the mathematical description of the adsorbate density’s temperature dependence has a significant impact especially on the estimation of the energetically relevant adsorption enthalpies. Here, we evaluate and compare different models existing in the literature and elucidate those leading to realistic predictions of adsorption enthalpies. This is an important prerequisite for accurate simulations of heat and mass transport ranging from the laboratory scale to the Reactor Level of the heat store.
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The Impact of Adsorbate Density Models on the Simulation of Water Sorption on Nanoporous Materials for Heat Storage
Energy Procedia, 2015Co-Authors: Thomas Nagel, Steffen Beckert, Roger Gläser, Norbert Böttcher, Olaf KolditzAbstract:Abstract The study of water sorption in microporous materials is of increasing interest, particularly in the context of heat storage applications. The potential-theory of micropore volume filling pioneered by Polanyi and Dubinin is a very useful tool for the description of adsorption equilibria. Based on one single characteristic curve, the system can be extensively characterised in terms of isotherms, isobars, isosteres, enthalpies etc. However, the mathematical description of the adsorbate density's temperature dependence has a significant impact especially on the estimation of the energetically relevant adsorption enthalpies. Here, we evaluate and compare different models existing in the literature and elucidate those leading to realistic predictions of adsorption enthalpies. This is an important prerequisite for accurate simulations of heat and mass transport ranging from the laboratory scale right up to the Reactor Level of the heat store.
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the influence of gas solid reaction kinetics in models of thermochemical heat storage under monotonic and cyclic loading
Applied Energy, 2014Co-Authors: Thomas Nagel, Haibing Shao, Christian Roskopf, Marc Linder, Antje Worner, Olaf KolditzAbstract:Thermochemical reactions can be employed in heat storage devices. The choice of suitable reactive material pairs involves a thorough kinetic characterisation by, e.g., extensive thermogravimetric measurements. Before testing a material on a Reactor Level, simulations with models based on the Theory of Porous Media can be used to establish its suitability. The extent to which the accuracy of the kinetic model influences the results of such simulations is unknown yet fundamental to the validity of simulations based on chemical models of differing complexity. In this article we therefore compared simulation results on the Reactor Level based on an advanced kinetic characterisation of a calcium oxide/hydroxide system to those obtained by a simplified kinetic model. Since energy storage is often used for short term load buffering, the internal Reactor behaviour is analysed under cyclic partial loading and unloading in addition to full monotonic charge/discharge operation. It was found that the predictions by both models were very similar qualitatively and quantitatively in terms of thermal power characteristics, conversion profiles, temperature output, reaction duration and pumping powers. Major differences were, however, observed for the reaction rate profiles themselves. We conclude that for systems not limited by kinetics the simplified model seems sufficient to estimate the Reactor behaviour. The degree of material usage within the Reactor was further shown to strongly vary under cyclic loading conditions and should be considered when designing systems for certain operating regimes.
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The influence of gas–solid reaction kinetics in models of thermochemical heat storage under monotonic and cyclic loading
Applied Energy, 2014Co-Authors: Thomas Nagel, Haibing Shao, Marc Linder, Antje Worner, Christian Roßkopf, Olaf KolditzAbstract:Abstract Thermochemical reactions can be employed in heat storage devices. The choice of suitable reactive material pairs involves a thorough kinetic characterisation by, e.g., extensive thermogravimetric measurements. Before testing a material on a Reactor Level, simulations with models based on the Theory of Porous Media can be used to establish its suitability. The extent to which the accuracy of the kinetic model influences the results of such simulations is unknown yet fundamental to the validity of simulations based on chemical models of differing complexity. In this article we therefore compared simulation results on the Reactor Level based on an advanced kinetic characterisation of a calcium oxide/hydroxide system to those obtained by a simplified kinetic model. Since energy storage is often used for short term load buffering, the internal Reactor behaviour is analysed under cyclic partial loading and unloading in addition to full monotonic charge/discharge operation. It was found that the predictions by both models were very similar qualitatively and quantitatively in terms of thermal power characteristics, conversion profiles, temperature output, reaction duration and pumping powers. Major differences were, however, observed for the reaction rate profiles themselves. We conclude that for systems not limited by kinetics the simplified model seems sufficient to estimate the Reactor behaviour. The degree of material usage within the Reactor was further shown to strongly vary under cyclic loading conditions and should be considered when designing systems for certain operating regimes.
Thomas Nagel - One of the best experts on this subject based on the ideXlab platform.
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Assessment of adsorbate density models for numerical simulations of zeolite-based heat storage applications
Applied Energy, 2017Co-Authors: Christoph Lehmann, Olaf Kolditz, Steffen Beckert, Roger Gläser, Thomas NagelAbstract:The study of water sorption in microporous materials is of increasing interest, particularly in the context of heat storage applications. The potential-theory of micropore volume filling pioneered by Polanyi and Dubinin is a useful tool for the description of adsorption equilibria. Based on one single characteristic curve, the system can be extensively characterised in terms of isotherms, isobars, isosteres, enthalpies etc. However, the mathematical description of the adsorbate density’s temperature dependence has a significant impact especially on the estimation of the energetically relevant adsorption enthalpies. Here, we evaluate and compare different models existing in the literature and elucidate those leading to realistic predictions of adsorption enthalpies. This is an important prerequisite for accurate simulations of heat and mass transport ranging from the laboratory scale to the Reactor Level of the heat store.
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The Impact of Adsorbate Density Models on the Simulation of Water Sorption on Nanoporous Materials for Heat Storage
Energy Procedia, 2015Co-Authors: Thomas Nagel, Steffen Beckert, Roger Gläser, Norbert Böttcher, Olaf KolditzAbstract:Abstract The study of water sorption in microporous materials is of increasing interest, particularly in the context of heat storage applications. The potential-theory of micropore volume filling pioneered by Polanyi and Dubinin is a very useful tool for the description of adsorption equilibria. Based on one single characteristic curve, the system can be extensively characterised in terms of isotherms, isobars, isosteres, enthalpies etc. However, the mathematical description of the adsorbate density's temperature dependence has a significant impact especially on the estimation of the energetically relevant adsorption enthalpies. Here, we evaluate and compare different models existing in the literature and elucidate those leading to realistic predictions of adsorption enthalpies. This is an important prerequisite for accurate simulations of heat and mass transport ranging from the laboratory scale right up to the Reactor Level of the heat store.
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the influence of gas solid reaction kinetics in models of thermochemical heat storage under monotonic and cyclic loading
Applied Energy, 2014Co-Authors: Thomas Nagel, Haibing Shao, Christian Roskopf, Marc Linder, Antje Worner, Olaf KolditzAbstract:Thermochemical reactions can be employed in heat storage devices. The choice of suitable reactive material pairs involves a thorough kinetic characterisation by, e.g., extensive thermogravimetric measurements. Before testing a material on a Reactor Level, simulations with models based on the Theory of Porous Media can be used to establish its suitability. The extent to which the accuracy of the kinetic model influences the results of such simulations is unknown yet fundamental to the validity of simulations based on chemical models of differing complexity. In this article we therefore compared simulation results on the Reactor Level based on an advanced kinetic characterisation of a calcium oxide/hydroxide system to those obtained by a simplified kinetic model. Since energy storage is often used for short term load buffering, the internal Reactor behaviour is analysed under cyclic partial loading and unloading in addition to full monotonic charge/discharge operation. It was found that the predictions by both models were very similar qualitatively and quantitatively in terms of thermal power characteristics, conversion profiles, temperature output, reaction duration and pumping powers. Major differences were, however, observed for the reaction rate profiles themselves. We conclude that for systems not limited by kinetics the simplified model seems sufficient to estimate the Reactor behaviour. The degree of material usage within the Reactor was further shown to strongly vary under cyclic loading conditions and should be considered when designing systems for certain operating regimes.
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The influence of gas–solid reaction kinetics in models of thermochemical heat storage under monotonic and cyclic loading
Applied Energy, 2014Co-Authors: Thomas Nagel, Haibing Shao, Marc Linder, Antje Worner, Christian Roßkopf, Olaf KolditzAbstract:Abstract Thermochemical reactions can be employed in heat storage devices. The choice of suitable reactive material pairs involves a thorough kinetic characterisation by, e.g., extensive thermogravimetric measurements. Before testing a material on a Reactor Level, simulations with models based on the Theory of Porous Media can be used to establish its suitability. The extent to which the accuracy of the kinetic model influences the results of such simulations is unknown yet fundamental to the validity of simulations based on chemical models of differing complexity. In this article we therefore compared simulation results on the Reactor Level based on an advanced kinetic characterisation of a calcium oxide/hydroxide system to those obtained by a simplified kinetic model. Since energy storage is often used for short term load buffering, the internal Reactor behaviour is analysed under cyclic partial loading and unloading in addition to full monotonic charge/discharge operation. It was found that the predictions by both models were very similar qualitatively and quantitatively in terms of thermal power characteristics, conversion profiles, temperature output, reaction duration and pumping powers. Major differences were, however, observed for the reaction rate profiles themselves. We conclude that for systems not limited by kinetics the simplified model seems sufficient to estimate the Reactor behaviour. The degree of material usage within the Reactor was further shown to strongly vary under cyclic loading conditions and should be considered when designing systems for certain operating regimes.
David W. Agar - One of the best experts on this subject based on the ideXlab platform.
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Optimal distribution of catalyst and adsorbent in an adsorptive Reactor at the Reactor Level
Industrial & Engineering Chemistry Research, 2006Co-Authors: Praveen S. Lawrence, Marcus Grünewald, Wulf Dietrich, David W. AgarAbstract:The concept of adsorptive Reactors has attracted considerable attention as a hybrid process to enhance reaction selectivity and conversion for heterogeneously catalyzed gas-phase reactions. The performance of adsorptive Reactors may be enhanced by the nonuniform distribution of catalyst and adsorbent particles within the Reactor and general guidelines for determining a suitable distribution are provided in this article. Simulation and optimization studies have been carried out using Claus process and its parametric variants as test cases. The study indicates the conditions under which a nonuniform distribution of catalyst and adsorbent is favorable for adsorptive Reactor performance. It also shows that a nonuniform distribution is not always essential for the optimal adsorptive Reactor performance and that under certain conditions a simple homogeneous distribution may well suffice.
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Spatial distribution of functionalities in an adsorptive Reactor at the particle Level
Catalysis Today, 2005Co-Authors: Praveen S. Lawrence, Marcus Grünewald, David W. AgarAbstract:The concept of adsorptive Reactors has attracted considerable attention as a hybrid process to enhance reaction selectivity and conversion for heterogeneously catalysed gas phase reactions. Transport resistances affect the performance of adsorptive Reactors adversely and the integration of functionalities within the same particle circumvents this limitation. Instead of a simple uniform integration of functionalities within the particle, one can also non-uniformly distribute the functionalities over the particle to exploit the concentration profiles arising from transport limitations for process enhancement. A detailed numerical investigation has been carried out to identify the optimal distribution of catalyst and adsorbent functionalities at a particle and Reactor Level using Aspen Custom Modeler. Though process enhancements are possible by non-uniform distribution within particle, the benefits are marginal. Nevertheless, the integration of functionalities within a particle offers significant improvements in adsorptive process performance.
Eduard Schreiner - One of the best experts on this subject based on the ideXlab platform.
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molecular dynamics simulations of surfactant adsorption at oil water interface under shear flow
Particuology, 2019Co-Authors: Ying Ren, Qiang Zhang, Ning Yang, Jialin Liu, Ruixin Yang, Christian Kunkelmann, Eduard SchreinerAbstract:Abstract Surfactants are extensively used in many chemical products to improve their stability, appearance, texture, and rheology. Precise control of the emulsion droplet size distribution, which depends on the characteristics of the surfactant used, is important for target-oriented product design. A complete understanding of the structures and dynamics of emulsion droplets at the Reactor Level requires coupling of two mesoscale physical constraints, that at the interfacial Level, i.e., smaller than a single droplet (Mesoscale-1), and that at the device Level, i.e., larger than a single droplet (Mesoscale-2). In this work, the structures and adsorption kinetics of Mesoscale-1 surfactant molecules were studied via coarse-grained molecular dynamics. A non-equilibrium model that could introduce stable shear flow into the simulation box was used to investigate the interfacial structures at the droplet interface under different shear rates. The configurations of the surfactant molecules and adsorption amounts were compared with those obtained without flow. The adsorption kinetics for different shear rates were compared to determine the effects of hydrodynamic interactions. The dominant mechanisms governing the dynamic structures can thus be summarized as maximization of the adsorption density at the interface and minimization of flow resistance in the bulk phase (water and/or oil molecules). A scheme for coupling between Mesoscale-1 and Mesoscale-2 is proposed. This method is promising for the incorporation of interfacial structure effects into the hydrodynamics at the Reactor device Level for the manipulation of chemical products.
Ruixin Yang - One of the best experts on this subject based on the ideXlab platform.
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molecular dynamics simulations of surfactant adsorption at oil water interface under shear flow
Particuology, 2019Co-Authors: Ying Ren, Qiang Zhang, Ning Yang, Jialin Liu, Ruixin Yang, Christian Kunkelmann, Eduard SchreinerAbstract:Abstract Surfactants are extensively used in many chemical products to improve their stability, appearance, texture, and rheology. Precise control of the emulsion droplet size distribution, which depends on the characteristics of the surfactant used, is important for target-oriented product design. A complete understanding of the structures and dynamics of emulsion droplets at the Reactor Level requires coupling of two mesoscale physical constraints, that at the interfacial Level, i.e., smaller than a single droplet (Mesoscale-1), and that at the device Level, i.e., larger than a single droplet (Mesoscale-2). In this work, the structures and adsorption kinetics of Mesoscale-1 surfactant molecules were studied via coarse-grained molecular dynamics. A non-equilibrium model that could introduce stable shear flow into the simulation box was used to investigate the interfacial structures at the droplet interface under different shear rates. The configurations of the surfactant molecules and adsorption amounts were compared with those obtained without flow. The adsorption kinetics for different shear rates were compared to determine the effects of hydrodynamic interactions. The dominant mechanisms governing the dynamic structures can thus be summarized as maximization of the adsorption density at the interface and minimization of flow resistance in the bulk phase (water and/or oil molecules). A scheme for coupling between Mesoscale-1 and Mesoscale-2 is proposed. This method is promising for the incorporation of interfacial structure effects into the hydrodynamics at the Reactor device Level for the manipulation of chemical products.
