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Jaka Sunarso - One of the best experts on this subject based on the ideXlab platform.
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rate determining step in sdc ssaf dual phase oxygen permeation membrane
Journal of Membrane Science, 2019Co-Authors: Claudia Li, Wenping Li, Jiuan Jing Chew, Jaka SunarsoAbstract:Abstract Dense mixed ionic-electronic conducting (MIEC) dual-phase Ce0.85Sm0.15O1.925–Sm0.6Sr0.4Al0.3Fe0.7O3-δ (SDC-SSAF) represents one of the most attractive oxygen-selective membrane materials for oxygen separation from air above 700 °C. Its high phase stability in reducing atmosphere and CO2 resistance allows its potential direct integration into oxyfuel combustion and membrane reactor applications. In this work, the oxygen permeation parameters and properties of SDC-SSAF are evaluated theoretically using the Zhu model, which analyses the role of interfaces in electrochemical oxygen permeation. The model produced good correlation with the experimental data (R2 = 0.9990), with the calculated resistance constants indicating higher resistance encountered at the feed side interface as compared to the permeate side. An analysis of the Characteristic Thickness indicates increasing influence of surface exchange reactions with decreasing temperature, feed side pressure, and permeate side pressure. Although oxygen permeation is dependent upon various operating conditions, our parametric study reveals that temperature effect surpasses oxygen partial pressure difference effect in enhancing the oxygen permeation flux. Oxygen permeation is limited by surface reactions between 800 and 850 °C and mixed bulk diffusion and surface exchange reactions between 850 and 875 °C. Above 875 °C, the rate determining step shifts to bulk diffusion.
Jānis Priede - One of the best experts on this subject based on the ideXlab platform.
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linear stability of magnetohydrodynamic flow in a square duct with thin conducting walls
Journal of Fluid Mechanics, 2016Co-Authors: Jānis Priede, Thomas Arlt, L BuhlerAbstract:This study is concerned with the numerical linear stability analysis of liquid-metal flow in a square duct with thin electrically conducting walls subject to a uniform transverse magnetic field. We derive an asymptotic solution for the base flow that is valid for not only high but also moderate magnetic fields. This solution shows that, for low wall conductance ratios , an extremely strong magnetic field with Hartmann number is required to attain the asymptotic flow regime considered in previous studies. We use a vector streamfunction–vorticity formulation and a Chebyshev collocation method to solve the eigenvalue problem for three-dimensional small-amplitude perturbations in ducts with realistic wall conductance ratios , 0.1 and 0.01 and Hartmann numbers up to . As for similar flows, instability in a sufficiently strong magnetic field is found to occur in the sidewall jets with Characteristic Thickness . This results in the critical Reynolds number and wavenumber increasing asymptotically with the magnetic field as and . The respective critical Reynolds number based on the total volume flux in a square duct with is . Although this value is somewhat larger than found by Ting et al. (Intl J. Engng Sci., vol. 29 (8), 1991, pp. 939–948) for the asymptotic sidewall jet profile, it still appears significantly lower than the Reynolds numbers at which turbulence is observed in experiments as well as in direct numerical simulations of this type of flow.
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linear stability of magnetohydrodynamic flow in a square duct with thin conducting walls
arXiv: Fluid Dynamics, 2015Co-Authors: Jānis Priede, Thomas Arlt, L BuhlerAbstract:This study is concerned with numerical linear stability analysis of liquid metal flow in a square duct with thin electrically conducting walls subject to a uniform transverse magnetic field. We derive an asymptotic solution for the base flow which is valid not only for high but also moderate magnetic fields. This solution shows that for low wall conductance ratios $c\ll1,$ an extremely strong magnetic field with the Hartmann number $Ha\sim c^{-4}$ is required to attain the asymptotic flow regime considered in the previous studies. We use a vector stream function/vorticity formulation and a Chebyshev collocation method to solve the eigenvalue problem for three-dimensional small-amplitude perturbations in ducts with realistic wall conductance ratios $c=1,0.1,0.01$ and Hartmann numbers up to $10^{4}.$ As for similar flows, instability in a sufficiently strong magnetic field is found to occur in the side-wall jets with the Characteristic Thickness $\delta\sim Ha^{-1/2}.$ This results in the critical Reynolds number and wavenumber increasing asymptotically with the magnetic field as $Re_{c}\sim110Ha^{1/2}$ and $k_{c}\sim0.5Ha^{1/2}.$ The respective critical Reynolds number based on the total volume flux in a square duct with $c\ll1$ is $\bar{Re}_{c}\approx520.$ Although this value is somewhat larger than$\bar{Re}_{c}\approx313$ found by Ting et al. (1991) for the asymptotic side-wall jet profile, it still appears significantly lower than the Reynolds numbers at which turbulence is observed in experiments as well as in direct numerical simulations of this type of flows.
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linear stability of magnetohydrodynamic flow in a perfectly conducting rectangular duct
Journal of Fluid Mechanics, 2012Co-Authors: Jānis Priede, Svetlana Aleksandrova, S MolokovAbstract:following the jets becomes confined in the layers of Characteristic Thickness Ha 1=2 located at the walls parallel to the magnetic field. In this case the instability is determined by ; which results in both the critical Reynolds number and wavenumber scaling as 1 : Instability modes can have one of the four different symmetry combinations along and across the magnetic field. The most unstable is a pair of modes with an even distribution of vorticity along the magnetic field. These two modes represent strongly non-uniform vortices aligned with the magnetic field, which rotate either in the same or opposite senses across the magnetic field. The former enhance while the latter weaken one another provided that the magnetic field is not too strong or the walls parallel to the field are not too far apart. In a strong magnetic field, when the vortices at the opposite walls are well separated by the core flow, the critical Reynolds number and wavenumber for both of these instability modes are the same: Rec 642Ha 1=2 C 8:9 10 3 Ha 1=2 and kc 0:477Ha 1=2 : The other pair of modes, which differs from the previous one by an odd distribution of vorticity along the magnetic field, is more stable with an approximately four times higher critical Reynolds number.
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linear stability of magnetohydrodynamic flow in a perfectly conducting rectangular duct
arXiv: Fluid Dynamics, 2011Co-Authors: Jānis Priede, Svetlana Aleksandrova, S MolokovAbstract:We analyse numerically the linear stability of a liquid metal flow in a rectangular duct with perfectly electrically conducting walls subject to a uniform transverse magnetic field. A non-standard three dimensional vector stream function/vorticity formulation is used with Chebyshev collocation method to solve the eigenvalue problem for small-amplitude perturbations. A relatively weak magnetic field is found to render the flow linearly unstable as two weak jets appear close to the centre of the duct at the Hartmann number Ha \approx 9.6. In a sufficiently strong magnetic field, the instability following the jets becomes confined in the layers of Characteristic Thickness \delta \sim Ha^{-1/2} located at the walls parallel to the magnetic field. In this case the instability is determined by \delta, which results in both the critical Reynolds and wavenumbers numbers scaling as \sim \delta^{-1}. Instability modes can have one of the four different symmetry combinations along and across the magnetic field. The most unstable is a pair of modes with an even distribution of vorticity along the magnetic field. These two modes represent strongly non-uniform vortices aligned with the magnetic field, which rotate either in the same or opposite senses across the magnetic field. The former enhance while the latter weaken one another provided that the magnetic field is not too strong or the walls parallel to the field are not too far apart. In a strong magnetic field, when the vortices at the opposite walls are well separated by the core flow, the critical Reynolds and wavenumbers for both of these instability modes are the same: Re_c \approx 642Ha^{1/2}+8.9x10^3Ha^{-1/2} and k_c \approx 0.477Ha^{1/2}. The other pair of modes, which differs from the previous one by an odd distribution of vorticity along the magnetic field, is more stable with approximately four times higher critical Reynolds number.
Claudia Li - One of the best experts on this subject based on the ideXlab platform.
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rate determining step in sdc ssaf dual phase oxygen permeation membrane
Journal of Membrane Science, 2019Co-Authors: Claudia Li, Wenping Li, Jiuan Jing Chew, Jaka SunarsoAbstract:Abstract Dense mixed ionic-electronic conducting (MIEC) dual-phase Ce0.85Sm0.15O1.925–Sm0.6Sr0.4Al0.3Fe0.7O3-δ (SDC-SSAF) represents one of the most attractive oxygen-selective membrane materials for oxygen separation from air above 700 °C. Its high phase stability in reducing atmosphere and CO2 resistance allows its potential direct integration into oxyfuel combustion and membrane reactor applications. In this work, the oxygen permeation parameters and properties of SDC-SSAF are evaluated theoretically using the Zhu model, which analyses the role of interfaces in electrochemical oxygen permeation. The model produced good correlation with the experimental data (R2 = 0.9990), with the calculated resistance constants indicating higher resistance encountered at the feed side interface as compared to the permeate side. An analysis of the Characteristic Thickness indicates increasing influence of surface exchange reactions with decreasing temperature, feed side pressure, and permeate side pressure. Although oxygen permeation is dependent upon various operating conditions, our parametric study reveals that temperature effect surpasses oxygen partial pressure difference effect in enhancing the oxygen permeation flux. Oxygen permeation is limited by surface reactions between 800 and 850 °C and mixed bulk diffusion and surface exchange reactions between 850 and 875 °C. Above 875 °C, the rate determining step shifts to bulk diffusion.
L Buhler - One of the best experts on this subject based on the ideXlab platform.
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linear stability of magnetohydrodynamic flow in a square duct with thin conducting walls
Journal of Fluid Mechanics, 2016Co-Authors: Jānis Priede, Thomas Arlt, L BuhlerAbstract:This study is concerned with the numerical linear stability analysis of liquid-metal flow in a square duct with thin electrically conducting walls subject to a uniform transverse magnetic field. We derive an asymptotic solution for the base flow that is valid for not only high but also moderate magnetic fields. This solution shows that, for low wall conductance ratios , an extremely strong magnetic field with Hartmann number is required to attain the asymptotic flow regime considered in previous studies. We use a vector streamfunction–vorticity formulation and a Chebyshev collocation method to solve the eigenvalue problem for three-dimensional small-amplitude perturbations in ducts with realistic wall conductance ratios , 0.1 and 0.01 and Hartmann numbers up to . As for similar flows, instability in a sufficiently strong magnetic field is found to occur in the sidewall jets with Characteristic Thickness . This results in the critical Reynolds number and wavenumber increasing asymptotically with the magnetic field as and . The respective critical Reynolds number based on the total volume flux in a square duct with is . Although this value is somewhat larger than found by Ting et al. (Intl J. Engng Sci., vol. 29 (8), 1991, pp. 939–948) for the asymptotic sidewall jet profile, it still appears significantly lower than the Reynolds numbers at which turbulence is observed in experiments as well as in direct numerical simulations of this type of flow.
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linear stability of magnetohydrodynamic flow in a square duct with thin conducting walls
arXiv: Fluid Dynamics, 2015Co-Authors: Jānis Priede, Thomas Arlt, L BuhlerAbstract:This study is concerned with numerical linear stability analysis of liquid metal flow in a square duct with thin electrically conducting walls subject to a uniform transverse magnetic field. We derive an asymptotic solution for the base flow which is valid not only for high but also moderate magnetic fields. This solution shows that for low wall conductance ratios $c\ll1,$ an extremely strong magnetic field with the Hartmann number $Ha\sim c^{-4}$ is required to attain the asymptotic flow regime considered in the previous studies. We use a vector stream function/vorticity formulation and a Chebyshev collocation method to solve the eigenvalue problem for three-dimensional small-amplitude perturbations in ducts with realistic wall conductance ratios $c=1,0.1,0.01$ and Hartmann numbers up to $10^{4}.$ As for similar flows, instability in a sufficiently strong magnetic field is found to occur in the side-wall jets with the Characteristic Thickness $\delta\sim Ha^{-1/2}.$ This results in the critical Reynolds number and wavenumber increasing asymptotically with the magnetic field as $Re_{c}\sim110Ha^{1/2}$ and $k_{c}\sim0.5Ha^{1/2}.$ The respective critical Reynolds number based on the total volume flux in a square duct with $c\ll1$ is $\bar{Re}_{c}\approx520.$ Although this value is somewhat larger than$\bar{Re}_{c}\approx313$ found by Ting et al. (1991) for the asymptotic side-wall jet profile, it still appears significantly lower than the Reynolds numbers at which turbulence is observed in experiments as well as in direct numerical simulations of this type of flows.
Y. Zhang - One of the best experts on this subject based on the ideXlab platform.
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Inhomogeneous deformation in metallic glasses
Materials Science and Technology, 2008Co-Authors: Y. ZhangAbstract:AbstractIn metallic glasses, the combination of metallic bonding with an amorphous structure gives excellent mechanical properties such as high yield stress and yield strain compared with conventional polycrystalline alloys. It is, therefore, of great interest to exploit bulk metallic glasses (BMGs) as structural materials, particularly as many are now available in bulk form. The plastic deformation of BMGs is generally inhomogeneous, severely localised into shear bands with a Characteristic Thickness of only ∼10 nm. This shear instability is associated with work softening and impedes the exploitation of the otherwise desirable mechanical properties of metallic glasses in structural applications. Recent progress in understanding work softening in metallic glasses and the consequent formation of shear bands is reviewed, considering both experimental work and molecular dynamics simulations. The basic phenomena of plastic deformation in BMGs are briefly introduced. The initiation of shear bands, their propag...
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Thickness of shear bands in metallic glasses
Applied Physics Letters, 2006Co-Authors: Y. Zhang, A L GreerAbstract:A review of measurements and atomistic modeling shows that shear bands in metallic glasses have a Characteristic Thickness of ∼10nm. Such extreme localization of plastic deformation, within a thicker liquidlike layer implied by fracture-surface morphology, cannot have a thermal origin. By analogy with granular materials, the Thickness is linked to the local structural rearrangements required to generate dilatation. This analysis suggests that first-coordination-shell clusters may be significant structural units in metallic glasses.