The Experts below are selected from a list of 219 Experts worldwide ranked by ideXlab platform

Dieter Eibl - One of the best experts on this subject based on the ideXlab platform.

  • Development of the Travelling Wave Bioreactor. Part I: Design Studies Based on Numerical Models
    Chemie Ingenieur Technik, 2015
    Co-Authors: Stephan C. Kaiser, Matthias Kraume, Dieter Eibl
    Abstract:

    In the travelling wave bioreactor (TWB) an orbital movement is used to set up a quasi-periodic wave motion in the partially filled, toroidal Shaped Vessel. Based on computational fluid dynamics (CFD) models, this study presents detailed analyses of the fluid flow in the TWB for a wide range of operational conditions. Even though the wave propagation is shown to be greatly influenced by the rotation, it was found that the regular Vessel shape facilitates a predominantly tangential flow with low back mixing, irrespective of the operational conditions. Hence, the influence of different bioreactor geometries without and with baffles is examined. The study indicates that CFD models can be used as a valuable tool for bioreactor development, because it provides a deep insight into the bioreactor's hydrodynamics and can help to reduce the number of prototypes.

  • Development of the Travelling Wave Bioreactor – A Concept Study
    Chemie Ingenieur Technik, 2012
    Co-Authors: Stephan C. Kaiser, Matthias Kraume, Dieter Eibl
    Abstract:

    This study presents the concept of the travelling wave single-use bioreactor, based on an orbitally shaken, annular-Shaped Vessel. A numerical model was developed for early design studies in order to reduce the number of prototypes. The flow characteristics in two different Vessel shapes were investigated. It was shown that the orbital motion combined with the toroidal shape of the bioreactor create the desired wave characteristics in the contents of the Vessel.

Bingmei M Fu - One of the best experts on this subject based on the ideXlab platform.

  • mechanical mechanisms of thrombosis in intact bent microVessels of rat mesentery
    Journal of Biomechanics, 2008
    Co-Authors: David Mirc, Bingmei M Fu
    Abstract:

    Abstract The hypothesis that thrombus can be induced by localized shear stresses/rates, such as in the bent/stretched microVessels, was tested both experimentally and computationally. Our newly designed in vivo experiments were performed on the microVessels (post-capillary venules, 20–50 μm diameter) of rat mesentery. These microVessels were bent/stretched with no/minimum injuries. In less than 60 min after the microVessels were bent/stretched, thrombi were formed in 19 out of 61 bent locations (31.1%). Interestingly, thrombi were found to be initiated at the inner wall of the curvature in these bent/stretched Vessels. To investigate the mechanical mechanisms of thrombus induction, we performed a 3-D computational simulation using commercial software, FLUENT. To simulate the bending and stretching, we considered the Vessels with different curvatures (0°, 90° and 180°) as well as different Shaped cross-sections (circular and elliptic). Computational results demonstrated that the highest shear stress/rate and shear stress/rate gradient are located at the inner wall of the curved circular-Shaped Vessels. They are located at the two apexes of the wall with shorter axis for the 0° (straight) elliptic-Shaped Vessel and towards the inner side when the Vessels are bent. The differences of the shear stresses/rates and of the shear stress/rate gradients between the inner and outer walls become larger in more bent and elliptic-Shaped microVessels. Comparison of our experimental and numerical simulation results suggests that the higher shear stress/rate and the higher shear stress/rate gradient at the inner wall are responsible for initiating the thrombosis in bent post-capillary venules.

David Mirc - One of the best experts on this subject based on the ideXlab platform.

  • mechanical mechanisms of thrombosis in intact bent microVessels of rat mesentery
    Journal of Biomechanics, 2008
    Co-Authors: David Mirc, Bingmei M Fu
    Abstract:

    Abstract The hypothesis that thrombus can be induced by localized shear stresses/rates, such as in the bent/stretched microVessels, was tested both experimentally and computationally. Our newly designed in vivo experiments were performed on the microVessels (post-capillary venules, 20–50 μm diameter) of rat mesentery. These microVessels were bent/stretched with no/minimum injuries. In less than 60 min after the microVessels were bent/stretched, thrombi were formed in 19 out of 61 bent locations (31.1%). Interestingly, thrombi were found to be initiated at the inner wall of the curvature in these bent/stretched Vessels. To investigate the mechanical mechanisms of thrombus induction, we performed a 3-D computational simulation using commercial software, FLUENT. To simulate the bending and stretching, we considered the Vessels with different curvatures (0°, 90° and 180°) as well as different Shaped cross-sections (circular and elliptic). Computational results demonstrated that the highest shear stress/rate and shear stress/rate gradient are located at the inner wall of the curved circular-Shaped Vessels. They are located at the two apexes of the wall with shorter axis for the 0° (straight) elliptic-Shaped Vessel and towards the inner side when the Vessels are bent. The differences of the shear stresses/rates and of the shear stress/rate gradients between the inner and outer walls become larger in more bent and elliptic-Shaped microVessels. Comparison of our experimental and numerical simulation results suggests that the higher shear stress/rate and the higher shear stress/rate gradient at the inner wall are responsible for initiating the thrombosis in bent post-capillary venules.

  • Mechanical mechanisms of thrombosis in intact bent microVessels of rat mesentery.
    Journal of biomechanics, 2008
    Co-Authors: Qin Liu, David Mirc
    Abstract:

    The hypothesis that thrombus can be induced by localized shear stresses/rates, such as in the bent/stretched microVessels, was tested both experimentally and computationally. Our newly designed in vivo experiments were performed on the microVessels (post-capillary venules, 20-50 microm diameter) of rat mesentery. These microVessels were bent/stretched with no/minimum injuries. In less than 60 min after the microVessels were bent/stretched, thrombi were formed in 19 out of 61 bent locations (31.1%). Interestingly, thrombi were found to be initiated at the inner wall of the curvature in these bent/stretched Vessels. To investigate the mechanical mechanisms of thrombus induction, we performed a 3-D computational simulation using commercial software, FLUENT. To simulate the bending and stretching, we considered the Vessels with different curvatures (0 degrees , 90 degrees and 180 degrees ) as well as different Shaped cross-sections (circular and elliptic). Computational results demonstrated that the highest shear stress/rate and shear stress/rate gradient are located at the inner wall of the curved circular-Shaped Vessels. They are located at the two apexes of the wall with shorter axis for the 0 degrees (straight) elliptic-Shaped Vessel and towards the inner side when the Vessels are bent. The differences of the shear stresses/rates and of the shear stress/rate gradients between the inner and outer walls become larger in more bent and elliptic-Shaped microVessels. Comparison of our experimental and numerical simulation results suggests that the higher shear stress/rate and the higher shear stress/rate gradient at the inner wall are responsible for initiating the thrombosis in bent post-capillary venules.

Stephan C. Kaiser - One of the best experts on this subject based on the ideXlab platform.

  • Development of the Travelling Wave Bioreactor. Part I: Design Studies Based on Numerical Models
    Chemie Ingenieur Technik, 2015
    Co-Authors: Stephan C. Kaiser, Matthias Kraume, Dieter Eibl
    Abstract:

    In the travelling wave bioreactor (TWB) an orbital movement is used to set up a quasi-periodic wave motion in the partially filled, toroidal Shaped Vessel. Based on computational fluid dynamics (CFD) models, this study presents detailed analyses of the fluid flow in the TWB for a wide range of operational conditions. Even though the wave propagation is shown to be greatly influenced by the rotation, it was found that the regular Vessel shape facilitates a predominantly tangential flow with low back mixing, irrespective of the operational conditions. Hence, the influence of different bioreactor geometries without and with baffles is examined. The study indicates that CFD models can be used as a valuable tool for bioreactor development, because it provides a deep insight into the bioreactor's hydrodynamics and can help to reduce the number of prototypes.

  • Development of the Travelling Wave Bioreactor – A Concept Study
    Chemie Ingenieur Technik, 2012
    Co-Authors: Stephan C. Kaiser, Matthias Kraume, Dieter Eibl
    Abstract:

    This study presents the concept of the travelling wave single-use bioreactor, based on an orbitally shaken, annular-Shaped Vessel. A numerical model was developed for early design studies in order to reduce the number of prototypes. The flow characteristics in two different Vessel shapes were investigated. It was shown that the orbital motion combined with the toroidal shape of the bioreactor create the desired wave characteristics in the contents of the Vessel.

Matthias Kunik - One of the best experts on this subject based on the ideXlab platform.

  • a critical look at the kinematic wave theory for sedimentation consolidation processes in closed Vessels
    Mathematical Methods in The Applied Sciences, 2001
    Co-Authors: Raimund Bürger, Matthias Kunik
    Abstract:

    The two-phase flow of a flocculated suspension in a closed settling Vessel with inclined walls is investigated within a consistent extension of the kinematic wave theory to sedimentation processes with compression. Wall boundary conditions are used to spatially derive one-dimensional field equations for planar flows and flows which are symmetric with respect to the vertical axis. We analyse the special cases of a conical Vessel and a roof-Shaped Vessel. The case of a small initial time and a large time for the final consolidation state leads to explicit expressions for the flow fields, which constitute an important test of the theory. The resulting initial-boundary value problems are well posed and can be solved numerically by a simple adaptation of one of the newly developed numerical schemes for strongly degenerate convection-diffusion problems. However, from a physical point of view, both the analytical and numerical results reveal a deficiency of the general field equations. In particular, the strongly reduced form of the linear momentum balance turns out to be an oversimplification. Included in our discussion as a special case are the Kynch theory and the well-known analyses of sedimentation in Vessels with inclined walls within the framework of kinematic waves, which exhibit the same shortcomings. In order to formulate consistent boundary conditions for both phases in a closed Vessel and in order to predict boundary layers in the presence of inclined walls, viscosity terms should be taken into account. Copyright © 2001 John Wiley & Sons, Ltd.

  • A critical look at the kinematic‐wave theory for sedimentation–consolidation processes in closed Vessels
    Mathematical Methods in the Applied Sciences, 2001
    Co-Authors: Raimund Bürger, Matthias Kunik
    Abstract:

    The two-phase flow of a flocculated suspension in a closed settling Vessel with inclined walls is investigated within a consistent extension of the kinematic wave theory to sedimentation processes with compression. Wall boundary conditions are used to spatially derive one-dimensional field equations for planar flows and flows which are symmetric with respect to the vertical axis. We analyse the special cases of a conical Vessel and a roof-Shaped Vessel. The case of a small initial time and a large time for the final consolidation state leads to explicit expressions for the flow fields, which constitute an important test of the theory. The resulting initial-boundary value problems are well posed and can be solved numerically by a simple adaptation of one of the newly developed numerical schemes for strongly degenerate convection-diffusion problems. However, from a physical point of view, both the analytical and numerical results reveal a deficiency of the general field equations. In particular, the strongly reduced form of the linear momentum balance turns out to be an oversimplification. Included in our discussion as a special case are the Kynch theory and the well-known analyses of sedimentation in Vessels with inclined walls within the framework of kinematic waves, which exhibit the same shortcomings. In order to formulate consistent boundary conditions for both phases in a closed Vessel and in order to predict boundary layers in the presence of inclined walls, viscosity terms should be taken into account. Copyright © 2001 John Wiley & Sons, Ltd.