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Jorge R. Frade - One of the best experts on this subject based on the ideXlab platform.

  • Porous hollow tubes processed by extrusion of ceramic emulsions
    Applied Clay Science, 2015
    Co-Authors: Nuno Vitorino, C. Freitas, M J Ribeiro, João C.c. Abrantes, Jorge R. Frade
    Abstract:

    The processing of ceramic materials by extrusion is widely used to obtain products with Constant Cross Section. Most of them are framed with applications as catalysis, filtration, building, fuel cells, isolators, etc., mainly if they are porous with special designed microstructural characteristics as pore size/distribution, liquid and gas permeability, mechanical properties, etc. Thus, in this work we combine a cellular ceramic preparation strategy based on a synergy of emulsification process and gel casting, with the extrusion process to obtain porous hollow tubes. Tree ceramic emulsions were extruded under different ram speeds and its effect was studied using Benbow-Bridgwater model.

Haiyan Wang - One of the best experts on this subject based on the ideXlab platform.

  • optimum thermal design of microchannel heat sink with triangular reentrant cavities
    Applied Thermal Engineering, 2011
    Co-Authors: Guodong Xia, Lei Chai, Haiyan Wang, Mingzheng Zhou, Zhenzhen Cui
    Abstract:

    Abstract The effect of geometric parameters on water flow and heat transfer characteristics in microchannel heat sink with triangular reentrant cavities is numerically investigated. A three-dimensional laminar flow model, consisting of Navier–Stokes equations and energy conservation equation, with the conjugate heat transfer between the silicon base and water taken into consideration is solved numerically. In order to find the optimum geometric parameters, four variables, representing the distance and geometry of the triangular reentrant cavity, are designed. It is found that the vortices in the triangular reentrant cavities lead to chaotic advection and can greatly enhance the convective fluid mixing. The thermal and hydraulic boundary layers are interrupted and the repeated developing flow enhances heat transfer in the Constant Cross-Section segment. Furthermore, the effects of the four design variables on heat transfer augmentation and pressure drop penalty are investigated depending on different Reynolds numbers by using the simulated annealing method. Based on the thermal enhancement factor performance maps, the optimal geometric parameters are obtained in principle.

  • effects of structural parameters on fluid flow and heat transfer in a microchannel with aligned fan shaped reentrant cavities
    International Journal of Thermal Sciences, 2011
    Co-Authors: Guodong Xia, Lei Chai, Mingzheng Zhou, Haiyan Wang
    Abstract:

    Abstract We provide three-dimensional numerical simulations of conjugate heat transfer in the newly proposed microchannels with different structural parameters. The structural parameters include the lengths and widths of the Constant Cross-Section region and the arcuate region. The effects of structural parameters on pressure drop and thermal resistance are presented. For the first part of the effect analysis, we study the fluid flow and heat transfer mechanism of the microchannel with aligned fan-shaped reentrant cavities in detail, which can attribute to the interaction of the increased heat transfer surface area, the redeveloping boundary layers, the jet and throttling effect and the slipping over the reentrant cavities. As to the second part of the present analysis, the effects of two design structural parameters on fluid flow and heat transfer of the new microchannel are individually prescribed and the two suitable ranges of structural parameter are found for the optimum geometric configuration.

Guodong Xia - One of the best experts on this subject based on the ideXlab platform.

  • optimum thermal design of microchannel heat sink with triangular reentrant cavities
    Applied Thermal Engineering, 2011
    Co-Authors: Guodong Xia, Lei Chai, Haiyan Wang, Mingzheng Zhou, Zhenzhen Cui
    Abstract:

    Abstract The effect of geometric parameters on water flow and heat transfer characteristics in microchannel heat sink with triangular reentrant cavities is numerically investigated. A three-dimensional laminar flow model, consisting of Navier–Stokes equations and energy conservation equation, with the conjugate heat transfer between the silicon base and water taken into consideration is solved numerically. In order to find the optimum geometric parameters, four variables, representing the distance and geometry of the triangular reentrant cavity, are designed. It is found that the vortices in the triangular reentrant cavities lead to chaotic advection and can greatly enhance the convective fluid mixing. The thermal and hydraulic boundary layers are interrupted and the repeated developing flow enhances heat transfer in the Constant Cross-Section segment. Furthermore, the effects of the four design variables on heat transfer augmentation and pressure drop penalty are investigated depending on different Reynolds numbers by using the simulated annealing method. Based on the thermal enhancement factor performance maps, the optimal geometric parameters are obtained in principle.

  • effects of structural parameters on fluid flow and heat transfer in a microchannel with aligned fan shaped reentrant cavities
    International Journal of Thermal Sciences, 2011
    Co-Authors: Guodong Xia, Lei Chai, Mingzheng Zhou, Haiyan Wang
    Abstract:

    Abstract We provide three-dimensional numerical simulations of conjugate heat transfer in the newly proposed microchannels with different structural parameters. The structural parameters include the lengths and widths of the Constant Cross-Section region and the arcuate region. The effects of structural parameters on pressure drop and thermal resistance are presented. For the first part of the effect analysis, we study the fluid flow and heat transfer mechanism of the microchannel with aligned fan-shaped reentrant cavities in detail, which can attribute to the interaction of the increased heat transfer surface area, the redeveloping boundary layers, the jet and throttling effect and the slipping over the reentrant cavities. As to the second part of the present analysis, the effects of two design structural parameters on fluid flow and heat transfer of the new microchannel are individually prescribed and the two suitable ranges of structural parameter are found for the optimum geometric configuration.

Sven Bingert - One of the best experts on this subject based on the ideXlab platform.

  • Constant Cross Section of loops in the solar corona
    Astronomy and Astrophysics, 2012
    Co-Authors: H Peter, Sven Bingert
    Abstract:

    Context. The corona of the Sun is dominated by emission from loop-like structures. When observed in X-ray or extreme ultraviolet emission, these million K hot coronal loops show a more or less Constant Cross Section. Aims. In this study we show how the interplay of heating, radiative cooling, and heat conduction in an expanding magnetic structure can explain the observed Constant Cross Section. Methods. We employ a three-dimensional magnetohydrodynamics (3D MHD) model of the corona. The heating of the coronal plasma is the result of braiding of the magnetic field lines through footpoint motions and subsequent dissipation of the induced currents. From the model we synthesize the coronal emission, which is directly comparable to observations from, e.g., the Atmospheric Imaging Assembly on the Solar Dynamics Observatory (AIA/SDO). Results. We find that the synthesized observation of a coronal loop seen in the 3D data cube does match actually observed loops in count rate and that the Cross Section is roughly Constant, as observed. The magnetic field in the loop is expanding and the plasma density is concentrated in this expanding loop; however, the temperature is not Constant perpendicular to the plasma loop. The higher temperature in the upper outer parts of the loop is so high that this part of the loop is outside the contribution function of the respective emission line(s). In effect, the upper part of the plasma loop is not bright and thus the loop actually seen in coronal emission appears to have a Constant width. Conclusions. From this we can conclude that the underlying field-line-braiding heating mechanism provides the proper spatial and temporal distribution of the energy input into the corona – at least on the observable scales.

  • Constant Cross Section of loops in the solar corona
    arXiv: Solar and Stellar Astrophysics, 2012
    Co-Authors: H Peter, Sven Bingert
    Abstract:

    The corona of the Sun is dominated by emission from loop-like structures. When observed in X-ray or extreme ultraviolet emission, these million K hot coronal loops show a more or less Constant Cross Section. In this study we show how the interplay of heating, radiative cooling, and heat conduction in an expanding magnetic structure can explain the observed Constant Cross Section. We employ a three-dimensional magnetohydrodynamics (3D MHD) model of the corona. The heating of the coronal plasma is the result of braiding of the magnetic field lines through footpoint motions and subsequent dissipation of the induced currents. From the model we synthesize the coronal emission, which is directly comparable to observations from, e.g., the Atmospheric Imaging Assembly on the Solar Dynamics Observatory (AIA/SDO). We find that the synthesized observation of a coronal loop seen in the 3D data cube does match actually observed loops in count rate and that the Cross Section is roughly Constant, as observed. The magnetic field in the loop is expanding and the plasma density is concentrated in this expanding loop; however, the temperature is not Constant perpendicular to the plasma loop. The higher temperature in the upper outer parts of the loop is so high that this part of the loop is outside the contribution function of the respective emission line(s). In effect, the upper part of the plasma loop is not bright and thus the loop actually seen in coronal emission appears to have a Constant width. From this we can conclude that the underlying field-line-braiding heating mechanism provides the proper spatial and temporal distribution of the energy input into the corona --- at least on the observable scales.

Nuno Vitorino - One of the best experts on this subject based on the ideXlab platform.

  • Porous hollow tubes processed by extrusion of ceramic emulsions
    Applied Clay Science, 2015
    Co-Authors: Nuno Vitorino, C. Freitas, M J Ribeiro, João C.c. Abrantes, Jorge R. Frade
    Abstract:

    The processing of ceramic materials by extrusion is widely used to obtain products with Constant Cross Section. Most of them are framed with applications as catalysis, filtration, building, fuel cells, isolators, etc., mainly if they are porous with special designed microstructural characteristics as pore size/distribution, liquid and gas permeability, mechanical properties, etc. Thus, in this work we combine a cellular ceramic preparation strategy based on a synergy of emulsification process and gel casting, with the extrusion process to obtain porous hollow tubes. Tree ceramic emulsions were extruded under different ram speeds and its effect was studied using Benbow-Bridgwater model.