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  • Cambridge University Press  (7)
  • Eggenstein-Leopoldshafen : Fachinformationszentrum Energie, Physik, Mathematik
  • 1
    Monograph available for loan
    Monograph available for loan
    Satellite measurements of radiation budget of the earth (1982)
    Eggenstein-Leopoldshafen : Fachinformationszentrum Energie, Physik, Mathematik
    Associated volumes
    Details Availability
    Call number: MOP 46122 / Mitte
    In: Forschungsbericht
    Type of Medium: Monograph available for loan
    Pages: 170 S. : Ill., graph. Darst., Kt.
    Series Statement: Forschungsbericht / Bundesministerium für Forschung und Technologie : W, Luft- und Raumfahrt, Weltraumforschung, Weltraumtechnologie 82-006
    Location: MOP - must be ordered
    Branch Library: GFZ Library
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  • 2
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    Laminar mixed convection in two-dimensional far wakes above heated/cooled bodies: model and experiments (2001)
    Cambridge University Press
    Details
    Publication Date: 2001-07-23
    Description: A heated or cooled body is positioned in a vertically rising forced flow. This develops both a kinematic and a thermal wake, the latter adding buoyant effects to the otherwise forced flow field. An asymptotic model is developed to treat this mixed convection in both plane and axisymmetric geometry. The model holds for laminar flow in the boundary layer approximation and uses a far-wake expansion for weak buoyant forces. For plane geometry the model is validated against both experiments in water and FEM simulations. It is found for a heated wake that buoyant forces accelerate the fluid in the thermal wake such that the vertical velocity deficit in the kinematic wake is reduced. For strong heating this may even lead to vertical velocities larger than the forced flow amplitude. In conjunction the entrainment is intensified in a heated wake. The effects in a cooled wake are opposite in that the vertical velocity deficit is increased within the thermal wake and the horizontal flow into the wake is wakened. In a strongly cooled wake the horizontal flow may even invert, going from the wake centre into the ambient. The Prandtl number controls the width of the thermal wake and, thus, the portion of the kinematic wake which is affected by buoyant forces. Large Prandtl numbers superimpose a narrow buoyant plume, small Prandtl numbers a wide buoyant plume, onto the kinematic wake.
    Print ISSN: 0022-1120
    Electronic ISSN: 1469-7645
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
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  • 3
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    Experiments on isothermal and non-isothermal spreading (1993)
    Cambridge University Press
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    Publication Date: 1993-12-01
    Description: Experiments are performed on axisymmetric spreading of viscous drops on glass plates. Two liquids are investigated: silicone oil (M-100), which spreads to ‘infinity’, and paraffin oil, which spreads to a finite-radius steady state. The experiments with silicone oil partly recover the behaviour of previous workers’ data; those experiments with paraffin oil provide new data. It is found that gravitational forces dominate at long enough times while at shorter times capillary forces dominate. When the plate is heated or cooled with respect to the ambient gas, thermocapillary forces generate flows that alter the spreading dynamics. Heating (cooling) the plate is found to retard (augment) the spreading. Moreover, in case of partial wetting, the drop radius finally approached is smaller (larger) for a heated (cooled) plate. These data are all new. All these observations are in good quantitative agreement with the related model predictions of Ehrhard & Davis (1991). A breakdown of the axisymmetric character of the flow is observed only for very long times and/or very thin liquid layers. © 1993, Cambridge University Press. All rights reserved.
    Print ISSN: 0022-1120
    Electronic ISSN: 1469-7645
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
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  • 4
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    Dynamical behaviour of natural convection in a single-phase loop (1990)
    Cambridge University Press
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    Publication Date: 1990-08-01
    Description: A one-dimensional model is derived for natural convection in a closed loop. The physical model can be reduced to a set of nonlinear ordinary differential equations of the Lorenz type. The model is based on a realistic heat transfer law and also accounts for a non-symmetric arrangement of heat sources and sinks. A nonlinear analysis of these equations is performed as well as experiments to validate the model predictions. Both the experimental and the analytical data show that natural convection in a loop is characterized by strong nonlinear effects. Distinct subcritical regions are observed in addition to a variety of stable steady flow regimes. Thus, in certain ranges of the forcing parameter the flow stability depends significantly on the presence of finite perturbation amplitudes. An absolutely unstable range also exists which is characterized by a chaotic time behaviour of the flow quantities. It is also shown that the steady solutions are subject to an imperfect forward bifurcation if heating of the loop is performed non-symmetrically. In such a case one flow direction is preferred at the onset of convection and, moreover, the corresponding steady solution is more stable than a second, isolated, steady solution. The second solution has the opposite flow direction and is stable only in a relatively small, isolated interval. The preferred steady solution becomes unstable against time-periodic perturbations at a higher value of the forcing parameter. A backward- or a forward-directed bifurcation of the periodic solutions is found depending on the non-symmetry parameter of the system. © 1990, Cambridge University Press. All rights reserved.
    Print ISSN: 0022-1120
    Electronic ISSN: 1469-7645
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
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  • 5
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    Measurements and simulations of time-dependent flow fields within an electrokinetic micromixer (2011)
    Cambridge University Press
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    Publication Date: 2011-04-14
    Print ISSN: 0022-1120
    Electronic ISSN: 1469-7645
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
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  • 6
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    Non-isothermal spreading of liquid drops on horizontal plates (1991)
    Cambridge University Press
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    Publication Date: 1991-08-01
    Description: A viscous-liquid drop spreads on a smooth horizontal surface, which is uniformly heated or cooled. Lubrication theory is used to study thin drops subject to capillary, thermocapillary and gravity forces, and a variety of contact-angle-versus-speed conditions. It is found for isothermal drops that gravity is very important at large times and determines the power law for unlimited spreading. Predictions compare well with the experimental data on isothermal spreading for both two-dimensional and axisymmetric configurations. It is found that heating (cooling) retards (augments) the spreading process by creating flows that counteract (reinforce) those associated with isothermal spreading. For zero advancing contact angle, heating will prevent the drop from spreading to infinity. Thus, the heat transfer serves as a sensitive control on the spreading. © 1991, Cambridge University Press. All rights reserved.
    Print ISSN: 0022-1120
    Electronic ISSN: 1469-7645
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
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  • 7
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    Marangoni effects caused by contaminants adsorbed on bubble surfaces (2010)
    Cambridge University Press
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    Publication Date: 2010-03-18
    Description: The influence of Marangoni stresses, caused by contaminants adsorbed on the surface of small air bubbles, rising in water, is examined by numerical simulations. A modified level set method is used to represent the deformable bubble interface, extended by a model for the contaminant transport on the bubble surface. We show that surface tension variations of less than 2% are sufficient to generate Marangoni stresses that are strong enough to change the rising characteristics of a bubble to that of a corresponding solid particle. In such situations, we find that the bubble surface is fully covered with contaminant and the shear stress profile resembles the shear stress profile around a solid sphere. © 2010 Cambridge University Press.
    Print ISSN: 0022-1120
    Electronic ISSN: 1469-7645
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
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  • 8
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    Measurements and simulations of time-dependent flow fields within an electrokinetic micromixer (2011)
    Cambridge University Press
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    Publication Date: 2011-04-14
    Description: We investigate the flow field in an electrokinetic micromixer. The concept of the micromixer is based on the combination of an alternating electrical field applied to a pressure-driven base flow in a meander-channel geometry. The presence of the electrical field leads to an additional electro-osmotic velocity contribution, which results in a complex flow field within the meander bends. The velocity fields within the meander are measured by means of a microparticle-image velocimetry method. Furthermore, we introduce a mathematical model, describing the electrical and fluid-mechanical phenomena present within the device, and perform simulations comparable to the experiments. The comparison of simulations and experiments reveals good agreement, with minor discrepancies in flow topology, obviously caused by small but crucial differences between experimental and numerical geometries. In detail, simulations are performed for sharp corners of the bends, while in the experiments these corners are rounded due to the microfabrication process. © 2011 Cambridge University Press.
    Print ISSN: 0022-1120
    Electronic ISSN: 1469-7645
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
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