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  • Fluid Transport in Compacted Porous Talc Blocks
  • Abstract It has been shown that talc powder can be compacted into tablets with a preferred orientation of the platelets. The tablets can be obtained with different controlled porosity depending on pressing methods and applied pressure. The tablets can be obtained with or without additives, which may, in turn, be adsorbed. The orientation of the high aspect ratio platy talc, the surface chemistry imparted by the additives and the transported fluid influence the imbibition and permeation rates. Non-polar hexadecane displays a higher imbibition and permeability than water for all particulate orientations during short timescale absorption, likely due to the oleophilic nature…
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  • Numerical and Experimental Study of Particle Motion in Plasma Arc Welding
  • Abstract The PTA (''Plasma-Transferred-Arc'') is a widespread variant of plasma powder processes to manufacture coatings against corrosion or abrasion. For the optimization of this technique, an explanation of the processes which lead to a maximal deposition performance (i.e. maximal quantity of powder converted per time) is required. Especially the gas and particle flow in the region between the burner nozzle and the work piece is of interest. In the present study, flow simulations (Computational Fluid Dynamics, CFD) have been done in order to investigate the determining factors for the dimensioning of the processes. Additionally, velocity measurements have been obtained with PIV…
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  • Profile Analysis of Regularly Microstructured Surfaces
  • Abstract Microstructured surfaces are of steadily increasing importance in a large variety of technological applications. For the purpose of quality assurance, e.g. during variation studies of experimental parameters or for comparison with results from simulations, the surface geometry must be precisely measured and described in terms of geometric parameters. An analysis tool for regularly structured surfaces is presented that performs a highly automated evaluation of surface scanning data and derives geometric quality control parameters. To demonstrate the power of the analysis tool it is exemplarily applied for the investigation of microcraters emerging after the evaporation of micrometer-sized toluene droplets on a…
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  • A Deformation and a Break of Hanging Thin Film under Microgravity Conditions
  • Abstract We consider a deformation of a thin film which is hanging between two solid flat walls under thermal load action. A two-dimensional model is applied to describe the motion of thin layers of viscous nonisothermal liquid under microgravity conditions. The model is based on the Navier-Stokes equations. A numerical analysis of the influence of thermal loads on the deformation and break of freely hanging thin films has been carried out. The mutual influence of capillary and thermo-capillary forces on thin film free surface position has been shown. The results of model problem solutions are presented.
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  • Effect of Large Eccentric Rotation on the Stability of Liquid Bridges
  • Abstract A cylindrical liquid bridge supported between two circular-shaped disks in isorotation is considered. The effect of an offset between the rotation axis and the axis of the two supporting disks (eccentricity) on the stability of the liquid bridge is investigated. In a previous work a numerical method used to determine the stability limit for different values of eccentricity was validated comparing these results with analytical and experimental results for small eccentricity values, recovering the same behavior. In this work we use the numerical method to extend the analysis to large values of the eccentricity, finding a change in the bifurcation…
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  • Axially Running Wave in Liquid Bridge
  • Abstract Thermocapillary convection in a long vertical liquid column (called liquid bridge) subjected to heating from above is considered for a three-dimensional Boussinesq fluid. The problem is solved numerically via finite-volume method. Full system of three dimensional Navier-Stokes equations coupled with the energy equation is solved for an incompressible fluid. Instability sets in through a wave propagating in axial direction with zero azimuthal wave number, which is a unique stable solution over a wide range of supercritical heating. Further increasing the applied temperature difference results in bifurcation of a second wave traveling azimuthally with a slightly higher frequency. The two waves…
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  • Instabilities and Pattern Formation in Thermocapillary Liquid Pools
  • Abstract The flow in thermocapillary liquid pools heated or cooled from above can exhibit various flow patterns depending on the thermal conditions and the geometrical constraints. This pattern formation and the respective physical mechanisms are studied numerically by means of a linear-stability analysis. We focus on the transition from the steady axisymmetric to a three-dimensional flow.
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  • Thin Films in the Presence of Chemical Reactions
  • Abstract We investigate the interaction between thin films and chemical reactions by using two prototype systems: a thin liquid film falling down a planar inclined substrate in the presence of an exothermic chemical reaction and a horizontal thin liquid film with a reactive mixture of insoluble surfactants on its surface. In the first case the chemical reaction has a stabilizing influence on the dynamics of the film and dampens the free-surface solitary pulses. In the second case the chemical reaction can destabilize the film and lead to the formation of free-surface solitary pulses.
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  • Coupling between Stationary Marangoni and Cowley-Rosensweig Instabilities in a Deformable Ferrofluid Layer
  • Abstract A horizontal thin layer of ferrofluid is bordered by a solid and open to an inert gas on the other side. It is submitted to a heat gradient and a weak magnetic field, both being normal to the free deformable surface, leading to a coupling between the Marangoni phenomenon, induced by the variation of surface tension along the free deformable surface and the isothermal Cowley-Rosensweig problem, consequence of the magnetic field. The study of the steady compatibility condition shows a new pattern of stationary instability. The critical wavenumber is of O(√Bo), the Bond number Bo being smaller than 1, at…
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  • Phase field models and Marangoni flows
  • Abstract We developed a phase field model for Marangoni convection in compressible fluids of van der Waals type far from criticality. The theoretical description is based on the Navier-Stokes equation with extra terms responsible for describing the Marangoni effect, the classical heat equation, and the continuity equation. The model previously developed for a two-layer geometry is now extended to drops and bubbles. Finally, we report on 2D numerical simulations for drop Marangoni migration in a vertical temperature gradient.
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