Bulletin of the American Physical Society
61st Annual Meeting of the APS Division of Fluid Dynamics
Volume 53, Number 15
Sunday–Tuesday, November 23–25, 2008; San Antonio, Texas
Session PG: Drops VIII |
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Chair: Alfonso M. Ganon-Calvo, University of Seville, Spain Room: 101A |
Tuesday, November 25, 2008 11:35AM - 11:48AM |
PG.00001: Absolute-convective instability of coaxial jets Conrado Ferrera, Miguel A. Herrada, Jose M. Montanero, Alfonso M. Ganan-Calvo A well established route for the massive microencapsulation of labile materials, microorganisms, pharmaceutical principles, flavors, or any active ingredients of any kind involves the generation and breakup of coaxial capillary jets. Here, surface tension is the ultimate molding mechanism, and therefore experience teaches that the product quality is optimized within operating condition ranges where Weber and Capillary numbers attain limited values. These ranges allow for a precise control of the product structure. However, surface tension also mandates whether compound capillary jets may form or not: Weber and Capillary numbers maps exhibit ``hard'' boundaries where jets become locally unstable (absolutely unstable) as opposed to convectively unstable, and the product shows dramatic changes in structure (generally a degradation) across these boundaries. In this work we perform a linear spatiotemporal analysis of coaxial capillary jets to provide cartographic maps of viable regions in the Weber and Capillary numbers space. A discussion on the connection of these maps with the morphology of the resulting products is also given, together with comparisons with published experimental literature. [Preview Abstract] |
Tuesday, November 25, 2008 11:48AM - 12:01PM |
PG.00002: Swirl Flow-Focusing: a new way for the generation of Microbubbles Miguel A. Herrada, Jose M. Lopez-Herrera, Alfonso M. Ganan-Calvo A volume of fluid (VOF) numerical method is used to predict the dynamics of bubble formation in an axisymmetric flow-focusing microfluidic device. Our numerical results for several gas- liquid configurations show that in all cases analyzed, the introduction of co-axial swirl in the focusing liquid fosters the stabilization of the gas-liquid meniscus promoting tapered geometries. Consequently, the use of swirl leads to a dramatic reduction of the size of the bubbles generated by the flow focusing device. Preliminary experiments support our numerical findings. [Preview Abstract] |
Tuesday, November 25, 2008 12:01PM - 12:14PM |
PG.00003: Viscoelastic effects on the jetting-dripping transition in co-flowing capillary jets Jose M. Montanero, Alfonso M. Ganan-Calvo Linear hydrodynamics stability analysis is used to determine the influence of elasticity on the jetting-dripping transition and on the temporal stability of non-axisymmetric modes in co-flowing capillary jets. The critical Weber number for which axisymmetric perturbations undergo a transition from convective to absolute instability is calculated from the spatio-temporal analysis of the dispersion relation for Oldroyd-B liquids, as a function of the density and viscosity ratios, and the Reynolds and corresponding Deborah numbers. Here we show that elasticity increases the critical Weber number for all cases analyzed and, consequently, fosters the transition from jetting to dripping. The temporal analysis of the dispersion relation for the $m=1$ non-axisymmetric mode shows that elasticity does not affect its stability. [Preview Abstract] |
Tuesday, November 25, 2008 12:14PM - 12:27PM |
PG.00004: Vortex Dynamics from 2D PIV Data in a Bubble Plume Duncan Bryant, Scott Socolofsky Bubble plumes are commonly used for aeration and destratification in lakes and show potential as a delivery method for carbon sequestration. The need to design bubble plumes for these uses has led to an increase in research and development of models. However, the dynamics of turbulence in bubble plumes has yet to be quantified. Physical experiments were conducted to quantify turbulence in bubble plumes with air flow rates of 0.5, 1.0, and 1.5L/min. A camera imaged the bubble plume illuminated along a plane with an Argon-Ion laser at 250Hz. The images were processed to remove all bubbles resulting in a new image with only seeding particles. These images were processed using Particle Image Velocimetry giving 2D vector fields for the fluid phase. These vector fields were spatially analyzed to identify vortices and their properties in the field of view. The results show that the expected non-dimensional vortex size is the same for all three flow rates. The results also show that when properly non-dimensionalized the time-average vortex properties such as size and circulation across the width of the bubble plume are similar for all three air flow rates. Finally, the data is used to find the turbulent energy spectrum and the characteristic length scale within the plume. These results agree with the identified vortex results and show the modulation of the turbulence due to the presence of bubbles. [Preview Abstract] |
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