Bulletin of the American Physical Society
2005 58th Annual Meeting of the Division of Fluid Dynamics
Sunday–Tuesday, November 20–22, 2005; Chicago, IL
Session HF: Surface Tension III |
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Chair: Vladimir Ajaev, Southern Methodist University Room: Hilton Chicago Continental C |
Monday, November 21, 2005 1:20PM - 1:33PM |
HF.00001: Very viscous electrically forced jets F.J. Higuera The dynamics of an axisymmetric jet of a very viscous liquid issuing into a region of uniform electric field, which is of interest for electrospinning, is described numerically using the leaky dielectric model. The jet is continuously strained by surface electric stresses. The flow depends on a capillary number Ca based on the liquid flow rate; an electric Bond number that measures the ratio of electric to surface tension stresses; the dielectric constant of the liquid; and the ratio T of a mechanical (viscous-capillary) time to the electric relaxation time required for the charge that is brought to the surface by the electric field to screen the liquid from the field. The electric current and the radius of the jet increase with Ca and tend to well defined limits for large values of this parameter, whereas a stationary jet ceases to exist when Ca decreases below a certain minimum. The radius of the jet decreases when the electric Bond number increases, due to the increased straining, and also when the time ratio T increases, which suggests that charge relaxation effects are always important in the formation of the jet. [Preview Abstract] |
Monday, November 21, 2005 1:33PM - 1:46PM |
HF.00002: Capillary rise between elastic sheets Ho-Young Kim, L. Mahadevan When a paintbrush is dipped into a bucket of paint and pulled out, surface tension forces cause the individual hairs in the brush to coalesce which simultaneously becomes impregnated with paint. We study a simple model of this elastocapillary interaction using the surface-tension-driven vertical rise of a liquid between two long flexible hydrophilic sheets that are held a small distance apart at one end. This leads to a modification of the classical law of Jurin and we provide an analytic theory for the static shapes of the sheets as well as the liquid rise height. It is shown that our experiments are quantitatively consistent with the theory. [Preview Abstract] |
Monday, November 21, 2005 1:46PM - 1:59PM |
HF.00003: Dynamics of drops dancing on the ceiling John Lister, Simon Rees, John Rallison A layer of fluid coating the underside of a horizontal ceiling is stabilised by surface tension and destabilised by gravity to yield pendent drops. We show that a single pendent drop is capable of self-sustained quasisteady translation in a straight line over an otherwise uniform film. The drop leaves behind it a `wake' in which the average film thickness is a factor 0.095 that of the initial uniform film, and the drop thus grows by accumulation. When such a self-translating drop encounters a region of nonuniform thickness, for example another drop or its wake, the drop is deflected on a curved trajectory. Curious dynamics ensue. [Preview Abstract] |
Monday, November 21, 2005 1:59PM - 2:12PM |
HF.00004: The Floating and Sinking of Small Interfacial Objects Dominic Vella, Robert Whittaker, Paul Metcalfe Small objects are able to float at a liquid--gas interface even if their density exceeds that of the bulk fluid because of the vertical force contribution of surface tension. If this force is reduced, for example by eliminating a portion of the meniscus through contact with another object, such objects may no longer be supported at the interface and sink. We discuss the conditions under which floating can occur as well as some simple models for the early stages of sinking, which compare favourably to experiments. [Preview Abstract] |
Monday, November 21, 2005 2:12PM - 2:25PM |
HF.00005: A trickle instability Benjamin Bossa, Emmanuel Villermaux We address the problem of the free fall of a long, horizontal and narrow liquid layer squeezed in a vertical open Hele-Shaw cell. The layer destabilizes as it falls down, evolving into a series of liquid blobs linked together by thin bridges, which ultimately break, leaving the initially connex fluid layer as a set a disjointed drops. The mechanism of this instability is the onset of a vertical pressure gradient due to the curvature difference of the moving contact line between the advancing interface and the rear interface. This instability, whose growth rate scales with a non-trivial power of the capillary number, amplifies indifferently a broad band of wavenumbers because of the flat shape of its dispersion relation in the thin layer limit. We will finally comment on the nature of the final fragmentation process and drop size distributions. [Preview Abstract] |
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