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 GB: Liquid Breakup and Coalescence I |
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Chair: Alfonso Ganan-Calvo, University of Seville Room: Hilton Chicago International Ballroom South |
Monday, November 21, 2005 10:34AM - 10:47AM |
GB.00001: Dynamics of drop formation of surfactant-containing liquids Hariprasad Janakiram Subramani, Ying-Chih Liao, Elias Franses, Osman Basaran Surfactants are used to control the breakup of jets and drops in applications as diverse as inkjet printing, pesticide spraying, and DNA microarraying. While the breakup of surfactant-free jets/drops has been exhaustively studied, little is known by comparison about interface rupture when the jet/drop liquids contain surfactants. High speed imaging is employed here to gain insights into differences between the dynamics of formation of drops of pure liquids, such as water, diethylene glycol, a 50 wt {\%} solution of 20 cSt and 50 cSt polydimethyl siloxane, and those of solutions consisting of different concentrations of a nonionic surfactant, pentaethylene glycol monododecyl ether C$_{12}$E$_{5}$ in mixtures of 75 wt {\%} (GW75) and 90 wt {\%} (GW90) glycerol/water, from a capillary tube. Equilibrium surface tensions of solutions of C$_{12}$E$_{5}$ are fitted with the Langmuir-Szyskowski equation and the critical micelle concentrations (cmc) are found to be 0.25 and 0.40 mM. Changes in dynamics of drop breakup are studied by varying surfactant concentration (below and above cmc), flow rate, tube radius, and liquid viscosity. [Preview Abstract] |
Monday, November 21, 2005 10:47AM - 11:00AM |
GB.00002: Effects of Soluble Surfactant on Drop Formation Ying-Chih Liao, Elias Franses, Osman Basaran Surfactants are routinely used to control the breakup of drops and jets in applications as diverse as emulsion and dispersion formation, ink jet printing, crop spraying, microarraying, and microencapsulation. Dynamics of formation of drops of incompressible Newtonian liquids containing a nonionic alkyl ethyleneoxide surfactant from a tube into air are studied experimentally using high-speed visualization and computationally using finite element analysis (FEA). Surfactant solutions at different concentrations below the critical micelle concentration (cmc) are formed by dissolving the surfactant in either water or mixtures of glycerol and water. In the absence of surfactant, computed results are shown to accord well with earlier predictions made with FEA. When surfactants are present, computed predictions are demonstrated to be in excellent agreement with the new experimental measurements. The effects of surfactant on volumes of primary drops and dynamics of satellite drops are also reported. [Preview Abstract] |
Monday, November 21, 2005 11:00AM - 11:13AM |
GB.00003: Observations of Tipstreaming in a Microfluidic Flow Focusing Device Hans Mayer, Shelley Anna We present experiments involving two-phase flows in a flow focusing microfluidic device. In particular we focus on the interaction of fluid motion and surfactant transport during the tipstreaming mode of droplet formation. Drop size, detailed interface shape, and frequency of drop formation are measured as a function of parameters such as surfactant concentration, dispersed and continuous phase flow rates, and device geometry. The capillary number in these experiments varies from \textit{Ca} $\sim $ 0.1 to 1, consistent with literature values for tipstreaming. Tipstreaming is a mode of drop breakup in which daughter droplets, usually orders of magnitude smaller than the parent drops, are ejected from the pointed tips of parent droplets or bubbles. An attractive characteristic of tipstreaming is that droplets produced are not limited by the device feature size. The overall motivation for our work is the controlled formation of highly monodisperse micron or sub-micron droplets and particles for high-value-added applications like drug delivery and pharmaceuticals. [Preview Abstract] |
Monday, November 21, 2005 11:13AM - 11:26AM |
GB.00004: Single Pass Drop Size Distributions in an Inline Rotor-Stator Mixer Karl Kevala, Ken Kiger, Richard Calabrese Rotor-stator mixers are employed to produce liquid-liquid dispersions. Despite their importance, there have been few studies that examine the fundamentals governing dispersion processes occurring in them. We have developed a technique to measure single pass drop size distributions (DSD) exiting an inline rotor-stator device. A continuous, turbulent water phase is fed to the mixer. At time zero, a single drop of oil is injected into the device, and the resulting daughter DSD is measured at the exit via Phase Doppler Anemometry. Bivariate statistics of drop size and residence time are obtained. Results indicate that, for the operating conditions studied, lower viscosity fluids have a bimodal distribution, with a shift towards a monomodal distribution at higher RPM or decreased throughput. More viscous fluids exhibit a monomodal distribution and a shift towards a bimodal distribution at higher RPM’s and decreased throughput. Turbulent RANS CFD simulations are being performed in order to assist in interpretation of experimental data. Preliminary results indicate that bimodal distributions may be the result of droplet reentrainment into the stator and / or a large spread in the internal time distributions that drops spend in the region close to the rotor blade. [Preview Abstract] |
Monday, November 21, 2005 11:26AM - 11:39AM |
GB.00005: Droplet breakup dynamics in a microfluidic T-junction Gordon Christopher, Nadia Noharuddin, Shelley Anna We present measurements of droplet breakup in shear-dominated flow in a microfluidic T-junction using high speed video imaging. In particular, we examine the transient drop shape as it breaks and relate this to critical behavior for drop breakup that has previously been reported in linear flows. We specifically focus on the capillary number, an important dimensionless variable in droplet breakup. In well-defined flows the capillary number is defined in terms of the characteristic shear rate and unperturbed drop size. In more complex geometries such as microfluidic devices it is more convenient to define capillary number through externally controlled parameters like flow rate and device geometry. We find that a `local' capillary number based on shear rate calculated from the time-varying gap between the emerging droplet and the channel wall is a more appropriate way of characterizing the breakup dynamics. We study the droplet breakup dynamics for a range of viscosity ratios and volume fractions. [Preview Abstract] |
Monday, November 21, 2005 11:39AM - 11:52AM |
GB.00006: Absolute instability of a flow focused capillary liquid microjet. The minimum liquid flow rate. Alfonso M. Ganan-Calvo, Pascual Riesco-Chueca The absolute instability of a gas-flow focussed capillary liquid microjet has been analyzed following a well established spatial- temporal linear stability analysis formalism (e.g. Leib and Goldstein 1986, Huerre and Monkewitz 1990, Chomaz 2005) for quasi-parallel developing flows. Under realistic conditions, a simple asymptotically exact model can be established from which a closed and simple analytical dispersion relation is obtained. This model reproduces the many earlier results from temporal stability analyses (back to Rayleigh 1878) existing in the literature for our fluidic configuration. In this work, however, in addition to provide a spatial-temporal stability analysis previously not attempted for our specific configuration, we unveil the fundamental role of the properly calculated gas-to- liquid momentum ratio and the asymptotic surface liquid velocity as a function of the Weber number. Thus, our approach asymptotically reduces the problem of finding the onset of absolute instability of a flow focused capillary microjet and the minimum liquid flow rate (for which the issuing microjet ceases to be steady and begins to drip) to find a critical Weber number which depends on the liquid properties and the geometry. Analytic results are then compared with experiments. [Preview Abstract] |
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