Bulletin of the American Physical Society
67th Annual Meeting of the APS Division of Fluid Dynamics
Volume 59, Number 20
Sunday–Tuesday, November 23–25, 2014; San Francisco, California
Session G13: Drops: General II |
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Chair: Howard Stone, Princeton University Room: 3020 |
Monday, November 24, 2014 8:00AM - 8:13AM |
G13.00001: Coffee-ring and uniform deposits from sessile nanofluid droplet evaporation Fei Duan, Xin Zhong Nanofluid droplet evaporation process has been investigated for the final deposits of particles for coffee-ring or uniform deposition. The 3-4 nm graphite nanoparticles are selected for preparing the nanofluids with surfactant or without the surfactant. The evaporation in term of contact angle, contact line, volume, spreading, etc, shows that the nanoparticles enhance the pinning effect and the evaporation rate, despite that the enhancement can be weakened as the nanoparticle concentration is higher in the samples without surfactant. In the sample with the surfactant, the variations of baseline, contact angle, volume and evaporation rate are abnormal at a certain surfactant concentration. Further discussion is conducted for the transition. The role of the surfactant influents the drying patterns from coffee ring to uniform deposition. The simulation is developed to help to understand the effect. [Preview Abstract] |
Monday, November 24, 2014 8:13AM - 8:26AM |
G13.00002: Inverse Floatation Saurabh Nath, Anish Mukherjee, Souvick Chatterjee, Ranjan Ganguly, Swarnendu Sen, Achintya Mukhopadhyay, Jonathan Boreyko We have observed that capillarity forces may cause floatation in a few non-intuitive configurations. These may be divided into 2 categories: i) floatation of heavier liquid droplets on lighter immiscible ones and ii) fully submerged floatation of lighter liquid droplets in a heavier immiscible medium. We call these counter-intuitive because of the inverse floatation configuration. For case (i) we have identified and studied in detail the several factors affecting the shape and maximum volume of the floating drop. We used water and vegetable oil combinations as test fluids and established the relation between Bond Number and maximum volume contained in a floating drop (in the order of $\mu$L). For case (ii), we injected vegetable oil drop-wise into a pool of water. The fully submerged configuration of the drop is not stable and a slight perturbation to the system causes the droplet to burst and float in partially submerged condition. Temporal variation of a characteristic length of the droplet is analyzed using MATLAB image processing. The constraint of small Bond Number establishes the assumption of lubrication regime in the thin gap. A brief theoretical formulation also shows the temporal variation of the gap thickness. [Preview Abstract] |
Monday, November 24, 2014 8:26AM - 8:39AM |
G13.00003: Vapor mediated droplet interactions - self-sensing droplet machines (Part 1) Nate Cira, Adrien Benusiglio, Manu Prakash Reducing contact angle hysteresis is one strategy for making droplets mobile. Typically this involves carefully preparing a near-ideal surface. Here we show that a class of two-component droplets is self-motile on any high energy surface. Surprisingly, these binary droplets have characteristics of both completely and partially wetting fluids which precludes any hysteresis. This allows us to easily create mobile droplet systems with simple everyday materials like glass slides and sharpie. We build on the fundamental mechanisms and models we developed for this system and present multiple fluidic machines which take advantage of interactions between the droplets to autonomously execute complex tasks such as sorting and pattern formation. Time permitting we will run a live experiment to highlight the phenomena being discussed.~ [Preview Abstract] |
Monday, November 24, 2014 8:39AM - 8:52AM |
G13.00004: Vapor mediated droplet interactions - models and mechanisms (Part 2) Adrien Benusiglio, Nate Cira, Manu Prakash When deposited on clean glass a two-component binary mixture of propylene glycol and water is energetically inclined to spread, as both pure liquids do.~Instead the mixture forms droplets stabilized by evaporation induced surface tension gradients, giving them unique properties such as negligible hysteresis. When two of these special droplets are deposited several radii apart they attract each other. The vapor from one droplet destabilizes the other, resulting in an attraction force which brings both droplets together. We present a flux-based model for droplet stabilization and a model which connects the vapor profile to net force. These simple models capture the static and dynamic experimental trends, and our fundamental understanding of these droplets and their interactions allowed us to build autonomous fluidic machines.~ [Preview Abstract] |
Monday, November 24, 2014 8:52AM - 9:05AM |
G13.00005: The Effect of Maxwell Slip on Gravitational Collisions of Viscous Drops Michael Rother When the gap between two spherical particles or liquid drops is comparable to the mean free path of surrounding fluid molecules, Stokes theory for the motion of the matrix fluid is no longer adequate. Use of the Maxwell slip approximation in this region shows that the resistance between two approaching surfaces decreases and that collision is possible, even for two solid particles. An important application of slip flow theory is to raindrop growth, where the mean free path of the air molecules is approximately 0.1 $\mu$m. Previous study of water drops in the atmosphere has treated small drops as solid spheres. In the current work, relative trajectories are calculated for two spherical liquid drops with exact methods for determining the hydrodynamic forces at finite Stokes number and low Reynolds number in gravitational flow. These constraints are met for drops between 10 and 30 $\mu$m in radius. In close approach, lubrication and attractive molecular forces are considered. In addition, Maxwell slip effects are determined exactly for motion along the drops' line of centers by bispherical coordinate techniques. Collision efficiencies for liquid drops, including Maxwell slip with allowance for internal circulation in the drops, are compared to those for solid spheres. [Preview Abstract] |
Monday, November 24, 2014 9:05AM - 9:18AM |
G13.00006: Rising motion of a suspension of drops in a linearly stratified fluid Sadegh Dabiri, Amin Doostmohammadi, Morteza Bayareh, Arezoo Ardekani Vertical variation of water temperature or salinity results in the generation of vertical density stratification in the water column in oceans and lakes and can affect the motion of particles, drops, and bubbles. Despite the broad body of research on the vertical motion of rigid particles in stratified fluids, the hydrodynamics of the vertical motion of deformable particles and drops in stratified fluids is currently poorly understood. In this manuscript, we report on the direct numerical simulations of a suspension of rising drops in a linearly stratified fluid. Our results show that density stratification suppresses both average rise velocity and velocity fluctuations of drops and results in an enhanced isotropy of velocity fluctuations. The combined effects of stratification, void fraction and deformability of drops on the motion of the suspension of drops are characterized. The results show that density stratification leads to an enhanced horizontal cluster formation. [Preview Abstract] |
Monday, November 24, 2014 9:18AM - 9:31AM |
G13.00007: Drop Size and Velocity Distributions of the Spray of Aerated Liquid Injection in Gaseous Crossflow Khaled Sallam, Adegboyega Adebayo In this study an experimental investigation of the drop size and velocity distributions of the spray of an aerated liquid injection in subsonic crossflow is described. The test conditions for this study include injector exit diameter of 1 mm, crossflow Mach number of 0.3, momentum flux ratio of 5, and gas-to-liquid mass ratio of 8{\%}. Double pulsed digital holography was used to investigate the spray characteristics at downstream distances of 50, and 100 jet diameter. The holograms are reconstructed into ``slices'' and analyzed using image-processing algorithms to yield information about the drop sizes and drop velocities. Four different drop size distributions are tested: the normal distribution, the Rosin-Rammler distribution, the log normal distribution, and the Simmons' universal root-normal distribution. It was found that the log normal distribution best quantified the data obtained in this study. The drop streamwise and cross stream velocities at downstream distances of 50 jet diameter were found to be still evolving. The crossflow drop velocities converged to almost uniform velocity at a distance of 100 jet diameters downstream from the injector exit. [Preview Abstract] |
Monday, November 24, 2014 9:31AM - 9:44AM |
G13.00008: On the Calculation of Planar Spray Characteristics from Point Sampled Data Kyle Bade, Rudi Schick An investigation into methods used to generate planar spray characteristics, such as mean drop size and velocity, from discrete measurement points is conducted. Two sprays are investigated, a hydraulic full cone spray, and an air-atomized multi-orifice spray, where an excessive number of sample-point locations are acquired using a Phase Doppler Interferometer (PDI) resulting in overly resolved spatial resolution, at a single axial plane. Due to the intentional spatial over-sampling, the data may be downsampled to determine the minimum number of required sample points to calculate reliable mean spray values. For each spray pattern, the influence of various spatial subsets of sampling points is investigated to determine the minimum number of required sample points for accurate planar results; normalized metric are developed to govern the number of sample points. In a related effort, meaningful average values are calculated using weighting methods and assessed for relative influence on the final calculations. Specifically, volume flux and discrete area weighting methods are developed and evaluated. evaluated. The results of this investigation allow a minimum number of data points to be processed into reliable planar spray characteristics. [Preview Abstract] |
Monday, November 24, 2014 9:44AM - 9:57AM |
G13.00009: Dynamics of Rising Dispersant Laden Oil Drops in a Quiescent Environment Khalil Castillo-Aponte, Faraz Mehdi, Jian Sheng We study the dynamics of rising oil drops in a quiescent fluid chamber under uniform and density stratified conditions. Digital in-line holography allows for high resolution topological measurements and tracking of drop trajectories. Statistics of rising velocities, drop shapes and sizes are compared as functions of different oil-dispersant ratios. A conceptual model of an oil drop developing appendages and its subsequent breakdown into much smaller droplets is also discussed. [Preview Abstract] |
Monday, November 24, 2014 9:57AM - 10:10AM |
G13.00010: The effects of aspect ratio on the flow invariants of droplets in an axisymmetric micro-tube Adam DeVoria, Kamran Mohseni In this study the potential benefits of using a digitized flow (droplets) in place of a continuous flow are investigated. In particular, the aspect ratio (AR) of the droplets is varied and is an important parameter representing how different the droplet flow is from continuous flow. The flow within the droplets is measured with micro digital particle image velocimetry. The measurements are used to compute the flow invariants, namely circulation, hydrodynamic impulse, and kinetic energy in the droplet. It is found that the non-dimensionalized experimental invariants for low-AR droplets are increased above those for a corresponding segment of continuous flow. Also increased are the fluxes of the invariants, as well as the momentum flux. These increases above continuous flow go as the inverse of AR. For jetting applications, the implication is that using a digitized flow can increase the rate of generation of momentum and energy compared to a continuous jet, and furthermore that the droplet AR controls the amount of increase. [Preview Abstract] |
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