Bulletin of the American Physical Society
68th Annual Meeting of the APS Division of Fluid Dynamics
Volume 60, Number 21
Sunday–Tuesday, November 22–24, 2015; Boston, Massachusetts
Session M3: Suspensions: General |
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Chair: Themistoklis Sapsis, MIT Room: 102 |
Tuesday, November 24, 2015 8:00AM - 8:13AM |
M3.00001: Mobility of membrane-trapped particles Hassan Masoud, Howard Stone The translation or diffusion of particles along membranes or interfaces is of interest because it is a model system for describing basic features of interfacial hydrodynamics. It is also important in cellular signalling in biology and biophysics, and it can be used to deduce the rheological properties of surface films. Here, we consider the translational mobility of spherical and oblate spheroidal particles protruding into the surrounding subphase liquid. Both the subphase and surface film contribute to the resistance experienced by the particle, which is calculated as a function of the degree of protrusion as well as the viscosity contrast between the surface film and the surrounding fluid. The calculations are based on a combination of a perturbation expansion involving the particle shape and the Lorentz reciprocal theorem. It appears that just considering one term of the expansions is in very good agreement with available analytical and numerical results. [Preview Abstract] |
Tuesday, November 24, 2015 8:13AM - 8:26AM |
M3.00002: Eulerian flow modeling of suspensions containing interacting nano-particles: application to colloidal film drying. I. Gergianakis, M. Meireles, P. Bacchin, Y. Hallez Nano-particles in suspension often experience strong non-hydrodynamic interactions (NHIs) such as electrostatic repulsions. In this work, we present and justify a flow modeling strategy adapted to such systems. Earlier works on colloidal transport in simple flows, were based on the solution of a transport equation for the colloidal volume fraction with a known fluid velocity field and a volume-fraction-dependent diffusion coefficient accounting for mass fluxes due to NHIs. Extension of this modelling to complex flows requires the coupled resolution of a momentum transport equation for the suspension velocity field. We use the framework of the Suspension Balance Model to show that in the $Pe\ll1$ regime relevant here, the average $suspension$ velocity field is $ independent$ $of$ $NHIs$ $between$ $nanoparticles$, while the average $fluid\,\, phase$ and $solid\,\,phase$ velocity fields both always depend of the NHIs. Lastly, we apply this modelling strategy to the problem of the drying of a colloidal suspension in a micro-evaporator [Merlin et al. 2012, Soft Matter]. The influence of the effective Peclet number on the 1D/2D character of the flow is evaluated and the possible colloidal film patterning due to defaults of substrate topography is commented. [Preview Abstract] |
Tuesday, November 24, 2015 8:26AM - 8:39AM |
M3.00003: Migration of rigid particles in two-phase shear flow of viscoelastic fluids Patrick Anderson, Nick Jaensson, Martien Hulsen In the Stokes regime, non-Brownian, rigid particles in a shear flow will not migrate across streamlines if the fluid is Newtonian. In viscoelastic fluids, however, particles will migrate across streamlines away from areas of higher elastic stresses, e.g. towards the outer cylinder in a wide-gap Couette flow. This migration is believed to be due to a difference in normal stresses. We simulate the two-phase case where this difference in normal stresses is not due to the flow field, but rather due to the properties of the fluids. We apply the diffuse-interface model for the interface between the two fluids, which can naturally handle a changing topology of the interface, e.g. during particle adsorption. Furthermore, the diffuse-interface model includes an accurate description of surface tension and can be used for a moving contact line. A sharp interface is assumed between the particles and the fluids. Initially, a particle is placed close to an interface of two fluids with different viscoelastic properties in a shear flow. We show that based on the properties of the fluids and the interfacial tension, four regimes can be defined: 1) migration away from the interface, 2) halted migration towards the interface, 3) adsorption of the particle at the interface and 4) penetration of the particle into the other fluid. This research forms part of the research programme of the Dutch Polymer Institute (DPI), Project {\#}746. [Preview Abstract] |
Tuesday, November 24, 2015 8:39AM - 8:52AM |
M3.00004: Elliptical Particle Clustering in Cellular Flows Severine Atis, Themistoklis Sapsis, Thomas Peacock The transport of finite-sized objects by fluid flows is relevant to a wide variety of phenomena, such as debris transport on the ocean surface or bacteria advection in fluid environment. The shape of the advected objects can strongly alter their coupling with the surrounding flow field, and hence, greatly affecting their dispersion by the flow. We present the results of investigations of the behavior of neutrally buoyant, elliptical particles in two-dimensional cellular flows. We find that their trajectories, and overall organization, are markedly different than for spherical particles, with clear clustering for the elliptical particles associated with vortices. [Preview Abstract] |
Tuesday, November 24, 2015 8:52AM - 9:05AM |
M3.00005: General and Rigorous Framework for Particle Adsorption on Fluid Interfaces Markus Schmuck, Serafim Kalliadasis Consider two arbitrary immiscible phases where one phase contains small and neutral particles of uniform size on the order of the interface. The wetting properties of the particles are accounted for by the contact angle formed at the interface between the two fluid phases and the particles. Under experimental observations that particles are adsorbed on the interface to lower the interfacial energy and hence the surface tension as well, we formulate a free-energy functional that accounts for these physical effects. By making use of variational methods and a consistent gradient flow formulation, we obtain partial differential equations that systematically describe the location of the interface and the density of the particles in the fluid phases and the interface. Our numerical experiments analyse the time evolution of the surface tension, the particle concentration, and the free energy over time and reflect the crucial property of a decreasing free energy under particle adsorption. [Preview Abstract] |
Tuesday, November 24, 2015 9:05AM - 9:18AM |
M3.00006: Gravity-Driven Particle-Laden Flow on an Incline Sarah Burnett, Jesse Kreger, Hanna Kristensen, Andrew Stocker, Jeffrey Wong, Li Wang, Andrea Bertozzi We present experimental results of the height profile of particle-laden viscous thin films with finite volume on an incline. For high angles of inclination and high concentrations of mixtures, negatively buoyant particles undergo resuspension then accumulate at the front of the suspending fluid; this leads to the development of a particle-rich \lq ridge\rq. Theoretically, the ridge corresponds to the shocks which take on two characteristic shapes: singular and double shocks. We observe the presence of both formations experimentally by varying the volume of the slurry and compare our results to the theoretical model. Our research also investigates the dependence of the fingering instability as the inclination angle or particle to liquid concentration is changed. The slurries have similar dynamics to those used in coating flow techniques and other industrial applications. [Preview Abstract] |
Tuesday, November 24, 2015 9:18AM - 9:31AM |
M3.00007: Particle-induced viscous fingering Feng Xu, Dillon Strack, Grace Fomani, Celina Lopez, Sungyon Lee A novel fingering instability is experimentally observed when a mixture of particles and viscous oil is injected radially into a Hele-Shaw cell. According to the Saffman-Taylor theory, the equivalent configuration without particles exhibits no fingering. To characterize this particle-induced instability, a series of experiments are conducted with varying particle volume fractions, flow rates, and gap thicknesses. The experimental results show that the onset of finering is most directly affected by the particle volume fraction: the interface is stable when the particle concentration is lower than 10\% and becomes unstable with more pronouced fingering patterns with an increasing concentration. The interfacial instability is accompanied by regularized clusters of particles inside the displacing phase, each of which corresponds to a finger. Based on the key observations, we discuss the physical mechanism that drives the instablity. [Preview Abstract] |
Tuesday, November 24, 2015 9:31AM - 9:44AM |
M3.00008: Reverse drainage of a particle-laden thin film. Antonio Mastroberardino, Javed Siddique Gravity driven flow of a thin film on a solid surface is a critical aspect of numerous industrial applications including the production of foams, wire and optical coating applications, and more recently, the coating of medicines. In particular the system in consideration is influenced by competing forces, such as gravity, surface tension, and viscous forces, to name a few. ~Recently, several researchers have investigated the control of thin film flow by adding a controlling agent that allows for manipulation of the fluid via an external field. ~In this talk, we investigate the case in which the controlling agent is an aqueous suspension of magnetic nanoparticles and the external field is a nonuniform magnetic field. ~We formulate a mathematical model based on lubrication theory, present numerical solutions for the evolution of the film, and discuss the roles played by the key parameters of the system. [Preview Abstract] |
Tuesday, November 24, 2015 9:44AM - 9:57AM |
M3.00009: ABSTRACT WITHDRAWN |
Tuesday, November 24, 2015 9:57AM - 10:10AM |
M3.00010: Transport and Deposition of Electrosprayed Nanoparticles Nicholas Brown, Paul Chiarot In an electrospray, high electric potentials are utilized to generate a fine aerosol of a conductive solvent. For this study, the solvent consisted of nanoparticles dispersed in alcohol. The nanoparticle suspensions act as printable nanoparticle inks. In this process, a glass capillary tube is held as a high electric potential relative to a grounded reference plate located below the tip. Droplets are ejected from the tube and are directed towards the ground plate. If the solvent is sufficiently volatile, it will rapidly evaporate while the droplets are in flight (due to the high surface area to volume ratio) leaving behind dry, highly charged nanoparticles. The droplets/nanoparticles are deposited onto a target substrate that is place onto the grounded plate. The transport of any individual droplet/nanoparticle from the emitter tip to the target substrate is a stochastic process. This transport can be modeled using a Monte Carlo simulation. The probability of an individual particle being deposited at a given location on the target substrate is directly related to the electric potential at that location. In other words, the probability function that determines the deposition is directly related to the electric potential at the substrate. The total potential is comprised of the applied electric potential required to generate the electrospray, the induced charge on the surface of the target dielectric, and the charge on the individual particles themselves. We report on the structure of droplet/nanoparticle deposits printed using electrospray. The evolution of the deposit is investigated over time using experimental studies and Monte Carlo simulations. The deposit structure passes through four distinct regimes that are characterized by repeatable bulk features. [Preview Abstract] |
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