Bulletin of the American Physical Society
64th Annual Meeting of the APS Division of Fluid Dynamics
Volume 56, Number 18
Sunday–Tuesday, November 20–22, 2011; Baltimore, Maryland
Session G2: Nanofluids II |
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Chair: Jens Walther, Technical University of Denmark Room: 302 |
Monday, November 21, 2011 8:00AM - 8:13AM |
G2.00001: Continuum and Molecular Dynamics Studies On the Diffusiophoretic Motion Nima Sharifi-Mood, Joel Koplik, Charles Maldarelli The self-propulsion of micron or sub-micron objects has a number of applications as miniaturized motors. One method for particle self propulsion is to utilize a surface chemical reaction on one part of the particle surface to create concentration gradients of solutes across the particle. These gradients drive a diffusiophoretic motion due to unbalanced (van der Waals) attractions between the particle and the solutes and solvent within an intermolecular length scale (L, 10-100 nm) of the particle surface. Prior continuum studies assume the interaction creates a local slip velocity at the particle surface, and find the terminal velocity U of spherical particles to be independent of the radius a. We provide numerical solutions for U which account directly for the solute transport and flow within L, and matched asymptotic solutions as L/a tends to zero. The leading order expression for U is independent of a, but U decreases with the particle radius for L/a greater than .01. Molecular dynamics simulation is also undertaken using Lennard-Jones potentials to provide a more complete picture of nanoscale propulsion. [Preview Abstract] |
Monday, November 21, 2011 8:13AM - 8:26AM |
G2.00002: Nanofluid heat transfer anomaly: Theoretical explanation of observations in the development region of microchannels J.T.C. Liu Continuing from http://meetings.aps.org/link/BAPS.2010.DFD.CP.7 is the work on analytical solutions to the first order perturbation problem for momentum, heat and volume concentration following the continuum conservation equations for nanofluids (Buongiorno 2006; Pfautsch 2008; Tzou 2008), simplified by the Rayleigh-Stokes approximation and perturbation in small free stream volume fraction. The disparate momentum, heat and volume fraction transport layer thicknesses$\delta _u >\delta _T >>\delta _\phi $, are estimated for metallic nanofluids, further structures the transport problems. From experiments of, e.g., Wen {\&} Ding 2004, Jung, et al. 2009, it is concluded that the observed large ``anomalous'' surface heat transfer rates for small increases in the volume fraction, especially at the leading edge of laminar microchannel nanofluid flows, is partially attributable to the nanofluid modification of the temperature profile by the inertial effects of modified density and heat capacity and of conduction effects of the modified thermal conductivity. The solutions obtained display these contributions explicitly. Thus the use of nanofluid transport properties in the correlation of laminar heat transfer must necessarily be accompanied by the detailed considerations of the temperature profile modification in nanofluid flow via the conservation equations. [Preview Abstract] |
Monday, November 21, 2011 8:26AM - 8:39AM |
G2.00003: Transport of nonaparticles flowing past a patterned substrate Rui Zhang, Joel Koplik We consider the defection of suspended particle trajectories due to flow past a patterned surface using complimentary Langevin numerical simulations and theoretical analyses based on the Fokker-Planck equation. The intended application is to vector particle separation in a nanofluidic channel. The simulations of flow past an alternating periodic striped pattern of attractive and repelling regions generally show that particles are deflected away from the imposed flow direction, to a degree that depends on the particle's size and the details of the substrate interaction. Both van der Waals and Coulomb interactions are studied, and in the latter case we explore the effects of the spatial distribution of bounding surface charge. Theoretically, both exactly in two dimensions and within the Fick-Jacobs approximation in three, we show that the effect of a periodic potential on the particle motion is always to impede the mean transport velocity in the orthogonal direction and deflect the trajectory, or equivalently reduce the effective diffusivity. Upper and lower bounds are found for the deflection angle, and explicit estimates are obtained in the limit of a weakly varying interaction. [Preview Abstract] |
Monday, November 21, 2011 8:39AM - 8:52AM |
G2.00004: Molecular dynamics simulations of Janus nanoparticles in evaporating droplets Weikang Chen, Joel Koplik, Ilona Kretzschmar We use numerical simulations to study the evaporation of sessile droplets containing Janus particles placed on a heated surface. The droplets are composed of a Lennard-Jones fluid, the particles are rigid spherical sections of an atomic lattice and heating is controlled through the temperature of the (atomistic) surface. The study focuses on the time evolution of the droplets shape, contact angle, velocity field and evaporative flux, as well as the motion of the particles and the effects of the Janus interactions on the structure of the particulate deposit. The results are compared with recent theory and experiment. [Preview Abstract] |
Monday, November 21, 2011 8:52AM - 9:05AM |
G2.00005: Properties of Water/Gold Nanofluids Gianluca Puliti, Samuel Paolucci, Mihir Sen Nanofluids belong to a new class of fluids with enhanced thermophysical properties and heat transfer performance. A broad spectrum of applications in science and engineering can potentially benefit from their use. However, the physical explanation for this enhancement is still lacking. The novelty of this work is in a fundamental, realistic, and comprehensive approach to the problem of understanding nanofluids through the use of molecular dynamics simulations with accurate potentials to model realistic materials. Specifically, this study treats the case of water confined between gold nanolayers to examine interfacial interactions and a water-based nanofluid with spherical gold nanoparticles. Thermodynamics and transport properties will be discussed for both systems. It is interesting to note that while the thermodynamic properties of the mixture are typically predicted using ideal mixture theory, such predictions are found to be generally poor for nanofluids. The anisotropy induced by the gold-water interface, and its effects appear to be responsible for the disagreement. We will also discuss the role of interfacial effects on the anomalous enhancement of nanofluid transport properties. [Preview Abstract] |
Monday, November 21, 2011 9:05AM - 9:18AM |
G2.00006: A comparative study of different ferrofluid constitutive equations. Purna Kaloni Ferrofluids are stable colloidal suspensions of fine ferromagnetic monodomain nanoparticles in a non-conducting carrier fluid.The particles are coated with a surfacant to avoid agglomeration and coagulation.Brownian motion keeps the nanoparticles from settling under gravity.In recent years these fluids have found several applications including in liquid seals in rotary shafts for vacuum system and in hard disk drives of personal computers,in cooling and damping of loud speakers, in shock absorbers and in biomedical applications. A continuum description of ferrofluids was initiated by Neuringer and Rosensweig [1] but the theory had some limitations. In subsequent years,several authors have proposed generalization of the above theory.Some of these are based upon the internal particle rotation concept, some are phemonological,some are based upon a thermodynamic framework,some employ statistical approach and some have used the dynamic mean field approach.The results based upon these theories ane in early stages and inconclusive. Our purpose is, first, to critically examine the basic foundations of these equations and then study the pedictions obtained in all the theories related to an experimental as well as a theoretical study. [1]J.L.Neuringer and R.E. Rosensweig, Physics Fluids,7.1727 (1964).. [Preview Abstract] |
Monday, November 21, 2011 9:18AM - 9:31AM |
G2.00007: Influence of Red Blood Cells on Nanoparticle Targeted Delivery in Microcirculation Jifu Tan, Antony Thomas, Yaling Liu In this paper, a particle-cell hybrid model is developed to model Nanoparticle (NP) transport, dispersion, and binding dynamics in blood suspension under the influence of Red blood cells(RBCs). The motion and deformation of RBCs is captured through the Immersed Finite Element Method. The motion and adhesion of individual NPs are tracked through Brownian adhesion dynamics. A mapping algorithm and an interaction potential function are introduced to consider the cell-particle collision. NP dispersion and binding rates are derived from the developed model under various rheology conditions. The influence of RBCs, vascular flow rate, and particle size on NP distribution and delivery efficacy is characterized. A non-uniform NP distribution profile with higher particle concentration near the vessel wall is observed. Such distribution leads to over 50{\%} higher particle binding rate compared to the case without RBC considered. The tumbling motion of RBCs in the core region of the capillary is found to enhance NP dispersion, with dispersion rate increases as shear rate increases. Results from this study contribute to the fundamental understanding and knowledge on how the particulate nature of blood influences NP delivery, which will provide mechanistic insights on the nanomedicine design for targeted drug delivery applications. [Preview Abstract] |
Monday, November 21, 2011 9:31AM - 9:44AM |
G2.00008: The Role of Hydrodynamic Behavior of DNA Molecules in Dielectrophoretic Polarization under the Action of an Electric Field Hui Zhao A continuum model is developed to predict the dielectrophoretic polarizability of coiled DNA molecules under the action of an alternating current electric field. The model approximates the coiled DNA molecule as a charged porous spherical particle. The model explains the discrepancies among scaling laws of polarizability of different-sized DNA molecules with contour length and such discrepancies are attributed to different hydrodynamic behavior. With no or one fitting parameter, theoretical predictions are in good agreements with various experimental data, even though in experiments there are some uncertainties in regards to certain parameters. [Preview Abstract] |
Monday, November 21, 2011 9:44AM - 9:57AM |
G2.00009: Emission and Charging of Nanoaerosol Plumes from a Taylor Cone-Jet Yunshan Wang, Ming K. Tan, David B. Go, Hsueh-Chia Chang We examine the explosive atomization at the tip of a Direct-Current Taylor cone-jet for an electrolyte, which is the most common mode for electrospray proteomic mass spectrometry applications but whose fundamental mechanism remains unknown. With scaling arguments and imaging experiments, we demonstrate the underlying physics to be the induction of a polarized region with a high space charge density in the microjet by the dominant Taylor harmonic of the cone. The induced space charge density increases along the jet until Coulombic repulsion among the space charges, when their separation is below the Bjerrum length, triggers the explosive microjet atomization and emits charged nanoaerosols in distinct conic plumes. As the induced microjet space charge can be estimated by a nonlinear Guoy-Chapman equilibrium analysis for strong electrolytes, the jet breakup length, current-flow rate correlation, aerosol size/charge and plume angle are strong functions of ionic strength and interfacial tension and are quantitatively captured by our universal scaling laws. [Preview Abstract] |
Monday, November 21, 2011 9:57AM - 10:10AM |
G2.00010: Computer simulation of DNA translocation in functionalized conical nanopores Guoqing Hu, Bao Jiao As a powerful research tool to rapidly investigate the dynamic and structural properties of single biomolecules such as DNA and protein, solid-state single nanopores have attracted a great deal of scientific interests. In a typical setup, DNA molecule is driven electrokinetically and its translocation is conveniently detected via the ionic current measurement through single nanopores. One of challenges arising from solid-state nanopore DNA sequencing technique is the molecular selectivity and detection resolution. Tuning the geometry and surface property of nanopores helps create sensing devices that control transport of ions and molecules in electrolyte. Here we present molecular dynamics simulation method to study the ion transport and DNA translocation phenomena in conically shaped nanopores coated with single-stranded DNA molecules. Computer simulations characterize the effects of the effective nanopore diameter, conical pore geometry, ionic strength, surface charge, and applied biasing voltage on the ionic current and DNA translocation dynamics. The findings can be used to improve and optimize the experimental design for DNA detection in single nanopore devices. [Preview Abstract] |
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