Bulletin of the American Physical Society
66th Annual Meeting of the APS Division of Fluid Dynamics
Volume 58, Number 18
Sunday–Tuesday, November 24–26, 2013; Pittsburgh, Pennsylvania
Session M7: Nanofluids II |
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Chair: Reza Sadr, Texas A&M University at Qatar Room: 329 |
Tuesday, November 26, 2013 8:00AM - 8:13AM |
M7.00001: A Statistical Perspective on the Effects of Brownian Particle Movements on the Induced Fluid Flow Field Way Lee Cheng, Reza Sadr Nanofluids, engineered fluids by dispersing nanometer-sized materials in a base fluid, are reported to have anomalous heat transfer characteristics. In spite of the large number of, sometimes conflicting, reports on the existence and magnitude of enhancement, the underlying principles governing the improvements in the heat transfer process is not thoroughly understood. The interaction between the discrete and continuous phases in the fluid is thought to be a major contributor of the observed phenomena. The current study examines the fluid-particles interactions, induced by randomly moving particles suspended in a base fluid, from a statistical perspective, using an affordable computational approach. The fluid-particle interactions are described by Navier-Stokes equations on the fluid phase coupled with Langevine equation for the random walk of the suspended nano particles. Effects of particle diameter, unsteady movement, and hydrodynamics inertia in the fluid are examined in the current model. Results of the simulations show that the random movements of the particles induce a small random flow within the fluid. Statistics of the induced flow field converges asymptotically as the Brownian time-step reduces. [Preview Abstract] |
Tuesday, November 26, 2013 8:13AM - 8:26AM |
M7.00002: Non-additive entrance effects in ionic conductance of an array of solid-state nanopores Alessandro Gadaleta, Catherine Sempere, Simon Gravelle, Remy Fulcrand, Alessandro Siria, Lyd\`eric Bocquet The ionic conductance of small pores has long been a topic of interest in many diverse areas of application, starting from electrophysiology in the 1950s to research on ultrarapid DNA sequencing and ion selective membranes in recent times. The so-called access resistance, induced by the convergence of field lines from the electrode to the pore, gives a significant contribution to the total ionic resistance. Here we investigate, experimentally and numerically, the access resistance of an array of solid-state nanopores, and show that it is not additive. We show how this problem can be approximately solved with simple electrostatics, presenting a matrix formalism which allows to quickly estimate the entrance effects in any given geometry. [Preview Abstract] |
Tuesday, November 26, 2013 8:26AM - 8:39AM |
M7.00003: Rheological assessment of nanofluids at high pressure high temperature Anoop Kanjirakat, Reza Sadr High pressure high temperature (HPHT) fluids are commonly encountered in industry, for example in cooling and/or lubrications applications. Nanofluids, engineered suspensions of nano-sized particles dispersed in a base fluid, have shown prospective as industrial cooling fluids due to their enhanced rheological and heat transfer properties. Nanofluids can be potentially utilized in oil industry for drilling fluids and for high pressure water jet cooling/lubrication in machining. In present work rheological characteristics of oil based nanofluids are investigated at HPHT condition. Nanofluids used in this study are prepared by dispersing commercially available SiO$_{2}$ nanoparticles ($\sim$20nm) in a mineral oil. The basefluid and nanofluids with two concentrations, namely 1{\%}, and 2{\%}, by volume, are considered in this investigation. The rheological characteristics of base fluid and the nanofluids are measured using an industrial HPHT viscometer. Viscosity values of the nanofluids are measured at pressures of 100kPa to 42MPa and temperatures ranging from 25$^{\circ}$C to 140$^{\circ}$C. The viscosity values of both nanofluids as well as basefluid are observed to have increased with the increase in pressure. [Preview Abstract] |
Tuesday, November 26, 2013 8:39AM - 8:52AM |
M7.00004: Automated Characterization and Sorting of Nanowires by Solution-Based Electro-Orientation Spectroscopy Cevat Akin, Jerry Shan The electrical conductivity and/or permittivity of nanowires and nanotubes are often poorly known and difficult to measure, requiring cleanroom-based microfabrication and precision positioning to measure directly. Traditional direct-characterization methods are also not compatible with further solution-based processing of nanowires. Electro-orientation spectroscopy, the rotation of nanowires in liquid suspension into alignment with external AC electric fields of different frequency, offers an alternative measurement technique that is simple and also compatible with further solution-based sorting and positioning of particles. We present the theory and our experimental results obtained by optical microscopy on the alignment rate of suspended nanowires of known conductivities under spatially uniform AC electric fields of different frequency. The deduced electrical conductivities of the nanowires are compared to direct 2-point-probe measurements. We demonstrate the compatibility of the electro-orientation method with further solution-based processing by implementing the technique in a novel microfluidic device capable of automated electrical characterization and sorting of nanowires. [Preview Abstract] |
Tuesday, November 26, 2013 8:52AM - 9:05AM |
M7.00005: Collective alignment of nanorods in thin Newtonian films Yu Gu, Ruslan Burtovyy, James Townsend, Jeffery Owens, Igor Luzinov, Konstantin Kornev We provide a complete analytical description of the alignment kinetics of magnetic nanorods in magnetic field. Nickel nanorods were formed by template electrochemical deposition in alumina membranes from a dispersion in a water--glycerol mixture. To ensure uniformity of the dispersion, the surface of the nickel nanorods was covered with polyvinylpyrrolidone (PVP). A 40--70 nm coating prevented aggregation of nanoroda. These modifications allowed us to control alignment of the nanorods in a magnetic field and test the proposed theory. An orientational distribution function of nanorods was introduced. We demonstrated that the 0.04{\%} volume fraction of nanorods in the glycerol--water mixture behaves as a system of non-interacting particles. However, the kinetics of alignment of a nanorod assembly does not follow the predictions of the single-nanorod theory. The distribution function theory explains the kinetics of alignment of a nanorod assembly and shows the significance of the initial distribution of nanorods in the film. It can be used to develop an experimental protocol for controlled ordering of magnetic nanorods in thin films. [Preview Abstract] |
Tuesday, November 26, 2013 9:05AM - 9:18AM |
M7.00006: Correlation between translational and rotational diffusion of a Janus nanoparticle in explicit solvent: A molecular dynamics simulation study Ali Kharazmi, Nikolai Priezjev Molecular dynamics simulations are used to study the diffusion of a single Janus particle immersed in a Lennard-Jones fluid. We consider a spherical particle with two hemispheres of different wettability. We analyzed the time dependence of the orientation tensor, particle displacement, and translational and rotational velocity autocorrelation functions. It was found that both translational and rotational diffusion coefficients increase with decreasing surface energy of the nonwetting hemisphere. We also observed that in contrast to homogeneous particles, the nonwetting hemisphere of the Janus particle tends to rotate in the direction of the displacement vector during the rotational relaxation time. [Preview Abstract] |
Tuesday, November 26, 2013 9:18AM - 9:31AM |
M7.00007: Molecular Dynamics of Reaction-Driven, Diffusiophoretic, Colloid Self-Propulsion Nima Sharifi-Mood, Joel Koplik, Charles Maldarelli Chemical-mechanical transduction mechanisms which can actuate the movement of colloids through pathways in liquids are highly sought after as engines to propel miniaturized micro and nanobots. One mechanism involves harnessing van der Waals attractive forces between the colloid and solute molecules. Self propulsion can be achieved by arranging for the solute to react on one face of the colloid, creating an asymmetric distribution which can propel the particle. We use molecular dynamics calculations to elucidate this propulsion for nanocolloids. The calculations assume Lennard-Jones interactions between the colloid (modelled as a rigid cluster of atoms), solvent atoms and solute atoms which react with the colloid atoms on one face of the cluster. The solute reacts when localized within the attractive landscape of the cluster atoms and is converted for simplicity to solvent. Quantitative calculations of the diffusiophoretic velocity demonstrate the interplay of Brownian rotation and diffusiophoretic propulsion, the dependence of the nano-colloid velocity on its radius and an agreement with a continuum model which therefore allows a description of the phenomena for propulsion of objects in size and over trajectories from the nanometer to the micron scale. [Preview Abstract] |
Tuesday, November 26, 2013 9:31AM - 9:44AM |
M7.00008: Repulsion parameters for carbon nanotubes in water in Dissipative Particle Dynamics simulations Minh Vo, Dimitrios Papavassiliou In Dissipative Particle Dynamics (DPD) simulations, the thermodynamic and transport properties of the DPD fluid are governed by the selection of the repulsion, dissipation, and random noise parameters, because these parameters control the interaction potential and the motion of each DPD bead at each time step. For the case of the motion of carbon nanotubes in a water nanochannel, appropriate choices need to be made to ensure that DPD beads represent the system. The dissipative parameter ($\gamma )$ should be equal to 4.5 for simulation stability. The noise parameter ($\sigma )$ can be calculated using dissipation fluctuation relation, when the temperature of the system reaches equilibrium. In order to determine the repulsion parameter (a$_{\mathrm{ij}})$ of CNT and water, we simulate the case of water flow past an array of single-walled CNTs. In this case, results from molecular dynamics simulations by Walther et al. (Phys. Rev. E, 2004, 062201) are available and can be used for validation. The hydrodynamic properties for a (32,0) single-walled CNT (32,0) with diameter of 2.5 nm were determined in different Reynolds number flows. With aij $=$ 60 (kT/r$_{\mathrm{c}})$, the drag coefficients of the CNT are quite similar to values from the analytical solution of the Stocks -- Oseen equation. Additionally, the slip length on the CNT wall is comparable with the Walther et al. results. In addition, the application of these parameters in longer length scales and time scale will be discussed by increasing the number of water molecules grouped into each DPD bead. [Preview Abstract] |
Tuesday, November 26, 2013 9:44AM - 9:57AM |
M7.00009: Fast Rotation of a Single Water Molecule in Buckyball Amir Barati Farimani, Yanbin Wu, Narayana Aluru Successful encapsulation of a single water molecule in C60 by Kurotobi and Murata (Science, 333, 2011) opens up an opportunity to study non-hydrogen bonded single water molecule. Here, we investigate the properties of a single water molecule in buckyball by using molecular dynamics (MD) and density functional theory (DFT). By using DFT, we found that there's a shift of 23 cm$^{-1}$ in vibrational frequencies of O-H bond of water molecule when it's inside C60. By using MD, we compute the rotational diffusion and entropy of water. Our findings show that water rotates about an order of magnitude faster compared to a single water molecule in bulk. While H$_{2}$O@C60 has near zero translational entropy, its rotational entropy is 6.5 times larger than rotational entropy of bulk water. [Preview Abstract] |
Tuesday, November 26, 2013 9:57AM - 10:10AM |
M7.00010: Electrophoretic mobility of spherical nanoparticles confined in nanochannels Yu-Wei Liu, Tom Wynne, Sumita Pennathur, Carl Meinhart We investigate the mobility of a charged spherical nanoparticle driven by weak electric fields that are confined in nanochannels. Factors affecting mobility include particle zeta potential, electrolyte concentration, and channel size. Classic models for electrophoretic mobility (e.g. Smoluchowski and Huckel) are valid only in the linear regime of small particle zeta potential, and for an unbounded fluid domain. The classical models fail to predict electrophoretic mobility estimated from experiments using $\sim$ 42 nm diameter particles confined in a $\sim$ 100 nm nanochannel. We adopt the asymptotically-expanded formulations of Khair and Squires (Phys. Fluids, 2009), and solve the fully-coupled equations on a well-resolved 3D finite element domain. For a charged 42 nm diameter nanoparticle, confined in a 100 nm high nanochannel, the electrophoretic mobility increases nonlinearly when particle zeta potential is greater than thermal potential $k_{B} T/e$. When the channel size is decreased from 2.5 um to 100 nm, the mobility is reduced by up to 20{\%}. The result suggests that particle/wall interactions, including overlapping double layers may affect electrophoretic mobility in a non-linear manner. [Preview Abstract] |
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