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 M9: Nanoscale Flows: Computations |
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Chair: Jason Reese, Edinburgh University Room: 109 |
Tuesday, November 24, 2015 8:00AM - 8:13AM |
M9.00001: Hybrid molecular-continuum techniques for micro and nano flows Jason Reese, Konstantinos Ritos, Matthew Borg, Duncan Lockerby Nano- and micro-confined fluid flows are often characterised by non-continuum effects that require special treatment beyond the scope of conventional continuum-fluid modelling. However, if the flow system has high-aspect-ratio components (e.g. long narrow channels) the computational cost of a fully molecular-based simulation can be prohibitive. In this talk we present some important elements of a heterogeneous molecular-continuum method that exploits the various degrees of scale separation in both time and space that are very often present in these types of flows. We demonstrate the ability of these techniques to predict the flow of water in aligned carbon nanotube (CNT) membranes: the tube diameters are 1-2 nm and the tube lengths (i.e. the membrane thicknesses) are 2-6 orders of magnitude larger. We compare our results with experimental data. We also find very good agreement with experimental results for a 1 mm thick membrane that has CNTs of diameter 1.59 nm. In this case, our hybrid multiscale simulation is orders of magnitude faster than a full molecular dynamics simulation. [Preview Abstract] |
Tuesday, November 24, 2015 8:13AM - 8:26AM |
M9.00002: Microscal Thermal Flow Field Fractionation of DNA by Size Jennifer Pearce, Faihan Alfahani We present results from a lattice-Boltzmann-base Brownian Dynamics simulation on the separation of DNA by length using thermal flow field fractionation in a microfluidic device. A temperature gradient in combination with fluid flow allows us to separate long and short strands of DNA. Shorter DNA fragments have higher Soret coefficients and therefore migrate more strongly in the temperature gradient than long strands. They are therefore closer to the channel walls and have a lower mean velocity than longer strands. The retention time in the channel for longer DNA chains is significantly shorter than for small chains. This technique has the advantage that long strands can be processed quickly, unlike traditional agarose gel techniques which require longer times for longer fragments. [Preview Abstract] |
Tuesday, November 24, 2015 8:26AM - 8:39AM |
M9.00003: Atomistic study of a nanometer-scale pump based on the thermal ratchet concept Elton Oyarzua, J. H. Walther, Harvey Zambrano In this study, a novel concept of nanoscale pump fabricated using Carbon Nanotubes (CNTs) is presented. The development of nanofluidic systems provides unprecedented possibilities for the control of biology and chemistry at the molecular level with potential applications in low energy cost devices, novel medical tools, and a new generation of sensors. CNTs offer a number of attractive features for the fabrication of fluidic nanodevices including fast flow, useful electronic and thermal properties, high mechanical strength and biocompatibility. Therefore, the transport of liquids in CNTs is now of great interest in nanofluidics. Thermophoresis is the phenomenon observed when a mixture of two or more types of motile objects experience a force induced by a thermal gradient and the different types of objects respond to it differently, inducing a motion and segregation of the objects. Using molecular dynamics simulations, we explore the possibility to design thermophoretic pumping devices fabricated of CNTs for water transport in nanoconduits. The design of the nanopumps is based on the concept of the Feynman-Smoluchowski ratchet. [Preview Abstract] |
Tuesday, November 24, 2015 8:39AM - 8:52AM |
M9.00004: Scattering of water molecules on silicon surface: Molecular beam experiments and molecular dynamics simulations Yusuke Kotsubo, Ikuya Kinefuchi, Shu Takagi The scattering behavior of water molecules on silicon(100) surface was investigated by experimental and numerical approach. Owing to the strong polarity of water molecules, water molecules and surface atoms would interact intricately compared to those of non-polar gas molecules such as rare gases, nitrogen, and oxygen. In the experiment, we employed the molecular beam method and changed the incident energy of water molecules between 35 and 130 meV, which corresponds to the energy of thermal motion of gas molecules at room temperature. The scattering distribution and the mean translational energy of scattered molecules in each scattering angle were obtained. The experimental results indicated that the scattering distribution was close to that of the cosine scattering due to the roughness of the silicon surface when the incident energy was 130 meV. In contrast, when the incident energy was 35 meV, the scattering distribution had a directivity toward a certain angle close to the specular reflection one. The directivity is usually observed when a surface is flat in an atomic scale and the incident energy is high. To clarify the reason of this anomalous directivity, we are analyzing the interaction between water molecules and the silicon surface using molecular dynamics simulations. [Preview Abstract] |
Tuesday, November 24, 2015 8:52AM - 9:05AM |
M9.00005: Mass transfer properties of nanoconfined fluids at solid-liquid interfaces: from atomistic simulations to continuum models Matteo Morciano, Matteo Fasano, Andreas Nold, Carlos Correia Braga, Petr Yatsyshin, David Sibley, Benjamin Goddard, Eliodoro Chiavazzo, Pietro Asinari, Serafim Kalliadasis At the nanoscale, traditional continuum models are not sufficient to describe fluid flow. For example, the no-slip assumption may not be valid for nanoscale flows, where interface effects dominate transport phenomena. Hence, classic boundary conditions should take into account possible interplays between fluid velocity, shear stress, surface chemistry and roughness. Unlike hydrodynamics, in molecular dynamics (MD), the boundary conditions are not specified a priori but arise naturally from computations. Here, mass transfer properties for a Lennard-Jones fluid confined in a nanochannel are studied by MD. Density, stress and velocity profiles within the fluid are evaluated with different nanoconfined conditions, shear rates and surface hydrophilicity. Our results show a strong anisotropic behavior of fluid properties along the channel section. Shear rates and velocity profiles allow calculating the spatial distribution of viscosity along the channel. We also observe that hydrophilic surfaces lead to increased viscosity. Our findings may have a potential impact on the design of nanofluidic devices for either engineering or biomedical applications. [Preview Abstract] |
Tuesday, November 24, 2015 9:05AM - 9:18AM |
M9.00006: A Nanoscale Hydrodynamical Model for Transport of Water Ravi Bhadauria, Tarun Sanghi, N. R. Aluru We present here a one-dimensional isothermal hydrodynamic transport model for SPC/E water. Two separate mechanisms of flow, viz. viscous and slip are incorporated in the present formulation. Spatially varying viscosity is modeled using the local average density method. Slip velocity is provided as a form of the boundary condition which in turn depends upon the macroscopic interfacial friction coefficient. The friction coefficient bridges the atomistic and continuum descriptions of the problem. The value of this friction coefficient is computed using particle-based wall-fluid force autocorrelations and wall-fluid force-velocity cross correlations, where the particle trajectory is generated using a Generalized Langevin Equation formulation. To test the accuracy of the model, gravity driven flow of SPC/E water confined between graphene and silicon slit shaped nanochannels are considered as examples for low and high friction cases. The proposed model yields good quantitative agreement with the velocity profiles obtained from non-equilibrium molecular dynamics simulations. Furthermore, we demonstrate that the slip length is constant for different channel widths for a fixed thermodynamic state under the linear response regime. [Preview Abstract] |
Tuesday, November 24, 2015 9:18AM - 9:31AM |
M9.00007: A multiscale quasi-continuum theory to determine thermodynamic properties of fluid mixtures in nanochannels Mohammad Hossein Motevaselian, Sikandar Y. Mashayak, Narayana R. Aluru We present an empirical potential-based quasi-continuum theory (EQT) that seamlessly integrates the interatomic potentials into a continuum framework such as the Nernst-Planck equation. EQT is a simple and fast approach, which provides accurate predictions of potential of mean force (PMF) and density distribution of confined fluids at multiple length-scales, ranging from few Angstroms to macro meters. The EQT potentials can be used to construct the excess free energy functional in the classical density functional theory (cDFT). The combination of EQT and cDFT (EQT-cDFT), allows one to predict the thermodynamic properties of confined fluids. Recently, the EQT-cDFT framework was developed for single component LJ fluids confined in slit-like graphene channels [Mashayak, S. Y., M. H. Motevaselian, and N. R. Aluru, Journal of chemical physics~142, 244116 (2015)]. In this work, we extend the framework to confined LJ fluid mixtures and demonstrate it by simulating a mixture of methane and hydrogen molecules inside slit-like graphene channels. We show that the EQT-cDFT predictions for the structure of the confined fluid mixture compare well with the MD simulations. In addition, our results show that graphene nanochannels exhibit a selective adsorption of methane over hydrogen. [Preview Abstract] |
Tuesday, November 24, 2015 9:31AM - 9:44AM |
M9.00008: Simulation of flow through nanochannels: a novel multi-scale approach Frederike Jaeger, Alex Wray, Erich Muller, Pietro Poesio, Omar Matar A novel method for the simulation of flow through nanochannels is proposed. We use molecular dynamics (MD) simulations to determine relations between the pressure, shear and bulk viscosities and the density, as well as the slip length for different fluid-wall combinations. These relations are then plugged into a steady, two-dimensional continuum-scale model that allows the simulation of a compressible (Lennard-Jones) fluid through channels. No restrictive assumptions are made on the nature of the fluid and its flow behaviour (e.g. fully-developed, parabolic velocity profiles for incompressible fluids). Direct comparisons between the MD and the continuum-scale predictions for the channel flow show good agreement. A major advantage of the proposed method is its computational efficiency, which allows for complex flow geometries to be studied whilst still retaining the accuracy of MD-based simulations. Furthermore, through the use of the statistical fluid associating theory (SAFT), more complex fluids can be modelled, providing a computational framework capable of representing realistic experimental set-ups. [Preview Abstract] |
Tuesday, November 24, 2015 9:44AM - 9:57AM |
M9.00009: Dissipative particle dynamics incorporating non-Markovian effect Ikuya Kinefuchi, Yuta Yoshimoto, Shu Takagi The coarse-graining methodology of molecular simulations is of great importance to analyze large-scale, complex hydrodynamic phenomena. In the present study, we derive the equation of motion for non-Markovian dissipative particle dynamics (NMDPD) by introducing the history effects on the time evolution of the system [Y. Yoshimoto et al., Phys. Rev. E 88, 043305 (2013)]. Our formulation is based on the generalized Langevin equation, which describes the motions of the centers of mass of clusters comprising microscopic particles. The mean, friction, and fluctuating forces in the NMDPD model are directly constructed from an underlying MD system without any scaling procedure. For the validation of our formulation, we construct NMDPD models from high-density Lennard-Jones systems, in which the typical time scales of the coarse-grained particle motions and the fluctuating forces are not fully separable. The NMDPD models reproduce the temperatures, diffusion coefficients, and viscosities of the corresponding MD systems more accurately than the conventional DPD models based on a Markovian approximation. Our results suggest that the NMDPD method is a promising alternative for simulating mesoscale flows where a Markovian approximation is not valid. [Preview Abstract] |
Tuesday, November 24, 2015 9:57AM - 10:10AM |
M9.00010: Effect of variable magnetic field on nanofluid flow and heat transfer Mohammadkazem Sadoughi, Mohsen Sheikholeslami, Hamed Shariatmadar In this paper, Control Volume based Finite Element Method is applied to simulate nanofluid flow and heat transfer in presence of variable magnetic field. Magnetohydrodynamic (MHD) equations are coupled with the energy equation due to the heat transfer by means of the Boussinessq approximation. Then, the 2D non-dimensional full MHD equations in terms of stream function, temperature, magnetic field and vorticity are solved by using CVFEM. The calculations were performed for different governing parameters namely; the Rayleigh number, nanoparticle volume fraction and Hartmann number arising from MHD. Results show that Nusselt number has direct relationship with Rayleigh number, nanoparticle volume fraction while it has reverse relationship with Hartmann number. Also it can be found that enhancement in heat [Preview Abstract] |
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