Bulletin of the American Physical Society
69th Annual Meeting of the APS Division of Fluid Dynamics
Volume 61, Number 20
Sunday–Tuesday, November 20–22, 2016; Portland, Oregon
Session D22: Nano Flows: Computations and Modeling |
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Chair: Dimitrios Papavassiliou, University of Oklahoma Room: E141/142 |
Sunday, November 20, 2016 2:57PM - 3:10PM |
D22.00001: A Langevin model for the Dynamic Contact Angle Parameterised Using Molecular Dynamics Edward Smith, Erich Muller, Richard Craster, Omar Matar An understanding of droplet spreading is essential in a diverse range of applications, including coating processes, dip feed reactors, crop spraying and biomedical treatments such as surfactant replacement theory. The default modelling tools for engineering fluid dynamics assume that the continuum hypothesis is valid. The contact line motion is very difficult to capture in this paradigm and requires some form of closure model, often tuned {\it a priori} to experiments. Molecular dynamics (MD), by assuming only an inter-molecular potential, reproduces the full detail of the three-phase contact line with no additional modelling assumptions. This provides an ideal test-bed to understand contact line motion. In this talk, MD results for a sheared liquid bridge are presented. The evolution and fluctuations of the dynamic contact angle are paramterised over a range of wall sliding speeds and temperatures. A Langevin model is proposed to reproduce the fluctuations and evolution of the contact angle. Results from this model are compared to molecular simulation data showing excellent agreement. The potential applications of this model, as well as limitation and possible extensions, are discussed. [Preview Abstract] |
Sunday, November 20, 2016 3:10PM - 3:23PM |
D22.00002: A Second Order Temporal Integrator for Brownian Dynamics of Rigid Bodies Brennan Sprinkle, Florencio Usabiaga, Neelesh Patankar, Aleksander Donev Simulating Brownian motion of passive or active rigid bodies, with arbitrary shape, suspended in a viscous solvent is examined. Existing numerical techniques which capture the correct stochastic drift term require the solution of two saddle point problems per time step and only achieve first order accuracy deterministically. The saddle point systems are required to enforce the rigidity constraint and can be quite expensive to solve, for a large number of rigid bodies. We propose a novel method which requires the solution of two saddle point problems per time step but achieves second order accuracy in time. [Preview Abstract] |
Sunday, November 20, 2016 3:23PM - 3:36PM |
D22.00003: Molecular dynamics simulations of the rotational and translational diffusion of a Janus rod-shaped nanoparticle. Ali Kharazmi, Nikolai Priezjev We investigate the diffusion of a Janus nanoparticle immersed in a dense Lennard-Jones fluid using molecular dynamic simulations. In particular we consider a rod-shaped particle with different surface wettability on each half-side of the particle and analyze the mean square displacement and the translational and rotational velocity autocorrelation functions. It is found that diffusion is enhanced when the wettability contrast is high and the local slip length on the nonwetting side is relatively large. We also examine the time evolution of the orientation tensor and correlate it with the particle displacement. These results are compared with our previously published results on diffusive dynamics of a Janus sphere with two hemispheres of different wettability. [Preview Abstract] |
Sunday, November 20, 2016 3:36PM - 3:49PM |
D22.00004: Investigating the gas cushion model for nano-structured superhydrophobic surfaces Jason Reese, Srinivasa Ramisetti, Matthew Borg, Duncan Lockerby We investigate the water slip properties of different nano-structured surfaces using non-equilibrium molecular dynamics (NEMD) simulations. We predict the fluid slip lengths of surface coatings comprising carbon nanotubes on platinum substrates, with nitrogen gas trapped in the interstitial gaps. Our NEMD results do not support the gas-cushion model proposed by Vinogradova (Langmuir 11:2213-2220, 1995) as this does not account for the rarefied gas effects present in nano/micro gas layers. We therefore propose a slip gas-cushion model which incorporates some of the rarefied gas effects and agrees better with our NEMD slip length calculations. [Preview Abstract] |
Sunday, November 20, 2016 3:49PM - 4:02PM |
D22.00005: A multiscale transport model for binary Lennard Jones mixtures in slit nanopores. Ravi Bhadauria, N. R. Aluru We present~a quasi-continuum multiscale hydrodynamic transport model for one dimensional isothermal, non-reacting binary mixture confined in slit shaped nanochannels. We focus on species transport equation~that~includes the viscous dissipation and interspecies diffusion term of the Maxwell-Stefan form. Partial viscosity variation is modeled by van der Waals one fluid approximation and the Local Average Density Method. We use friction boundary conditions~where the wall-species friction parameter~is computed using a~novel species specific Generalized Langevin Equation model. The transport model accuracy is tested by predicting the velocity profiles of Lennard-Jones (LJ) methane-hydrogen and LJ methane-argon mixtures in graphene slit channels of different width. The resultant slip length from the continuum model is found to be invariant of channel width for a fixed mixture molar concentration. The mixtures considered are observed to behave as single species pseudo fluid, with~the~friction parameter displaying a linear dependence on the~molar composition. The proposed model yields atomistic level accuracy with continuum scale efficiency. [Preview Abstract] |
Sunday, November 20, 2016 4:02PM - 4:15PM |
D22.00006: Behavior of a nano-particle and a polymer molecule in a nano-scale four-roll mill Minh Vo, Dimitrios Papavassiliou The four-roll mill device could be used to create a mixed flow from purely extensional stresses to completely rotational through the proper selection of speed and direction of each of the four cylindrical rollers. Considerable research has been done with this device for macroscale rheological studies.. In our study, the dissipative particle dynamics (DPD) method was employed to investigate the behavior of a nano-sphere and a polymer molecule in different conditions within a four-roll mill device. Hydrophilic properties of each roll were generated by adjusting interaction parameters and using bounce back boundary condition at the solid surface. All simulations were run up to 4x10$^{\mathrm{6}}$ time steps at room temperature using the open source LAMMPS package. After the flow in the system reached equilibrium, a nano-sphere and then a polymer chain were released at the center of the simulation box. Their trajectories were recorded at different shear rate conditions. The propagation of nanosphere in different rotational flow will be discussed. Additionally, the deformation of polymer chains will be compared to that in a simple shear flow. [Preview Abstract] |
Sunday, November 20, 2016 4:15PM - 4:28PM |
D22.00007: Spontaneous Ion Depletion and Accumulation Phenomena Induced by Imbibition through Permselective Medium Hyomin Lee, Yeonsu Jung, Sungmin Park, Ho-Young Kim, Sung Jae Kim Generally, an ion depletion region near a permselective medium is induced by predominant ion flux through the medium. External electric field or hydraulic pressure has been reported as the driving forces. Among these driving forces, an imbibition through the nanoporous medium was chosen as the mechanism to spontaneously generate the ion depletion region. The water-absorbing process leads to the predominant ion flux so that the spontaneous formation of the ion depletion zone is expected even if there are no additional driving forces except for the inherent capillary action. In this presentation, we derived the analytical solutions using perturbation method and asymptotic analysis for the spontaneous phenomenon. Using the analysis, we found that there is also spontaneous accumulation regime depending on the mobility of dissolved electrolytic species. Therefore, the rigorous analysis of the spontaneous ion depletion and accumulation phenomena would provide a key perspective for the control of ion transportation in nanofluidic system such as desalinator, preconcentrator, and energy harvesting device, \textit{etc}. [Preview Abstract] |
Sunday, November 20, 2016 4:28PM - 4:41PM |
D22.00008: Analysis of micro-fluidic tweezers in the Stokes regime Longhua Zhao, Yang Ding Nanowire fluidic tweezers have been developed to capture and manipulate micro objects. The fluidic trapping force and the fluid field are important to achieve accurate control, but have not been fully understood yet. Utilizing singularity method, we construct the exact velocity field to analyze flows induced by a spheroid nanowire tumbling in the Stokes regime. To further explore the trapping, we analyze the trajectories of rigid or deformable microspheres near the tumbling nanowire using regularized Stokeslet method. The fluid structure, the trapping phenomenon and mechanism, and precise relation about trapping with the geometry will be presented. [Preview Abstract] |
Sunday, November 20, 2016 4:41PM - 4:54PM |
D22.00009: The filtration of colloidal gold nanoparticles with carbon nanotubes Frans Jan de Jong, Adeline Buffet Understanding the local filtering of nanoparticles (NPs) is essential for the development and optimization of medical and industrial applications. Microfocus small-angle X-ray scattering ($\mu $SAXS) was used to determine the local filtration kinetics of 100 nm sized colloidal gold nanoparticles (Au NPs) within a multi-walled carbon nanotube (MWCNT) forest. To get a physical insight into the Au NP filtration process within the MWCNT forest a novel model based on the well-known DLVO theory was developed. The DLVO theory is commonly used to describe the interaction between colloidal particles. In addition to the attractive Van de Waals force and the electrostatic double-layer force, a non-DLVO force is added to account for hydration and hydrophobic effects. The model presented here shows that the Au NPs are mainly unfavorably deposited into the so-called secondary energy minimum. This latter finding is in good agreement with the experimental observations and the literature, in which unfavorable particle deposition is related to deposition into the secondary energy minimum. The use of $\mu $SAXS to get a physical insight into the local deposition kinetics of submicrometer particles opens up new pathways to optimize the preparation of MWCNT forests for filtration purposes. [Preview Abstract] |
(Author Not Attending)
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D22.00010: DSMC Simulation of Radiometric Flow in a Ratchet-Channel Nano-Pump Ehsan Roohi, Vahid Shahbi, Tobias Baier, Steffen Hardt The current paper presents a description of the fluid and pumping characteristics of a ratchet-type nano-scale pump suggested by Donkov et al. [1] and presents the optimum geometry and working conditions of the pump. The pump consists of a ratchet channel with the temperature gradient applied between the opposing walls. Here, we report the physical mechanism of flow induction within the pump and show that the combination of configuration and boundary temperature of this pump induces a radiometric-type flow. Benefiting from the DSMC simulations, we suggest the optimum working condition/geometrical size of the pump. Comparison of DSMC simulation with analytical relations is reported. [Preview Abstract] |
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