Bulletin of the American Physical Society
70th Annual Meeting of the APS Division of Fluid Dynamics
Volume 62, Number 14
Sunday–Tuesday, November 19–21, 2017; Denver, Colorado
Session D14: Nanoscale Flows: Basics and ModelingMicro

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Chair: Mittu Walia, National Institute of Technology Kurukshetra Room: 507 
Sunday, November 19, 2017 2:15PM  2:28PM 
D14.00001: Atomistic Modeling of the FluidSolid Interface in Simple Fluids Nicolas Hadjiconstantinou, Gerald Wang Fluids can exhibit pronounced structuring effects near a solid boundary, typically manifested in a layered structure that has been extensively shown to directly affect transport across the interface. We present and discuss several results from molecularmechanical modeling and moleculardynamics (MD) simulations aimed at characterizing the structure of the first fluid layer directly adjacent to the solid. We identify a new dimensionless group  termed the Wall number  which characterizes the degree of fluid layering, by comparing the competing effects of wallfluid interaction and thermal energy. We find that in the layering regime, several key features of the first layer layer  including its distance from the solid, its width, and its areal density  can be described using meanfieldenergy arguments, as well as asymptotic analysis of the NernstPlanck equation. For dense fluids, the areal density and the width of the first layer can be related to the bulk fluid density using a simple scaling relation. MD simulations show that these results are broadly applicable and robust to the presence of a second confining solid boundary, different choices of wall structure and thermalization, strengths of fluidsolid interaction, and wall geometries. [Preview Abstract] 
Sunday, November 19, 2017 2:28PM  2:41PM 
D14.00002: Layering at the FluidSolid Interface and Anomalous Diffusion in Nanoconfined Fluids Gerald Wang, Nicolas Hadjiconstantinou Molecular selfdiffusion in a fluid under nanoconfinement can differ considerably from its counterpart in the bulk; this ``anomalous" diffusion can have profound implications for applications involving transport in nanoconfined systems. In this talk we study the contribution of fluid layering at the solidliquid interface to anomalous diffusion, using molecularmechanical modeling and moleculardynamics (MD) simulations of simple fluids confined within a graphene nanoslit. We find that fluid layering near the fluidsolid interface strongly affects molecular diffusion; the former can be characterized by a nondimensional group  referred to as the Wall number  which compares the competing effects of wallfluid interaction and thermal energy. We specifically demonstrate that the dependence of the {\it overall} diffusion coefficient on the confinement lengthscale can be modeled by superposing the contributions of the bulk and nearwall regions. The anomalous diffusive behavior in the nearwall region is due to a ``dimensional restriction" of the nearwall fluid. MD simulation results suggest that the difference between the bulk and nearwall diffusivity can be modeled using the excess entropy of the fluid in each region. [Preview Abstract] 
Sunday, November 19, 2017 2:41PM  2:54PM 
D14.00003: Confinement effects on liquid oxygen flows in carbon nanotubes: A MD simulation study Kazuhiko Suga, Rintaro Moritani, Yuki Mori, Masayuki Kaneda Molecular dynamics simulations are performed to investigate the liquid flow mechanism of diatomic molecules in armchair carbon nanotubes (CNTs). Oxygen molecules are considered as the fluid inside armchair (n,n) (n=620) CNTs at a temperature of 133[K] and a bulk density of 1680[kg$/$m$^3$] for the liquid state. The velocity profiles and slip lengths are discussed considering the radial distributions of the fluid density by the finite differencebased velocity fitting method. It is shown that as the diameter of the CNT increases, the slip length and the flow rate enhancement generally become smaller while irregular tendencies (discontinuity points) are observed in the distribution profiles. Between the (7,7) and (8,8) CNTs, a steep drop can be seen in the profiles. Between the (9,9) and (11,11) CNTs, and between the (12,12) and (14,14) CNTs transitional profiles are observed. It is confirmed that those phenomena are caused by an instability of the fluid molecule cluster due to the discontinuous confinement of the CNTs. [Preview Abstract] 
Sunday, November 19, 2017 2:54PM  3:07PM 
D14.00004: The investigation of contact line effect on nanosized droplet wetting behavior with solid temperature condition Lee Haegon, Lee Joonsang In many multiphase fluidic systems, there are essentially contact interfaces including liquidvapor, liquidsolid, and solidvapor phase. There is also a contact line where these three interfaces meet. The existence of these interfaces and contact lines has a considerable impact on the nanoscale droplet wetting behavior. However, recent studies have shown that Young's equation does not accurately represent this behavior at the nanoscale. It also emphasized the importance of the contact line effect.Therefore, We performed molecular dynamics simulation to imitate the behavior of nanoscale droplets with solid temperature condition. And we find the effect of solid temperature on the contact line motion. Furthermore, We figure out the effect of contact line force on the wetting behavior of droplet according to the different solid temperature condition. With solid temperature condition variation, the magnitude of contact line friction decreases significantly. We also divide contact line force by effect of bulk liquid, interfacial tension, and solid surface. [Preview Abstract] 
Sunday, November 19, 2017 3:07PM  3:20PM 
D14.00005: Determination of the shear and bulk viscosity from equilibrium moleculardynamics simulations Frederike Jaeger, Erich Muller, Omar K. Matar Determining fluid properties accurately is essential for largescale fluid dynamics simulations where only a few parameters determine the behaviour of an entire system. Even though many properties are well known, others are more obscure and difficult to determine experimentally. One such property is the bulk viscosity which plays a particularly large role in compressible fluids but is rarely considered in fluiddynamics simulations. We determine both the shear and bulk viscosity using equilibrium methods within the moleculardynamics framework using both atomistic and coarsegrained models with a view of assessing both the accuracy of coarsegrained models for transportproperty calculations and the necessity of including such properties at various scales and scenarios. [Preview Abstract] 
Sunday, November 19, 2017 3:20PM  3:33PM 
D14.00006: Transport properties at fluids interfaces: a molecular study for a macroscopic modelling Antonio Russo, Matteo Morciano, David N. Sibley, Andreas Nold, Benjamin D. Goddard, Pietro Asinari, Serafim Kalliadasis Rapid developments in the field of micro and nanofluidics require detailed analysis of the properties of matter at the molecular level. But despite numerous works in the literature, appropriate macroscopic relations able to integrate a microscopic description of fluid and soft matter properties at liquidvapour and multifluid interfaces are missing. As a consequence, studies on interfacial phenomena and microdevice designs often rely on oversimplified assumptions, e.g. that the viscosities can be considered constant across interfaces. In our work, we present nonequilibrium MD simulations to scrutinise efficiently and systematically, through the tools of statistical mechanics, the anisotropic properties of fluids, namely density variations, stress tensor, and shear viscosity, at the fluid interfaces between liquid and vapour and between two partially miscible fluids. Our analysis has led to the formulation of a general relation between shear viscosity and density variations validated for a wide spectrum of interfacial fluid problems. In addition, it provides a rational description of other interfacial quantities of interest, including surface tension and its origins, and more generally, it offers valuable insight of molecular transport phenomena at interfaces. [Preview Abstract] 
Sunday, November 19, 2017 3:33PM  3:46PM 
D14.00007: Water imbibition by mica pores: what happens when capillary flow is suppressed? Chao Fang, Rui Qiao The imbibition of liquids into porous media plays a critical role in numerous applications. Most prior studies focused on imbibition driven by capillary flows. In this work, we study the imbibition of water into slitshaped mica pores filled with pressurized methane using molecular simulations. Despite that capillary flow is suppressed by the high gas pressure, water is imbibed into the pore as monolayer liquid films. Since the classical hydrodynamic flow is not readily applicable for the monolayer water film propagating on the mica wall and the imbibition is driven by the strong affinity of water molecules to the mica walls, the observed imbibition is best taken as surface hydration. We show that the dynamics of water's imbibition front follows a simple diffusive scaling law. The effective diffusion coefficient of the imbibition front, however, is more than ten times larger than the diffusion coefficient of the water molecules in the water film adsorbed on the mica walls. Using a molecular theory originally developed for the spreading of monolayer films on solid substrates, we clarify the mechanism underlying the rapid water imbibition observed here. [Preview Abstract] 
Sunday, November 19, 2017 3:46PM  3:59PM 
D14.00008: Storage and recovery of methaneethane mixtures in single shale pores. Haiyi Wu, Rui Qiao Natural gas production from shale formations has received extensive attention recently. While great progress has been made in understanding the adsorption and transport of singlecomponent gas inside shales' nanopores, the adsorption and transport of multicomponent shale gas under reservoir conditions (CH4 and C2H6 mixture) has only begun to be studied. In this work, we use molecular simulations to compute the storage of CH4 and C2H6 mixtures in single nanopores and their subsequent recovery. We show that surface adsorption contributes greatly to the storage of CH4 and C2H6 inside the pores and C2H6 is enriched over CH4. The enrichment of C2H6 is enhanced as the pore is narrowed, but is weakened as the pressure increases. We show that the recovery of gas mixtures from the nanopores approximately follows the diffusive scaling law. The ratio of the production rates of C2H6 and$_{\mathrm{\thinspace }}$CH4 is close to their initial mole ratio inside the pore despite that the mobility of pure C2H6 is much smaller than that of pure CH4 inside the pores. By using scale analysis, we show that the strong coupling between the transport of CH4 and C2H6 is responsible for the effective recovery of C2H6 from the nanopores. [Preview Abstract] 
Sunday, November 19, 2017 3:59PM  4:12PM 
D14.00009: Thermophoresis of a spherical particle: Modeling through momentbased, macroscopic transport equations Juan C. Padrino, James Sprittles, Duncan Lockerby Thermophoresis refers to the forces on and motions of objects caused by temperature gradients when these objects are exposed to rarefied gases. This phenomenon can occur when the ratio of the gas mean free path to the characteristic physical length scale (Knudsen number) is not negligible. In this work, we obtain the thermophoretic force on a rigid, heatconducting spherical particle immersed in a rarefied gas resulting from a uniform temperature gradient imposed far from the sphere. To this end, we model the gas dynamics using the steady, linearized version of the socalled regularized 13moment equations (R13). This set of equations, derived from the Boltzmann equation using the moment method, provides closures to the mass, momentum, and energy conservation laws in the form of constitutive, transport equations for the stress and heat flux that extends the NavierStokesFourier model to include rarefaction effects. Integration of the pressure and stress on the surface of the sphere leads to the net force as a function of the Knudsen number, dimensionless temperature gradient, and particletogas thermal conductivity ratio. Results from this expression are compared with predictions from other momentbased models as well as from kinetic models. [Preview Abstract] 
Sunday, November 19, 2017 4:12PM  4:25PM 
D14.00010: Investigating Nonexistence of the reversed flow characteristics in a FalknerSkan equation. Mittu Walia Existence of a class of similarity solutions for a nonlinear differential equation were considered in the case of accelerating and decelerating flows, in this article we proposed nonexistence of reversed flows in a Falkner Skan equation. A new converted nonlinear ordinary differential system is studied for reversed flows. Numerical results for various instances are calculated related to velocity profile, shear stress and their behaviors. In aeronautics, we can use these reversed flow solutions to estimate the critical value of separation. [Preview Abstract] 
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