Bulletin of the American Physical Society
61st Annual Meeting of the APS Division of Fluid Dynamics
Volume 53, Number 15
Sunday–Tuesday, November 23–25, 2008; San Antonio, Texas
Session MK: Nano-Fluids II |
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Chair: Daniel Maynes, Brigham Young University Room: 102B |
Tuesday, November 25, 2008 8:00AM - 8:13AM |
MK.00001: A hydrodynamic model for DNA translocation in a nanopore Lei Chen, A.T. Conlisk One of the recent applications of nanopores is the possibility to use them as detectors and even analyzers for (bio)molecules. A hydrodynamic model is established to investigate the translocation velocity of an electrokinetically driven DNA through a nanopore. Previous work done on this problem does not consider the globular part of the DNA residing outside the pore and can not account for the dependence of the translocation velocity on DNA length as shown in the experimental data. In the present work, the drag force acting on the blob-like DNA configuration outside the pore is considered by using the formula for flow past a porous sphere. There is an electroosmotic flow inside the nanopore and the velocity field inside the nanopore is calculated. The force balance on the DNA is used as an additional condition to determine the translocation velocity. The numerical results compare well with experimental data. [Preview Abstract] |
Tuesday, November 25, 2008 8:13AM - 8:26AM |
MK.00002: Fluid Dynamics of Magnetic Nanoparticles in Simulated Blood Vessels Lauren Blue, Mary Kathryn Sewell, Christopher S. Brazel Magnetic nanoparticles (MNPs) can be used to locally target therapies and offer the benefit of using an AC magnetic field to combine hyperthermia treatment with the triggered release of therapeutic agents. Here, we investigate localization of MNPs in a simulated environment to understand the relationship between magnetic field intensity and bulk fluid dynamics to determine MNP retention in a simulated blood vessel. As MNPs travel through blood vessels, they can be slowed or trapped in a specific area by applying a magnetic field. Magnetic cobalt ferrite nanoparticles were synthesized and labeled with a fluorescent rhodamine tag to visualize patterns in a flow cell, as monitored by a fluorescence microscope. Particle retention was determined as a function of flow rate, concentration, and magnetic field strength. Understanding the relationship between magnetic field intensity, flow behavior and nanoparticle characteristics will aid in the development of therapeutic systems specifically targeted to diseased tissue. [Preview Abstract] |
Tuesday, November 25, 2008 8:26AM - 8:39AM |
MK.00003: Spontaneous break-up of cylindrical nano-sheet into filament arrays by thermal drawing Daosheng Deng, N. Orf, A. Abouraddy, Y. Fink Thermal drawing has been state-of-art in the optical fiber community, during which macroscopic preform is heated into viscous fluid and stretched into extended long fiber while preserving the cross-section structure. Recently, a new type of multi-materials fiber that incorporates cylindrical sheets of glass into polymer matrix has emerged. Here, we report a novel physical phenomenon in which a cylindrical thin sheet spontaneously evolves into a periodic array of filaments when the sheet thickness reaches a critical length scale. Surprisingly, in contrast to other related phenomena, the axial dimension remains continuous. We propose a fluid instability mechanism to explain the observed phenomenon. A controlled and reproducible approach of thermal drawing processing is developed allowing us to follow the fleeting evolution of fluid breakup in a frozen solid state, resulting in unprecedented extended semiconductor nanofilaments. [Preview Abstract] |
Tuesday, November 25, 2008 8:39AM - 8:52AM |
MK.00004: Breakup Characteristics of Nanocylinders Harinath Reddy, Anupam Tiwari, Saumyadip Mukhopadhyay, John Abraham Liquid breakup at the macroscale has been studied extensively for over a hundred years, but breakup at the nanoscale has only recently attracted attention. The focus of the present work is on the breakup of liquid nanocylinders. Nanocylinders are encountered in several engineering applications and biological systems, e.g. printing on micro-circuitry, precision manufacturing, Golgi apparatus. Breakup at the nanoscale is primarily through the Rayleigh capillary mechanism since the Reynolds numbers are low. The specific research question we address is: does the breakup-time of liquid cylinders at the nanolevel follow the classical scaling relationships derived for capillary breakup at the macrolevel. A coarse-grained molecular dynamics approach is employed for the studies. We will show that for changes in cylinder radius, the scaling holds; but, when viscosity and surface tension are varied, the scaling does not hold. Possible reasons, attributed primarily to the origin of the instability that leads to the breakup, are discussed. Comparisons of other outcomes at the two levels will also be presented. [Preview Abstract] |
Tuesday, November 25, 2008 8:52AM - 9:05AM |
MK.00005: Mechanism of fast water transport through carbon nanotubes Alan McGaughey, John Thomas Water flow through carbon nanotubes (CNTs) with diameters ranging from 1.66 nm to 4.99 nm is examined using molecular dynamics simulations. A reflecting particle membrane is used to drive the flow and the relationship between the axial pressure gradient and volumetric flow rate in each tube is examined. The results are compared to predictions from the slip-modified Hagen-Poiseuille flow relation. In CNTs with diameters greater than 3.5 nm, flow is well described by the slip-modified Hagen-Poiseuille flow relation with a 30 nm slip length and bulk water properties. In CNTs with diameters smaller then 3.5 nm, the slip length at the water/carbon boundary increases and the viscosity of the confined water decreases with decreasing tube diameter. Accounting for these variations in slip length and viscosity, we demonstrate that the slip-modified Hagen-Poiseuille flow relation can be used to accurately predict water flow rates in CNTs with diameters as small as 1.66 nm. [Preview Abstract] |
Tuesday, November 25, 2008 9:05AM - 9:18AM |
MK.00006: Subcontinuum water transport through carbon nanotubes John Thomas, Alan McGaughey, Ottoleo Kuter-Arnebeck The structure and flow of water inside carbon nanotubes (CNTs) with diameters ranging from 0.86 nm to 1.66 nm are examined using molecular dynamics simulations. A sample of each CNT is placed between two water reservoirs, and a pressure difference is established between the reservoirs to induce flow through the CNTs. In CNTs with diameters greater than 1.4 nm, the axial distribution of water molecules is uniform and the molecules at the center of the CNT display hydrogen bonding characteristics similar to those found in bulk water. In CNTs with diameters less than 1.4 nm, both the axial distribution of water molecules and the hydrogen bonding characteristics at the center of the CNT vary with tube diameter. The diameter-dependent behavior leads to mass transport phenomena that cannot be explained using continuum fluid mechanics. For example, under the same pressure gradient, flow velocity is found to increase with decreasing CNT diameter. The effect of water entering and exiting the CNT from the reservoir is also examined. [Preview Abstract] |
Tuesday, November 25, 2008 9:18AM - 9:31AM |
MK.00007: Single-file flows in carbon nanotubes: A simplified molecular dynamics model Thomas Sisan, Seth Lichter Carbon nanotubes (CNT) are ideal systems for the study of nanofluidics and hold promise for diverse applications, such as desalination and power generation. Subnanometer CNTs adsorb single-file chains of water that transport at high speeds--equal to that measured in aquaporin channels. Molecular dynamics (MD) simulations of these fast-moving single-file water chains suggest simultaneous hopping of the whole chain and the invariance of water transport properties to CNT length. We investigate these claims using simplified one-dimensional MD with appropriate boundary conditions, thus achieving a highly-reduced system size and rapid simulations. The model is verified by comparison with full MD simulations. We find that simultaneous hopping of water molecules is an invalid approximation for very long channels where the transit time for a kink in the one-dimensional chain becomes important. Finally, our rapid prototyping capability is used to investigate the effects of chemical and geometric changes to the nanotube wall in order to enhance water transport through CNTs. [Preview Abstract] |
Tuesday, November 25, 2008 9:31AM - 9:44AM |
MK.00008: Collision of Nanoscale Jets Ganesh Balasubramanian, Ishwar K. Puri We use Molecular Dynamics simulations to investigate the collision of nanojets and the overall strain rate from the resulting velocity distribution. Liquid is retrained between two walls, one of which has an orifice of 5nm radius. Liquid is squeezed by the solid wall and forced out of the pore to form a nanojet. We focus on the interaction of two such opposing jets, whose exits lie on the same axis and are separated by few tens of molecular diameters. The averaged velocity distribution shows an initial rise from the jet exit to a few molecular layers and then linearly decays to half the separation distance between the exits. The length over which the velocity uniformly reduces conforms to the continuum results for strain rate. The transient nature of strain rate varies since pressure across the orifice changes with time. Strain rate results for different rates of squeezing at different times are presented. Further, to investigate the applicability of a mesoscopic modeling for the problem, we apply Lattice Boltzmann Method and attempt to achieve a better understanding of the fluid dynamics post collision. [Preview Abstract] |
Tuesday, November 25, 2008 9:44AM - 9:57AM |
MK.00009: Low dimensional molecular dynamics of water inside a carbon nanotube Junichiro Shiomi, Yuan Lin, Gustav Amberg, Shigeo Maruyama While carbon nanotubes (CNTs) have attracted a number of researches as the key building blocks for nanotechnology, they have also caught attentions as ideal materials that realize quasi-one-dimensional channel environment, a key system in bioscience. Such materials stimulate studies in fluid dynamics under low dimensional confinement, which is restricted and departs significantly from that in three-dimension. The current study serves to explore such atomic scale dynamics by performing a series of molecular dynamics (MD) simulations on water confined in a CNT with a diameter of the order of 1 nm. The MD simulations have successfully probed the phase transition of a water cluster confined in a CNT to an ice-nanotube with anomalous diameter dependence. It has also been applied to investigate the possibility of transporting water through a CNT by a temperature gradient. In this study, we particularly highlight the dielectric properties of water confined inside a CNT. The confinement gives rise to strongly anisotropic dielectric relaxation, where the relaxation becomes faster and slower in the cross sectional and axial directions, respectively. The diameter dependences of the dielectric properties are discussed in connection with water dynamics and structures in quasi-one-dimension. [Preview Abstract] |
Tuesday, November 25, 2008 9:57AM - 10:10AM |
MK.00010: Investigation of the convective heat transfer in waterbased Alumina nanofluid Sheng-Qi Zhou, Rui Ni, Ke-Qing Xia Recent research has suggested that nanofluids have great potential in thermal applications due to their significantly high thermal conductivity [1]. But the buoyancy- driven convective flow would play an important role in the heat transport process. We have conducted an experimental measurement of the convective heat transfer in water-based Al$_2$O$_3$ nanofluid in a cylindrical cell (19 cm in both height and diameter). The nominal diameter of Al$_2$O$_3$ particle is 45 nm. At the fixed heating power, $Q =513 W$, it has been found that the convective heat transfer coefficient ($h=Q/{\Delta T}$, $\Delta T$ is the temperature difference across the cell.) decreases to 2{\%} when the volume fraction of nanoparticle, $\phi$, increases from 0.03{\%} to 1.1{\%}. At $\phi =1.1{\%}$, we examined the relationship between Nusselt number ($Nu$) and Rayleigh number ($Ra$) of nanofluid. It has been found that the $Nu-Ra$ scaling of nanofluid follows that of pure water at higher $Ra$ ($>3\times10^{9}$). At lower $Ra$ ($<3\times10^{9}$), a deviation occurs, and it becomes more pronounced with decreasing $Ra$.// [1]. J. A. Eastman {\it et. al.}, Annu. Rev. Mater. Res. {\bf 34} 219, (2004). [Preview Abstract] |
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