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 E14: Nanoscale Flows: Special TopicsMicro
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Chair: Jie Feng, Princeton University Room: 507 |
Sunday, November 19, 2017 4:55PM - 5:08PM |
E14.00001: Drag reduction in silica nanochannels induced by graphitic wall coatings. Enrique Wagemann, J. H. Walther, Harvey A. Zambrano Transport of water in hydrophilic nanopores is of significant technological and scientific interest. Water flow through hydrophilic nanochannels is known to experience enormous hydraulic resistance. Therefore, drag reduction is essential for the development of highly efficient nanofluidic devices. In this work, we propose the use of graphitic materials as wall coatings in hydrophilic silica nanopores. Specifically, by conducting atomistic simulations, we investigate the flow inside slit and cylindrical silica channels with walls coated with graphene (GE) layers and carbon nanotubes (CNTs), respectively. We develop realistic force fields to simulate the systems of interest and systematically, compare flow rates in coated and uncoated nanochannels under different pressure gradients. Moreover, we assess the effect that GE and CNT translucencies to wettability have on water hydrodynamics in the nanochannels. The influence of channel size is investigated by systematically varying channel heights and nanopore diameters. In particular, we present the computed water density and velocity profiles, volumetric flow rates, slip lengths and flow enhancements, to clearly demonstrate the drag reduction capabilities of graphitic wall coatings. [Preview Abstract] |
Sunday, November 19, 2017 5:08PM - 5:21PM |
E14.00002: Thermophoretic transport of water nanodroplets confined in carbon nanotubes: the role of friction. Elton Oyarzua, Jens H. Walther, Harvey A. Zambrano The development of efficient nanofluidic devices requires driving mechanisms that provide controlled transport of fluids through nanoconduits. Temperature gradients have been proposed as a mechanism to drive particles, fullerenes and nanodroplets inside carbon nanotubes (CNTs). In this work, molecular dynamics (MD) simulations are conducted to study thermophoresis of water nanodroplets inside CNTs. To gain insight into the interplay between the thermophoretic force acting on the droplet and the retarding liquid-solid friction, sets of constrained and unconstrained MD simulations are conducted. The results indicate that the thermophoretic motion of a nanodroplet displays two kinetic regimes: an initial regime characterized by a decreasing acceleration and afterwards a terminal regime with constant velocity. During the initial regime, the magnitude of the friction force increases linearly with the droplet velocity whereas the thermophoretic force has a constant magnitude defined by the magnitude of the thermal gradient and the droplet size. Subsequently, in the terminal regime, the droplet moves at constant velocity due to a dynamic balance between the thermophoretic force and the retarding friction force. [Preview Abstract] |
Sunday, November 19, 2017 5:21PM - 5:34PM |
E14.00003: Pressure driven water flow through hydrophilic alumina nanomembranes Ali Beskok, Anil Koklu, Sevinc Sengor We present an experimental study that focuses on pressure-driven flow of distilled water through alumina membranes with 5, 10 and 20 nm pore radii. The nanopore geometry, pore size and porosity are characterized using scanning electron microscopy images taken pre and post-flow experiments. Comparisons of these images have shown reduction in the pore size, which is attributed to precipitation of hydroxyl groups on alumina surfaces. Measured flowrates compared with the Hagen--Poiseuille flow relations consistently predict 2.2 nm reductions in the pore size for three different membranes. This behavior can be explained by the formation of a thick stick layer of water molecules over hydroxylated alumina surfaces, evidenced by water droplet contact angle measurements that exhibit increased hydrophilicity of alumina surfaces. Other possible effects of the mismatch between theory and experiments such as unaccounted pressure losses in the system or the streaming potential effects were also considered, but shown to be negligible for current experimental conditions. [Preview Abstract] |
Sunday, November 19, 2017 5:34PM - 5:47PM |
E14.00004: Nanofluid flow and heat transfer in boundary layers: the influence of the concentration diffusion layer on heat transfer enhancement Joseph T C Liu, Cintia Juliana Barbosa DeCastilho, Mark E. Fuller, Aakash Sane The present work uses a perturbation procedure to deduce the small nanoparticle volume concentration conservation equations for momentum, heat and concentration diffusion. Thermal physical variables are obtained from conventional means (mixture and field theories) for alumina-water and gold-water nanofluids. In the case of gold-water nano fluid molecular dynamics results are used to estimate such properties, including transport coefficients. The very thin diffusion layer at large Schmidt numbers is found to have a great impact on the velocity and temperature profiles owing to their dependency on transport properties. This has a profound effect on the conduction surface heat transfer rate enhancement and skin friction suppression for the case of nano fluid concentration withdrawal at the wall, while the diffusional surface heat transfer rate is negligible due to large Schmidt numbers. Possible experimental directed at this interesting phenomenon is suggested. [Preview Abstract] |
Sunday, November 19, 2017 5:47PM - 6:00PM |
E14.00005: Fabrication and flow characterization of vertically aligned carbon-nanotube/polymer membranes Richard Castellano, Eric Meshot, Francesco Fornasiero, Jerry Shan Membranes with well-controlled nanopores are of interest for applications as diverse as chemical separations, water purification, and ``green'' power generation. In particular, membranes incorporating carbon nanotubes (CNTs) as through-pores have been shown to pass fluids at rates orders-of-magnitude faster than predicted by continuum theory. However, cost-effective and scalable solutions for fabricating such membranes are still an area of research$^{\mathrm{1}}$. We describe a solution-based fabrication technique for creating polymer composite membranes from bulk nanotubes using electric-field alignment and electrophoretic concentration$^{\mathrm{2}}$. We then focus on flow characterization of membranes with single-wall nanotube (SWNT) pores. We demonstrate membrane quality by size-exclusion testing and showing that the flowrate of different gasses scales as the square root of molecular weight. The gas flowrates and moisture-vapor-transmission rates are compared with theoretical predictions and with composite membranes -fabricated from CVD-grown SWNT arrays$^{\mathrm{1}}.\\ \\$[1]$N. Biu, E. R. Meshot, S. Kim, J. Pe\~{n}a, P. W. Gibson, K. J. Wu, F. Fornasiero. \newline \textit{Adv. Mat.} (2016)\newline[2]R. J. Castellano, C. Akin, G. Giraldo, S. Kim, F. Fornasiero, J. W. Shan. \newline\textit{J. Applied Physics.}(2015) [Preview Abstract] |
Sunday, November 19, 2017 6:00PM - 6:13PM |
E14.00006: Flash NanoPrecipitation (FNP) for bioengineering nanoparticles to enhance the bioavailability Jie Feng, Yingyue Zhang, Simone McManus, Robert Prud'homme Nanoparticles for the delivery of therapeutics have been one of the successful areas in biomedical nanotechnology. Nanoparticles improve bioavailability by 1) the higher surface-to-volume ratios, enhancing dissolution rates, and 2) trapping drug molecules in higher energy, amorphous states for a higher solubility. However, conventional direct precipitation to prepare nanoparticles has the issues of low loading and encapsulation efficiency. Here we demonstrate a kinetically controlled and rapid-precipitation process called Flash NanoPrecipitation (FNP), to offer a multi-phase mixing platform for bioengineering nanoparticles. With the designed geometry in the micro-mixer, we can generate nanoparticles with a narrow size distribution, while maintaining high loading and encapsulation efficiency. By controlling the time scales in FNP, we can tune the nanoparticle size and the robustness of the process. Remarkably, the dissolution rates of the nanoparticles are significantly improved compared with crystalline drug powders. Furthermore, we investigate how to recover the drug-loaded nanoparticles from the aqueous dispersions. Regarding the maintenance of the bioavailability, we discuss the advantages and disadvantages of each drying process. These results suggest that FNP offers a versatile and scalable nano-fabrication platform for biomedical engineering. [Preview Abstract] |
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