Bulletin of the American Physical Society
66th Annual Meeting of the APS Division of Fluid Dynamics
Volume 58, Number 18
Sunday–Tuesday, November 24–26, 2013; Pittsburgh, Pennsylvania
Session M28: Industrial Applications I |
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Chair: Hazel Marie, Youngstown State University Room: Spirit of Pittsburgh Ballroom B/C |
Tuesday, November 26, 2013 8:00AM - 8:13AM |
M28.00001: Keeping a surface ice/frost free with electro-conducting water-repellent coatings Arindam Das, Shreyas Kapatral, Constantine M. Megaridis Ice/frost formation on aircraft, wind turbines, power grids, marine vessels, telecommunication devices, etc. has propelled scientific research on surfaces that facilitate the removal of the water solid phase or retard its formation. Superhydrophobic, self-cleaning surfaces have been investigated recently (Jung et al., Langmuir 2011) for their passive anti-icing properties. Although superhydrophobic surfaces have been shown to delay the onset of frosting and icing, they cannot prevent it entirely. Hence active deicing/defrosting approaches are required to keep surfaces free of ice/frost. Defrosting experiments have been carried out on glass substrates coated with textured polymeric nanocomposite films of different surface wettability, porosity and roughness. A strong influence of these parameters on condensation, condensation frosting and defrosting was observed. The coatings are electro-conducting, thus allowing skin heating at the interface between ice and the substrate. Sustained ice- and frost-free operation is demonstrated at substrate temperatures well below the freezing point and in humid ambient atmospheres. [Preview Abstract] |
Tuesday, November 26, 2013 8:13AM - 8:26AM |
M28.00002: One-way water permeable valve via water-based superhydrophobic coatings Joseph E. Mates, Constantine M. Megaridis Spray-cast superhydrophobic coatings have shown promise in commercial applications for fluid management due to their intrinsic low-cost, large-area capabilities and substrate independence (Schutzius et al. 2011). A technique of applying a light ($<$ 2gsm) water-based superhydrophobic coating on inherently hydrophilic cellulosic substrates to generate a preferred directionality for water absorption and transmission is presented. The mechanism described allows water to pass through a thin treated porous substrate in one direction under negligible pressure, but does not allow water to return from the opposite direction unless much greater pressure is applied. This pressure disparity ``window'' effectively creates a one-way fluid valve, with envisioned applications ranging from personal hygiene products, to oil-water separation and filtration. Combining SEM imaging with theoretical robustness factors (Tuteja et al. 2008), the penetration pressures are found to be tunable for application-specific designs by choosing a substrate based on limiting factors of fiber diameter and spacing. The process can also be modified with the addition of functionalized (e.g. antibacterial, conductive) nanoparticle fillers suited for the desired application. [Preview Abstract] |
Tuesday, November 26, 2013 8:26AM - 8:39AM |
M28.00003: Mixing of two miscible fluids at high Schmidt number Mark Simmons, Federico Alberini, Christopher Pain, Omar Matar The blending of two miscible liquids at high Schmidt number is an increasingly common industrial problem: as processes push towards shorter timescales yet the rheology of the fluids becomes increasingly complex. This leads to phenomena which resemble a quasi two-phase system with zero interfacial tension. In this study, we compare experimental results with computational fluid dynamics simulations using unstructured-mesh adaptivity for the flow of two Newtonian, or two power-law fluids through a complex geometry representative of a Kenics type static mixer used in industry. The geometry induces a stretching and folding of the fluid elements which causes exponential growth of the interface length down the geometry. The interfacial topology obtained from the simulations is compared with experiments carried out using Planar Laser Induced Fluorescence (PLIF), which enables the spatial distribution of each phase, and the interfaces between them, to be determined at the outlet of the geometry. [Preview Abstract] |
Tuesday, November 26, 2013 8:39AM - 8:52AM |
M28.00004: Internal Concentration Polarization in Asymmetric Membrane in Forward Osmosis System Gabriela Gadelha, Hermes Gadelha, Nick Hankins There has been a re-emerging interest in the study of the osmotic-driving desalination process known as Forward Osmosis (FO), due to its potential for significantly lower energy demand. However, the employed asymmetric semi-permeable membranes are notorious for the formation of unstirred boundary layers. These boundary layers may be dilutive or concentrative, causing an undesired decline on the osmotic flux. To date, although several models have been proposed in the literature to describe various applications in membrane separation processes, the fundamental theoretical basis has remained unchanged. Here, we detail an alternative formulation for the solute concentration profile and the water flux decline in terms of the osmotic Peclet number and the dimensionless solute permeability. Our analysis shows that the osmotic potential efficiency and the resulting water flux are inversely related, preventing any simultaneous optimization of the system, i.e. the larger the water flux is, the less osmotically efficient it becomes. We equally investigated the effect of distinct flat-sheet membrane configurations on the water flux. In this case, when the active layer faces the solution of low concentration (feed solution), under normal operations conditions, the water flux can be 60{\%} lower than its counter configuration, when the active layer faces the solution of high concentration (draw solution). Finally, we contrast the theoretical formulation with experiments using inorganic ions and micelle as draw solutions. [Preview Abstract] |
Tuesday, November 26, 2013 8:52AM - 9:05AM |
M28.00005: Optimizing cross-flow-filtration efficacy using variable wall permeabilities James Herterich, Ian Griffiths, Robert Field, Dominic Vella Water filtration systems typically involve flow along a channel with permeable walls and suction applied across the wall. In this ``cross-flow'' arrangement, clean water leaves the channel while impurities remain within it. A limiting factor for the operation of cross-flow devices is the build-up of a high concentration of particles near the wall due to the induced flow. Termed concentration polarization (CP), this effect ultimately leads to the blocking of pores within the permeable wall and the deposition of a ``cake'' on the wall surface. Here we show that, through strategic choices in the spatial variations of the channel-wall permeability, we may reduce the effects of CP by allowing diffusion to smear out any build up of particles that may occur. We demonstrate that, for certain classes of variable permeability, there exist optimal choices that maximize the flux of clean water out of a device. [Preview Abstract] |
Tuesday, November 26, 2013 9:05AM - 9:18AM |
M28.00006: Fluid Mechanics of a High Performance Racing Bicycle Wheel Jean-Pierre Mercat, Brieuc Cretoux, Francois-Xavier Huat, Benoit Nordey, Maxime Renaud, Flavio Noca In 2012, MAVIC released the most aerodynamic bicycle wheel on the market, the CXR 80. The french company MAVIC has been a world leader for many decades in the manufacturing of bicycle wheels for competitive events such as the Olympic Games and the Tour de France. Since 2010, MAVIC has been in a research partnership with the University of Applied Sciences in Geneva, Switzerland, for the aerodynamic development of bicycle wheels. While most of the development up to date has been performed in a classical wind tunnel, recent work has been conducted in an unusual setting, a hydrodynamic towing tank, in order to achieve low levels of turbulence and facilitate quantitative flow visualization (PIV). After a short introduction on the aerodynamics of bicycle wheels, preliminary fluid mechanics results based on this novel setup will be presented. [Preview Abstract] |
Tuesday, November 26, 2013 9:18AM - 9:31AM |
M28.00007: Numerical simualtions of fouling in crude-oil processing Junfeng Yang, Omar Matar The aims of this study are to achieve fundamental understanding of the transfer processes underlying the development of a fouling layer on the inside of heat exchangers used in crude-oil processing. The numerical models developed are based on the solution of the mass and momentum conservation equations, coupled to the energy transport equation. These are complemented by relations that capture the dependence of the layer density, viscosity, and surface tension on temperature. In order to capture ageing effects, the thermal conductivity of the layer is allowed to depend on temperature, and a functional form is chosen for its viscosity that accounts for dynamic structure-building and destruction. Importantly, a chemical equilibria model is used to model the phase behaviour of the oil, and this is also coupled to the governing equations. The turbulence in the fluid phase is modelled using large eddy simulations. Numerical solutions of the model equations are obtained in a channel geometry using a volume-of-fluid approach. Our results capture the complex fouling dynamics that include phase separation, wall-layer deposition, and removal. [Preview Abstract] |
Tuesday, November 26, 2013 9:31AM - 9:44AM |
M28.00008: Parametric Study on the Evolution of Thermal Patterns and Coherent Flow Structures in the Rotated Arc Mixer Ozge Baskan, Michel Speetjens, Guy Metcalfe, Herman Clercx Advective-diffusive scalar transport in spatially or temporally periodic flow fields has been investigated in numerous studies, which exposed that the global transport relies on the kinematic/geometric parameters governing the advection and the ratio between the advective and diffusive time scales. These studies mainly employ numerical/analytical methods. However, experimental analysis remains outstanding. This research concerns an experimental parametric study on the evolution of the thermal patterns in a representative configuration, the Rotated Arc Mixer (RAM), and its correlation with the coherent flow structures. The RAM is an inline mixer composed of a stationary inner cylinder with systematically oriented apertures and a rotating outer cylinder inducing transverse flow at the apertures. Design of the experimental facility is based on a 2D time-periodic simplification of the 3D spatially-periodic RAM, where the cross-sectional progression is represented by the temporal evolution. The test section is a shallow circular tank with apertures on the circumference and motor-driven belts imitate the rotating outer cylinder of the RAM. Circumferential temperature is kept constant via an enclosing hot-water reservoir. The 2D flow and temperature fields are measured by 2D Particle Image Velocimetry and Infrared Thermography and analyzed. [Preview Abstract] |
Tuesday, November 26, 2013 9:44AM - 9:57AM |
M28.00009: Erosion resistance of pipe bends with bio-inspired internal surfaces Chengchun Zhang, Omar Matar Guided by the structure of a shell surface, a bio-inspired surface is proposed to enhance the erosion resistance of pipe bends carrying crude-oil and sand in the turbulent flow regime. A comparison of the erosion rate between a smooth bend and the bio-inspired one is carried out using numerical simulations: large eddy simulations are used to simulate turbulence, and these are coupled to a discrete element method for the solid particles. The results indicate that the bio-inspired surface can control effectively the liquid-solid flow near the wall, and decrease the particle-wall force. This, then, leads to a reduction in the erosion rate brought about by the sand transported by the crude-oil in the pipe bend. [Preview Abstract] |
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