Bulletin of the American Physical Society
68th Annual Meeting of the APS Division of Fluid Dynamics
Volume 60, Number 21
Sunday–Tuesday, November 22–24, 2015; Boston, Massachusetts
Session E1: Porous Media Flows: Clogging and Filtration |
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Chair: Ian Griffiths, University of Oxford Room: Auditorium |
Sunday, November 22, 2015 4:50PM - 5:03PM |
E1.00001: How gradients in porosity can make a better filter Ian Griffiths, Maria Bruna, Mohit Dalwadi Depth filters are a common device for removing contaminants from fluid. Porosity-graded filters, whose porosities decrease with depth, have been shown experimentally to offer improved filtration efficiency over filters with uniform porosity, by allowing contaminants to be trapped more evenly within the filter media. However, experiments are unable to probe the microscopic behavior, and so the underlying mechanisms that are responsible for this improved filtration are unclear. We use homogenization theory to derive a macroscopic model for the fluid flow and particle trapping within a porosity-graded depth filter. We find that gradients in porosity induce a macroscale particle advection in the direction of reducing porosity and show how particle trapping is more evenly spread through the filter for a decreasing porosity compared with a uniform porosity. By quantifying the removal rate, we show how a given operating regime can be fine-tuned to improve filter efficiency. The talk is accompanied by an online demonstration of MEMFI, a software package in which audience members may explore for themselves the effect of porosity gradients in user-specified operating regimes. [Preview Abstract] |
Sunday, November 22, 2015 5:03PM - 5:16PM |
E1.00002: Gravity filtration of suspensions: permeability effects Tejaswi Soori, Mengyu Wang, Thomas Ward This paper examines the filtration rates of mono-modal suspensions as a function of time and a cake layer builds up through theory and experimentation. Darcy's Law, which describes fluid flow through porous media, was applied along with the Kynch theory of sedimentation, which provides the basis for analyzing low concentration ($\phi$$\leq$20\%) cake formation. Experiments were performed to study the effects of varying particle sizes (45 $\mu$m $\leq$ $d$ $\leq$ 1400 $\mu$m) and total solid concentration $\phi$ on both the formation rate of the cake layer and its flow permeability (k) in conjunction with the filter media. A CCD camera was used to capture images of the cake formation and fluid drainage processes, and subsequent image and theoretical analysis found the fluid flow experienced a constant pressure loss due to the permeability of the filter media, whereas the experienced pressure loss due to the cake formation varies as a function of time, $\phi$ and $d$. The rate of cake formation was also found to be independent of $\phi$ but dependent on $d$ which can be attributed to a change in porosity affecting permeability. Studies on similar systems with multi-modal suspensions are in-progress. [Preview Abstract] |
Sunday, November 22, 2015 5:16PM - 5:29PM |
E1.00003: Flow and fouling in membrane filters: Effects of membrane morphology Pejman Sanaei, Linda J. Cummings Membrane filters are widely-used in microfiltration applications. Many types of filter membranes are produced commercially, for different filtration applications, but broadly speaking the requirements are to achieve fine control of separation, with low power consumption. The answer to this problem might seem obvious: select the membrane with the largest pore size and void fraction consistent with the separation requirements. However, membrane fouling (an inevitable consequence of successful filtration) is a complicated process, which depends on many parameters other than membrane pore size and void fraction; and which itself greatly affects the filtration process and membrane functionality. In this work we formulate mathematical models that can (i) account for the membrane internal morphology (internal structure, pore size \& shape, etc.); (ii) fouling of membranes with specific morphology; and (iii) make some predictions as to what type of membrane morphology might offer optimum filtration performance. [Preview Abstract] |
Sunday, November 22, 2015 5:29PM - 5:42PM |
E1.00004: Permeability modification in 3D porous media due to polymer retention Shima Parsa, Hubert Sizaret, David Weitz We combine confocal microscopy and bulk transport measurements to quantify the changes in the permeability of a model porous media after flow of a polymer solution. The 3D micromodel is made of closely packed glass beads with diameter of 150 micrometers. By matching the index of refraction of the fluid with beads we are able to measure the fluid velocities at pore level deep in the medium using particle image velocimetry. Our measurement shows that the medium permeability decreases 60{\%} after flow of multiple pore volumes of polymer solution and then flushing with water. At constant flow rate we estimate that the pore velocity increases almost 23{\%} due to this reduction in permeability. Our microscopic measurements of the velocities in pores shows that the average velocity increases considerably more than estimated bulk value. Also the distribution of velocities has a slower decay indicating somewhat higher probability of large velocities in the medium after retention of polymer. These changes in velocities are not uniform and depends on the pore size. [Preview Abstract] |
Sunday, November 22, 2015 5:42PM - 5:55PM |
E1.00005: DEM Simulation of Particle Clogging in Fiber Filtration Ran Tao, Mengmeng Yang, Shuiqing Li The formation of porous particle deposits plays a crucial role in determining the efficiency of filtration process. In this work, an adhesive discrete element method (DEM), in combination with CFD, is developed to dynamically describe these porous deposit structures and the changed flow field between two parallel fibers under the periodic boundary conditions. For the first time, it is clarified that the structures of clogged particles are dependent on both the adhesion parameter (defined as the ratio of interparticle adhesion to particle inertia) and the Stokes number (as an index of impaction efficiency). The relationship between the pressure-drop gradient and the coordination number along the filtration time is explored, which can be used to quantitatively classify the different filtration regimes, i.e., clean filter stage, clogging stage and cake filtration stage. Finally, we investigate the influence of the fiber separation distance on the particle clogging behavior, which affects the collecting efficiency of the fibers significantly. The results suggest that changing the arrangement of fibers can improve the filter performance. [Preview Abstract] |
Sunday, November 22, 2015 5:55PM - 6:08PM |
E1.00006: Effect of long-range electrostatic interaction on pore clogging in viscous particle flow Sheng Chen, Mengmeng Yang, Shuiqing Li In this study, we implement the long-range electrostatic interactions (both Coulomb and dipole interactions) into the discrete-element method simulation of small adhesive particles to investigate their influence on the formation of clogging patterns at single-pore level. The relationship between microscopic interparticle forces and the macroscopic clogging quantities, i.e. the flow permeability and clogging structures, is established. Simulated results indicate that the early-stage capture of charged particles is enhanced by the attraction between these particles and their induced charge on the wall surface. However, further aggregation is suppressed by the repulsive Coulomb interaction between the deposited particles and the suspended ones. Meanwhile, the attraction among polarized particles causes the formation of long particle chains on the surface. These particles chains, bended by flow stress, enhance the bridging phenomenon that leads to a rapid pore clogging. Comparatively, the final clogging structures have lower volume fraction and higher flow permeability in contrast to the neutral case. The results suggest that the controlled charging or polarizing of particles provide a feasible way to tune the formation process and the final state of pore clogging. [Preview Abstract] |
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