Bulletin of the American Physical Society
62nd Annual Meeting of the APS Division of Fluid Dynamics
Volume 54, Number 19
Sunday–Tuesday, November 22–24, 2009; Minneapolis, Minnesota
Session HR: Porous Media Flows |
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Chair: Bojan Markicevic, Kettering University Room: 200F |
Monday, November 23, 2009 10:30AM - 10:43AM |
HR.00001: The fate of the sessile droplet imprint in porous medium: simultaneous capillary flow and evaporation B.I. Markicevic, H.K. Navaz The fate of a liquid droplet imbibed into a porous medium is formulated as a multiphase problem, and a numerical solution is developed using the capillary network model with a micro-force balance at the liquid$\vert $gas interface. Momentum transport - capillary flow, and mass transport - evaporation are solved simultaneously. The physics of the multiphase capillary flow includes the formation of local gas clusters, and liquid ganglia, whose distribution can be determined from the force balance on the gas$\vert $liquid interface. The clusters and ganglia distribution is further altered by evaporation. The evaporation tends to shrink the ganglia size and open the gas clusters; both due to the liquid mass loss from the porous medium. Still, the capillarity tends to disperse the liquid back into the regions from where the liquid previously evaporated. In order to quantify the liquid distribution, besides the diffusion coefficient, the dispersion coefficient for the capillary flow is defined. The latter is found from the porous medium permeability, liquid viscosity and capillary pressure. As expected, for a larger dispersion coefficient, the liquid remains closer to the evaporating boundary, and the evaporation rate is higher. The opposite is true for a small dispersion coefficient. Finally, the changes in liquid dispersion influence the liquid persistence time, where this time increases for a liquid dispersed deeper in the medium. [Preview Abstract] |
Monday, November 23, 2009 10:43AM - 10:56AM |
HR.00002: Capillary Flow Limitations of Nanowicks Conan Zhang, Carlos Hidrovo Thermal management is an important issue in microelectronic systems. The inaccessibility and diminishing size of these systems, however, requires that the heat management components be reliable and compact, such as is the case with heat pipes. In most intermediate temperature heat pipes typically found in microelectronics, the critical heat flux is governed by the capillary limit. Given the projected increases in computer chip heat fluxes, it is important to investigate the use of nanowicks as a means of raising this capillary limit. A theoretical model was developed to simulate flow through a vertical nanopillar array by balancing the capillary driving forces and the viscous losses in a quasi-steady state dynamic formulation. Based on this model, the maximum mass flow and its critical heat flux can be found for a wick given its microstructure geometry. These values were also found experimentally for commercially available wicks and nanowicks. We found that nanowicks provide lower mass flow rates than conventional wicks, mainly due to a reduced cross section. However, nanowicks achieved higher velocities and show promise over some conventional heat pipe wicks. [Preview Abstract] |
Monday, November 23, 2009 10:56AM - 11:09AM |
HR.00003: Thermo-chemical energy storage and heat transfer in a flow of hydrated magnesium sulfate Ganesh Balasubramanian, Sohail Murad, Ishwar K. Puri Salt hydrates undergo desorption on being heated above certain charging temperatures, releasing water and forming anhydrous salts which have a higher energy content. Since these salts are hygroscopic, energy is easily retrieved back by passing water vapor over the anhydrous form. Such a technique of energy conversion, storage and retrieval enables these salts to be impregnated into porous media for thermo-chemical energy application. However, to investigate the thermal transport at the interface of the porous material and the salt, atomistic simulations are necessary. We employ molecular dynamics to simulate the heat transfer mechanism in a flow of hydrated magnesium sulfate impregnated into mesoporous silica and understand the role of interfacial thermal resistance on the charging temperature and total heat storage capacity of such salts. [Preview Abstract] |
Monday, November 23, 2009 11:09AM - 11:22AM |
HR.00004: Drainage in Gas diffusion Layers of PEM fuel cells Ezequiel Medici, Jeff Allen Percolation through porous transport layers (PTL) of proton exchange membrane (PEM) fuel cells have distinct fluid flow patterns depending on the PTL morphological and wetting properties as well as injected/displaced fluid properties and flow rates. These distinct fluid flow patterns include stable displacement, capillary fingering, and viscous fingering. A pseudo Hele-Shaw cell experimental setup was developed to effectively characterize different gas diffusion layers based on their susceptibility to the formation of these fluid flow patterns. The wetted area is determined by tracking the injected fluid from a top view of the cell. The percolation pressure is measured at the injection location of the cell. These two outputs are essential to identify the mechanism controlling the percolation process. The goal of this work is to link the wetted area and percolation pressure through non-dimensionalization that collapses these onto a single curve. Preliminary results from capillary fingering and stable displacement data show a constant shift between the curves for different PTL samples. This allows for unique characterization of PTLs based on their morphological and wettability properties. [Preview Abstract] |
Monday, November 23, 2009 11:22AM - 11:35AM |
HR.00005: ABSTRACT WITHDRAWN |
Monday, November 23, 2009 11:35AM - 11:48AM |
HR.00006: Natural convection and the evolution of a reactive porous medium Lindsey Ritchie, David Pritchard In many geological settings the equilibrium concentration of a dissolved chemical species depends on the vertically varying chemical properties of the rock. As a prototype for such systems, this study considers the solutal convection of a reactive fluid in a permeable medium, subject to chemical equilibrium on the bounding surfaces, and where the chemical equilibrium varies vertically throughout the layer. Over relatively short timescales, the exchange of solute between fluid and matrix stabilises the system against the onset of convection and promotes the development of narrower convective cells: we investigate this process using linear stability analysis and numerical simulation. Over longer timescales, when convection has developed, the reaction drives spatial and temporal changes to the porosity and permeability of the rock. We describe numerical results which reveal novel interactions between the convection pattern and the evolving matrix. Ultimately these interactions can restabilise the system, shutting down the convection but preserving ``signatures'' of convective cells or more complex structures in the varying porosity of the rock. [Preview Abstract] |
Monday, November 23, 2009 11:48AM - 12:01PM |
HR.00007: Post-Injection Migration of CO$_2$ in Saline Aquifers subject to Groundwater Flow, Aquifer Slope, and Capillary Trapping Christopher MacMinn, Michael Szulczewski, Ruben Juanes We study a sharp-interface mathematical model for the post-injection migration of a plume of CO$_2$ in a deep saline aquifer under the influence of natural groundwater flow, aquifer slope, gravity override, and capillary trapping. The model leads to a nonlinear advection-diffusion equation, where the diffusive term describes the upward spreading of the CO$_2$ against the caprock. We find that the advective terms dominate the flow dynamics even for moderate gravity override, and we solve the model analytically in the hyperbolic limit. We use this solution to estimate the capacity of various target formations in the United States. [Preview Abstract] |
Monday, November 23, 2009 12:01PM - 12:14PM |
HR.00008: Uncertainty characterization of solubility trapping of CO2 in saline aquifers Amir Riaz, Marc Hesse, Hamdi Tchelepi Buoyancy driven unstable convection of CO2 saturated plumes in brine aquifers that results from the Rayleigh-Benard hydrodynamic instability in a porous medium is one of the principle mechanisms of CO2 sequestration by solubility trapping. The finite time of the onset of instability has been analyzed in detail by many authors previously but an agreement as to its precise value as a function of the Rayleigh number has not yet emerged. Rather, the onset time obtained from various analyses is known to vary by an order of magnitude. In an attempt to resolve this discrepancy we carry out high accuracy numerical simulations and measure the critical time. We find that the critical time and the closely related time-to-initiate-convection are fundamentally dependent on the magnitude and realization of the field of initial random perturbations employed to induce instability and are hence not deterministic. We therefore provide a probabilistic description of the processes of initialization of instability and convection and formulate correlations with late time events such as the total amount of CO2 dissolved to provide a reliable characterization of the process of CO2 solubility trapping in brine aquifers. [Preview Abstract] |
Monday, November 23, 2009 12:14PM - 12:27PM |
HR.00009: Gravity currents propagating along channels in porous media Madeleine Golding, Herbert Huppert The effect of impermeable channel boundaries on gravity currents propagating in a porous medium is investigated. The problem admits similarity solutions for currents of a variety of rates of input flux and channel shapes. Experiments were conducted in V-shaped and semicircular channels and the results are generally found to be in good agreement with theoretical predictions. One motivation for the study of gravity currents in a porous medium is the process of carbon dioxide (CO$_2$) sequestration, whereby supercritical CO$_2$ is pumped deep underground into rock saturated with denser salt water. The CO$_2$ rises as a buoyant plume until it reaches an impermeable boundary, at which point it spreads laterally as a gravity current. Our knowledge of geological structure deep underground is limited. Therefore the theory developed in this study aims to help understand to what extent the presence of more complex boundaries, namely channel boundaries, would affect predictions for the propagation of gravity currents in porous media. [Preview Abstract] |
Monday, November 23, 2009 12:27PM - 12:40PM |
HR.00010: Localised leakage from porous and viscous gravity currents Jerome Neufeld, Dominic Vella, Herbert Huppert, John Lister Motivated by the geological sequestration of CO$_2$ we investigate the effect of localized leakage on the spreading of porous and viscous gravity currents in a variety of both two and three dimensional geometries. Generically, we find that these systems tend towards a steady state in which the input flux is exactly balanced by the leakage flux. Of particular importance is the efficiency of storage defined as the instantaneous fraction of fluid that does not leak. We compare analytic expressions for the asymptotic behavior of the efficiency to full numerical results and laboratory models of both porous and viscous gravity currents. These results bear on the time scales over which CO$_2$ may be safely stored in saline aquifers. [Preview Abstract] |
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