scholarly journals Technical Note: The use of an interrupted-flow centrifugation method to characterise preferential flow in low permeability media

2015 ◽  
Vol 12 (1) ◽  
pp. 67-92
Author(s):  
R. A. Crane ◽  
M. O. Cuthbert ◽  
W. Timms
Keyword(s):  
Preferential Flow ◽  
Molecular Diffusion ◽  
Breakthrough Curves ◽  
Technical Note ◽  
Dual Porosity ◽  
Low Permeability ◽  
Efficiency Coefficient ◽  
Transport Modelling ◽  
Induced Flow ◽  
Interrupted Flow

Abstract. We present an interrupted-flow centrifugation technique to characterise preferential flow in low permeability media. The method entails a minimum of three phases: centrifuge induced flow, no flow and centrifuge induced flow, which may be repeated several times in order to most effectively characterise multi-rate mass transfer behaviour. In addition, the method enables accurate simulation of relevant in situ total stress conditions during flow by selecting an appropriate centrifugal force level. We demonstrate the utility of the technique for characterising the hydraulic properties of smectite clay dominated core samples. All samples exhibited a non-Fickian tracer breakthrough (early tracer arrival), combined with a decrease in tracer concentration immediately after each period of interrupted-flow. This is indicative of dual (or multi) porosity behaviour, with solute migration predominately via advection during induced flow, and via molecular diffusion (between the preferential flow network(s) and the low hydraulic conductivity domain) during interrupted-flow. Tracer breakthrough curves were simulated using a bespoke dual porosity model with excellent agreement between the data and model output (Nash–Sutcliffe model efficiency coefficient was >0.97 for all samples). In combination interrupted-flow centrifuge experiments and dual porosity transport modelling are shown to be a powerful method to characterise preferential flow in low permeability media.

scholarly journals Technical Note: The use of an interrupted-flow centrifugation method to characterise preferential flow in low permeability media

2015 ◽  
Vol 19 (9) ◽  
pp. 3991-4000 ◽  
Author(s):  
R. A. Crane ◽  
M. O. Cuthbert ◽  
W. Timms
Keyword(s):  
Preferential Flow ◽  
Molecular Diffusion ◽  
Breakthrough Curves ◽  
Dual Porosity ◽  
Low Permeability ◽  
Efficiency Coefficient ◽  
Transport Modelling ◽  
Core Samples ◽  
Induced Flow ◽  
Interrupted Flow

Abstract. We present an interrupted-flow centrifugation technique to characterise preferential flow in low permeability media. The method entails a minimum of three phases: centrifuge-induced flow, no flow and centrifuge-induced flow, which may be repeated several times in order to most effectively characterise multi-rate mass transfer behaviour. In addition, the method enables accurate simulation of relevant in situ total stress conditions during flow by selecting an appropriate centrifugal force. We demonstrate the utility of the technique for characterising the hydraulic properties of smectite-clay-dominated core samples. All core samples exhibited a non-Fickian tracer breakthrough (early tracer arrival), combined with a decrease in tracer concentration immediately after each period of interrupted flow. This is indicative of dual (or multi-)porosity behaviour, with solute migration predominately via advection during induced flow, and via molecular diffusion (between the preferential flow network(s) and the low hydraulic conductivity domain) during interrupted flow. Tracer breakthrough curves were simulated using a bespoke dual porosity model with excellent agreement between the data and model output (Nash–Sutcliffe model efficiency coefficient was > 0.97 for all samples). In combination, interrupted-flow centrifuge experiments and dual porosity transport modelling are shown to be a powerful method to characterise preferential flow in low permeability media.

scholarly journals SOLUTE TRANSPORT MODELLING IN LOW-PERMEABILITY HOMOGENEOUS AND SATURATED SOIL MEDIA

2021 ◽  
Vol 36 (2) ◽  
pp. 25-32
Author(s):  
Muhammad Zaheer ◽  
Hadayat Ullah ◽  
Saad Ahmed Mashwani ◽  
Ehsan ul Haq ◽  
Syed Husnain Ali Shah ◽  
...  
Keyword(s):  
Solute Transport ◽  
Preferential Flow ◽  
Relative Concentration ◽  
Breakthrough Curves ◽  
Saturated Soil ◽  
Low Permeability ◽  
Transport Modelling ◽  
Variation Of Parameters ◽  
Solute Transport Modeling ◽  
Soil Media

Fickian and non-Fickian behaviors were often detected for contaminant transport activity owed to the preferential flow and heterogeneity of soil media. Therefore, using diverse methods to measure such composite solute transport in soil media has become an important research topic for solute transport modeling in soil media. In this article, the continuous-time random walk (CTRW) model was applied to illustrate the relative concentration of transport in low-permeability homogeneous and saturated soil media. The solute transport development was also demonstrated with the convection-dispersion equation (CDE) and Two Region Model (TRM) for comparison. CXTFIT 2.1 software was used for CDE and TRM, and CTRW Matlab Toolbox v.3.1 for the CTRW simulation of the breakthrough curve. It was found that higher values of determination coefficient (R2) and lower values of root mean square error (RMSE) concerning the best fits of CDE, TRM, and CTRW. It was found that in the comparison of CDE, TRM, and CTRW, we tend to use CTRW to describe the transport behavior well because there are prevailing Fickian and non-Fickian transport. The CTRW gives better fitting results to the breakthrough curves (BTCs) when β has an increasing pattern towards 2.00. In this study, the variation of parameters in three methods was investigated and results showed that the CTRW modeling approach is more effective to determine non-reactive contaminants concentration in low-permeability soil media at small depths.

Technical Note: Finite State Induced Flow Model in Vortex Ring State

2000 ◽  
Vol 45 (4) ◽  
pp. 318-320 ◽  
Author(s):  
Chengjian He ◽  
C. S. Lee ◽  
Weibin Chen
Keyword(s):  
Vortex Ring ◽  
Flow Model ◽  
Technical Note ◽  
Finite State ◽  
Induced Flow ◽  
Vortex Ring State

A Comparision of Laboratory and Field Based Determinations of Molecular Diffusion Coefficients in a Low Permeability Geologic Medium

2009 ◽  
Vol 43 (17) ◽  
pp. 6730-6736 ◽  
Author(s):  
M. Jim Hendry ◽  
S. Lee Barbour ◽  
Brigitte E. J. Boldt-Leppin ◽  
Laura J. Reifferscheid ◽  
Leonard I. Wassenaar
Keyword(s):  
Diffusion Coefficients ◽  
Molecular Diffusion ◽  
Low Permeability ◽  
Geologic Medium

Pore-scale Mixing and the Evolution from Anomalous to Normal Hydrodynamic Dispersion

2021 ◽  
Author(s):  
Marco Dentz ◽  
Alexandre Puyguiraud ◽  
Philippe Gouze
Keyword(s):  
Porous Media ◽  
Large Scale ◽  
Molecular Diffusion ◽  
Pore Space ◽  
Breakthrough Curves ◽  
Heterogeneous Porous Media ◽  
Hydrodynamic Dispersion ◽  
Pore Scale ◽  
Sandstone Sample ◽  
Flow Variability

<p>Transport of dissolved substances through porous media is determined by the complexity of the pore space and diffusive mass transfer within and between pores. The interplay of diffusive pore-scale mixing and spatial flow variability are key for the understanding of transport and reaction phenomena in porous media. We study the interplay of pore-scale mixing and network-scale advection through heterogeneous porous media, and its role for the evolution and asymptotic behavior of hydrodynamic dispersion. In a Lagrangian framework, we identify three fundamental mechanisms of pore-scale mixing that determine large scale particle motion: (i) The smoothing of intra-pore velocity contrasts, (ii) the increase of the tortuosity of particle paths, and (iii) the setting of a maximum time for particle transitions. Based on these mechanisms, we derive an upscaled approach that predicts anomalous and normal hydrodynamic dispersion based on the characteristic pore length, Eulerian velocity distribution and Péclet number. The theoretical developments are supported and validated by direct numerical flow and transport simulations in a three-dimensional digitized Berea sandstone sample obtained using X-Ray microtomography. Solute breakthrough curves, are characterized by an intermediate power-law behavior and exponential cut-off, which reflect pore-scale velocity variability and intra-pore solute mixing. Similarly, dispersion evolves from molecular diffusion at early times to asymptotic hydrodynamics dispersion via an intermediate superdiffusive regime. The theory captures the full evolution form anomalous to normal transport behavior at different Péclet numbers as well as the Péclet-dependence of asymptotic dispersion. It sheds light on hydrodynamic dispersion behaviors as a consequence of the interaction between pore-scale mixing and Eulerian flow variability. </p>

scholarly journals Trait-specific dispersal of bacteria in heterogeneous porous environments: from pore to porous medium scale

2020 ◽  
Vol 17 (164) ◽  
pp. 20200046 ◽  
Author(s):  
David Scheidweiler ◽  
Filippo Miele ◽  
Hannes Peter ◽  
Tom J. Battin ◽  
Pietro de Anna
Keyword(s):  
Preferential Flow ◽  
Cell Attachment ◽  
Flow Direction ◽  
Time Lapse ◽  
Breakthrough Curves ◽  
Porous System ◽  
Dispersal Patterns ◽  
Multi Scale ◽  
Motile Cells ◽  
Hydrodynamic Shear

The dispersal of organisms controls the structure and dynamics of populations and communities, and can regulate ecosystem functioning. Predicting dispersal patterns across scales is important to understand microbial life in heterogeneous porous environments such as soils and sediments. We developed a multi-scale approach, combining experiments with microfluidic devices and time-lapse microscopy to track individual bacterial trajectories and measure the overall breakthrough curves and bacterial deposition profiles: we, then, linked the two scales with a novel stochastic model. We show that motile cells of Pseudomonas putida disperse more efficiently than non-motile mutants through a designed heterogeneous porous system. Motile cells can evade flow-imposed trajectories, enabling them to explore larger pore areas than non-motile cells. While transported cells exhibited a rotation in response to hydrodynamic shear, motile cells were less susceptible to the torque, maintaining their body oriented towards the flow direction and thus changing the population velocity distribution with a significant impact on the overall transport properties. We also found, in a separate set of experiments, that if the suspension flows through a porous system already colonized by a biofilm, P. putida cells are channelled into preferential flow paths and the cell attachment rate is increased. These two effects were more pronounced for non-motile than for motile cells. Our findings suggest that motility coupled with heterogeneous flows can be beneficial to motile bacteria in confined environments as it enables them to actively explore the space for resources or evade regions with unfavourable conditions. Our study also underlines the benefit of a multi-scale approach to the study of bacterial dispersal in porous systems.

scholarly journals Tracing Septic Pollution Sources Using Synthetic DNA Tracers: Proof of Concept

2019 ◽  
Vol 12 ◽  
pp. 117862211986379 ◽  
Author(s):  
Christine B Georgakakos ◽  
Paul L Richards ◽  
M Todd Walter
Keyword(s):  
Preferential Flow ◽  
Quantitative Polymerase Chain Reaction ◽  
Breakthrough Curves ◽  
Septic Systems ◽  
Proof Of Concept ◽  
Septic System ◽  
Flow Paths ◽  
Synthetic Dna ◽  
Preferential Flow Paths ◽  
Polymerase Chain

Contamination from septic systems is one of the most difficult sources of nonpoint source (NPS) pollution to quantify. Quantification is difficult in part because locating malfunctioning septic systems within a watershed is challenging. This study used synthetic-DNA-based tracers to track flows from 2 septic systems. Sample DNA was quantified using quantitative polymerase chain reaction (qPCR). This technology could be especially useful for simultaneously assessing multiple septic systems because there are essentially infinite unique combinations of DNA bases such that unique tracers could be engineered for each septic system. Two studies were conducted: the first, to determine whether the tracers move through septic systems (experiment 1), and the second, to determine whether the tracers were detectable at watershed scales (experiment 2). In both cases, clear, although complex, breakthrough curves were detected. Experiment 1 revealed possible preferential flow paths that might not have been otherwise obvious, indicative of short circuiting systems. This proof of concept suggests that these tracers could be applied to watersheds suspected of experiencing NPS septic system pollution.

Computational Analysis of Straight Nozzle: Technical Note

2019 ◽  
Vol 11 (2) ◽  
Author(s):  
F. Ferdaus ◽  
R. Sridhar ◽  
G. Sathishkumar ◽  
S. Sivabalan
Keyword(s):  
Flow Separation ◽  
Supersonic Flows ◽  
Technical Note ◽  
Flow Conditions ◽  
Convergent Nozzle ◽  
Turbine Engine ◽  
Sonic Flow ◽  
Induced Flow ◽  
Exit Mach Number ◽  
Maximum Thrust

Most of the modern aircraft and military aircraft are powered by the modern gas turbine engine. They have nozzles to produce the required speed. Depending upon the required exit Mach number, a nozzle can be designed to be used for subsonic and supersonic flows. For the sonic flows, the convergent nozzle is used and for supersonic flows a convergent–divergent (CD) nozzle is used. In a CD nozzle, a straight nozzle flow is accelerated from low subsonic to sonic velocity at the throat and further expanded to supersonic velocities at the exit. This paper focuses on designing a straight nozzle to attain super-sonic flow and optimizing it to achieve maximum thrust without flow separation due to shock waves. This research also confirms that at which angle of deflection on the divergent portion produces more speed. The flow conditions were selected in view of the pressure, temperature and gases that are accessible at the exit of the combustion chamber. At the exit of the nozzle, the shock induced flow separation due to, over, under and optimum expansion conditions were studied.

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