Displacement Regime Research Articles

Estimation of Recovery Efficiency in High‐Temperature Aquifer Thermal Energy Storage Considering Buoyancy Flow

AbstractWith their high storage capacity and energy efficiency as well as the compatibilities with renewable energy sources, high‐temperature aquifer thermal energy storage (HT‐ATES) systems are frequently the target today in the design of temporally and spatially balanced and continuous energy supply systems. The inherent density‐driven buoyancy flow is of greater importance with HT‐ATES, which may lead to a lower thermal recovery efficiency than conventional low‐temperature ATES. In this study, the governing equations for HT‐ATES considering buoyancy flow are nondimensionalized, and four key dimensionless parameters regarding thermal recovery efficiency are determined. Then, using numerical simulations, recovery efficiency for a sweep of the key dimensionless parameters for multiple cycles and storage volumes is examined. Ranges of the key dimensionless parameters for the three displacement regimes, that is, a buoyancy‐dominated regime, a conduction‐dominated regime, and a transition regime, are identified. In the buoyancy‐dominated regime, recovery efficiency is mainly correlated to the ratio between the Rayleigh number and the Peclet number. In the conduction‐dominated regime, recovery efficiency is mainly correlated to the product of a material‐related parameter and the Peclet number. Multivariable regression functions are provided to estimate recovery efficiency using the dimensionless parameters. The recovery efficiency estimated by the regression function shows good agreement with the simulation results. Additionally, well screen designs for optimizing recovery efficiency at various degrees of intensity of buoyancy flow are investigated. The findings of this study can be used for a quick assessment and characterization of the potential HT‐ATES systems based on the geological and operational parameters.

A Weierstrass approach to the analysis of rarefaction solitary waves in tensegrity mass-spring systems

Abstract The Weierstrass‘ theory of one-dimensional Lagrangian systems and a quasi-continuum approach are employed to study the propagation of solitary waves in tensegrity mass-spring chains, which exhibit softening-type elastic response in the large displacement regime and are subject to external pre-compression. The presented study analytically derives the shape of the traveling rarefaction pulses, and limiting values of the speeds of such pulses. Use is made of a tensegrity-like interaction potential that captures the main features of the real force-displacement response of the examined units. The Weierstrass approach is validated through numerical applications that establish comparisons between the theory developed in the present work and previous results available in literature.

(Digital Presentation) The Effect of Coating Quality on Water Transport in the Gas Diffusion Layer of PEM Fuel Cells

Present study examines the impact of the quality of the GDL non-wetting coating on water transport. It is found that there are two distinct regions defined by the coating quality which present fundamentally distinct behaviours, one region characterized by few coating defects with the second marked by significant coating degradation. Simulations consider the influence of heterogeneous wetting and pinning conditions on protruding water droplets in contact with the GDL fibrous matrix. The impact is assessed by examining the breakthrough pressure as a function of protruding droplet volumes. When a non-wetting coating such as PTFE is applied, inherent coating defects determine a mixed-non-wetting (MNW) behaviour of water passing through the pores of the GDL. The MNW behaviour for a quasi-uniform non-wetting coating having less than 25% defects is characterized by a high breakthrough pressure, yielding improved transport properties in the stable displacement regime. The MNW meniscus is critical to establishing a high breakthrough pressure and a small characteristic droplet volume, parameters considered to be important in the design of a GDL that promotes optimal water transport. The coating degrades under normal operating conditions and as a consequence it changes the water transport characteristics of the porous medium. In this range where coating defects are predominant it is found that the water breakthrough pressure changes significantly, rendering poor performance below that of a non-coated wetting GDL. Various degrees of coating degradation are considered and the corresponding Laplace pressure is determined as a function of breakthrough droplet volumes.

Influence of binder content on gas-water two-phase flow and displacement phase diagram in the gas diffusion layer of PEMFC: A pore network view

Understanding the gas-water flow dynamics in the gas diffusion layer (GDL) is one of the keys to improving the proton exchange membrane fuel cell's (PEMFC) overall performance and avoiding water flooding. Yet, the relationship between the two-phase flow and micro-scale GDL structures (including binder, PTFE, and fiber skeleton) is not well understood. In this study, three-dimensional GDL structures with different fractions of binder contents (φb=0%∼50%) and a fixed porosity of 75.6 % are confidently reconstructed based on high-resolution images from the confocal microscope, implying that the addition of binder will increase the number of large pores and cause a bimodal throat size distribution through morphology analysis. Thereafter, drainage simulations are performed under a wide range of capillary number (−9 < log Ca <0) and viscosity ratio (−3 < log M < 2) by the pore network model (PNM), which robustly predicts the displacement phase diagram of viscous fingering, capillary fingering, stable displacement, and transitional regime. In the viscous fingering and stable displacement regime, the nonwetting phase saturation (Snw) is nearly the same for different φb, implying the fluid invading pathway does not change much with the addition of binder. However, in the capillary fingering regime (refer to the actual operating conditions), Snw increases rapidly with φbat the breakthrough time and its transient value continues to increase until the steady state, which may be attributed to the increased fractions of pores above the capillary threshold attributed by the bimodal throat size distribution. In addition, the effective water permeability increases sharply with φb, whereas the gas permeability remains almost constant, which means such pore structure alteration by adding the binder is beneficial to water disposal in PEMFC. This research provides insights into delineating the effect of pore and throat size distribution alteration by adding binder on two-phase dynamics in GDL.

(Digital Presentation) The Effect of Coating Quality on Water Transport in the Gas Diffusion Layer of PEM Fuel Cells

Present study examines the impact of the quality of the GDL non-wetting coating on water transport. It is found that there are two distinct regions defined by the coating quality which present fundamentally distinct behaviours, one region characterized by few coating defects with the second marked by significant coating degradation. Simulations consider the influence of heterogeneous wetting and pinning conditions on protruding water droplets in contact with the GDL fibrous matrix. The mixed-non-wetting behaviour for a uniform non-wetting coating having less than 25% defects is characterized by a high breakthrough pressure, yielding improved transport properties in the stable displacement regime. The coating degrades under normal operating conditions and it changes the water transport characteristics unfavorably through a significant decrease in breakthrough pressure, and an up to six-fold increase in droplet volume. Various degrees of coating degradation are considered and the corresponding Laplace pressure is determined as a function of droplet volumes at breakthrough.

An Experimental Investigation on the Energy Signature Associated With Multiphase Flow in Porous Media Displacement Regimes

AbstractThis study investigates the energy signature associated with multiphase flow in porous media displacement regimes. We proposed that net efficiency, as the conversion of external work applied to surface energy generated, provides new insights into the transition of flow regimes. The combined effects of wettability and flow rates on immiscible fluid‐fluid displacement is experimentally investigated using high‐resolution imaging in microfluidic flow cells, which allows for tracking the evolution of interfacial area under applied external work. Our study focuses on the morphology of invasion patterns and the efficiency of conversion of external work to surface energy. The results show that the morphology of invasion patterns under unfavorable displacement condition is sharper than that under favorable displacement condition with larger ratios of length and width for fingers. The efficiency of conversion of external work to surface energy decreases with the increase of contact angles and reduces greatly with the increase of Capillary numbers. With favorable displacement conditions, the efficiency of conversion is consistently higher than that for unfavorable displacement. The trends of external work and surface energy serve as a signature of the transition between different flow regimes, which exhibits alteration especially at low Capillary numbers. The findings highlight the importance of wettability and flow rates in determining the efficiency of fluid‐fluid displacement in porous media. Understanding the energy signature associated with multiphase flow can have implications for various geoscience applications, such as oil/gas recovery, groundwater remediation, and underground energy storage.

Pore-scale study of the effects of grain size on the capillary-associated interfacial area during primary drainage

This study investigates the capillary-associated interfacial area during primary drainage in unconsolidated porous media for different mean grain diameters, employing pore-scale numerical simulation with the phase-field method. Five, two-dimensional porous media are generated with the same grain/pore size uniformity, but different mean grain diameters, ranging between 0.24 mm and 0.94 mm. Three cases are considered, representing stable displacement, crossover zone and viscous-fingering regimes. The findings reveal that the capillary-associated interfacial production rate increases with decreasing grain size. Specifically, the capillary-associated interfacial production rate is higher for the viscous-fingering regime compared to the stable displacement. The maximum capillary-associated interfacial area obtained for different grain sizes agrees with the correlation established in our previous study using the kinetic interface-sensitive tracer. Furthermore, the capillary-associated interfacial area is divided into two parts: one related to the disconnected water clusters and the other related to the connected water. The disconnected capillary-associated interfacial area correlates with the average volume of the clusters, following an exponential function. Furthermore, the average volume of the clusters depends on both, the grain size and displacement regime. Moreover, it is found that the displacement regime has a great impact on the connected capillary-associated interfacial area. For stable displacement, the connected capillary-associated interfacial area is larger for larger mean grain diameter. In contrast, for fingering, the connected capillary-associated interfacial area is smaller for increasing mean grain diameter.

Failure mechanism in a highway embankment founded on a sloping tectonised flysch formation

A highway embankment founded on a slope in a tectonised flysch formation of the Apennines chain (Central Italy) has been affected for about 30 years by continuous slow movements that caused some fractures on the road paving thus requiring periodic maintenance works. Due to the relevance of the damaged infrastructure, different investigation and monitoring campaigns have been carried out to collect information about the properties of the involved soils, the groundwater regime and the displacement field. Field monitoring, in particular, revealed that the movements were the result of a failure mechanism affecting both the embankment and the foundation soils. In particular, the observed displacements showed a weather-induced seasonal trend featured by acceleration/deceleration stages during the wet/dry periods. In order to better understand the detected mechanical response, a numerical model accounting for a soil hydrological balance of the interested area has been developed allowing a reliable historical reconstruction of the displacement regime.

Transient characteristics of in-plane water transport in gas diffusion layers of PEM fuel cells

During the operation of proton exchange membrane (PEM) fuel cells, water and heat are produced as two byproducts. A reliable and continuous operation of a PEM fuel cell requires an efficient water removal from the porous structure of the electrodes. In PEM fuel cells, gas diffusion layers (GDL) are used to effectively remove the produced water from the electrodes and also to supply reactant gases across them. The focus of this study is to characterize liquid water percolation within the plane of the GDL by utilizing a nondimensional energy ratio-time scale model (Ce-t∗). The transport phenomena are investigated for various GDL compressions, GDL samples with the microporous layer (MPL), and a degraded GDL sample. The transition between flow regimes is characterized based on the variation of slopes in Ce-t∗ curves. The flow regimes were observed to change from fingering and channeling in the capillary fingering regime to macro-transport along with uniform percolation in the stable displacement regime. It was observed that GDL compression can expedite flow regime transition and can cause faster energy dissipation during steady state periods. When MPLs were added to the GDL, the wetted areas were observed to occur at more dispersed locations. Finally, the experiment conducted with a degraded GDL without an MPL demonstrated higher slopes in the Ce-t∗ curve, indicating more frequent liquid water flooding. This could ultimately result in reduced cell performance.

Immiscible displacement flows in axially rotating pipes

We experimentally study buoyant immiscible displacement flows in an axially rotating pipe, with varying flow parameters, such as the mean imposed flow velocity, density difference, pipe rotation speed, and pipe inclination angle. Via employing image processing and ultrasound Doppler velocimetry techniques, we analyze key flow features, including displacement regimes, interfacial instabilities, interfacial front velocities, and velocity and concentration fields. We find that immiscible displacement flows are distinguished by the emergence of one or two heavy fluid fronts, particularly depending on the rotation speed. Furthermore, our dimensional analysis reveals that the displacement flow is governed by four dimensionless parameters, including the Reynolds, densimetric Froude (or Archimedes), and Rossby numbers, as well as the pipe inclination angle. Using these dimensionless groups, we succeed in categorizing the main flow regimes as efficient and inefficient displacements. Moreover, we classify the interfacial regimes as stable, intermittently unstable, kinks, and separating interfacial patterns. Our analysis shows that the interfacial instabilities observed are indeed characterized by the Kelvin–Helmholtz instability. Our analysis of the velocity fields suggests remarkable differences between displacements in stationary and rotating pipes, especially in terms of the absence and presence of a countercurrent flow, respectively. Finally, our assessment of concentration fields using a Fourier transform approach provides a preliminary fundamental understanding of the characteristics of concentration waves and their corresponding amplitudes.

Data-Driven Identification and Analysis of the Glass Transition in Polymer Melts.

Understanding the nature of glass transition, as well as the precise estimation of the glass transition temperature for polymeric materials, remains open questions in both experimental and theoretical polymer sciences. We propose a data-driven approach, which utilizes the high-resolution details accessible through the molecular dynamics simulation and considers the structural information on individual chains. It clearly identifies the glass transition temperature of polymer melts of weakly semiflexible chains. By combining principal component analysis and clustering, we identify the glass transition temperature in the asymptotic limit even from relatively short time trajectories, which just reach into the Rouse-like monomer displacement regime. We demonstrate that fluctuations captured by the principal component analysis reflect the change in a chain's behavior: from conformational rearrangement above to small fluctuations below the glass transition temperature. Our approach is straightforward to apply and should be applicable to other polymeric glass-forming liquids.

Impact of wettability on immiscible displacement in water saturated thin porous media

The characterization of immiscible displacement processes at the pore scale is crucial in order to understand macroscopic behaviors of fluids for efficient use of multiphase transport in various applications. In this study, the impact of porous material wetting properties on gas invasion behavior at various gas injection rates was investigated for thin hydrophilic porous media. An experimentally validated two-phase computational fluid dynamics model was employed to simulate the dynamic fluid–fluid displacement process of oxygen gas injection into liquid water saturated thin porous media. A phase diagram was developed through a parametric characterization of the thin porous media in terms of the material hydrophobicity and gas flow rates. In addition to calculating the saturation of the invading gas, gas pressure variations were calculated and used to identify the locations of phase diagram boundaries. Non-wetting phase streamlines resolved at the microscale were visualized and presented as a novel indicator for identifying displacement regimes and phase diagram boundaries. It was observed that the crossover from the capillary fingering regime to the stable displacement regime occurred between contact angles of 60° and 80°. By increasing the gas injection rate, due to viscous instabilities, flow patterns transitioned from the capillary fingering and stable displacement regimes to viscous fingering regime.

Dynamics of Compression-Driven Gas-Liquid Displacement in a Capillary Tube.

We study two-phase displacement via the steady compression of an air reservoir connected to an oil-filled capillary tube. Our experiments and modeling reveal complex displacement dynamics depending on compression rate and reservoir volume that, for large reservoirs, depend on a single dimensionless compressibility number. We identify two distinct displacement regimes, separated by a critical value of the compressibility number. While the subcritical regime exhibits quasisteady displacement after an initial transient, the supercritical regime exhibits burstlike expulsion.

Influence of initial water saturation on three-phase displacement efficiency and residual distribution during NAPL invasion into unsaturated porous media based on low-field NMR

Three-phase displacement events often occur in unsaturated porous media, especially when immiscible contaminants (e.g., non-aqueous phase liquid, NAPL) inadvertently enter the subsurface. In this study, the influence of initial water saturation on the three-phase displacement efficiency and residual distribution during NAPL invasion into unsaturated porous media was experimentally investigated. The low-field nuclear magnetic resonance (LF-NMR) technique was used to dynamically monitor the spatial distribution of water in unsaturated porous media during the invasion of NAPL. The residual distributions (e.g., volume fraction) of NAPL/water/gas were quantitatively analyzed. The results showed that both the initial water saturation and the NAPL injection rate had a significant influence on the three-phase displacement. We found that the displacement efficiency of water/gas exhibited a non-monotonic relationship with the initial water saturation in the unsaturated porous media at certain NAPL invasion rates. A method was proposed to characterize the three-phase displacement regime in terms of the classical two-phase Lenormand’s diagram. A significant increase in the volume fraction of residual NAPL after NAPL invasion was observed during the transition from the strong drainage region to the transitional displacement region. However, the initial water saturation was insensitive to the volume fraction of residual NAPL, once the characterized three-phase displacement regime transitioned to the stable displacement region. This study not only highlighted the influence mechanism of initial water saturation and NAPL injection rate on the three-phase displacement efficiency, but also endowed the classical two-phase Lenormand’s diagram with the three-phase displacement regime.

Effects of injection directions and boundary exchange times on adaptive pumping in heterogeneous porous media: Pore-scale simulation

Adaptive pumping, changing pumping rates or exchanging injection and extraction wells, is an enhancement of traditional Pump-and-Treat (P&T) technology. Since most previous studies on adaptive pumping are conducted through field-scale simulations, the mechanism behind it is not fully understood. An in-depth investigation of the pore-scale remediation mechanism of adaptive pumping is undoubtedly helpful in combining it with other decontamination methods to further enhance the remediation efficiency. In this study, coupling the Cahn–Hilliard phase field method and the Navier-Stokes equations, the dynamic displacement process in a heterogeneous porous medium is obtained. The effects of initial injection direction, boundary exchange times, and displacement regimes on the interface evolution and the remediation efficiency are systematically investigated. The results present that a significant increase in phase interface area is the most critical remediation mechanism for adaptive pumping. The effects of injection directions and boundary exchange times on remediation performance are mainly determined by the differences in pore connectivity and flow parameters. Higher pore connectivity under high and low viscosity ratios inhibits and promotes remediation performance, respectively. At high viscosity ratios, the residual oil morphology in the matrix after adaptive pumping is similar to that obtained by positive pumping with the opposite initial injection direction. The improvement in remediation performance of adaptive pumping is more significant under low viscosity ratio conditions. These results provide new pore-scale insights into the remediation mechanism of adaptive pumping, which contribute to the design and application of innovative remediation methods.

Dynamic Criteria for Physical Modeling of Oil Displacement by Gas Injection

In this work, slim tube displacement tests for minimum miscibility pressure MMP were carried out. Based on the displacement data, the MMP was calculated by statistical regression using linear and quadratic extrapolation with threshold values of 90% and 95% oil recovery as well as the intersection of trend lines for immiscible and miscible displacement regimes. The obtained data show a significant variation in the range of MMP values depending on the calculation method. To clarify the MMP value, an analysis of displacement dynamics was carried out. The ratio of the volume flow rate of reservoir oil to the volume flow rate of the injected gas—flow rates ratio (FFR)—was used as a new parameter. The MMP value calculated from the FRR value extrapolation was determined as 37.09 MPa. According to the results obtained, the proposed methodology based on the displacement dynamics can be useful as a criterion for clarifying the MMP value in slim tube displacement experiments.

Autotopographies of Forced Displacement: City Walking Tours as a Path for Political Visibility

Abstract Though forced displacement is prominent within academic research, as well as within public, political, and media debates, all too often the image of forcibly displaced persons is that of voiceless victims and the structural causes behind their trauma are overlooked. The article works to disrupt this problematic visualization through an original study of walking tours offered by refugees and internally displaced persons in Berlin and Jaffa. It utilizes walking as the method and theme of research, mapping the potential of walking as a collaborative pedagogy and a subaltern design tactic to claim political participation and belonging in the city. Through this, the article offers a new analytical perspective concerning the agency of discalced persons to navigate the politics of their (im)mobility and (in)visibility. The main argument is that these guided tours or ‘autotopographies’ of forced displacement hold the political capacity to alter the public visibility of displaced people, but also to illuminate aspects that are overlooked or erased within the city’s official display of memory. The article therefore advances debates about the politics of urban space and heritage sites and contributes to research which seeks to theorize the multiple geo-temporal colonial entanglement of forced displacement regimes.

Influence of pre-dewatering on the success of cake washing

ABSTRACT Cake washing is one key challenge after filtration. It is used to improve the product quality of filter cakes. Many studies deal with washing of saturated filter cakes and are used as the basis for cake washing models. However, to avoid mixing of supernatants (e.g. suspension liquid and wash liquid) on the cake surface during production processes, the cake is pre-dewatered and thus the pores are undersaturated. This paper demonstrates the influence of different start saturations (different pre-dewatering times) on the displacement regime of a washing curve compared to washing saturated filter cakes. An increase in saturation (filling) also takes place at the beginning of the washing of undersaturated filter cakes. A new filling regime located at the beginning of the washing process is clearly defined before the known displacement regime. The extent of the filling regime depends mainly on the initial saturation before washing process.

IDENTIFICATION OF WAVE DEFORMATION PROCESSES OF LANDSLIDES IN THE NORTHWESTERN BLACK SEA USING THE INSTRUMENTAL OBSERVATION DATA

Problem Statement and Purpose. At present, considering the conditions of slopes equilibrium, only the stresses caused by gravity, hydrodynamic and seismic effects are most often taken into account. As for tectonic stresses, their effect on landslide slopes has hardly been studied. At the same time, landslides and deformations ofslopes in a wide spatio-temporal range (with the frequency from several months to several dozens of years and the levels of massifs tectonic discreteness from first tensof meters to first kilometres) is also recorded in fact. Empirical data indicate that wave mechanism caused by rotational regime of the Earth can be one of the possible mechanisms explaining the high-frequency quasi-cyclic spatio-temporal variability of the rock mass stress-strain state. Purpose of the work has been to identify wave deformation processes in the Earth’s upper crust according to the data of instrumentalobservation of landslide slopes and relatively long line facilities deformation regime. In this work, we also intend to substantiate the thesis that wave exotectogenesis isone of the factors reducing the overall stability of landslide slopes. Data&amp;Methods. The data of instrumental observations of structural components deformation in the underground drainage facilities of the landslide prevention works on Odesa coast that have accumulated during 50 years of operation, as well as the results of geodetic monitoring of landslide slope and the crest of plateau on the right bank of the Malyi Adzhalyk Liman within the territory of the Port Plant (ammonium plant) in 2000–2019 have been used to study the dynamics of deformation wave processes in the Earth’s upper crust. Statistical and cartographic analyses of the data sets mentioned above were carried out according to traditional methods using the Statistica, Matlab and Surfer software packages. Results. It has been found that modern dynamics of landslide slopes is significantly influenced by the periodic change of the stress-strainstate of rocks in space and time. The authors interpret the empirically revealed alternating in space zones of compression and extension, which cause the dynamics of vertical and horizontal reference benchmarks displacements in the inter-annual regime of marks displacement on the right bank of the Malyi Adzhalyk Liman and in the tunnels of Odesa coast as thereflection of wave geodynamics with periodic change of the stress-strainstate of rocks in space and time. Hierarchical layering of the tectonosphere in depth (the presence of layers with different elastic properties), tectonic discreteness and blockiness of rock massifs determine the spatial framework of the dynamically complex structure of the deformation field. Multiple cycles of compression-extensionof rocks lead to decrease in the rocks strength, accumulation of plastic deformations and activation of landslide displacements even on the coastal areas where anti-landslide measures have been implemented. To prepare design models correctly, it is important to take into account both the landslide formation mechanism and the factors that reduce the overall stability of the slope. The latter include the quasiperiodic variability of the rock mass stress-strain state controlled by rotational dynamics via wave mechanism.

Pore-scale characterization of CO2 front progress through a porous medium using a free energy model based on Phase-Field Lattice Boltzmann Method

Pore-scale simulation of CO2 front progression through a porous medium has been investigated by a free energy model based on phase-field lattice Boltzmann method. Visualization of the fluids distribution in the breakthrough time reveals a strong dependence of front pattern on viscous and capillary forces interaction. Therefore, the dominance of each force imposes a different front pattern on the system. According to the percolation theory, increasing the capillary number reduces the invading fluid saturation and, consequently, the sweep efficiency, because the viscous fingering regime will intensify. However, a uniform pattern is observed when the mobility ratio is high, whereas the front evolution is facilitated in the opposite case. Impressive results have also been obtained regarding the wetting conditions. Since an upward trend in the displacement efficiency from strong drainage to strong imbibition processes is expected, this trend has changed due to the capillary suction effects in the strong imbibition process. According to experimental studies, the viscous fingering phenomenon will be proportional to the capillary suction. Furthermore, new areas have also been introduced to predict the displacement regimes.