Capillary Fingering Research Articles

Stair climbing interventions reduce postprandial hyperglycemia but not cognitive functions: findings of a randomized cross-over trial

Prolonged sitting can negatively impact postprandial glucose levels and cognitive functions. Stair climbing interventions have potential to mitigate these risks however remains unexplored. The present study aimed to explore the effects of stair climbing bouts on postprandial glucose and cognitive functions during prolonged sitting. Twenty-eight sedentary young adults (aged 20 – 30 years) underwent two intervention visits after standardized lunch for two hours: (1) STAIR: the participants climbed two flight of stairs for two minutes every 30 minutes; (2) SIT: the participants continued to sit. Blood glucose was measured using capillary finger prick method while attention function was measured using computer-based cognitive tests at baseline, end of 1st hour and 2nd hour. Significant interaction (F2, 54 = 15.96, p <0.001) was observed for conditions and time. During STAIR visit, significant changes in postprandial glucose at 1st hour (β = - 2.6 mmol/dl, p <0.001) and 2nd hour (β = 3.0 mmol/dl, p <0.001). No significant difference in the attention functions with time and conditions was observed. Stair climbing interruptions may be a promising solution to prevent high glycemic excursion occurring during prolonged sitting following postprandial sessions. However, the clinical benefits of stair climbing on attention functions remain unconvinced.

Study of the effect of pore properties of microporous layer on water transport process in proton exchange membrane fuel cell

Aiming at the “water flooding” phenomenon inside the Gas Diffusion Layer (GDL) of the Proton Exchange Membrane Fuel Cell (PEMFC), this paper visualizes the effects of the pore properties and gradient structure of the microporous layer (MPL) on water transport. Specifically, we visualize the impact of pore properties and gradient structure on water transport. For this purpose, a liquid water capillary finger advancement visualization test platform is constructed to analyze the evolution of liquid water in the porous medium and reveal the effects of single porosity, single pore diameter, gradient porosity, and gradient pore diameter of the MPL on the liquid water transport. Moreover, the time of the non-wetting liquid touching the top, the maximum spreading length, and the residual volume in the MPL are analyzed to evaluate the drainage capacity. The results highlight that the microporous layer's smaller porosity and pore size could limit the interface's extended width between the microporous and gas diffusion layers. Additionally, the residual volume of non-wetting liquid is 21.6 % less in the case of φ = 0.3 than for φ = 0.45, and the residual volume of non-wetting liquid is 11.8 % less in the case of d = 0.82 mm compared to d = 2.45 mm. Furthermore, the residual volume of the microporous layer in the Catalyst layer (CL) side of the microporous layer is 11.8 % less than that in the case of d = 2.45 mm. Finally, we conclude that when the pore gradient law is opposite, it is unfavorable for liquid water discharge.

7484 Pseudohypoglycemia In A Patient With Raynaud’s Phenomenon

Abstract Disclosure: J. Fedorko: None. P. Subarajan: None. A.P. Amblee: None. C.A. Poku: None. Background: The term ‘pseudohypoglycemia’ is used to describe the disparity between actual and measured capillary glucose and clinical presentation. It has been used to describe situations when a patient has the characteristic symptoms of low blood glucose (BG) Whipple’s triad), but the patient’s BG levels are within normal limits. Alternatively, this term can also be used to describe falsely low BG levels on finger-stick (capillary) readings in a patient with normal serum glucose levels and without the characteristic Whipple’s triad. Case: A 55-year-old female with Raynaud’s phenomenon was seen in Endocrine clinic with persistent hypoglycemia noted on finger-stick glucose readings. Her finger-stick glucose reading was 43, and was subsequently given 24 grams of glucose gel. Ten minutes later, a repeat finger stick BG was 44. She had no weakness, tremors, shakiness, vision changes, confusion, seizures, lightheadedness, dizziness, tachycardia, palpitations, nervousness, hunger, paresthesias irritability, confusion, seizures, loss of consciousness, or any other symptoms or signs of hypoglycemia. She had no such previous episodes and her fasting BG ranged from mid-70s to 80, with post-meal BG ranging from 100 to mid-100’s. Her most recent hemoglobin A1c was 5.5. She regularly experiences cyanosis of fingers consistent with Raynaud’s phenomenon, triggered by cold air in winter and air conditioners in summer. She does not take any medications for these episodes. Given the absence of classic Whipple triad and normal BG from peripheral blood draw, the patient’s low finger stick BG readings were attributable to Raynaud’s phenomenon. It is postulated to be secondary to decreased perfusion in the digital microcirculation and increased blood transit time in the fingers, resulting in a local increase in glucose consumption and thus low capillary finger stick BG levels. Simultaneously done serum glucose levels are usually normal. Conclusion: Pseudohypoglycemia can occur in patients with impaired peripheral circulation such as Raynaud’s phenomenon, acrocyanosis, peripheral vascular disease, shock, or with increased glycolysis by blood cells like in leukemia, polycythemia and rare infections like African trypanosomiasis, hyperviscosity syndromes like Waldenstrom’s and monoclonal gammopathy of undetermined significance. In patients with low finger-stick (capillary) glucose levels who do not display Whipple’s triad, and have comorbid conditions that might interfere with the BG reading, it is important for clinicians to recognize the difference between true and pseudohypoglycemia. This can be confirmed with a simultaneously done normal serum glucose level and will prevent unnecessary investigations or excessive treatment. Presentation: 6/3/2024

Fluorescence visualization dynamics of carbonated water injection processes in homogeneous glass micromodels

Understanding the flow behavior of oil–water phases in porous media is crucial for revealing the kinetic mechanisms underlying oil–water movement. In this study, we designed and constructed a fluorescence visualization experimental platform for carbonated water injection (CWI). We evaluated the effects of nine distinct injection rates on oil production and CO2 sequestration capabilities using three types of homogeneous porous structure micromodels. The microscale oil–water seepage behavior at the pore scale was also explored. The experimental results indicate that optimally increasing the injection rate can improve displacement efficiency, whereas excessively high rates may lead to viscous and capillary fingering. The geometry of the micromodels, particularly the hexagonal matrix, demonstrates potential advantages in enhancing oil displacement due to its uniform flow paths. The capillary number (Ca) significantly influences oil droplet capture behavior within micromodels. For instance, micromodel A captures the largest ganglion area at low Ca values, with a noticeable reduction in average ganglion area as Ca increases. Conversely, micromodels B and C exhibit similar trends in ganglion size variation at high Ca values, suggesting a more uniform impact of pore structure on oil droplet capture behavior. At elevated Ca values, capillary forces exert a more uniform and controlled effect on oil droplet capture and release, minimizing size variability. Additionally, the injection rate plays a critical role in CO2 sequestration, with higher rates promoting convective mixing between CO2 and reservoir fluids, thereby enhancing dissolution and storage efficiency. The complexity of the pore structure, characterized by the presence of micropores and macropores, affects the dissolution kinetics and mobility of CO2, influencing sequestration efficiency. These experimental findings provide valuable insights into the dynamics of oil–water motion and the potential for enhanced oil recovery (EOR) and CO2 storage, offering essential guidance for optimizing CWI strategies in the petroleum industry.

Aperture Field Anisotropy Control on Immiscible Displacement Patterns in Rough Fractures

AbstractTwo‐phase flow displacement in rock fractures is crucial for various subsurface mass transfer processes and engineering applications. In fractures, the displacement of a less viscous fluid by a more viscous one (i.e., viscosity ratio M &gt; 1) involves viscous forces help stabilizing the displacement front in presence of capillary pressure fluctuations. Although previous studies have reported displacement patterns in isotropic fractures, the impact of anisotropic fractures on displacement patterns has not been systematically examined. In this study, we conducted flow‐rate‐controlled drainage experiments to examine how anisotropic aperture fields affect displacement patterns. We observed the transition of displacement patterns from capillary fingering (CF) to crossover zone (CZ) to compact displacement pattern (CD) based on variations in transverse pore‐filling event (TPFE) frequency, which characterizes the competition between capillary and viscous forces. Increasing aperture correlation length in the transverse direction leads to increased TPFE frequency at a low flow rate, destabilizing displacement front. While the increasing aperture correlation length in longitudinal direction suppressed TPFE frequency, stabilizing displacement front. Therefore, the critical capillary number (CaCF‐CZ), which indicates the onset of the CF‐CZ transition, decreases as the aperture field varies from transversely to longitudinally correlated. At high flow rates, TPFEs almost disappeared, indicating that anisotropy did not affect CZ‐CD transition (CaCZ‐CD). Furthermore, we modified theoretical models of CaCF‐CZ and CaCZ‐CD by incorporating the aperture anisotropy factor, achieving a good fit with the experimental data. This study demonstrates the critical role of aperture field anisotropy in controlling two‐phase displacement patterns and provides a theoretical framework for predicting multiphase flow behavior in natural fractures.

Experimental Study on Oil-Gas Interface Stability Mechanism and Control Method of Gas-Assisted Gravity Drainage

Abstract The stability of oil-gas interface is an important factor affecting the recovery of the gas-assisted gravity drainage (GAGD). In this paper, the interface morphology characteristics of GAGD in porous media under 8 flow rates and 3 displacement dip angles were studied by using a visual physical model. The non-dimensional parameters such as capillary number and bond number were introduced to qualitatively characterize the oil gas interface morphology, and the process of gas invading the pore throat of porous media under different interface morphologies was revealed. The fractal dimension is employed for quantitative characterization of the morphology of the oil gas interface during the GAGD process, and the boundary of stable interface and unstable interface was divided. The study showed that the balance effect of gravity on the competition between capillary force and viscous force was the main reason for the stability of GAGD flooding leading edge. The stability of the oil-gas interface can be ensured by controlling the bond number to be greater than 2.75×10−4 and the capillary number to be less than 2.48×10−3. With a constant bond number, an increase in the capillary number leads to a gradual transition of the oil-gas interface from stable to unstable. Similarly, with a constant capillary number, an increase in the bond number causes the oil-gas interface to shift from stable to unstable. The fractal dimension divides the boundary between stable and non-stable displacement. When Df is greater than 1.87, the oil interface is stable, when Df is less than 1.75, the oil interface is viscous fingering, and when Df is between 1.75 and 1.87, the oil interface is mainly capillary fingering.

Pore-scale numerical investigation on spontaneous imbibition in natural fracture with heterogeneous wettability using the volume of fluid method

Understanding the spontaneous imbibition in the natural fracture with heterogeneous wettability is crucial for predicting and mitigating the impacts of unstable displacement on unconventional recovery. In this paper, the fracture structured mesh model is reconstructed based on the micro-computed tomography (micro-CT) image of naturally fractured tight sandstone. The mineralogy map-based modeling method for heterogeneous-wetting fracture is developed by combining the thin section images, X-ray diffraction (XRD) analysis, and multiple point statistics method. The simulation of the single-phase flow is performed to test the mesh independence. The effects of gravity and wettability on spontaneous imbibition in natural fracture and corresponding imbibition front dynamics are analyzed and discussed using the volume of fluid (VOF) method. The results show that (1) The structured mesh reconstruction method proposed in this paper can more effectively preserve the fracture structure compared to the unstructured mesh reconstruction method. (2) Gravity has a negligible impact on the pore-scale spontaneous imbibition in natural fracture. Under homogeneous-wetting conditions, spontaneous imbibition in natural fracture consistently exhibits stable displacement without significant residual gas formation. However, under the heterogeneous-wetting condition, the spontaneous imbibition displays typical capillary fingering, resulting in approximately 24.04% of the gas being trapped after spontaneous imbibition. The residual gas trapping mechanisms mainly include adhered, isolated, and connected gas. (3) Under both homogeneous- and heterogeneous-wetting conditions, the imbibing water saturation and the length of the imbibition front are proportional to the power of imbibition time during spontaneous imbibition in the natural fracture.

Home self-testing of complete blood counts in patients with breast cancer during chemotherapy: A proof-of-concept cohort study in e-oncology.

Before administration of myelosuppressive chemotherapy, complete blood counts (CBC) collected at the hospital/nursing stations are evaluated to avoid severe bone marrow suppression. This maintains disease fixation which often reduces their quality of life. This mixed-method study examined at home self-testing of CBC, the test quality, and the effects on patients' mental well-being. Patients with breast cancer receiving chemotherapy were recruited and trained to perform capillary finger prick CBC testing at home using the HemoScreen Point-of-Care instrument and to upload the test results to the hospital's IT system subsequently. A venous reference CBC sample was taken and tested at the hospital on the day of self-testing. Semi-structured interviews with open-ended components were performed to investigate the user experience and the impact of self-testing on the patients' everyday lives. Thirty-nine patients completed the self-testing education using the HemoScreen instrument. Eight patients withdrew, while the remaining 31 patients performed 161 home tests (2-11 tests per patient) over a 4-month period. The test results compared well with the venous reference CBCs except for platelet counts (correlation coefficient 0.26). Qualitative interviews with nine of the 31 patients emphasized that the patients were comfortable using the self-testing instrument and becoming an active partner in their own treatment. CBC self-testing at home produced clinically valid hemoglobin and white blood cell counts with the added benefit that the patients became active partners in their own treatment course, which was of great importance for the patients and increased their wellbeing.

Numerical Study of Liquid Water Formation and Transport in Porous Media

Fundamental understanding of liquid water formation and transport in fuel cells is of great importance for achieving high durability, reliability, and maximizing cell performance. For low temperature fuel cells, water may exist as vapor or liquid phase and is involved in various electrochemical reactions and transport mechanisms. The condensation process occurs when local water vapor pressure exceeds the saturation pressure. In this work, we first investigate the permeation of liquid water in the gas diffusion layer (GDL). To this aim, a two-dimensional isothermal model considering reconstructed GDL microstructure in conjunction with VOF model is implemented. The effects of mixed wettability of materials, operating temperature, and Polytetrafluoroethylene (PTFE) loadings on liquid water transport in the porous media are investigated numerically. The liquid water breakthrough and the capillary fingering regime are captured and compared. The results show that liquid water saturation in the GDL increases with decreasing PTFE loadings. Moreover, the results demonstrated that the local microstructure in the GDL has a strong effect and can dominate the overall water distribution. To further study water condensation, the isothermal model is expanded to non-isothermal for including physics of phase change heat transfer and species transport. In addition, anisotropic thermal conductivity is incorporated to study its effect on temperature distribution and liquid water distribution. The results show that initially the liquid water is formed as micro droplets and then these micro droplets are combined to form large droplets. Moreover, the impacts of water generation rate, temperature gradient, operating pressure, and contact angle on condensation have been investigated. The findings of this work are expected to provide insights into designing more reliable GDL in fuel cells. Figure 1

Influence of Local Aperture Heterogeneity on Invading Fluid Connectivity During Rough Fracture Drainage

Determining the (in)efficiency of wetting phase displacement by an invading non-wetting phase (drainage) in a single fracture is key to modelling upscaled properties such as relative permeability and capillary pressure. These constitutive relationships are fundamental to quantifying the contribution, or lack thereof, of conductive fracture systems to long-term leakage rates. Single-fracture-scale modelling and experimental studies have investigated this process, however, a lack of visualization of drainage in a truly representative sample at sufficient spatial and temporal resolution limits their predictive insights. Here, we used fast synchrotron X-ray tomography to image drainage in a natural geological fracture by capturing consecutive 2.75 μm voxel images with a 1 s scan time. Drainage was conducted under capillary-dominated conditions, where percolation-type patterns are expected. We observe this continuously connected invasion (capillary fingering) only to be valid in local regions with relative roughness, λb ≤ 0.56. Fractal dimension analysis of these invasion patterns strongly aligns with capillary fingering patterns previously reported in low λb fractures and porous media. Connected invasion is prevented from being the dominant invasion mechanism globally due to high aperture heterogeneity, where we observe disconnected invasion (snap-off, fragmented clusters) to be pervasive in local regions where λb ≥ 0.67. Our results indicate that relative roughness has significant control on flow as it influences fluid conductivity and thus provides an important metric to predict invasion dynamics during slow drainage.

Influence of cationic surfactants on two-phase air–liquid displacement in porous media

The displacement efficiency of leaching agent solution in orebody pores is the key factor affecting the leaching rate of rare earth ions. To improve the displacement efficiency, cationic surfactants were added to the solution as the invading phase fluid, and microfluidic visualization experiments were carried out. Based on the experimental results, the effects of cationic surfactants on air-liquid two-phase displacement and its mechanism were analyzed. The results show that cationic surfactants can change the capillary fingering to stable displacement mode. Moreover, the closed air clusters are significantly reduced, and the displacement efficiency is greatly improved, up to 96.75 %. In addition, displacement efficiency is negatively correlated with the porosity of the porous media. Cationic surfactants primarily affect the displacement by changing the interfacial properties of the solution. The research results provide theoretical guidance for the efficient mining of ionic rare earths.

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.

Dynamic simulation of immiscible displacement in fractured porous media

Investigating immiscible displacement in fractured porous media is essential for understanding the two-phase flow behavior within pores and fractures. In this work, a three-dimensional pore-fracture network model was developed to address the influence of fracture on flow patterns and to characterize fracture-matrix crossflow under different flow conditions. Sensitivity studies at a wide range of viscosity ratios and capillary numbers underscored that fracture significantly influenced flow patterns in the capillary fingering zone. Fracture with an advantageous path effect in the displacement direction caused a shift in the boundary of capillary fingering zone toward an increase in capillary numbers. As fracture aperture decreased and aspect ratio increased, there was a discernible decline in the crossflow rate. When fracture aperture equaled average matrix throat diameter, fracture lose advantageous path effect in compact displacement zone but retained it in viscous fingering and capillary fingering zones. Distinct matrix-fracture crossflow development processes were observed in different zones: in cross zone, following displacement breakthrough, the crossflow underwent a “long-term” process to attain stability. Viscous fingering zone promptly achieved stability post-breakthrough, whereas both capillary fingering and compact displacement zones had already reached a stable state before breakthrough. Nonlinear variations in breakthrough saturation were observed in the cross zone between compact displacement and capillary fingering zones. The control process of immiscible displacement exhibited variability under different flow conditions: compact displacement zone was characterized by matrix dominance, viscous fingering zone was jointly controlled by matrix displacement and fracture-matrix crossflow, and capillary fingering zone was primarily governed by fracture-matrix crossflow. These findings enhance scholarly comprehension of immiscible displacement behavior in fractured porous media.

Numerical simulation of fingering in the underground hydrogen storage

Underground hydrogen storage has garnered interest in recent years owing to the considerable demand for clean energy. Hydrogen is more diffusive than air and has relatively low density and viscosity. These unique properties induce distinct hydrodynamic phenomena during hydrogen storage. Cushion gas has been proven to be a potential remedy for attenuating the adverse impacts of underground hydrogen storage. To investigate the influence of the cushion gas, a microscopic numerical simulation was performed with Fluent software using the Eulerian multi-fluid model. Carbon dioxide, nitrogen, and methane are usually used as the preferred candidates for cushion gases in underground hydrogen storage systems. In this study, nitrogen was used as the cushion gas and was injected along with hydrogen into heterogeneous porous media with volume fractions ranging from 0% to 70%. A parameterization study was then performed to elucidate the influences of the injection rate and viscosity of the fluid on the fingering pattern. Two representative types of fingering, viscous fingering and capillary fingering, were observed under different gas mixtures and boundary conditions. After the simulation, an image analysis was performed to capture the evolution of the fingering pattern. The specific fingering area, number of branches, and fractal dimensions are proposed as geometric indices to describe the shape of the fingering pattern. The results showed that there was a remarkable enhancement in saturation due to the injection of the cushion gas, depending on the concentration of the gas mixture. This study offers insight on the design of gas mixture injection in underground hydrogen storage and can be further extended to the hydrochemo–mechanical coupled numerical simulation of multiphase gas injection in porous media.

Insight into evolution of invasive patterns on fingering phenomenon during immiscible two-phase flow through pore structure

Understanding fingering, as a challenge to stable displacement during the immiscible flow, has become a crucial phenomenon for geological carbon sequestration, enhanced oil recovery, and groundwater protection. Typically governed by gravity, viscous and capillary forces, these factors lead invasive fluids to occupy pore space irregularly and incompletely. Previous studies have demonstrated capillary numbers, describing the viscous and capillary forces, to quantificationally induce evolution of invasion patterns. While the evolution mechanisms of invasive patterns have not been deeply elucidated under the constant capillary number and three variable parameters including velocity, viscosity, and interfacial tension. Our research employs two horizontal visualization systems and a two-phase laminar flow simulation to investigate the tendency of invasive pattern transition by various parameters at the pore scale. We showed that increasing invasive viscosity or reducing interfacial tension in a homogeneous pore space significantly enhanced sweep efficiency, under constant capillary number. Additionally, in the fingering crossover pattern, the region near the inlet was prone to capillary fingering with multi-directional invasion, while the viscous fingering with unidirectional invasion was more susceptible occurred in the region near the outlet. Furthermore, increasing invasive viscosity or decreasing invasive velocity and interfacial tension promoted the extension of viscous fingering from the outlet to the inlet, presenting that the subsequent invasive fluid flows toward the outlet. In the case of invasive trunk along a unidirectional path, the invasive flow increased exponentially closer to the outlet, resulting in a significant decrease in the width of the invasive interface. Our work holds promising applications for optimizing invasive patterns in heterogeneous porous media.

Physicochemical Properties, Glycaemic Index and Glycaemic Load of Chocolate Energy Bars Prepared with High Polyphenols Cocoa Powder and Guar Gum

This study aimed to determine the physicochemical properties, Glycaemic Index (GI) and Glycaemic Load (GL) of chocolate energy bars prepared with different percentages of guar gum (0.5%, 1.0%, 1.5%) and high polyphenols cocoa powder. Proximate analysis was determined following the official methods Association of Official Analytical (AOAC). Ten eligible respondents who met the inclusion and exclusion criteria participated in the GI and GL determination. Test and reference food were given to the participants after overnight fasting. Blood capillary finger pricks were drawn for 7 interval time at 0 until 120 min. The blood glucose responses were calculated based on Incremental Area Under Curve (IAUC). The result revealed that the fat and calorie content were significantly lower in formulations with highest guar gum percentage (p˂0.05). On the other hands the moisture, ash, carbohydrate contents, crude fibre, energy value, hardness, fracturability, pH value, and colour were all comparable to the control sample. The control and chocolate energy bars with 0.5% guar gum were in the category of high GI and GL. Whereas, the chocolate energy bars with 1.0% and 1.5% guar gum were in the medium category for both GI and GL. This study demonstrated that incorporating different percentages of guar gum in the high polyphenols chocolate energy bar changed some of the proximate compositions but not the physical properties. Furthermore, addition of guar gum affected the GI and GL as the values were reduced with the increased amount of guar gum.

Impact of gas type on microfluidic drainage experiments and pore network modeling relevant for underground hydrogen storage

Underground hydrogen storage (UHS) in geological reservoirs is proposed as a technically feasible solution to balance mismatch between supply and demand in emerging markets. However, unique hydrogen properties and coupled flow mechanisms require new investigations to fully understand transport and storage of hydrogen in porous media across scales. Here we use microfluidics to investigate the effect of gas type and injection rate on flow patterns, saturation and connectivity of the gas phase. We visually observe that gas flow is characterized by capillary fingering, further confirmed by fractal dimension analysis. At lower injection rates, the gas saturation after drainage appears to increase with gas viscosity, with lower hydrogen saturation compared to methane and nitrogen. The maximum gas saturations (39–46 %) were achieved at higher injection rates, showing no clear correlation to gas type. However, the high-rate injections lead to undesired outcomes in terms of formation of disconnected gas ganglia, mostly pronounced for nitrogen. We identify an optimal injection rate to achieve maximum gas saturation with the least amount of disconnected gas. The experimental results are supported with pore network modeling to derive relative permeability and capillary pressure functions.

Probing multiphase reactive transport interactions in the polymer electrolyte fuel cell catalyst layer degradation

The multiphase, multicomponent reactive transport plays a critical role in the degradation of the cathode catalyst layer in Polymer Electrolyte Fuel Cells. This warrants a fundamental understanding of the pore-scale, mechanistic interactions in the catalyst layer. Herein, the interfacial and transport interactions due to the flooding dynamics in the presence of carbon support corrosion, which is a primary degradation mode in the cathode catalyst layer, are delineated based on a comprehensive mesoscale model. The mechanistic interrogation of the degradation-transport interactions reveals the spatio-temporal heterogeneity of the pristine and aged microstructures. An electrode-averaged saturation front of 80 % unveils a critical limit of percolation which results in an onset of limiting current density. Further, it is observed that the reactant severity is amplified at progressively higher stages of corrosion owing to the appearance of dead pores and a thicker ionomer film. We also shed light on the fluid displacement patterns which reveal the existence of a capillary fingering regime. The interplay of the operating current density and carbon corrosion in governing the substrate-ionomer interaction is described through an electrochemical Damköhler number.

Research on the Influence of Heterogeneity and Viscosity on the Fluid Intrusion Mechanism of the Water Flooding Process Based on the Microscopic Visualization Experiment.

The flow law of immiscible fluids in porous media plays an important role in the development of oil and gas fields. In the process of water flooding reservoir development, when the water phase displaces the oil phase, a fluid with higher viscosity, as a fluid with lower viscosity, the oil-water interface will always be unstable, resulting in different fingering effects. After water flooding, the distribution law of oil and water in the reservoir is mainly affected by the fluid intrusion mechanism. Due to the difference of capillary force, viscous force, and other microscopic forces, the fluid intrusion mechanism is mainly divided into two types: viscous fingering and capillary fingering. At the same time, due to the influence of reservoir heterogeneity, the fingering effect in the process of water displacement in porous media will be influenced to a certain extent. Based on the two-dimensional microscopic visualization experiment, this paper extracted the variance of the static parameter G in the capillary number calculation method of the two-dimensional microscopic model to represent the heterogeneity and conducted displacement experiments with different viscosities and flow rates to study the influence of the flow rate, viscosity, and heterogeneity on the results of water flooding. The experiments found that as for the influence of flow velocity, with the increase of flow velocity, that is, with the increase of capillary number, the recovery degree decreases first and then increases. As for the influence of viscosity, from a numerical point of view, the displacement efficiency and conformance coefficient of the low-viscosity group are higher than those of the high-viscosity group. From the trend, with the increase of the capillary number, the displacement efficiency of both the low-viscosity and high-viscosity groups increases, while the conformance coefficient decreases first and then increases, indicating that capillary fingering and viscous fingering can occur in different viscosity reservoirs. As for the influence of heterogeneity, the conformance coefficient of the water flooding decreases with the increase of heterogeneity, and the viscous pointing trend caused by heterogeneity is stronger, resulting in an uneven water injection sweep and higher oil displacement efficiency within the swept area. It can be seen from the fluid intrusion mechanism diagram that with the increase of heterogeneity, the viscous fingering trend becomes more obvious; with the increase of viscosity, the fluid intrusion mechanism boundary moves down and the viscous fingering trend becomes more obvious.

Effect of perforated cracks on liquid water in microporous layers by lattice Boltzmann method

Microporous layer (MPL), as a critical constituent of the proton exchange membrane fuel cell (PEMFC), plays a key role in mass, heat, electron, and species transport. The cracks formed during the deposition process on the surface of MPL change the overall transport capacity and effect the output performance of PEMFC. In this study, a 2D Lattice Boltzmann Method (LBM) pseudopotential multicomponent model is used to investigate the effects of perforated cracks in MPL on distribution, pressure drop and flow state of liquid water. The simulation results show that Capillary number (Ca) of liquid water in perforated cracks is around two orders of magnitude higher than Ca in twisty pores. Perforated cracks in MPL can not only reduce capillary resistance but also convert liquid water from capillary fingering to viscous fingering essentially, thus enhancing the permeability of liquid water in the through-plane direction while reducing the invasion in the in-plane direction. In consideration of gas-liquid transportation and other structural characteristics of GDL, the proper interval between perforated cracks with width of 10 μm is 3–6 crack diameters. This study provides reference for the design of functional pore structure MPL and conducts guidance for further research on PEMFC.