Search Results (293)

This study investigates the optimization of airflow distribution and pressure drops in H14 HEPA minipleat filters through the introduction of the hot-melt cell as the fundamental hydraulic unit governing local flow behavior. A coupled analytical framework integrating Falkner–Skan boundary-layer theory, Darcy–Weisbach channel friction, and Darcy porous-medium flow was developed and experimentally tested using velocity measurements obtained in a 600 m³/h test bench operating at a frontal velocity of 0.45 m/s under laminar-flow conditions. Ten primary geometric configurations and 21 hot-melt distribution scenarios (totaling 31 cases plus an optimized design case) were systematically evaluated by varying cell width (W), inlet height (H_i), and pleat length (L). Experimental and analytical results reveal significant velocity heterogeneity in the vicinity of the filter surface, which progressively decreases with distance from the filter, while localized velocity amplification is observed near the hot-melt separators. The analysis demonstrates that hydraulic diameter, pleat angle, and hot-melt spacing are the dominant parameters governing pressure drop generation and flow redistribution. Among the configurations investigated, a model-predicted optimized design (W = 46.25 mm, L = 55.00 mm, 230 pleats) yields a theoretical pressure drop reduction of up to 29.23% without significantly compromising the effective filtration area. These results provide an analytical framework for pre-prototyping optimization, although experimental verification of physical prototype validation for mechanical integrity and the preservation of initial efficiency, among other governing physical quantities, remains essential. The results demonstrate that the proposed hot-melt cell concept provides a practical engineering framework for the aerodynamic optimization of minipleat HEPA filters, enabling improved flow uniformity and reduced energy consumption in cleanroom applications. Full article

In this paper, we study the existence of positive solutions for a nonlinear fifth-order boundary value problem arising from fully developed couple-stress fluid flow through a porous channel. Under a natural restriction relating the couple-stress and permeability parameters, the associated linear operator factorizes into two positive second-order operators; we construct the corresponding Green function, show that it is strictly positive, and obtain it in an explicit closed form. By reformulating the problem as a completely continuous operator on a cone in $C[0,1]$ and applying Krasnosel’skiĭ’s fixed point theorem of cone compression–expansion type, sufficient conditions for the existence of positive solutions are established in terms of the load parameter. The positivity of the velocity further yields a strictly positive cumulative-flow solution on $(0,1]$. Several examples and a numerically calibrated application are given to illustrate the main results. Full article

In porous media grouting, highly viscous non-Newtonian fluids often trigger viscous fingering (Saffman–Taylor instability) due to adverse mobility ratios, creating fractal-like preferential channels that severely weaken the reinforcement volume. To overcome this, a novel swirl-driven grouting method is proposed. A 2.5D swirl seepage model is established to derive the analytical solution for tangential velocity spatial decay. Integrating the Capillary Bundle and Herschel–Bulkley models elucidates the nonlinear coupling mechanism of centrifugal force and shear-thinning. The swirl flow creates an in situ centrifugal pump, reshaping pressure gradients and triggering a sudden viscosity plunge via extremely high comprehensive shear rates. Furthermore, a modified Saffman–Taylor dispersion relation is constructed and validated via indoor sandbox experiments. Theoretical analysis yields a conditional critical Swirl Number threshold of approximately 0.6 under the tested parameters to suppress the fractal-like evolution of fingering. Experiments demonstrate that exceeding this threshold transitions the grout from preferential seepage to uniform isotropic diffusion. The measured isotropic index is closely enveloped within the 10% theoretical error band. Consequently, the effective projected area experiences a substantial leap of 83.3% due to synergistically enhanced driving forces and reduced medium resistance. This mechanism fundamentally overcomes viscous fingering and suppresses the fractal-like growth tendency of the displacement front, providing a solid theoretical basis for controlling grout diffusion morphology in underground engineering. Full article

Inadequate cleaning of flexible endoscope channels remains a major cause of healthcare-associated infections despite established reprocessing protocols. We developed biomimetic carbon balls inspired by mustard seed surface features as a brush-free adjunct for endoscope channel cleaning, combining mild mechanical action with adsorption-based removal of organic debris. Activated carbon (AC) balls and carbon fiber (CF) balls with diameters of 1.8–3.0 mm were fabricated to fit 2.5–3.5 mm working channels and characterized by TGA, BET, SEM, and EDS. Cleaning performance was evaluated using tomato powder residue and microbiological validation, and computational fluid dynamics was used to assess flow behavior in a 2.7 mm channel containing a 2.6 mm ball under suction. CF balls showed more uniform thermal degradation (8.9% residual mass at 1000 °C) and a ribbed fibrous morphology. In contrast, AC balls exhibited porous, irregular structures with strong adsorption capacity, characterized by high thermal stability (86.4–89.3% residual mass) and pore volumes of 0.087–0.108 cm³/g and BET surface areas of 63.00 m²/g and 21.65 m²/g. After residue exposure, AC surfaces retained more particulate matter, while CF surfaces remained cleaner and promoted more pronounced wall interaction. Microbiological testing showed effective decontamination, with bacterial counts reduced below the detection limit. CFD analysis demonstrated pressure-driven gap flow, elevated local velocity, and vortex-induced wall shear stress sufficient to enhance debris removal without apparent channel damage. These results suggest that mustard seed-inspired carbon balls provide a promising brush-free strategy for endoscope reprocessing by integrating adsorption, hydrodynamic agitation, and gentle scouring to improve cleaning safety and efficacy. Full article

The influence of pleat angle on the pressure drop of H14 HEPA filters was investigated through a mathematical model that represents the filter as a system of converging–diverging channels coupled with porous filtration media. The analysis was conducted for pleat angles ranging from 1° to 20° under a constant laminar airflow rate of 0.167 m³/s and 0.45 m/s velocity. The model combines Darcy–Forchheimer flow through the filtration media with laminar channel flow theory, enabling the total pressure drop to be expressed as a function of pleat geometry and subsequently optimised through analytical differentiation. The results show that the pressure drop contribution of the filtration media increases with the pleat angle, from 10.57 Pa at 1° to 213.49 Pa at 20°, whereas channel losses decrease sharply from 1121.71 Pa to 2.75 Pa over the same interval. The competing behaviour of these two mechanisms generates a minimum total pressure drop of 94.56 Pa at a pleat angle of approximately 6°, compared with 120 Pa for the current industrial configuration operating at 3.73°. This represents a pressure drop reduction of approximately 21.2%, implying a corresponding decrease in fan energy consumption without compromising filtration performance. The analysis further demonstrates that very small pleat angles (1–2°) are highly unfavourable, producing total pressure drops between 301 and 1132 Pa due to severe channel constriction, while for angles above 13–14°, the channel contribution becomes negligible, and the overall pressure drop is governed almost entirely by the filtration media. These findings provide quantitative design criteria for optimising HEPA, EPA, and ULPA filter geometries, highlighting pleat angle as a critical parameter for improving aerodynamic performance, flow uniformity, and energy efficiency in high-purity environments. The proposed model was further assessed using a commercially available H14 HEPA filter with 188 pleats, an effective filtration area of 10.618 m², and a nominal airflow rate of 600 m³/h, demonstrating its applicability to real industrial filter configurations. Full article

The demand for a versatile and portable point-of-use (POU) sensor platform has surged due to the pandemic, especially in countries with limited medical laboratory facilities. We recently unveiled a portable, non-planar, interdigitated, flow-through, porous electrode platform that automatically measures electrochemical impedance spectroscopy (EIS) signals from various biomarkers. However, the packed powder exhibited a loss of performance over time due to displacement, leaching, and poor stability. Herein, we modified the packing strategy by synthesizing the sensing material within the channel, thereby improving adhesion, structural integrity, and stability. Leveraging the exceptional thermal stability, mechanical strength, and chemical resistance of polyimide (PI), we developed a novel fabrication approach that combines liquid-phase inversion and breath-figure techniques to create a porous PI manifold with single-walled carbon nanotubes (SWCNTs) under varying humidity conditions. Scanning electron microscope (SEM) analysis revealed that lower relative humidity (RH) conditions yield larger but less uniformly distributed pores, leading to increased channel pressure. The manifold demonstrated exceptional stability under rigorous flow conditions, withstanding a high flow rate of 30 µL/min while maintaining consistent pressure-EIS responses. The device produced a measurable proof-of-concept impedance response following exposure to a femtomolar concentration of complementary target ssDNA in 1× PBS within 15 min. A formal limit of detection was not determined in the present study. We developed a mechanically stable sensor design with improved durability under repeated flow conditions by systematically optimizing synthesis conditions and manifold configuration. This innovative fabrication strategy demonstrates the importance of packing methodology in sensor design and paves the way for robust, scalable, and efficient diagnostic solutions in resource-limited settings. Full article

Aqueous humor (AH) is a watery fluid continuously circulating through the posterior and anterior chambers of the human eye and is essential to maintain a healthy intraocular pressure in the eyeball and keep the eye clean from waste products of metabolism and external agents. This paper presents a stationary compartment model of AH dynamics consisting of three integrated modules (M): M1 for AH production, M2 for AH passive flow and M3 for AH drainage. M1 is a zero-dimensional (0D) reduction of the velocity-extended Poisson-Nernst-Planck model and simulates solute transfer and fluid movement across the cellular structure of the ciliary epithelium (CE). M2 is the electric equivalent representation of Poiseuille flow across the series of two linear hydraulic resistors. M3 is a 0D reduction of the Darcy equations for a porous medium and simulates AH flow across the parallel between a nonlinear and a linear resistor. Compared to existing compartment approaches, the present model integrates at the macroscopic scale the multi-physical description of the human eye at the cellular scale. Numerical simulations suggest that (1) sodium channels in the CE are essential for maintaining proper AH dynamics; and (2) increased episcleral vein pressure reduces AH drainage, potentially explaining the development of secondary open-angle glaucoma. These insights advance the understanding of the mechanisms regulating AH dynamics and offer new perspectives for patient-specific therapies. Full article

This study numerically investigates how a finite, circular patch of emergent vegetation alters microplastic (MP) transport, concentration, and retention in open-channel flow. A validated numerical model was developed to represent the vegetation patch as a porous zone and simulate MP transport. The framework was validated against laboratory data for two configurations: a low-blockage case and a high-blockage case. After validation, 36 MP cases, comprising four polymer densities, three particle diameters ranging from 0.1 to 0.5 mm, and two categories of shape factors (elongated and spherical), were released upstream and tracked over 180–420 s. Results show that vegetation density, represented by the blockage parameter and solid volume fraction, primarily controls the interception of microplastics. Dense patches create persistent recirculation and low-velocity zones that increase residence time and trapping, whereas sparse patches induce only transient disturbances, allowing rapid downstream advection. Quantitatively, retention in the dense configuration was ≈62% for the smaller MP sizes (0.1–0.2 mm) versus ≈35% in the sparse configuration at 300 s. Polymer density, particle shape, and particle size had only secondary effects under the tested moderate flow conditions. Smaller microplastics and elongated particles showed slightly higher retention. The findings identify dense vegetation as a selective hydrodynamic filter, demonstrating that vegetation-induced flow restructuring is the dominant control on MP fate. These effects should be considered in river restoration and pollution mitigation strategies. Full article

Polymer flooding is an important enhanced oil recovery technology for high-water-cut heterogeneous reservoirs, where long-term waterflooding commonly leads to preferential flow channels and insufficient mobilization of remaining oil in less-swept intervals. In this study, a hydrophobically modified partially hydrolyzed polyacrylamide-type polymer containing hydrophobic associative groups was evaluated for mobility control and enhanced oil recovery in heterogeneous porous media with the assistance of well-log-interpreted reservoir parameters. Reservoir heterogeneity was first characterized using interpreted effective thickness, porosity, permeability, oil saturation, and water saturation, and the polymer performance was then examined through rheological measurements, core-flooding experiments, and field production response analysis. The results show that the representative reservoir layers exhibit a wide permeability range of 7.9–186.5 mD, with higher water saturation in high-permeability layers and higher oil saturation in medium- and low-permeability layers. The polymer solution shows concentration-dependent thickening, shear-thinning behavior, salinity tolerance, and thermal-aging stability, retaining a viscosity of 139.5 mPa·s at 180,000 mg/L salinity and 74.9% viscosity retention after aging for 504 h. Core-flooding results indicate that the medium-permeability core achieves the highest polymer incremental recovery of 14.5 ± 0.8%, reflecting a favorable balance between injectivity and residual flow resistance. Field production data further show that daily oil production increases from 11.6 to 20.4 t/d, water cut decreases from 93.1% to 81.6%, and cumulative oil increment reaches 2055 t after polymer injection. The proposed mechanism involves associative thickening, pore-throat-adaptive transport, residual flow resistance, flow-path redistribution, and remaining-oil mobilization. This study establishes a heterogeneity-constrained mobility-control framework linking well-log-interpreted reservoir parameters, permeability-dependent polymer transport, residual flow resistance, and field production response, showing that effective polymer flooding depends on balancing injectivity, flow resistance, and remaining-oil availability rather than maximizing bulk viscosity alone. Full article

This research analyzes the wavy, axisymmetric flow of a Ree–Eyring non-Newtonian nanofluid, infused with motile microorganisms, within a porous, tapered cylindrical channel under a transverse magnetic field. This investigation presents a theoretical framework that may inform the improvement of energy efficiency and thermal management in biomedical engineering applications, such as drug delivery systems and microfluidic biosensors. The work provides an extended insight by a contribution to the evaluation of entropy generation, explicitly considering the influence of motile microorganisms, thereby bridging a gap in the existing literature. The comprehensive physical model further incorporates the combined effects of Joule heating, viscous dissipation, nonlinear thermal radiation, and chemical reactions. Methodologically, the governing nonlinear equations of the system were rendered tractable under long-wavelength and low-Reynolds-number assumptions and subsequently solved using the numerical Runge–Kutta–Fehlberg technique. The key conclusion is that, based on the present numerical model, careful selection of magnetic field strength and microorganism motility parameters may reduce irreversible energy losses, potentially improving the net usable work in advanced nanofluid transport systems for biomedical applications, subject to experimental validation. The most significant finding reveals that the magnetic field serves as a dual-purpose control parameter: increasing its strength boosts total entropy generation by 20–30% while simultaneously raising the Bejan number, confirming heat transfer as the dominant irreversibility mechanism in the system. Additionally, nanoparticle concentration diminishes substantially with elevated chemical reaction rates and Schmidt numbers, while microorganism density is highly sensitive to the Péclet number, which causes flow disruptions. Full article

High-permeability reservoirs at the extra-high water-cut stage commonly exhibit preferential flow, limited sweep expansion, and complex remaining-oil occurrence. To clarify the pore-scale mechanisms controlling waterflood sweep and remaining-oil retention, this study integrates CT-assisted core flooding and microfluidic chip visualization using a high-permeability sandstone core from the Guantao Formation in the Bohai Bay Basin. The CT-assisted core flooding experiment was used to quantify the stage-wise evolution of pores swept by the water phase, while the microfluidic experiment was used to visualize displacement pathways, local bypassing, and remaining-oil morphology under controlled pore-network conditions. The results show that waterflood sweep exhibits clear stage-wise evolution. During the low water-cut stage, injected water preferentially advances through large pore channels, resulting in limited sweep efficiency. With increasing water cut, pores newly swept by the water phase gradually shift from large pores to medium and small pores, accompanied by increasing displacement pressure. Under the present experimental conditions, the lower radius limit of pores newly swept by the water phase is approximately 7.54 μm, corresponding to a capillary force of about 0.9 MPa. When the injected volume exceeds approximately 2.5 PV, the sweep efficiency approaches a plateau and increases only from 0.72 to 0.75 at 5.0 PV, indicating that approximately 25% of the pore space remains difficult to be effectively swept. Image-based classification indicates that remaining oil can be divided into six occurrence types: clustered, porous, columnar, dead-end, film-like, and granular. Clustered and porous are the dominant occurrence types, accounting for a combined 59.7% of the total remaining oil. Pore-structure heterogeneity controls the microscopic sweep boundary through the combined effects of intra-unit structural dispersion and cross-unit structural contrast, which together regulate capillary resistance, seepage resistance, preferential flow, local bypassing, and remaining-oil retention. Microfluidic observations further show that permeability contrast and displacement velocity affect pore-scale displacement pathways and remaining-oil morphology. These findings provide experimental evidence for understanding the lower sweep-radius limit and remaining-oil occurrence mechanisms in high-permeability heterogeneous reservoirs at the extra-high water-cut stage, while the chip-scale velocity effects should be interpreted as pore-scale mechanistic evidence and require further validation before field-scale application. Full article

To achieve efficient separation of Sr²⁺ under complex ionic-strength conditions, porous geopolymer particles (PGs) were used as a support to construct a K₂SbPO₆-loaded porous geopolymer composite, denoted as K₂SbPO₆@PGs, via in situ loading of one-dimensional K₂SbPO₆ by a high-temperature solid-state route. Its adsorption performance and mechanism were systematically compared with those of pristine PGs. Structural characterization (SEM/EDS, XRD, FTIR, XPS, and BET) confirmed that the K₂SbPO₆ crystalline phase was uniformly anchored onto the PGs framework while preserving interconnected mesoporous channels. K₂SbPO₆@PGs exhibited excellent Sr²⁺ removal over a wide pH range (3–12), with a removal efficiency of approximately 92% at pH 3, which was significantly higher than that of PGs (approximately 5%). The isotherm data were better fitted by the Sips model (R² = 0.982), and the maximum adsorption capacity reached 189.35 mg·g⁻¹ (theoretical qm = 201.14 mg·g⁻¹). Kinetic fitting showed that PGs followed the pseudo-first-order model, whereas K₂SbPO₆@PGs were better described by the pseudo-second-order model, indicating that chemical adsorption dominated the process through K⁺/Sr²⁺ exchange and surface complexation. Coexisting-ion experiments demonstrated strong resistance to monovalent ions, whereas Ca²⁺ and Mg²⁺ caused more pronounced competitive effects. The results indicate that PGs mainly provide interconnected mass-transfer pathways and granular structural support, whereas K₂SbPO₆ provides selective exchange sites with high affinity for Sr²⁺. The synergy between these two components endows the composite with good pH adaptability and enhanced adsorption performance and suggests its potential for subsequent continuous-flow separation studies. Full article

Flow over permeable beds is important in sediment transport and mixing processes, yet detailed velocity and stress measurements remain difficult to obtain, particularly close to the sediment–water interface (SWI). In this work, we use refractive-index-matched PIV to study turbulent open-channel flow over and within a permeable bed composed of monodisperse borosilicate glass beads. Measurements are reported for three low-$R{e}_K$ cases, $R{e}_K=0.224$, $R{e}_K=0.335$, and $R{e}_K=0.360$, to resolve the mean velocity structure and the associated viscous, turbulent, Reynolds, and dispersive stress distributions. The results show that both the mean velocity and the turbulence intensity decrease rapidly below the SWI, indicating strong damping within the porous bed. Above the bed, the flow retains a boundary-layer structure, and increasing $R{e}_K$ enhances the turbulence intensity without changing the overall regime. The results indicate a shift from turbulent transport above the bed to viscous control within the porous layer, while dispersive stresses peak near the interface. Overall, the SWI controls momentum exchange within a thin region and the porous bed suppresses turbulence penetration into the subsurface. Full article

Geothermal energy extraction, hydrocarbon recovery, and CO₂ geological sequestration are frequently hindered by interfacial barriers and slow mass transfer. While high-power ultrasound offers a sustainable, purely physical method for reservoir stimulation, its field effectiveness remains debated because traditional macroscopic experiments fail to isolate mechanisms like acoustic streaming and cavitation. This review systematically examines acoustic mechanisms in porous media via microfluidic visualization, focusing on pore-scale fluid dynamics during enhanced oil recovery, hydrate dissociation, and CO₂ sequestration. Microscopic evidence reveals that fluid transport mechanisms depend heavily on pore geometry and local acoustic intensity. In wider channels, nonlinear acoustic flow provides sustained, directed convection to strip away concentration boundary layers; in narrow throats, microjets and pulsed stresses generated by transient cavitation are responsible for physically breaking capillary barriers. The spatiotemporal synergy of these mechanisms is critical for multiphase fluid transport in tight porous networks. Pore geometry serves not only as the application context but also as a core physical variable. To translate microfluidic results into reservoir-scale applications, future research must address two-dimensional simplifications, thermodynamic discrepancies under high-temperature and high-pressure conditions, and bubble cluster interactions, alongside the development of adaptive frequency-modulated control and multiscale computational models. Full article

The characteristics of two-phase flow in heterogeneous shale porous structures are of critical importance for oil and gas extraction and for evaluating the efficiency of underground resource recovery and carbon sequestration. However, although non-isothermal two-phase flow has been investigated in previous studies, systematic research on non-isothermal CO₂–crude oil displacement in heterogeneous shale porous structures remains relatively scarce. In this study, a multi-phase simulator was employed to simulate non-isothermal CO₂–crude oil displacement in heterogeneous porous structures, and the effects of injection rate, injection temperature, and wettability on two-phase flow characteristics in heterogeneous porous media were systematically analyzed. The results indicate that changes in the viscosity ratio between the displacing and displaced phases—induced by heat transfer—may be a key factor governing immiscible two-phase interfacial dynamics and flow behavior in heterogeneous porous structures. Injection temperature exerts a significant influence on both the main flow channels and local flow pathways within the porous structure; increasing the injection temperature of the displacing phase can effectively enhance displacement efficiency, with the steady-state CO₂ saturation increasing from 43.15% to 50.62% as the injection temperature increased from 293.15 K to 363.15 K. In addition, increasing the injection rate improves CO₂ sweep efficiency, with the steady-state CO₂ saturation increasing from 45.35% to 55.98% as the injection rate increased from 50 to 250 μm/s; however, excessively high injection rates lead to non-piston-like displacement and premature fluid breakthrough, and the CO₂ saturation decreased to 49.81% at 350 μm/s. Under strongly water-wet conditions, the CO₂ saturation after displacement stabilization is higher. Full article