Search Results (344)

Viscous fingering is a canonical nonlinear interfacial instability that arises when a less viscous fluid displaces a more viscous one under an adverse viscosity contrast. Despite extensive investigations into the effects of fluid properties, operating conditions, and rheology, systems involving a shear-thickening displaced phase remain largely unexplored. Here, three-dimensional numerical simulations of immiscible air–fluid displacement in a Hele–Shaw cell are performed to elucidate how interfacial tension, air-inlet velocity, and gap-depth gradient regulate instability evolution. Increasing interfacial tension strengthens the Laplace-pressure barrier, suppresses shear-induced necking and pinch-off, and preserves finger topology; however, it intensifies flow diversion and delays the advancement of the central finger. Increasing the inlet velocity markedly amplifies the local interfacial shear rate and triggers pronounced shear thickening. The resulting viscous-resistance barrier redistributes momentum toward paths of least hydraulic resistance, directly promoting tip splitting and severe topological breakup. Even a small gap-depth gradient reorganizes the local hydraulic resistance and pressure field. Positive and negative gradients induce resistance-reduction and throttling effects, respectively, generating pronounced pressure shielding that governs asymmetric momentum transfer and preferential flow-path selection. These findings identify the capillary, rheological, and geometric mechanisms controlling viscous fingering during the air-driven displacement of shear-thickening fluids. Because such instabilities compromise the integrity of geological-fracture seals and the operating efficiency of semi-solid flow batteries, this study provides a mechanistic basis for stabilizing immiscible displacement and optimizing industrial fluid-transport systems. Full article

Lost circulation is a major technical bottleneck restricting safe and efficient while-drilling plugging operations. Polyacrylamide gel has become a widely used plugging material in drilling engineering. Unlike rigid, cement-like plugging materials, the gel system formed in this study does not develop a hardened, consolidated structure capable of anchoring or binding the drill bit during subsequent drilling operations, thereby eliminating the risk of bit-sticking. Nevertheless, the gel possesses sufficient elastic (viscoelastic) structural strength—reflected in its storage modulus (G′)—to effectively resist deformation and displacement under differential pressure, thereby providing reliable fracture-sealing performance, which effectively prevents pipe-sticking risks. However, high-concentration PAM molecular chains easily stretch and entangle in aqueous solution, triggering an abnormal increase in initial viscosity and poor pumpability. Although Ca²⁺ can inhibit the premature water absorption and thickening of PAM to maintain system fluidity, an excessively high Ca²⁺ concentration will suppress the hydrolysis of Al³⁺ and hinder the formation of hydroxyaluminum—the key crosslinking component of the gel system. To solve the above contradiction, a CaCl₂-tolerant delayed-release crosslinker was synthesized. ZnO was selected as a carrier to adsorb and immobilize polynuclear hydroxyaluminum complexes hydrolyzed from an inorganic aluminum crosslinker at 70 °C, realizing the controlled delayed release of the crosslinker. The microstructures and chemical bonding were characterized by SEM elemental mapping, FT-IR and ²⁷Al MAS NMR. The results confirm that abundant aluminum species are uniformly loaded on the ZnO surface to form stable Zn–O–Al covalent bonds, and the loaded aluminum exists mainly in the form of hydroxyaluminum. With increasing temperature, the Zn–O–Al bonds gradually break and slowly release hydroxyaluminum species. A novel delayed crosslinking gel system was ultimately optimized, composed of 6% CaCl₂, 10.4% PAM and 3% ZnO loaded with polynuclear hydroxyaluminum. The system exhibits excellent delayed gelation behavior, with a fluidity loss time longer than 120 min and a gelation time over 200 min. It maintains favorable fluidity within 30–90 °C, and the formed gel shows a stable elastic modulus (G′) and viscous modulus (G″). Moreover, the system achieves a plugging rate of more than 90% and a breakthrough pressure above 5 MPa, demonstrating superior comprehensive plugging performance for while-drilling plugging applications. Full article

Droplet impact on curved porous media involves coupled spreading, wrapping, recoiling, and penetration. A three-dimensional level set model was developed in COMSOL and validated using high-speed imaging experiments to quantify axial and circumferential spreading lengths, central liquid film height, penetration depth, and energy partitioning at maximum spreading. As the We increased from 10 to 40, the maximum axial and circumferential spreading factors increased by 15.58% and 25.80%, respectively, while viscous dissipation increased by 17.32% and the recoiling-stage peak central liquid film height decreased by 16.70%. Increasing porosity from 0.4 to 0.6 had little effect on macroscopic spreading but raised the penetration peak and reduced the recoiling-stage liquid film height by 18.25%; similarly, increasing particle diameter from 0.15 to 0.25 mm increased the penetration depth at 20 ms by 49.75%, by reducing Darcy–Forchheimer resistance. Increasing surface tension from 0.0273 to 0.1092 N/m reduced the peak axial and circumferential spreading factors by 26.08% and 36.49%, respectively, whereas increasing viscosity from 0.003 to 0.009 Pa·s reduced the peak axial spreading factor and penetration peak by 15.96% and 45.95%. These results demonstrate that pore-scale parameters and liquid properties jointly regulate droplet impact on curved porous media, with pore structure affecting penetration and liquid properties controlling spreading and recoiling. Full article

Low-slenderness-ratio, flat-ended autonomous underwater vehicles must balance hydrodynamic resistance against internal volume retention, yet classical slender-body criteria do not fully represent their coupled forebody wake response. A generalized Myring forebody was assessed for an AUV with L = 0.8 m, D = 0.2 m, and L/D = 4.0 using 53 steady three-dimensional Reynolds averaged Navier-Stokes simulations with the shear stress transport k-ω model. Gaussian process regression and the non-dominated sorting genetic algorithm II (NSGA-II) were used only for candidate-region screening; production grid direct CFD samples were used to determine nondominance. Strict fold-wise leave-one-out cross-validation gave ${\mathrm{Q}}^2$ = 0.173 globally and RMSE = 0.001399 and ${\mathrm{Q}}^2$ = 0.683 in the predefined 18-sample decision region, indicating local screening utility rather than global surrogate validation. The direct CFD audit identified 13 globally and seven locally nondominated samples; both previously selected test configurations were dominated after CFD back-substitution. Their three grid drag sequences were monotonic but non-asymptotic. Pressure drag comprised 75.88–79.20% of total drag. However, the reduction in the low-drag test configuration relative to the baseline arose mainly from a lower viscous contribution; axial pressure fields therefore indicate redistribution rather than exclusive drag-reduction causation. Paired CFD samples showed that the sign of the drag responded to N reversal between the two sampled ${\mathrm{L}}_{\mathrm{nose}}$ values, whereas analytical volume increased with N in both pairs. The results reveal a discrete, configuration-dependent drag volume trade-off and local N-${\mathrm{L}}_{\mathrm{nose}}$ coupling. The rectangular regions are sampling envelopes rather than validated optimum windows, and the conclusions are restricted to steady, deeply submerged, smooth-wall bare-hull conditions. Full article

This study evaluates the network-forming and gelation capabilities of quinoa protein (QP) nanocomplexes formed with alginate (QP–Al) and chitosan (QP–C) for the development of structured food emulsion gels and their application in reduced-fat food dressings. Rheological and nanometric characterisation revealed that QP–C complexes exhibited strong shear-thinning behaviour and particle-size instability with increasing concentration, indicating the breakdown of an organised internal network at rest. Conversely, QP–Al showed Newtonian behaviour, smaller particle sizes (~100–250 nm) and high surface charge stability. Upon oil incorporation, the chitosan-based systems underwent an abrupt, concentration-dependent transition from a liquid-like state to a solid-like gel network between 1.2% and 1.6% w/v chitosan. The EQP–C8 gel network exhibited severe structural fragility, degrading into a purely viscous fluid over 28 days. Conversely, the alginate-based system (EQP–AL8) formed a weak physical hydrogel network characterised by a progressive build-up of structure that resisted creaming and maintained structural integrity across temperature changes. EQP–AL8 was successfully used to develop a plant-based, reduced-fat dressing with high organoleptic acceptance; 98% of participants were willing to purchase the product. These findings demonstrate that QP–AL8 provides a clean-label technological path to designing tunable, highly stable food emulsion gels. Full article

Sludge-conditioning strategies are commonly optimized for filtration performance, with less attention paid to the rheological and textural properties of concentrated sludge and their relevance to low-temperature drying. Here, thermally modified drinking-water sludge (HDWS) was evaluated as a waste-derived mineral conditioner for filtration dewatering and low-temperature drying. The specific resistance to filtration (SRF) was lowest at 30% DS, whereas the 60% DS treatment reduced the moisture content to 35.66% after drying at 60 °C for 30 min, indicating that the optimum filtration condition did not deliver the best drying performance. Increasing the HDWS dosage from 0 to 60% DS reduced the Jenike shear stress from approximately 565 to 490 Pa and the apparent yield stress from approximately 670 to 380 Pa, while also decreasing adhesiveness and cohesiveness. At higher dosages, the sludge retained relatively high small-strain stiffness but exhibited lower nonlinear elastic and viscous resistance. These responses were consistent with weakened macroscopic bonding and altered deformation-dependent energy dissipation after HDWS addition. A possible contribution from mineral-particle contacts is suggested, although the underlying microstructural mechanism was not directly resolved. The 60% DS treatment shortened the time required to reach 20% water content to approximately two-thirds of that for raw sludge but reduced the cake calorific value from approximately 9.6 to 4.3 kJ g⁻¹. HDWS, therefore, exhibited process-specific trade-offs, and its dosage should be selected according to the targeted unit operation and downstream management route rather than regarded as a single overall optimum. Full article

This paper investigates the occurrence characteristics, mobilization behavior, and controlling mechanisms of microscopic remaining oil in heavy-oil systems at different water-cut stages by using a visual microfluidic platform. A series of displacement and pressure-ramping experiments were conducted at 65 °C on homogeneous and heterogeneous chips with different permeabilities and oil viscosities. Image-based saturation processing and oil-phase area recognition were further employed to quantify remaining-oil morphology, area fractions, and unit threshold pressure. Results show that, with increasing water saturation, the continuity of the oil phase deteriorates progressively, and the remaining oil evolves from cluster oil to elongated cluster oil and spot and corner-trapped oil. Accordingly, the threshold pressure increases nonlinearly, especially at high-water-cut stages. For the same water saturation, higher permeability leads to lower threshold pressure because of larger pore-throat radii and better connectivity, whereas higher viscosity raises the threshold pressure due to stronger viscous resistance. Compared with homogeneous chips, heterogeneous chips exhibit higher threshold pressure because local pore-throat bottlenecks dominate capillary resistance. The image-recognition analysis indicates that the areal fraction of cluster oil decreases continuously, while that of the discontinuous oil phase, comprising elongated cluster oil and spot and corner-trapped oil, generally increases. The unit threshold pressure of cluster oil rises monotonically, whereas that of the discontinuous oil phase first decreases and then increases, reflecting the combined effects of oil fragmentation, migration, and trapping during water flooding. Full article

In this study, a three-dimensional transient multi-physics coupled numerical model of narrow-gap tungsten inert gas (TIG) welding of TC4 alloy is established, and the heat transfer, flow behavior of the liquid metal in the molten pool, and the formation mechanism of sidewall lack-of-fusion defects are quantitatively investigated. The results show that, along the groove width direction, the temperature and flow velocity of the liquid metal gradually decrease from the center toward the sidewall. Along the welding direction, the fluid velocity presents multi-peak fluctuation characteristics. As the weld pass increases, the maximum velocity of the liquid metal significantly increases, enhancing the overall fluidity of the molten pool, and the temperature distribution becomes more uniform due to the weakened geometric constraints of the sidewall and the inter-pass heat accumulation effect. Furthermore, excessively high welding speeds (0.2 m/min) or insufficient welding currents (150 A) drastically reduce the per-unit-length heat input, resulting in diminished molten pool volume and decreased maximum liquid metal velocities of 0.075 m/s and 0.1 m/s, respectively. Under these conditions, lateral driving forces generated by the Marangoni effect are insufficient to overcome the viscous resistance of the molten metal. Consequently, the liquid metal solidifies prior to reaching the sidewall, inducing pronounced sidewall lack-of-fusion defects and localized humping on the weld top surface. Full article

The incorporation of bio-derived modifiers in bitumen binders presents a practical pathway toward sustainable, carbon-sequestering road pavement infrastructure. This study evaluates commercially produced ECHO2 softwood biochar as a modifier for Australian viscosity-graded C170 bitumen, combining microstructural, thermal, physical, and rheological characterization to assess its suitability as a high-temperature reinforcing modifier. In this study, biochar was incorporated at 3%, 6%, 9%, and 12% by weight, utilizing particles smaller than 75 µm to maximize interfacial interaction. Characterization via SEM-EDS, XRD, and TGA revealed a highly stable, carbon-rich, amorphous material with a rough, porous morphology, favourable for physical interlocking with the bitumen matrix. Physical and rheological investigations demonstrated that ECHO2 biochar measurably enhances binder stiffness and high-temperature deformation resistance. Compared with the control, 12% biochar modification reduced penetration by approximately 27% and increased the softening point by approximately 10%, indicating a reduction in temperature susceptibility. Dynamic shear rheometer (DSR) temperature sweeps highlighted substantial increases in the complex shear modulus (G*) and rutting factor (G*/sinδ) without altering the phase angle (δ), confirming the modifier acts as a rigid, particulate reinforcing agent rather than an elastomer. Multiple stress creep recovery (MSCR) testing supported these findings; non-recoverable creep compliance (J_nr) decreased progressively. Critically, under the AASHTO M 332 specification, while the neat bitumen binder barely met the standard traffic (S) criteria, the progressive reduction in J_nr (particularly at 12%) delivered a substantially higher factor of safety against rutting within the standard traffic designation. Finally, ECHO2 biochar demonstrates strong potential as a sustainable modifier that restricts viscous flow through particulate stiffening, enhancing high-temperature rutting resistance at elevated temperatures. Full article

This research presents a physics-informed deep learning framework for investigating the magnetohydrodynamic flow of a dissipative non-Newtonian micropolar nanofluid induced by a stretching sheet, incorporating Stefan blowing, internal heat generation, and the zero nanoparticle mass flux condition. The physical model consists of the interplay between the microrotation dynamics, resistance of porosity on the microrotation, Brownian diffusion, and thermophoretic transport phenomenon. The numerical solutions for the nonlinear yielded equations that result from the above interaction are obtained by employing a PINN that considers the laws of physics and boundary conditions. With this technique, the flow behavior, temperature, concentration, and microrotation fields can be predicted accurately without requiring huge datasets. This shows the ability of PINNs to numerically treat highly-coupled nonlinear transport equations in a very efficient manner compared to other traditional methods. The important discoveries from this study include that the porous and magnetic factors increased the skin friction coefficient, but the magnetic effect and viscous dissipation decreased the rate of heat transfer, and the thermophoresis effect decreased the rate of mass transfer while the Brownian effect increased it. The precision of the PINN algorithm is confirmed by comparison of the results with the earlier findings, which proves very high accuracy and hence the robustness of the current computing framework. Results of this research are useful for the development of some thermal management systems, energy converters, cooling methods, chemical reaction processes, fuel cell technology, porous media reactors, and ocean engineering involving the transport of complicated non-Newtonian nanofluids. Full article

The phase transition of paraffin powder mixed in wellbore concrete is generated by baking it, so that the paraffin powder is melted. The influence of baking temperature and paraffin dosage on phase transition degree of paraffin powder and the carbonation resistance of wellbore concrete was studied. Combined with microscopic testing methods such as scanning electron microscopy, the microscopic morphology of phase-transited paraffin films within the cement matrix and the mechanism by which they enhance the carbonation resistance of cement-based materials were analyzed. The results indicate that when baking temperature reaches 80 °C, the paraffin particles in the cement-based material can melt into viscous droplets. Partially melted paraffin particles condense within the internal pores of the cement matrix upon cooling, sealing the transmission pathways of CO₂ gas into the cement-based material. Fully melted paraffin droplets flow within the internal pores of the cement matrix and, upon condensation, firmly adhere to the pore walls, forming a relatively dense and smooth film. This film isolates CO₂ gas contact with the cement matrix, significantly improving carbonation resistance of the cement-based material. When the paraffin dosage exceeds 3% and the baking temperature surpasses 100 °C, the phase transition of paraffin powder achieves a fully carbonation-resistant effect. Full article

Current industrial standards for gas pipeline leak testing often assume inert testing gases are universally interchangeable, neglecting specific fluid dynamics. This study quantifies how testing gas properties affect integral pressure decay leak tests. Experimental measurements (5000 Pa initial pressure) were conducted on a PE100RC (polyethylene resistant to crack propagation) pipe assembly with artificial capillary defects (0.13 mm diameter) using five media: nitrogen, air, argon, carbon dioxide, and a propane−butane (PB) mixture. Results demonstrate that in the continuous viscous flow regime, leak rates depend strictly on the gas’s dynamic viscosity. For identical defects, PB (the lowest viscosity gas tested) increased the leak rate by up to 129% compared to standard nitrogen. This relationship is statistically validated by a strong negative Pearson correlation (r = −0.92). To facilitate industrial application, a preliminary mathematical correction procedure is proposed for safely extrapolating these trends to infrastructure intended for pure hydrogen operation. To prevent false-positive tightness certifications during the transition to low-viscosity alternative fuels like pure hydrogen, implementing a dynamic viscosity correction factor is essential. Full article

Bigels (BGs) were formulated using gelatin (GA) or gellan gum (GG) hydrogels (HGs) combined with beeswax-structured oleogels (OGs). Carob fruit extracts—an inositol-rich fraction (I-CFE) and a polyphenol-rich fraction (P-CFE)—were incorporated into the HG and OG phases, respectively, to enable dual delivery. The effects of composition on rheological, textural, thermal, color, and stability properties were evaluated at HG/OG ratios of 70/30, 60/40, and 50/50. GG-based BGs formed rigid, coherent, and crystal-reinforced networks, exhibiting the highest oscillatory stiffness and complex viscosity. GA-based BGs developed softer, more deformable, and viscous structures, with mechanical behavior strongly governed by damping and water content. Increasing OG content reinforced GG BGs through beeswax–crystal integration, whereas in GA it increased oscillatory stiffness but weakened the cohesive, viscous, and recoverable characteristics of the protein network. Categorical principal component analysis (CATPCA) revealed two mechanical domains: a GA-associated regime dominated by viscosity, penetration resistance, and loss factor (tan δ), and a GG-associated regime governed by elastic stiffness. Correlations confirmed tan δ_max as a marker of structural fragility in GA, while stiffness parameters dominated GG behavior. Melting points remained within 53–54 °C, and all BGs showed excellent physical stability. Overall, GA and GG provide complementary design spaces, offering a mechanistic basis for the rational design of BGs with controlled structural and functional properties. Full article

Fused filament fabrication (FFF) is a widely used additive manufacturing method in which the process forces within the hotend play an important role in terms of print quality and speed, particularly in high-throughput applications. This work reports on the influence of filament diameter, melting zone length, and nozzle set temperature on the process forces and the maximum achievable volumetric flow rate. Experimental measurements were carried out using a test rig that integrates a load cell to capture the resulting forces, complemented by non-isothermal numerical simulations. The results show that increasing the melting zone length reduces process forces and increases the attainable volumetric flow rate at high feed rates, as the filament has more time to melt. However, the effect depends strongly on filament diameter. For a diameter of 2.85 mm, extending the melting zone leads to a monotonic increase in the maximum achievable flow rate across the entire investigated range. For a diameter of 1.75 mm, an optimum is observed at an intermediate melting zone length, beyond which additional flow resistance outweighs the benefit of improved melting and thus reduces the attainable flow rate. When normalizing for the maximum transferable extruder force, the smaller filament diameter consistently yields superior throughput performance. The simulations reproduce the experimentally observed trends well and support the interpretation that throughput is limited by the competition between heat-transfer-controlled melting and viscous pressure losses. Full article

Cross-flow micro heat exchangers enable compact thermal management for high-density electronics, but their design is traditionally constrained by a strict trade-off between heat transfer and hydraulic resistance. To mitigate this limitation, we investigate the influence of mixed-geometry channel designs on the coupled thermal and hydraulic performance using a three-dimensional conjugate heat transfer model of water flowing through a stainless-steel micro-matrix with a 40-micrometer hydraulic diameter. Numerical simulations show that at low Reynolds numbers (100 to 200), corner-induced steady three-dimensional flow redistribution modifies the thermal boundary layer, causing convective and hydraulic performance to deviate from standard macroscale predictions. By expanding the transverse microchannel spacing from 10 to 60 μm, the Nusselt number increases from 1.15 to 2.07 while maintaining a nearly constant pressure gradient. These results provide geometric guidelines for designing high-efficiency microfluidic cooling systems by mitigating the traditional trade-off between heat-transfer enhancement and hydraulic resistance. Among the geometries evaluated, pure square channels maximize heat transfer, hybrid circular-square configurations optimize hydraulic efficiency, and triangular designs perform poorly due to high viscous drag. These results provide geometric guidelines for mitigating the traditional trade-off between heat-transfer enhancement and hydraulic resistance in microfluidic cooling systems. Full article