Search Results (27)

Microreactors offer remarkable advantages in intensifying mixing/mass transfer and hold promising prospects for industrial applications. In this study, T-shaped microreactors (TMRs) integrated with baffle, orifice-plate, and venturi structures (featuring different contraction angles) were designed. Based on the Villermaux–Dushman reaction system, three-dimensional computational fluid dynamics (CFD) models were established to simulate the fluid flow and mixing-reaction processes in these microreactors. The results demonstrate that peaks in velocity, turbulent kinetic energy, and turbulent dissipation rate consistently emerge in the confluence region of the two fluid streams. In the operating range of this study, the baffle configuration exhibits the highest micromixing performance but also induces the largest pressure drop, followed by the orifice-plate structure. Notably, the venturi structure not only enhances micromixing efficiency but also results in a minimal increase in pressure drop and eliminates flow dead zones. Specifically, the venturi structure with a 45° contraction angle achieves a balance between energy consumption and micromixing efficiency. Using the agglomeration model, the micromixing times of the microreactors with various structures were determined to range from 0.025 to 0.234 ms. Full article

Background/Objectives: The variability in the structure of the deep cerebral venous system in neonates is increasingly recognised, as are the vascular structural factors involved in the development of the germinal matrix/intraventricular haemorrhage (GM/IVH) in premature infants. We aimed to characterise the ultrasound patterns of these veins in different categories of newborns and to assess if there is a correlation between certain patterns and angles and the presence of GM/IVH. Methods: One hundred neonates (68 at-term and 32 preterm) were included in this research. The pattern of venous drainage and the angle at the confluence between the terminal vein (TV) and internal cerebral vein (ICV) were identified on coronal sections through the anterior fontanel. The normal pattern was considered as that in which the confluence between the TV and the ICV could be identified, and the atypical pattern was considered the situation in which no confluence or terminal vein was identified. Results: There was no statistically significant difference regarding the normal or atypical venous patterns between the groups (p < 0.443), neither regarding the angles between TV and ICV between term and preterm neonates (p < 0.279—left; p < 0.718—right), and singletons and twins (p < 0.745 left; p < 0.418 right), or between the angles on the left and on the right in the whole group (p < 0.121 and the subgroups of term (p < 0.440) and preterm neonates (p < 0.092). The mean value of the angle at the confluence between the TV and the ICV on the left, was significantly lower in the premature infants with GM/IVH (124.90° vs. 137.02°; p = 0.012), being a good predictor for the occurrence of the lesion (AUC = 0.793; IC 95%: 0.580–1.006; p = 0.018), with a sensitivity of 79%, a specificity of 67%, and a cut-off value of 126.90°. In patients with GM/IVH, the angle was significantly lower on the side with the haemorrhage than on the side without haemorrhage (p < 0.043). Conclusions: There is no difference in the central venous pattern or angle at the confluence of the TV and the ICV between different categories of neonates. The angle at the confluence between the TV and ICV could identify the cases at risk for GM/IVH as well as the side of occurrence of the haemorrhage, offering the opportunity of developing personalised prevention strategies. The lack of an MRI comparator of these measurements limits the practical importance of this study. Full article

Understanding flow dynamics in open-channel node systems is crucial for designing effective hydraulic engineering solutions and minimizing energy losses. This study investigates how junction geometry—specifically the lateral inflow angle (α = 45° and 60°) and the longitudinal bed slope (I = 0.0011 to 0.0051)—influences the water velocity distribution and hydraulic losses in a rigid-bed Y-shaped open-channel junction. Experiments were performed in a 0.3 m wide and 0.5 m deep rectangular flume, with controlled inflow conditions simulating steady-state discharge scenarios. Flow velocity measurements were obtained using a PEMS 30 electromagnetic velocity probe, which is capable of recording three-dimensional velocity components at a high spatial resolution, and electromagnetic flow meters for discharge control. The results show that a lateral inflow angle of 45° induces stronger flow disturbances and higher local loss coefficients, especially under steeper slope conditions. In contrast, an angle of 60° generates more symmetric velocity fields and reduces energy dissipation at the junction. These findings align with the existing literature and highlight the significance of junction design in hydraulic structures, particularly under high-flow conditions. The experimental data may be used for calibrating one-dimensional hydrodynamic models and optimizing the hydraulic performance of engineered channel outlets, such as those found in hydropower discharge systems or irrigation networks. Full article

The flow characteristics at the tributary entrance are crucial for ensuring safe navigation where the main channel and tributary converge. Along the inter-basin canal, numerous tributaries feature large confluence angles and significant flow discharge ratios. An experimental study investigated how these factors influence flow patterns, leading to proposed mitigation measures. This research employed a 1:50-scale physical river model and a sediment deposition model. It analyzed navigable flow conditions including velocity, flow patterns, the confluence ratio, the bottom elevation difference, and the confluence angle at the main channel–tributary junction. Focusing on the Jiuzhou River tributary entrance (Pinglu Canal), which has a large confluence ratio, significant bottom elevation difference, and wide confluence angle, this study tested two solutions: a single energy dissipator and a combined energy dissipator system. Sediment deposition modeling compared the effectiveness of these approaches. The results showed that implementing a steep slope with a three-stage stilling pool in the Jiuzhou River entrance section effectively manages confluences with large elevation differences, wide angles, and high flow discharge ratios. This configuration significantly improves entrance flow characteristics. Full article

Asymmetrical river confluence zones play a critical role in water quality protection and remediation. This study develops a three-dimensional numerical model to simulate the hydraulic characteristics and contaminant dispersion processes within river channels. The results indicate that variations in the two geometric factors—the confluence angle and elevation difference—can produce a range of effects. Under the combined influence of these factors, the trajectory line at the pollutant-mixing interface follows a “logarithmic” growth pattern. As indicated by the inhomogeneity index, an increase in the junction angle and elevation difference significantly accelerates the mixing rate of pollutants and enhances dispersion. These insights suggest that, in cases with large confluence angles and significant elevation variations, intense mixing of water flow facilitates the rapid transport and extensive dispersion of pollutants, which may help reduce localized pollution loads. These findings are crucial for developing effective water environment management strategies. Full article

The geometry of non-pressurized tunnel intersections governs the hydraulic behavior of the confluence flows, which are critical to the safe operation of pumped storage power stations. To address the issue of water surface levels exceeding the permissible height of the vertical walls at the intersection of the sediment discharge and emptying tunnels close to the lower reservoir of a pumped storage power station, a hydraulic model with a scale of 1:45 was constructed to optimize the intersection design. The optimization process included replacing the straight connection with an arc connection, incorporating an energy dissipation basin into the emptying tunnel, reducing the intersection angle, and increasing the arc radius. During the optimization, the hydraulic behavior of the confluence flow was thoroughly analyzed. This study determined that an arc connection with a 21° intersection angle represented the optimal design. Using the RNG k-ε turbulence model and the volume-of-fluid (VOF) method, a three-dimensional (3D) numerical model was developed to further evaluate the flow patterns, velocity fields, and bottom pressure distributions under both the optimized-design and model-verification conditions. The numerical simulation results, validated against experimental data, exhibited close agreement. The findings demonstrate that the optimized design ensures compliance with specifications, as the maximum water depth no longer exceeds the height of the straight walls. This study offers valuable insights for optimizing tunnel intersections of high-elevation-difference non-pressurized tunnels in pumped storage power stations. Full article

(1) This paper selects the modern delta formed by the Ganjiang tributary in Poyang Lake. By performing high density statistical analysis of distribution channel parameters in the area using satellite images and geographic information processing software (LucaSpaceViewer 4.5.2, ArcGIS Pro 3.0.2, Global Mapper v23.1), including length, width, bifurcation angle, bifurcation frequency, and channel sinuosity, the distribution characteristics of delta distribution channels are derived and quantitatively characterized. (2) Classification and evaluation of these characteristics are carried out using factor and cluster analysis, ultimately identifying controlling factors affecting the morphology and distribution of the distribution channels. By statistically analyzing the geometric and bifurcation data of the channels, factor and cluster analysis for data reduction and classification, the channel is finally divided into three categories: Type I channels have relatively high channel length, width, sinuosity, bending amplitude, and a lower bifurcation (or confluence) growth rate; Type II channels are characterized by low channel length, moderate channel width, low sinuosity, low bending amplitude, and a high bifurcation (or confluence) growth rate; Type III channels are defined by moderate channel length, low width, high sinuosity, high bending amplitude, and low bifurcation (or confluence) frequency. (3) After excluding the influence of other factors, it was found that the main controlling factor for the morphology of the Ganjiang Delta channel is flow velocity, which is influenced by changes in the terrain slope. Flow velocity directly affects channel sinuosity, bending amplitude, and bifurcation (or confluence) frequency, and indirectly affects channel length and width. Full article

This article examines the flight dynamics and trajectory analysis of a parachute–payload system deployed from a C-17 aircraft. The aircraft is modeled with an open cargo door, extended flaps, and four turbo-fan engines operating at an altitude of 2000 feet Above Ground Level (AGL) and an airspeed of 150 knots. The payloads consist of simplified CONEX containers measuring either 192 inches or 240 inches in length, 9 feet in width, and 5.3 feet in height, with their mass and moments of inertia specified. At positive deck angles, gravitational forces cause these payloads to begin a gradual descent from the rear of the aircraft. For aircraft at zero deck angle, a ring-slot parachute with approximately 20% geometric porosity is utilized to extract the payload from the aircraft. This study specifically employs the CREATE-AV Kestrel simulation software to model the chute-payload system. The extraction and suspension lines are represented using Kestrel’s Catenary capability, with the extraction line connected to the floating confluence points of the CONEX container and the chute. The chute and payload will experience coupled motion, allowing for an in-depth analysis of the flight dynamics and trajectory of both elements. The trajectory data obtained will be compared to that of a payload (without chute and cables) exiting the aircraft at positive deck angles. An adaptive mesh refinement technique is applied to accurately capture the engine exhaust flow and the wake generated by the C-17, chute, and payloads. Friction and ejector forces are estimated to align the exit velocity and timing with those recorded during flight testing. The results indicate that the simulation of extracted payloads aligns with expected trends observed in flight tests. Notably, higher deck angles result in longer distances from the ramp, leading to increased exit velocities and reduced payload rotation rates. All payloads exhibit clockwise rotation upon leaving the ramp. The parachute extraction method yields significantly higher exit velocities and shorter exit times, while the payload-chute acceleration correlates with the predicted drag of the chute as demonstrated in prior studies. Full article

The Bailong River Basin is one of the most developed regions for debris flow disasters worldwide, often causing severe secondary disasters by blocking rivers. Therefore, the early identification of potential debris flow disasters that may block the river in this region is of great significance for disaster risk prevention and reduction. However, it is quite challenging to identify potential debris flow disasters that may block rivers at a regional scale, as conducting numerical simulations for each debris flow catchment would require significant time and financial resources. The purpose of this article is to use public resource data and machine learning methods to establish a relationship model between debris flow-induced river blockage and key influencing factors, thereby economically predicting potential areas at risk for debris flow-induced river blockage disasters. Based on the field investigation, data collection, and remote sensing interpretation, this study selected 12 parameters, including the basin area, basin height difference, relief ratio, circularity ratio, landslide density, fault density, lithology index, annual average frequency of daily rainfall exceeding 40 mm, river width, river discharge, river gradient, and confluence angle, as critical factors to determine whether debris flows will cause river blockages. A relationship model between debris flow-induced river blockage and influencing factors was constructed based on machine learning algorithms. Several machine learning algorithms were compared, and the XGB model performed the best, with a prediction accuracy of 0.881 and an area under the ROC curve of 0.926. This study found that the river width is the determining factor for debris flow blocking rivers, followed by the annual average frequency of daily rainfall exceeding 40 mm, basin height difference, circularity ratio, basin area, and river discharge. The early identification method proposed in this study for river blockage disasters caused by debris flows can provide a reference for the quantitative assessment and pre-disaster prevention of debris flow-induced river blockage chain risks in similar high-mountain gorge areas. Full article

The hydraulic collector is an important device for collecting seafloor polymetallic nodules. In this study, a hydraulic polymetallic nodule collector with two acquisition nozzles and one transmission nozzle is described. The numerical model of the hydraulic collector is established based on the solid–liquid two-phase flow method, and it is verified by experimental tests. On this basis, the collection mechanism of the hydraulic collector is analyzed, and the effects of structural parameters and working parameters on its collection performance are explored. The results show that the collection height and slant angle of the acquisition nozzle are key factors for collection efficiency, with optimal heights below 150 mm and angles between 45 and 49${}^{\circ }$. The recommended range for the center distance between the two acquisition confluence tubes is 650–730 mm. Excessive acquisition and transmission flow rates make a negligible contribution to improving the collection efficiency, but can also cause a significant increase in energy consumption. Therefore, the recommended ranges for acquisition and transmission flow rates are 140–160 m${}^3$/h and less than 80 m${}^3$/h, respectively. All of the results indicated that the parameters of the developed hydraulic collector were set reasonably, which thus ensured a balance between the collection efficiency and energy consumption. Full article

Soft tissue adhesion and sealing around dental and maxillofacial implants, related prosthetic components, and crowns are a clinical imperative to prevent adverse outcomes of periodontitis and periimplantitis. Zirconia is often used to fabricate implant components and crowns. Here, we hypothesized that UV treatment of zirconia would induce unique behaviors in fibroblasts that favor the establishment of a soft tissue seal. Human oral fibroblasts were cultured on zirconia specimens to confluency before placing a second zirconia specimen (either untreated or treated with one minute of 172 nm vacuum UV (VUV) light) next to the first specimen separated by a gap of 150 µm. After seven days of culture, fibroblasts only transmigrated onto VUV-treated zirconia, forming a 2.36 mm volume zone and 5.30 mm leading edge. Cells migrating on VUV-treated zirconia were enlarged, with robust formation of multidirectional cytoplastic projections, even on day seven. Fibroblasts were also cultured on horizontally placed and 45° and 60° tilted zirconia specimens, with the latter configurations compromising initial attachment and proliferation. However, VUV treatment of zirconia mitigated the negative impact of tilting, with higher tilt angles increasing the difference in cellular behavior between control and VUV-treated specimens. Fibroblast size, perimeter, and diameter on day seven were greater than on day one exclusively on VUV-treated zirconia. VUV treatment reduced surface elemental carbon and induced superhydrophilicity, confirming the removal of the hydrocarbon pellicle. Similar effects of VUV treatment were observed on glazed zirconia specimens with silica surfaces. One-minute VUV photofunctionalization of zirconia and silica therefore promotes human oral fibroblast attachment and proliferation, especially under challenging culture conditions, and induces specimen-to-specimen transmigration and sustainable photofunctionalization for at least seven days. Full article

The T-type tee is a crucial part of liquid distribution systems and is widely used in irrigation, drainage, water delivery, and agricultural fertilizer injection, among other areas. Confluence angle, pipe diameter ratio, and flow rate ratio have been the main focus of previous research. Research on the hydraulic characteristics and resistance optimization brought about by the main-side pipe intersection’s chamfering treatment is, nevertheless, incredibly rare. Optimizing the structure of the T-type tee could improve its sustainability in many aspects, such as its energy consumption, durability, and production process. In order to fill this void in the literature, the current investigation concentrated on the resistance reduction and flow properties of T-type tees by means of chamfering treatment. Using a newly proposed coefficient called the integrated local resistance coefficient, the integral flow characteristics and resistance reduction effects of T-type tees were addressed. Through the use of the verified computational fluid dynamics (CFD) method, the crossed effects of five chamfer ratios (R = 0D, 0.5D, 1D, 2D, and 3D), nine flow rate ratios (0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, and 0.9), and two pipe diameter ratios were examined. When the Reynolds number exceeded 3 × 10⁵, the flow remained in the quadratic drag region, meaning that the local resistance coefficient of T-type tees was no longer dependent on the flow velocity. In both confluence and shunt conditions for equal tees, chamfering treatment was proven to be an efficient method for reducing local resistance under these conditions. For instance, following a 1D chamfering treatment on the T-type confluence tee, at a flow ratio of 0.5, the local resistance coefficients ζ₁ and ζ₂ dropped by 68% and 82%, respectively, in comparison to the 0D condition. The effects of resistance reduction were improved by a wider chamfer radius and a higher side pipe flow rate ratio. The highest overall performance was obtained by chamfering a T-type tee with a curvature radius of 1D, taking into account flow characteristics, sustainability, processing technology, economic cost, and promotion difficulties. The chamfering procedure produced a more noticeable reduction in resistance for unequal tees with comparable velocities in the main and side pipes when the pipe diameter ratio was greater than 0.5. Full article

As the power electronics landscape evolves, pushing for greater vertical integration, capillary underfilling is considered a versatile encapsulation technique suited for iterative development cycles of innovative integration concepts. Since a defect-free application is critical, this study proposes a capillary two-phase flow simulation, predicting both the flow pattern and velocity with remarkable precision and efficiency. In a preliminary performance evaluation, Volume of Fluid (VOF) outperforms the Level-Set method in terms of accuracy and computation time. Strategies like HRIC blending, artificial viscosity, and implicit Multi-Stepping prove effective in optimizing the numerical VOF scheme. Digital mapping using physical experiments and virtual simulations validates transient flow predictions, achieving excellent agreement with deviations as low as 1.48–3.34%. The accuracy of flow predictions is thereby greatly influenced by non-Newtonian viscosity characteristics in the low shear range and time-dependent contact angle variations. The study further explores flow manipulation concepts, focusing on local flow speed adjustment, gap segmentation, and the use of arcuate shapes to influence interface confluence near the chip. Experimental validation corroborates the effectiveness of each design intervention. In conclusion, this research highlights the potential of predictive engineering to develop flow-optimized package designs that enhance reliability while supporting high manufacturing yields. Full article

Iliac vein compression syndrome (IVCS, or May–Thurner syndrome) occurs due to the compression of the left common iliac vein between the lumbar spine and right common iliac artery. Because most patients with compression are asymptomatic, the syndrome is difficult to diagnose based on the degree of anatomical compression. In this study, we investigated how the tilt angle of the left common iliac vein affects the flow patterns in the compressed blood vessel using three-dimensional computational fluid dynamic (CFD) simulations to determine the flow fields generated after compression sites. A patient-specific iliac venous CFD model was created to verify the boundary conditions and hemodynamic parameter set in this study. Thirty-one patient-specific CFD models with various iliac venous angles were developed using computed tomography (CT) angiograms. The angles between the right or left common iliac vein and inferior vena cava at the confluence level of the common iliac vein were defined as α1 and α2. Flow fields and vortex locations after compression were calculated and compared according to the tilt angle of the veins. Our results showed that α2 affected the incidence of flow field disturbance. At α2 angles greater than 60 degrees, the incidence rate of blood flow disturbance was 90%. In addition, when α2 and α1 + α2 angles were used as indicators, significant differences in tilt angle were found between veins with laminar, transitional, and turbulent flow (p < 0.05). Using this mathematical simulation, we concluded that the tilt angle of the left common iliac vein can be used as an auxiliary indicator to determine IVCS and its severity, and as a reference for clinical decision making. Full article

This study aims to analyze the influences of momentum ratio (M_r) and confluence angle (α) on the transverse dispersion in an urban scale confluence channel from the numerical simulation results using the Environmental Fluid Dynamics Code model. By changing the momentum flux and confluence angle from the simulation results, the analysis focused on the relations between the vertical variations of transverse velocity and transverse dispersion. The high momentum tributary aligned the mixing interface toward the outer bank and created a strong helical motion, which transported the contaminated water along the channel bed and inflows into the recirculation zone. The high momentum ratio induced the large vertical shear in transverse velocity with a strong helical motion and increased the transverse dispersion. However, the helical motion persistence rapidly decreased as the flow reached downstream and led to a decrease in the transverse dispersion for the large confluence angle. Thus, the transverse dispersion coefficient increased with a high momentum ratio and low confluence angle, and the dimensionless transverse dispersion coefficient was in the range of 0.39–0.67, which is observed in meandering channels, for Mr > 1 and α = 45°. Full article