Scouring Effect Research Articles

Analysis of the Source Tracing and Pollution Characteristics of Rainfall Runoff in Adjacent New and Old Urban Areas

This study aimed to examine the pollution characteristics of rainfall runoff as well as the runoff scouring effect and pollution traceability in adjacent new and old urban areas. The sampling and monitoring of rainfall runoff for different rainfall underlying surfaces were conducted for roads, green spaces, roofs, and a food market. The concentration of chemical oxygen demand (COD) and nutrients in the rainfall runoff of the market area was higher than that measured for roads, green spaces, and roofs. The initial scouring effect of each underlying surface was obvious during rainstorms, and 30% of the runoff transported nearly 50% of the pollutants. Further, 30% of the runoff transported about 30% of the pollutants under moderate and heavy rain conditions, and the overall initial scouring effect was not obvious. The results of this study showed that, as a considered underlying surface area, the market and possibly other similar service facilities had a significant impact on the calculation of runoff pollution load, and these should be included in the research scope of rainfall runoff and the impact of underlying surfaces. The purpose of this study was to provide reliable and practical information for water pollution prevention and control, especially for pollution prevention and control of rainfall runoff in areas where new and old urban parts of cities exist side by side.

Characteristics of Nitrogen Output during Typical Rainfall in Different Sugarcane Growth Stages in a Southern Subtropical Watershed

Excessive fertilizer application, majorly nitrogen- and phosphorus-based fertilizers, in farmland has intensified environmental pollution of rivers, lakes, and other surface water bodies worldwide by agricultural non-point sources, especially the highly-mobile nitrogen. To solve nitrogen pollution in sugarcane areas, exploring the nitrogen output characteristics of agricultural watersheds in crop fields becomes necessary. Therefore, the objective of the study was to evaluate the characteristics of nitrogen output during typical rainfall events in different sugarcane growth stages in a southern tropical watershed in China. Dynamic monitoring of runoff and nitrogen concentration was carried out for four rainfall events and compared among four sugarcane growth stages (Establishment; Vegetative growth; Grand growth; Ripening) during the growing season of 2018 in the Nala watershed, Kelan Reservoir, Guangxi, China. The results showed that the total dissolved nitrogen flux of the 4 rainfall events ranged from 0.08 to 9.88 kg·hm−2 for the different growth stages. Nitrate nitrogen was the main component of the total flux, accounting between 75.7 and 92.1% of the total dissolved nitrogen while ammonium nitrogen accounted between 1.80 and 5.26% of the total flux for the 4 rainfall events. Total dissolved nitrogen and nitrate-nitrogen were significantly and negatively correlated with runoff (p < 0.05), while total dissolved nitrogen concentration did not correlate with runoff. The incipient scouring effect of total dissolved nitrogen and nitrate-nitrogen was not noticeable. The concentration of total dissolved nitrogen in the Nala watershed was inferior to class V water quality standard, indicating water eutrophication danger. The study showed that nitrogen nutrient inflow into the river was promoted by N-fertilization time and rainfall. Therefore, reasonably reducing N-fertilization dose and post-rain fertilization could effectively reduce nitrogen inflow into rivers and avoid the intensification of eutrophication in sugarcane areas. We recommend multiple years of studies to verify the possible impacts of differences in weather conditions.

Corrosion Mechanism of Typical Shale Gas Gathering and Transportation Pipelines in Southwest China

The shale gas surface gathering and transportation pipeline in southwest China has experienced serious internal corrosion, which affects the production of shale gas wells and has great potential safety hazards. To find out the corrosion type and corrosion mechanism, the corrosion analysis and mechanism research of gathering and transportation pipelines are carried out, including corrosion morphology observation, corrosion product analysis, fluid mechanics calculation, etc. The results show that the corrosion products of the gathering and transportation pipeline are mainly FeCO3 with high S content, and the corrosion type is sulfate-reducing bacteria (SRB) and CO2 corrosion. At the same time, the corrosion pits are mainly distributed on the approach stream side, which is closely related to the scouring effect of the medium flow in the vertical branch pipe on the wall surface of the tee. The corrosion weight loss test shows that the corrosion rate of sterile solution is significantly lower than that of bacterium solution, indicating that the presence of SRB significantly expedites the corrosion of materials.

Insights into the foulants characteristics in a walnut shell biofilm-membrane bioreactor during treatment of hypersaline oilfield produced water

The characteristics and behavior of membrane fouling in oilfield produced water treatment systems are highly affected by the complex nature of this stream. The present study is dedicated to the characterization of the membrane foulants in a hybrid moving bed and membrane bioreactor (MBBR-MBR) system using walnut shell as a bio-carrier, for treatment of real produced water at total dissolved solids (TDS) concentrations of 35,000, 90,000 and 200,000 mg/L. The impact of using walnut shell on fouling was also investigated. Various analytical methods including attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR), gas chromatography- mass spectrometry (GC–MS) were used to identify the organic compounds and inductively coupled plasma- optical emission spectrometry (ICP- OES), X-ray fluorescence (XRF), energy-dispersive X-ray spectroscopy (EDS) and X-ray powder diffraction (XRD) were applied in order to investigate the inorganic constituents present in the foulants. Additionally, field emission scanning electron microscopes (FE-SEM), atomic force microscopy (AFM) and particle size distribution (PSD) analysis were used as auxiliary tools to investigate the morphology and particle size distribution of the cake layer. The results indicated that the most important organic compounds identified included microorganisms, microbial products, and hydrocarbons. Also, the most important inorganic elements included Na, Cl, K, Ca, S, and P which probably originated from NaCl, CaCO3, and Ca-P precipitates. Walnut shell was effective in reducing membrane fouling due to the scouring effect, as well as altering the properties of sludge, and adsorption of oil compounds.

Study on the Variation Law of Reservoir Physical Properties in High Water Cut Stage

Difficulty in water injection during the water injection development (water injection production refers to the injection of water into the reservoir from injection wells during the development process of an oil field; due to its good economic efficiency and high feasibility, it has become the main method of oil field development) process of the G block reservoir is an important problem to solve. Three cores of the G block are used as the object of this study, and the laser particle size test is conducted on the target core to obtain the particle size distribution of the core. X-ray diffraction mineral content analysis is used to obtain the proportion of different mineral contents. On this basis, online nuclear magnetic technology is used to carry out the research on the change of reservoir physical properties during the high-magnification water injection process. The experiment shows that three cores (cores 8-2, 16-1, and 9) are identified as medium sandy fine sandstone with silt (the three-level naming method was adopted and the name has been changed to medium sandy fine sandstone containing silt, because the proportion of fine sand is greater than 50%, the content of medium sand is between 25%~50%, and the content of silt is between 10%~25%), medium sandy fin sandstone containing silt, and silt fine sandstone, by laser particle size testing. Their clay mineral contents are 2.47%, 2.51%, and 4.76%, respectively; the permeability (water) of the three cores continues to decrease with the increase in water injection, but the nuclear magnetic porosity and the signal intensity of different fluids in the nuclear magnetic T2 and nuclear magnetic two-dimensional spectrum show different variation patterns with the increase in water injection. The clay minerals of core 8-2 and core 16-1 are relatively small. The nuclear magnetic porosity increases rapidly to the maximum value and then decreases slowly with the increase in water injection. The right peak signal intensity in the T2 spectrum rises first and then drops, while the clay mineral content of core 9 is relatively high. The change trend of nuclear magnetic porosity is firstly decreasing and then increasing, and the signal intensity of the right peak in the T2 spectrum decreases first and then increases. The research concludes that in the early stage of water injection, clay minerals undergo hydration and a small amount of particle migration; in the later stage of water injection, due to the scouring effect of water, the fine silt and clay minerals in the cement easily fall off and migrate to the pore throat to the block. Some damage to the pore throat leads to a decrease in permeability, thus affecting the development effect.

Active learning-based hydrodynamic shape optimization and numerical simulation of auxiliary structures for circular bridge piers

Cylinders as a common form of bridge piers are widely used in engineering practices, yet the hydrodynamic forces and local scouring of the cylinder due to the fluid flow cause significant concern about the functionality of circular bridge piers. In this paper, two novel auxiliary structural types are proposed for passive control of flow around bridge piers, and their optimal structural parameters are determined efficiently using a surrogate model-based hydrodynamic shape optimization framework. Specifically, a Kriging-based active learning algorithm is proposed for hydrodynamic shape optimization of auxiliary structures, which are placed at the rear and both the front and rear of a cylinder. The hydrodynamic performance of the circular bridge pier with the optimized auxiliary structures (F3 and F6) is investigated through 2D and 3D numerical simulations. The effectiveness of the optimized auxiliary structures in mitigating the adverse effect of local scouring around a cylinder is also revealed through a case study. Results indicate that the optimized auxiliary structures F3 and F6 can dramatically reduce the drag coefficient compared with the bare cylinder, i.e., with a reduction rate of 69.8% and 77.2%, respectively; and the reduction rate is more pronounced for the lift coefficient, i.e., with a reduction rate higher than 90% for both F3 and F6. The reduction of drag and lift coefficients is mainly attributed to the positive effects of the optimized auxiliary structures for adjusting the pressure distribution around the cylinder, elongating the free shear layer, improving the wake stability etc. Interestingly, the auxiliary structure F6 also exhibits a high potential to mitigate the scouring effect of fluid flow around a cylinder by decreasing the flow velocity and bed shear stress around the cylinder. However, it should be noted that placing the auxiliary structure at the rear of a cylinder (such as the auxiliary structure type F3) could introduce an adverse effect on reducing local scouring. This study provides valuable guidance for designing effective auxiliary structures for passive control of fluid flow around cylinders.

Influence of Free Water Droplets on Film Formation Under Point Contact Grease Lubrication

Abstract The influence of the grease-water two-phase emulsion on the bearing tracks on the film formation has been studied by carrying out optical interferometry experiments on a ball disk test rig to observe the dynamic film-forming behavior of lubricating grease under steady-state and micro-oscillation conditions. It is found that free water causes a brief rise in the grease film under steady-state conditions, specifically due to the grease-water phase connecting the oil reservoirs on both sides. The experiment determines that the state of the phase before entering the elastohydrodynamic lubrication (EHL) contact is water-in-oil. For the reciprocating motion and oscillation, the effects of the amount of free water and the length of the motion stroke are discussed in detail. It is found that for reciprocating movements with long stroke lengths, the effect of free water is summarized to enhance the fluidity of the fibrous mass of the grease thickener in the first few cycles of the movement. For shorter stroke lengths, the effect of free water is a scouring effect on the contact zone grease after 100 cycles. This paper provides new insights into the effects that cause water pollution to the point of contact lubrication during the transformation from reciprocating motion to fretting.

Effect of aspect ratio on PCM melting behavior in a square cavity

For latent heat thermal energy storage applications with phase change material (PCM) in restricted space, the factors such as container shape and heating surface must be considered. In this paper, a 2D square cavity PCM is taken as the research object, and the melting process of PCM with different square cavity aspect ratio (AR) was simulated under the condition of constant heat flux (60 W) at the left wall/bottom wall. An innovative and effective indicator, i.e., differential liquid fraction curve along with solid-liquid interface evolution is proposed to reveal the melting rate and typical phase change characteristics. The results show that the complete melting time increases with the increase of AR for both left wall and bottom wall heating conditions. For general applications, the bottom wall heating has a higher melting rate compared with left wall, especially for the cavity with AR >1. During the phase change process, the melting rate can reach its maximum value at the peak of differential liquid fraction curve with an observation of the longest solid-liquid interface. In addition, the melting pattern of high AR cavity during the latter part of the left wall heating process would become similar to the low AR case under the “scouring effect” of natural convection on the solid-liquid interface. For bottom wall cases, the natural convection waveform presents Rayleigh-Benard convection cells, and with the increase of AR, the irregularity of the vortex structure becomes more obvious. The results can provide useful guidance for accurately evaluating phase change characteristics and designing thermal energy storage system.

Effect of needled structures on in-plane tensile behaviors of 2.5D-Cf/Mg composites fabricated by the liquid-solid extrusion and vacuum pressure infiltration process

In this study, a novel magnesium matrix composite (2.5D-C f /Mg) with 2.5-dimensional needled carbon fiber preform and enhanced interlaminar shearing strength was prepared by the liquid-solid extrusion and vacuum pressure infiltration process. The microstructure and interlaminar shear strength (ILSS) of the 2.5D-C f /Mg were fully investigated. Meanwhile, tensile behaviors of the composites were also studied by the tensile tests along 0° / 90° and ± 45° fiber orientations. The results demonstrated that a high-quality infiltration in the composite preform could be realized at the 50 MPa pressure. The micro-cracks were more easily formed in the fiber directional change regions as well as in the vicinal areas of the needled fibers. The ILSS of the composites along ± 45° and 0°/90° shearing directions could reach to 64 MPa and 31 MPa respectively, which was attributed to the stabilizing effect of the needled structures along the thickness direction. The ultimate tensile strength (UTS) of the composites loaded along the 0° / 90° fiber orientation was 203 MPa, 40% higher than the matrix, in which the fracture mode of 0° fibers was interfacial debonding, whereas the 90° fibers were pull-out/rupture. Regarding the 45° loading direction, the peeling/shearing fracture mode was observed for the 45° fibers. The failures of the composites in the above two loading cases were mainly attributed to the damage of needled fibers to long fibers in non-woven cloth ply. • A novel 2.5D-C f /Mg composite was prepared by the liquid-solid extrusion and vacuum pressure infiltration process. • Gradually increasing the pressure, rather than suddenly, can reduce the scouring effect of the liquid alloy on fibers. • The interlaminar shearing strength of the 2.5D-C f /Mg in 45° direction is three times higher than that of the 2D-C f /Mg. • The UTS of the 2.5D-C f /Mg loaded along the 0°/90° orientation can be increased by 40% compared to the matrix. • The long fibers are damaged in needled regions, which reduces the strengthening abilities of the preform to the composite.

Experimental study of unsteady evolution characteristics of ventilated air mass on the cylinder surface

The ventilated air film covered by the surface of the underwater vehicle has an important influence on its hydrodynamic characteristics. In this paper, the development characteristics of the vehicle shoulder ventilated air mass under different environmental pressures and ventilation pressures are studied through experiments. The results show that in the ventilation process, the ventilated air mass reduces the scouring effect of the incoming flow on the exhaust holes and ensures the continuous discharge of the air flow. With increasing ventilation pressure, more gas in the ventilated air mass is entrainment into the ventilated cavity, which can improve the circumferential coverage of the ventilation cavity to the vehicle and increasing the size of the ventilation cavity by about 26.4%. When the ratio of ventilation pressure to environmental pressure is reduced, the occurrence of a re-entrained jet can be restrained, and the entrainment at the end of the ventilated cavity is weakened, which reduces the maximum size of ventilation cavity by about 61.5%.

Double diffusive dissolution model of UO2 pellet in molten Zr cladding

ABSTRACT The rapid dissolution of UO2 in molten Zr that could occur during fuel-cladding liquefaction at high temperatures and its kinetics were reformulated considering the convective mass transfer and the scouring effect at the UO2/Zr interface. The mass transfer coefficient of U was obtained as a correlation including the aspect ratio term by computational fluid dynamics (CFD) analysis. To explain the gap between the rapid dissolution rate observed in the experiments and the density-driven convective mass transfer, we introduced an idea in which the eutectic melting at the UO2/Zr interface promotes the solid oxide detachment owing to infiltration of the U-Zr-O liquid into the UO2 grain boundaries (scouring effect). The developed model was validated with UO2-Zr crucible experiments at 2273 and 2373 K. The calculated mass percentage ratios of U/Zr agreed with the measurements, and the transition timings from rapid dissolution stage were consistent with the metallographic observations.

Degradation of imidacloprid by fluidized-bed Fenton process

Wastewater containing imidacloprid (IMI), a new and widely used insecticide, can harm human health and aquatic organisms. To remove IMI, this study applied a fluidized-bed Fenton process due to its low capital cost. The degradation of IMI was investigated in a bench-scale reactor with synthetic wastewater. The studied conditions included pH 2–5, 1.0–10.0 mM Fe2+, 1.0–15.0 mM H2O2, 1.0 mM IMI, 100–400% bed expansion, 100 g of SiO2 and at 25 °C. Under the conditions of 3 mM Fe2+, 5 mM H2O2, 400% bed expansion, and pH of 3.0, degradation efficiencies of 97%, 41%, and 12% for IMI, COD, and TOC, respectively, were obtained within 45 min of reaction period while total iron removal reached 10%. Increasing bed expansion up to 400% did not have a significant impact on IMI degradation; however, it slightly deteriorated the total iron removal performance due to a scouring effect. At 100% bed expansion, total iron removal increased to 22%. The apparent rate law for IMI degradation by the fluidized-bed Fenton reactor under the studied conditions can be expressed as follows:d[IMI]dt(mM min-1) =-0.2218H2O20.1182Fe2+0.3717

Thermodynamic study on the natural gas condensation in the throttle valve for the efficiency of the natural gas transport system

The condensation of natural gas in the throttle valve may affect and even damage the downstream equipment, which threatens the safety and efficiency of the natural gas transport system. However, the mainly used method based on the isenthalpic hypothesis can hardly solve this problem. In this work, we developed a spontaneous condensation model of condensed natural gas with high temperature and pressure in the throttle valve using CFD modelling, which defined a hypothetical saturation line and introduced two empirical correction coefficients (α and β) into the nucleation and growth models. The scouring effect of natural gas on the valve was analysed, and the condensation characteristics and effect of latent heat of condensation on the flow were discussed in detail. The results show that the average absolute relative deviation (AARD) of the outlet temperature of the angle throttle valve (ATV) obtained by this model is 0.39% when α and β equal 10-10 and 10-2, respectively, while that without considering condensation is 1.13%. The inner wall near the throat of the straight-through throttle valve (STV) and ATV are susceptible to the scouring effect of natural gas. For STVs (type I, type II) and ATVs (type I, type II), after the droplet nucleation (1026 m−3·s−1) and growth (10-2 m/s) stage, the droplets are condensed and accumulated with a maximum liquid mass fractions of 3.12 %, 2.22 %, 3.42 %, and 3.24 %, respectively, then flow along the wall with a flow pattern of the annular flow and stratified flow. Compared to the case without condensation, the pressure and temperature at the condensation position increase slightly due to the latent heat of condensation, the condensation shock wave, while the velocity decreases slightly due to the momentum exchange between the natural gas and liquid phase.

Cutting Migration and Core Disturbance Caused by the Hydraulic Structure of Pressure- and Gas-Maintaining Coring Bits

Gas disaster prevention and control is essential to coal mine safety production, with accurate measurement of gas pressure and content being the challenging key aspect. Pressure- and gas-maintaining coring devices can characterize cores in situ to achieve this accurate measurement. As an important part of these devices, the hydraulic structure of the coring bit plays a decisive role in the migration, coring rate, and core disturbance of the bottom-hole cuttings, and studying this structure is thus of great significance. In this paper, the fluid simulation software FLUENT is used to carry out numerical simulation of the bottom-hole flow field to study the cutting movement and core disturbance caused by coring bits with different hydraulic structures. The results show that (1) the best nozzle azimuth angle of 75° is beneficial to bottom-hole cutting discharge and reduces the scouring effect of the drilling fluid on the core. (2) The larger the diameter of the nozzle of the coring bit is, the weaker the cutting removal ability of the drill bit and the smaller the cutting scouring effect of the drilling fluid. The optimal nozzle diameter is 12 mm. (3) Adding a sluice channel inside the water barrier ring can reduce the erosion of drilling fluid on the core. (4) Bits with a rectangular inner passage promote cutting migration. Field application results show that the designed coring bit performs well, and the research results can provide a reference for the structure optimization of coring bits for pressure and gas retention.

Layer-by-layer and non-halogenated solvent processing of benzodithiophene-free simple polymer donors for organic solar cells

High performance and easy-synthesis benzodithiophene (BDT)-free simple active layer materials, green non-halogen solvent processing and convenient device fabrication with batch-to-bath stability are all crucial to realize the industrial production of organic solar cells (OSCs) in the future. In this work, we develop two BDT-free polymer donors, PBTz-TC and PBTz-TTC, for green halogen-free solvent and layer-by-layer (LBL) processed high performance OSCs. The strong molecular aggregation of BTz units helps to improve the crystallinity and film-forming properties of the polymers, while the introduction of ester groups assists in enhancing the solubility of conjugated polymers in both halogen and non-halogen solvents and down-shifting the energy levels. The synergistic implementation of LBL method and orthogonal solvents can significantly reduce the scouring effect during the sequential deposition process, which is conducive to construct planar heterojunction. Due to the more planar conformation, PBTz-TTC possesses more robust film-forming property with superior corrosion resistance to the upper-layer than PBTz-TC. While, PBTz-TC better balances the independent film formation and moderate miscibility with IT-4F acceptor to favor stronger interaction at the donor/acceptor interfaces. Consequently, PBTz-TC shows much better performance than PBTz-TTC in both bulk heterojunction and LBL devices, ascribed to the better energy alignment, more favorable morphology and more efficient charge dynamic process. Notably, when treated with halogen-free solvent, an outstanding power conversion efficiency (PCE) of 12.81% with improved stability is achieved for PBTz-TC/IT-4F-based LBL device, which is the highest value of non-halogenated solvent processed devices based on benzodithiophene-free simple polymer donors. These findings provide a guideline for rational design of the environmental friendly simple polymer donor materials for further acceleration of the industrial production of OSCs.

Analysis on the Source Tracing and Pollution Characteristics of Rainfall Runoff in the Old Urban Area of Nanning City

Rainfall runoff is one of the important sources of urban river pollution. In order to understand the pollution characteristics of rainfall runoff, the synchronous sampling and monitoring of rainfall runoff in the old urban area of Nanning were carried out; the pollution condition, initial scouring effect, and pollution contribution ratio of different underlying surfaces under different rainfall conditions were analyzed; and the calculation method and influence factor analysis of initial scouring of runoff pollution were discussed. According to the underlying surface of the vegetable market in the old urban area, the selection standard and necessity of the underlying surface of rainfall runoff were discussed. The results showed that the average concentration (EMC) of COD and TSS in roads and vegetable markets were greater than those in green spaces and roofs in the runoff pollution of the old urban area of Nanning, and the EMC values of nutrient pollutants in field rainfall runoff were ranked in decreasing order as vegetable markets, green spaces, roofs, and roads. Under the condition of heavy rain, each underlying surface had an obvious initial scouring effect, the average value of initial scouring coefficient (b) was 0.67, and there were many pollutants transported by roads and green spaces at the initial stage. Under light rain and moderate rain conditions, there was no obvious initial scouring effect, and the average b values were 0.83 and 0.94, respectively. The b value calculated by the whole process was preferred for evaluating the scouring effect. Based on multivariate statistical analysis, the EMC value of TSS in road runoff was significantly positively correlated with the total rainfall duration (RD), and the EMC value of TN in green land runoff was significantly negatively correlated with the average rainfall intensity (ARI). Whether the vegetable market was considered as the underlying surface had a great impact on the calculation results of nutrient pollution load but had little impact on the calculation results of COD and TSS load. The difference percentage of nutrient pollution load under heavy rain reached 80%. Under this condition, the difference percentage of pollutant EMC between the road and vegetable market reached 1012%.

Effects of the Air Inlet Angle on the Combustion and Ablation Environment of a Hybrid Powder-Solid Ramjet

A hybrid powder-solid ramjet (HPSR) that combined the advantages of a solid rocket ramjet (SRJ) and a powder ramjet engine was investigated in this research. To improve the combustion efficiency and optimize the inner wall thermal protection of the afterburner, the effects of the air inlet angle on the combustion and wall ablation environment were studied. The standard k - ε model, the eddy-dissipation model (EDM), and the boron particle ignition and combustion model were adopted to simulate the two-phase flow in the afterburners with different air inlet angles (45°, 60°, 75°, and 90°). The results showed that the global flow field and the distribution of the vortexes in the afterburner that had a significant influence on the ablation environment of the inner wall and the combustion efficiency were determined by the impact effect and the squeezing effect of the ram air on the primary fuel gas, which was affected by the air inlet angle. As the air inlet angle increased, the total combustion efficiency of the four cases first increased and then decreased, reaching 80.38%, 81.64%, 84.34%, and 83.26% for angles of 45°, 60°, 75°, and 90°, respectively. At the same time, the inner wall ablation became more severe because both the erosion effect of the condensed phase particles and the gas-flow scouring effect were enhanced, and a large temperature gradient was generated on the inner wall. The study results can provide a reference for designing the air inlet angle of an HPSR.

Electroporation-coupled electrochemical oxidation for rapid and efficient water disinfection with Co3O4 nanowire arrays-modified graphite felt electrodes

Biologically unsafe drinking water occurs in developing regions lack of centralized water treatment plants. Herein, Co3O4 nanowire electrodes with Co3O4 nanowire arrays grown on graphite felt were fabricated and employed to construct a flow-through electrode system (FES) for rapid and efficient water disinfection, which achieved over 6.7-log E. coli removal under applied voltage of 2.5 V and flow rate of 65 mL/min (HRT ∼ 4.5 s) with energy consumption of 2.3 Wh/m3. The FES also achieved over 6.7-log removal at 2.5 V for the Gram-negative P. aeruginosa under ∼ 60 mL/min and for Gram-positive bacteria (E. faecalis and S. aureus) under ∼ 40 mL/min, and the Gram-negative bacteria were more vulnerable to FES disinfection than Gram-positive ones due to their larger sizes and thinner cell walls. In-situ sampling and live/dead backlight staining experiments revealed that pathogen inactivation mainly occurred on anode via the sequential adsorption, inactivation and desorption processes under the mass transfer forces of electric field attraction and flow scouring effect in porous electrodes. The disinfection mechanisms on the Co3O4 nanowire anode were recognized to be electroporation and electrochemical oxidation, and the pores generated by electroporation can provide diffusion channels for reactive species into the pathogen cells, promoting the disinfection performance.

Experimental Study on Temperature Field Evolution Mechanism of Artificially Frozen Gravel Formation under Groundwater Seepage Flow

Artificially ground freezing method is increasingly applied in formations with high permeability. The groundwater seepage flow should be considered because an excessive groundwater seepage flow would make the merging of the frozen wall challenging. Therefore, in this study, we investigate the temperature field and frozen wall merging characteristics at varying groundwater seepage flow rates in gravel formation. Results show that the heat exchange between the seepage flow and freezing pipes delays the merging of the frozen wall and reduces its total thickness. The groundwater seepage flow restricts the freezing of the upstream zone and accelerates the freezing of the downstream zone. The upstream and downstream temperature fields are symmetrical in nonseepage flow conditions but are asymmetrical in the presence of seepage flow. The merged frozen wall presents an arched shape and shifts to the downstream zone. The “scouring effect” and “water barrier effect” simultaneously act on the merging process of the frozen wall. The total thickness of the frozen wall decreases by more than 30% when the flow rate increases from 0 to 5.0 m/d. Optimising the layout of the freezing pipes in gravel formations is a reasonable solution for a safe and economical design.

Local flow convergence, bed scour, and aquatic habitat formation during floods around wooden training structures placed on sand-gravel bars

Riverine ponds, which are formed and sustained through sediment erosion and deposition, are key habitats for enhancing biodiversity in river reaches. The objective of this study was to understand the roles of traditional river-training wooden structures called “seigyu” on the formation of ponds on nonvegetated bars. Here, the spatial and temporal patterns of the flow and bedform coupled with pond formations for several flood events were assessed. The surface flow patterns were monitored by an unmanned aerial vehicle (UAV) and evaluated by large-scale particle image velocimetry (LSPIV); the maximum flow velocities were 1.3 m s−1 and 1.9 m s−1 during floods when seigyu units were partially and fully submerged, respectively. Although the overall mean flow velocity was greater for the latter events, the spatial variation in flow velocity and dissipation rate of turbulent kinetic energy (TKE) around seigyu was greater for the former events. Such flow patterns affected both bed formation and ecological habitats; ponds were formed at locations beside and behind seigyu, where the flow converged and bed scouring occurred during floods. The frequency and size of ponds around seigyu increased in the early half of the season, and they decreased in the other half when floods were greater in magnitude, which suggests that the bed scouring effect of seigyu was greater in flood stages with partial than fully submergence. Although the bar ponds lack shade to temper the effects of incident light and atmospheric conditions, the ponds displayed smaller daily oscillations in temperature than did the main river, probably due to hyporheic water supply to the ponds. Because many aquatic species cannot tolerate extremely high temperatures in summer, the generation and maintenance of deeper ponds by scouring with sufficient water exchange with the hyporheic zone can be key to enhancing colonization by various aquatic species.