Hydraulic Exchange Research Articles

Microplastic transport and ecological risk in coastal intruded aquifers based on a coupled seawater intrusion and microplastic risk assessment model

Seawater-groundwater interactions can enhance the migration process of microplastics to coastal aquifers, posing increased associated environmental risks. Here, we aim to analyze the relationship between seawater intrusion (SWI) and groundwater microplastic pollution in Laizhou Bay (LZB), which is a typical area of sea-land interactions. The results showed that modern seawater intrusion was the main process controlling the migration of microplastics. The detected microplastics in the study area showed a migration pattern from nearshore marine areas to groundwater aquifers along the SWI direction. In addition, the microplastics also reached the brine formed by palaeo-saltwater intrusion through hydraulic exchange between aquifers. By comparing the spatial distributions of different microplastic parameters, we found that nearshore fisheries, commercial, tourism, textile, and agricultural activities were the main sources of microplastics in groundwater in the study area. A risk assessment model of microplastics associated with SWI was further optimized in this study using a three-level classification system by assigning appropriate weights to different potential influencing factors. The results showed moderate comprehensive ecological risks associated with microplastics from seawater intrusion in the study area, with high microplastic enrichment risks. This study provides a scientific basis for future research on seawater-groundwater interactions and microplastic pollution in coastal regions.

Spatiotemporal profiles and underlying mechanisms of the antibiotic resistome in two water-diversion lakes

Human-induced interventions have altered the local characteristics of the lake ecosystems through changes in hydraulic exchange, which in turn impacts the ecological processes of antibiotic resistance genes (ARGs) in the lakes. However, the current understanding of the spatiotemporal patterns and driving factors of ARGs in water-diversion lakes is still seriously insufficient. In the present study, we investigated antibiotic resistome in the main regulation and storage hubs, namely Nansi Lake and Dongping Lake, of the eastern part of the South-to-North Water Diversion project in Shandong Province (China) using a metagenomic-based approach. A total of 653 ARG subtypes belonging to 25 ARG types were detected with a total abundance of 0.125–0.390 copies/cell, with the dominance of bacitracin, multidrug, and macrolide-lincosamide streptogramin resistance genes. The ARG compositions were sensitive to seasonal variation and also interfered by artificial regulation structures along the way. Human pathogenic bacteria such as Acinetobacter calcoaceticus, Acinetobacter lwoffii, Klebsiella pneumoniae, along with the multidrug resistance genes they carried, were the focus of risk control in the two studied lakes, especially in summer. Plasmids were the key mobile genetic elements (MGEs) driving the horizontal gene transfer of ARGs, especially multidrug and sulfonamide resistance genes. The null model revealed that stochastic process was the main driver of ecological drift for ARGs in the lakes. The partial least squares structural equation model further determined that seasonal changes of pH and temperature drove a shift in the bacterial community, which in turn shaped the profile of ARGs by altering the composition of MGEs, antibacterial biocide- and metal-resistance genes (BMGs), and virulence factor genes (VFGs). Our results highlighted the importance of seasonal factors in determining the water transfer period. These findings can aid in a deeper understanding of the spatiotemporal variations of ARGs in lakes and their driving factors, offering a scientific basis for antibiotic resistance management.

Spatial distribution characteristics and migration of microplastics in surface water, groundwater and sediment in karst areas: The case of Yulong River in Guilin, Southwest China

Karst regions, due to their unique topography, may be more susceptible to contaminants such as microplastics from other ecosystems. However, few studies reported the occurrence of microplastics in karst areas. Here, we investigated the abundance of microplastics in surface water, sediments and groundwater. In addition, their spatial distribution characteristics and migration were also analyzed in a typical karst area, Yulong River, Guilin, China. Microplastic pollution was found in the sediments, surface water and especially groundwater in Yulong River. The abundance of microplastics was 0–4 items/L, 247–1708 items/kg and 0–4 items/L in surface water, sediments and groundwater, respectively. Microplastics in surface water and groundwater were fiber-based, while those in sediments were fragment-based. Polypropylene (PP), Polystyrene (PS) and Polyethylene terephthalate (PET) are dominant microplastic types in Yulong River. Moreover, the abundance of microplastic pollution in different functional areas ranked as follows: living area > agricultural area > landscape area. Clustering analysis showed that disposable tableware and plastic bags used in tourism activities might be the main source of microplastics. More importantly, our findings suggested that microplastics in groundwater could be the result of hydraulic exchange between groundwater and surface water in karst areas, rather than soil infiltration. These findings provided us with a further understanding of the pollution of microplastics in karst rivers.

A comparative study of integral and coupled approaches for modeling hydraulic exchange processes across a rippled streambed

Although both are crucial parts of the hydrological cycle, groundwater and surface water had traditionally been addressed separately. In recent decades, considering them as a single hydrological continuum in light of their continuous interaction has become well established in the scientific community through the development of numerous measurement and experimental techniques. Nevertheless, numerical models, as necessary tools to study a wide range of scenarios and future event predictions, are still based on outdated concepts that consider groundwater and surface water separately. This study compares these “coupled models”, which result from the successive execution of a surface water model and a groundwater model, to a recently developed “integral model”. The integral model uses a single set of equations to model both groundwater and surface water simultaneously, and can account for the continuous interaction at their interface. For comparison, we investigated small-scale flow across a rippled porous streambed. Although we applied identical model domain details and flow conditions, which resulted in very similar water tables and pressure distributions, comparing the integral and coupled models yielded very dissimilar velocity values across the groundwater–surface water interface. These differences highlight the impact of continuous exchange across the interface in the integral model, which imitates such flow processes more realistically than the coupled model. A few decimeters away from the interface, modeled velocity fields are very similar. Since the integral model and the surface water component of the coupled model are both CFD-based (computational fluid dynamics), they require very similar computational resources, namely access to cluster computers. Unfortunately, replacing the surface water component of the coupled model with the widely used shallow water equations model, which indeed would reduce the computational resources required, produces inaccuracy.

Occurrence and distribution of Pharmaceuticals and Personal Care Products (PPCPs) in wastewater related riverbank groundwater

Pharmaceutical and personal care products (PPCPs) are among the most frequently reported groups of emerging contaminants in groundwater worldwide. PPCPs in rivers may infiltrate into groundwater through hydraulic exchange and potentially threaten drinking water safety and human health. In the present study, the occurrence and distribution of nine PPCPs in riverbank groundwater and adjacent rivers (distance up to 113 m) were investigated at four sites with different lithological features and permeabilities of aquifers in a city in North China. Seven of nine PPCPs were detectable in groundwater, ranging from <LOQ (limit of quantification) to 128 ng/L. N,N-diethyl-meta-toluamide (DEET), carbamazepine, and caffeine had the highest detection frequencies (>90%). The concentrations and major compounds in river water varied with the sampling location and water system distribution, resulting in distinct compositions of PPCPs in the groundwater at each site along with different lithology and hydrological conditions. The spatial distribution of PPCPs in riverbank groundwater was affected by the hydraulic connection between the groundwater and river and the lithology of aquifers. Direct hydraulic connection of a fine sand aquifer to the adjacent river caused a decrease in PPCPs with increasing distance. The results also suggested that sandy gravel aquifers had a lower capacity to attenuate PPCPs compared to that of fine sand. Significant correlations between PPCP concentrations and thirteen physicochemical factors of groundwater were discovered, including nitrate, potassium, and manganese. Overall, this study provides important evidence on the role of lithology and hydrological conditions on the composition, distribution, and influential physicochemical factors of PPCPs in riverbank groundwater.

Nitrate Removal and Woodchip Properties across a Paired Denitrifying Bioreactor Treating Centralized Agricultural Ditch Flows

Treatment of nitrate loads by denitrifying bioreactors in centralized drainage ditches that receive subsurface tile drainage may offer a more effective alternative to end-of-pipe bioreactors. A paired denitrifying bioreactor design, consisting of an in-ditch bioreactor (18.3 × 2.1 × 0.2 m) treating ditch base flow and a diversion bioreactor (4.6 × 9.1 × 0.9 m) designed to treat high-flow events, was designed and constructed in an agricultural watershed (3.2 km2 drainage area) in Illinois, USA. Flow and water chemistry were monitored for three years and the woodchip and bioreactor-associated soil were analyzed for denitrification potential and chemical properties after 25 months. The in-ditch bioreactor did not significantly reduce nitrate concentrations in the ditch, likely due to low hydraulic connectivity with stream water and sedimentation. The diversion bioreactor significantly reduced nitrate concentrations (58% average reduction) but treated only ~2% of annual ditch flow. Denitrification potential was significantly higher in the in-ditch bioreactor woodchips versus the diversion bioreactor after 25 months (2950 ± 580 vs. 620 ± 310 ng N g−1 dry media h−1). The passive flow design was simple to construct and did not restrict flow in the drainage ditch but resulted in low hydraulic exchange, limiting nitrate removal.

Multi Frequency Isotopes Survey to Improve Transit Time Estimation in a Situation of River-Aquifer Interaction

The Barthelasse alluvial aquifer is used to supply water to 180,000 inhabitants. The pumping field is located less than 200 m from the Rhône and is 100% fed by water from the Rhône, which makes it particularly vulnerable to any pollution from the Rhône. Between the Rhône and the pumping field is a Girardon unit, an arrangement that can be found regularly along the banks of the lower and middle reaches of the Rhône, and whose role is to stabilise the banks (alluvial deposits) and to facilitate river navigation. In order to know the transfer times between the Rhône and the pumping field, fortnightly monitoring was carried out over a hydrological year, as well as hourly monitoring during a flood in the winter of 2019. The Rhône shows a cyclicality in its isotopic signature with enrichment in heavy isotopes during the winter period, particularly during floods, and a depletion during the summer period. This variation is found well within the associated alluvial aquifer. The application of LPMs models showed that the average transfer time between the Rhône and the Girardon unit was 20 days and 50 days between the Rhône and the Barthelasse pumping. This study highlighted the importance of using several sampling frequencies to consider the diversity of hydrological situations. For the Rhône, event-based monitoring (flooding) proved to be relevant to account for isotopic variability throughout the year. This work also highlighted the impact of the disruption of hydraulic exchanges between the river and the water table caused by the presence of the Girardon unit in terms of the propagation of contaminants.

Investigation of Submarine Groundwater Discharge using Thermal Satellite and Radon mapping along the East Coast of the Tamil Nadu and Pondicherry Region, India

Submarine groundwater discharge (SGD) demarcated as a significant component of hydrological cycle found to discharge greater volumes of terrestrial fresh and recirculated seawater to the ocean associated with chemical constituents (nutrients, metals, and organic compounds) aided by downward hydraulic gradient and sediment-water exchange. Delineating SGD is of primal significance due to the transport of nutrients and contaminants due to domestic, industrial, and agricultural practices that influence the coastal water quality, ecosystems, and geochemical cycles. An attempt has been made to demarcate the SGD using thermal infrared images and radon-222 (222Rn) isotope. Thermal infrared images processed from LANDSAT-8 data suggest prominent freshwater fluxes with higher temperature anomalies noted in Cuddalore and Nagapattinam districts, and lower temperature noted along northern and southern parts of the study area suggest saline/recirculated discharge. Groundwater samples were collected along the coastal regions to analyze Radon and Physico-chemical constituents. Radon in groundwater ranges between 127.39 Bq m-3 and 2643.41 Bq m-3 with an average of 767.80 Bq m-3. Calculated SGD fluxes range between -1.0 to 26.5 with an average of 10.32 m day-1. Comparison of the thermal infrared image with physio-chemical parameters and Radon suggest fresh, terrestrial SGD fluxes confined to the central parts of the study area and lower fluxes observed along with the northern and southern parts of the study area advocate impact due to seawater intrusion and recirculated seawater influence.

Hydrochemical Zoning and Chemical Evolution of the Deep Upper Jurassic Thermal Groundwater Reservoir Using Water Chemical and Environmental Isotope Data

A comprehensive hydrogeological understanding of the deep Upper Jurassic carbonate aquifer, which represents an important geothermal reservoir in the South German Molasse Basin (SGMB), is crucial for improved and sustainable groundwater resource management. Water chemical data and environmental isotope analyses of δD, δ18O and 87Sr/86Sr were obtained from groundwater of 24 deep Upper Jurassic geothermal wells and coupled with a few analyses of noble gases (3He/4He, 40Ar/36Ar) and noble gas infiltration temperatures. Hierarchical cluster analysis revealed three major water types and allowed a hydrochemical zoning of the SGMB, while exploratory factor analyses identified the hydrogeological processes affecting the water chemical composition of the thermal water. Water types 1 and 2 are of Na-[Ca]-HCO3-Cl type, lowly mineralised and have been recharged under meteoric cold climate conditions. Both water types show 87Sr/86Sr signatures, stable water isotopes values and calculated apparent mean residence times, which suggest minor water-rock interaction within a hydraulically active flow system of the Northeastern and Southeastern Central Molasse Basin. This thermal groundwater have been most likely subglacially recharged in the south of the SGMB in close proximity to the Bavarian Alps with a delineated northwards flow direction. Highly mineralised groundwater of water type 3 (Na-Cl-HCO3 and Na-Cl) occurs in the Eastern Central Molasse Basin. In contrast to water types 1 and 2, this water type shows substantial water-rock interaction with terrestrial sediments and increasing 40Ar/36Ar ratios, which may also imply a hydraulic exchange with fossil formation waters of overlying Tertiary sediments.

A REGENERATIVE COOLING SYSTEM FOR THE CHAMBER OF A LIQUID-PROPELLANT ROCKET ENGINE WITH INTERCHANNEL COOLANT FLOW THROUGH A METAL MESH

The paper discusses a new method for regenerative cooling of the chamber of liquid-propellant rocket engines using the concept of interchannel coolant flow through a porous metal mesh made by vacuum diffusion welding of woven metal netting. It provides a theoretical rationale for switching from unidimensional (longitudinally channeled) flow to two-dimensional (interchannel) inter-mesh flow coolant through a porous mesh. It provides experimental data for hydraulic resistance and heat exchange in porous metal meshes. Based on the experimental data, a generalized criterial equation was obtained for surface heat release in the paths with interchannel two-dimensional intermesh coolant flow through metal mesh. The paper examines the efficiency of heat exchange in the paths with interchannel coolant flow. Key words: regenerative cooling, interchannel flow; vacuum diffusion technology, metal mesh; hydraulic resistance; heat exchange, heat exchange efficiency.

A regenerative cooling system for the chamber of a liquid-propellant rocket engine with interchannel coolant flow through a metal mesh

The paper discusses a new method for regenerative cooling of the chamber of liquid-propellant rocket engines using the concept of interchannel coolant flow through a porous metal mesh made by vacuum diffusion welding of woven metal netting. It provides a theoretical rationale for switching from unidimensional (longitudinally channeled) flow to two-dimensional (interchannel) inter-mesh flow coolant through a porous mesh. It provides experimental data for hydraulic resistance and heat exchange in porous metal meshes. Based on the experimental data, a generalized criterial equation was obtained for surface heat release in the paths with interchannel two-dimensional intermesh coolant flow through metal mesh. The paper examines the efficiency of heat exchange in the paths with interchannel coolant flow. Key words: regenerative cooling, interchannel flow; vacuum diffusion technology, metal mesh; hydraulic resistance; heat exchange, heat exchange efficiency.

Organic carbon and nutrients drive prokaryote and metazoan communities in a floodplain aquifer

In an alluvial aquifer in the River Fulda Valley (Germany) the influence of agricultural inputs on the subterranean physical, chemical and biological relationships was examined. A 40-year-old (1977–1981) comprehensive data set on the groundwater microbiome plus metazoa was now analysed for the first time in full (measurements for up to 4 years: hydrological, chemical, physical, prokaryote, and metazoa characteristics). Four hydrogeochemically different groundwater zones were identified across the floodplain. In addition, the prokaryote (Archaea and Bacteria) and metazoan communities differed among the four zones. The hydraulic exchange between the alluvial aquifer and the River Fulda influenced the sites closest to the river, leading to the highest prokaryote and metazoan biomasses at these locations. An organic carbon plume zone of anthropogenic origin exhibited high prokaryote abundances and production, which were higher than in the surrounding mixing zone. This mixing zone represented a transition area to the river-influenced sites as well as to the fourth zone, which was characterized by high nutrient levels from intense agriculture and which exhibited low prokaryote abundance and activity and intermediate metazoan abundance. Despite high prokaryote productivity, metazoa did not favor the organic carbon plume, due probably to low oxygen concentrations. At the sites, where metazoa occurred, their biomass corresponded mostly to about one hundredth of the prokaryote biomass. The main implication from this new analysis of an old data set is that even on a coarse taxonomical resolution, patterns emerge that show – in a geologically homogeneous area – an unprecedented complexity among different groundwater zones resulting from different external influences of natural as well as anthropogenic origin. Future studies need to ascertain an adequate temporal and spatial resolution.

Revealing the impact of water conservancy projects and urbanization on hydrological cycle based on the distribution of hydrogen and oxygen isotopes in water.

In recent years, the development and utilization of water resources have imposed great impacts on hydrological characteristics and ecological environment. In this paper, methods based on stable isotopes were used to analyze the cumulative effect of water projects and urbanization on the hydrological cycle in Qingbaijiang River Basin. Isotope evidence shows that the hydrological processes affected by water regulation and urbanized runoff generation differentiate greatly from the natural state. The annual mean isotopic values follow an order of groundwater > rainwater > river water. Consistent isotopic composition and variation trend between the near-bank groundwater and river water were only observed from May to late June 2018 and from February to April 2019 in the upper zone, indicating the dominant recharge of river to the groundwater. However, the isotopic variations between the two waters in the middle and lower zones suggested that the hydraulic exchange was limited, demonstrating the significant changes in river water level caused by the reservoir impoundment. The isotopic enrichment rate along the flow path is highest in January (0.0265‰/km), followed by October (0.0160‰/km), indicating the significant evaporation, while slight spatial changes in July (0.0027‰/km) reflected masked evaporation effect. This variability can be mainly attributed to the flow rate change and increase of water salinity in anthropic zones. Periodic regression analysis was employed to evaluate the difference in rainfall-runoff responses between hydrographic zones and estimate the mean residence time (MRT). Periodicity of isotopes in river water increased from upper to lower reaches with increasing R2 values from 0.04 in SW1 to 0.46 in SW8. The MRT grew shorter along the flow path from 870days in SW1 to 293days in SW8, reflecting accelerated rainfall-runoff process due to the increasing impervious surface area and drainage system. These results identify the sensitivity of stable isotopes to the land use changes, runoff generation, and topography, and have implication for the potential water and environmental risks. Based on these understandings, suggestions for sustainable water-environment management in urban and rural areas were proposed.

Study on the Improved Method of Urban Subcatchments Division Based on Aspect and Slope- Taking SWMM Model as Example

The storm water management model (SWMM) is widely used in urban rainfall runoff simulations, but there are no clear rules for the division of its sub catchment areas. At present, the popular sub catchment area division method takes the average slope as the slope parameter of the sub catchment area, which brings errors to the model in mechanism. Based on the current method, this paper proposes a new method to further subdivide the sub catchment area of the SWMM model, according to the Digital Elevation Model (DEM) data of underlying surface, slope and aspect information. By comparing with the previous methods, it was found that the division method based on slope and aspect can make the setting of model parameters and hydraulic exchange conditions clearer, and improve the accuracy of the model on a certain level.

STUDY OF THE PROPERTIES A FRAGMENT OF THE HYDRAULIC CIRCUIT OF THE SPACECRAFT, OBTAINED BY MEANS OF ADDITIVE TECHNOLOGIES

The article discusses the course and results of experimental work on the initial study of the possibility of using one of the varieties of additive technologies – the method of layer-by-layer selective laser melting (SLM) in the manufacture of elements of heat exchangers and hydraulic circuits of spacecraft. Traditional manufacturing techniques for hydro-control elements and spacecraft heat exchangers are based on machining and high-temperature vacuum soldering, leading to a long cycle and high manufacturing costs. As an alternative, the method of layer-by-layer selective laser melting can be considered as a manufacturing method using a three-dimensional model of the product and not requiring additional equipment. This method is based on sequential layer-by-layer fusion of a metal powder with previous fused product layers under the action of a laser beam forming a local region of liquid melt. The article describes experimental work to assess the possibility of using the selective laser melting method. Assessed weld-ability of a sample made by selective laser fusion technology with tips made by traditional technology. Directions for testing the method of selective laser sintering on real structures of heat exchanging units of spacecraft have been determined. A technique is proposed and the results of a study of a sample synthesized by selective laser sintering are presented. Based on the results obtained, an analysis is made of the prospects for using this method in the production of elements of hydraulic circuits and heat exchange units of spacecraft.

Evaluation of surface water and groundwater interactions in the upstream of Kui river and Yunlong lake, Xuzhou, China

Understanding the interaction between groundwater and surface water is of great significance to the rational development and utilization of water resources and the protection of ecological environment. Here we present a combination of several methods (radon balance method, EC conservation method and flow balance method) for evaluating the hydraulic exchange of groundwater and surface water in a small watershed of Kui river and Yunlong lake. The exchange fluxes of Kui river, Yunlong lake and groundwater were estimated by one-dimensional steady state model and box model. The results indicate that the lake water is mainly recharged by groundwater from the surrounding mountains and the lake renewal time is approximately 26 days. Meanwhile, multiple transformations occur between groundwater and river water, and river water leakage is dominant. The existence of several tributaries complicates the hydraulic exchange, and groundwater discharge is also evident. Furthermore, the advantages and disadvantages of these three methods were analyzed. This study successfully demonstrated that radon and EC as tracers can be used to estimate the exchange flux between groundwater and surface water, particularly in areas lacking conventional hydrological data. Combining these three methods, the hydraulic exchange between groundwater and surface water can be evaluated more effectively. The analysis of hydraulic exchange is also crucial for Xuzhou area where water resources are extraordinary scarce and polluted.

Evaporation-Induced Capillary Siphoning Through Hydraulically Connected Porous Domains: The Vedernikov–Bouwer Model Revisited

Evaporation-driven wicking of soil water through porous domains with contrasting hydraulic properties is studied analytically by conformal mappings and compared to numerical solutions. Initially, the connected rectangular domains are fully saturated. The first rectangle, Gp, is comprised of a coarse-textured porous medium with large permeability and low capillary forces. Evaporation-induced capillary flow pulls water horizontally across the domains to the surface of fine-textured rectangular domain, Gz, through an interfacial hydraulic exchange region that shrinks with time. The flow field in Gz is 2-D and is analytically expressed by the Vedernikov–Bouwer model that assumes a constant hydraulic conductivity for pressure heads higher than the air-entry value. The rate of 1-D drop of the phreatic surface in Gp is proportional to the evaporation rate (decreasing with time) from the Gz surface. The complex potential domain Gw “shrinks” with time, and at any time instance, it is conformally mapped onto Gz via two auxiliary planes using the Schwarz–Christoffel and Mobius transformations. The resulting Cauchy problem for an integro-differential equation with respect to an affix of the conformal mapping is solved using numerical algebra routines. A similar capillary coupled flow problem was numerically simulated using HYDRUS2D considering 2-D flow in both Gp and Gz. New insights into process dynamics are gained from a solution of an auxiliary optimization for a vertical imbibition in a column brought in contact with a water table where particle size (linking capillarity and permeability) is used as a control variable and counter-gravity front propagation dynamics as criteria.

Optimizing the riparian zone width near a river for controlling lateral migration of irrigation water and solutes

Riparian zones are essential to preserve water quality of rivers adjacent to large areas of irrigated agriculture. We used HYDRUS (2D/3D) to quantify the long-term (8 years) influence of crops (almonds, wine grapes and potato-carrot) irrigated with recycled water on water and solute exchange at the Gawler River interface in relation to vegetation buffer widths from 10 to 110 m. We found that under almond and annual horticulture the likely average annual water flow from the irrigated area to the river was nearly twice as much (2.1 and 1.8, respectively) that under wine grapes. The hydraulic exchange at river interface for different irrigated crops was found to be sensitive to the buffer widths. For wine grapes, almonds and annual horticulture, the average annual hydraulic balance reached an equilibrium at 20, 65 and 55 m buffer widths, respectively. Furthermore, for wine grapes, with a 20 m buffer width, the average annual load of salts became negligible. This study shows that buffer widths of 20, 60, and 40 m for irrigated wine grapes, almond, and annual horticulture, respectively, are needed to restrict the migration of salts to the river. Further refinements are possible by incorporating the influence of preferential flow paths, improved water stress response functions, and addressing the data limitations for calibration of the model for solute dynamics.

MATHEMATICAL LOW-REYNOLDS MODELING OF HEAT EXCHANGE IIN TURBULENT FLOW IN FLAT CHANNELS WITH TURBULATORS SYMMETRICALLY LOCATED ON BOTH SIDES

ObjectivesThe aim of the study was to simulate the heat transfer in flat channel with turbulators, symmetrically located on its both sides, depending on the channel's geometric parameters and the coolant flow modes followed by the verification of the obtained calculated data by the existing experiment.MethodsThe calculation was carried out on the basis of a theoretical method based on the solution of the Reynolds equations, closed with the help of the Menter shear stress transport model, by factored finite-volume method, as well as the energy equation on multiscale intersecting structured grids (Fast COmposite Mesh method, FCOM).ResultsA theoretical mathematical calculation model for intensified heat exchange in turbulent flow for a flat channel with turbulators, symmetrically located on both sides, depending on the channel's geometric parameters and coolant flow modes was generated. The calculation results of the intensified heat exchange in flat channels with double turbulators, depending on the determining parameters, are in very good agreement with the existing experimental material and have an undeniable advantage over the latter, since the assumptions made in their derivation cover a much wider range of determining parameters than the limitations of the experiments (Pr = 0.7 ч 100; Re = 103ч 106; h / dЭ= 0.005 ч 0.2; t / h= 1 ч 200). ConclusionAccording to the calculation results based on the developed model, it is possible to optimise the heat exchange intensification in flat channels with double turbulators, as well as to control the process of heat exchange intensification. The comparative calculations of the intensified hydraulic resistance and heat exchange for flat channels with two-sided symmetrical flow turbulators with corresponding data for round channels with turbulators were carried out and analysed. From the point of view of heat exchange intensification, all other conditions being equal, the reduction of a flat channel with two-sided symmetrical turbulators with respect to a round tube with turbulators takes place because a smaller increase in heat exchange is achieved with a greater increase in hydraulic resistance. It was established by calculation that the relative hydraulic resistance ξП/ ξT for channels with turbulators is always higher than for smooth channels; however, the relative heat exchange NuП/ NuT for channels with turbulators can be higher than for smooth channels. Therefore, there is an enhanced redistribution of the temperature drop over the channel section with an intensified heat exchanger. The developed theoretical method based on the solution of the Reynolds equations by the factored finite-volume method, combined with the energy equation on multiscale intersecting structured grids and closed by means of the Menter shear stress transport model, makes it possible, with reasonable accuracy, to calculate heat exchange coefficients and hydraulic resistance in flat channels of practically any forms of double symmetrically located flow turbulators.

Multi-tracer assessment of seasonal water source changes in coastal water systems along the southeastern coast of Ivory Coast (West Africa)

ABSTRACTProper management of coastal freshwater resources depends on an understanding of processes controlling their chemistry and seasonal flowpaths. A quantitative approach involving the coupling of major solutes and isotopes (δ18O, δ2H) of 180 samples in end-member mixing analysis (EMMA) was adopted to elucidate seasonal patterns of hydraulic exchanges amongst coastal waters along the Ebrié Lagoon catchment, Ivory Coast. The results show that the Ebrié Lagoon is a hydrologically dynamic system. In the dry season, evaporation and seawater inflow are the dominating processes, while in the wet season, river discharge is the main water source in the lagoon. Regional geology plays a significant role in aquifer recharge patterns. The Quaternary aquifer responds faster to precipitation, while the Mio-Pliocene aquifer is recharged indirectly via floodplain seepages. Salinization of over 90% of wells arises from hydrological exchanges with the Ebrié Lagoon. A diluted seawater effect was recorded in wells during the wet season owing to the relative increase in freshwater inflow.