Stream Surface Research Articles

Computation of EMHD ternary hybrid non-Newtonian nanofluid over a wedge embedded in a Darcy-Forchheimer porous medium with zeta potential and wall suction/injection effects

The field of engineering is witnessing an increasing number of applications for intelligent electromagnetic nano-coatings. These recent advancements serve as the impetus for an investigation into a theoretical and computational study of an unsteady electro-magneto-hydrodynamic (EMHD) incompressible two-dimensional tangent hyperbolic non-Newtonian ternary hybrid nanofluid boundary layer coating flow external to a two-dimensional porous wedge geometry adjacent to a Darcy-Forchheimer porous medium. Both aligned electrical and transverse magnetic field effects are included. The effects of zeta-potential and surface injection/suction are included. The ternary composite nanofluid comprises three nanoparticles ( A l 2 O 3 , T i O 2 and S i O 2 ) with aqueous base fluid ( H 2 O ) The governing conservation partial differential equations for continuity and momentum and associated boundary conditions at the wedge surface and free stream are transformed with appropriate similarity variables. The emerging ordinary differential nonlinear boundary value problem is numerically solved in MATLAB. Validation with earlier studies is included. A significant deceleration is induced in the flow of a ternary hybrid nanofluid with an increase in the electric field parameter. An increment in Falkner-Skan power-law constant (moving wedge angle parameter) boosts the local skin friction coefficient for both the ternary hybrid nanofluid (THNF) and unitary A l 2 O 3 nanofluid (UNF) cases. The flow is boosted with an increase in the power-law rheological characteristic, which ranges from shear-thinning n < 1 to shear-thickening n > 1.

Methodological proposal to remote detection and management of areas that are naturally vulnerable to floods

Floods are the main natural disasters in Brazil, causing loss of life and socioeconomic damage. This work proposes a model for the remote detection of areas that are naturally flood-prone due to the morphometric characteristics of their relief and drainage networks in the Alto Sapucaí River in Minas Gerais, Brazil. The morphometric parameters used were the drainage density, river density, relief ratio, roughness index, maintenance coefficient, form factor and stream surface length. The risk areas had a compactness coefficient of 0.75 and a form factor of 0.56, and both were considered a high risk for floods. The obtained results allowed the identification of a significant predictive equation that suggested a cutoff value of 3.82 for the discriminant function; areas with values under this cutoff were considered naturally more vulnerable to floods occurrences. These areas were corroborated with the emergency maps of the municipalities. The map obtained by the proposed model was compared with the Civil Defense map, and its accuracy, according to the Kappa coefficient, was 0.83, indicating strong similarity between the two maps.

Monitoring the dynamics of acid mine drainage affected stream surface water hydrochemistry at Jaintia Hills, Meghalaya, India.

Streams are pristine natural life-thriving water sources for people living in the mountainous proximity of NE India, where water scarcity is a common occurrence in most villages and towns. In the last few decades, factors like coal mining had drastically reduced the usability of stream water in the region; as such, an attempt has been made to assess the spatiotemporal variation of stream water chemistry affected by acid mine drainage (AMD) at Jaintia Hills, Meghalaya. The water variables were subjected to a multivariate statistical technique of principal component analysis (PCA) to understand their condition at each sampling point while comprehensive pollution index (CPI) and water quality index (WQI) was incorporated to assess the quality status. Maximum WQI was recorded in S4 (541.14) during summer, while minimum value was estimated in winter at S1 (14.65). Throughout the seasons, the WQI revealed "Good" quality in S1 (unimpacted stream), while the impacted streams (S2, S3, and S4) exhibited a "Very poor" to "Water unsuitable for drinking" status. Similarly, in S1, the CPI showed a ranged value of 0.20 to 0.37, presenting a water quality status of "Clean to Sub-Clean," whereas, CPI of the impacted streams indicated "Severely polluted" status. In addition, PCA bi-plot presented higher affinity of free CO2, Pb, SO42-, EC, Fe, and Zn in AMD-impacted streams than in unimpacted streams. The result demonstrates the environmental issues induced by coal mine waste and in particular, stream water being severely affected by AMD in mining areas of Jaintia Hills. Thus, measures to stabilized the mine repercussions and cumulative effects on the water bodies need to be formulated by the government, as stream water will remain the primary water source for the tribal communities in this region.

Importance guided stream surface generation and feature exploration

Exploring flow features and patterns hidden behind the data has received extensive academic attention in flow visualization. In this paper, we introduce an importance-guided surface generation and exploration scheme to explore the features and their connections. The features are expressed as an importance field, which can either be derived from a scalar field or be specified as a flow pattern. Guided by the importance field, we sample a pool of seeding curves along the binormal direction and construct stream surfaces to fit the regions of high- importance values. Our scheme evaluates candidate seeding curves by collecting importance scores from the curve and corresponding streamlines. The candidate seeding curves are refined using the high-score segments to identify the optimal surfaces. Comparative visualization among different kinds of flow features across time steps can be easily derived for flow structure analysis. In order to reduce the visual complexity, we leverage SurfRiver to achieve clearer observation by flattening and aligning the surface. Finally, we apply our surface generation scheme guided by flow patterns and scalar fields to evaluate the effectiveness of the proposed tool.

Generalized magnetostatic target field method for shielded magnetic field coils in a separable coordinate system.

A theoretical method is described to analytically calculate a pair of surface current densities, which produce a desired static magnetic field in one region of the space and zero magnetic field in another. The analysis is based on the known relationship between a surface current density and a stream function, the equivalence of stream functions and surface magnetic dipole density, and the scalar potential representation of the associated magnetic field in free space. From these relations, we formulate the magnetostatic problem, which is often treated as a vector field problem, as a scalar field problem in which a two-dimensional scalar field (stream function) is related to a three-dimensional one (magnetic scalar potential) via the differentiation of the electrostatic Green's function 1/|r-rs|. It is shown that, in a coordinate system in which a separated form of the Green's function exists (separable coordinate system), there exists a simple relationship between a harmonic component of a stream function and a harmonic component of the magnetic scalar potential. The method is applied to calculate idealized surface current patterns for actively shielded, linear gradient field coils in the Cartesian, cylindrical, and spherical coordinates.

Stream nitrate enrichment and increased light yet no algal response following forest harvest and experimental manipulation of headwater riparian zones.

Disturbances to forested watersheds often result in increases of nutrients and light to nearby streams. Such changes are generally expected to produce a shift to a more autotrophic aquatic ecosystem, with measurable increases in algae, and associated implications for food webs and fisheries. Although this paradigm is widely established, results from our 10-year study (2007-2016) in 12 headwater streams and four sites downstream in the Trask River Watershed (Oregon, USA), did not concur. In 2012, one watershed was thinned, three were clearcut harvested with variable buffers and three with uniform riparian buffers. After harvest, light to the stream surface significantly increased at the three watersheds with variable buffers while dissolved inorganic nitrogen (DIN) significantly increased in all of the clearcut harvested streams. Despite the increase in DIN and light, algal standing stocks and chlorophyll a concentrations did not significantly increase. The common assumption of increased autotrophic responses in stream food webs following increases of nitrogen and light was not supported here. We postulate the co-limitation of nutrients, driven by low phosphorus concentrations, which unlike DIN did not increase post-harvest, and the characteristics of the algal community, which were dominated by low light adapted diatoms rather than green algae, contributed to our findings of no responses for standing stocks of epilithic algae or concentrations of chlorophyll a. The inclusion of multiple statistical analyses provided more certainty around our findings. This study documents responses to current forest practices and provides cautionary information for management and restoration activities aiming to increase fish abundance and standing stocks by opening riparian canopies and adding nutrients.

Efficiency of Magnetically Treated Water on Decontamination of Chlorpyrifos® Residual: A Practically Water Insoluble Organophosphate in Brassica chinensis Linn.

Chlorpyrifos® (Thaion Agro Chemical CO., Ltd. Yannawa, Bangkok 10120, Thailand) (an almost water insoluble organophosphate insecticide) has been extensively used, resulting in the presence as a surface contaminant in foodstuffs, surface streams and soils. It is thus critically essential to develop methods to degrade or remove and eliminate this pollutant from environments. Chlorpyrifos® has very limited solubility and so it is primarily a contaminant of the surfaces of foodstuffs. We present the effect of magnetically treated water (MTW) to remove Chlorpyrifos® contaminating in Brassica chinensis Linn., a commonly eaten vegetable in Thailand and globally. Samples were washed with magnetically treated water (MTW) prior to detection of Chlorpyrifos® with GC-MS (Gas Chromatograph-Mass Spectroscopy). Chlorpyrifos® was removed by a factor of 413 times (−99.7%) by MTW compared to the un-washed sample, whereas the removal factor for tap water washing was only 9.6 (−89%). The MTW washed material easily passed safety criteria (Maximum Residue Load—MRL), but the tap water washed vegetables did not do so reliably. Although Chlorpyrifos® may be banned in many countries, the binding properties of replacement organophosphates are likely to be similar, and so our results should generalize to pesticides in the organophosphate chemical class that are not readily water soluble.

Identify nitrogen transport paths and sources contribution in karst valley depression area using isotopic approach

Karst groundwater provides drinking water for a quarter of Earth's population. However, in intensive agricultural regions worldwide, karst water is commonly polluted by nitrate (NO3−), particularly in the valley depression areas with well hydrological connectivity. The valley depression aquifers are particularly vulnerable to anthropogenic pollution because their pipes and sinkholes respond quickly to rainfall events and anthropogenic inputs. Identifying nitrate sources and transport paths in the valley depression areas is key to understanding the nitrogen cycle and effectively preventing and controlling NO3− pollution. This study collected high-resolution samples at four sites including one surface stream–SS, two sinkholes–SH and reservoir–Re, during the wet season in the headwater sub-catchment. The chemical component concentrations and stable isotopes (δ15N–NO3– and δ18O–NO3–) were analyzed. The stable isotope analysis model in R language (SIAR) was used to quantitatively analyze the contribution rate of NO3− sources. The results showed that the down section site (Re) has the highest [NO3−–N], followed by SH and the lowest SS. The sources calculation of SIAR demonstrated that, during the non-rainfall period, soil organic nitrogen was the primary source of the down section site, followed by fertilizer and the upper reaches sinkholes. During the rainfall period, fertilizer was the primary source of the down section site, followed by soil organic nitrogen and from upper reaches sinkholes. Rainfall events accelerated fertilizer–leaching into the groundwater. Slight denitrification may have occurred at the sampling sites but the assimilation of Re and SH could not occur. In conclusion, agricultural activities were still the primary influencing factor of [NO3−–N] in the study area. Therefore, the focus of NO3− prevention and control in the valley depression areas should consider the methods and timing of fertilization and the spatial distribution of sinkholes. To reduce nitrogen flux in the valley depression area, effective management policy should consider, e.g., prolongation of water residence time by wetland, and blocking nitrogen loss paths by sinkholes.

Pre-arranged sequences of micropillars for passive mixing control of water and ethanol

Microfluidic reactors have enabled the continuous conduction of chemical reactions with exceptional control of fluids and operating conditions. To enhance reagent mixing in laminar flow conditions, the effective strategy of adding cylindrical obstacles (i.e., pillars) in the mixing channel is appealing. Indeed, they can passively extend the contact surface of the incoming fluid streams, where diffusion and reaction occur. From our previous work, optimized sequences of pillars in a T-microchannel – that differ in diameter and position – can significantly improve the mixing for single-phase flow (i.e., mixing of miscible fluids of similar density and viscosity). However, real-world mixing applications often require the merging of fluids with significantly different fluid properties before, during, and after mixing. Hence, further investigations are required to unveil efficiency and robustness in these more complex practical mixing conditions. We jointly carried out experiments and numerical simulations on miscible fluids in an optimized sequence of pillars called IAF. Our analysis shows how the fluid velocity (i.e., the Reynolds number, Re) and the pillar configuration affect the formation of horseshoe vortices, which we consider crucial for water mixing when 1<Re<100. Then, we analyzed water–water and water–ethanol mixtures at Re=40 to observe how fluid properties alter the flow passively controlled by the pillar sequence. Eventually, the analysis extends within Re=10–100, showing efficiency and pressure drops of optimized designs that depend on the evolution of physical properties. These findings provide insights into the predictions of confined fluid flow around obstacles and its optimization for engineering processes, e.g., nanoparticle precipitation.

Mercury in multimedia system of Itacaiúnas Basin, Brazilian Amazon: An integrated approach to understand its distribution, origin, and ecological risk

This study presents the first integrated study on total Hg (THg) level in surface soil (SS), bottom soil (BS), stream sediments (SD), lake sediments (LS), stream water (SW), and lake water (LW) of Itacaiúnas River Watershed (IRW), Brazil to investigate the source and distribution of Hg in different environmental media considering contrasts of geological domains and sub-basins and its potential ecological and human risk. Hg content in most of the soils and sediments were above the upper crustal average values (56 μg/kg), however, when compared to the legal limits set by the Resolution CONAMA (Conselho Nacional de Meio Ambiente: soil 500 μg/kg; sediment 486 μg/kg), only 1 soil sample from Parauapebas sub-basin and 4 sediment samples from Violão Lake exceeded the limit. None of the SW and LW samples (<0.2 μg/L; CONAMA limit for Class II freshwater) are markedly contaminated by Hg. The SS and BS show similar contents and spatial distribution of Hg with higher contents being registered mostly in the Itacaiúnas and Parauapebas sub-basins, which are closely correlated with SD. This suggests that Hg levels are largely of geogenic origin and anthropogenic effect is highly limited. Principal Component Analysis (PCA) results show that Hg is strongly associated with total organic carbon (TOC), loss on ignition (LOI), and SO3, indicating organic matter as the main factor controlling the distribution of Hg and this is the major cause of accentuated Hg enrichment in lake sediments. The ecological risk index revealed a low pollution risk for most of the solid samples, except 11% LS and <1.5% SS and SD samples, which registered moderate risk. Health risk assessment indicated no adverse non-carcinogenic health effect on either adults and children in terms of Hg contamination. This information will be useful for Hg risk assessment in the Carajás region and future environmental research in this direction in the Amazonia.

Temperature responses vary between riffle beetles from contrasting aquatic environments

Organisms living in environmentally stable ecosystems are hypothesized to exhibit narrow environmental tolerance ranges; however, previous experiments testing this prediction with invertebrates in spring habitats are equivocal. Here we examined the effects of elevated temperatures on four riffle beetle species (family: Elmidae) native to central and west Texas, USA. Two of these, Heterelmis comalensis and Heterelmis cf. glabra are known to occupy habitats immediately adjacent to spring openings and are thought to have stenothermal tolerance profiles. The other two, Heterelmis vulnerata and Microcylloepus pusillus are surface stream species with more cosmopolitan distributions and are assumed to be less sensitive to variation in environmental conditions. We examined performance and survival of elmids in response to increasing temperatures using dynamic and static assays. Additionally, changes in metabolic rate in response to thermal stress were assessed for all four species. Our results indicated that spring-associated H. comalensis is most sensitive while the more cosmopolitan elmid M. pusillus is least sensitive to thermal stress. However, there were differences in temperature tolerances among the two spring-associated species: H. comalensis had relatively narrow thermal tolerance in comparison to H. cf. glabra. This could be due to differences in the climatic and hydrological conditions in the geographical regions which the respective riffle beetle populations reside. However, despite these differences, H. comalensis and H. cf. glabra showed a dramatic increase in their metabolic rates with increasing temperatures indicating that these species are indeed spring specialists and likely have a stenothermal profile.

S2 Stream Surface Approximation Approach for Quasi Three-Dimensional Turbine Time-Marching Design Method

A fast and reliable turbine design method is necessary in aeroengine development practice. As Q3D time-marching method iteration process can be time consuming and unstable, a novel S2 stream surface approximation approach coupled with flow tangential condition is proposed to reduce the computation requirement. The surface approximation uses a quadratic function of axial coordinate x to formulate distribution of circumferential coordinate θ . The flow tangential condition inherently represents inviscid blade force effect, and the formulation of inviscid blade force is not needed. A corresponding personal Q3D turbine computer code was developed, which was suitable for both design and analysis applications. The Q3D design method solves Euler’s equation through third-order Godunov’s scheme with TVD property in finite volume method. Semi-implicit Crank-Nicolson’s temporal scheme is implemented. Profile, secondary, and tip clearance energy loss models are added to predict viscous losses. Blade row exit swirl is required as the convergence target for Q3D design. A two-stage turbine and a single-stage high-pressure turbine were designed and analyzed by the Q3D method. Viscous 3D CFD was utilized to check design performances. The results showed that the Q3D method could finish a design case within 1 min. At design point, Q3D mass flow rate error was no more than 1.25%, expansion ratio error was no less than -0.022, and isentropic efficiency error was no more than 0.37 percentage points. The Q3D design method is fast and accurate. The stream surface approximation approach is suitable for Q3D design and analysis.

Documenting the impacts of increasing salinity in freshwater and coastal ecosystems: Introduction to the special issue

Documenting the impacts of increasing salinity in freshwater and coastal ecosystems: Introduction to the special issue

SCREENING OF PIGMENT PRODUCING FUNGI FROM FLORAL WASTE AS A PROSPECTIVE ANTI-MICROBIAL TOOL

Floral waste management in Indian purview is seemingly diffused. The main contributors of floral waste are religious offerings spanning across PAN India level. Certainly, floral waste appropriately referred to as temple waste is either dumped into adjoining surface waters and streams or is being piled up with municipal solid waste for its further processing. Predominantly, floral waste consists of Tagetes sp. Our preliminary study is inspired by the fact that floral waste has an immense potential to develop value added products through microbiological interventions by utilizing the natural attenuation property of autochthonous microbes. This led to planning of bio-prospective study aimed to screen indigenous pigment producing fungal isolates from Tagetes sp. with diversified applications in healthcare, textile, food and pharmaceutical industries. Two promiscuous isolates with pigment producing efficacy were screened by Solid State Fermentation (SSF) and Submerged Fermentation (SmF) and were identified as Mucor sp. and Penicillium sp. Briefly, an attempt was made to ascertain anti-microbial efficacy of Bacillus sp. by Disc Diffusion Assay through Minimum Inhibitory Concentration (MIC) against pigment produced by both the fungal isolates with Chloremphenicol, Amoxycillin and Vancomycin as positive controls. A significant (p

There is No Such Thing as a Quick Fix: Travel Times to Subsurface Drains

Highlights Bromide tracer was applied at different distances from subsurface drains to assess travel times and preferential flow. Some bromide arrived at the drain outlet with the first water flow after application, indicating preferential flow. Total time for “cleanout” of bromide from the plots varied with drain spacing and relative distance from the drain. When changing management practices, the full impact of the new system will not be reflected until several years later. Abstract. Subsurface “tile” drains are an important water management practice for many productive agricultural soils, but drains also deliver nitrate-nitrogen and other soluble chemicals from the bottom of the rootzone to surface ditches and streams. Many studies have focused on determining different ways to reduce the delivery of nitrate and other chemicals to subsurface drains while still providing adequate drainage for crop production. One important consideration in such studies that is often overlooked is the response time of drainage outflow to changes in management at the soil surface. Drains integrate flow from distances immediately adjacent to the drain all the way to the midplane between parallel drains, which means changes in management will not be fully reflected in drainage waters for months to several years, depending on the drainage intensity, soil characteristics, and precipitation. This bromide tracer study was conducted at the Southeast Purdue Agricultural Center (SEPAC) in Indiana, USA. Bromide tracer was applied at the beginning of the drainage season (November) at different distances from the drains on multiple plots of different drain spacings. The bromide concentration in the drainflow was monitored over the next five years to determine breakthrough curves and the amount of time required to flush the bromide from the system. The initial breakthrough of bromide occurred during the first appearance of drainage after application, regardless of the location of the bromide strip, suggesting some preferential flow was occurring. This was further investigated with comparison to curves of theoretical travel time following Kirkham’s analytic solution for flow to a tile drain. The full transport of the bulk of the chemical took 2-3 years, but varied greatly among the different treatments, reflecting the longer travel times for locations further from the drain. Keywords: Keywords., Drainage, Preferential flow, Streamlines, Subsurface drainage, Travel times.

Microplastic pollution in vulnerable karst environments: case study from the Slovenian classical karst region

Since the start of mass production of plastic materials more than a century ago, the problem of accumulating plastic waste in the environment has reached epic proportions. Recently, the problem of smaller plastic particles (microplastic, MP) in the environment has become a widely studied topic, but the amount and types of MP in karst environments are still poorly known. Thus, the objective of this study was to collect and analyse samples from various karst habitats and to try and determine the scope of pollution in karst springs that are in part used as sources for drinking water. Of the potential pollution sources, we sampled rainwater, two discharges from wastewater treatment plants, and a leachate from a landfill. We conducted polymer analyses of potential MP particles using FTIR-ATR. The results showed that eight samples from the Postojna region (Postojna–Planina Cave System, rainfall sample and surface streams) contain up to 444 MP particles per m3. However, 32 samples taken from the Škocjan–Kačna–Jama 1 v Kanjaducah Cave System contain up to 60,000 MP particles per m3, with the bulk of particles found in the sediment samples from Škocjan Caves – Kačna Cave System. Samples from Postojna region contained mostly PET, PU and PA polymers, with a minor inclusion of polymers of plastic sponge used for cleaning. Samples from Škocjan region contained mostly PP, PET and PE polymers, with some of PA and PU polymers. Sediment samples contained much less MP particles compared to water samples, which indicates fast transport through karst aquifer.

Diversity and Differentiation of Duckweed Species from Israel.

Duckweeds (Lemnaceae) are tiny plants that float on aquatic surfaces and are typically isolated from temperate and equatorial regions. Yet, duckweed diversity in Mediterranean and arid regions has been seldom explored. To address this gap in knowledge, we surveyed duckweed diversity in Israel, an ecological junction between Mediterranean and arid climates. We searched for duckweeds in the north and center of Israel on the surface of streams, ponds and waterholes. We collected and isolated 27 duckweeds and characterized their morphology, molecular barcodes (atpF-atpH and psbK-psbI) and biochemical features (protein content and fatty acids composition). Six species were identified-Lemna minor, L. gibba and Wolffia arrhiza dominated the duckweed populations, and together with past sightings, are suggested to be native to Israel. The fatty acid profiles and protein content further suggest that diverged functions have attributed to different haplotypes among the identified species. Spirodela polyrhiza, W. globosa and L. minuta were also identified but were rarer. S. polyrhiza was previously reported in our region, thus, its current low abundance should be revisited. However, L. minuta and W. globosa are native to America and Far East Asia, respectively, and are invasive in Europe. We hypothesize that they may be invasive species to our region as well, carried by migratory birds that disperse them through their migration routes. This study indicates that the duckweed population in Israel's aquatic environments consists of both native and transient species.

Interpretation of ametryn biodegradation in rice based on joint analyses of transcriptome, metabolome and chemo-characterization

Agrochemicals such as pesticide residues become environmental contaminants due to their ecotoxic risks to plant, animal and human health. Ametryn (AME) is a widely used farmland pesticide and its residues are widespread in soils, surface stream and groundwater. However, its toxicological and degradative mechanisms in plants and food crops are largely unknown. This study comprehensively investigated AME toxicology and degradation mechanisms in a paddy crop. AME was freely absorbed by rice roots, translocated to the above-ground and thus repressed plant elongation, and reduced dry weight and chlorophyll concentration, but increased oxidative injury and subcellular electrolyte permeability. Analysis of the transcriptome and metabolome revealed that exposure to AME evoked global AME-responsive genes and step-wise catabolism of AME. We detected 995 (roots) and 136 (shoots) upregulated and differentially expressed genes (DEGs) in response to AME. Metabolomic profiling revealed that many basal metabolites such as carbohydrates, amino acids, glutathione, hormones and phenylpropanoids involved in AME catabolism were accordingly accumulated in rice. Eight metabolites and twelve conjugates of AME were characterized by HPLC-Q-TOF-HRMS/MS. These AME metabolites and conjugates are closely related to DEGs, differentially accumulated metabolites (DAMs) and activities of antioxidative enzymes. Collectively, our work highlights the specific mechanisms for AME degradative metabolism through Phase I and II reactive pathways (e.g. hydroxylation and dealkylation), with will help develop genetically engineered rice used to bioremediate AME-contaminated paddy soils and minimize AME accumulation rice crops.

Multiphase numerical simulation of exergy loss and thermo-hydraulic behavior with environmental cosiderations of a hybrid nanofluid in a shell-and-tube heat exchanger with twisted tape

In the foreseeable future, heat exchangers will continue to play an important role in environmental management and have numerous applications, their geometry has been the subject of interest for many researchers. The main goal of this research is improving the heat exchangers' thermal performance and investigating the exergy using SIMPLE algorithm, k-w turbulent model and the Eulerian- Eulerian method for multiphase flow. Hence, the operation of Al2O3CuO-water hybrid nanofluid in a 3D shell-and-tube heat exchanger is simulated to enhance the contact surface of hot and cold fluid streams using computation fluid mechanics techniques. Reynolds number is 10,000, 15,000, 20,000, and 25,000 and volume fraction of nanoparticle is 2–6%. The innovations of this research are the use of the use of hybrid nanofluid and turbulator. The hybrid nanoparticles are employed to enhance the thermal conductivity and the turbulator is utilized to increase flow turbulence. The results demonstrated that the hybrid nanofluid, the turbulator, and high amount of Reynolds number can have a remarkable impact on increasing the thermal performance. The obtained results revealed that a 6% increment in hybrid nanoparticles volume fraction and an enhancement in Reynolds number from minimum to maximum lead to a 126% improvement in thermal performance in the presence of the turbulator. Lastly, environmental damage, energy consumption, and emissions are reduced by nanofluids.

The effect of reservoir expansion from underground karst cave to surface reservoir on water quality in southwestern China.

Due to the excessive exploitation of traditional energy sources, the attention paid to water energy has increased in recent years. As an important means to effectively utilize water energy, reservoirs play an important role in drinking water, irrigation, flood control, and drought resistance. However, utilizing reservoirs often led to water quality issues resulting from the interaction of nutrients and hydrological conditions, especially due to the special structure of karst areas. Because of the change of hydrological conditions by the effect of dam construction, the dynamic of water quality will be more obvious in karst areas with a fast exchange of water and contaminants between underground and surface streams. In the present study, the change in water quality of a karst reservoir, the Muzhu Reservoir in the Houzhai Catchment, was studied. Long-term monitored datasets (1981-2002) and water quality datasets of more recent years were used to assess the effect on the water quality of reservoir expansion from the underground reservoir to the surface reservoir in a karst area. Long-term series datasets had shown that the hydro-chemistry type had been changed from HCO3-·SO42--Ca2+·Mg2+ type to HCO3--Ca2+ type in the short term after the reservoir's expansion. The chemical components of water originating from a rock background reduced markedly after the reservoir's expansion, whereas the content of the anthropogenic contribution in the water decreased after the expansion, except in April and May. Isotopic characteristics showed that δ15N-NO3- and δ18O-NO3- values were positively correlated before and after the reservoir expansion, but the slope of the linear regression before the expansion was 0.34, while the slope of the linear regression before the expansion was close to 0.7. This indicated that although denitrification and assimilation may occur simultaneously after the reservoir's expansion, the role of denitrification on nitrate removal decreased, which resulted in nitrate accumulation in the karst reservoir. The results highlighted that nitrate accumulation in karst reservoirs should be monitored to decrease nitrate concentration in the future.