Changes In Flow Regime Research Articles

Impacts of dike systems on hydrological regime in Vietnamese Mekong Delta

Abstract This paper examines the impact of the dike systems on river flows in the Vietnamese Mekong Delta (VMD). The study combined a hydrological change index method and the Mann–Kendall test to assess the temporal dynamics of both discharge and water levels along the main rivers of the VMD. Results highlight that the system of rivers and canals helps facilitate waterway traffic and drainage during the flood season. However, the low elevation of the delta has created conditions suitable for saline water to increasingly penetrate upstream during the dry season. Observed changes in the hydrological indicators at the upstream stations of Tan Chau (Mekong River) and Chau Doc (Bassac River) are not only due to the dike system but also upstream alterations to the flow regime. More research is needed to consider the various drivers of flow-regime change associated with natural and human activities both inside and outside of the study area.

Hydraulic Sensitivity and Stomatal Regulation of Two Desert Riparian Species

AbstractCharacterizing plant response to water stresses is among the keys to understanding ecosystem functions. Despite increasing recognition of plant hydraulic and stomatal dynamics not captured by isohydricity, defined as the sensitivity of leaf water potential Ψl to soil water potential, it remains unclear which plant traits are critical to improved representation of plant hydraulic and stomatal dynamics beyond isohydricity, especially in dryland ecosystems. Here, we examine eco‐physiological responses of two typical desert riparian species, Populus euphratica and Tamarix ramosissima, to hydro‐meteorological variations. Based on measured hydraulic traits, variations of Ψl, leaf gas exchange, groundwater table, and soil moisture across vertical profiles, we investigated how subsurface hydraulic conditions control plant hydraulic sensitivity and stomatal regulation. We found both species exhibited anisohydric behaviors, which, however, were attributed to drying soil at different depths because of root distributions. The similar anisohydric behaviors also led to distinct stomatal regulation, due to the impact of atmospheric dryness decoupled from soil moisture and different sensitivities of stomatal conductance (gs) to Ψl. The latter was found to be dynamic throughout the growing season, which dominated the seasonal variation of gs and thus should not be neglected. The results suggest similar anisohydric behaviors could imply diverging hydraulic behaviors as the evaporate demand and flow regime change. Root morphological trait and stomatal sensitivity to Ψl are identified as keys to characterize responses to water stresses in desert riparian ecosystems. Our findings highlight that improved measurements and representations of these traits could contribute to better assessments of dryland ecosystem functions.

A deep learning-based method for mapping alpine intermittent rivers and ephemeral streams of the Tibetan Plateau from Sentinel-1 time series and DEMs

Flow regime changes of Intermittent Rivers and Ephemeral Streams (IRES) can serve as an indicator under global warming, yet the distribution of IRES is rarely extracted at the alpine catchment scale due to their narrow water surface and the heavy cloud contamination on the Tibetan Plateau. Here, a new two-stage method using the deep learning model is proposed for Mapping alpine IRES from Sentinel-1 time series and Digital elevation models (MISD). Firstly, the median images of cross-orbits double-periods (i.e., the flowing period and the drying-up period of alpine IRES) Sentinel-1 time series are input to the deep learning model to synoptically extract alpine IRES in mixed pixels under the heavy cloud contamination. Secondly, the deep learning-based output is corrected by the critical drainage accumulation derived from digital elevation models to remove the disturbance of the non-channelized overland flow on upland. The MISD method was first applied to an alpine catchment, namely the Duodigou Catchment, and then was assessed in the whole Lhasa River Basin. The results showed that the application of cross-orbits double-periods Sentinel-1 time series in the deep learning model is helpful in handling the mixed-pixel problem. And the critical drainage accumulation correction further improves the deep learning-based output with F2 (the metric that measures precision and recall of model) and the median Euclidean distance error of 0.72 and 64.0 m, respectively. Subsequently, the newly proposed MISD method outperforms other river extraction methods in alpine IRES mapping with higher F2 (increased by 0.5) and lower median Euclidean distance error (decreased by 145.7 m). Moreover, the MISD method is characterized by the capability for detecting narrower or lower flow IRES with river width > 1.7 m and discharge >2 L/s, which is significantly ignored in the current global water products. Furthermore, the MISD method successfully recognizes most of the channelized IRES from permanent rivers in the whole Lhasa River Basin through essential training. Therefore, the MISD method is a powerful tool for monitoring the changes of IRES induced by the glacier retreats or the permafrost degradation, etc., on the warming Tibetan Plateau.

Research on the characteristics of cavitation flow and pressure load during vertical water exit of different head-shaped vehicles

It is a complex process for a vehicle to emerge from the water. During this period, the cavitation flow state and the load on the vehicle change sharply, which has a great impact on the movement of the vehicle. It is necessary to study the cavitation flow state and loading characteristics during the process of water-exit. At present, the research on this aspect at home and abroad mostly focuses on the use of commercial software or self-written programs to simulate the pressure distribution on the surface of the extended vehicle and the flow field at the head of the vehicle during the process of water exit. However, there is a lack of relevant experimental data on the changes of pressure and cavitation flow regimes during the water-exit process of different head-shaped vehicles. The research on water plumes mostly focuses on the interaction between the explosion bubble and the free surface, but there is little research on the water plumes generated when different head-shaped vehicles exit the water. Based on this, this paper designs a set of surface pressure load measurement system for the water-exit process of the vehicle under the decompression environment, and designs and processes the vehicle with different head types such as cone head, hemispheric head, and swelling conical head. The flow characteristics and pressure loads of different head-shaped vehicles in the initial stage, development stage and collapse stage of cavitation were studied. The study found that the shape of the vacuoles in the initial stage, the development stage and the collapse stage of different head-shaped vehicles is quite different, and the change process of the pressure is also different; In addition, the water plumes generated when the vehicle is out of water can be divided into three categories according to the collapse method, and the collapse time of each type are also different.

Evaluation of narrowed weld pool shapes and their effect on resulting potential defects during deep penetration laser beam welding

This study presents mechanisms of the evolution of a narrowed region in the weld pool center during deep penetration laser beam welding. In numerous numerical studies presented in this study, it was also found that the local reduction of the weld pool size can cause detrimental effects on the melt flow behavior and the resulting properties of the welds. A particularly large influence of this effect was identified in three aspects. First, the local variation of the solidification sequence of the weld pool causes an increase in the hot-cracking susceptibility due to a locally delayed solidification. Second, it was proven that a change in the local length and width of the weld pool is associated with an adverse impact on the potential flow routes of the molten material that induces stronger local variations of its solidification. Thus, the element mixing, e.g., during the welding with filler materials, is blocked. This leads to a nonhomogeneous chemical composition of the final weld and can cause undesired effects on the final material properties. Finally, another observed effect is related to the reduced ability of process pores to reach the top surface. As this type of porosity is usually produced around the keyhole tip, the change of the fluid flow regime above this area plays a significant role in determining the final path of the pores until the premature solidification in the middle of the weld pool captures them. This study summarizes mainly numerical results that were supported by selected experimental validation results.

Flow reversal inside a drop evaporating on a soluble substrate

During the evaporation of a water drop on a salt substrate, the inner flows experience a reversal, their inward motion being progressively replaced by an outward one. The transition between the two flow directions proceeds via the migration of a stagnation line, where the radial velocity is zero, from the periphery to the center of the drop. This reversal is a consequence of the change of flow regime inside the drop, from a Marangoni flow to a coffee-stain capillary flow, due to the progressive homogenization of the concentration.

Hydraulic properties of capillary mats used for low-energy cooling and heating of buildings

The article deals with the hydraulic behaviour of capillary mats most often used for high-temperature cooling or low-temperature heating of buildings. On the basis of experimental measurements, the dependences of the pressure loss of the capillary mats on the water flow rate in relation to their geometrical arrangement were obtained. The measured values were compared with the manufacturer's data and it was found that the measured values differ significantly. The CFD simulation method was used to model the pressure losses of the capillary mats. The main emphasis was placed on the friction losses in the capillary during laminar fluid flow and local losses during the branching and coupling of the flows for the changing flow regime. Based on the simulation calculations, the dependences of the local loss coefficient during the flow diverging and converging and the relationship for the calculation of the coefficient of friction in the unsteady region of laminar flow were obtained. Based on the obtained results, an analytical computational model was built to determine the pressure losses of the capillary mats based on an iterative and approximate solution. The example shows the differences between the different approaches to the solution. The results of the presented model are compared with the experimentally obtained data. The article presents the share of partial components in the total pressure loss of the mats.

Addressing climate uncertainty and incomplete information in transboundary river treaties: A scenario-neutral dimensionality reduction approach

• We enumerate 25,000 + solutions for the Ganges water sharing treaty, renewed in 2026. • Hierarchical clustering identifies redundant objectives and governing trade offs. • Pareto-optimization & scenario-neutral analysis finds climate-robust treaty solution. Climate change will alter the flow availability and expected water allocations in international river treaties, many of which were designed using historical flow records. Effective transboundary treaties should anticipate these concerns and seek to satisfy the priorities of all riparian countries while being robust to impending changes in climate. This task is complicated by the fact that specific objectives associated with each party’s priorities are not necessarily common knowledge (framing uncertainty), and the direction, amplitude and effect of long term changes in hydro-climatic drivers can be highly uncertain (climate uncertainty). We frame the design of a transboundary treaty as a multi-objective optimization problem. We use hierarchical clustering to address problem-framing uncertainty by identifying the subset of objectives associated with the governing trade-offs imposed by the bio-physical characteristics of the shared river system. We then carry out a scenario-neutral climate sensitivity analysis to identify climate-robust Pareto-optimal treaty solutions. We illustrate the approach for the Ganges water agreement, which is due to be renewed in 2026. Based on an enumerated population of 25,121 feasible treaty solutions, we identify governing objectives and 16 treaty solutions that are Pareto optimal under most considered combinations of changes in sea level and dry season flow regime. This work provides a path towards improving transboundary allocations for the Ganges water treaty and, more broadly, a template to support transboundary cooperation over shared international rivers.

Intense droughts affect temporal stability of Amazonian stream fish assemblages

Abstract The frequency and duration of exceptionally intense droughts is increasing as a consequence of ongoing climate change in many regions of the planet. Lower rain fall in some regions and the increasing in the use of water resources by human populations is increasing the number of water bodies experiencing drying processes. Such changes in ecosystem dynamics have direct impacts on biological communities. Here, we investigated the temporal structure of fish assemblage in terra‐firme (i.e., non‐floodable) streams in the Eastern Brazilian Amazon by sampling over three seasonal cycles (2012, 2013, 2014). The research investigated the temporal dynamics of the ichthyofauna of streams that experienced temporary flow interruption in 2012; using the ichthyofauna of perennial streams (not interrupted by the effects of drought) as controls to determine the effects of flow cessation on the temporal structure of fish assemblages and their recovery after drought. The species composition of perennial streams remained stable over 3 years (2012, 2013, 2014), not differing between the dry and rainy periods. On by contrast, the species composition of the streams that temporarily dried changed after the flow interruption event. Responses to the temporary flow interruption were not uniform among species, with some increasing in abundance after the event while others decreased. The species whose abundance increased immediately after flow interruption tended to return to initial conditions in the third year of sampling, which might be related to low resource availability in those streams. Species whose abundance decreased tended to remain in low abundance, possibly as a result of local/regional rarity of these species, hindering population restoration processes. The dissimilarity in fish assemblage composition (based on the relative abundance of species) between sampling events revealed that the changes caused by the temporary flow interruption were significantly greater than the temporal changes recorded in perennial streams. Overall, the results indicated that intense drought events may alter fish species composition in terra‐firme streams and that such changes may persist for some years. Our results also provide evidence that the responses of fish species to flow regime change are not uniform, highlighting the need for a better understanding of the basic biology of fishes to predict the effects of increased climate disturbances more accurately in aquatic communities. Untangling the effects of natural cyclical factors from the effects deriving from unpredictable extreme events is crucial to better predict the impacts of global climate change on the structure of biological communities.

Rheological behaviour of dilute soil-water mixtures: role of interactions from colloidal and non-colloidal particles

The rheological behaviour of dilute soil-water mixtures, such as hyperconcentrated mixtures and interstitial fluids in debris flows, can significantly affect the flow dynamics of flow-type landslides. These mixtures often contain clay, silt, and sandy particles. Despite great efforts, the effects of soil type and texture on the rheological behaviour of these mixtures are still not well understood. To tackle this issue, an experimental investigation is carried out using a narrow-gap rotational viscometer to evaluate the interactions from colloidal (clay) and non-colloidal (silt and sand) particles and possibility of flow regime change. The flow curves of dilute mixtures are determined with and without a dispersion agent. A functional curve between spindle speed and Reynolds Number or Froud Number is proposed to distinguish different flow regimes in the narrow-gap rotational viscometer. Results demonstrate the applicability of the Bingham model for describing the bulk rheological behaviour of dilute mixtures. The mixture viscosity governs the contribution of the hydrodynamic effects from all particles, while the yield stress governs the contribution of the colloidal effects from colloidal particles. Results also reveal that for dilute mixtures containing particles up to medium sand size, the main cause of the flow regime change is the flow boundary conditions.

Unraveling the role of operating pressure in the rapid formation of Cu-BDC MOF via a microdroplet approach

A microdroplet-based spray process has been recently developed for the synthesis of metal–organic frameworks (MOFs) which features a short processing time and scalable manner. In this process, atomized microdroplets of the MOFs precursor solution undergo well-controlled physiochemical transformations with each droplet serving as a microreactor. Droplet transformation is closely related to the flow patterns of the spray system. A conventional spray system is operated at atmospheric pressure (under the continuum flow regime). By lowering the operating pressure, the spray system is transitioned to a free-molecular flow regime, where the transport phenomena of the microdroplet become distinct due to the discrete surrounding gas. It is hypothesized that the MOFs formed under this condition could have unique morphological and structural features. Nevertheless, this topic has rarely been investigated. This work studies the formation of the copper 1,4-benzenedicarboxylate (Cu-BDC) MOF under changing flow regimes by modulating the operating pressure. Specifically, changes in crystal size, morphology, and orientation, as well as surface oxidation state, are observed with decreasing operating pressure. Heat and mass transfer calculations, accounting for the transition of flow regimes, suggest that these variations are related to different evaporation rates of the microdroplets. Our study also suggests that the dissociation of solvent molecules from Cu-BDC under sub-ambient pressure increases open metal sites which lead to a strong CO2 binding affinity. This work illustrates the synthesis of MOFs under substantially low operating pressures and offers many new opportunities in the controlled synthesis of MOFs for selective gas adsorption.

Feasibility study to increase the reactor power at natural convection mode in Tehran Research Reactor (TRR) through a hybrid thermal-hydraulic simulation and analysis using the RELAP5 code and Computational Fluid Dynamic (CFD) modeling by ANSYS-FLUENT

Some irradiating applications can be used economically at a low power range and energy consumption. Moreover, removing the decay heat by the natural convection plays a very crucial role in Design Basis Accidents (DBAs) such as Loss of Flow Accident (LOFA) or Station Black Out (SBO). In such cases, the reactor can be operated by natural convection instead of forced convection. Such an operation needs careful thermal-hydraulic analyses to confirm nuclear safety. In this paper, Tehran Research Reactor (TRR) is chosen as the case study. A careful hybrid methodology is taken into account for safety analyses and visualizing the fluid streamlines and temperature profiles assuming both short-term and long-term cooling terms and conditions. Firstly, the RELAP5 code is used for the relevant simulation and safety analysis. Moreover, it is also used to trace any perturbation or oscillation and for the hot spot responses due to the flow regime changes and the reactor dynamic. Then the ANSYS-FLUENT is used for further Computational Fluid Dynamic (CFD) simulation of natural convection flow in detail. A modified 3-D porous media is modeled to simulate and observe the overall behavior of the reactor core in the reactor pool for long-term operations. The Boussinesq approximation is assumed for the buoyancy force. The pressure drop along the porous media is replaced with an accurate model of the Standard Fuel Element (SFE). Moreover, the k- ω turbulence model is also included in the Navier-Stokes equations to fix approximations. The relevant correlations have been also chosen for the heat transfer from the reactor pool to ambient air by convection, radiation, and surface evaporation. Finally, an accurate 2-D model of the hot-channel is also used for the accurate single-channel analysis regarding short-term operating conditions. Presented velocity vectors and temperature profiles depict the domain and behavior of the natural convection in both fuel channels and the reactor pool as well. Concerning both short-term and long-term issues, results are quite promising to increase the maximum operating limit of the natural convection mode from 100 kW to 200 kW. Moreover, regarding short-term operations or emergency conditions, this limit can be also increased to 400 kW due to the safety limit of 378 K for the maximum permissible fuel cladding temperature to protect the fuel from long-term corrosions. Keeping this limit also prohibits any perturbation or oscillation as well.

Computational study of subcooled water injection into steam line: effect of Reynolds number on flow transition to study condensation induced water hammers

Abstract The direct contact condensation (DCC) of steam in subcooled water encounters in wide range of the industrial applications. On one side, it is an efficient and rapid, mass and heat transfer phenomenon. But, on the other side, it may generate condensation induced water hammers (CIWH) events which may cause high pressure peaks resulting in severe damage to the mechanical systems. This computational study intends to explore the underlying physics of CIWH events while injecting subcooled water into steam filled horizontal pipe section. The Reynolds number is varied from, Re w = 60,750 to 646,900, to study the flow regimes (stratified and slug), onset of CIWH and local flooding conditions. The results have been compared with the published data and found in good agreement. It has been observed that for Re w = 182,300, flow remains stratified. However, the flow regime changes from stratified to slug flow at Re w = 303,850–646,900, possibly due to the onset of CIWH. Extensive steam pockets have been observed at Re w = 303,850, which may be considered as onset of CIWH. Local flooding condition is also started at Re w = 303,850 and is observed to be shifted upstream with the increase in Reynolds number. This study is considered to be useful for the safe design and economical operation of the relevant systems in nuclear and other related industry.

Environmental flow methodology approach based on ecological impact assessment for hydroelectric power plants and hydraulic structures on stream ecosystems in Turkey.

Use areas of streams such as agricultural irrigation, drinking water and energy are important for people's needs. The uncontrolled increase in all these demands on the streams leads to a change in flow amount and regime thereof over time, causing the stream and dependent ecosystems to be adversely affected. The hydrological system and the stream ecosystems may not be significantly affected, with the removal of some water and/or the use of the stream for energy such that a stream does not differ substantially from the natural flow regime in the past. In this context, environmental flow assessments are considered, which are called the flow that should be provided in order to minimize the environmental impacts specific to each stream's flow basin characteristics and its ecosystem. The most reliable method is to determine the environmental water need in different stream systems with a holistic ecological impact assessment, as well as different scientific assessment methods. This study reveals environmental flow methodology studies, which have been revealed by integrated ecological impact assessment aiming to determine the principles and methods suitable for the geographical and climatic conditions of Turkey in order to minimize environmental risks for the design of river type hydroelectric power plants and water retention structures such as ponds and dams, which have been intensively planned, constructed and used for hydroelectric energy especially after 2010 in Turkey, and assessment of the "environmental flow" results established by these studies.

Impact of Hydrologic Alteration on Brazos River Pelagophilic Minnows

AbstractThe lower Brazos River has been profoundly altered since the construction of multiple impoundments. The resulting river regulation poses problems for organisms adapted to a natural flow regime and is thought to play a major role in the imperilment of seven native minnows (Smalleye Shiner Notropis buccula, Sharpnose Shiner N. oxyrhynchus, Shoal Chub Macrhybopsis hyostoma, Plains Minnow Hybognathus placitus, Ghost Shiner N. buchanani, Silverband Shiner N. shumardi, and Chub Shiner N. potteri) that synchronize spawning during high flow pulses. Four of the species are presumably extirpated from the region, but their declines and losses differed across time. To address potential reasons for species' declines, we assessed pre‐ and postimpoundment changes in flow regime from five gauging stations across the lower Brazos River to identify river flow characteristics that depart from the natural preimpoundment flow regime. For the seven minnows, there was a strong relationship between the year they were last documented and their historical percentage occurrence in the lower river. Differences in flow duration curves and flow behavior were generally consistent with position in the drainage such that the greatest changes occurred in the highly fragmented upper reach of the study area. However, extensive hydrologic alteration was apparent at all five localities. The extirpated species in the lower Brazos River may have been more sensitive to altered flow regimes and accompanying geomorphic change or were population sinks dependent on recolonization or drift from upstream populations. The relationships between pelagic‐broadcast‐spawning minnows and the flow regime are complex, and nonflow variables, such as population fragmentation, thermal regimes, geomorphology, and larval habitat dynamics, should be considered in environmental flow assessments to aid our understanding of biodiversity loss in this group of species across the North American plains. Managing flows to support species that depend on natural flow regimes will require not only a better understanding of their reproductive life histories, but also the ecology and physiology of early life history stages.

Measurement of the coefficient of seepage characteristics in pore-crushed coal bodies around gas extraction boreholes

Gas extraction is a form of energy extraction. The seepage and transport of gas during extraction is complex. The accurate determination of its permeation parameters is an important technical parameter. A tri-axial permeation test of the crushed grain media was designed to determine the permeation pattern of gas fuels within the crushed coal around the borehole. The resistance to gas fuel seepage was explored. The results show that: the pore structure formed by the crushed coal grains will be compressed and closed again under three-dimensional stress. The process of deformation and destruction of crushed coal grains can be divided into three stages: when the grains are subjected to a force of 1.2 kN–1.4 kN, the grains may compress each other to form a colloid. The coefficient of resistance is dependent on the permeability of the crushed coal sample, and the non-Darcian phenomenon caused by inertial loss during permeation can be characterized by the distribution of Re values f = 149.1/Re + 1.5. The two coefficients of the quadratic term in the Forchheimer equation change dynamically as the flow regime changes. This result can provide a theoretical basis for the efficient extraction of gas resources.

Accumulation of Heavy Metals in Dam Sediments Effects on Plankton Productivities of the Arabian Gulf

Purpose: Metal accumulation in sediments threatens adjacent ecosystems due to the potential of metal mobilization and the subsequent uptake into food webs. Dams produce important changes in flow regime and sediment deposition. When inundation starts with the building of dams, water surface area increases, flow rate decreases, and sediment carried by the valleys is deposited in the dams. However, there is a lack of research on the chemical properties of deposited sediment in dams. Method: We aimed to fill this gap in the literature by providing valuable data on the particle size and heavy metal of sediment in different dams. Therefore, the aim of this study conducted within the Northern emirates of United Arab Emirates dams, to estimate heavy metal concentration of sediment, including particle size distribution. A total of eight sediment samples from each dams were collected and analyzed for heavy metals. The concentrations of Iron (Fe), Nickle (Ni), Copper (Cu), Zinc (Zn), Lead (Pb), Cadmium (Cd), Chromium (Cr), and Cobalt (Co) in sediment samples were determined using Atomic Absorption Spectrophotometer (AAS). Results: The concentrations of the heavy metals studied in the sediment samples were accumulated as Fe> Ni> Cr> Zn> Co> Pb> Cu. The concentrations of Ni and Cr have exceeded the threshold in the sediments of in line with W.H.O standards. Cadmium was not detected in soil, while other elements detected were in trace amount below the allowable limits in soil. The consideration of environmental factors is required to develop pollution managements and assess environmental risks for dam sediments. Conclusion: The studies conducted provide background to a discussion on the extent of anthropogenic pressure on the natural environment in the Arabian Gulf, further underlining the relationship between retention of sediments in the dam and the increase in heavy metal contamination of bottom sediments and to the marine environment which effects possible to plankton productivity.

Small Run-of-River Dams Affect Taxonomic and Functional β-Diversity, Community Assembly Process of Benthic Diatoms

Being increasingly constructed worldwide, dams are a main driver of flow regime change and biodiversity decline. Although small run-of-river dams have exceeded the number of large dams, their impacts on taxonomic and functional β-diversity as well as community assembly process of aquatic organisms have been largely neglected. Ninety sites within twenty three small run-of-river dams in the Xiangxi River were selected, and the hydrological and physicochemical variables for each site were measured. We analyzed the traits and β-diversity of benthic diatoms, and explored the key driving mechanism of benthic diatom community assembly. Our results indicated that the construction of small run-of-river dams could affect the β-diversity of benthic diatoms and the mechanism of community assembly. Specifically, we found that small run-of-river dams could change the relative contribution of nestedness components to the trait-based β-diversity of benthic diatoms, but generally the taxonomy-based β-diversity was relatively higher than the trait-based β-diversity. Furthermore, the community assembly process of benthic diatoms was also affected. In areas affected directly by small run-of-river dams, dispersal assembly was the key mechanism for community assembly. Compared to unregulated habitats, the dispersal assembly process between the impacted and the unregulated habitats has been enhanced. We advocate that this study can be expanded to other organisms (such as macroinvertebrates, phytoplankton, fish) in future to fully understand impacts of small run-of-river dams on biodiversity from a multi-trophic level aspect. Based on our results, we suggest that maintaining genetic and ecological connectivity based on an effective impact assessment in dry seasons is a potential solution to mitigate the impacts of such dams, as key to adaptive management and sustainability.

Heat transfer to a sphere immersed in a fluidized bed of coarse particles with transition from bubbling to turbulent flow regime

The present work concerns an experimental study on heat transfer in gas-solid fluidized bed of coarse (Geldart D) particles to a larger immersed sphere at high superficial velocities from 2 to 5.5 U mf. The heat transfer coefficient was determined by measuring the temperature of the test sphere during its heating in a fluidized bed in the temperature range of 65–175 °C. The test spheres of different sizes and different materials were utilized. For the given gas-particles system the flow regime changes from rapidly growing bubbles to turbulent fluidization at superficial velocity U c ≈ 3Umf. It has been found that in rapidly growing bubbles regime, the heat transfer coefficient is higher for smaller test spheres while it is almost independent of the superficial gas velocity. In turbulent regime, the heat transfer coefficient increases with increase of gas velocity while the size of the test sphere exhibits less influence. In the rapidly growing bubbles regime, experimental data for heat transfer coefficient can be predicted adequately with correlation of Scott et al.. For the turbulent flow regime a new correlation for prediction of the heat transfer coefficient has been proposed.

Parametric study and optimization of oil drop process in a co-flowing minichannel

Droplet formation in two-phase flow inside minichannels, has been the subject of many studies in recent years. In this work, the process of droplet formation in a co-flowing minichannel has been investigated using the volume of fluid method and the influence of effective parameters such as dispersed phase velocity continuous phase viscosity, interfacial tension, contact angle and dispersed density has been investigated. When the velocity reaches 0.013 m/s the flow regime changes from dripping to jetting. The accuracy of the simulation results was confirmed by comparing against laboratory data. The error is about 5% for droplet size and about 4% for sphericity. A Box-Behnken statical model was developed to study the interaction of parameters and to optimize the process of droplet formation in co-flowing minichannel. At the optimum conditions, the droplet size was measured as 2.34 mm, and the sphericity was calculated as 0.94. Using the analysis of variance and by calculating the p-value, the significant system parameters were determined. It is worth noting that an accurate statistical model can prevent lengthy and costly CFD simulations.