Fast Flow Conditions Research Articles

The effect of slow adsorption of phosphate on its transport during the infiltration process in saturated agricultural soils

ABSTRACT Assessment of phosphorus (P)-infiltrating croplands is essential for the preservation of the water environment. It has been pointed out that a huge discrepancy lies in the different evaluation methods of P adsorption, such as batch experiments and column experiments, which makes it difficult to demonstrate P mobility under flow conditions. The objective of this study was to evaluate the applicability of the convective-dispersion equation using the parameters of the Langmuir-type isotherm obtained from batch experiments with different reaction times: the adsorption capacity of soil (q max) = 0.112 (g kg−1) for a Gray lowland soil with 24 h reaction time, q max = 0.484 (g kg−1) for an Andosol (volcanic ash soil) with 24 h reaction time, and q max = 1.17 (g kg−1) for an Andosol with 32 d reaction time, for describing P mobility in typical Japanese agricultural soils under fast flow conditions. The breakthrough curves of P infiltrating the soil columns demonstrate nonequilibrium P adsorption by the soil. The chemical nonequilibrium model, with a kinetic adsorption rate of α = 0.40 (Gray lowland soil) and 0.098 (Andosol), succeeded in describing the observations in the column experiments. Compared with Gray lowland soil, which is relatively rich in iron oxide, P mobility was largely affected by kinetic sorption in Andosol, which is relatively rich in allophane. It is suggested that the P adsorption capacity of soils should be evaluated reflecting the soil composition in order to simulate the P mobility under flow conditions. In particular, the slow adsorption (long-lasting adsorption) of P by the soil should be considered in the estimation of the P transport.

CFD simulation of hydrodynamics and heat transfer characteristics in gas–solid circulating fluidized bed riser under fast pyrolysis flow condition

• Proper heat is needed for Circulating fluidized bed riser for fast pyrolysis. • A 3D EE-TFM model was developed and validated with experiment. • Hydrodynamics and heat transfer characteristics were examined for CFB riser. • Demonstrate the gas–solid heat transfer affected under different hydrodynamics. Pyrolysis process through circulating fluidized bed (CFB) is a promising technology to produce synthetic fuel and other products from biomass feedstocks. Computational fluid dynamics (CFD) computing means provide valuable insights to better understand gas–solid flow hydrodynamics, troubleshoot performance issues and optimize reactor operations. In this study, gas–solid flow hydrodynamics and heat transfer characteristics of a CFB riser for fast pyrolysis are investigated using a three-dimensional (3D) Eulerian-Eulerian CFD model. The main observations are discussed to provide insights on the factors affecting CFB riser performance. The model parameters, specularity and particle–particle restitution coefficients, were considered and tuned to accurately predict of gas–solid flow hydrodynamics and heat distribution with respect to different gas velocities and solid circulation rates. The results have shown that the CFD model predicted well the flow hydrodynamics and both specularity and particle–particle restitution coefficients are critical parameters as they affect particle behavior and temperature distribution fields. The lower specularity coefficient (Φ − 0.00001) was fairly able to predict the axial solid holdup profile into CFB riser. However, the lower value for particle–particle restitution coefficient ( e s s - 0.8) significantly overpredict the bottom dense region. The results shows that the increase of operating velocity promotes the mixing behaviors and heat transfer performance. In this work the suitable gas and solid circulation flow rates are U g = 4.5 m/s and G s = 81.23 kg/m 2 s.

Nitro to amine reductions using aqueous flow catalysis under ambient conditions

SummaryA catalyst based on Pd on glass wool (Pd@GW) shows exceptional performance and durability for the reduction of nitrobenzene to aniline at room temperature and ambient pressure in aqueous solutions. The reaction is performed in a flow system and completed with 100% conversion under a variety of flow rates, 2 to 100 mLmin−1 (normal laboratory fast flow conditions). Sodium borohydride or dihydrogen perform well as reducing agents. Scale-up of the reaction to flows of 100 mLmin−1 also shows high conversions and robust catalytic performance. Catalyst deactivation can be readily corrected by flowing a NaBH4 solution. The catalytic system proves to be generally efficient, performing well with a range of nitroaromatic compounds. The shelf life of the catalyst is excellent and its reusability after 6-8 months of storage showed the same performance as for the fresh catalyst.

Modeling vorticity stretching of viscoelastic droplets during shearing flow

In the present work, we focus on the large deformation of a viscoelastic droplet suspended in a Newtonian matrix. We use the constrained volume model as a basic theoretical framework for the description of droplet shape evolution, and we account for the viscoelasticity of the droplet phase using the single-mode Giesekus model. The velocity gradient term describing flow inside the droplet is modified by the viscoelastic stresses, and the resulting model—we herein call the non-Newtonian constrained volume model—is calibrated by matching its predictions to those of the model of Yu et al. [J. Rheol. 48, 417–438 (2004)] at small deformation and slow flow conditions. The non-Newtonian constrained volume model is then examined under conditions of large deformation and/or fast flow, and its predictions are compared against experimental results. The new model shows the growth of the droplet's width in the vorticity direction at conditions of large capillary number, moderate-to-large viscosity ratio, and small elastocapillary number.

Generalized Newtonian fluid constitutive equation for polymer liquids considering chain stretch and monomeric friction reduction for very fast flows modeling

In this work, the recently proposed frame-invariant Generalized Newtonian Fluid (GNF) constitutive equation [M. Zatloukal, “Frame-invariant formulation of novel generalized Newtonian fluid constitutive equation for polymer melts,” Phys. Fluids 32(9), 091705 (2020)] has been modified to provide uniaxial extensional viscosity at a high strain rate limit corresponding to molecular expression for a fully extended Fraenkel chain reported in Ianniruberto et al. [“Melts of linear polymers in fast flows,” Macromolecules 53(13), 5023–5033 (2020)]. It uses basic rheological and molecular parameters together with the ratio of monomeric friction coefficients for equilibrium and fully aligned chains. The modified GNF model was successfully tested by using steady-state uniaxial extensional viscosity data for well-characterized entangled polymer melts and solutions [namely, linear isotactic polypropylenes, poly(n-butyl acrylate), polyisoprenes, and polystyrenes] covering a wide range of strain rates, including those, at which the chain stretch occurs. Only two fitting parameters were sufficient to describe all uniaxial extensional viscosity data, one related to the Rouse stretch time and the other controlling the extensional thinning and thickening behavior at medium and high strain rates. The model was compared to five different advanced viscoelastic constitutive equations, which are based on Doi–Edwards theory and include chain stretch along with a number of important additions. The ability of the proposed GNF model to represent steady uniaxial extensional viscosities under fast flow conditions for entangled polymer fluids has been shown to be superior to the predictions of selected advanced viscoelastic constitutive equations. It is believed that the modified GNF model can be used in the stable modeling of non-Newtonian polymer liquids, especially in very fast steady-state flows where chain stretch begins to occur.

Evaluating SWMM capabilities to simulate closed pipe transients

One of the most used 1D tools to model collection systems is the Storm Water Management Model (SWMM). Solving the full form of the Saint Venant equations, this model represents typical unsteady flow conditions in sewer systems. However, it may be insufficient to address fast transient flow conditions that can be present during extreme events or unscheduled operational conditions. SWMM version 5.1.013 was implemented the Preissmann slot as an alternative method to handle pressurization. To date, no studies were found analysing the applicability of SWMM to represent closed-pipe fast transient flows applying the Preissmann slot pressurization algorithm. Therefore, the present work investigates the ability to model different fast transients conditions in SWMM under various spatial and temporal discretizations along with variations in the Preissmann slot algorithm. Using an alternative implementation of the SLOT pressurization algorithm, along with artificial spatial discretization and routing time-steps estimated by the Courant stability condition, it is shown that SWMM is capable to perform satisfactory certain types of closed pipe transient simulations.

Evaluation of arsenic sorption performance using dendritic anatase and polycrystalline rutile nano-TiO2 for environmental applications

Two synthetic nano-TiO2-based materials, aggregated dendritic anatase nano-TiO2 and polycrystalline rutile nano-TiO2 attached to the surface of SiO2, were analyzed and compared for geo-environmental engineering applications. Characterization of crystal structure, purity, and morphologic, microscopic features of the materials were examined by X-ray powder diffraction, X-ray fluorescence, and scanning electron microscope, respectively. Arsenic removal rates/efficiencies were compared between the two materials in different settings for laboratory batch experiment. The adsorption curve on arsenic was obtained. Subsequently, different concentrations of arsenic solutions were injected in batches at different flow rates 0.67, 0.83, 1.00, 1.25, 1.67, 2.50, 5.00, and 10.00 ml/min to simulate field conditions. Results show that both of TiO2-based materials demonstrate outstanding capabilities for arsenic removal. Removal rates are 83% (± 0.025) and 95% (± 0.024) for aggregated TiO2, while 82% (± 0.031) for 93% (± 0.013) for attached TiO2. Results suggest that attached form of TiO2 is more effective for arsenic removal under fast groundwater flow condition, while aggregated form TiO2 can be suitable for high arsenic concentration and low water flow rate. Both materials are considered cost-effective as both can be recovered and reused after regeneration process.

Parylene-Coated Polytetrafluoroethylene-Membrane-Based Portable Urea Sensor for Real-Time Monitoring of Urea in Peritoneal Dialysate.

A portable urea sensor for use in fast flow conditions was fabricated using porous polytetrafluoroethylene (PTFE) membranes coated with amine-functionalized parylene, parylene-A, by vapor deposition. The urea-hydrolyzing enzyme urease was immobilized on the parylene-A-coated PTFE membranes using glutaraldehyde. The urease-immobilized membranes were assembled in a polydimethylsiloxane (PDMS) fluidic chamber, and a screen-printed carbon three-electrode system was used for electrochemical measurements. The success of urease immobilization was confirmed using scanning electron microscopy, and fourier-transform infrared spectroscopy. The optimum concentration of urease for immobilization on the parylene-A-coated PTFE membranes was determined to be 48 mg/mL, and the optimum number of membranes in the PDMS chamber was found to be eight. Using these optimized conditions, we fabricated the urea biosensor and monitored urea samples under various flow rates ranging from 0.5 to 10 mL/min in the flow condition using chronoamperometry. To test the applicability of the sensor for physiological samples, we used it for monitoring urea concentration in the waste peritoneal dialysate of a patient with chronic renal failure, at a flow rate of 0.5 mL/min. This developed urea biosensor is considered applicable for (portable) applications, such as artificial kidney systems and portable dialysis systems.

Physical Conditions of Fast Glacier Flow: 3. Seasonally-Evolving Ice Deformation on Store Glacier, West Greenland.

Temporal variations in ice sheet flow directly impact the internal structure within ice sheets through englacial deformation. Large‐scale changes in the vertical stratigraphy within ice sheets have been previously conducted on centennial to millennial timescales; however, intra‐annual changes in the morphology of internal layers have yet to be explored. Over a period of 2 years, we use autonomous phase‐sensitive radio‐echo sounding to track the daily displacement of internal layers on Store Glacier, West Greenland, to millimeter accuracy. At a site located ∼30 km from the calving terminus, where the ice is ∼600 m thick and flows at ∼700 m/a, we measure distinct seasonal variations in vertical velocities and vertical strain rates over a 2‐year period. Prior to the melt season (March–June), we observe increasingly nonlinear englacial deformation with negative vertical strain rates (i.e., strain thinning) in the upper half of the ice column of approximately −0.03 a−1, whereas the ice below thickens under vertical strain reaching up to +0.16 a−1. Early in the melt season (June–July), vertical thinning gradually ceases as the glacier increasingly thickens. During late summer to midwinter (August–February), vertical thickening occurs linearly throughout the entire ice column, with strain rates averaging 0.016 a−1. We show that these complex variations are unrelated to topographic setting and localized basal slip and hypothesize that this seasonality is driven by far‐field perturbations in the glacier's force balance, in this case generated by variations in basal hydrology near the glacier's terminus and propagated tens of kilometers upstream through transient basal lubrication longitudinal coupling.

An upscaled rate law for mineral dissolution in heterogeneous media: The role of time and length scales

An upscaled rate law is developed for mineral dissolution in heterogeneous media under variable residence time (flow velocity) and length scale conditions, expanding the previous rate law under one flow and length condition (Wen and Li, 2017). A total of 640 Monte-Carlo numerical experiments were carried out with magnesite dissolution within quartz matrix in spatially heterogeneous media characterized by permeability variance (σ2lnκ = 6.0) and correlation length (λ = 2–50 cm) under a range of domain length (1.0–5.0 m) and flow velocity (2.7 × 10−4 to 27.0 m/day) conditions. The upscaled rate law Rht=kAT1-exp-τeqτa1-exp-Lτaτad,rα consists of two parts. The first is the rate law in equivalent homogeneous media Rhm=kAT1-exp-τeqτa, where rates depend on rate constants (k), total mineral surface area (AT), and the relative timescales of reactions (τeq) and advection (τa)Da=τaτeq. The second term χ=1-exp-Lτaτad,rα is the heterogeneity factor that quantifies the deviation of heterogeneous systems from their homogeneous counterparts. The term includes the relative transport time ratio τaτad,r, domain length (L), and geostatistical characteristics of spatial heterogeneity (permeability variance in α=5σlnκ2. The ratio τaτad,r quantifies the relative timescales of transport at the domain scale (τa approximates τad) versus transport in the reactive zones (τad,r). Under low flow velocity and/or long domain length conditions where τa >τad,r, homogenization occurs so that χ is close to 1 and heterogeneity effects are negligible. In contrast, χ deviates from 1 by up to 2 orders of magnitude under short length and fast flow conditions where τa <τad,r and Lτaτad,r is small. Under such conditions, transport rates in and out of the reactive zones limits the overall dissolution at the domain scale. The rate law predicts that 1) heterogeneity effects are governed by the relative magnitude of mineral-water contact in reactive zones versus in the whole domain; 2) dissolution rates in heterogeneous media ultimately approach asymptotic values in homogeneous media at “sufficiently” long lengths. It takes longer distance (and time) for more heterogeneous systems with longer τad,r values to reach the asymptotic values. This is supported by carbonate dissolution rates calculated from river water chemistry data. Although the rate law is derived based on magnesite dissolution, it is expected to be applicable for the dissolution of other minerals, as long as the dissolution characteristics of other minerals (e.g., k, AT, and Keq) are incorporated in the rate law.

Physical Conditions of Fast Glacier Flow: 1. Measurements From Boreholes Drilled to the Bed of Store Glacier, West Greenland

Marine‐terminating outlet glaciers of the Greenland Ice Sheet make significant contributions to global sea level rise, yet the conditions that facilitate their fast flow remain poorly constrained owing to a paucity of data. We drilled and instrumented seven boreholes on Store Glacier, Greenland, to monitor subglacial water pressure, temperature, electrical conductivity, and turbidity along with englacial ice temperature and deformation. These observations were supplemented by surface velocity and meteorological measurements to gain insight into the conditions and mechanisms of fast glacier flow. Located 30 km from the calving front, each borehole drained rapidly on attaining ∼600 m depth indicating a direct connection with an active subglacial hydrological system. Persistently high subglacial water pressures indicate low effective pressure (180–280 kPa), with small‐amplitude variations correlated with notable peaks in surface velocity driven by the diurnal melt cycle and longer periods of melt and rainfall. The englacial deformation profile determined from borehole tilt measurements indicates that 63–71% of total ice motion occurred at the bed, with the remaining 29–37% predominantly attributed to enhanced deformation in the lowermost 50–100 m of the ice column. We interpret this lowermost 100 m to be formed of warmer, pre‐Holocene ice overlying a thin (0–8 m) layer of temperate basal ice. Our observations are consistent with a spatially extensive and persistently inefficient subglacial drainage system that we hypothesize comprises drainage both at the ice‐sediment interface and through subglacial sediments. This configuration has similarities to that interpreted beneath dynamically analogous Antarctic ice streams, Alaskan tidewater glaciers, and glaciers in surge.

Physical Conditions of Fast Glacier Flow: 2. Variable Extent of Anisotropic Ice and Soft Basal Sediment From Seismic Reflection Data Acquired on Store Glacier, West Greenland

Outlet glaciers of the Greenland Ice Sheet transport ice from the interior to the ocean and contribute directly to sea level rise because discharge and ablation often exceed the accumulation. To develop a better understanding of these fast‐flowing glaciers, we investigate the basal conditions of Store Glacier, a large outlet glacier flowing into Uummannaq Fjord in west Greenland. We use two crossing seismic profiles acquired near the centerline, 30 km upstream of the calving front, to interpret the physical nature of the ice and bed. We identify one notably englacial and two notably subglacial seismic reflections on both profiles. The englacial reflection represents a change in crystal orientation fabric, interpreted to be the Holocene‐Wisconsin transition. From Amplitude‐Versus‐Angle (AVA) analysis we infer that the deepest ∼80 m of ice of the parallel‐flow profile below this reflection is anisotropic with an enhancement of simple shear of ∼2. The ice is underlain by ∼45 m of unconsolidated sediments, below which there is a strong reflection caused by the transition to consolidated sediments. In the across‐flow profile subglacial properties vary over small scale and the polarity of the ice‐bed reflection switches from positive to negative. We interpret these as patches of different basal slipperiness associated with variable amounts of water. Our results illustrate variability in basal properties, and hence ice‐bed coupling, at a spatial scale of ∼100 m, highlighting the need for direct observations of the bed to improve the basal boundary conditions in ice‐dynamic models.

Cooling tests, numerical modeling and economic analysis of semi-open loop ground source heat pump system

Ground source heat pump (GSHP) systems are serving the heating and cooling demands of buildings worldwide. However, the widespread usage of these systems is limited because of their higher initial costs compared with conventional heating and cooling systems, especially in countries with high drilling costs like Japan. The semi-open loop GSHP system was introduced by authors and the results of heating tests and numerical modeling have been published. This system comprises two ungrouted vertical Ground heat exchangers (GHEs) in which groundwater is pumped from one well and injected to another using a water pump. The purpose of the water pumping and injection is to create an artificial groundwater flow around the GHEs to increase the heat advection between the GHEs and the surrounding environment.In this study, cooling tests on the semi-open loop GSHP system were performed and the thermal performance of the system was measured in each test. The developed numerical model was validated using the results of the cooling tests. Then, a sensitivity analysis was performed to evaluate the system performance under different operational and geological conditions during cooling operation. The results showed that in comparison with conventional GSHP operation, cooling coefficient of performance (COP) and system coefficient of performance (COPsys) can be enhanced by 13.1% and 6.6%, respectively, under fast groundwater flow conditions, as expected at the experimental site. In the absence of groundwater flow, the semi-open loop system is estimated to boost the cooling COP and COPsys by 101% and 62%, respectively, for cooling operations. Finally, an economic analysis was performed, considering the capital and running costs of the system and also the additional equipment costs associated with semi-open loop systems. The results of the economic analysis showed that water pumping and injection can reduce GSHP system costs by 22–36%.

Eurasian ice-sheet dynamics and sensitivity to subglacial hydrology

ABSTRACTIce-stream dynamics are strongly controlled by processes taking place at the ice/bed interface where subglacial water both lubricates the base and saturates any existing, underlying sediment. Large parts of the former Eurasian ice sheet were underlain by thick sequences of soft, marine sediments and many areas are imprinted with geomorphological features indicative of fast flow and wet basal conditions. Here, we study the effect of subglacial water on past Eurasian ice-sheet dynamics by incorporating a thin-film model of basal water flow into the ice-sheet model SICOPOLIS and use it to better represent flow in temperate areas. The adjunction of subglacial hydrology results in a smaller ice-sheet building up over time and generally faster ice velocities, which consequently reduces the total area fraction of temperate basal ice and ice streaming areas. Minima in the hydraulic pressure potential, governing water flow, are used as indicators for potential locations of past subglacial lakes and a probability distribution of lake existence is presented based on estimated lake depth and longevity.

受動空力弾性翼の提案と機構的考察 第2報

This paper proposes a Passive Aeroelastic Wing. The wing mechanism is constructed mainly from flexible materials. Thus, the range of fluid resistance becomes different between high-speed flows and low-speed flows. Under fast-flow conditions, the flexible wing mechanism is compressed, and the range of the shape control becomes low. Then, the mechanism can control the posture of the robot under various flow speeds. This reports explain the construction of the proposed mechanisms by using closed loop dynamics based on the task space P-SD servo controller. The repeatability of the position control based on the proposed system were explained in the results.

Characterization of performance reference compound kinetics and analyte sampling rate corrections under three flow regimes using nylon organic chemical integrative samplers

Performance reference compounds (PRCs) can be spiked into passive samplers prior to deployment. If the dissipation kinetics of PRCs from the sampler corresponds to analyte accumulation kinetics, then PRCs can be used to estimate in-situ sampling rates, which may vary depending on environmental conditions. Under controlled laboratory conditions, the effectiveness of PRC corrections on prediction accuracy of water concentrations were evaluated using nylon organic chemical integrative samplers (NOCIS). Results from PRC calibrations suggest that PRC elimination occurs faster under higher flow conditions; however, minimal differences were observed for PRC elimination between fast flow (9.3cm/s) and slow flow (5.0cm/s) conditions. Moreover, minimal differences were observed for PRC elimination from Dowex Optipore L-493; therefore, PRC corrections did not improve results for NOCIS configurations containing Dowex Optipore L-493. Regardless, results suggest that PRC corrections were beneficial for NOCIS configurations containing Oasis HLB; however, due to differences in flow dependencies of analyte sampling rates and PRC elimination rates across the investigated flow regimes, the use of multiple PRC corrections was necessary. As such, a “Best-Fit PRC” approach was utilized for Oasis HLB corrections using caffeine-13C3, DIA-d5, or no correction based on the relative flow dependencies of analytes and these PRCs. Although PRC corrections reduced the variability when in-situ conditions differed from laboratory calibrations (e.g. static versus moderate flow), applying PRC corrections under similar flow conditions increases variability in estimated values.

Study on removal effect of suspended particulate matter by humidity swing air cleaning method

A humidity swing air cleaning method has been studied experimentally for improving a SPM (suspended particulate matter) removal effect. This method uses humidity swing of the air with evaporation of water and condensation of moisture, and removes the SPM by making a nuclear condensation with the SPM as nuclei and gravitational settling of the grown droplet. According to our previous study, the SPM removal effect of 90 % level was obtained at humidity swing of 0.2 kg/kgDA at flow rate of 5 L/min. The purpose of this study is to improve the SPM removal performance, especially in a high flow rate conditions. We have tested two ways; one is a modification of the dehumidifier geometry for promoting the nuclear condensation effect and the gravitational sedimentation effect. The other is an introduction of an inertial impaction as the grown droplets removal method using a coarse mesh filter as an obstacle in the fast flow condition. The geometry changes of the dehumidifier made the improvement in removal ratio up to 99.9% level at the flow rate of 5 L/min. Moreover, the introduction of the mesh filter resulted in the same removal ratio of 99.9% level at a fast flow condition of 10 L/min.

Engineered crumpled graphene oxide nanocomposite membrane assemblies for advanced water treatment processes.

In this work, we describe multifunctional, crumpled graphene oxide (CGO) porous nanocomposites that are assembled as advanced, reactive water treatment membranes. Crumpled 3D graphene oxide based materials fundamentally differ from 2D flat graphene oxide analogues in that they are highly aggregation and compression-resistant (i.e., π-π stacking resistant) and allow for the incorporation (wrapping) of other, multifunctional particles inside the 3D, composite structure. Here, assemblies of nanoscale, monomeric CGO with encapsulated (as a quasi core-shell structure) TiO2 (GOTI) and Ag (GOAg) nanoparticles, not only allow high water flux via vertically tortuous nanochannels (achieving water flux of 246 ± 11 L/(m(2)·h·bar) with 5.4 μm thick assembly, 7.4 g/m(2)), outperforming comparable commercial ultrafiltration membranes, but also demonstrate excellent separation efficiencies for model organic and biological foulants. Further, multifunctionality is demonstrated through the in situ photocatalytic degradation of methyl orange (MO), as a model organic, under fast flow conditions (tres < 0.1 s); while superior antimicrobial properties, evaluated with GOAg, are observed for both biofilm (contact) and suspended growth scenarios (>3 log effective removal, Escherichia coli). This is the first demonstration of 3D, crumpled graphene oxide based nanocomposite structures applied specifically as (re)active membrane assemblies and highlights the material's platform potential for a truly tailored approach for next generation water treatment and separation technologies.

Characterization of the main karst aquifers of the Tezbent Plateau, Tebessa Region, Northeast of Algeria, based on hydrogeochemical and isotopic data

Chemical properties and hydrogeological characterization of water resources were studied in the Hammemt Plain, which is located in the northwest of the Tezbent mountain range, City of Tebessa, northeast of Algeria, which drains carbonate aquifers through various large karst springs. The physical and chemical characteristics of spring and well water samples were studied for 2 years in order to assess the origin of groundwater and determine the factors driving its geochemical composition. The ionic speciation and mineral dissolution/precipitation were calculated where we found that water wells, characterizing groundwater circulation at shallow depths, are moderate to highly mineralized waters of the Na-HCO3 type. In contrast to the shallow environment, the CO2-rich, deeper waters are of the Ca-HCO3 type, and undergo significant changes in their baseline chemistry along flow lines with increasing residence time. The main factors controlling the groundwater composition and its seasonal variations are geology, because of the presence of different carbonate formations, additionally elevation, and the rate of karst development. Supersaturation with respect to calcite indicates CO2 degasing occurs either inside the aquifer in open conduits or at the outlet in reservoirs. Undersaturation with respect to calcite shows the existence of fast flow and short residence-time conditions inside the aquifer. The main springs and wells of the Tazbent Mountain have been studied by means of stable isotope measurement, where the values are varied in 18O; between −8.2 and −7.76 for spring samples and from −8.26 to −7.15 for well samples and in 2H between −52.92 and −49.11 for spring samples and from −55.47 to −47.44 for well samples, showing that the groundwater recharge is of meteoric origin and suggests the absence of the evaporation effect on the isotopic composition.

Optimization of gravity flow discharge chutes under the speed dependent resisting forces: Maximizing exit velocity

Using the optimal control theory, the problem of finding profiles of gravity flow discharge chutes required to achieve maximum exit velocity of granular material under the speed dependent resisting forces is solved. A model of a particle moving down a curve which is treated as a unilateral constraint is used. The fast flow condition and the condition that the particle does not leave the curve are introduced as the additional inequality constraints. The influence of the initial particle speed and the power of the speed in the expression for the resisting force on the optimal chute profile are analyzed.