High Water Flow Velocity Research Articles

Laboratory investigation of DNAPL migration in porous media

Laboratory experiments have been carried out with and without groundwater flow in a two-dimensional laboratory-scale tank to assess the influence of layered media and hydraulic gradient on DNAPL infiltration and redistribution processes. Hydrofluoroether has been used as DNAPL and glass beads have been utilized as porous medium. An image analysis procedure has been used to determine saturation distribution during infiltration and redistribution processes. This method allows quantitative time dependent full fields mapping of the DNAPL saturation, as well as the monitoring of DNAPL saturation variation. By means of performed experiments important information were obtained about the migration and redistribution process, the infiltration and migration velocity, the characteristics of migration body. The experimental results show that the hydraulic gradient promotes the infiltration process, increasing the infiltration rate. It hampers DNAPL spread and fingering bringing to a reduction of residual DNAPL and it also promotes the DNAPL redistribution, and it reduces the amount remaining at residual saturation. Furthermore the hydraulic gradient promotes downward and down-gradient migration. DNAPL migration in the direction of water flow, can be considered important due to significant errors in the location of sources in the case of high gradients and high aquifer thicknesses, and for high water flow velocities, such as those which can be expected during pumping actions in water supply or in remediation activities.

Influence of water flow velocity, water depth and colony distance on distribution and foraging patterns of terns in the Wadden Sea

AbstractSurface‐feeding seabirds, such as Common (Sterna hirundo) and Arctic Terns (Sterna paradisaea) in the German Wadden Sea, are dependent on biological and physical processes that affect prey availability close to the water surface. We proposed the following four hypotheses: (i) relationships should exist between high water flow velocity and foraging activity of terns, as turbulence should enhance prey availability at the surface; (ii) the areas of highest foraging success should be located within areas of low water depth, due to enhanced biological productivity; (iii) as terns are known to have small foraging radii, the location of their breeding grounds should be related to the location of their foraging grounds; (iv) terns should forage intensely in river estuaries, as these should hold ample food supplies. The time between terns leaving the colony and their first foraging attempt differed significantly among different tidal stages: the time was shortest during flood and ebb tides (i.e., highest water flow velocities). Modelling of a long‐term data set revealed the highest probability of foraging activity in conditions of high water currents, in both shallow areas and in areas of around 15–20 m depth. Foraging activity was negatively correlated with distance from colony. The distance to the closest estuary had no significant effect on foraging behaviour. Our findings emphasize the physical–biological coupling in the Wadden Sea and highlight the overall importance of small‐scale physical processes in directly influencing prey availability for surface‐feeding seabirds.

Production of Hydrogen by Electrolytic Purification of Water

AbstractElectrolytic purification of water is not new but has never been widely applied because of failure to meet realistic standards of economy. A continuous process with low cost consumables can compete with standard water treatment processes, even without energy recovery in the form of hydrogen. In order to extend the lower limit of feasible conductivities a specialised cell conjguration was developed. This utilkes a novel form of corroding anode that produces a highly eflective flocculant, in close proximity to a cathode, separated by a simple porous membrane. The active surface of the corroding anode is continually replenished. Flocculant clearance is achieved by high water flow velocity in a flume. Hydrogen is produced separately from anodic products. Other functions like electrolytic flotation, redox and sterilisation are synergistic. Because electrical energy input dominates the operating cost there is a strong incentive to recover the hydrogen, which is produced at about 0.02 Nm3 per m3 of water treated and about 25% eficiency.

Effects of irradiance and water flow on formation and growth of spongy and filamentous thalli of Codium fragile

Effects of irradiance and water flow on formation and growth of filamentous and spongy thalli of Codium fragile (Suringar) Hariot growing on vinylon threads were investigated at the laboratory culture. They showed clear differences in their irradiance and water flow requirements for their formation and growth. Spongy thalli were formed from the cultured filamentous thalli only at the high water flow velocity (10 cm s −1). Number of the spongy thalli remarkably increased with increasing irradiance because those at 10, 50 and 100 μmol m −2 s −1 reached 0, 2 and 76 thalli m −1, respectively, by 10 weeks of culture. In contrast, filamentous thalli were formed from the cultured spongy thalli at 0 and 3 cm s −1, and difference in irradiance had no effect on their formation. Growth of the spongy thalli greatly accelerated under the combination of the high irradiance and high water velocity (200 μmol m −2 s −1 and 10 cm s −1) because their relative growth rate in wet weight under the condition was two–four times higher than those at the other examined irradiances and water velocities. On the other hand, difference in water velocity had no effect on growth of the filamentous thalli under flowing water, and their growth decelerated at the high irradiance (200 μmol m −2 s −1). This demonstrates that water flow is a major factor controlling the formation of the spongy and filamentous thalli. The formation and growth of the spongy thalli surely occur under the combination of the high irradiance and fast flowing water. In contrast, the formation of the filamentous thalli occurs in the calm water, and their growth is inhibited under the high irradiance.

Temporal export of nitrogen from a constructed wetland: influence of hydrology and senescing submerged plants

Nitrogen export was measured during monthly monitoring in an 18-ha constructed wetland in southeast Sweden 1998–2001. To investigate the influence of increased water flow on wetland nitrogen export, we performed intensive sampling (eight samples per day) of total-N, urea-N, NH 4 +-N, NO 3 −-N in January–March 2001. Investigations of wetland plant distribution 1997–2001 and submerged plant biomass were combined with investigations of plant nitrogen content 1998–2001, to test the hypothesis that nitrogen export was linked to wetland plant decomposition. Nitrogen was exported from the wetland (3.3 kg N ha −1 d −1), during the end of the intensive sampling period (19 February–12 March), coinciding with increased water flow (from 0.2 to 0.6 m 3 s −1). Plant cover expanded rapidly and nitrogen assimilated in the submerged plant community was estimated to be 39 kg ha −1 in July 2001. After senescence in April the following year, plant biomass was reduced by 75%. We concluded that a significant part (40%) of this wetland nitrogen export might be associated with the release of organic and inorganic nitrogen from the senesced submerged plant community. Moreover, we hypothesize that nitrogen removal in wetlands in cold temperate climate may be limited by temporal nitrogen export induced by high water flow velocity when wetland plants are decomposing.

Overview of the 100 mA average-current RF photoinjector

High-average-power FELs require high-current, low-emittance and low-energy-spread electron beams. These qualities have been achieved with RF photoinjectors operating at low-duty factors. To date, a high-average-current RF photoinjector operating continuously at 100% duty factor is yet to be demonstrated. The principal challenges of a high-duty-factor normal-conducting RF photoinjector are related to applying a high accelerating gradient continuously, thus generating large ohmic losses in the cavity walls, cooling the injector cavity walls and the high-power RF couplers, and finding a photocathode with reasonable Q.E. that can survive the poor vacuum of the RF photoinjector. We present the preliminary design of a normal-conducting 700 MHz photoinjector with solenoid magnetic fields for emittance compensation. The photoinjector is designed to produce 2.7 MeV electron beams at 3 nC bunch charge and 35 MHz repetition rate (100 mA average current). The photoinjector consists of a 2 1 2 -cell, π-mode, RF cavity with on-axis electric coupling, and a non-resonant vacuum plenum. Heat removal in the resonant cells is achieved via dense arrays of internal cooling passages capable of handling high-velocity water flows. Megawatt RF power is coupled into the injector through two tapered ridge-loaded waveguides. PARMELA simulations show that the 2 1 2 -cell injector can produce a 7 μm emittance directly. Transverse plasma oscillations necessitate additional acceleration and a second solenoid to realign the phase space envelopes of different axial slices at higher energy, resulting in a normalized rms emittance of 6.5 μm and 34 keV rms energy spread. We are developing a novel cesiated p-type GaN photocathode with 7% quantum efficiency at 350 nm and a cesium dispenser to replenish the cathode with cesium through a porous silicon carbide substrate. These performance parameters will be necessary for the design of the 100 kW FEL.

Study of the performance of four repairing material systems for hydraulic structures of concrete dams

Four types of repairing materials are studied as function of either a conventional concrete or a reference-concrete (RefC), these are: polymer-modified cement mortar (PMor), steel fiber concrete (SFco), epoxy mortar (EMor) and silica fume mortar (SFmo), to be applied in hydraulic structures surfaces subjected to a high velocity water flow. Besides the mechanical requests and wearing resistance of hydraulic concrete dam structures, especially the spillway surfaces, the high solar radiation, the environmental temperature and wet and dry cycles, contribute significantly to the reduction of their lifespan. RefC and the SFco were developed based on a usual concrete mixture used in slabs of spillways. The average RefC mixture used was 1: 1.61: 2.99: 0.376, with Pozzolan-modified Portland cement consumption of 425 kg/m³. EMor and PMor mixtures followed the information given by the manufacturers and lab experience. Tests on concrete samples were carried out in laboratory simulating normally found environmental situations in order to control the mechanical resistance and the aging imposed conditions, such as solar radiation and humidity. Also, physicochemical characterizing tests were made for all used materials. From the analyzed results, two of them presented a higher performance: the EMor and SFmo. SFco presented good adherence to the RefC and good mechanical performance. However, it also presented apparent metal corrosion in humidity tests, being indicated for use, with caution, as an intermediate layer in underwater repairs. In a general classification, considering all tests, including their field applications, the better performance material systems were EMor- SFmo> SFco> PMor.

Effects of Pulsed, High-Velocity Water Flow on Larval Robust Redhorse and V-Lip Redhorse

Abstract The pulsed, high-velocity water flow characteristic of water-flow patterns downstream from hydropower-generating dams has been implicated in the declining abundance of both aquatic insects and fishes in dam-regulated rivers. This study examined the effects of 0, 4, and 12 h per day of pulsed, high-velocity water flow on the egg mortality, hatch length, final length, and survival of larval robust redhorse Moxostoma robustum, a presumedly extinct species that was rediscovered in the 1990s, and V-lip redhorse M. collapsum (previously synonomized with the silver redhorse M. anisurum) over a 3–5 week period in three separate experiments. Twelve 38.0-L aquaria (four per treatment) were modified to simulate pulsed, high-velocity water flow (>35 cm/s) and stable, low-velocity water flow (<10 cm/s). Temperature, dissolved oxygen, zooplankton density, and water quality variables were kept the same across treatments. Fertilized eggs were placed in gravel nests in each aquarium. Hatch success was estimated v...

Resistance of Steep Concrete Block Pavements to High-Velocity Water Flow

In some locations, the use of concrete block pavement (CBP) involves the combination of a very steep and storm-sensitive region with the consequent risk of high-velocity water flow on pavements. Under these conditions, and because of the special characteristics of CBP and its unknown response to high-velocity water flow, two problems must be addressed: ( a) the danger of sand erosion from the bedding layer and the joints between the blocks, because of surface drainage and water flow, and ( b) the danger of development of uplift forces from the downward water seepage. The cumulative effect of these two dangers may cause a gradual loss of support of the CBP, leading to total failure. CBP was tested under high-velocity water flow on a one-to-one scale, with definition of flow and failure mechanisms in the CBP and with the adoption of proper solutions. Five tests were performed in an experimental water flume, differing in type of bedding. Use of conventional sand bedding under continuous water-flow conditions was found to be inappropriate. Such bedding cannot provide the necessary stability for the CBP. However, the use of fine aggregate as bedding material ensured the stability of the CBP under continuous supercritical flow velocities and steep channel slopes. Excellent performance of the CBP was observed with the underlying fine aggregate bedding. The use of sufficiently coarse aggregate as bedding material is the proper engineering solution for preventing erosion and ensuring the absolute stability of a CBP under high water-flow velocities under supercritical conditions.

Accelerated High Speed Water Erosion Test for Concrete Wear Debris Analysis

This paper contains investigations of wear particles generated during the erosive wear of four different concrete, mixtures by high velocity water flow at velocities of about 700 m/s.i The wear particles were collected, dried and analyzed by sieve experiments. Based on the sieve analysis, specific surface and average grain diameter of the particle samples were estimated. 'Using simple, comminution relations, the specific crack length of every' sample is calculated. It is shown that all estimated parameters exhibit a strong relationship to characteristic material properties, such as compressive strength, Young's modulus, and absorbed fracture energy. It was found by regression analysis that the average debris wear size can be effectively characterized by the absorbed fracture energy of the concrete sample. It is concluded that these relations are the result of different paths of fracture propagation through the materials during the generation of a microcrack network. Presented as a Society of Tribologists ...

The Fracture of Concrete due to Erosive Wear by High Velocity Water Flow

Wear and erosion of concrete structures by high velocity water flow is a basic aspect of the durability of marine and water constructions. The mechanism of concrete failure in such constructions is not well understood. Using high velocity water jets for simulating the loading, the authors observed the general behavior of the material during failure and investigated the influence of water velocity and exposure time. The results show that the interface between hardened cement paste and aggregate grains plays the main role in the fracture process. The basic mechanism of material failure is the generation and propagation of cracks at this interface. It is found that a critical loading intensity, which is characterized by a threshold velocity and a threshold exposure time, must be achieved in order to induce the erosion process. Through mass removal measurements, a mathematical relation between both parameters and the erosion intensity is found. Using a computer program for simulating the hydrodynamics inside a crack, the water pressure and flow velocities in a model crack were calculated.

Fundamental investigations on concrete wear by high velocity water flow

A primary concern in the design of marine constructions is the wear and erosion of concrete structures by high velocity water flow. The mechanism of concrete failure for this type of loading is not well understood. By using high velocity water jets to simulate the loading, the authors observed the general behaviour of concrete during failure and investigated the influence of water velocity and exposure time. The results show that the interface between hardened cement paste and aggregate grains plays the main role in the fracture process. It is found that a critical threshold velocity w c and a critical threshold exposure time t c must be achieved in order to induce the erosion process. A mathematical relation between both parameters and the erosion intensity is found through mass removal measurements.

Effects of Microhabitat Selection on Feeding Rates of Net‐Spinning Caddisfly Larvae

Net—spinning caddisfly larvae of the family Hydropsychidae are known to prefer microhabitats with large, stable substrate and high water flow velocity. It is often assumed that net spinners in high—velocity microhabitats have higher feeding or growth rates than larvae in less preferred sites, but there is no direct evidence to support this assumption. We hypothesized that net—spinning caddisflies would select microhabitats that offered the greatest feeding rates. This hypothesis was tested by field experiments in which we determined if net—spining caddisfly larvae preferred high—velocity sites even when substrate size and type were held constant. We then measured feeding rates of net spinners in microhabitats with different flow characteristics. High—flow positions were selected by 96% of hydropsychid arvae colonizing artifical moss substrates. Artemia nauplii released into the water column were captured by individual larvae in high—flow sites at a rate of 0.016%/m, significantly higher than the capture rate in low—flow sites. Combing this rate of prey capture with mean hydropsychid densities of 1125 individuals/m2, we estimate that hydropsychid larvae in riffles remove drifting invertebrate prey at a rate of ° 18%/m. Assuming exponential prey removal, a prey item in the drift would travel an average of only 5.5 m before being consumed. This study is one of the first to show that the distribution of a stream filter feeder is related to the feeding rates obtainable in different microhabitats.

4889126 Method for determining the turnover of organic material in living tissue and NMR spectrometer for performing this method

High-average-power FELs require high-current, low-emittance and low-energy-spread electron beams. These qualities have been achieved with RF photoinjectors operating at low-duty factors. To date, a high-average-current RF photoinjector operating continuously at 100% duty factor is yet to be demonstrated. The principal challenges of a high-duty-factor normal-conducting RF photoinjector are related to applying a high accelerating gradient continuously, thus generating large ohmic losses in the cavity walls, cooling the injector cavity walls and the high-power RF couplers, and finding a photocathode with reasonable Q.E. that can survive the poor vacuum of the RF photoinjector. We present the preliminary design of a normal-conducting 700 MHz photoinjector with solenoid magnetic fields for emittance compensation. The photoinjector is designed to produce 2.7 MeV electron beams at 3nC bunch charge and 35 MHz repetition rate (100 mA average current). The photoinjector consists of a 212-cell, π-mode, RF cavity with on-axis electric coupling, and a non-resonant vacuum plenum. Heat removal in the resonant cells is achieved via dense arrays of internal cooling passages capable of handling high-velocity water flows. Megawatt RF power is coupled into the injector through two tapered ridge-loaded waveguides. PARMELA simulations show that the 2½-cell injector can produce a 7μm emittance directly. Transverse plasma oscillations necessitate additional acceleration and a second solenoid to realign the phase space envelopes of different axial slices at higher energy, resulting in a normalized rms emittance of 6.5 μm and 34keVrms energy spread. We are developing a novel cesiated p-type GaN photocathode with 7% quantum efficiency at 350 nm and a cesium dispenser to replenish the cathode with cesium through a porous silicon carbide substrate. These performance parameters will be necessary for the design of the 100kW FEL.PACS: 41.60.Cr; 29.17. + w; 29.27.Bd; 41.75.Fr

Miscible displacement of ions in aggregated soils

A model was proposed for the prediction of multiple ion species in aggregated porous media under steady water flow conditions. The model is based on the two-region or mobile-immobile concept coupled with ion interactions based on thermodynamic equilibrium. This resulted in a set of convective-dispersive equations equivalent to the number of ions considered which were simultaneously solved using numerical methods. In another part of the study the two-region model was utilized for the purpose of predicting chloride-36 and tritium transport in a soil column of Abist soil under high but constant water flow velocity. Breakthrough curves (BTC) were obtained for two aggregate sizes (1–2 mm and 4–5 mm). Predicted BTC's using the two-region model provided unrealistically high retardation factors ( R) for both chloride-36 and tritium. In contrast R-values close to unity were obtained using the one-region model. Solute exchange between intra- and inter-aggregate pores appeared to be near equilibrium conditions even though high water flow velocities were used.

X-ray lithography source using a stationary solid Pd target

This paper describes a relatively high power density (10–15 kW/cm2) x-ray source for x-ray lithography applications. The source utilizes a stationary solid Pd target cooled by a high velocity water flow. This source has been operated for several months in a shop environment. No degradation in performance has been observed.

Construction Finishes and High-Velocity Flow

Laboratory research and field experience shows that finish tolerances are essential and important for construction surfaces that are to support high-velocity water flows. Surface irregularities must be prevented, minimized, or treated to prevent cavitation damage to these surfaces. Irregularities frequently encountered during the construction of hydraulic structures are illustrated and their cavitation potential examined. How these irregularities affect pressure conditions on the flow surface and cause cavitation damage is explained. The results of a limited number of research programs that give the critical sizes of various types of surface irregularities for numerous combinations of flow velocity and pressure are presented. Charts for sharp cornered, round cornered, and chamfered cornered offsets-into-the-flow are presented. Similar offsets receding from the flow are reviewed. The effects of orientation of the irregularities with the direction of flow on cavitation potential are mentioned. Treatment by grinding the irregularities to non-critical proportions and shapes is suggested. Field experience and test results that support specification limitations practiced by the USBR are included.