Flux Zone Research Articles

Pilot Study on Dosing Suspended Fillers to Alleviate Membrane Fouling

In this article, Vertical A/O-MBR was used as the experimental device to study membrane fouling through dosing cylindrical rigid suspended fillers, and the best conditions for membrane fouling control and effluent quality with fillers was discussed. Results showed that the critical flux zone decreased. When the MLSS was 5g/L and the suspended fillers dose was 1%, 5%, 10%, respectively, TMP increased rapidly with the quantity, greater quantity of fillers speeded up the membrane fouling process, and in small quantity membrane fouling had some delay action. The best dosing of fillers was determined as 7% in the condition of MLSS=5g/L, and the effluent quality was good.

Interannual Variation of the Late Spring–Early Summer Monsoon Rainfall in the Northern Part of the South China Sea

Abstract Major rainfall (≥60%) in the northern part of the South China Sea (between North Vietnam and Taiwan) during May–June (the mei-yu season—the first phase of the Southeast–East Asian monsoon) is produced by rainstorms originating over the northern Vietnam–southwestern China region and the northern part of the South China Sea. As observed in this study, the occurrence frequency of rainstorms and rainfall contribution by these rainstorms undergoes a distinct interannual variation, in-phase with those of monsoon westerlies in northern Indochina and sea surface temperature (SST) anomalies over the NOAA Niño-3.4 region ΔSST (Niño-3.4). This in-phase relationship between monsoon westerlies and the ΔSST (Niño-3.4) anomalies is a result of the filling (deepening) of the subtropical Asian continental thermal low in response to the ΔSST (Niño-3.4) warm (cold) anomalies. Accompanied with this response is a slight southward (northward) shift of the North Pacific convergence zone (NPCZ), which extends from southern China to the North Pacific east of Japan. Thus, a favorable environment that meets the Charney–Stern instability criterion in initiating rainstorm genesis is enhanced (suppressed) by the intensification (weakening) of the monsoon shear flow formed by the midtropospheric northwesterly flow around the northeast periphery of the Tibetan Plateau and the monsoon westerlies. The meridional shift of the NPCZ established an elongated anomalous convergence (divergence) zone of water vapor flux along rainstorm tracks to increase (reduce) the rain-producing efficiency of rainstorms. Consequently, this interannual rainfall variation between northern Vietnam and Taiwan is primarily caused by rainstorm genesis and rain-producing efficiency.

Assessment of thermo-electric techniques for scrape-off layer current drive in flux-tube geometry

The magnitude of the parallel current that can be driven by asymmetries between divertor target plates is calculated in magnetic flux-tube geometry. Current can be driven between ends of the flux-tube by passive techniques that generate a thermo-electric potential by heating or cooling one side relative to the other through pumping or neutral gas injection. The induced thermo-electric potential depends on the total particle flux pumped relative to the total recycling flux. For the geometry considered, pumping efficiency is higher for pumping by the target plate or from the private flux zone than for pumping from the outer side of the plate. Neutral gas injection is not as effective at generating an asymmetry. An important constraint for these methods may be the additional heat flux delivered to the hotter target, but additional Ohmic heating is much smaller than that generated by electrical biasing.

Experimental simulation of ITER rampdown in DIII-D

Because of the high value of the stored energy in planned ITER plasmas, the safe and controlled termination of ITER discharges is an important aspect of ITER operation. In a series of experiments on the DIII-D tokamak, we have simulated the proposed ITER rampdown for the 15 MA baseline operating scenario. These scaled discharges match the reference scenario (including scaled time dependence) with regard to key parameters such as scaled current, poloidal beta, elongation and internal inductance. The scaled plasma current is reduced to the equivalent of less than 1 MA, well below the 1.4 MA specified for ITER as the maximum allowable for disruptive termination. The plasma shape and position are controlled during rampdown so that the high heat flux zones near the strike points of the separatrix are held within the equivalent of the armoured zones of the ITER divertor; the regulation of the strike-point location is an order of magnitude better than required. Scans of the current rampdown rates indicate that a more rapid rampdown than the ITER reference case may be needed to avoid excessive current in the ITER central solenoid. Rampdown with a full-size plasma was studied, but was found to be unsuitable for ITER because of transitions to ELM-free H-mode with a consequent lack of density control, as well as large excursions in poloidal beta and internal inductance. We find that ELMs play an important role during the H-mode phase of the rampdown, helping to reduce the density as the current is reduced.

Design Optimization of High-Performance Helium-Cooled Divertor Plate Concept

A helium-cooled plate-type divertor design concept has being proposed within the framework of the ARIES power plant study. W tiles are used as sacrificial armor, W-alloy as main structural material and advanced ODS (oxide dispersion-strengthened) steel as the coolant manifold. An impinging jet cooling scheme is employed to enhance the heat transfer characteristics of the concept in the high heat flux zone. This paper describes the design optimization of the helium-cooled plate divertor through parametric studies including thermo-fluid and thermo-mechanical analyses.

An innovative research reactor design

A new and innovative core design for a research reactor is presented. It is shown that while using the standard, low enriched uranium as fuel, the maximum thermal flux per MW of power for the core design suggested and analyzed here is greater than those found in existing state of the art facilities without detrimentally affecting the other design specs. A design optimization is also carried out to achieve the following characteristics of a pool type research reactor of 10 MW power: high thermal neutron fluxes; sufficient space to locate facilities in the reflector; and an acceptable life cycle. In addition, the design is limited to standard fuel material of low enriched uranium. More specifically, the goal is to maximize the maximum thermal flux to power ratio in a moderate power reactor design maintaining, or even enhancing, other design aspects that are desired in a modern state of the art multi-purpose facility. The multi-purpose reactor design should allow most of the applications generally carried out in existing multi-purpose research reactors. Starting from the design of the German research reactor, FRM-II, which delivers high thermal neutron fluxes, an azimuthally asymmetric cylindrical core design with an inner and outer reflector, is developed. More specifically, one half of the annular core (0 < θ < π) is thicker than the other half. Two variations of the design are analyzed using MCNP, ORIGEN2 and MONTEBURNS codes. Both lead to a high thermal flux zone, a moderate thermal flux zone, and a low thermal flux zone in the outer reflector. Moreover, it is shown that the inner reflector is suitable for fast flux irradiation positions. The first design leads to a life cycle of 41 days and high, moderate and low (non-perturbed) thermal neutron fluxes of 4.2 × 10 14 n cm −2 s −1, 3.0 × 10 14 n cm −2 s −1, and 2.0 × 10 14 n cm −2 s −1, respectively. Heat deposition in the cladding, coolant and fuel material is also calculated to determine coolant flow rate, coolant outlet temperature and maximum fuel temperature under steady-state operating conditions. Finally, a more compact version of the asymmetric core is developed where a maximum (non-perturbed) thermal flux of 5.0 × 10 14 n cm −2 s −1 is achieved. The core life of this more compact version is estimated to be about 23 days.

IFMIF High Flux Test Module—Recent progress in design and manufacturing

The International Fusion Material Irradiation Facility (IFMIF) is an accelerator driven neutron source for irradiation tests of candidate fusion reactor materials. Within the High Flux Test Module (HFTM) a testing volume of 0.5 l filled by qualified small scale specimens will be irradiated at displacement rates of 20–50 dpa/fpy in structural materials. The Forschungszentrum Karlsruhe (FZK) has developed a HFTM design which closely follows the design premise of maximising the space available for irradiation specimens in the IFMIF high flux zone and in addition allows keeping the temperature nearly constant in the rigs containing the specimen. Complementary analyses on nuclear, thermo-hydraulics and mechanical performance of the HFTM were performed to optimize the design. The present paper highlights the main design characteristics as well as recent progress achieved in this area. The contribution also includes (i) recommendations for the use of container, rig and capsule materials, and (ii) a description of the fabrication routes for the entire HFTM including brazing and filling procedures which are currently under development at the Forschungszentrum Karlsruhe.

Internal waves, baroclinic energy fluxes and mixing at the European shelf edge

The energy flux in internal waves generated at the Celtic Sea shelf break was estimated by (i) applying perturbation theory to a week-long dataset from a mooring at 200m depth, and (ii) using a 2D non-hydrostatic circulation model over the shelf break. The dataset consisted of high resolution time-series of currents and vertical stratification together with two 25-h sets of vertical profiles of the dissipation of turbulent kinetic energy. The observations indicated an average energy flux of 139Wm−1, travelling along the shelf break towards the northwest. The average energy flux across the shelf break at the mooring was only 8Wm−1. However, the waves propagating onshelf transported up to 200Wm−1, but they were only present 51% of the time. A comparison between the divergence of the baroclinic energy flux and observed dissipation within the seasonal thermocline at the mooring showed that the dissipation was at least one order of magnitude larger. Results from a 2D model along a transect perpendicular to the shelf break showed a time-averaged onshelf energy flux of 153–425Wm−1, depending on the magnitude of the barotropic forcing. A divergence zone of the energy flux was found a few kilometre offshore of the location of the observations in the model results, and fluxes on the order of several kWm−1 were present in the deep waters further offshelf from the divergence zone. The modelled fluxes exhibited qualitative agreements with the phase and hourly onshelf magnitudes of the observed energy fluxes. Both the observations and the model results show an intermittent onshelf energy flux of 100–200Wm−1, but these waves could only propagate ∼20–30km onshore before dissipating. This conclusion was supported by a 25-h dataset sampled some 180km onto the shelf, where a weak wave energy flux was found going towards the shelf break. We therefore conclude that shelf break generated internal waves are unlikely to be the main source of energy for mixing on the inner part of the shelf.

Gas/particle flow characteristics of a centrally fuel rich swirl coal combustion burner

A three-component particle-dynamics anemometer is used to measure the characteristics of two-phase gas/particle flows in the near-burner region for a centrally fuel rich swirl coal combustion burner using a gas/particle two-phase test facility. Velocities, mean particle diameters and particle-volume flux profiles were obtained. The primary air and glass beads partially penetrate the central recirculation zone and are then deflected radially. At the center of the central recirculation zone, the mean radial velocities and tangential velocities are low and a zone of high particle-volume flux and large particle size is formed. The influence of gas/particle flow characteristics on combustion is analyzed.

Fouling in air sparged submerged hollow fiber membranes at sub- and super-critical flux conditions

The overall objective of the present study was to characterize the effect of operating a submerged air sparged membrane system over a wide range of operating conditions (i.e. sub- and super-critical flux conditions) on the extent and mechanisms of membrane fouling during drinking water treatment. The sub- and super-critical flux conditions considered were generated by varying the operating permeate flux, the bulk cross-flow velocity, the flow characteristics (i.e. with or without air sparging) and the configuration of the membrane modules. Regardless of the operating conditions, the increase in the trans-membrane pressure during operation could be effectively modeled using a simple exponential relationship of the form P V = P 0 e KV where P V was the trans-membrane pressure after filtering a given volume of permeate V, P 0 was the initial trans-membrane pressure, and K was the overall fouling coefficient. The type and extent of fouling could be characterized into three operating zones based on a flux index. At a relatively low flux index, a ‘true’ sub-critical flux zone was observed in which the overall fouling coefficient was constant for the different experimental conditions examined. For operation in this zone, fouling appeared to be predominantly due to internal fouling. At a flux index greater than zero, a super-critical flux zone was observed in which a linear relationship was observed between the overall fouling coefficient and the flux index. For operation in this zone, fouling appeared to be predominantly due to surface fouling. A transition zone was observed between ‘true’ sub-critical flux conditions and super-critical flux conditions, in which fouling appeared to be increasingly due to surface fouling. The overall fouling coefficient, as well as the evolution of the trans-membrane pressure in a submerged air sparged hollow fiber membrane system, could be effectively modeled for all operating zones using a relatively simple semi-empirical relationship which considered the back-transport of particles (i.e. foulants) from the membrane surface. It is expected that this simple relationship can be used in parallel with pilot-scale testing and reduce the extent of testing needed to identify the parameters that minimize fouling.

Experimental investigation of steady buoyant-thermocapillary convection near an evaporating meniscus

Micro-particle image velocimetry measurements of the three-dimensional (3D) convection patterns generated near an evaporating meniscus in horizontally oriented capillary tubes are presented. Analysis of the vapor diffusion away from the meniscus reveals a zone of intense heat flux near the solid-liquid-vapor junction that creates a temperature gradient along the meniscus. This results in a surface tension gradient which, coupled with buoyancy effects, causes buoyant-thermocapillary convection in the liquid film. The relative influence of buoyancy and thermocapillarity on the flow was investigated for tube diameters ranging from 75 to 1575μm. A transition from a pure two-dimensional thermocapillary flow to a 3D buoyant-thermocapillary flow is observed with an increase in tube diameter. For the 75μm tube, a symmetrical toroidal vortex is observed near the meniscus. For larger tubes, buoyancy effects become apparent as they dominate the flow field. The high mass fluxes in smaller-diameter tubes drive stronger vortices. Particle streaks and micro-particle image velocimetry images obtained in multiple horizontal and vertical planes provide an understanding of this three-dimensional flow behavior. A scaling analysis shows the importance of thermocapillary convection in evaporating menisci.

Analysis of the mass flux profiles of an aeolian saltating cloud

Aeolian researchers have recognized the importance of measuring the height profile of aeolian saltating flux and devoted a lot of effort to reliable measurement. In this paper, the height profiles of aeolian saltation flux are reconstructed on the basis of the profiles of mean particle velocity and relative particle concentration obtained by particle image velocimetry, a nonintrusive technique, in a wind tunnel. The results suggest that the mean particle velocity increases with an increase in wind velocity and height but decreases with an increase in particle size. The height profile of mean particle velocity can be expressed by a power function, essentially in agreement with previous studies. Particle concentration decays exponentially with the square root of height rather than height itself as proposed in most previous studies. Mass flux profiles are derived by multiplying the mean particle velocity and concentration profiles. The reconstructed mass flux profiles are characterized by three sections. In the near‐surface layer, mass flux increases with height. In the upper layer, mass flux decays exponentially with height. Between the near‐surface and upper layers is a peak flux zone whose height above the surface increases with an increase in wind velocity but decreases with an increase in particle size. The reconstructed mass profiles are essentially in reasonably good agreement with those measured by a segmented sand sampler in a wind tunnel. Two significant parameters, average saltation height and relative decay factor, are proposed to characterize variation with height of aeolian saltating flux. They are well correlated and imply that saltating particles can reach higher levels as wind velocity increases and particle size decreases and that mass flux decays more rapidly as wind velocity decreases and particle size increases.

Pilot study on municipal wastewater treatment by a modified submerged membrane bioreactor

A pilot-scale modified submerged membrane bioreactor (SMBR) with the capacity of 18.1 m3d(-1) was developed on the basis of the principle of air-lift internal-loop reactor. Economical aeration intensity of the SMBR was determined as 96 m3m(-2)h(-1) according to hydrodynamic investigation. Corresponding economical air-flow rate was selected as the working air-flow rate in the long-term run. Under economical aeration intensity, the critical flux zone of the modified SMBR was as high as 30-35 Lm(-2)h(-1) when MLSS was less than 13 gL(-1). Therefore, a sub-critical flux of 30 Lm(-2)h(-1) was selected as the working membrane flux in the long-term run. Membrane fouling was effectively controlled by sub-critical flux operation and periodic on-line chemical cleaning in the long-term run. When the average influent CODCr, NH3-N and turbidity were 310 and 44.3 mgL(-1) and 161 NTU, respectively, the average permeate were 38.5 and 19.5 mgL(-1) and 0.96 NTU under hydraulic retention time (HRT) was only 2.8 h. Corresponding removal was 86, 58.2 and 99.4%. DO deficiency caused by high MLSS was demonstrated as the main reason for low NH3-N removal.

Synthesis and Rietvald structure refinement of K–Zn priderite single crystals

High purity and twin free single crystals of one dimensional KxZnyTi8−yO16 priderites have been grown from a melt of K2O–MoO3 using the flux zone technique. The crystal structure has been investigated by Rietvald analysis of powder X-ray diffraction data. The crystal symmetry could be best described by the space group of I4/m. The exact coordinates of atoms, the unit cell dimensions, the atom occupation factors, the profile shape parameters as well as the interatomic distances have been determined. It was found that substitution of Zn increases the cell dimensions when compared to K–Mg priderites but similar to K–Nb based compounds. The composition and the nature of habit planes were identified from the scanning electron microscope observations. The conductivity parameters using impedance spectroscopy between 300 and 820 K indicated that the compound exhibits a low DC conductivity and a conductivity of 1.68×10−3 S cm−1 at 100 kHz.

Re-construction of detached divertor plasma conditions in DIII-D using spectroscopic and probe data

For some divertor aspects, such as detached plasmas or the private flux zone, it is not clear that the controlling physics has been fully identified. This is a particular concern when the details of the plasma are likely to be important in modeling the problem – for example, modeling co-deposition in detached inner divertors. An empirical method of ‘reconstructing’ the plasma based on direct experimental measurements may be useful in such situations. It is shown that a detached plasma in the outer divertor leg of DIII-D can be reconstructed reasonably well using spectroscopic and probe data as input to a simple onion-skin model and the Monte Carlo hydrogenic code, EIRENE. The calculated 2D distributions of ne and Te in the detached divertor were compared with direct measurements from the divertor Thomson scattering system, a diagnostic capability unique to DIII-D.

CO 2 soil flux at Vulcano (Italy): comparison between active and passive methods

Carbon dioxide soil flux has been used for many years to monitor Italian active volcanoes and both the active Dynamic Concentration (DCM) and the passive Accumulation Chamber (ACM) methods are employed. These two methods have been compared by means of 218 simultaneous flux measurements carried out in the La Fossa area of Vulcano Island, where a large variation of CO 2 soil release occurs. Results indicate that DCM overestimates CO 2 flux and is proportional to it only in high flux zones (flux higher than 100 gm −2 day −1). Using ACM fluxes and the Stefan–Maxwell equation, the measured CO 2/depth curves in the soil could be reproduced. In high flux points CO 2 is transported mostly by viscous flow up to a very shallow depth and then by diffusive flow, which is the dominant gas transport mechanism in low flux points. Carbon dioxide soil flux values are controlled by proximity to active gas releasing fractures, by changes in the barometric pressure and by variations in soil permeability.

The Si cycle in the Pacific sector of the Southern Ocean: seasonal diatom production in the surface layer and export to the deep sea

Abstract Dissolved silicic acid (Si(OH) 4 ) and biogenic silica (BSiO 2 ) concentrations were measured on four different cruises in the Southern Ocean along 170°W from late October 1997 to mid-March 1998. These data were used to construct a vertically integrated Si budget in the surface layer from 58° to 68°S. Throughout that period there was a distinct, southward-moving meridional [Si(OH) 4 ] gradient, with concentrations increasing to the south. In October the gradient was centered on the Antarctic Polar Front (APF) at 61°S. Surface layer [Si(OH) 4 ] increased from 10 to >40 mmol m −3 between 58° and 62°S, while BSiO 2 concentrations were −3 and −2 throughout the study area. As the surface mixed layer stratified and shoaled in December, diatoms bloomed in response to the more favorable light conditions, consuming Si(OH) 4 in the process. By late December BSiO 2 concentrations were exceptionally high for the open ocean, with maximum integrated values of 700 mmol Si m −2 around 62°S, while vertically integrated [Si(OH) 4 ] in the upper 50 m had dropped from 2500 to 870 mmol m −2 , an average decrease of >30 mmol Si m −3 . The diatom bloom persisted into January with maximum integrated BSiO 2 of 600 mmol m −2 between 64° and 65°S, while [Si(OH) 4 ] was depleted to −3 in surface waters as far south as 64.5°S. The center of the [Si(OH) 4 ] gradient had moved southward to 65°S by late January, coincident with maximal diatom biomass at that time. The bloom ended by March with the disappearance of most of the diatom biomass from the surface layer, deeper mixed layers, and increased [Si(OH) 4 ]. By late January, diatom production had removed >70% of the of Si(OH) 4 initially present in the upper 50 m everywhere north of 65°S, and had displaced the [Si(OH) 4 ] gradient >400 km southward, while the APF remained stationary. Between November and late January (∼80 days), an average of 2200 mmol Si m −2 had been removed from the upper 50 m between 61° and 65°S. Based on changes in vertically integrated Si(OH) 4 and BSiO 2 concentrations between November and March, an average of 2 mol Si m −2 was exported from the upper 50 m between 61° and 65°S, with 59% of that export occurring between late December and late January. The observed seasonal export is very high in comparison with other oceans, and the high export coincides spatially with a well-documented zone of high opal flux to 1000 m and high opal content in modern sediments. North of 61°S BSiO 2 export was limited by the low initial standing stock of Si(OH) 4 in surface waters, and south of 65°S export was likely limited by the shorter growing season. Thus, the combined effect of a large initial supply of Si(OH) 4 in surface waters and conditions that permit efficient use of that Si by diatoms appears to be the primary cause of opal-rich sediment accumulation in the Pacific sector of the Southern Ocean.

Forest Edges as Nutrient and Pollutant Concentrators: Potential Synergisms between Fragmentation, Forest Canopies, and the Atmosphere

Abstract: Forest fragmentation leads to a dramatic increase in forest edge, and these edges may function as traps and concentrators for wind‐borne nutrients and pollutants. We assessed the influence of forest edges on atmospheric deposition and subsequent inputs to the forest floor in deciduous‐forest fragments in the eastern United States. To quantify these inputs, we collected throughfall—water that has passed through the forest canopy—from edge and interior zones of forests adjacent to open fields. During the 1995 growing season, atmospheric input (wet and dry deposition) of sulfur to forest edge zones was elevated compared with input to forest interiors. Throughfall fluxes of dissolved inorganic nitrogen and calcium were also greater at edges than interiors. The mean edge increases ranged from 17% to 56% for the nutrients and pollutants we measured. When we manipulated the structure of forest edges by removing all vegetation below half the canopy height, throughfall flux in the edge zone declined sharply and was less than that of the respective interior zone. Changing the vegetation structure of the edge also shifted the zone of highest throughfall flux farther into the interior of the forest. Our data suggest that forest edges can function both as significant traps for airborne nutrients and pollutants from adjoining agricultural or urban landscapes and effective concentrators of below‐canopy chemical fluxes. These enhanced fluxes may have cascading effects on soil‐nutrient cycling, microbial activity, seedling dominance, and other ecological processes near forest edges.

The effect of cake and fibre properties on flux declines in hollow-fibre microfiltration membranes

The use of hollow-fibre membranes for microfiltration introduces trans-membrane pressure gradients that have important implications for flux decline mechanisms. A model is developed to elucidate these mechanisms for typical hollow-fibre membranes during the dead-end microfiltration of particulate suspensions. The model accommodates both compressible and incompressible cakes, and predicts highly-localised fluxes which are completely absent in planar membranes. These localised fluxes combine with trans-membrane pressure gradients to produce non-uniform cake growth patterns and non-uniform cake resistance profiles. When a cake is moderately compressible, the permeate flux declines through the axial motion of a uniform flux front. When a cake is highly compressible, the flux declines through the axial motion of a localised flux zone which leaves a low-permeability cake in its wake. Cake growth patterns are non-uniform in both axial and transverse directions. However, after substantial flux decline, a uniform cake growth pattern is established and thereafter the hollow fibre filters like a planar membrane. These flux decline mechanisms produce permeate flux declines with throughput which depend on hollow-fibre aspect ratio and permeability in addition to the properties of the retained cake.

Application of Mass-Balance Modeling of Sources, Pathways, and Sinks of Supergene Enrichment to Exploration and Discovery of the Quebrada Turquesa Exotic Copper Orebody, El Salvador District, Chile

Application of Mass-Balance Modeling of Sources, Pathways, and Sinks of Supergene Enrichment to Exploration and Discovery of the Quebrada Turquesa Exotic Copper Orebody, El Salvador District, Chile