Wet Screen Research Articles

Numerical investigation of non-uniform sand retention behavior in sand screens

Non-uniform sand retention behavior often occurs to the serviced screen deteriorating erosion. However, this phenomenon is poorly understood. This paper presents a numerical study of the sand retention on wire-wrapped screens, with special reference to non-uniform behaviors. This is done by the combined approach of computational fluid dynamics (CFD) and discrete element method (DEM). The validity of the model has been validated for dry and wet sand screen systems. It is used here to study sand retention behaviors at different solid concentrations and particle size distributions (PSD). Via this model, five distinct sand retention modes are identified: No sand retention (Mode I), partial sand retention (Mode II), sand retention with slow sequential bridging (Mode III), sand retention with fast sequential bridging (Model IV) and sand retention with instantaneous bridging (Mode V). Modes II and III belong to non-uniform sand retention, which develops strong local flows that induce local erosion or hot spot on the screen. A phase diagram is introduced to predict these five modes and their transition with respect to solid concentration and PSD. Additionally, the predicted flow and force structures are analyzed in detail. The results indicate that the bridging over a slot heavily relies on the particle accumulation on the screen. A new screen with a converging slot configuration is proposed to improve this particle accumulation. This improvement helps develop uniform sand retention on the screen.

Behavior of nanobentonites in adsorption of cesium and strontium

Bentonites contain a large amount of montmorillonite and this nano-structured and nano-porous member of the smectite group determines the adsorption properties of bentonites. In this study, four types of Iranian commercial bentonite clays have been examined to determine the adsorption capacity of cesium and strontium. The physicochemical and mineralogical properties of the four types have been experimentally analyzed with the focus on the moisture content, pH, dry (granulometric) and wet screen analyses; swell, sediment and Methylene Blue (M.B.) indices; cation exchange capacity (C.E.C) measurements. The pH and C.E.C values of B3 were 9.48 and 71.9 mEq/100g, respectively. The high values of C.E.C; swell, sediment and M.B. indices along with the high amount of granulometric values (particles finer than 36 um) showed that the B3 had a high amount of montmorillonite. X-Ray Fluorescence (XRF) analysis showed that the major of competing cations such as Ca2+ and K+ existing in B2 affects the Sr adsorption. The experimental analysis also showed that B2 had almost high pH and C.E.C values as well. The results of the separation process of Cs and Sr indicate that the B3 and B2 have the highest adsorption capacity of 59.75 and 45.5 for Cs and Sr adsorption, respectively.

马尾松人工林土壤各粒径团聚体湿筛后的有机碳分配

选取25a、45a和65a马尾松人工林为研究对象，采用湿筛法对各粒径土壤团聚体分别湿筛。探究了马尾松人工林各粒径团聚体湿筛后的团聚体有机碳分配，以探讨各粒径团聚体湿筛后分配到同一粒级团聚体有机碳含量及其对团聚体水稳性的贡献差异。结果表明：种植年限增加显著降低土壤团聚体水稳性（P<0.05）；各粒径团聚体湿筛后分配的有机碳随粒级减小含量呈先降后增趋势，以保持原粒级团聚体有机碳（12.96-32.01 g/kg）含量最高，其次是<0.25 mm粒级（8.08-23.53 g/kg）。各粒径团聚体湿筛分配到同一粒级的有机碳以保持原粒级的含量最高（P<0.05）；土壤团聚体水稳性与各粒径团聚体湿筛后保持原粒径的有机碳呈显著或极显著正相关（P<0.05或0.01），分配到越小的粒级正相关性越不显著。此外，团聚体水稳性与各粒径团聚体湿筛分配到同一粒级的有机碳呈正相关，以保持原粒级相关性最高（P<0.01或0.05）；回归方程及相关性系数表明，有机碳与保持原粒径团聚体呈显著呈或极显著正相关（P<0.05或0.01），与消散到其他粒级的团聚体呈负相关或极显著负相关（P>0.05或<0.01）。本研究得出有机碳含量增加促进更大粒径团聚体形成。反之，促使大粒径团聚体向较小粒径团聚体转化。同一粒级团聚体间，保持原粒级团聚体比易转化形成更大粒级团聚体有更高的有机碳含量和更强的水稳性，这对团聚体的固碳提供了新的认识。;Compared with the traditional Elliott wet screen method, the modified wet screen method can be used to analyze the difference in organic carbon for the wet sieving of each particle size aggregate to the same size. This study selected 25a, 45a and 65a Masson Pine plantations as the research objects. Soil aggregates with different particle sizes were wet-screened by wet screening method. The organic carbon distribution of soil aggregates with different particle sizes in Masson Pine plantation was investigated after wet screening. The purpose is to explore the difference of the organic carbon distribution to the same size after wet screening of aggregates of various particle sizes and its influence on the water stability of aggregates. The results showed that the increase of planting years significantly decreased the water stability of soil aggregates (P<0.05); After wet screening, the organic carbon content of each particle size aggregates decreased firstly and then increased with the decrease of grain size, so as to maintain the highest organic carbon content of the original particle size aggregates (12.96-32.01 g/kg), followed by <0.25 mm particle size aggregates (8.08-23.53 g/kg). Wet sieve agglomerates of various particle sizes allocated to the same size of organic carbon to maintain the highest content of the original size (P<0.05); There was significantly or extremely significantly positive correlation between the water stability of soil aggregates and the organic carbon of the aggregates with the original particle size after wet screening (P<0.05 or 0.01). The smaller the particle size was allocated, the less significant the positive correlation was. In addition, the water stability of aggregates was positively correlated with the organic carbon allocated to the same grain size in the wet screen of aggregates with different particle sizes, and it had the strongest correlation with the organic carbon that maintained the original grain size (P<0.01 or 0.05). The regression equation and correlation coefficient showed that the organic carbon had a significantly or extremely significantly positive correlation with the aggregates with original particle size (P<0.05 or 0.01), and an extremely significantly negative correlation with the aggregates dispersed to other particle sizes (P>0.05 or <0.01). This study concludes that organic carbon is an important cementing material for the formation of aggregates, and the increase of organic carbon content can promote the formation of larger size aggregates. On the contrary, it promotes the conversion of large particle size aggregates to small particle size aggregates. In addition, comparison among aggregates of the same grain size, maintaining the original particle size aggregates have higher organic carbon content and stronger water stability than easily transforming into larger particle size aggregates, which provides a new understanding for the carbon sequestration of aggregates.

B-39 ウェットスクリーンを用いた防排煙システムの概要と性能評価 : 超高層オフィスビルにおける設計事例

B-39 ウェットスクリーンを用いた防排煙システムの概要と性能評価 : 超高層オフィスビルにおける設計事例

Characteristics of soil stability and carbon sequestration under water storage and drainage model

This research was conducted to investigate the influence of saline alkali soil on soil physical properties, stability and organic carbon storage under water storage and drainage, and to provide scientific basis for improving soil quality in Fuping County of Shaanxi Province, China. Saline alkali soil model test was conducted and the process was assessed with two different methods: i) traditional drainage and ecological water storage, measure and analyze 0-30 cm soil bulk density, porosity, field water capacity, mean mass diameter (MWD), geological mean diameter (GMD), stability of water stable aggregate (WASR), aggregate destruction rate (PAD), fractal dimension (D) and; ii) organic carbon storage, comprehensively analyze the relationship between stability index and soil organic carbon. The results show that: (1) compared with traditional drainage treatment, water treatment may effectively reduce the soil bulk density by 1.3%-4.2%, and improve soil porosity and field capacity at the same time; (2) under dry and wet screen treatment, soil stability, the water storing treatment is higher than the drainage treatment. Performance trend of soil MWD and GMD increases with the increase of soil depth. The stability of soil water stable aggregates increased 14.5%-53.4%. The average aggregate destruction rate was 3.2% lower than that of the drainage treatment and the difference is obvious (P< 0.05). (3) Soil organic carbon content and organic carbon storage in 0-30 cm soil layer could be increased effectively by water storage. Both of them were 13.4%-27.9% and 9.9%-18.8% higher than the drainage treatment. (4) There is a negative correlation among average aggregate destruction rate, fractal dimension and soil organic carbon storage. The correlation coefficient is, respectively, R2=0.86 and R2=0.94, and the difference is obvious (P<0.05). To sum up, the water storage treatment can effectively improve the soil quality, improve soil stability and soil organic carbon storage, which can be a good control of saline alkali soil.

Process Improvement on the Gradation Uniformity of Steel Slag Asphalt Concrete Aggregate

A great amount of steel slag aggregate is used to prepare cement concrete and asphalt concrete in road construction However, the steel slag aggregate processed by the traditional aggregate production line is not uniform, which is not conducive to the full-size utilization of steel slag. Therefore, a new method of steel slag aggregate processing was proposed in this study in order to obtain the high quality steel slag aggregate with different specifications Experimental results indicated that the specifications stability of the steel slag was improved significantly when the steel slag was crushed by the combination equipments of jaw crusher and cone crusher. The screening efficiency and stability of the aggregate can be improved as the multi-level screening equipments were used into the production line. The wet rolling screen was also developed to remove the dust on the surface of aggregates. The specifications stability and pavement performance indexes of the steel slag aggregate produced by the new production line have been improved significantly compared to the steel slag aggregate produced by the traditional production line.

Ultrasonic Attenuation Changes with Damage Level in Various Sized Concrete Specimens

The attenuation of ultrasonic pulse velocity in various sized concrete specimens under uniaxial compression loading is tested. Tests were conducted on prisms of 25×25×50 cm fabricated with dam concrete(maximum aggregate of 80mm),and standard 15×15×30 cm prisms,10×10×20 cm prisms which were made with the wet-screened components of dam concrete. Ultrasonic attenuation has been shown to increase significantly as distributed damage in concrete increases. Large changes in attenuation with increasing damage levels were found for all specimens at all power levels. Results also show that the rule of ultrasonic propagation in concrete is apparently affected by the scale effect and the effect of wet screen sieve of aggregate. These conclusions proposed can be applied to determining the extent of damage of mass concrete due to the complex load and other environmental effects.

Fabrication and field emission characteristics of SnO 2 electron sources based on planar-gate-type cathode arrays

An SnO 2 electron source based on planar-gate-type cathode arrays was successfully fabricated by conventional photolithography, chemical wet etching and screen printing. A screen printing process was developed to deposit SnO 2 field emitters onto the triode structure. An image of planar-gate-type field emission arrays (FEAs) with SnO 2 field emitters were measured by the optical microscopy and scanning electron microscopy (SEM). The structure parameters and electric field strength distributions and trajectories of planar-gate-type triode were simulated by an ANSYS software. In addition, field emission characteristics of planar-gate-type triode with SnO 2 field emitters were investigated. The experiment results show that the turn-on voltage of this triode structure at current density of 1 μA/cm 2 is approximately 60 V. The anode current and gate current comes to 484 and 330 μA, at gate and anode voltages of 120 and 3000 V, respectively, and at the anode–cathode spacing of 2000 μm. Although the emission efficiency is modified from 72.7% to 59.3%, the luminescent uniformity and lightness of the fabricated cathode arrays obviously improve with the increases of gate voltage from 90 to 120 V. Moreover the emission current fluctuation was smaller than 15% for 15 h, which indicates that the fabricated device has a good field emission performance and long lifetime.

Endochronic damage constitutive model for fully-graded aggregate mass concrete

The behavior of deformation and strength of a fully-graded aggregate concrete under complex stress state is the basis of the nonlinear analysis and design for mass concrete structures such as concrete dams. In this paper, based on the combined endochronic theory with damage mechanics and on the quantities of experimental data, an endochronic damage constitutive model suitable for various aggregate grade concrete is proposed. This model takes into consideration the scale effect and the effect of wet screen sieve of aggregate in which the concept of yield surface is not needed and the difference of damage evolution rule of various graded aggregate concrete is a concern. The proposed model is used to analyze the deformation and strength of fully-graded aggregate mass concrete and the wet screened aggregate concrete specimens. The calculated results are in good agreement with experimental data, which can be used as a guide for the design of arch dams and other mass concrete structures.

Graded porous TiO 2 membranes for microfiltration

Membrane technology can be integrated into many advanced system concepts for the production of liquid energy carriers and chemicals, for microfiltration, oxygen generation, low-CO 2-emission power generation, hydrogen technology and carbon dioxide capture. Forschungszentrum Jülich has developed a composite membrane consisting of a ceramic TiO 2 membrane with pores in the range of 100 nm deposited on a thin planar metallic substrate made of 316L stainless steel powder. Fabrication of substrate and membrane is described in this paper and the composite structure is characterized. The stainless steel substrate is produced by tape casting, the TiO 2 membrane by wet powder spraying or screen printing. Light microscopy, scanning electron microscopy, EDX and XRD are used to characterize the starting materials and layers. The measurement of air flow rates as a function of the pressure drop is given.

Fabrication of monolithic piezoelectric drive units for a miniature robot

In this paper, we present the design and assembly of a miniature robot, with a size of a few cm3, which should be able to move freely over distances in the centimetre range performing high precision manipulating operations on micrometre-sized objects with a precision in the nanometre range. The final robot will carry an application specific integrated circuit containing power drivers and a digital control system with a fast serial interface protocol. Two six-legged monolithic piezoelectric drive units generate the motion. Each leg is a three-axial multilayer piezoceramic enabling a five-axial manipulation operation. The fabrication of the drive units is described in detail. The multilayer structures are fabricated with wet building and screen printing. The green material is machined to single components using a high precision CNC micromilling machine. The motion capacity of the legs has been evaluated and major limitations restraining the motion capacity and further miniaturization have been identified. Firstly, the patterning of the internal electrodes should be improved, but also the milling operation has to be considered.

Gas flow across a wet screen: analogy to a relief valve with hysteresis

The flow of gas through a wet fine-mesh screen is analysed in terms of the capillary forces of the liquid wetting the screen and the pressure difference across the screen thickness driving the gas flow. Several different types of time-dependent flow are shown to be possible. The most interesting type is one in which the pressure difference opens small channels in the liquid, which are then closed rapidly by the wetting action of the liquid. The opening and closing exhibit hysteresis, and the flow is highly oscillatory.

Effect of Sieve Size for wet and Dry Screening on the Physical Properties of Lactose Granules and Their Corresponding Tablets

AbstractVarious batches of lactose granules were prepared by wet granulation process using acacia, cassava starch and polyvinylpyrrolidone separately as binders by inter-changing sieves for wet and dry screening, The effects of wet and dry screen aperture sizes together with the effects of the binders used on the physical properties of such granules and the corresponding tablets were investigated. The bulk volume of granules was found to be increased as the aperture size of sieves for dry screening increased while keeping a particular sieve constant for wet screening. No significant difference was observed with regards to the effect of sieve size upon the flow rate.It was also observed that keeping the sieve size for wet screening constant, the mean tablet weight increased while the tablet weight variation decreased as the sieve size for dry screening decreased. There found to be an observable relationship between the sieve sizes used for dry and wet screening, average granule size and hardness of tablets...

Effect of limestone type and grind on SO2 scrubber performance. The cost‐reduction effect of finer limestone grinding on SO2 scrubber efficiency can be very considerable

The major objective of this paper is to compare the amount of limestone feed required as a function of particle size, to obtain a given SO/sub 2/-removal efficiency. Experimental data were also obtained with limestones from four different quarries ground to similar sizes, 90 percent -325 mesh and 70 percent -200 mesh, to test the geological or type effect on limestone reactivities. The second objective of this paper is to test the effectiveness of wet screen analysis as a means of classifying limestone grinds for scrubber use. A mass-transfer model and Coulter-counter particle-size distribution data were also tested as a means of defining limestone reactivities.

Studies on Wet Screen for the Elimination of Low Level H2S

Studies on Wet Screen for the Elimination of Low Level H2S

Components of the Radiation Balance of Irrigated Plots in a Dry Monsoonal Environment

Over irrigated crops of cotton grown in a dry monsoonal environment, net radiation was measured daily over a period of one year together with total radiation, duration of sunshine, and wet and dry bulb screen temperature. Daily estimates of total, effective terrestrial, and net radiation were obtained from several empirical relationships, and these were compared with measured values. The reliability of alternative modes of estimating these components of the radiation balance was assessed. When estimating total radiation from relative duration of sunshine, a hyperbolic relation was found more effective in accommodating low values than the commonly used linear relationship. When estimating effective terrestrial radiation from a relationship used by Penman, it was necessary to derive constants appropriate to this environment using data an clear days. Effective terrestrial radiation was also estimated using a relationship based upon a proposal by Swinbank which does not include a vapor pressure term. Although wet-season estimates were found to be in significantly better agreement with observation when vapor pressure was included, satisfactory estimates can nevertheless be obtained without vapor pressure data. Significantly better estimates were obtained when total radiation was used rather than relative duration of sunshine in accounting for the effect of cloudiness on the downward long-wave radiation flux. Errors in the estimated effective terrestrial radiation were found to be the major contributors to inaccuracy in the estimation of net radiation.