Anisotropic Oxidative Growth Of Goethite-Coated Sand Particles In Column Reactors During 4-Chloronitrobenzene Reduction by Fe(II)/Goethite

Reduction of nitroaromatic compounds (NACs), an important class of groundwater pollutants, by Fe(II) associated with iron oxides, a highly reactive reductant in anoxic aquifers, has been studied widely, but there...

Research of the resistance process of casing column filters at their contact with rock

The analysis of theoretical solutions and experimental data given in numerous literatures to justify the choice of the ratio of the size of gravel in relation to the size of formation sand showed that with the development of experimental methods and the accumulation of laboratory and field data, this ratio tends to decrease. When installing filters in an open hole, pressure losses at the interface between gravel and the formation play a significant role, and it should be noted that the greatest productivity and efficiency of the filter in an open hole is achieved when there is a packing around it, which can be created by crushing the sandy massif of the formation by cyclical changes debit. When choosing a filter design, along with the ability to provide them with a reliable hydraulic connection in the reservoir-filter system, the main task is also solved - to prevent sand flow into the well. The study of the conditions for the removal of sand particles through the flow sections in perforated, mesh and slotted filters during their operation both in homogeneous and in sands of different size, made it possible to recommend empirical dependences for determining the size of the holes. Keywords: porous medium; coarse fraction; sand; particle; well.

Efficient Sandstorm Image Enhancement Using the Normalized Eigenvalue and Adaptive Dark Channel Prior

A sandstorm image has features similar to those of a hazy image with regard to the obtaining process. However, the difference between a sand dust image and a hazy image is the color channel balance. In general, a hazy image has no color cast and has a balanced color channel with fog and dust. However, a sand dust image has a yellowish or reddish color cast due to sand particles, which cause the color channels to degrade. When the sand dust image is enhanced without color channel compensation, the improved image also has a new color cast. Therefore, to enhance the sandstorm image naturally without a color cast, the color channel compensation step is needed. Thus, to balance the degraded color channel, this paper proposes the color balance method using each color channel’s eigenvalue. The eigenvalue reflects the image’s features. The degraded image and the undegraded image have different eigenvalues on each color channel. Therefore, if using the eigenvalue of each color channel, the degraded image can be improved naturally and balanced. Due to the color-balanced image having the same features as the hazy image, this work, to improve the hazy image, uses dehazing methods such as the dark channel prior (DCP) method. However, because the ordinary DCP method has weak points, this work proposes a compensated dark channel prior and names it the adaptive DCP (ADCP) method. The proposed method is objectively and subjectively superior to existing methods when applied to various images.

Effect of Nutrient Solution Composition on Bio-Cemented Sand

Microbial-induced carbonate precipitation is an environmentally friendly foundation treatment technology that effectively improves soil engineering performance. The various nutrient components of liquid curing compounds significantly influence the curing effect. On the basis of penetration, dry density, water absorption, and unconfined compressive strength tests, this study showed the effect of nutrient solution composition, including urea, calcium chloride, sodium bicarbonate, ammonium chloride, and nutrient broth, on the physicomechanical properties of bio-cemented sand. The morphological differences of calcium carbonate precipitates under nutrient solution composition were compared through scanning electron microscopy (SEM). Results showed that the curing effect of compound nutrient solution was improved compared with the basic nutrient solution (urea and calcium chloride). Among the individual components added, ammonium chloride had the most remarkable effect, followed by sodium bicarbonate and nutrient broth. Among the paired components added, sodium bicarbonate + ammonium chloride had the most significant effect, followed by sodium bicarbonate + nutrient broth and ammonium chloride + nutrient broth. The strength of bio-cemented sand cured with compound nutrient solution containing five components could reach 3.43 MPa, which was 1.92 times higher than the strength of the basic nutrient solution. As shown by the SEM image, the calcium carbonate precipitation in the solidified sand was distributed in the clearance of sand particles, effectively bonding the sand particles. The calcium carbonate obtained by the composition of the compound nutrient solution precipitated the sand particles, and some of the sand particles were wrapped. Moreover, the amount of precipitation was evidently greater than that of the basic nutrient solution. Compared with the basic nutrient solution, the compound nutrient solution effectively reduced the apparent porosity and average pore size of the sand. Thus, the curing effect of the compound nutrient solution was better than that of the basic nutrient solution.

The Analysis of Erosive Wear Resistance of WC-Co Carbides Obtained by Spark Plasma Sintering Method

WC-Co (tungsten carbide-cobalt) composites are widely used in industry, wear-resistant parts, and cutting tools. As successful tool materials, WC-Co carbides are widely applied in metal cutting, wear applications, chipless forming, stoneworking, wood, and plastic working. These materials are exposed to severe solid particle erosion by sand particles, such as in the wood industry. During the production of furniture with HDF (High Density Fibreboard), MDF (Medium Density Fibreboard), or OSB (Oriented Strand Board), there are observed problems with tool erosion. Contamination, mainly of the HDF by sand, is quite often, which is why all tools used for the machining of such materials are exposed to erosion by sand particles. Although many studies have been performed on the erosion of various metals, and erosion models exist to predict their erosion behavior, the issue is still relevant. The aim of the study was to determine the effect of grain size (submicron, ultrafine) and the manufacturing technology (SPS—Spark Plasma Sintering, conventional) used on the erosive properties of WC-Co sintered carbides. Sinters produced by the SPS method with different sizes of WC grains and commercial samples were used for the tests. Ten two-hour cycles were carried out under medium conditions of quartz sand and quartz sand with 10% SiC added. Used samples were characterised using scanning electron microscopy (SEM) and roughness was determined. Furthermore, erosion studies allowed individuating a wear mechanism as well as the possibility to foresee cutting performance in prospective application.

Wind Tunnel Test on Windblown Sand Two-Phase Flow Characteristics in Arid Desert Regions

Windblown sand two-phase flow characteristics become an essential factor in evaluating the windblown sand load on infrastructures and civil structures. Based on the measured wind characteristics in arid desert regions, windblown sand flow fields with three kinds of sand beds are simulated in the wind tunnel, respectively. The results indicate that the characteristic saltation height of sand particles increases with the wind speed and particle size in the windblown sand flow field. As the sand concentration increases, the wind speed decreases, and the turbulence intensity increases. The concentration, energy, and impact pressure of sand particles increase with increasing wind speed and decrease exponentially with increasing height. At the same wind speed, the concentration, energy, and impact pressure of the coarse sand, fine sand, and mixed sand increases, in turn. Moreover, the variation of kinetic energy with height is similar to that of total energy with height and the proportion of potential energy to total energy is quite small.

Flow hydraulic simulation through two sand traps, using Ansys fluent

Computational fluid dynamics is a tool that allows to simulate and observe the behavior of any fluid, based on a physical, hydraulic, and hydrodynamic analysis. This research analyses the behavior of the flow in a sand trap, which is a structure used to remove sand particles with a minimum size of 0.10 mm, prior to treatment in a drinking-water plant. The objective of this study is to determine the highest efficiency between two sand traps, one with a double smooth screen and the other with a double perforated screen (with diffusers), based on the simulation and analysis behavior of the flow inside each sand trap. The methodology used includes the traditional design of each unit based on Hazen’s model and Stokes viscosity law, to later carry out the numerical model simulation from Ansys Fluent (pre-processing, processing, and post-processing). The result shows that perforated double screen sand trap generates a removal efficiency of 78%, while the smooth double screen 28%. In addition, other four units of interleaved screens are proposed, in these cases efficiencies of up to 50% are observed and it is shown that it is necessary to implement at least two perforated screens (with diffusers) to guarantee an efficiency greater than 70%. Hydraulic simulation has a broad impact on infrastructure works and consulting.

The Mechanical Properties and Microstructure of Reticulated Red Clay-Sand Mixture Using X-Ray Diffraction

To assess the behavior of Reticulated Red Clay (RRC)-sand mixtures, a series of laboratory tests were performed on RRC-sand mixtures in which the weight ratio of sand ranging from 0% to 80%. Compaction test and direct shear test were conducted to evaluate the compactness of mixtures. The threshold sand content for the change of the mechanical properties of the mixture is 50%, and the mixture at this time has the densest structure. Oedometer test to the mixture indicate that the coefficient and compression modulus of it are only related to the ratio of its components. As the sand content in the mixture increases, the phenomena that the clay particles enclosing the sand particles and filling into the gaps of particles make the mixture denser. During the same time, there is a phenomenon of internal friction between sand particles caused by the inadequate wrapping of clay particles. Combined with the results of scanning electron microscopy and optical microscopy, the appearance of these phenomena and the transition process of the structure of the mixture from the clay structure to the sand structure were confirmed.