Mechanical trapping of fine particles in a medium of mono‐sized randomly packed spheres     

M. Mahdi Roozbahani  Lori Graham‐Brady  J. David Frost 《国际地质力学数值与分析法杂志》2014,38(17):1776-1791

Mechanical trapping (or straining) of fine particles is a key mechanism in many filtration systems. For example, the performance of rapid sand filters depends in part on mechanical trapping of larger fine particles, while relying on adsorptive processes to trap very small fine particles and microbes. The ability to trap these particles is directly related to the construction of the packed bed used for filtration in this system. Thus, the ability to model the effect of the inner structure of the packed bed can lead to more efficient design for improved filtration. Because of its significant efficiency, gravitational sphere packing is employed in this work to simulate a bed of mono‐sized randomly packed spheres. The simulated bed provides a way to visualize the pore network and estimate the pore size distribution associated with the void space between particles. Furthermore, by subsequently introducing fine particles into the bed, we evaluate the mass‐rate of fine particles passing through and possibly saturating the packed bed. Results show that fine particles between 15% and 25% of the coarse particle size can be physically strained within the randomly packed bed. These results differ significantly from the results obtained assuming a periodically spaced bed. The technique therefore provides an efficient yet accurate alternative for understanding how fine particles pass through a coarse particulate medium. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

高密度低失水泥浆体系在煤田绳索取心钻探中的应用研究          下载免费PDF全文

陈尔志  陈礼仪  向昆明  章述  尹亮先  李跃成 《探矿工程》2011,38(2):15-18

煤田钻探中,经常会遇到比较破碎、易坍塌、易水化膨胀等复杂地层,给钻进造成较大的困难。开发了具有良好的防塌性能、较好的抑制性并具有适当密度的高密度低失水泥浆体系。现场使用证明,该泥浆体系在煤田小口径金刚石绳索取心钻探中能很好维持孔壁稳定、有效抑制泥页岩的水化膨胀,降低孔内事故的发生率。  相似文献   

基于遥感数据的江苏省水稻收获期时空分析研究          下载免费PDF全文

朱晓晨  李强宇  曾燕  董恒鑫  祝嗣嫄 《气象科学》2023,43(4):534-542

本研究基于2001—2020年中分辨率成像光谱仪遥感产品,使用谐波分析重建完整作物生长过程植被指数变化曲线,对江苏省范围内水稻种植区域的收获期进行提取。同时利用Sen趋势分析与相关分析方法,研究水稻收获期时空动态变化趋势与影响因子。结果表明:利用谐波分析方法能够较好地重建作物生长期生理参数变化曲线,滤波值与原始值线性相关系数达到0.8;水稻收获期分布在9月中旬到12月上旬之间,2010年之后,10月中下旬之后占比增加,达到50%以上;部分地区水稻收获期呈现延迟趋势,南京北部、扬州、盐城北部地区为3 d·a^-1及以上,泰州、南通等地区保持稳定,趋势绝对值低于1 d·a^-1;9—11月降水日数与降水量均对水稻收获期有影响,10月降水量与收获期存在负相关,10、11月降水日数与收获期存在正相关。本研究的基于遥感的水稻收获期提取方法为大范围的水稻农业物候信息提取提供参考。  相似文献   

氨氮在垂向河床渗滤系统中的环境行为   总被引：1，自引：0，他引：1  

黄瑞华  吴耀国  杨炳超  妙颖 《地球科学与环境学报》2006,28(1):92-95

采用自行设计的室内土柱实验装置,以恒定氨氮质量浓度为18.27 mg/L的氯化铵溶液为淋滤液,模拟氨氮在垂向河床中的渗滤过程,来探讨氨氮在垂向河床渗滤系统中的环境行为,借以了解河床渗滤系统对氮污染的净化机理。研究结果表明:氨氮在河床渗滤过程中分别参与吸附及硝化作用,主要发生在距离河床1~3 cm处;由于这两种作用的影响,该河床渗滤系统对氨氮的去除率达87%。同时还发现,该河床渗滤系统对氨氮的硝化能力有限,可以考虑向污水中补充溶解氧及添加石灰等强化措施来提高硝化能力。  相似文献   

Dispersion of guided waves in thin anisotropic waveguides   总被引：1，自引：0，他引：1  

Min Lou  Stuart Crampin 《Geophysical Journal International》1991,107(3):545-555

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Fractionation and concentration of suspended particulate matter in natural waters     

G. B. Douglas  R. Beckett  B. T. Hart 《水文研究》1993,7(2):177-191

A scheme for the fractionation and concentration of suspended particulate matter (SPM) from natural waters has been tested. This scheme involves the sequential use of three fractionation techniques—sieving, continuous flow centrifugation and tangential flow filtration to collect gram amounts of SPM over the entire particulate and colloidal size range. The separation scheme is able to process large samples (ca. 1001), within reasonable times (ca. 1 day) and the apparatus is portable. Reproducibility and potential artifacts introducing during the fractionation and concentration of SPM, particularly when tangential flow filtration is used, are discussed. It has been shown that there is a systematic increase in the content of organic carbon, Mg, Ca, Na, K, Cu and Zn with decreasing particle size, highlighting the importance of the colloidal ( < 1 μm) fraction.  相似文献   

The nature of iron and manganese species in dam waters     

Barry Chiswell  Myint Zaw 《水文研究》1989,3(3):277-288

The molecular weight (M. W.) distributions of iron and manganese species in dam water samples were investigated by use of gel filtration, while the ion-exchangeable and non-ion-exchangeable fractions of these metals were also analysed by ion-exchange chromatography. For the samples studied, more than 96 per cent of the manganese species present were found to be ion-exchangeable, whilst less than 35 per cent of iron species were ion-exchangeable. These results correlated with the finding that all the manganese species had molecular weights less than 700, but that the molecular weights of the iron species were mostly in excess of 5000. Electron paramagnetic resonance (EPR) spectroscopy has been used to support the finding that manganese is almost totally present in the form of simple aquated Mn(II) ions.  相似文献   

Economic valuation of suspended sediment and phosphorus filtration services by four different wetland types: A preliminary assessment for southern Ontario,Canada     

Tariq Aziz  Philippe Van Cappellen 《水文研究》2021,35(12):e14442

Wetlands are known for their water filtration (or purification) function. Although different wetland types differ in their filtration capacity, they are usually aggregated together in economic valuation studies. Here, we explicitly separate the valuation of the suspended sediment and phosphorus (P) filtration services of the four major wetland types—bogs, fens, marshes and swamps—found in southern Ontario, Canada. The areal extents of the four wetland types are derived from the Canadian Wetland Inventory (CWI) progress map, while the sediment accretion rate is used as the key variable regulating the suspended sediment and P filtration functions. Based on available literature data, we assess the relationship of the sediment accretion rate to wetland size. Because only weak positive correlations are found, we assign a mean (average) sediment accretion rate to each wetland type. The sediment accretion rates are combined with mean soil P concentrations to estimate Pretention rates by the wetlands. The replacement cost method is then applied to valuate the sediment and P filtration services. The unit values for both sediment and P retention decrease in the order: marshes > bogs ≈ swamps > fens. The total value of sediment plus phosphorus removal by all wetlands in southern Ontario amounts to $4.2 ± 2.9 billion per year, of which about 80% is accounted for by swamps. We further assess the costs of different options to offset the additional P loading generated in a hypothetical scenario whereby all wetlands are converted to agriculture. The results demonstrate that replacing the P filtration function of existing wetlands with conventional land management and water treatment solutions is not cost-effective, hence reinforcing the importance of protecting existing wetlands.  相似文献   

Particle Shapes in the Drinking Water Filtration Process     

Michał Zielina 《洁净——土壤、空气、水》2011,39(11):941-946

Depth filtration is still one of the most important water treatment processes. It remains difficult to model mathematically because of the complexity of the process and the impact of numerous suspension parameters. The shape of the grains and suspension particles or flocs are among these parameters. The results of theoretical calculations suggest their visible impact on filtration. The shape of the media grain is relatively easy to measure. The shapes of the flocs or suspension particles, which are commonly not perfectly spherical, are much more difficult to predict. However, a few apparatuses developed lasting recent years make this possible. The FPIA 3000, manufactured by Malvern Instruments, uses flow particle image analysis method to measure 26 shape parameters of the suspension particles. Experimental measurement of suspension particle shape after flocculation and after depth filtration has allowed us to answer the question regarding the possible application of this measuring technique in water filtration technology. The experiments have also provided us with detailed information about the shape of flocs and suspension particles in filtered water. High number of particles characterized by circularity lower than 0.8 was detected in flocculated water inflowing to the filter. The particles remained in the outflow was characterized by visibly higher circularity than the particles inflowing to the filter. The results revealed much better removal of the particles characterized by lower circularity during filtration, whereas relation between convexity of the particles and their removal efficiency was not so evident.  相似文献   

渤海湾盆地应用增强型地热系统（EGS）的地质分析   总被引：2，自引：0，他引：2  

蒋林 《地质与勘探》2013,49(1):167-178

全球地下3～ 10 km普遍分布的高温低渗岩体中蕴藏着巨大的热能,利用增强型地热系统(EGS)技术可以实现这部分热能的开发.本文通过对近年增强型地热系统的研究进展和经验的综述,结合区域地质分析和有限元模拟,探讨了渤海湾盆地应用增强型地热系统开发的可行性.我国渤海湾盆地处于岩石圈减薄区,区域大地热流值高,地热资源丰富;基于该区的岩石圈热状态、基底构造形态对渤海湾盆地典型剖面地下10 km内的地温场进行了有限元模拟,结果表明,在基底凹陷区埋深5 km处地温可达150 ～180℃,地温等温线随基底起伏而变化.相比美国、欧洲现有的EGS开发地区,渤海湾盆地具有相似的地温条件和地质条件,适于开发增强型地热系统.通过分区块的资源概算,得出渤海湾盆地陆上部分的增强型地热系统可及资源量可达3775GWe,具有广阔的开发前景.  相似文献