Application of CFD on the sensitivity analyses of some parameters of the modified Hartmann tube

The aim of this work is to determine the influence of operating parameters such as the dispersion pressure, the ignition delay and height on the dust flammability. A Computational Fluid Dynamics (CFD) simulation, based on an Euler–Lagrange approach, was developed with Ansys Fluent™ and validated experimentally. Such analysis will facilitate the choice of the most conservative conditions for a flammability test. This paper is focused on a case study performed on wheat starch with the modified Hartmann tube. The dispersion process of the powder was studied with granulometric analyses performed in situ and high speed videos. Tests were performed with injections at gas pressure ranging from 3 to 6 bars and the evolution of the particle size distribution (PSD) was recorded at different ignition heights (5, 10 and 15 cm over the dispersion nozzle). The observations highlighted the presence of agglomeration/deagglomeration processes and dust segregation. Besides, a CFD simulation analysis was aimed at evaluating the impact of a set of parameters on the PSD and the local turbulence, which are closely linked to some flammability parameters. For this computational analysis, the CFD simulation was coupled with a collision treatment based on a Discrete Element Method (DEM) in order to consider the cohesive behavior of the combustible dust. Thus the results suggest performing the injection of the gases at approximately 5 bars for the flammability tests of wheat starch in order to obtain the finest PSD at a given ignition height. It is also shown that the finest PSD are obtained at 5 cm over the dispersion nozzle. However, the local instabilities and turbulence levels are so high during the first stages of the dispersion that the flame growth can be disturbed for short ignition delays. Moreover, the stabilization of the bulk of the dust cloud requires longer periods of time when the ignition sources are located at 15 cm. As a result, the recommended height to perform a flammability test is 10 cm in this case. Finally, this study proposes some tools that might improve the procedure of dust flammability testing.     

Composition and source apportionment of dust fall around a natural lake

The aim of this study was to determine the source apportionment of dust fall around Lake Chini, Malaysia. Samples were collected monthly between December 2012 and March2013 at seven sampling stations located around Lake Chini. The samples were filtered to separate the dissolved and undissolved solids. The ionic compositions(NO-3, SO2-4, Cl-and NH+4) were determined using ion chromatography(IC) while major elements(K, Na, Ca and Mg) and trace metals(Zn, Fe, Al, Ni, Mn, Cr, Pb and Cd) were determined using inductively coupled plasma mass spectrometry(ICP-MS). The results showed that the average concentration of total solids around Lake Chini was 93.49 ± 16.16 mg/(m2·day). SO2-4, Na and Zn dominated the dissolved portion of the dust fall. The enrichment factors(EF) revealed that the source of the trace metals and major elements in the rain water was anthropogenic, except for Fe. Hierarchical agglomerative cluster analysis(HACA) classified the seven monitoring stations and 16 variables into five groups and three groups respectively. A coupled receptor model, principal component analysis multiple linear regression(PCA-MLR), revealed that the sources of dust fall in Lake Chini were dominated by agricultural and biomass burning(42%),followed by the earth's crust(28%), sea spray(16%) and a mixture of soil dust and vehicle emissions(14%).     

深埋水平岩层隧道开挖稳定性分析及控制*

针对深埋高地应力水平岩层掌子面开挖稳定性及支护结构失效问题,以大峡谷隧道为工程背景,通过现场测试、室内试验、数值模拟等方法,探究深埋高地应力水平岩层失稳机理及控制措施。研究结果表明:坚硬岩体被节理面切割后,在高地应力作用下容易发生挤压破碎,破碎岩体遇水发生软化,导致掌子面发生大范围塌方,初支和超前支护失效;隧道开挖后岩层发生不均匀沉降,浅部岩层最先发生弯折破坏,层内块体错动滑移,继而向上方岩层发展,并伴随层间分离和层内裂隙发育,最终形成宏观破裂面;提出的台阶法、2 m开挖进尺、砼喷层、双层小导管、提高初支强度的整体优化控制措施,可有效提高现场支护效果。     

Estimation of Landscape Potential for Construction of Surface-Flow Wetlands for Wastewater Treatment in Estonia

The main aim of this article is to demonstrate a method of complex landscape analysis in order to estimate the landscape suitability for the construction of surface-flow wetlands (SFW) for wastewater treatment. This is a multilevel suitability analysis from a more general regional (landscape) assessment based on a map of landscape types (1:100,000) toward a detailed analysis based on aerial orthophotos and detailed soil maps (1:10,000). The assessment scheme consists of landscape classification according to the physical-chemical properties of landscape factors (soil conditions, landforms, hydrogeology, expert decisions concerning landscape values, and suitability analysis). The partial suitability values of SFWs are derived by summarizing expert values for landscape factors (each ranging from -1 to +1). By multiplying the summarized partial suitability values with nature protection values (ranging from 0 to 1), we obtain the final suitability value for each landscape type. Any kind of nature protection area has been considered nonsuitable and excluded at regional-level analysis. The results of the regional analysis demonstrate that suitability is distributed relatively equally over the study area. The high suitability potential (classified as "very suitable") is relatively evenly distributed in lowland regions throughout the country. The share of "very suitable" and "suitable" areas in different counties varies from 5 to 23% and 7 to 49%, respectively. The detailed analysis based on aerial orthophotos showed that areas suitable for SFWs can also be found within the areas determined to be unsuitable based on the less detailed map of landscape types, whereas differences are much greater between settlements chosen for the detailed suitability analysis.     

焙烧炉筒体结构强度有限元分析

对焙烧炉筒体结构进行有限元建模仿真,考虑热应力、压力和重力对筒体结构受力的影响,计算了焙烧炉关键部位的蠕变疲劳寿命,同时探究进气温度、保温层及对流系数等参数的影响。结果表明:热应力是影响结构强度的关键因素;焙烧炉筒体在许用蠕变变形量为5%的情况下,其使用寿命超过设计寿命;在筒体加热过渡段铺设保温层,降低与外界空气对流和提高进气温度,有利于降低筒体应力。     

关于区域可持续发展的系统分析

本文从更高、更新、更综合的高度和角度,对区域社会可持续发展系统进行了单元要素分析、结构层次分析。提出了三单元要素、三结构层次、三种发展类型的设想。这种分析尽管还是初步的、定性的、不很深刻的,但是为研究可持续发展系统提供了一种新的思路。     

Ammonia volatilization and availability of Cu, Zn induced by applications of urea with and without coating in soils

Ammonia volatilization and the distribution of Cu and Zn were investigated in two types of soil treated with coated and uncoated urea. The rate of ammonia volatilization in two weeks after fertilizing with coated urea was 8% in soil 1 (soil derived from river alluvial deposits in Dongting Lake Plain) and 5.15% in soil 2 (red soil derived from quaternary red clay), about half the rates observed when fertilizing with common urea, implying that the hydrolysis speed of the coated urea was lower than for common urea, and that the coated urea can increase nitrogen use efficacy. As for the availability of Cu and Zn, their concentrations decreased in the first week after fertilization, and then increased, which was contrary to the effect of treatment on soil pH. For example, when the pH was 7.99, there was 0.79 mg/kg exchangeable Cu and 0.85 mg/kg exchangeable Zn in the soil derived from river alluvial deposits in Dongting Lake Plain. However, the concentrations of exchangeable Cu and Zn were generally lower for the common urea treatments than those with the coated urea because the peak pH for the common urea treatment was greater. The concentrations of these elements correlated well with pH in the range 4-8 in second order polynomial fits.     

某海洋平台上海水篮式过滤器事故分析

目的研究分析东海某一海上平台海水用篮式过滤器发生的腐蚀和堵塞事故原因。方法从海洋平台海水系统用篮式过滤器的原理、工艺流程、材料选择、滤网精度,滤芯设计、人工操作等多方面进行分析。结果受内压滤芯结构要优于受外压滤芯结构,如果过滤精度选择过高,会增加压差,造成滤芯堵塞。结论篮式过滤器滤芯单元应采用多滤芯的受内压结构,过滤精度应根据下游用户要求来确定。     

闽江口秋茄红树林凋落物产量及分解动态

于2017年以闽江口粗芦岛秋茄(Kandelia obovata)红树林为研究对象,分别采用凋落物收集框和分解袋法,研究秋茄凋落物产量及其碳(C)、氮(N)、磷(P)含量月动态及凋落叶分解过程中C、N、P含量与水解酶活性.结果表明:①秋茄凋落物年产量为618.79 g·m~(-2)·a~(-1),其中,叶占61.2%,果、枝和花分别占23.7%、10.5%和4.6%.②凋落叶总氮(TN)含量8月显著高于其他月份(p0.05),而TP含量在1—3月显著高于其他月份;C/N在8月显著低于其他月份(p0.05),而C/P及N/P在9月显著升高(p0.05).③在凋落叶分解过程中,C、N、P含量及其化学计量比随时间存在明显差异(p0.01),并且地上组TC、TN、C/N和C/P明显不同于地下组(p0.05).④在分解过程中,4种水解酶随时间存在明显差异(p0.01).⑤凋落叶酸性磷酸酶活性与土壤温度、电导率和凋落叶TP含量存在显著相关关系(p0.01).这些结果说明,秋茄凋落物产量及元素含量随季节变化存在明显差异;沉积作用对凋落叶分解过程中元素含量有显著影响,水解酶活性主要受凋落叶元素含量和土壤环境因子的控制.     

Response of the sediment geochemistry of the Changjiang River (Yangtze River) to the impoundment of the Three Gorges Dam

Based on the measurement of major and trace elements in suspended sediments in the low reaches of the Changjiang River during throughout a whole hydrologic year, the origins, seasonal variations, and fluxes of multielements and the human impacts on multielements transport processes have been analyzed along with the influence of weathering in the Changjiang River basin. The results show that most element contents were high in both autumn and winter and low in summer, which was largely caused by the dilution of discharge. Weathering detritus in the Changjiang River basin is the main source of most elements in suspended sediments. However, riverine pollution could bring more loadings of Cd, Pb, As and Zn into river water than it did a few decades ago. The annual average fluxes of Cd, Pb and Zn, which are major contamination elements, to the sea were 179 ± 21 tons/year, 7810 ± 675 tons/year, and 12,000 ± 1320 tons/year,respectively, in which approximately 8.7%, 11.9% and 2.7% of their loadings, respectively,were contributed by pollution inputs. Element exports mainly occurred in the summer(44.4%–57.4%) in the lower part of the Changjiang River. A general relationship between sediment retention and element content suggests a positive feedback mechanism for the decreased number of particles, in which element riverine loadings are reduced due to the enhanced trapping effect by the Three Gorges Dam(TGD). Compared to those in 1980,current element shares of the Changjiang River compared to the global budget have declined due to the construction of the TGD.