粒径对中密度纤维板粉尘爆炸特性影响实验研究

为探究粒径对中密度纤维板粉尘爆炸及相关特性的影响,采用20 L爆炸球、粉尘云最低着火温度装置、锥形量热仪和哈特曼管装置,对不同粒径粉尘的爆炸下限、最大爆炸压力、最低着火温度、热释放速率和火焰传播规律进行研究。结果表明,随着粉尘粒径减小,爆炸下限和粉尘云最低着火温度降低,最大爆炸压力逐渐增大;粉尘燃烧过程分为升温、着火、过渡、加剧和熄灭5个阶段,并出现2个峰值,热释放速率变化时间和吸热时间随着粒径减小而增加,热释放速率峰值增大;火焰在管道内的传播随着粒径减小先增强后减弱,管道外“火球”形状更大,火焰消散后火星数量变少,火焰尾端更加细长。     

Coefficient of earth pressure at rest for normally and overconsolidated peat ground in Hokkaido area

Peat, which is widely distributed in Hokkaido, is a very soft and problematic soil. To perform an elasto-plastic Finite Element (FE) analysis, it is important to accurately determine the initial stress conditions, and among them, the value of the coefficient of earth pressure at rest (K₀ value) is particularly important. A K₀-consolidation test using triaxial testing apparatus and a flat dilatometer were performed to investigate the K₀ value for peat ground in Hokkaido, Japan. It was found that the K₀ value for normally consolidated peat and organic clay (K_0NC) decreases with an increase in the ignition loss. The K₀ value for overconsolidated peat and organic clay (K_0OC) is more strongly dependent on the over consolidation ratio (OCR) than that of usual inorganic clay. That is, it is known that K_0OC is empirically related to K_0NC, as expressed by K_0OC=K_0NCOCR^m, and in peat and organic clay the power of m increases with their ignition loss. An experimental equation to estimate K₀ using a flat dilatometer for peat ground is also proposed.     

Flow patterns and vortex shedding behavior behind a square cylinder

The flow structures, wake-flow characteristics and drag coefficients of a square cylinder at various Reynolds numbers (Re) and incidence angles (θ) were experimentally studied in an open-loop wind tunnel. The cross section of square cylinder is characterized by the aspect ratio (AR) and blockage ratio (BR) of 25% and 4%, respectively. The Reynolds number is changed from 4000 to 36,000 and the incidence angle is adjusted from 0° to 45°. The flow patterns near/behind the square cylinder were determined using the smoke-wire scheme. The global velocity fields and streamline patterns were analyzed using the particle image velocimetry (PIV). Additionally, the flow-topology method was applied to analyze the flow patterns by calculating the separatrices, alleyways and critical points. Experimental results showed that the flow structures around the square cylinder exhibit three modes—leading-edge separation, separation bubble and attached flow. The surface-pressure profile, drag coefficient (C_D), lift coefficient (C_L) and vortex shedding frequency were detected/calculated using a pressure transducer and hot-wire anemometer. The lift coefficient did not significantly vary with Re. The minimum C_D occurs at θ=12°, whereas the minimum C_L occurs at θ=13°. The minimum projected-Strouhal-number (St_d) occurs at θ=0° while the maximum St_d occurs at θ=15°.     

Lead and cadmium composition in indoor dust

Pb and Cd levels in different size fractions of indoor dust have been analyzed by differential pulse anodic stripping voltammetry (DPASV) after digestion with HNO₃ and HF using a microwave oven. The relationship between Pb and Cd levels with dust size have been investigated and the metal levels in different sources of indoor dust are compared. In addition, the Pb and Cd composition in different size fractions of dust have been investigated by a sequential extraction method. Dusts are dominated by particulate matter < 500 μm. Pb levels in office dust in the particulate fraction > 75 μm are clearly shown to be higher than that in domestic dust. Generally, for domestic premises, Pb and Cd levels increase with a decrease in the particle size and with an increase in house age, while for office dust, the Pb level increases with an increase of particle size. For domestic houses, most of the metals are bound to carbonate and FeMn oxides in fine dust. For office dust, the situation is more complicated, with a clear increase in Pb in the organic and residue fractions in coarse dust.     

Emissions from power plants fueled by peat,coal, natural gas and oil

Measurements were carried out to investigate the emissions of SO₂, NO_x, fly ash, heavy metals, radioactive elements and polycyclic aromatic hydrocarbons (PAH) from one oil-fired, two coal-fired, five peat-fired and four natural gas-fired power plants or district heating plants.The emissions of sulphur dioxide depended mainly on the sulphur content of the fuel. In the combustion of oil, practically all the sulphur in the fuel reached the atmosphere as sulphur dioxide. When coal and peat were used as fuel, the amounts of sulphur retained in the ash were about 15 and 20%, of the original sulphur content, respectively. The SO₂ emissions from oil, coal, peat and natural gas were typically 1000, 600, 120, and < 10 mg MJ⁻¹, respectively.The emissions of oxides of nitrogen depended on the nitrogen content of the fuel and also on the combustion temperature. The NO_x emissions from plants burning oil, coal peat and natural gas were typically 100, 300, 160 and 100 mg MJ⁻¹, respectively. The lowest emissions were measured in the small natural gas-fired district heating plants (20–30 mg NO_x MJ⁻¹).The emissions of fly ash and various elements depended mainly on the ash content of the fuel and on the efficiency of the dust collectors, which decreases sharply when the power plant output exceeds its nominal value. When the dust separation efficiency is 99% for coal- and peat-fueled power plants, and when there are no dust collectors in oil-fueled power plants, the typical fly ash emissions are 45, 20 and 25 mg MJ⁻¹, respectively. Characteristic emissions of heavy metals and natural radioactive elements were greatest in the combustion of coal, with the exception of vanadium and nickel, of which the greatest emissions were from oil; the greatest emissions of ²¹⁰Po were from peat.The PAH emissions of the different fuel-fired power plants were, with one exception, similar (2–10 μg MJ⁻¹). Emissions from the circulating fluidized bed combustion of peat were about 10 times (40 μg MJ⁻¹) those of the other methods of combustion.     

Evaluating the arsenic attenuation of soil amended with calcium–magnesium composites of different particle sizes

An attenuation layer composed of ground mixed with stabilising agents can prevent the contamination of the surrounding area when using soils and rocks with geogenic contaminants in embankments. The optimum particle size of the stabilising agent must be selected based on the requirements of the construction site because the mechanical and chemical properties of the attenuation layer are site-specific. However, the relationship between the particle size of the stabilising agent and the attenuation performance of soil–agent mixtures has yet to be fully clarified. This study employs batch sorption tests to evaluate the attenuation of arsenic by a soil mixed with a calcium–magnesium composite with different particle sizes, ranging from powder particles (<0.075 mm in size) to granular particles with diameters between 2.0 and 9.5 mm. Amended soil more effectively attenuates the contaminant than the original soil. In one experiment, a stabilising agent of granular particles (between 2.0 and 9.5 mm) for the amendment increased the soil’s partition coefficient K_d from 14.5 to 22.2 cm³/g, which is more than a 50% improvement in the attenuation. Using a stabilising agent with a smaller particle size for the amendment has a greater impact. K_d increases linearly as the particle size of the stabilising agent decreases down to 0.075 mm. Using the K_d from laboratory tests, simulations with a one-dimensional advection–dispersion equation demonstrate the durability of the attenuation layer. Both the powder and the granular particles show promise as attenuation layer materials.     

Behavior of cantilever and geosynthetic-reinforced walls on deformable foundations

A series of plane-strain model tests was performed to investigate the behavior of cantilever soil retaining walls (CWs) and geosynthetic-reinforced soil retaining walls with a rigid facing (GRS-RWs) placed on non-deformable and deformable foundations with various subgrade reaction moduli (k_v). The walls were designed to have configurations similar to those used in practice, with similar controlling safety factors against sliding. Screw jacks and springs were used to simulate undeformable and deformable grounds, respectively, with various maximum foundation settlements of S_max ≒ 0, 2.5, 5, and 10% of the backfill height (H). Test results show that the GRS-RW has better settlement-tolerating performances, in terms of the tilting angle (θ), the horizontal displacement (D_h), and the settlement of the crest of the backfill (D_v1), than those of the CW. For both CWs and GRS-BWs, the worst scenario of the wall performance, in terms of D_h, θ and D_v1, occurred at a moderate foundation settlement of S_max/H ≒ 5% (or k_v = 1.8 kPa/mm), rather than at a greater foundation settlement of S_max/H ≒ 10%, which facilitates a tilting-backward displacement mode. Experimental results also indicate that local lateral pressure coefficients against facing (K_f,z) for CWs may reach the at-rest (or K_o) state at the central portion; values of K_f,z may reach the passive (or K_p) state at the lower portion of the wall. In the case of CWs, the measured values of local and global lateral pressure coefficients (K_f,z and K_f) tend to increase with increasing maximum foundation settlement. This is not the case for GRS-RWs, which exhibited a relatively settlement-independent response, in terms of K_f and K_f,z, against facing. To develop relevant limit-equilibrium-based design methods for CWs and GRS-RWs placed on deformable foundations, knowledge of lateral pressure coefficients associated with various displacement and tilting induced by the foundation settlement are required.     

Effect of initial water content on undrained shear strength of K0 consolidated clay

This study investigates the effect of initial water content on the pore pressure response and undrained shear behavior of K₀ consolidated reconstituted clay. A series of K₀ consolidated undrained triaxial compression tests were conducted on reconstituted Lianyungang clay. Results were compared to those obtained by isotropic consolidated undrained triaxial tests. The testing results showed that the K₀ consolidated undrained strength envelope of reconstituted soil content is a straight line passing through the origin regardless of the initial water content. The initial water content would affect the undrained strength of K₀ consolidated clay as decreased normalized undrained shear strength was observed with clay at higher initial water content. The slope C of normalized pore pressure and stress ratio is affected by the consolidation method, where C is found to be a soil constant for K₀ consolidated clay and the value would be higher with clay under K₀ consolidation. The pore pressure increases with increasing initial water content at a certain axial strain under given consolidation pressure, and the difference in excess pore pressure increases with the increasing consolidation pressure. Pore pressure coefficient at failure (A_f) increases as the initial water content increases, where a trendline can be well fitted between the pore coefficient at failure and the ratio of initial water content to the liquid limit of clay. The undrained strength indexes, i.e., effective cohesion and effective internal friction angle have decreasing tendency with increasing initial water content; however, changes in the total strength indexes of soil in this study are insignificant with varying initial water content.     

Sorption of hydrophobic pollutants on natural sediments

The sorption of hydrophobic compounds (aromatic hydrocarbons and chlorinated hydrocarbons) spanning a concentration range in water solubility from 500 parts per trillion (ppt) to 1800 parts per million (ppm) on local (North Georgia) pond and river sediments was investigated. The sorption isotherms were linear over a broad range of aqueous phase pollutant concentrations. The linear partition coefficients (K_p) were relatively independent of sediment concentrations and ionic strength in the suspensions. The K_p ś were directly related to organic carbon content for given particle size isolates in the different sediments. On an organic carbon basis (K_{oc = Kp/fraction}) organic carbon), the sand fraction (> 50 μm particle size) was a considerably less effective sorbent (50–90% reduction in K_oc) than the fines fraction (> 50 μm particles). Differences in sorption within the silt and clay fractions were largely related to differences in organic carbon content. Reasonable estimates of K_ocś can be made from octanol/water distribution coefficients, which are widely catalogued or easily measured in the laboratory.     

HDPE粉尘云最小点火能试验研究

为研究高密度聚乙烯(HDPE)粉尘云燃爆的敏感性参数,采用粉尘云最小点火能(MIE)试验装置对HDPE粉尘进行试验研究.首先研究3个单一因素(粉尘粒径、粉尘云质量浓度和喷粉压力)对MIE的影响,然后对一定条件下不同质量浓度的HDPE粉尘云在哈特曼管中燃烧的火焰传播行为进行分析,最后采用正交试验法分析了多因素对MIE的影...     

Asian dust event observed in Seoul, Korea, during 29-31 May 2008: Analysis of transport and vertical distribution of dust particles from lidar and surface measurements

In this study, we investigate the transport of dust particles, its vertical distribution, and the associated meteorological conditions during an Asian dust event that was observed in Seoul, Korea on May 29-31, 2008. This study analyzes data from ground-based and space-borne 2-wavelength polarization lidars, particulate mass concentrations, and synoptic weather data. Surface meteorological station observations of dust phenomena, dust transport model, and weather maps consistently show that the dust particles were transported from the source regions (Inner Mongolia, Man-Ju, and Ordos areas) to Korea via the northeastern part of China. Network observations of the PM₁₀ concentrations in Korea revealed that a majority of the heavy dust particles traveled across South Korea from the northwest to the southeast direction with a horizontal scale of 250-300 km and a traveling speed of approximately 40 km h^− 1. This extraordinary dust event, in terms of its intensity and timing during the year, occurred due to the blockage of an unusually intensified low-pressure system in the northeastern part of China as well as high-pressure system centered over the Sea of Okhotsk and the Kuril Islands. The low values of the particle depolarization ratio (δ₅₃₂) (≤0.05) and color ratio (CR) during the pre-dust period indicate the presence of spherical, non-dust, and relatively small particles. The mean δ₅₃₂ value was approximately 0.123 ± 0.069 between altitudes of ground ~ 2.8 km, and 0.161 ± 0.049 for near-surface dust layer (ground ~ 1.2 km). This value is quite similar to that obtained during the 3-year SNU-Lidar measurements in Seoul (δ₅₃₂ ~0.136 ± 0.027). The value of δ₅₃₂ during the 2nd multilayered dust episode ranged between 0.081 and 0.120 for near-surface dust layers, and between 0.076 and 0.114 for elevated dust layers. The CALIPSO measurements of β₅₃₂, δ₅₃₂, and CR also revealed the presence of dense dust aerosols along the transport route.     

微米级褐煤粉尘爆炸压力试验研究

摘 要：使用近球形煤尘爆炸装置,以微米级褐煤粉尘为研究对象,测试爆炸压力特性变化规律。研究表明：微米级褐煤粉尘爆炸最大压力为0.73 MPa,最大压力上升速率为65.78 MPa/s,该爆炸强度可对爆源附近人员造成极大危害。爆炸前后参与爆炸的挥发分质量分数达到26.25%,表明挥发分是参与褐煤粉尘爆炸的主体成分。随喷尘压力在1.4~2.6 MPa范围内增大,爆炸最大压力和最大压力上升速率均先增大后减小。喷尘压力为1.8~2.2 MPa时,爆炸最大压力相对较大,表明该条件下褐煤粉尘在点火头附近扩散得最充分。随点火延迟时间在70 ~130 ms范围内增大,爆炸最大压力和最大压力上升速率均先增大后减小,最佳点火延迟时间约为100 ms,说明该条件下褐煤粉尘颗粒达到最佳分散状态,爆炸强度最大。     

A parameterization of dust concentration (PM₁₀) of dust events observed at Erdene in Mongolia using the monitored tower data

Hourly mean time series of dust concentration (PM₁₀) measured at 3 m high and a sonic-anemometer measured momentum and kinematic heat fluxes at 8 m high above the surface have been obtained from a 20-m monitoring tower located at Erdene in the Asian dust source region of Mongolia for years of 2009 and 2010. These time series were used to identify dust events and to develop optimal regression equations for the dust concentration of dust events with the friction velocity (u_*) and the convective velocity scale (w_*). In total, 68 dust events were identified in 2009 (except for November) and 43 dust events for the period from March to August in 2010. The duration of each dust event ranged from 3-29 h in 2009 and 5-35 h in 2010. The maximum hourly mean dust concentration of the dust event was found to be 4,107 μg m^− 3 in May in 2009 and 4,708 μg m^− 3 in March in 2010 while a minimum of 251 μg m^− 3 in August in 2009 and 662 μg m^− 3 in June in 2010. The optimal regression equation for the dust concentration (C) of dust events was found to have the form of log C = a + b(u_* + cw_*)ⁿ, where a, b, c and n are constants that vary month to month. The convective velocity scale (w_*) that has not been taken into account in most dust modelings was found to enhance the dust concentration of dust events during the cold period from December to March when the soil temperature was below the freezing level for both the stable (w_* < 0) and unstable (w_* > 0) stratifications, whereas the convective velocity caused a reduction in the dust concentrations during the warm period from April to October, suggesting the importance of the convective velocity to estimate dust concentration of dust events.     

HMX粉尘云火焰传播规律研究

采用改进的可视化Hartmann装置,研究HMX粉尘云爆炸火焰传播规律,观察不同HMX粉尘云质量浓度及粒度对其粉尘云爆炸火焰传播速度及火焰传播高度的影响。结果表明：HMX粉尘质量浓度从74.1 g/m³变化为185.1 g/m³,火焰传播最大高度从29.97 cm增加为60.81 cm,最大速度从58.91 m/s增加为175 m/s;火焰波动幅度随质量浓度的增加而增大,同时,火焰波动出现的时间明显提前。HMX粉尘粒径从19.02 μm增大为53.56 μm时,火焰传播最大高度由55.45 cm降低为40.02 cm,最大火焰传播速度由181.93 m/s降低为121.28 m/s,火焰波动幅度显著降低,火焰波动出现的时间推迟。     

Fabric and Particle Shape Influence on K0 of Granular Materials

This paper discusses the influence of fabric and particle shape on K₀-values of cohesionless materials using micromechanical analysis and the results from a series of tests. Following a simple analysis using Harr's probabilistic theory that illustrates the dependency of K₀ on particle shape, a rigorous micromechanical analysis is provided to take into account the effect of interparticle friction, particle shape and particle arrangement. The fabric effect is introduced via a joint density function of branch vectors. Both micromechanical analyses and experimental results show that the K₀-values are affected by fabric related to both the direction and the length of branch vectors. The effect of particle shape may be undermined if one only considers the directional variation of the density of branch vectors (or contact normals). The K₀-values are shown to be also affected by the direction in which deformation is restrained.     

Availability of dissolved iron from Tjeukemeer,The Netherlands,for iron-limited growing Scenedesmus quadricauda

Ultrafiltration of water from eutrophic, alkaline and humic lake Tjeukemeer, The Netherlands, revealed that most dissolved Fe (< 0.2 μm) is found in colloids between 350 and 2000 Å. All dissolved Fe from NH₄Fe(SO₄)₂·12H₂O in the growth medium occurred in particles $\text{< 350}\text{A}\text{?}$, half of which did not exceed 100 Å. The half-saturation growth constant (K_s) of Fe-limited growth of Scenedesmus quadricauda in the presence of EDTA at pH 8.0 and using the natural Fe colloids was almost 3 times that using NH₄Fe(SO₄)₂·12H₂O. The maximum growth rate (μ_max) was not affected by the particle size of the limiting Fe substrate. It is concluded that Fe from the natural colloids is approx. one-third as much available as from NH₄Fe(SO₄)₂·12H₂O.The implications of the effect of the particle size of the growth rate limiting substrate to our understanding of species succession in natural phytoplankton communities are briefly discussed.     

基于MCS-CB的三通管内铝粉爆炸风险分析

为研究粉尘爆炸及抑爆后的风险变化,构建了基于蒙特卡罗模拟的粉尘爆炸不确定性风险及其概率变量评估方法,对三通管内铝粉爆炸压力动态不确定性变化及粉尘爆炸超压不确定性风险进行分析。结果表明：中位粒径为35 μm、质量浓度为500 g/m3的铝粉在典型位置三通管处爆炸超压服从Gamma分布,其爆炸超压平均值为0.10 MPa;蒙特卡罗模拟结果显示,以超过50%概率区间为例,分岔口处铝粉爆炸超压致管道结构损坏的风险性为85.41%,加入7.5%磷酸二氢铵后,超压对于管道结构的致损风险减小至45%。     

Dust storms in China: a case study of dust storm variation and dust characteristics

The paper discusses the nature of dust storms, which have inherent environmental implications. The physical, chemical and mineralogical properties of dust sediments collected in Kashi, Taklimakan desert, Kunlun mountains, Donghuang, Lanzhou, Ningxia, Xi'an, Inner Mongolia and Beijing from 1990 to 1994 were studied. The texture of most aeolian deposits ranges from silty clay to clay loam with median particle diameters (Mds) generally between 5 and 63 μm; similar to the loess of central China and the silt/fine sand in western and northern China. The dust sediments were characterized by a predominance of SiO₂ and Al₂O₃ and a high amount of K₂O with molar ratios for SiO₂/Al₂O₃ and K₂O/SiO₂ from 5.17 to 8.43 and 0.009 to 0.0368 respectively. The triple peak spectrum is the main form of mass concentration in a clear sky. In a dust storm it shows as a single peak, with quartz, feldspar, chlorite, illite, calcite and dolomite being the dominant minerals. The physical, chemical and mineralogical properties of the present atmospheric dust are similar to those of wind-blown soils in western and central China. The results suggest that aeolian deposits and the fine-grained fractions of dust sediments collected in northern China are mainly soils transported from the arid and semi-arid regions of China and Mongolia by the prevailing winds. Electronic Publication