甲烷-煤尘爆炸波与障碍物相互作用的数值研究

为了探讨煤矿瓦斯和煤尘爆炸的物理机制 ,基于对甲烷和煤尘爆炸传播的理论分析 ,采用数值模拟方法研究障碍物对甲烷和煤尘爆炸传播的影响 ;为了更系统地考虑颗粒相各种输运特性、相间滑移和耦合 ,采用双流体模型建立了数学模型 ,该模型的出发点是把颗粒群和气体都作为连续介质 ,两者相互渗透充满整个空间形成没有间隙的“流体”———拟流体 ,在欧拉坐标系下考虑气 -固两相流动 ,气相和颗粒相的计算网格统一 ,易于处理。数值方法采用LU分解和迎风TVD格式分别处理对流项的隐式和显式部分 ,扩散项采用中心差分 ;同时研究了不同形状的障碍物对流场的影响 ,计算结果与实验吻合较好     

Study on convection and dispersion characteristics of dense gases in urban environment considering trees

Although several studies on the dispersion of heavy toxic gas released from ruptured tanks on vehicles during transportation have considered complex terrain such as urban buildings, the influence of trees on the flow field in urban areas during gas dispersion tends to be ignored. In this study, a Computational Fluid Dynamics (CFD) model was proposed to investigate the characteristics of gas release and dispersion from loaded vehicle in the urban environment. In this model, the tree crown was treated as a porous medium, and the influence of drag due to the crown was incorporated into the model by a momentum source term through a user-defined function. In this study, the dynamic characteristics of chlorine (Cl₂) dispersion under the conditions of building distribution, tree species and porosities were comprehensively analysed, to cover the influence of urban complexity, leaf density, and tree planting configuration. The results show that compared with flat terrain, the presence of urban buildings will prolong the dense gas retention time and increase the dangerous distance. It is found that the horizontal dispersion distance can increase by 63% and the isosurface of 25 ppm hazardous gas can increase by 130% with the introduction of buildings. Compared with the terrain with only buildings, the introduction of arbors or shrubs can result in a 147% or 359% increase in the maximum concentration. Also, trees will prolong the dispersion duration. It is also found that the higher the porosity, the less the wind blocking effect, and the weaker the ability of capturing gas. The wind field affected by arbores and shrubs are different in height, and arbores capture more Cl₂. Planting short shrubs around buildings can effectively reduce the spread of harmful gases.     

生物滴滤塔净化含低浓度苯乙烯废气的研究

利用菌丝体热解炭作为填料,采用两座相同实验室规模的生物滴滤塔,分别填装热解炭-木屑混合填料和木屑单一填料,并联操作,进行微生物净化含苯乙烯废气的实验,研究并对比了两座生物滴滤塔的净化性能.结果表明,由于热解炭具有比表面积大、孔隙率高等特点,热解炭-木屑混合作为生物滴滤塔填料,比单一的木屑填料挂膜速度快,净化效果好,停运恢复能力强.适宜操作条件为:入口气体浓度50～ 450mg·m-3,停留时间21.6～43.2 s,气液比110.7 ～55.3,净化效率92％ ～ 100％,最大去除负荷可达153.1 g·m-3· h-1.整个实验过程中,系统的压降始终维持在0～255 Pa,动力消耗小.研究发现,循环液中氨氮(NH4+-N)浓度只需能够保证微生物正常的生命活动即可,不宜过量或不足.生物滴滤塔循环液的紫外吸光度(UV254)与苯乙烯去除率具有一定的相关性,可通过测定循环液UV254,了解生物滴滤塔的运行状况.     

Impact of combining chlorine dioxide and chlorine on DBP formation in simulated indoor swimming pools

The main objective of this study was to assess the combined use of chlorine dioxide (ClO2) and chlorine (Cl2) on the speciation and kinetics of disinfection by-product (DBP) formation in swimming pools using synthetic pool waters prepared with a body fluid analog (BFA) and/or fresh natural water. At 1:25 (mass ratio) of ClO2 to Cl2, there was no significant reduction in the formation of trihalomethanes (THMs) and haloacetic acids (HAAs) for both BFA solution and natural water compared to the application of Cl2 alone. When the mass ratio of ClO2 to Cl2 increased to 1:1, substantial decreases in both THMs and HAAs were observed in the natural water, while there was almost no change of DBP formations in the BFA solution. Haloacetonitriles and halonitromethanes levels in both water matrices remained similar. In the presence of bromide, the overall DBP formation increased in both BFA solution and natural water. For the DBP formation kinetics, after 72 hr of contact time, very low formation of THMs and HAAs was observed for the use of ClO2 only. Compared to Cl2 control, however, applying the 1:1 mixture of ClO2/Cl2 reduced THMs by > 60% and HAAs by > 50%. Chlorite was maintained below 1.0 mg/L, while the formation of chlorate significantly increased over the reaction time. Finally, in a bench-scale indoor pool experiment, applying ClO2 and Cl2 simultaneously produced less THMs compared to Cl2 control and kept chlorite at < 0.4 mg/L, while HAAs and chlorate accumulated over 4-week operation period.     

数值模拟技术在二沉池设计中的应用

二沉池的运行状况对整个污水处理系统的处理效果有重要影响。沉淀池的处理效果与沉淀池内水流特性密切相关。传统的沉淀池设计基于理想沉淀池假设和静置沉淀实验,对沉淀池内的水流特性考虑不多,设计参数选择范围宽,经验性强,不能保证沉淀池内的泥水分离和浓缩效果。计算流体力学是一种较为成熟的数值模拟技术,已广泛应用于水处理构筑物在设计条件下的内部水流特性和行为的研究,为预测沉淀池的运行状况和结构改进的效果提供了有效手段。本文对沉淀池内的水流特性和流体力学在沉淀池研究中的应用进行了描述。     

抗高温环保钻井液体系研究

文章选择清洁环保的钻井液处理剂进行抗高温钻井液体系实验研究与评价,对包被增粘剂、降失水剂等进行优选,对抗高温环保钻井液配方进行评价,研究出无毒、无害,抗温能力强、流变性好,失水较低的钻井液体系,现场应用满足高温深井的钻井生产要求。     

The characterization of heat transfer fluid P-NF aerosol combustion: Ignitable region and flame development

Heat transfer fluids tend to form aerosols due to the operating conditions at high pressure when accidental leaking occurs in pipelines or storage vessels, which may cause serious fires and explosions. Due to the physical property complexity of aerosols, it is difficult to define a standard term of “flammability limits” as is possible for gases. The study discussed in this paper primarily focuses on the characterization of ignition conditions and flame development of heat transfer fluid aerosols. The flammable region of a widely-used commercial heat transfer fluid, Paratherm NF (P-NF), was analyzed by electro-spray generation with a laser diffraction particle analysis method. The aerosol ignition behavior depends on the droplet size and concentration of the aerosol. From the adjustment of differently applied electro-spray voltages (7–10 kV) and various liquid feeding rates, a flammable condition distribution was obtained by comparison of droplet size and concentration. An appropriate amount (0.3–1.2 ppm) of smaller droplets (80–110 μm) existing in a given space could result in successful flame formation, while larger droplets (up to 190 μm) have a relatively narrowed range of flammable conditions (0.7–0.9 ppm). It is possible to generate a more useful reference for industry and lab scale consideration when handling liquids. This paper provides initial flammability criteria for analyzing P-NF aerosol fire hazards in terms of droplet size and volumetric concentration, discusses the observation of aerosol combustion processes, and summarizes an ignition delay phenomenon. All of the fundamental study results are to be applied to practical cases with fire hazards analysis, pressurized liquid handling, and mitigation system design once there is a better understanding of aerosols formed by high-flash point materials.     

Eleventh week amniocentesis for prenatal diagnosis of some metabolic diseases

We report the results of 23 prenatal diagnoses performed at the 11th or 12th week of gestation by the simultaneous analysis of chorionic villi (for direct or indirect enzymatic analysis) and cell-free amniotic fluid (for search of accumulated catabolites). For six cases of citrullinaemia, four cases of argininosuccinic aciduria, seven cases of propionic acidaemia, and six cases of methylrnalonic acidaemia, three discrepancies were observed between the two methods used. The amniotic fluid analysis for accumulated catabolites seems to be a safe method and should always be used in conjunction with the enzymatic assays performed for the prenatal diagnosis of these diseases.