Feasibility Study of 316L Stainless Steel for the Ultrasonic Consolidation Process

The viability of using 316L stainless steel in the ultrasonic consolidation process was examined in this work. Ultrasonic consolidation is an additive, free-form manufacturing process that employs ultrasonic welding and machining to form a part. The process ultrasonically joins layers of metal together by welding them one at a time. Once four layers of metal foil are welded together, welding is suspended and the system machines the part outline, and repeats this cycle until a component is completed. Experiments were conducted to determine the feasibility and processing parameters for ultrasonically welding stainless steel. Mechanical testing and optical microscopy were conducted. 316L stainless steel was successfully welded. Increasing welding amplitude and decreasing welding speed were the most effective way to increase weld peel strength. Unlike work in aluminum alloys, these experiments found no relationship between horn force and peel strength. Rough processing windows for ultrasonically welding 316L were identified.     

The nature and large eddy simulation of coherent deflagrations in a vented enclosure-atmosphere system

The nature of coherent deflagration phenomena in a vented enclosure-atmosphere system is analysed. The study is based on experimental observations of SOLVEX programme in the empty 547-m³ vented enclosure and consequent analysis of the same test by large eddy simulations (LES). A comparison between simulated and experimental pressure transients and dynamics of flame front propagation inside and outside the enclosure gave an insight into the nature of the complex simultaneous interactions between flow, turbulence and combustion inside the enclosure and in the atmosphere. It is revealed through LES processing of experimental data that the substantial intensification of premixed combustion occurs only outside the empty SOLVEX enclosure and this leads to steep coherent pressure rise in both internal and external deflagrations. The external explosion does not affect burning rate inside the enclosure. There is only one ad hoc parameter in the LES model, which is used to account for unresolved subgrid scale increase of flame surface density outside the enclosure. The model allows reaching an excellent match between theory and experiment for coherent deflagrations in the empty SOLVEX facility. The mechanism of combustion intensification in the atmosphere is discussed and the quantitative estimation of the model ad hoc parameter is given.     

Radioactivity in fungi in Slovenia,Yugoslavia, following the Chernobyl accident

Caesium (¹³⁷Cs and ¹³⁴Cs) concentrations in higher fungi (Basidiomycetes) from Slovenia, north-west Yugoslavia, are reported following the Chernobyl accident. Special attention was paid to the Cortinariaceae, already known as Cs accumulators. The highest levels were found in Cortinarius armillatus, C. traganus (both inedible species) and Rozites caperata. The median concentration of ^137,134Cs in R. caperata from over 40 sampling sites was about 22 kBq/kg dry weight. High levels were also found in Xerocomus badius and Laccaria amethystina.From the ¹³⁷Cs/¹³⁴Cs ratios, which reflect the depth of the mycelium and the excess ¹³⁷Cs from historic pre-Chernobyl fallout, it may be surmised that radiocaesium levels in certain species will probably increase further next year and subsequently as Cs migrates down the soil profile.In addition, ^110mAg was found at concentrations up to 500 Bq/kg dry weight in certain species known to be Ag accumulators, particularly Agaricaceae and Lycoperdaceae.     

Large eddy simulation and experimental study of the effect of wire mesh on flame behaviours of methane/air explosions in a semi-confined pipe

Preventing the propagation of flames in a pipeline is an effective measure for avoiding gas explosion accidents and reducing losses. To evaluate the effect of wire mesh, acting as a porous media, experimental and simulation studies are conducted to determine the influence of the wire mesh on the dynamics of premixed methane/air flame propagation in a semi-closed pipe. Four different kinds of wire mesh with different numbers of layers are chosen in the experiments and simulation, and the mechanism of wire mesh quenching of the flame is investigated. The experimental and simulation results are consistent. Flames are quenched when 4 layers of 40-mesh or 3 layers of 60-mesh wire mesh are used; however, once the flame propagates through the wire mesh, the risk of methane combustion may increase. The wire mesh becomes the key factor causing flame folds and acceleration, and the greater the number of layers or the larger the mesh size is, the more obvious the folds after the flame passes through the wire mesh. Moreover, the combination of heat absorption and disruption of the continuous flame surface by the mesh causes flame quenching. Wire mesh can effectively attenuate the flame temperature during premixed flame propagation in a pipe, and the attenuated maximum rate reaches approximately 79% in the case of adding 3 layers of 60-mesh wire mesh.     

Characterizing the generation and spatial patterns of carbon emissions from urban express delivery service in China

Express delivery services, as an indispensable part of our daily life, have grown rapidly because of the booming e-commerce and logistics industries. Accordingly, there is increasing concern about the environmental load from delivering letters and parcels, such as road freight transportation emissions and packaging waste, which have not been seriously considered in previous work. In this study, a spatially based dynamic model has been created to quantify the impacts (measured in carbon emissions, CO₂eq.) from the express delivery sector in China. Specifically, intracity (urban) express delivery services—delivery and pick-up services located within the same city—was chosen for analysis. The results indicated that the carbon emissions from the transportation phase of the express delivery sector in Chinese cities varied from 20 t to 4000 t in 2017, of which 18% was attributable to the weight of extra packaging materials. Carbon emission intensities for all cities showed a close relationship with their socioeconomic status. For example, the spatial pattern of intracity express delivery volumes and associated carbon emissions showed a significant clustering property: high-value cities were clustered in eastern China and low-value cities in western China. Furthermore, the carbon hotspots were mainly located in the Yangtze River Delta and Pearl River Delta urban agglomerations. Overall, our research method and preliminary findings could be helpful for the green development of the booming express delivery sector in China and beyond.     

侧向风速作用下聚氨酯泡沫双火源火蔓延研究

为探究环境风作用下逆向双点火源聚氨酯泡沫火蔓延及融合行为,开展多组对照实验并从材料传热机理角度分析侧向风速对火蔓延行为中火羽流形态、质量损失和辐射热流场等特征参数的影响。结果表明:风速与上述参数之间存在非线性关系。环境风效应使火焰被拉长且敷贴于预热区表面,增大预热区面积和热反馈;侧向风速的增加对FPU板材质量损失的影响逐渐弱化,且板材的熔滴率与风速呈正相关;无论侧向风是否存在,两侧逆向火焰融合后均达到整个蔓延过程中的峰值温度;风速的存在限制了火焰温度与辐射热通量峰值,也缩短了温度和辐射峰值出现的时间。     

Theoretical pressure prediction of confined hydrogen explosion considering flame instabilities

In order to ensure the safe utilization of hydrogen energy, the explosion pressure behavior is extremely important to design chemical equipment and evaluate explosion accident consequence. This paper is aimed at establishing a theoretical method of predicting explosion pressure behavior in the confined chamber by considering flame instabilities. The tendency of flame wrinkling factor in the pressure-buildup stage is firstly evaluated using large eddy simulation and the compensation theory. The limiting value of flame wrinkling factor during entire explosion process is calculated using the fractal theory. Finally, the dynamic model of flame wrinkling factor is implemented into the smooth flame model. The results demonstrated that the flame wrinkling factor in the pressure-buildup stage almost increases linearly with time. The limiting value of flame wrinkling factor is 2.4649. The explosion pressure will be underestimated using the smooth flame model, and the calculated explosion pressure in the isothermal condition is smaller than that in the adiabatic condition. When the fully turbulent flame is considered, the explosion pressure will be overpredicted significantly. By changing the confined chamber size, the explosion pressure could be reproduced relatively satisfactorily when the flame wrinkling factor is assumed to increase exponentially. The explosion pressure prediction must consider the effect of adiabatic compression and flame instabilities on burning rate.     

壬基酚降解菌产酶条件的优化

通过单因素试验和正交试验确定了实验室保藏的壬基酚降解菌株沙雷氏菌(Serratiasp.LJ)的最佳产酶条件:以壬基酚、硫酸铵为碳源、氮源,培养基初始pH为6.8,培养温度为30℃,种子活化时间为24h,接种量为3%(体积分数)。在此条件下培养72h后,最高酶活力为1.314IU/mL,是优化前的1.77倍。     

极端温度下帐篷内部热环境适应性实验及模拟研究*

为揭示民用救灾帐篷热环境适应性变化规律,通过大尺度环境气候舱构建高温与低温环境,采用Ansys Fluent商用软件代码进行仿真验证,并对帐篷蓬围结构和内部热环境分布变化规律进行实验与数值模拟。研究结果表明:使用大尺度环境舱直接进行模拟帐篷内外热环境变化可行,其内部热环境变化规律与实验基本一致;帐篷特殊的篷围结构导致高温环境下帐篷内部温度高于外界,帐内人员头部和脚部温差可达5 ℃,低温环境下帐篷同一高度横向区域温度对称分布,在中心区域温度较低,边缘和中心温差近8 ℃。