Simplified model for droplet combustion in a slow convective flow

An idealized model for droplet vaporization or combustion in the Burke-Schumann reaction-sheet approximation is analyzed in terms of a Peclet number based on the Stefan velocity, taken to be of order unity, for Lewis numbers of unity and for small values of a parameter ?, defined as the ratio of the convective velocity far from the droplet to the Stefan velocity at its surface. Asymptotic solutions for the velocity, pressure, and mixture-fraction fields are obtained through second order in ?. The results are employed to calculate the effects of convection on the burning rate and on the flame shape. The prediction that the burning-rate constant increases linearly with ? for small values of ? is shown to be consistent with available experimental data. It is demonstrated that reasonable values of diffusivities provide approximate agreement of predicted burning rates and flame shapes with results of measurements.     

Virus attenuation by microbial mechanisms during the idle time of a household slow sand filter

The biosand filter (BSF) is a household slow sand filter that is operated intermittently such that an idle time of typically 18-22 h occurs in between daily charges of water. Virus attenuation during the idle time was investigated over repeated daily filtration cycles to capture the effect of media aging that encompasses processes occurring throughout the filter depth rather than restricted to the schmutzdecke at the media surface. A threshold aging period of about one to two weeks was required before virus attenuation began. The observed rates of MS2 and PRD-1 reduction were first-order and reached maxima of 0.061- and 0.053-log per hr, respectively, over seven-to-ten weeks. Suppression of microbial activity by sodium azide eliminated virus reduction during the idle time thus indicating that the operative media aging process was microbially mediated. The mechanism of virus reduction was not modification of media surfaces by physical/chemical or microbial processes. Instead, it appears that the activity of the microbial community within the filter is responsible. The most likely biological pathways are production of microbial exoproducts such as proteolytic enzymes or grazing of bacteria and higher microorganisms on virus particles. Implications of these findings for BSF design and operation and their relevance to other biological filtration technologies are discussed.     

GH903合金的离子注入表面改性研究

用离子注入、氧化和慢正电子束分析研究了ＧＨ９０３合金的氧化性能的改善与微观作用机理。注入的Ｃｒ＋．Ｙ＋的能量均为６０ｋｅＶ，注入的剂量分别由１ｘ１０１７．ｃｍ－２（Ｃｒ＋）、１ｘ１０１５Ｃｍ－２（Ｙ＋）和［１ｘ１０１５．ｃｍ－２（Ｙ＋）＋１ｘ１０１７·ｃｍ－２（Ｃｒ＋）］。结束显示，注入样品与未样品相比。氧化增重分别减少４．８％（注Ｃｒ＋）、２４．２％（注Ｙ＋）和３２．３％（注Ｙ＋＋Ｃｒ＋）。这表明合金氧化性能改善的作用机理主要是注入离子对样品浅表层内缺陷的填充与退火。同时，注入元素的化学性能和使样品表面更致密也起了重要作用。     

大功率行波管新型慢波线技术的进展

全金属慢波结构由于具有热耗散能力强，功率容量大，比耦合腔慢性线带宽度，结构整体性好，尺寸大等一系列优点而备受人们关注。本文着重介绍了螺旋槽、环板、曲折波导及周期加载波导四类结构的发展现状，包括理论研究与实际应用情况，探讨了新型慢波线在技术上存在的问题及今后的努力方向，指出全金属慢波结构将在毫米波行波管、返波管、毫米波回旋行波管及相对论器件等方面得到广泛应用。     

动态速度渐变技术提升慢波结构注波互作用效率的仿真研究

行波管采用动态速度渐变（DVT）技术能获得很高的效率。本文分析了一种采用DVT技术的慢波结构,并将这一结构与常规设计的慢波结构进行仿真比较,最后对这一结构进行了实验验证,结果证明了这一技术的优越性和可行性。     

低压大功率电机转子压铸模的设计与工艺参数探讨

500T压力铸铝模具设计时,通过对上、下模增设排气槽及下模进铝口的合理布置,保证了在整个压铸的短暂瞬间的排气及进铝量,另外还通过使用梅花形筋板式假轴有效降低了模具的成本。压铸过程中通过对铝液清化、铝水温度、慢压射时间、压射力等多种工艺参数的严格控制保证了铸铝转子的压铸质量。     

Thermal Analysis Studies on the Slow‐Propagation Tungsten Type Delay Composition System

Thermal analysis techniques were applied to investigate the reaction characteristics of a slow‐propagation tungsten type delay composition system by means of differential scanning calorimetry (DSC) and thermogravimetry (TG). The ingredients of the delay composition were tungsten, barium chromate, potassium perchlorate, diatomaceous earth, and Viton. A formula of delay composition with a weight percentage of W/BaCrO₄/KClO₄/D. E./Viton=27 : 54 : 11 : 6 : 2 has been used in a self‐destruction mechanism of fuse, which was set as the original formula. In the first place, the reaction heat and weight loss for different compositions without Viton were measured during the reaction. The influence of each ingredient of the formula on the reaction system was analyzed from these experimental results. Afterward Viton was added in the samples of experiment to measure and analyze the influence of Viton on the reaction system. Finally, 28 experimental formulas of delay composition were designed on the condition that the weight percentage of Viton was kept constant and the maximum variation of weight percentage of all the others was limited within 20%. The delay compositions of various formulas were granulated and then the variations of reaction characteristics were measured to analyze the influence of weight variation of each ingredient on reaction characteristics. The results of this study are very important and useful for improving the self‐destruction mechanism of fuse.     

WONDERLAND IS A SLOW PLACE

The author first examines the origin and development of the international Citta Slow movement, and points out that the growing Citta Slow movement in China can be understood as a New Ruralism Movement for urban residents and the vision of Citta Slow in China is a romantic ideal of the Beautiful Countryside. The article then argues that slowing cities which operate at a moderate speed can create more pleasant and livable environments through the smart use of space, an energy-saving development, and harmony between man and nature. Finally, in the critical period of Beautiful China Construction and the new stage of China’s urbanization, five principles are proposed for designers and developers to apply into planning and design of slowing cities.     

Effect of residual hydrogen content on the tensile properties and crack propagation behavior of a type 316 stainless steel

The tensile properties and crack propagation rate in a type 316 austenitic stainless steel prepared by vacuum induction melting method with different residual hydrogen contents (1.1–11.5 × 10⁻⁶) were systematically investigated in this research work. The room temperature tensile properties were measured under both regular tensile (12 mm/min) and slow tensile (0.01 mm/min) conditions, and the fracture properties of the tensile fractures with both rates were analyzed. It shows that the hydrogen induced plasticity loss of stainless steel strongly depends on the tensile rate. Under regular tensile condition, there is no plastic loss even when the hydrogen content is up to 11.5 × 10⁻⁶ while in the slow tensile condition, the plastic loss can be clearly identified rising with the increasing H contents. The fatigue crack propagation rate was tested at room temperature, and the crack growth rate formula (Paris) of the 316 stainless steels with varied H contents were obtained. The fatigue crack propagation rate test shows that the crack growth rate of the 316 stainless steel with 8.0–11.5 × 10⁻⁶ hydrogen is significantly higher than that of benchmark steel.     

Differences between internal and external hydrogen effects on slow strain rate tensile test of iron-based superalloy A286

To investigate the evaluation method of hydrogen compatibility of A286 superalloy in high pressure hydrogen gas, SSRT tests of hydrogen-charged specimens were conducted at ambient temperature at various strain rates. The relative reduction in area (RRA), one of the ductility parameters, was determined. The hydrogen content in the hydrogen-charged specimen was the same as the equilibrium hydrogen content on the specimen surface at 150 °C in 70 MPa hydrogen gas. The strain rate dependence of RRA was smaller than that of RRA obtained in 70 MPa hydrogen gas at 150 °C. All the hydrogen-charged specimens showed slip-plane fractures in the grains in their cores. However, the specimens in 70 MPa hydrogen gas at 150 °C showed fracture surfaces morphology ranging from dimples to quasi-cleavages and intergranular fractures with decreasing strain rate. These dissimilarities are expected to arise from differences in the hydrogen concentration behaviors of the specimens during the deformation process.