城郊排水沟渠溶质传输的暂态存储影响及参数灵敏性

选择Na Cl为示踪剂,于2013年9~10月在合肥城郊的关镇河支渠开展5次瞬时投加示踪实验.从暂态存储、侧向补给和对流-扩散等作用机制层面,设置4种模拟情景,解析暂态存储作用对于排水沟渠溶质传输规律的影响,并对OTIS模型参数进行灵敏性分析.结果表明,暂态存储对于主流区Cl-模拟浓度穿透曲线(BTCs)峰值大小影响很大,相对偏差高达24.23%~117.26%,显著高于对峰值出现时间的影响,且暂态存储影响显著超过了侧向补给作用;由相关性分析,主流区Cl-模拟浓度BTCs峰值大小和出现时间的相对偏差与As/A具有极显著相关性;4个主要参数的灵敏度排序为AAsαD.     

Modeling thermal analysis for predicting thermal hazards relevant to transportation safety and runaway reaction for 2,2′-azobis(isobutyronitrile)

The pure decomposition behavior of 2,2′-azobis (isobutyronitrile) (AIBN) and its physical phase transformation were examined and discussed. The thermal decomposition of this self-reactive azo compound was explored using differential scanning calorimetry (DSC) to elucidate the stages in the progress of this chemical reaction. DSC was used to predict the kinetic and process safety parameters, such as self-accelerating decomposition temperature (SADT), time to maximum reaction rate under adiabatic conditions (TMR_ad), and apparent activation energy (E_a), under isothermal and adiabatic conditions with thermal analysis models. Moreover, vent sizing package 2 (VSP2) was applied to examine the runaway reaction combined with simulation and experiments for thermal hazard assessment of AIBN. A thorough understanding of this reaction process can identify AIBN as a hazardous and vulnerable chemical during upset situations. The sublimation and melting of AIBN near its apparent onset decomposition temperature contributed to the initial steps of the reaction and explained the exothermic attributes of the peaks observed in the calorimetric investigation.     

Hydroxyurea explosion: a thermoanalytical and calorimetric study

An accident occurred during a production process of hydroxyurea. Several thermoanalytical techniques were used in order to understand the reason for the accident, even utilising a simulation program. Thermogravimetric analysis and Fourier transform infra-red spectroscopy were performed to identify the decomposition products according to European Directive 96/82/EC, the so-called Seveso II.     

MR阻尼器的简化参数模型及其应用

MR阻尼器应用于控制风振、地震等引起的随机振动时需用参数化表达式来描述MR阻尼器简化的力学模型 ,从而更好地揭示MR阻尼器的减振机理。本文采用偏最小二乘法误差估计、Chebyshev多项式拟合建立了MR阻尼器简化模型的参数化表达式 ,并应用于斜拉索振动控制中 ,为合理选择MR阻尼器提供了便捷、可靠的手段     

环境模型参数识别与不确定性分析

在对水文模型实例的参数不确定性分析基础上,分别采用传统灵敏度分析方法、HSY算法、线性回归等方法对模型参数特性进行了识别与比较研究.结果表明参数优化算法与传统灵敏度分析方法不能解释模型结构复杂性特征,采用不确定性分析方法对环境模型参数进行识别提供了深入分析与理解模型系统的有效途径.     

Influence of vacuum degree on the effect of gas explosion suppression by vacuum chamber

In order to study the influence of vacuum degree on gas explosion suppression by vacuum chamber, this study used the 0.2 mm thick polytetrafluoroethylene film as the diaphragm of vacuum chamber to carry out a series of experiments of gas explosion suppression by vacuum chamber with the vacuum degree from −0.01 MPa to −0.08 MPa. The experimental results show that: under the condition of any vacuum degree, vacuum chamber can effectively suppress the explosion flame and overpressure; as vacuum degree changes, the effect of gas explosion suppression using vacuum chamber is slightly different. Vacuum chamber has obvious influence on propagation characteristics of the explosion flame. After explosion flame passes by vacuum chamber, the flame signal weakens, the flame thickness becomes thicker, and the flame speed slows down. With the increase of the vacuum degree of vacuum chamber, the flame speed can be prevented from rising early by vacuum chamber. The higher the vacuum degree is, the more obviously the vacuum chamber attenuates the explosion overpressure, the smaller the average overpressure is, and the better effect of the gas explosion suppression is. Vacuum chamber can effectively weaken the explosion impulse under each vacuum degree. From the beginning of −0.01 MPa, the vacuum chamber can gradually weaken explosion impulse as the vacuum degree increases, and the effect of gas explosion suppression gradually becomes better. When the vacuum degree is greater than −0.04 MPa, the increase of vacuum degree can make the explosion overpressure decrease but have little influence on the explosion impulse. Therefore, the vacuum chamber has the preferable suppression effect with equal to or greater than −0.04 MPa vacuum degree.     

Collecting representative dust samples: A comparison of various sampling methods in underground coal mines

Former methods used in the U.S. to assess hazardous and explosible coal dust date back to the 1950s. As mining technologies advanced, so too have the hazards. Given the results of the recent coal dust particle size survey and full-scale experimental mine explosion tests, the National Institute for Occupational Safety and Health (NIOSH) recommended a new minimum standard, in the absence of background methane, of 80% total incombustible content (TIC) be required in the intake airways of bituminous coal mines, replacing the previous 65% TIC requirement. Most important to monitoring and maintaining the 80% TIC is the ability to effectively collect and analyze representative dust samples that would likely disperse and participate in dust explosion propagation. Research has shown that dust suspended on elevated surfaces is usually finer, more reactive, and more readily dispersible while floor deposits of dust are generally coarser and more difficult to disperse given the same blast of air. The roof, rib, and floor portions of the dust samples were collected and analyzed for incombustible content separately and the results were compared to a band sample of the roof, rib, and floor components. Results indicate that the roof and rib dust samples should be kept separate from floor dust samples and considered individually for analyses. The various experimental collection methods are detailed along with preferred sampling approaches that improve the detectability of potentially hazardous accumulations of explosible dust.     

综合拉底、扩漏和出矿全过程的底部结构安全性颗粒流模拟技术研究

为探明自然崩落法从拉底崩落至出矿全过程中底部结构节理连续扩展过程与破坏过程规律，采用PFC2D软件，结合RocLab软件反演节理岩体参数，建立229 m×129 m的岩体扩大模型，对拉底崩落至出矿过程进行连续综合计算。研究结果表明:模拟结果及破坏现象与现场监测结果相近，建模与细观参数反演方法适用于该类岩体工程研究；裂纹扩展贯通导致岩体失稳破坏，破坏过程与裂纹扩展具有相对应的阶段特征，裂纹扩展分为崩落前稳定扩展期，崩落与聚矿槽开挖过程加速扩展期和后续持续扩展期；结构破坏分为蕴育过程，扰动失稳过程和宏观破坏过程；较大范围的宏观破坏主要在出矿阶段。该模拟方法与结果可为底部结构维护以及节理岩体长期稳定性研究提供参考。     

Evaluation of the spontaneous combustion characteristics of coal of different metamorphic degrees based on a temperature-programmed oil bath experimental system

Research on the micro- and macrocharacteristics of different metamorphic degrees of coal helps improve the control and protection techniques used during spontaneous combustion. Nine coals with different properties were thoroughly investigated in this study. Fourier transform infrared spectroscopy and a self-designed temperature-programmed oil bath experimental system were adopted to analyze the molecular structure and macrocharacteristic parameters of the spontaneous combustion of coal. Additionally, the influence of particle size on spontaneous combustion was considered. Various functional groups were employed as microcharacteristic parameters to capture the principal active groups in oxidation. The gas production rate, oxygen consumption rate, gas concentration, heat energy release rate, and characteristic temperatures were evaluated as macrocharacteristic parameters to investigate the changes in coal during oxidation. The results establish that the microcharacteristics of coal molecules determine the degree of spontaneous combustion based on intrinsic properties and that changes in the macrocharacteristics of the spontaneous combustion of coal reflect the microstructural changes. The contents of the hydroxyl groups, carbonyl groups, alkyl ether and aryl ether in the coal molecules gradually decrease with the metamorphic increase. Oxygen-containing functional groups have higher reactivities and easily react with oxygen, causing the macroparameters, such as the oxygen consumption rate, the gas generation rate and the heat energy release rate, to consistently decrease with the increase of the metamorphic degree. Small-particle-size coal molecules have more active aliphatic hydrocarbons, oxygen-containing functional groups and a larger specific surface area, increasing the chances of adsorbing the oxygen of active groups and promoting the reaction between coal and oxygen. The experimental results indicate that coal samples with higher metamorphic degrees or larger sizes exhibit lower tendencies toward spontaneous combustion. Evaluation of the spontaneous combustion of coal based on a temperature-programmed oil bath experimental system is of great practical importance for preventing the spontaneous combustion of coal during storage, processing and utilization and can serve as a convenient reference for production safety in mining applications.     

Ammonium nitrate thermal decomposition with additives

Runaway reactions present a potentially serious threat to the chemical process industry and the community; such reactions occur time and time again often with devastating consequences. The main objective of this research is to study the root causes associated with ammonium nitrate (AN) explosions during storage. The research focuses on AN fertilizers and studies the effects of different types of fertilizer compatible additives on AN thermal decomposition. Reactive Systems Screening Tool (RSST) has been used for reactivity evaluation and to better understand the mechanisms that result in explosion hazards. The results obtained from this tool have been reported in terms of parameters such as “onset” temperature, rate of temperature and pressure rise and maximum temperature. The runaway behavior of AN has been studied as a solid and solution in water. The effect of additives such as sodium sulfate (Na₂SO₄) and potassium chloride (KCl) has also been studied. Multiple tests have been conducted to determine the characteristics of AN decomposition accurately. The results show that the presence of sodium sulfate can increase the “onset” temperature of AN decomposition thus acting as AN thermal decomposition inhibitor, while potassium chloride tends to decrease the “onset” temperature thus acting as AN thermal decomposition promoter.