Numerical simulation of flame acceleration and deflagration-to-detonation transition of ethylene in channels

Ethylene (C₂H₄) is a hydrocarbon fuel and widely used in chemical industry, however, ethylene is highly flammable and therefore presents a serious fire and explosion hazard. This work is initiated by addressing the hazard assessment of ethylene mixtures in different scale channels (d = 5 mm, 10 mm and 20 mm) from the aspect of flame acceleration (FA) and deflagration-to-detonation transition (DDT) by using large eddy simulation (LES) method coupled with the artificially thickened flame (ATF) approach. The fifth order local characteristics based weighted essentially non-oscillatory (WENO) conservative finite difference scheme is employed to solve the governing equations. The numerical results confirm that flame velocity increase rapidly at the beginning stage in three channels, and the flame acceleration rate is slower in the subsequent stage, afterwards, the flame velocity has an abrupt increase, and the onset of detonation occurs. Due to the fact that wall effect is significant in the narrow channel (e.g.,5 mm), especially in the ignition stage of the flame, flames have different shapes in wider channels (10 mm and 20 mm) and narrow channel (5 mm). Both the pressure and temperature profiles confirm DDT run-up distances are 0.251 m, 0.203 m and 0.161 m in 20 mm, 10 mm and 5 mm channels, respectively, which indicates that a shorter run-up distance is required in narrower channel. The cellular detonation structures for the ethylene-air mixture in different channels indicate that multi-headed detonation structures can be found in 20 mm channel, as the channel width decreases to 10 mm, detonation has a single-headed spinning structure, as the width is further reduced to 5 mm, only large longitudinal oscillation of the pressure can be observed.     

南方地区公路建设环评中的水土流失评价要点

水土流失是南方多雨地区公路建设项目的主要生态问题,全面考虑水土流失点、正确预测水土流失量、切实可行地提出减少或消除不利影响的水土防护措施,是公路建设生态环境影响评价的重点。基于南方地区公路建设过程中水土流失的特点,对南方地区公路建设环评中的水土流失评价要点进行了分析探讨。分析结果表明,对南方地区公路建设项目的水土流失影响进行评价时,应选择最佳预测时段并划分不同的预测区,优先选用适宜于当地实际情况的预测模型,从而确保预测结果的可靠性。应从水土流失防护角度筛选最佳的公路设计方案,将水土保持体现在各项具体的工程措施中,以最大限度地减轻公路建设带来的水土流失影响。     

光纤光栅监测技术在桥涵加固中的应用

在土木工程领域,光纤智能健康监测方法是对建筑物或构筑物的健康状况进行检测的一种新方法.采用200 mm×300 mm×3 000mm试件,对比试验研究桥梁监测中广泛应用的振弦传感器与布拉格光栅传感器.结果表明,布拉格光栅传感器具有更好的检测精度、线性响应和重复性.根据光纤光栅传感器的应变传感特性标定试验,在武黄高速公路的典型桥涵中布设光栅传感器,采集分析加固前后静载试验工况下底部钢筋以及桥涵加铺层钢筋的应变数据,评估高速公路桥梁加固效果,并对桥涵结构进行长期监测.监测结果表明,埋入的光纤光栅可方便地监测桥涵安全状况,其稳定性与耐久性满足钢筋混凝土桥梁结构长期健康的要求.同时,根据光纤光栅传感技术在桥梁监测中的应用实践,探讨了其在桥梁监测中应用所面临的一些关键问题及解决途径.     

一株架桥细菌的共凝集能力及强化生物膜反应器效能的研究

测定了架桥细菌Bacillus cereus G5与活性污泥中分离得到的13株土著细菌及3株复杂有机物降解菌配对组合后的共凝集能力和成膜能力.结果表明:凝集2 h和20 h时的共凝集率分别达到40%~70%和55%~80%;架桥细菌与其中15株细菌混合培养时的生物膜形成量高于单菌培养时的生物膜量.这表明在废水处理系统外G5能与土著菌和降解菌发生较强程度的共凝集,并可促进多数菌株生物膜量的增加.进一步考察了G5与3,5-二硝基苯甲酸降解菌Comamonas testosterone A3投加到序批式生物膜反应器(SBBR)中的生物强化效果.32 d的运行结果表明,同时投加A3与G5菌株的反应器,24 h时出水中3,5-二硝基苯甲酸由100.0 mg·L-1降解至10.1 mg·L-1,降解最快;3,5-硝基苯甲酸负荷由100 mg·L-1增加到1000 mg·L-1的运行过程中,平均降解率稳定在65.0%~88.1%的范围内,表现出最强的抗冲击能力;生物膜量在1.4~2.0 mg·cm-2之间,比其他两组反应器同期时的生物膜量略高.表明在废水处理系统内Bacillus cereus G5亦可能通过其广泛的共凝集能力,促进反应器中生物膜的形成,并辅助降解菌以自固定化方式定殖于生物膜,从而表现出快速的生物强化作用和较强的抗冲击能力.