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661.
利用自行研发的气体扩散系数测试装置及测定方法,分别测定和分析了常温常压下,不同扩散管径、扩散距离、体系温度、气体进气方式及其流量、扩散时间等对气体扩散系数测定的影响情况。基于拟稳态扩散模型,得出气体扩散系数测定的合理条件：扩散距离为9~14 cm;吹气流量为0.22~0.33 m3·h-1;体系温度应低于液体沸点且不要太接近沸点;扩散时间根据液体挥发性情况,一般不小于12 h,具体以能够明显观测到测定前后液面高度差为基准;扩散管管径应在保证扩散管截面积较小、液面以上气体以单向自然扩散为主、液体蒸发速度相对较慢的范围内选取。研究结果确定了气体扩散系数测定的合理条件,对加深油气空间传质机理的认识以及确保扩散系数测定的准确度具有重要指导意义。 相似文献
662.
针对石化企业中可燃气体报警器校准工作存在着校准周期长、维护困难、准确性不能保证的现状,提出了一种通过将高浓度可燃气体物质经过定量稀释配制成用于可燃气体报警器标定的多种浓度气体物质的方法,并设计了一种由两路流量检测与控制模块和一个监控单元构成的可燃气体报警器快速标定装置。叙述了可燃气体报警器快速标定装置的原理、元器件构成、设计结构、流量控制方法和防爆措施的实现。 相似文献
663.
The complexity of the evacuation process is associated with the flow of occupants through various egresses available inside the building. Several methods and algorithms are now available to analyse the problem related to evacuation. In the present paper an algorithm, evacuation discrete time model (EDTM) has been presented to analyse the building egress evacuation time problem with previous works. The algorithm is based on the crowd flow theory and uses discrete computational approach to identify various widths of egresses available for movement of the people, which is more accurate and practicable because the crowd flow rate is variable. The developed model has been compared with an existing model to show the capabilities of the developed algorithm. A case of stadium stand egress is chose for the validity of EDTM, and a comparison of EDTM, previous model and computer simulation indicates that both the EDTM and the simulation curves were found to give better predictions than the previous model. Based upon the comparison analysis with stranded crowd and evacuation crowd at a certain time, EDTM shows great value in explaining the cause of stampede-trampling and crushing incident of egress or narrow passage zone. 相似文献
665.
减阻剂可以有效改变管道内流动结构,减少流动阻力,在保证管道输量的前提下,降低管道的工作压力,提高管道的安全性能。采用Giesekus模型对表面活性剂减阻流动进行直接数值模拟,并基于模拟计算结果,采用小波多分辨分析方法研究减阻剂对流动结构的影响,定量计算减阻剂的作用效果,分析其对管道运行安全的影响。计算结果表明:在减阻剂作用下,流向速度分量的大尺度脉动所含能量显著增强,与牛顿流体相比,减阻流体的大尺度结构增大约1.5倍,而小尺度流动结构明显减少,进一步证明了减阻剂对小尺度湍流结构的抑制作用。得到的减阻率为47.07%,可使管道在较低压力下运行,降低管道的安全风险,提升管道的安全性能。 相似文献
666.
The current conceptual hydrogeologic model established for source water to the Amargosa River was tested in order to help inform management decisions regarding the Amargosa River's Federal designation as Wild and Scenic through an Act of Congress. The limited availability of water in this region results in the critical need for effective management in the basin to maintain its Wild and Scenic attributes inclusive of habitat for several endangered and threatened species. The use of forensic tools and integration of multiple lines of geologic, hydrogeologic, geochemical, and stable isotopic evidence suggest that the simple historical model for primary groundwater transport through this region is incorrect and that a large supply of regional baseflow does not provide the hydrogeological foundation of the Amargosa River basin. Data collected is consistent with an alternative model requiring complex source mixing and shallow alluvial groundwater that supports river flow. This conclusion also suggests Wild and Scenic conditions in this basin are more precarious than previously understood. 相似文献
667.
八步里沟位于大渡河上游,沟口堆积扇为金川县城,历史上泥石流灾害严重。20世纪80年代以来,对泥石流灾害进行了综合治理,工程防治效果明显,通过近30a的演化,防治工程与泥石流灾害共同作用形成了独特的泥沙资源并进行了初步开发。分析了八步里沟的资源特征、综合开发利用的制约因素、开发与保护的优化配置以及进一步开发的空间等问题,发现拦砂坝库区的建材开发有效延长了工程运行年限,沟内种植经济林抑制了泥石流灾害,拦砂坝抬高沟床侵蚀基准面为小水电开发和灌溉提供了水头,经济发展与灾害防治形成良性循环,达到可持续发展的目的。为提高资源利用率,最大化发挥防灾工程的经济效益和社会效益,可进一步利用现有治理工程建立泥石流防治的科普基地,沟口堆积扇泥石流排导工程两侧设立限制开发区、建立生态公园,达到优化资源开发的目的。 相似文献
668.
Brendan J. Russo Peter T. Savolainen Timothy J. Gates Jonathan J. Kay Sterling Frazier 《Traffic injury prevention》2017,18(5):521-527
Objective: Although a considerable amount of prior research has investigated the impacts of speed limits on traffic safety and operations, much of this research, and nearly all of the research related to differential speed limits, has been specific to limited access freeways. The unique safety and operational issues on highways without access control create difficulty relating the conclusions from prior freeway-related speed limit research to 2-lane highways, particularly research on differential limits due to passing limitations and subsequent queuing. Therefore, the objective of this study was to assess differences in driver speed selection with respect to the posted speed limit on rural 2-lane highways, with a particular emphasis on the differences between uniform and differential speed limits.
Methods: Data were collected from nearly 59,000 vehicles across 320 sites in Montana and 4 neighboring states. Differences in mean speeds, 85th percentile speeds, and the standard deviation in speeds for free-flowing vehicles were examined across these sites using ordinary least squares regression models.
Results: Ultimately, the results of the analysis show that the mean speed, 85th percentile speed, and variability in travel speeds for free-flowing vehicles on 2-lane highways are generally lower at locations with uniform 65 mph speed limits, compared to locations with differential limits of 70 mph for cars and 60 mph for trucks.
Conclusions: In addition to posted speed limits, several site characteristics were shown to influence speed selection including shoulder widths, frequency of horizontal curves, percentage of the segment that included no passing zones, and hourly volumes. Differences in vehicle speed characteristics were also observed between states, indicating that speed selection may also be influenced by local factors, such as driver population or enforcement. 相似文献
669.
The inflow and stock (amount in use) of heavy metals (cadmium(Cd), chromium (Cr), copper (Cu), lead (Pb), mercury (Hg), nickel (Ni) and zinc (Zn)) in goods in 1995 have been quantifiedin the anthroposphere of Stockholm, Sweden. Statistics on national, regional and local level were used. Contacts were established with representatives from production and constructionin the industrial sector and with authorities. The results show that the stock of Cd is 0,2 kg per capita. For the other heavymetals the corresponding result per capita is: Cr 8, Cu 170, Hg 0,01, Ni 4, Pb 73 and Zn 40 kg. The inflow varies between2–8%of the stock indicating the importance of the stock. The lowestlevels are for Cu and Pb. Heavy metal levels in solid waste are high, between 15–45% of the amount in the inflow (Hg excluded), the lowest values were for Cu and Pb. Thus, recyclingis incomplete. Long life expectancy goods form the majority of the stock but there is a tendency that short life expectancy goods increase their importance in the inflow. Concealedgoods are also more frequent in inflow than in the stock. 相似文献
670.