A closer look at BLEVE overpressure

The overpressure produced by the boiling liquid expanding vapor explosion (BLEVE) is still not well understood. Various methods have been published on the overpressure modeling in the far field. They mostly differ by the modeling of the expansion energy, used to scale the distance to the source where the overpressure needs to be calculated. But these methods usually include a experimentally fitted reduction factor, and are mostly overestimating the overpressures. Today there is a growing interest in modeling the BLEVE overpressure in the near field, for studying the blast effect on critical infrastructure such as bridges and buildings. This requires a much better understanding of the BLEVE blast. This paper goes deeper in the understanding of the physical phenomenon leading to the BLEVE blast wave generation and propagation. First, mid-scale BLEVE experiments in addition to new experimental data for near field blast from a small scale supercritical BLEVE are analyzed. And second, an analysis method of the shocks observed in the experiments is presented based on fundamental gas dynamics, and allows the elaboration of a new modeling approach for BLEVE overpressure, based on the calculation of the initial overpressure and radius of the blast.     

Influence of new town development on the urban heat island - The case of the Bundang area

Five new towns have been developed around the Seoul metropolitan area since 1996. However, these new towns generate lots of traffic and related problems in the areas including those new towns and Seoul as a result of increases in population and a lack of ecological-self-sufficiency. Currently, construction of another new town is under deliberation, and what should be a major consider is the notion that the new town be located within a wide, green zone. Many studies have revealed that green space can play an important role in improving urban eco-meteorological capability and air quality. In order to analyze the urban heat island which will be created by the new urban development, and to investigate the local thermal environment and its negative effects caused by a change of land use type and urbanization, Landsat TM images were used for extraction of urban surface temperature according to changes of land use over the last 15 years. These data are analyzed together with digital land use and topographic information. As a study result, it was found the urban heat island of the study area from 198.5 to 1999 rapidly developed which showed a difference of mean temperature above 2.0. Before the Bundang new town construction the temperature of the residential area was the same as a forest, but during the new town construction in 1991 analysis revealed the creation of an urban heat island. The temperature of a forest whose size is over 50% of the investigation area was lowest, and thus the presence of a forest is believed to have a direct cooling effect on the urban environment and its surroundings. The mean temperature of the residential and commercial areas in the study was found to be 4.5 higher than the forest, and therefore this part of land use is believed to be the main factor causing the temperature increase of the urban heat island.     

用预先热处理的材料加工长杆高强度双头螺柱

用预先热处理的材料生产长杆高强度双头螺柱新工艺 ,消除了长杆的热处理变形 ,降低了机械性能的不稳定性 ,提高了产品质量及螺纹联接的可靠性。     

锅炉房工艺设计中确定煤场面积的一种方法

本文以管理科学的库存理论为基础，以提高经济效益为目的，提出了一种全新的锅炉房煤场面积确定方法。     

中国科学技术协会五届二次全委会明年在京召开我会两名代表参加全会活动

中国科学技术协会五届二次全委会明年在京召开我会两名代表参加全会活动中国科协第五届全国委员会第二次会议将于１９９７年２月２２日至２４日在北京召开。我会副理事长、中国科协全国委员会委员程映雪教授作为正式代表，我会副秘书长、“中国安全科学学报”主编徐德蜀高...     

不锈钢板式热沉传热特性的实验与模拟研究

目的 研究流量、胀高及焊点排布方式对不锈钢板式热沉传热特性的影响。方法 搭建实验平台,加工出结构参数不同的板式热沉实验件,同时采用静力隐式算法建立相应的几何模型,通过实验与数值模拟相结合的方法,研究流量、胀高和焊点排布方式的变化对板式热沉热阻的影响规律,并分析热沉流道内部流场状态。结果 首先计算了6个工况下的热阻,发现实际换热量为540 W时,数值模拟与实验结果的最大相对误差不大于25%。然后分析了误差来源,最后得到了热沉全流道速度场与温度场的分布情况。结论 实验与模拟结果有较好的符合程度,证明了数值模拟方法的可靠性。在换热量相同时,板式热沉的热阻随流量与胀高的增大而减小,焊点为菱形排布的热沉传热性能相对更好。板式热沉内部的流场具有周期性,焊点使流体扰动增强,并形成射流和旋涡,起到了强化传热的效果。     

随机振动加速度响应谱及与冲击等效性分析

目的 获得随机振动的加速度响应谱,提升随机振动与冲击的等效性分析精度。方法 首先,基于维纳-辛钦定理,推导单自由度系统在随机振动基础激励作用下加速度响应均方值的通用表达式;其次,分别推导单自由度系统在理想白噪声和限带非均匀谱随机振动基础激励作用下的加速度响应均方值;再次,基于3σ准则,推导限带非均匀谱随机振动的3σ加速度响应谱;最后,基于加速度响应等效,通过将装备随机振动条件的3σ加速度响应谱与冲击条件的冲击响应谱进行等效性分析,对GJB 150.18A—2009中的冲击试验剪裁条件进行精细优化。结果 精细优化后,可有效改善冲击试验剪裁条件的工程实施精度。结论 获得了限带非均匀谱随机振动的3σ加速度响应谱,并基于此对GJB 150.18A—2009中的冲击试验剪裁条件进行了精细优化,对于装备合理剪裁冲击试验具有借鉴意义。     

盐溶法去除糖厂滤泥中蛋白质的条件优化

通过盐溶法去除糖厂滤泥中蛋白质,以处理后滤泥中剩余的蛋白质含量为评估指标,研究了温度,NaCl的浓度,料液比,时间对蛋白质去除的影响.在单因素实验分析的基础上进行正交实验,对相关因素在不同水平上对实验结果的影响进行了分析.结果表明,盐溶法去除蛋白质的最优条件是温度为40℃,氯化钠溶液的浓度为1%,料液比为1:10,时间为90 min.处理后糖厂滤泥的蛋白质含量为1.36%,去除率为80%.     

沼气增温与控制系统的设计与仿真

冬季北方寒冷地区温度偏低,难以满足大中型沼气厌氧发酵系统对于温度的要求。为了解决该问题,针对天津地区某奶牛场沼气工程,设计了一套回收发电机余热并辅助电加热为发酵罐体供热的沼气增温控制系统,且实验确定最佳控制温度为35℃。在该系统中,罐体内部均匀布置竖直型循环加热管路,从而使料液温度分布更加均匀,热响应更加迅速,6 d左右即可将发酵罐内发酵料液提升到所需最佳温度;另外,采用罐内部温度及循环水流量的反馈调节,使料液的温度波动维持在±1℃范围内,解决了在冬季由于温度过低而导致沼气产气率偏低、甚至停滞的问题;同时,采用MATLAB软件对基于F-PID及传统PID的温度控制系统进行了仿真。对比结果表明,F-PID控制器较传统PID控制器超调量减小3℃,响应时间缩短60%,表明F-PID系统具有更高的效率、稳定性及实用价值。     

聚氨酯泡沫材料阴燃发展过程的特性分析

分析对比了相同加热条件下的聚氨酯泡沫材料在有氧和无氧气氛下的升温过程,并对不同加热条件下的聚氨酯泡沫材料的阴燃传播速度进行研究.结果表明:沿着反应进行的方向,分离点的温度越来越低,不同热流条件下的温度分离曲线斜率在实验稳定发展段的变化规律表现得很相似,并在分离点出现后,有氧气氛中的该位置温度在短时间内急剧上升;在阴燃不稳定传播阶段时,热解前锋的速度小于氧化前锋的速度,在稳定传播阶段时,热解前锋速度与氧化前锋速度近乎相等.