Effects of premixed methane concentration on distribution of flame region and hazard effects in a tube and a tunnel gas explosion

Study of flame distribution laws and the hazard effects in a tunnel gas explosion accident is of great importance for safety issue. However, it has not yet been fully explored. The object of present work is mainly to study the effects of premixed gas concentration on the distribution law of the flame region and the hazard effects involving methane-air explosion in a tube and a tunnel based on experimental and numerical results. The experiments were conducted in a tube with one end closed and the other open. The tube was partially filled with premixed methane-air mixture with six different premixed methane concentrations. Major simulation works were performed in a full-scale tunnel with a length of 1000 m. The first 56 m of the tunnel were occupied by methane–air mixture. Results show that the flame region is always longer than the original gas region in any case. Concentration has significant effects on the flame region distribution and the explosion behaviors. In the tube, peak overpressures and maximum rates of overpressure rise (dp/dt)_max for mixtures with lower and higher concentrations are great lower than that for mixtures close to stoichiometric concentration. Due to the gas diffusion effect, not the stoichiometric mixture but the mixture with a slightly higher concentration of 11% gets the highest peak overpressure and the shock wave speed along the tube. In the full-scale tunnel, for fuel lean and stoichiometric mixture, the maximum peak combustion rates is achieved before arriving at the boundary of the original methane accumulation region, while for fuel rich mixture, the maximum value appears beyond the region. It is also found that the flame region for the case of stoichiometric mixture is the shortest as 72 m since the higher explosion intensity shortens the gas diffusion time. The case for concentration of 13% can reach up to a longest value of 128 m for longer diffusion time and the abundant fuel. The “serious injury and death” zone caused by shock wave may reach up to 3–8 times of the length of the original methane occupied region, which is the widest damage region.     

Price perceptions in water demand

Economists advocate for using the price mechanism to manage water scarcity, but complex nonlinear rate structures prevalent in markets for municipal water obscure price signals. We conduct a randomized field experiment that jointly elicits knowledge about the cost of water and examines the impact of improved information on demand by linking a survey to water billing records. Half of our sample of 30,000 single family homeowners are randomly sent an invitation to a survey that asks questions about the water bill and the costs of water-use activities (e.g. the cost of taking a shower), and subsequently provides personalized accurate information. Results show that consumers have poor information about the marginal price of water and overestimate the costs of using water. Respondents are relatively better informed about their total bill and water consumption. In aggregate, respondents increase water use in response to the survey, potentially due to learning that water is cheaper than they previously thought. Increased consumption is concentrated among low users who are more likely to over-estimate the costs of using water.     

开展清洁生产审计实现企业经济与环境双效益─—绍兴市清洁生产示范项目企业试点及其效益分析

对绍兴市清洁生产示范项目的试点企业清洁生产审计方法、程序及初步成果作了系统的分析。论述了采用清洁生产审计，进行污染预防，是企业实现经济与环境双重效益的最佳途径。提出了现阶段企业开展清洁生产的部份政策和制度的建议。对我国的清洁生产审计方法学与政策制订具有一定的理论与实践意义。     

受限空间烟气运动的盐水模拟实验初探

考虑到盐水在清水中扩散过程与烟气在受限空间内运动的相似性，本文用实验的方法，初步探讨了用盐水的扩散来模拟烟气在建筑物（单室）内运动的可行性。并对烟羽流主轴线速度和顶篷水平分层烟气流厚度的生长规律进行了测量。本文所得结果基本合理，正确，对建筑火灾烟气控制和人员疏散有参考作用．     

电梯困人应急救援理论的初步建立

针对备受社会关注的电梯困人应急救援的快速实现,在电梯应急救援体系建设下,研究电梯困人救援的快速实现的影响因素、改进措施及标准化电梯困人应急救援体系的建立,提出了一种建立标准化电梯困人应急救援体系的理论,该理论在提升电梯应急救援效率,缩短电梯困人救援时间上给出了指导性理论,通过以某医院为实施对象进行了试验数据采集、统计与分析及过程持续改进,同时验证了这一理论在电梯轿厢困人救援工作中的有效性和可靠性,为分析电梯救援人员组织、影响要素、对策拟定及救援标准程序建立提供了理论支撑和试验数据,为重点单位实施电梯困人救援工作的标准化程序建立提供了一种方法,也为全面降低电梯困人救援时间的实施提供新的思路和可能性,该理论及方法具有重大的现实指导意义。     

Experimental research on the variational characteristics of vertical stress of soft coal seam in front of mining face

Permeability of coal seam is extremely sensitive to the in situ stress loaded. The techniques of “Pressure relief” have been proved significantly effective in practice to improve the gas permeability and the gas extraction rate to the soft coal seam. It is very necessary to make clear of the variational characteristics of the stress distribution in front of coal mining face with the production process. The vertical stress values of the top and bottom layer of the coal seam at different distances in front of the coal face are respectively measured, and the corresponding curves of the vertical stress variation along the mining direction have been obtained. According to the research conclusions in this paper, some available technical measures of “Pressure relief” at different distances and different layers of soft coal seam in front of mining face, are expected to make and to put into practice. The research methods and correlative data included in this paper also can be referred to conduct some further and deep-seated exploration to get new theories and practical techniques for the gas drainage of the soft and low permeability coal seam.     

Experimental investigation of the influence of inert solids on ignition sensitivity of organic powders

This work presents the results of the experimental characterization of the ignition sensitivity of solid inertant/combustible powders mixtures. Three inert solids (alumina, Kieselguhr, aerosil) and eleven organic powders have been considered and the following parameters have been determined: (1) the minimum ignition energy, (2) the minimum ignition temperature in cloud and (3) the minimum ignition temperature in 5 mm layer. The effects of the addition of inert solids are described and a simple model is proposed to represent the experimental results.Generally, increasing inert solid content in a powder leads to a higher minimum ignition energy as well as a higher minimum ignition temperatures in cloud and in layer. In some cases, the flammability is influenced above a threshold concentration value, which can be quite high (up to 85 wt.%). Indeed, the proposed model shows a zone below the minimum ignition concentration (MIC), which does not enable an efficient or safe inerting: either the admixed inert solid does not provide a sufficient effect, or it can even facilitate the ignition of the dust by notably improving its dispersability.The influence of key parameters such as the thermal conductivity or optical properties on the efficiency of the inerting by admixed solid need to be further assessed in a future work in view to better understand the mechanisms involved and to extend the scope to other types of oxidizable materials.     

地震动对人生理反应的影响初探

本文采用实验心理学的基本原理和方法,在模拟地震振动台上进行了在真实地震波作用下心理反应试验,研究了地震动作用下人的生理变化过程。     

多层建筑火灾烟气运动的模拟实验研究

火灾烟气是导致多层建筑火灾中人员伤亡的主要原因。结合多层建筑的实际情况 ,利用缩尺度模型实验楼模拟多层建筑火灾的典型情况 ,对其火灾烟气自火源产生后的运动特性进行实验研究。结果表明 ,烟气沿程由于热交换温度不断降低 ,会迅速达到顶部楼层并立即沉降 ,而且不同工况条件下所包含的有毒成分浓度随着火源温度的升高而上升。实验结果的分析能够较好地符合实际火灾的一些典型调查结果。     

火灾过程中火源热释放速率模型及其实验测试方法

详细分析了目前常用的火源热释放速率模型，并对其特点和参数范围进行对比讨论；同时还介绍了基于氧消耗原理的热释放速率测试方法和基于质量损失速率的热释放速率测试方法，并给出了部分实验测试结果。