富氧燃烧对烟气组分影响的数值模拟研究

以4×104m3/h顶烧式常压加热制氢转化炉为研究对象,分析富氧燃烧对烟气组分的影响,采用有限体积法建立制氢转化炉辐射室流体的三维有限元模型,选取合理的数学模型研究了不同富氧工况对制氢转化炉辐射室内及出口处烟气组分的影响规律.研究结果表明:随着助燃空气中含氧量的增加,燃料气燃烧愈加完全,烟气中碳氢化合物(HC)和一氧化...     

不同流条件下随温度变化的流体黏性和热泳微粒沉积对自由传热传质作用的Lie群分析

研究二维稳定不可压缩流体在竖向延伸平面上的流动．流体黏性假设为与温度相关的线性函数．对控制方程进行伸缩群变换,由于变换参数之间的关系让方程解保持不变．在找到3个绝对不变量后,推导对应动量方程的一个三阶一般微分方程和两个对应能量方程和扩散方程的二阶一般微分方程．求出具有边界条件方程的数值解,发现随着平面延伸距离增加,随温度变化的流体黏性降低让流速变慢．在平面的某个特定点处,随着黏性减少流速变慢但温度增加．热泳微粒沉积在浓度边界层起着关键作用．最后对计算结果进行讨论并给出图例．     

竖板表面温度的变化对磁流体动力学流动的影响

在横向磁场作用下,不可压缩的粘性导电流体,流经一个半无限的竖板,完成了壁面温度变化对磁流体动力学流动的分析．假定由粘性耗散和感应磁场产生的热量可以忽略不计．无量纲的控制方程为二维非稳态耦合的非线性方程．结果显示,磁场参数对空气和水的速度有着抑制作用．     

湍流运动论中的化学反应速率扰动

在分子与分子之间发生碰撞时,如果分子的动能足够大,当超过一定的阈值E时,分子碰撞就会发生化学反应.然而气体分子化学反应速率是受到一定因素影响的,诸如分子数密度n、温度T以及速度V.日本学者Sagara于上世纪70年代曾对分子数密度n和温度T对反应速率的变化做了深入的探究.主要是在此基础上利用二粒碰撞机理论对速度以及温度和速度的共同作用来研究反应速率的变化情况.     

煤粉起动速度与粒径及湿度的关系

在煤码头和车站的煤堆积场上,煤粉的扬起是污染环境的主要原因之一.作者根据力学的基本原理,考虑颗粒和液滴重力、煤粉颗粒尺寸和湿度的影响,利用煤粉颗粒起动时的力平衡条件,推导出在风的作用下,具有一定湿度的煤粉颗粒开始扬起的起动风速的理论表达式.最后.根据煤粉起动速度与煤粉颗粒粒径及湿度的关系,将理论公式和风洞实验结果进行了比较,理论和实验结果符合得相当好.     

Wall effect on determination of laminar burning velocity in a constant volume bomb using a quasi-dimensional model

In experiment, two optical and pressure-based methods are frequently used to evaluate laminar burning velocity of a combustible mixture. In the currently reported work, the pressure-based method was utilized to find the laminar burning velocity using the measurement of pressure variations during the combustion process in a spherical bomb and analyzing them through a multi-zone quasi-dimensional model. To check the results of the method, isooctane–air mixtures were used at equivalence ratios of 0.85 and 1.0 and initial pressures of 95 and 150 kPa with 343 K initial temperature. The time history of the bomb pressure during the combustion event, initial pressure and temperature, fuel type, and equivalence ratio were applied as input to a Fortran program written by the author based on the multi-zone combustion model; and, flame radius-time, flame speed, and laminar burning velocity at different pressures and temperatures were evaluated assuming spherical flame growth. The obtained results were compared with those of some other researchers and a reasonable agreement was observed. The wall effect on the laminar burning velocity at the end of the combustion process was clearly highlighted and a reliable range of burning velocity was distinguished. The results showed that the evaluated laminar burning velocity was not reliable at the late part of the combustion process due to possible local contact of flame front and the bomb wall, the wall effect on the reacting species, flow to small crevices, and the boundary layer effect.     

图的存活率与消防员问题

消防员问题可视为传染病、火灾、谣言、计算机病毒等传播的一个简化模型.假设一把火在一个图的某个点或多个点燃起,消防员选择若干个未着火的顶点进行防护,然后火蔓延到前一步着火点的未燃邻点.当火不再蔓延时整个过程结束.消防员问题自1995年提出以来引起了人们的广泛关注.本文简述了与消防员问题相关的最近研究进展,包括算法复杂性、无限图和有向图的消防员问题、图的存活率、图的燃烧数及一些有待于进一步研究的问题.     

Heat transfer for laminar flow through parallel porous disks of different permeability

The problem of temperature distribution and heat transfer for laminar flow through two parallel porous disks of different permeability, has been investigated when the flow is entirely due to injection and/or suction at the two disks. Viscous dissipation terms have been included in the energy equation and the injection and/or suction velocities at the two disks are assumed to be small. The boundaries are kept at constant temperatures. The variation of temperature and Nusselt numbers at the two disks has been graphically depicted for various values of the injection and suction velocities.     

基于模糊群子论的可燃性粉尘点着温度试验与分析

为了探讨模糊群子论模型在可燃性粉尘中粒度分布的评价作用及适用性,针对可燃性粉尘颗粒粒度分布的不确定性,依据模糊群子论特有的多层性、模糊性、最可几性和可变性,采用激光粒度仪测定了不同粒度分布范围下可燃性粉尘颗粒粒度分布,通过模糊群子论方法,分析可燃性粉尘颗粒粒度的竞争参数.实验结果表明:粉尘颗粒体系越趋向于小粒径集团为主的分布,其相对应的点着温度也就越低;当粉尘颗粒足够小时,由于受到颗粒间的力、颗粒间的碰撞以及颗粒充装的密实程度的影响,导致其点着温度上升;采用模糊群子论模型可对可燃性粉尘颗粒粒度分布进行定性及定量分析,有助于粉尘爆炸防治技术的发展.     

Effect of flame retardants on the properties of monolithic and foamed polyurethanes at low temperatures

The dependence of physical and mechanical properties of monolithic and foamed rigid polyurethanes on the content of flame retardants was investigated at 293 and 98 K. The character of the influence of the content of trichloroethyl phosphate on the ultimate tensile elongation and the coefficient of linear thermal expansion for monolithic and foamed polyurethanes at a temperature of 98 K was established. Latvian State Institute of Wood Chemistry, Riga, LV-1006 Latvia. Translated from Mekhanika Kompozitnykh Materialov, Vol. 35, No. 5, pp. 671–676, September–October, 1999.