Study of the mechanisms of the flame propagation and stabilization in porous media

The CH4/air premixed gas combustion processes in porous media were numerically studied using the two-temperature reacting fluid model with dispersions and detailed chemical reaction mechanism GRI 3.0. The mechanisms of the propagation and stabilization of submerge flames and surface flames in porous media were illuminated distinctly by considering the magnitude of the terms in the two energy equations, analyzing the sensibility of flame propagation speed to flame location, heat exchange coefficient between gas and solid, thermal conductivity and radiative extinction coefficient of porous media. It was concluded that the propagation mechanism of a submerged flame is similar to that of a free flame with an additional preheat zone and that the surface-flame propagation mechanism in porous media is similar to that of a free flame with heat loss in reaction zone. Supported by the National Natural Science Foundation of China (Grant No. 50376060)     

自由堆积多孔介质内超绝热燃烧的试验研究

为探索多孔介质内超绝热燃烧的特性,搭建了自由堆积多孔介质超绝热燃烧试验台架,测量了不同化学当量比（0.4～0.7）的甲烷/空气预混气体的超绝热燃烧特性.自由堆积多孔介质由直径为3和6 mm的Al2O3小球在陶瓷管（Φ38 mm×500 mm)中堆积而成,孔隙率为0.42.试验结果表明,在多孔介质中只有当燃烧波正向传播时才可能产生超绝热燃烧.在贫燃条件下超绝热燃烧的上限化学当量比为0.7,下限化学当量比为0.4;当化学当量比小于0.4或大于0.7时,在贫燃条件下的超绝热燃烧将不能实现.多孔介质中预混燃烧的火焰锋面速度约为7.82 μm/s,最大燃烧锋面温度超过绝热燃烧温度139 K.     

Analysis of wave propagation on human body based on stratified media model

Human body communication （HBC） is a promising near-field communication （NFC） method emerging in recent years. But existing theoretical models of HBC are too simple to simulate the wave propagation on human body. In this work, in order to clarify the propagation mechanism of electromagnetic wave on human body, a surface waveguide HBC theoretical model based on stratified media cylinder is presented. A numerical model analyzed by finite element method （FEM） is used for comparing and validating the theoretical model. Finally, results of theoretical and numerical models from 80 MHz to 200 MHz agree fairly well, which means that theoretical model can characterize accurate propagation mechanism of HBC signal. Meanwhile, attenuation constants derived from two kinds of models are within the range from 1.64 to 3.37, so that HBC signal can propagate effectively on human body. The propagation mechanism derived from the theoretical model is useful to provide design information for the transmitter and the modeling of the propagation channel in HBC.     

New method for wave radiation and propagation in anisotropic stratified media

A matrix-exponent method is proposed to treat wave radiation and propagation in aniotropic stratified media. By using matrix-exponent formulations, the present method is elegant for expressions and reliable for computations. As an example, the method is used to calculate the ELF excitation of the Earth-ionosphere waveguide by an equivalent dipole resulting from heating the lower ionosphere with modulated HF waves.     

Effects of interlayer on SH wave propagations

0　ＩＮＴＲＯＤＵＣＴＩＯＮＩｔｉｓｗｅｌｌｋｎｏｗｔｈａｔｉｔｉｓｖｅｒｙｎｅｃｅｓｓａｒｙｆｏｒｕｎｄｅｒ ｓｔａｎｄｉｎｇｔｈｅｎａｔｕｒａｌｐｈｅｎｏｍｅｎａａｎｄｓｏｌｖｉｎｇｔｈｅｅｎｇｉｎｅｅｒ ｉｎｇｐｒｏｂｌｅｍｓｔｏｒｅｓｅａｒｃｈｔｈｅｅｌａｓｔｉｃｗａｖｅｐｒｏｐａｇａｔｉｏｎｓｉｎｌａｙｅｒｍｅｄｉａ .Ｔｈｅｒｅｆｏｒｅ ,ｔｈｅｐｅｏｐｌｅｈａｓｐａｉｄａｇｏｏｄｄｅａｌｏｆａｔｔｅｎｔｉｏｎｔｏｉｔａｎｄｍａｄｅｃｏｎｓｉｄｅｒａｂｌｅｒｅｓｅａｒｃｈ .Ｂｕｔ,ｉｎｔｈｅ…     

多孔介质中有效孔扩散系数的试验测量

提出了通过实时测量扩散过程中多孔介质浮重变化,直接测定有效扩散系数的方法.首先建立了联系有效扩散系数和试件浮重变化的数学模型,并求出了该模型的解析解;利用非线性超定方程组优化求解的方法,结合问题的解析解和实测数据,反求出模型中的参数,有效扩散系数和边界层传质系数.用上述参数预测的试件浮重变化与实测浮重变化相差很小.表明该方法的实用性和可靠性.     

饱和孔隙介质中的波

通过对饱和孔隙介质的运动方程的分解,证明了饱和孔隙介质体中存在两种类型的膨胀波和一种剪切波传播;给出了不同波型的传播运动方程;对饱和孔隙介质的几种特殊情形,讨论了波的传播物性以及波速计算公式。     

Determination of permeability using fractal method for porous media

A theoretical formulation was developed to express permeability as a function of different fractal dimensions and other scales for porous media . The effective fractal void ratio, the spectral dimension and the fractal dimension of particle mass distribution were introduced. The permeabilities for different soils in China are calculated. The predicted permeability for rice soil was compared with the measured data available in literature.     

堆积型含湿多孔介质导热系数测试实验研究

以砂子模拟堆积型多孔介质,采用Hot Disk热常数分析仪（TPS 2500）对不同含湿率砂的有效导热系数进行测量和实验研究。研究发现,非饱和含湿砂有效导热系数随含湿率的增加而增大。低含湿率（体积含湿率低于25％）情况下,砂子的有效导热系数难以准确测得,其主要原因是测试过程中,由于加热影响,贴近探头附近的水分因蒸发扩散而逐渐减少,探头周围试样构成不能保持恒定,导致测试环境持续发生变化。     

大孔隙对多孔介质导热性能影响的数值分析

采用有限体积方法求解Laplace方程,对非均匀多孔介质中大孔隙对导热性能的影响规律进行数值分析。研究结果表明,有效导热系数随着大孔隙的形状、排列方式、连通性和方向的不同呈现出很大的波动性,其中大孔隙的连通性和方向对多孔介质导热性能的影响尤其严重。研究结果可为非均匀多孔介质导热性能预测模型的改进提供参考依据。     

各向异性分层介质的电磁波传播特性

为了分析电磁波在分层各向异性介质中的传播特性 ,从无源区域的Maxwell旋度方程出发研究了非均匀各向异性介质中的特征波 .导出了一般各向异性介质中电场和磁场横向分量的耦合矩阵 ,由此得到了传播矩阵 ,进而给出了计算分层各向异性材料的反射系数和透射系数的解析表达式 .这种方法对于分析分层各向异性介质的电磁反射和透射特性是有效的     

Theoretical study on thermal radiative properties of semitransparent porous media

Thermal radiative properties are significant to radiative transfer processes in semitransparent media.In order to calculate thermal radiative properties,conventional Mie formulism and its various abbreviations are generally used,which are based upon electromagnetic scattering by a sphere submerged in a non absorbing medium.For some semitransparent porous media such as ceramics where the matrix is absorbing,the conventional Mie solution is no longer valid.In this study a rigid Mie solution of electromagnetic scattering by a sphere in an absorbing medium is introduced to analyze the radiative properties of such a medium,and reliability of conventional Mie formulism is also tested.Parametric studies show that scattering coefficient and phase function of porous media are influenced significantly by matrix refractive index and size parameter.The matrix absorbing index usually has little influence.But when the absorbing index is greater than 0.01,especially under the condition where the size parameter is greater than 30,the conventional Mie formulism is not appropriate.Such a porous media may exhibit scattering or absorbing dominated characters under different conditions and an optimal pore diameter exists for a specified wavelength,which decreases with the matrix refractive index.     

考虑裂隙的多孔介质中对流扩散现象的仿真模拟

为研究裂隙多孔介质中的对流扩散现象,采用光滑粒子流体动力学(SPH)方法从孔隙尺度下模拟了裂隙中孔隙水的流动过程,仿真实现了考虑裂隙时溶质穿透多孔介质的真实运移过程,并提出一种简化处理的两流区模型对穿透过程加以描述.计算中首先采用SPH方法求解纳维斯托克斯方程,建立能考虑复杂多孔颗粒边界的二维流场模型,并基于此模型进行了溶质穿透三种不同裂隙宽度的多孔介质的仿真实验.随着介质中裂隙宽度增大,裂隙区域流速与基质区域流速差增大,穿透曲线中早期穿透和拖尾现象越明显;采用两流区模型能够描述这一现象,但一般化的模型难以得到精确解,因此提出一种简化处理办法,并给出了该简化模型的解析解.结果表明,该简化模型能够很好地描述裂隙多孔介质中溶质的运移规律,并可反演得到裂隙流中对流扩散的相关参数.     

往复式多孔介质燃烧器温度分布的试验研究

研究了往复式多孔介质燃烧器在热态试验条件下的温度分布，分析了当量比、空截面流速、
切换半周期对多孔介质中温度分布的影响，以及切换半周期对燃烧器出口温度的影响。随着系统周期性地
运行，多孔介质中的温度呈动态周期性变化。在当量比为0.3～1.4时，随着当量比的增大，多孔介质中的
温度先上升后下降。在切换周期和当量比一定时，随着空截面流速的增大，多孔介质中的温度随之升高；
在当量比和燃气质量流量保持不变时，随着切换半周期的增大，多孔介质中的温度先升高后降低，最后基
本保持不变，而燃烧器出口温度随切换半周期的增大而升高。与单个多孔介质燃烧相比，往复式多孔介质
中的温度整体分布较均匀。     

Experimental investigations on the fluid flow mechanism in porous media of enhanced oil recovery by alkli/surfactant/polymer flooding

Nowadays, most oil fields in China are in the later period of production, and the water cut increases rapidly with even over 80 percent. It is hard for the water flooding tech- nique to meet the needs of oil fields production. Thus, it is inevitable to develop new oil production techniques to replace water flooding. ASP flooding is a new technique which is developed out on the basis of alkali flooding, surfactant flooding and polymer flood- ing in the late 1980s. ASP flooding synthetically m…     

多孔介质内低热值气体燃烧及传热数值模拟

以一个简化的氧化铝(Al2O3)堆积小球多孔介质燃烧器为模拟对象,使用计算流体力学(CFD)方法对低热值气体燃烧进行模拟研究.考虑气体的湍流扩散和气固间的对流换热及固体间的辐射和导热换热,通过研究多孔介质内的压力分布、速度分布、温度分布及组分分布,对多孔介质内的总的热流密度及辐射热流密度进行对比分析,揭示燃烧器内不同轴向位置的燃烧及换热规律.结果表明,低热值气体在氧化铝(Al2O3)堆积小球多孔介质燃烧器内燃烧时火焰面前沿气固温差大于火焰面后气固温差.火焰面前沿固体温度高于气体温度,热量由固体传向气体,对流换热强度较大;火焰面后沿气体温度高于固体温度,热量由气体传向固体,对流换热强度较小.     

Combustion characteristics of low concentration coal mine methane in divergent porous media burner

Low-concentration methane (LCM) has been one of the biggest difficulties in using coal mine methane. And previous studies found that premixed combustion in porous media is an effective method of low calorific gas utilization. This paper studied the combustion of LCM in a divergent porous medium burner (DPMB) by using computational fluid dynamics (CFD), and investigated the effect of gas initial temperature on combustion characteristic, the distribution of temperature and pollutant at different equivalence ratios in detail. Besides, the comparison of divergent and cylindrical burners was also performed in this paper. The results show that: the peak temperature in DPMB increases as the increasing of equivalence ratio, which is also suitable for the outlet NO discharge; the linear correlation is also discovered between peak temperature and equivalence ratios; NO emission at the initial temperature of 525 K is 5.64 times, larger than NO emission at the initial temperature of 300 K. Thus, it is preferable to balance the effect of thermal efficiency and environment simultaneously when determining the optimal initial temperature range. The working parameter limits of divergent burner are wider than that of cylindrical one which contributes to reducing the influence of LCM concentration and volume fluctuation on combustion.     

多孔介质预混燃烧气固温度分布特性试验研究

为研究多孔介质燃烧、传热和生成物特性，采用非接触式红外测温仪对多孔介质预混燃烧室中气、固两相温度分布进行了试验研究.结果表明预混气体在多孔介质中燃烧时，气相和固相的温度是不同的，存在－60～+100 K的温差.试验得到了不同当量比、热流密度和孔径下的燃烧室气、固温度分布.在火焰前缘，固体骨架的温度高于多孔介质内气体的温度，对气体有预热作用；在火焰后缘，气体温度高于固体骨架温度，对固体骨架有蓄热作用.当量比降低，气、固温差波动变小；当量比不变，热流密度增大，气、固温度差值在轴向长度方向变化小.     

基于孔隙尺度的方腔内多孔介质融化模拟研究

由于单松弛(LBGK)格子Boltzmann模型在用反弹格式处理无滑移边界时存在缺陷。基于孔隙尺度,采用多松弛(MRT)格子Boltzmann模型研究封闭方腔内多孔介质的自然对流融化过程,其中,通过焓方法考虑相变潜热。分析了Rayleigh数和Prandtl数对融化的影响。结果表明:采用的多松弛模型能很好的预测导热和对流融化过程;多孔介质的导热融化界面不再与垂直壁面平行,自然对流融化界面呈现不规则形状;Rayleigh数和Prandtl数对多孔介质的融化有较大影响。     

低热值燃气往复多孔介质燃烧特性

为了研究低热值预混燃气（当量比<0.4）在往复式多孔介质燃烧器中的燃烧特性,建立两端布置蓄热段的往复多孔介质燃烧试验台,研究温度波动、轴向温度分布及燃烧极限的特性.结果表明,低热值预混燃气温度波动特性与火焰面位置有直接关系,两端布置蓄热段能够减小泡沫陶瓷多孔介质温度波动幅度.随着当量比的降低,轴向温度分布形状从“马鞍形”、“梯形”、“椭圆形”,变化到系统达到燃烧极限时形成的“三角形”分布.加入蓄热小球使高温段平均温度升高、排烟温度降低.燃烧极限与系统半周期、空截面流速及热负荷密切相关.系统能够达到的最低燃烧当量比为0.1.