多组分气体在多孔介质中扩散过程的数值模拟

通过对已有的多组分气体在多孔介质中的扩散模型与实验结果对比,发现尘气模型(DGM)与实验结果吻合较好,并利用该模型对CH_4/O_2/N_2三元混合气体在不同孔径的多孔介质内扩散过程进行了数值模拟,分析了扩散与对流两种机理在有/无压差下对扩散通量的影响,对比分析了干燥和含水非饱和多孔介质中的扩散过程.结果表明在无压差的扩散过程中也存在对流;气体的扩散速度随孔径的减小先增大后减小;含水非饱和多孔介质中扩散速度减弱。     

带有气体吹扫边界多孔介质内干燥过程可视化实验

为了对多孔介质干燥过程进行准确的观察、分析,了解其干燥机理,采用可视化实验方案对带有气体吹风通道的多孔网络干燥进行观察,考察了不同吹扫条件下多孔网络的干燥机理。基于MATLAB数字图像识别方法编写了由背景图像预处理、边界提取、图像匹配及饱和度计算四部分组成的程序,利用这一程序来分析采集的多孔网络干燥图像。结果表明,以matlab为基础编写的多孔介质干燥图像分析程序初步实现了多孔介质干燥特征的原位识别,通过该程序提取干燥图像信息发现吹扫流量的改变在干燥初期对干燥速率影响显著,而当干燥进行到后期,吹扫流量对干燥速率的影响较小。     

非固结多孔介质干燥的双尺度孔道网络模型与模拟

以农产品颗粒物料中常见孔隙直径范围(10~(-4)～10~(-3) m)的非固结多孔介质为研究对象,运用孔道网络方法和传递过程原理等知识,建立了考虑骨架吸湿、汽相对流、温度梯度和孔道结构特征等因素对干燥过程影响的非固结多孔介质双尺度孔道网络干燥模型,并进行了相应的干燥实验.模拟与实验结果表明:该模型可有效模拟非固结多孔介质的干燥过程;非固结多孔介质的孔隙率、直径(包括粒径与孔径)分布对干燥的影响十分显著,孔隙率越大,物料干燥越快,达到相同湿含量干燥所需时间越短;直径分布的不均匀程度越高,干燥所需时间越长,物料湿含量分布的差异也越大。对于窄筛分农产品颗粒物料,进行干燥计算时可以采用同一直径分布代替实际分布.     

气孔分布特性对含水多孔介质气体扩散的影响

本文基于多孔介质的气孔分布特性,计算了多孔介质在含水状态下的扩散性能,并且比较了采用两种方式计算相对渗透率时的相对扩散性能。其结果表明,基于气孔分布的计算结果低于与气孔分布无关的计算结果。另外,疏水性含水多孔介质的扩散性能低于亲水性含水多孔介质的扩散性能,基于气孔分布计算含水多孔介质的气体扩散性能时,Wyllie公式并不适用。     

多孔介质快速干燥过程中热质耦合效应的研究

本文针对一维多孔介质的第一类边界条件,对高强度快速干燥条件下热质交换的普遍微分方程组进行求解。研究了高强度快速干燥过程中多孔介质内部传热传质之间的相互耦合现象以及初始边界条件的变化对热质传递的影响,为多孔介质内部温度场和湿度场的控制奠定理论基础。     

微细多孔介质中对流换热实验研究

本文对空气流过烧结微细多孔介质内部的对流换热进行了实验研究。实验段为烧结多孔介质,颗粒的平均直径为0．2 mm。通过“单吹法”的实验方法进行瞬态实验,并用两种不同的数据处理方法得到了多孔介质内部对流换热系数。数据处理方法1利用局部非热平衡能量方程,结合实验数据,数值求得了多孔介质内部对流换热系数。方法2利用实验数据直接求得内部对流换热系数。研究表明:用数据处理方法1得到的多孔介质内部对流换热系与用方法2得到的结果相差在10％以内,与已有结果基本吻合。     

双层多孔介质内预混燃烧的实验和二维数值模拟

对双层多孔介质燃烧器内丙烷/空气预混燃烧进行实验和数值研究.实验对多孔介质燃烧器内固体温度场分布进行测量分析;数值计算利用商业软件FLUENT6.2,通过添加用户自定义标量方程和用户自定义函数,对有壁面散热的双层多孔介质内预混燃烧进行了二维模拟,并与实验结果进行了比较.结果表明,双层多孔介质燃烧器具有良好的稳定燃烧范围和较低的污染物排放;壁面散热对多孔介质燃烧的影响不可忽视.     

快速干燥过程中多孔介质内部湿分迁移机理的研究

本文对快速干燥过程中多孔介质内部湿分迁移机制进行了实验研究和理论分析。实验本体是一台Ｘ－６５０扫描电子显微镜;实验样品分别为大蒜;胡萝卜和土豆片。提出了压力梯度作用下的毛细管通道内的挤压流动是高强度干燥过程中湿分迁移的主要机理并对单毛细管通道内的挤压流动进行了理论分析。     

多孔介质中甲烷预混气火焰传播特性实验研究

本文对甲烷预混气在多孔介质中的火焰传播特性进行了实验研究,在开口竖直管中充填多孔介质,通过改变预混气氧含量使火焰在不同多孔介质中传播并测量火焰传播速度。预混气中氧含量最高达到29％。实验结果表明:多孔介质中甲烷可燃预混气火焰传播速度大于其层流火焰传播速度,可达到5倍以上(当量比的甲烷-空气预混气);多孔介质当量孔直径越大,或预混气层流火焰速度越高,则预混气火焰传播速度越高;多孔介质中可燃混气的火焰传播界限变小,当量孔直径大的多孔介质其界限值较大。实验结果与Babkin提出的多孔介质中的火焰传播机理相符。     

多孔介质非饱和渗流的阈梯度理论

一、前言 毛细滞后现象对非饱和多孔体中的传热与传质过程有重要的影响,但由于对毛细滞后现象尚缺少基本的认识,目前关于多孔介质传热传质的理论暂且都回避对这一问题的处理,这也正是当前有关多孔介质传热传质特性数据和实用计算方法缺乏和可靠性差的重要原因。     

Electrophoretic NMR studies of electrical transport in fluid-filled porous systems.

An NMR technique is described which allows the observation of ionic charge carriers moving in the electric field within a porous system saturated with electrolyte solution. This method, which was recently developed in our laboratory, gives experimental access to the study of electric transport in disordered media on a microscopic level and offers new potential for morphology studies. We performed 1H NMR PFG self-diffusion measurements on ions combined with ionic drift velocity measurements by electrophoretic NMR (ENMR), each as a function of observation time Delta. In this way we obtained time-dependent self-diffusion coefficients D(+/-) (Delta) and time-dependent electric mobilities mu(+/-) (Delta) of polyatomic cations and anions in porous media. The porous media used were gels and glass bead packs. From the behaviour of D(+/-) (Delta) and mu(+/-) (Delta) at long observation times the tortuosities T(p) (D(+/-)) and T(p) (mu(+/-)) are derived, allowing a direct experimental check of the validity of the Einstein relation (D(+/-) is proportional to mu(+/-)) in a disordered medium. The tortuosities obtained via the diffusivity of ions are compared with those obtained via the diffusivity of water molecules. We also make a first attempt to derive the specific surface S/V(p) from the time-dependence of the ionic mobility at short observation times and discuss possible advantages of those measurements in morphology studies of porous media.     

确定多孔介质流动参数的格子Boltzmann方法

本文采用D2Q9不可压缩Lattice-Boltzmann模型模拟了多孔介质中的流场,该模型从介观层次上描述了多孔介质孔隙中的流动特性,验证了Darcy定律,给出了一种计算渗透率的简便方法,本文还运用图像处理方法来构造多孔介质,该方法构造的二维多孔介质能较好地体现实际多孔介质的几何特征。     

Reproducibility experiments on measuring acoustical properties of rigid-frame porous media (round-robin tests)

This paper reports the results of reproducibility experiments on the interlaboratory characterization of the acoustical properties of three types of consolidated porous media: granulated porous rubber, reticulated foam, and fiberglass. The measurements are conducted in several independent laboratories in Europe and North America. The studied acoustical characteristics are the surface complex acoustic impedance at normal incidence and plane wave absorption coefficient which are determined using the standard impedance tube method. The paper provides detailed procedures related to sample preparation and installation and it discusses the dispersion in the acoustical material property observed between individual material samples and laboratories. The importance of the boundary conditions, homogeneity of the porous material structure, and stability of the adopted signal processing method are highlighted.     

Temperature mapping in bread dough using SE and GE two-point MRI methods: experimental and theoretical estimation of uncertainty

Two-dimensional (2D)-SE, 2D-GE and tri-dimensional (3D)-GE two-point T(1)-weighted MRI methods were evaluated in this study in order to maximize the accuracy of temperature mapping of bread dough during thermal processing. Uncertainties were propagated throughout each protocol of measurement, and comparisons demonstrated that all the methods with comparable acquisition times minimized the temperature uncertainty to similar extent. The experimental uncertainties obtained with low-field MRI were also compared to the theoretical estimations. Some discrepancies were reported between experimental and theoretical values of uncertainties of temperature; however, experimental and theoretical trends with varying parameters agreed to a large extent for both SE and GE methods. The 2D-SE method was chosen for further applications on prefermented dough because of its lower sensitivity to susceptibility differences in porous media. It was applied for temperature mapping in prefermented dough during chilling prior to freezing and compared locally to optical fiber measurements.     

Spatial dependence of dispersion

The use of Pulsed Gradient Spin Echo (PGSE) NMR to investigate flow in porous media is well established. Using two pairs of position-encoding pulses in the PGSE experiment gives the possibility of examining velocity fluctuations, by comparing displacements, during the two encoding intervals. This method may be used to measure the asymptotic dispersion coefficient as well as the Velocity Auto-Correlation Function (VACF) in porous media flow. Some examples of two-dimensional maps of density and velocity distributions are accompanied by the first attempt to perform localized measurements of flow dispersion in porous media.     

A new numerical method for the analysis of the permeability anisotropy ratio

By combining the lattice Boltzmann method with the three-dimensional computer-simulated images of porous media,a new numerical experimental methodology is used to determine the permeability anisotropy ratio of porous media.The results compare well with the laboratory experimental data.     

Lattice Boltzmann方法模拟多孔介质Klinkenberg效应

格子Boltzmann数值模拟方法是研究复杂的多孔介质结构特别是Klinkenberg效应的有效方法之一，对处理复杂边值问题尤其有效，用格子Boltzmann方法研究了气流穿越多孔介质问题，并将数值计算结果与实验结果进行了比较，结果表明格子Boltzmann方法是数值模拟气流穿越多孔介质问题的有效方法之一。     

未反应炸药冲击绝热线的近似计算

 综合考虑了炸药作为一类多组分和疏松材料的特点,在已知炸药各组分冲击绝热参数的条件下,利用叠加原理和疏松材料冲击绝热线的计算方法,对未反应炸药的冲击绝热线进行了计算。计算结果与实验数据符合较好。