Infiltration and redistribution of perchloroethylene in partially saturated, stratified porous media

Contamination of the subsurface by nonaqueous phase liquids (NAPLs) is a widespread problem. To investigate the behavior of a nonspreading, dense NAPL (DNAPL) in the vadose zone, we conducted perchloroethylene (PCE) infiltration experiments in nominally 1- and 2-dimensional (D), stratified porous media. In addition, the usefulness and limitations of a multifluid flow simulator to describe PCE infiltration and redistribution under the experimental conditions were tested. The physical simulations were conducted in a column (1-D) and a flow container (2-D) which were packed with two distinct layers of coarse-grained sand and a fine-grained sand layer in between. Volumetric water and PCE contents were determined with a fully automated dual-energy gamma radiation system. While migrating through the drier parts of the coarse-grained sand layers, PCE appeared to wet the water–air interface rather than displacing any water. In the wetter parts of the porous medium, PCE displaced water and behaved as a true nonwetting fluid. PCE showed a limited response to gradients in capillary pressure and rather high values for the volumetric PCE content were measured in the fine-grained sand layers. This was attributed to the nonspreading nature of PCE. The multifluid flow simulator appeared to predict the initial PCE movement in the vadose zone reasonably well. However, the model was not capable of predicting the final amounts of PCE retained in either the unsaturated or saturated part of the flow domain, mainly because the simulator does not consider the nonspreading flow behavior of NAPLs.     

Numerical Analysis of Heat Transfer and Gas Flow in PEM Fuel Cell Ducts by a Generalized Extended Darcy Model

Abstract

In this work, gas flow and heat transfer have been numerically investigated and analyzed for both cathode/anode ducts of proton exchange membrane (PEM) fuel cells. The simulation is conducted by solving a set of conservation equations for the whole domain consisting of a porous medium, solid structure, and flow duct. A generalized extended Darcy model is employed to investigate the flow inside the porous layer. This model accounts for the boundary-layer development, shear stress, and microscopic inertial force as well. Effects of inertial coefficient, together with permeability, effective thermal conductivity, and thickness of the porous layer on gas flow and heat transfer are investigated.     

20世纪80年代以来洪湖流域营养物质输移模拟研究

选择位于长江中游的洪湖流域作为研究对象，应用流域分布式水文模型SWAT，探讨现代农业条件下流域面源营养盐输移的规律。模拟时段选择为1983～2002年。模拟的边界条件设置为自然地形、土壤、现代农业生产及土地利用方式，其中土壤资料包括营养盐（N和P）、有机质含量、粒径等理化参数。径流量与营养盐输出模拟结果与实测值有较好的吻合程度，可以通过置信度95％的显著性检验。模拟结果显示，现代农业条件下流域营养盐输出，TN和TP浓度变化有明显的季节特征，体现了区域耕作方式、径流对营养盐输出浓度的影响。模拟时段内营养盐输出浓度呈明显增长趋势，体现了农药化肥的施用对流域营养盐输移的影响。     

余热锅炉磨损的数值模拟分析

利用数值模拟方法对余热锅炉进行流场及湍流密度计算结果总结出锅炉主要磨损规律,原因及主要磨损部位,与现场磨损的部位正好吻合,为减少磨损等复杂工程问题提供了理论依据,并就磨损的部位提出了应对措施。     

On some studies about the dynamic mechanisms of carbon monoxide flow and diffusion during high energy gas fracturing

High energy gas fracturing (HEGF) technique has been one of central stimulating measures to enhance oil recovery in low permeability reservoirs. But, in recently few years, some serious CO poisoning accidents took place in oilfields here in China. It is very important to reveal the dynamic mechanisms of carbon monoxide flow and diffusion to operating safety during high energy gas fracturing. In this paper, some dynamic mechanisms of carbon monoxide CO flowing inside a oil wellbore and diffusion on the top of the well during high energy gas fracturing were studied with fluid/gas hydrodynamics. The CO flow model within a wellbore and the diffusion model in air were established. The key factors affecting CO flow and diffusion such as wellbore pressure, gas-oil ratio, wind speed, leakage speed, air-permanence were inspected with mathematical simulation. It will be of significance to provide an important guidance for monitoring and preventing CO poisoning accidents during high energy gas fracturing.     

The caving and sliding control of surrounding rocks on large coal roadways affected by abutment pressure

For the caving and sliding control of roadways with large cross-section, thick mudstone roof and abutment pressure influence, the cable truss system is proposed and its support mechanism is thoroughly analyzed in this paper. Furthermore, according to the geometric size and ground pressure conditions on field coal roadways Nos. 101, 102 and 103 in Xinyuan Coal Mine, three types of cable truss support systems are designed for obtaining the optimum cable truss support system. Then the corresponding parameters for each support design are determined by use of the numerical simulation method, and three kinds of support systems are put into practice. The field observation results show that roof should be effectively controlled by the normal cable truss structure consisting of two long cables and one connector, and both coal sides can be protected by the simplified cable truss structure composed of two short cables and one channel bar. Finally, the optimal support system is gotten which is much better than the other two support designs in rock deformation control effect and economic profits.     

某酒吧特大火灾场景的数值重构

基于FDS对某酒吧特大火灾事故进行数值重构研究,再现了火灾发生、发展的全过程,并与火灾现场勘查报告、现场照片比对;与此同时,详细地分析和研究了火场中典型部位的温度、CO浓度及FED指数等细节性参数的发展变化趋势,结果表明,模拟中的火灾蔓延过程、烟气填充过程、热释放速率、温度等参数与火灾现场勘查笔录和电子物证基本吻合,可与火灾调查其它证据相佐证,完善火灾调查结论,为进一步研究和改善此类场所的防火措施和灭火救援方案提供了依据。     

山地林火蔓延模型的研究

建立了有风速有坡度条件下的林火蔓延模型,并进行了模拟山丘条件下的数值计算和实验模拟。通过对计算结果和实验结果的分析比较,获得了模拟山地条件下的一些流场变化规律,为进一步预测林火行为为奠定了基础,同时也证明了采用该模型的必要性。     

On spurious water flow during numerical simulation of steam injection into water-saturated soil

Numerical simulation of steam injection into a water-saturated porous medium may be hindered by unphysical behavior causing the model to slow down. We show how spurious water flow may arise on the boundary between a steam zone and a saturated zone, giving rise to dramatic pressure drops. This is caused by the discretization of the temperature gradient coupled with the direct relation between pressure and temperature in the steam zone. The problem may be a severe limitation to numerical modeling. A solution is presented where the spurious water flow is blocked and this widely enhances the performance of the model. This new method is applied to a previously reported example exhibiting numerical problems. Furthermore, it is applied to the simulation of 2-D sandbox experiments where LNAPL is remediated from a smearing zone by steam injection. These experiments would have been difficult to analyze numerically without the adjustment to prevent spurious flow.     

惰性气体抑制油气爆炸的机理分析及实验模拟

从经典燃烧学、化学反应动力学的基本理论出发,分析了惰性气体抑制油气爆炸的作用机理,通过试验模拟研究了惰性气体抑制油气爆炸的作用规律,为惰性气体防爆抑爆技术的工艺实施、系统设计和关键参数计算提供了依据.