Numerical simulation of three‐dimensional gas‐solid particle flow in a horizontal pipe

A three‐dimensional model of particulate flows using the Reynolds Averaged Navier‐Stokes method is presented. The governing equations of the gas–solids flow are supplemented with appropriate closure equations to take into account all the relevant forces exerted on the solid particles, such as particle‐turbulence interactions, turbulence modulation, particle–particle interactions, particle–wall interactions, as well as gravitational, viscous drag, and lift forces. A finite volume numerical technique was implemented for the numerical solution of the problem. The method has been validated by comparing its results with the limited number of available experimental data for the velocity and turbulence intensity of the gas–particle flow. The results show that the presence of particles in the flow has a significant effect on all the flow variables. Most notably, the distribution of all the parameters becomes asymmetric, because of the gravitational effect on the particles and particle sedimentation. © 2011 American Institute of Chemical Engineers AIChE J, 2011     

数值模拟与极限平衡方法在复杂边坡优化中的应用研究

露天矿山最终边坡角的设计是否合理,将对边坡的稳定性、矿山的生产安全和经济效益产生重大影响。结合一露天矿山的二期扩采需要,采用大型非线性固-流耦合FLAC数值模拟方法进行了边坡多种方案的应力场、破坏场、监测点位移、位移速度变化趋势等多种指标分析,并采用传统的极限平衡分析方法对数值模拟分析推荐的边坡设计方案进行稳定性计算, 最后,综合分析得出最佳方案。研究表明,数值模拟方法和极限平衡方法相结合是进行复杂边坡优化的一条合理有效途径,该方法可为矿山提出安全、经济、切实可行的边坡设计方案。     

Numerical study on the formation of Taylor bubbles in capillary tubes

Numerical simulations have been carried out for the transient formation of Taylor bubbles in a nozzle/tube co-flow arrangement by solving the unsteady, incompressible Navier–Stokes equations. A level set method was used to track the two-phase interface. The calculated bubble size, shape, liquid film thickness, bubble length, drift velocity, pressure drop and flow fields of Taylor flow agree well with the literature data. For a given nozzle/tube configuration, the formation of Taylor bubbles is found to be mainly dependent on the relative magnitude of gas and liquid superficial velocity. However, even under the same liquid and gas superficial velocities, the change of nozzle geometry alone can drastically change the size of Taylor bubbles and the pressure drop behavior inside a given capillary. This indicates that the widely used flow pattern map presented in terms of liquid and gas superficial velocities is not unique.     

岩体边坡渐进破坏的物理模拟和数值模拟研究

为了揭示岩体边坡渐进破坏的机理,在对边坡渐进破坏进行物理模拟的同时,应用FLAC软件对边坡渐进破坏过程进行了数值模拟。研究表明,只有将物理模拟和FLAC数值模拟相结合,才能既从表象上又从本质上揭示出边坡渐进破坏的机理。     

Changing patterns of localization of the tobacco mosaic virus movement protein and replicase to the endoplasmic reticulum and microtubules during infection

Tobacco mosaic virus (TMV) derivatives that encode movement protein (MP) as a fusion to the green fluorescent protein (MP:GFP) were used in combination with antibody staining to identify host cell components to which MP and replicase accumulate in cells of infected Nicotiana benthamiana leaves and in infected BY-2 protoplasts. MP:GFP and replicase colocalized to the endoplasmic reticulum (ER; especially the cortical ER) and were present in large, irregularly shaped, ER-derived structures that may represent "viral factories." The ER-derived structures required an intact cytoskeleton, and microtubules appeared to redistribute MP:GFP from these sites during late stages of infection. In leaves, MP:GFP accumulated in plasmodesmata, whereas in protoplasts, the MP:GFP was targeted to distinct, punctate sites near the plasma membrane. Treating protoplasts with cytochalasin D and brefeldin A at the time of inoculation prevented the accumulation of MP:GFP at these sites. It is proposed that the punctate sites anchor the cortical ER to plasma membrane and are related to sites at which plasmodesmata form in walled cells. Hairlike structures containing MP:GFP appeared on the surface of some of the infected protoplasts and are reminiscent of similar structures induced by other plant viruses. We present a model that postulates the role of the ER and cytoskeleton in targeting the MP and viral ribonucleoprotein from sites of virus synthesis to the plasmodesmata through which infection is spread.     

Impact of the reaction conditions on the photocatalytic reduction of water on mesoporous polymeric carbon nitride under sunlight irradiation

Sacrificial hydrogen evolution was studied with sol–gel prepared carbon nitride photocatalysts loaded in-situ with platinum in a photocatalytic setup with defined geometry and a solar simulator as light source. Reaction conditions (e.g. photocatalyst concentration, triethanolamine concentration, amount of Pt precursor, water quality, etc.), and catalyst properties (e.g. BET surface area) were varied to optimize the catalysts for hydrogen evolution. We found that most of the parameters strongly influence the in-situ co-catalyst loading. The optimum platinum loading is between 0.03 and 0.09 wt%, which is less than 5% of the initial amount of platinum. A long term stability test was conducted showing a stable hydrogen evolution rate for more than 10 days indicating a stable catalyst under applied reaction conditions. We found that a change in the BET surface area affects the photocatalytic activity rather than the experimental conditions.     

通过ISO14001环境管理体系认证提高施工企业的市场竞争力

1　ＩＳＯ140 0 1认证证书是绿色通行证国际标准化组织于 1987年和 1996年分别发布了ＩＳＯ90 0 0和ＩＳＯ140 0 0两大管理体系标准。ＩＳＯ140 0 0则后来居上 ,其发展势头远远超过了ＩＳＯ90 0 0。到目前为止 ,在短短的四年多的时间里 ,世界各国取得ＩＳＯ140 0 1认证的单位已达到 2 0 0 0 0多家 ,我国也有 5 0 0多家取得了ＩＳＯ140 0 1的认证 ,今后每年将以数倍的速度发展。其原因是 :人们在严酷的现实面前 ,逐渐深刻地认识到对环境的破坏而造成的沉重后果 ,“我们只有一个地球”的说法越来越深入人心。而对环境问题的关注 ,实质上是社会…     

The Brazilian experience of rural electrification in the Amazon with decentralized generation - The need to change the paradigm from electrification to development

There are at least 607 thousand households in the Brazilian Amazon that need to be attended with some form of regular electricity service. These households are not attended by the electricity sector through its electricity distribution companies and most of them have some form of precarious decentralized electricity generation that is not registered or regulated in the institutional framework. Diverse initiatives were taken by Brazilian government to attend these household through alternatives that relied on locally available renewable energy. This paper accesses this initiatives of rural electrification in the Brazilian Amazon. First an overview of the problems of rural electricity are discussed and its specificities in the Brazilian Amazon. Then the Brazilian institutional framework that organizes the decentralized electricity generation is described with its various limitations. The diverse initiatives undertaken to attend the rural communities in the Amazon since the 1990s are described, as well as how these initiatives are linked to the policies for rural electrification. The results shows that it can be inferred that sole market mechanisms are not sufficient to guarantee economic sustainability of these projects. This can be one of the reasons why traditional electricity distribution companies showed the lack of interest in promoting rural electrification with other means than grid extension. The most successful projects had financed efforts to integrate the generation of electricity into local development initiatives in order to guarantee sustainability and used substantial part of funding for local mobilization and organization. It needs a paradigm chance by treating these initiatives as local development initiatives and promoting alternative ways for its implementation through partnership between local new actors in the electricity sector and government and implementing policy on a local municipal level.     

A contact model for rough crushable sand

Sand roughness is now accessible to measurement. Incorporating this parameter into sand models using the discrete element method (DEM) is known to improve bulk small strain response. In this work we explore the effect on problems where particle crushing takes place. A well-established DEM particle crushing model and a rough Hertzian contact model are here combined to incorporate both effects in a single contact model. Including contact roughness results in stronger particles whilst all other material parameters being equal. The model is then used to simulate high pressure oedometric compression tests on a strong silica sand. It is shown that including realistic values of surface roughness enables to correctly capture both load-unload behaviour and particle size distribution evolution while using realistic values of elastic bulk properties for the sand grains. Roughness is then a model refinement that may result in simpler, more objective DEM calibrations.