Numerical simulations and comparative analysis of two- and three-dimensional circulating fluidized bed reactors for CO2 capture

Carbon dioxide(CO2),the main gas emitted from fossil burning,is the primary contributor to global warming.Circulating fluidized bed reactor(CFBR)is proved as an energy-efficient method for post-combustion CO2 capture.The numerical simulation by computational fluid dynamics(CFD)is believed as a promising tool to study CO2 adsorption process in CFBR.Although three-dimensional(3D)simulations were proved to have better predicting performance with the experimental results,two-dimensional(2D)simulations have been widely reported for qualitative and quantitative studies on gas-solid behavior in CFBR for its higher computational efficiency recently.However,the discrepancies between 2D and 3D simulations have rarely been evaluated by detailed study.Considering that the differences between the 2D and 3D simulations will vary substantially with the changes of independent operating conditions,it is beneficial to lower computational costs to clarify the effects of dimensionality on the numerical CO2 adsorption runs under various operating conditions.In this work,the comparative analysis for CO2 adsorption in 2D and 3D simulations was conducted to enlighten the effects of dimensionality on the hydrodynamics and reaction behaviors,in which the separation rate,species distribution and hydrodynamic characteristics were comparatively studied for both model frames.With both accuracy and computational costs considered,the viable suggestions were provided in selecting appropriate model frame for the studies on optimization of operating conditions,which directly affect the capture and energy efficiencies of cyclic CO2 capture process in CFBR.

Influence of bed elevation discordance on flow patterns and head losses in an open-channel confluence

Confluences play a major role in the dynamics of networks of natural and man-made open channels, and field measurements on river confluences reveal that discordance in bed elevation is common.Studies of schematized confluences with a step at the interface between the tributary and the main channel bed reveal that bed elevation discordance is an important additional control for the confluence hydrodynamics.This study aimed to improve understanding of the influence of bed elevation discordance on the flow patterns and head losses in a right-angled confluence of an open channel with rectangular cross-sections.A large eddy simulation (LES)-based numerical model was set up and validated with experiments by others.Four configurations with different bed discordance ratios were investigated.The results confirm that, with increasing bed elevation discordance, the tributary streamlines at the confluence interface deviate less from the geometrical confluence angle, the extent of the recirculation zone (RZ) gets smaller, the ratio of the water depth upstream to that downstream of the confluence decreases, and the water level depression reduces.The bed elevation discordance also leads to the development of a large-scale structure in the lee of the step.Despite the appearance of the large-scale structure, the reduced extent of the RZ and associated changes in flow deflection/contraction reduce total head losses experienced by the main channel with an increase of the bed discordance ratio.It turns out that bed elevation discordance converts the lateral momentum from the tributary to streamwise momentum in the main channel more efficiently.

自动循环床系统设计与应用

针对盆花生产人工劳动强度大、效率低和劳动成本高等问题,开发了一种自动循环床系统。该系统可配合育苗设备、输盆设备和包装设备等完成盆花育苗、生产、输盆、剪枝、灌溉和采收等需求的运输操作,实现盆花在不同功能区及配套设备之间的快速转移。

NUMERICAL INVESTIGATION OF THREE-DIMENSIONAL FLOW AND BED SHEAR STRESS DISTRIBUTION AROUND THE SPAN SHOULDER OF PIPELINE

Three-dimensional flow around a pipeline span shoulder is simulated using afractional step finite element method. The Reynolds number, based on the pipe-diameter and theapproaching flow velocity, is set at 500 and 5 x 10~5 to simulate both laminar and turbulent flow.In high Reynolds number case, Smagorinsky SGS closure is used to model the turbulent flows. The flowfield visualization by vorticity iso-surfaces shows that a spiral vortex tube is formed around thespan shoulder and extends around the span shoulder. The vortex cores defined by the eigenvalues ofthe symmetric tensor S^2 + Ω~2 (S and Ω are respectively the symmetric and antisymmetric parts ofthe velocity gradient tensor) gives more details of the flow field. It is also found that there aresignificant bed shear stress concentrations in the span shoulder area. The reasons for the shearstress concentration are discussed.

A computational particle fluid-dynamics simulation of hydrodynamics in a three-dimensional full-loop circulating fluidized bed: Effects of particle-size distribution

A computational particle fluid-dynamics model coupled with an energy-minimization multi-scale(EMMS)drag model was applied to investigate the influence of particle-size distribution on the hydrodynamics of a three-dimensional full-loop circulating fluidized bed.Different particle systems,including one monodisperse and two polydisperse cases,were investigated.The numerical model was validated by comparing its results with the experimental axial voidage distribution and solid mass flux.The EMMS drag model had a high accuracy in the computational particle fluid-dynamics simulation of the three-dimensional full-loop circulating fluidized bed.The total number of parcels in the system(Np)influenced the axial voidage distribution in the riser,especially at the lower part of the riser.Additional numerical simulation results showed that axial segregation by size was predicted in the two polydisperse cases and the segregation size increased with an increase in the number of size classes.The axial voidage distribution at the lower portion of the riser was significantly influenced by particle-size distribution.However,radial segregation could only be correctly predicted in the upper region of the riser in the polydisperse case of three solid species.

A three-dimensional k-ε-k_p model in curvilinear coordinates for sediment movement and bed evolution

To aim at the substitution of the magnitude and direction of water flow movement near bed for those of bed load transport in solid-liquid two-phase one-fluid model, and to simulate the effect of secondary flow on transverse bed load transport in channel bends and the effect of bed slope on bed load trans- port in a better way, a three-dimensional k-ε-kp solid-liquid two-phase two-fluid model in curvilinear coordinates is solved numerically with a finite-volume method on an adaptive grid for studying wa- ter-sediment movements and bed evolution in a 120° channel bend. Numerical results show that the trajectories of solid-phase deviate from those of liquid-phase in the channel bend, and the deviation increases with the increase of the particle diameters. The calculated bed deformation by the k-ε-kp model is in better agreement with measured bed deformation than those by one-fluid model. It is proved that the k-ε-kp model can simulate the effect of secondary flow on lateral bed load transport with the higher accuracy than the one-fluid model.

广州园林绿地节庆主题花境与花坛应用调查

以广州园林绿地节庆主题花境与花坛为研究对象,通过对7个代表性园林绿地花境或花坛的实地调查,分析其应用的植物种类与配置、设计手法等。结果显示,应用的植物共78种,隶属45科72属;节庆主题花境与花坛根据主题可梳理为传统节庆、红色节庆、大型会议与活动、城市生活4类。基于对不同主题花境与花坛的应用特点与配置手法的分析,以及创新表达方式、合理选择植物、融入地域文化等的优化策略,凝练出具有广州花文化、岭南文化、红色文化等特色的节庆主题花境或花坛的配置模式。

Three-dimensional heat transfer in a particulate bed in a rotary drum studied via the discrete element method

We simulated three-dimensional heat transfer inside a horizontal rotating drum using the discrete element method and a thermal conduction model.The aim was to determine the effect of end-wall heating on thermal behavior of a granular bed.The simulation showed that the end-wall heating significantly affects the axial temperature profile of the bed,particularly when the length-to-diameter ratio is low.Particles near the wall heated faster and became more thermally uniform than those in the center of the drum.The region affected by the end heating gradually increased over time.Increasing the rotation speed enhanced the heat conduction rate,and increasing the fill level reduced the mean temperature and thermal uniformity of the granular bed.Heat transfer was also simulated for drums with different length-to-diameter ratios.

海绵城市建设低影响开发设施的改良

针对海绵城市建设中经常存在海绵设施破坏景观效果,雨水调蓄设施(下沉式绿地等)出现“大水坑”,导致蚊蝇滋生等现象,经分析研究,对雨水花园、高位花坛、植草沟和下沉式绿地、渗透渠等海绵设施进行了技术上的创新改良,使之能融合景观,彰显海绵城市低影响开发的理念。

多峰值降雨下典型源头LID设施对径流污染物的去除特性

以我国西北某市为例,结合大雨量双峰与小雨量多峰雨型的实际降雨,对该市海绵城市建设区内的雨水花园、高位花坛、透水铺装3种典型源头低影响开发(LID)设施进出水污染物浓度进行实测分析。分析得出,在大雨量双峰值降雨事件中,典型源头LID设施出口污染物浓度分布呈单峰型;在小雨量多峰值降雨事件中,典型源头LID设施出口污染物浓度分布呈负斜率直线型。雨水花园和高位花坛在小雨量多峰值降雨事件中的污染物去除率比大雨量双峰值降雨事件的要高,而透水铺装在小雨量多峰值降雨事件中的污染物去除率比大雨量双峰值降雨事件中的低。

南宁市节日花坛花卉种类调查与应用研究

对南宁节日花坛花卉种类进行调查。结果表明,南宁市应用于花坛中的植物种类主要为一二年生草本花卉、宿根花卉及少量的木本植物、球根花卉等,共计20个科、38个种、60多个品种。总结了3年来花坛花卉在南宁市的应用现状,对目前花坛花卉应用提出可行性建议。

花台在岭南四大名园中的应用

花台是在高型的植床内栽花植树、盛水置石的一种景观形式。在岭南古典园林中,花台的台座多为规则式,并常饰以独具地方特色的山水、花鸟、人物的灰塑、隐雕或彩绘等,或镶嵌竹节状石湾釉陶栏杆,装饰感、美感极强。岭南四大名园中的花台形式多样,与四大园林要素结合形成独特的景观。通过调查、研究和总结岭南庭园中花台的应用状况,期望为当代岭南园林的发展和花台的应用推广、创新注入传统园林的精华与活力,并在此基础上发扬光大,进一步衍生出更加丰富的花台内涵及应用形式。

城市花坛周年布置的花卉种类筛选研究

通过对宜昌市夷陵广场2003年～2005年连续3年种植的155种次城市花坛花种进行适应性筛选研究,结合宜昌气候特点、城市园林规划、植物形态特征和生产实践,筛选出了适合宜昌地区种植的23个花卉主要种(含6个骨干种),力求为城市广场园艺生产提供指导。

节日花坛设计初探

节日花坛近年来已经发展成为节日期间市民游玩赏花不可缺少的一道风景。在阐述节日花坛的定义、形式的基础上,明确了节日花坛设计侧重的原则,并以亲身设计的北海公园南门花坛为例,对节日花坛设计的构思过程做了一个简要的概述。

五色草花坛的创新应用及发展前景

五色草是指大叶红(Alternanthera dentate'Rubiginosa')、小叶红(Alternanthera amoena.Voss)、绿草(Alternanthera bettzickiana.Nichols)、小叶黑(Alternanthera bettzickiana.Nichols)、白草(Sedum lineare.Thunb)等5种草的总称;五色草在哈尔滨市的栽培和应用已有近百年的历史,是哈尔滨市的园林品牌植物,是栽植花坛的特色花卉,近年来,五色草用于造型、拼字、标志、广告宣传等,更加时尚化地与现代雕塑、人文休闲空间相结合的大体量的景观建造,随着栽培技术和工程技术的不断进步,造型精美、制作工艺先进、主题丰富的五色草花坛应用会更加广泛,在城市绿化、美化中有着广阔的发展前景。

花坛在城市景观中的应用

对花坛的概念、作用、分类进行了介绍,提出了植物选择、色彩搭配和花坛维护等在花坛造景中应注意的问题,以期为花坛在城市景观中的应用提供借鉴.

南京青年奥林匹克运动会期间花坛用花调查

于2014年南京青年奥林匹克运动会期间,对南京重点绿化地段的花坛用花进行调查,内容包括花坛类型、花坛植物种类、花坛植物频度等。认为南京重点绿化的花坛节点共有121个,应用的花坛植物共有91种,隶属于39科77属。根据对频度数据的分析,得出各种类型花坛的主要植物及其应用特点。在此基础上,提出花坛用花的优势和解决存在主要问题的可行性建议。

作为“主题道具”的花坛——《邱园记事》解析

《邱园记事》中开创的是多组人物形象的意识流文本创作方式。小说借助"邱园花坛"来组合、叠合多个人物组合的意识流,在这里,"邱园花坛"就是伍尔夫用来组织意识流的"主题道具",她依靠这一道具,向读者展示了邱园里男男女女的内心意识,构建了一个完整的主题逻辑。本文通过对《邱园记事》中"主题道具"现象剖析,对伍尔夫的小说创作做了一个文学性反思,以反拨当前伍尔夫研究、现代派文学研究中一味重视文化意味而非文学意味的探寻现象。

花坛的设计原则与方法

花坛作为一种园林绿化形式,占地不大,但对美化环境、活跃气氛、提高绿化效果有着突出的作用,因此其应用愈来愈受到人们的重视和青睐。从花坛的概念、花坛的作用、花坛的设计原则、盛花花坛和模纹花坛的设计要求这4个方面对花坛的设计作了较为系统的概括,为今后花坛在园林造景中的应用提供科学依据。

盛花花坛在福州市区绿化应用中的调查研究

通过对福州市区盛花花坛应用现状的调查与分析,结果表明:盛花花坛在福州市区的应用类型比较丰富,包括基础花坛、移动花坛、立体花坛、组合式花坛和街道花坛等。大多采用形式简单的移动花坛、基础花坛,对于一些工艺技术要求较高的立体花坛、中大型花坛、图案内容丰富的组合花坛较为少用。盛花花坛的材料还缺乏多样化,花坛的空间形态也较单调,施工技术和工艺还有待提高。并提出了盛花花坛在福州的发展建议。