循环流化床中颗粒聚团特性的模拟

考虑到循环流化床中分散颗粒和颗粒聚团同时存在的多尺度结构,确定了密相和稀相加速度与计算网格局部参数之间的关系,建立了多尺度曳力消耗能量最小的稳定性条件,基于双变量极值理论,构建了考虑颗粒团聚效应的多尺度气固相间曳力模型。结合双流体模型,对循环流化床内气固流动特性以及颗粒聚团特性进行了模拟研究。通过与实验值比较,考虑颗粒聚团影响的计算模型可以更好地贴近实验结果,颗粒聚团直径随颗粒浓度增大呈现先增大后减小的分布趋势,气体和颗粒的加速度在模拟中与重力加速度同处一个数量级,求解过程中不能被忽略。     

循环流化床中颗粒聚团特性的模拟

考虑到循环流化床中分散颗粒和颗粒聚团同时存在的多尺度结构,确定了密相和稀相加速度与计算网格局部参数之间的关系,建立了多尺度曳力消耗能量最小的稳定性条件,基于双变量极值理论,构建了考虑颗粒团聚效应的多尺度气固相间曳力模型。结合双流体模型,对循环流化床内气固流动特性以及颗粒聚团特性进行了模拟研究。通过与实验值比较,考虑颗粒聚团影响的计算模型可以更好地贴近实验结果,颗粒聚团直径随颗粒浓度增大呈现先增大后减小的分布趋势,气体和颗粒的加速度在模拟中与重力加速度同处一个数量级,求解过程中不能被忽略。     

小波在分析流态化系统多尺度动态行为中的应用

利用小波分解方法,对用激光相位多普勒颗粒分析仪（ＰＤＰＡ）、光纤探针及压差传感器同时测得的二维循环流化床中的信号进行了分解,并对分解信号和三种原始信号进行了比较．研究表明：将动态过程分解为三种尺度是合理的,ＰＤＰＡ信号包含了循环流化床所有尺度的全部信息．分解后三种尺度信号均具有混沌性态,但可预测性比原始信号好,为增加对动态过程的认知和建立较好的动态表达模型提供了途径．     

非均匀气固两相系统中多尺度传质模型

建立了适用于气固循环流化床的多尺度传质模型 .从过程与尺度的角度出发 ,将非均匀气固两相流中的传质过程分解为静态与动态的过程 ,并将前者分解为稀相内、密相内以及稀密相间 3个尺度下的传质 ;在用多尺度能量最小 (EMMS)模型求解已知物系性质和操作条件的非均匀气固两相流体动力学参数的基础上 ,借助于前人的研究结果 ,利用相对滑移速度、空隙率等参数求解传质系数 ,求得轴向的浓度场分布 ,并讨论非均匀两相流动结构对传质效率的影响     

循环流化床稀相流动局部空隙率的测量

本文采用激光相让多普勒颗粒分析仪（PDPA）测量流化床气固两相流局部瞬时流动结构．通过测量瞬时颗粒直径、速度及颗粒通过测量体的渡越时间，分析导出了一种计算局部瞬时空隙率的方法实验证明即使在很稀的稀相流动中仍存在着不均匀的流动结构．在同一流动条件下，还用光纤探针测量了瞬时空隙率．结果表明PDPA测量方法能够测量出光纤探针无法测量到的稀相流动中微观瞬时流动结构的变化．     

提升管内气固流动的小波分析

对由光纤探头获得的提升管循环流化床内颗粒体积分数的瞬态信号,采用Dauchveies小波(db4)进行15层的小波分解,并计算各尺度能量分率,以研究提升管底部浓相段与顶部稀相段气固流动结构。结果表明:颗粒速度、体积分数、能量分率在径向分布都呈典型的环核结构;底部浓相段和顶部稀相段的高、中、低频能量分率基本相同,分别在10%,60%,30%左右,说明提升管内大多数的颗粒以聚团形式或密度较大的颗粒群的形式在流化床内流动。操作条件的改变对稀密段气固流动结构的影响不同:颗粒循环流率的改变对密相段的流动影响较大,而气体速度的变化对稀相段的流动影响较大。     

ＣＦＢ稀相段直长对颗粒内循环流动规律的影响

采用光纤探头测定Ｄ１m射流循环流化床（半圆形）稀相区颗粒速度、颗粒浓度和颗粒流通量的径向分布规律,并考察了操作条件及其轴向的影响,实验结果表明,在循环流化床（ＣＦＢ）中,颗粒流动在床层径向有较大的不均匀性,并呈明显的内循环流动结构,进而考察了影响其流动规律的,以期进一步理解循环流化床颗料流动机理,强化和改善反应器的设计操作。     

CFB密相区内颗粒横向扩散对燃烧的影响

循环流化床(CFB)床内燃料颗粒的扩散、混和，特别是复杂的密相区内的混和特性在很大程度上影响了燃烧状况，密相区颗粒横向扩散的规律，对于循环流化床的设计具有重要意义，在循环流化床密相区颗粒横向扩散实验研究的基础上，总结了密相区内颗粒横向扩散系数的经验公式，以此为基础，研究了密相区内碳的分布规律，并建立了相应的燃烧模型，模型包括两个子模型，即密相区二维流动及燃烧子模型、稀相区一维流动及燃烧子模型。通过模型定性模拟了流化风速、给料点布置对床内燃烧的影响，有效地反映了实际情况，并确认了将密相区颗粒横向扩散规律引入现有循环流化床燃烧模型的重要意义。     

气固两相流内中空多孔催化剂性能的数值模拟

气固流态化过程中流体和颗粒分别聚集,形成稀密两相,严重限制其传质效率和反应速率的提高。针对此问题,本工作设计了一种中空多孔结构的催化剂颗粒,通过模拟方法研究该颗粒对稀密两相气相传质与反应的影响,及其在稀密相间转换的时间尺度。结果表明,一定的流动强度时,在颗粒稀密相转换的时间尺度内,中空多孔结构的颗粒能够有效地在稀相存储反应气体,并在密相释放,为密相提供额外的反应气体,增强体系的整体反应效率。当催化反应速率高于传质速率时,在所研究的流动条件下中空多孔颗粒体系的反应效率比实心球形颗粒体系高出26.92%~29.55%。可以预见在稀密相分布更广的大型气固流化床反应器中,中空多孔结构的催化剂颗粒能够更为有效地提高反应器的整体效率。     

环形截面提升管内颗粒的运动行为

采用PDPA(phase Doppler particle analyzer system)及磷光颗粒示踪技术对环形截面提升管中颗粒的运动行为进行了研究。与传统提升管相比，环形截面提升管中颗粒速度分布的均匀性有所改善，其最高速度与最低速度之差变小。环形截面提升管最大速度值出现在相对径向位置φ=0.3-0．4处。与传统提升管相似，环形截面提升管内颗粒的轴向返混较严重，停留时间分布曲线存在较明显的拖尾，其中颗粒的轴向Peclet数与传统提升管也处于同一数量级范围。提升管床结构的改变并未显著改变其中气固流动的微观相结构，稀相与密相颗粒团微观两相仍然存在，这种微观相结构是造成颗粒严重返混的决定性原因：稀相中的颗粒与密相颗粒团中的颗粒分别造成了颗粒停留时间分布曲线的前峰与拖尾峰。     

Effect of particle acceleration/deceleration on particle clustering behavior in dilute gas-solid flow

Effect of particle acceleration/deceleration on particle clustering behavior in dilute gas-solid flow was studied by experimental measurements and mathematical modeling. Calculation results of the model are in good agreement with experimental data from Phase Doppler Particle Analyzer (PDPA) measurements. The variation of voidage inside particle clusters is strongly dependent upon the change of the number of particles within the clusters. During acceleration, particle clusters are gradually disaggregated into smaller clusters with increasing voidage, while during deceleration, particle clusters are aggregated into larger clusters with decreasing voidage.     

PDPA测量体积对测量结果的影响

本文采用激光相位多普勒粒子分析仪（PDPA）测量气固两相流局部颗粒的运动速度和粒度．通过比较在不同测量体积下测得的颗粒直径、速度及捕获粒子的速率，发现PDPA的测量体积对测量结果有明显的影响，特别是对较密的气固两相流影响非常显著．为了正确测量气固两相流中粒子大小和瞬时流动特性，木文提出PDPA测量体积不能小于或远大于被测粒子的平均体积；设置适当的测量体积，有利于测量较密集的颗粒流体系统．     

循环流化床中颗粒团聚物性质的PDPA测量

提出了一种利用相位多普勒粒子分析仪（PDPA）来测量气固循环流化床中颗粒团聚物性质的方法,并运用此方法初步考察了操作条件对循环流化床稀相区中颗粒团聚物性质的影响.在本实验操作条件下,颗粒团聚物的时间分率、频率、内部空隙率以及轴向速度等性质都存在轴径向的不均匀分布,具有较明显的环核特征;固体循环速率对颗粒团聚物性质径向分布影响不大,表观气速的变化可引起其轴向分布规律发生显著改变,但其径向的环核特性仍然存在.     

旋风分离技术研究进展(英文)

Centered on the techniques and industrial applications of the reinforced cyclonic separation process,its principles and mechanism for separation of ions,molecules and their aggregates using polydisperse droplets are discussed generally;the characteristics and influential factors of fish-hook phenomenon of the grade efficiency curve in cyclonic separation for both gas and liquid are analyzed;and the influence of shear force on particle behavior(or that of particle swarm) is also summarized.A novel idea for cyclonic separation is presented here:enhancing the cyclonic separation process of ions,molecules and their aggregates with monodisperse microspheres and their surface grafting,rearranging the distribution of particles by size using centrifugal field,reinforcing the cyclonic separation performance with orderly arranged particle swarm.Also the investigation of the shortcut flow,recirculation flow,the asymmetric structure and non-linear characteristics of the cyclonic flow field with a combined method of Volumetric 3-component Velocimetry(V3V) and Phase-Doppler Particle Anemometer(PDPA) are elaborated.It is recommended to develop new systems for the separation of heterogeneous phases with cyclonic technology,in accordance with the capture and reuse of CO 2,methanol to olefins(MTO) process,coal transfer,and the exploitation of oil shale.     

Flow patterns in granulating systems

Particle flow patterns were investigated for wet granulation and dry powder mixing in ploughshare mixers using Positron Emission Particle Tracking (PEPT). In a 4-l mixer, calcium carbonate with mean size 45 μm was granulated using a 50 wt.% solution of glycerol and water as binding fluid, and particle movement was followed using a 600-μm calcium hydroxy-phosphate tracer particle. In a 20-l mixer, dry powder flow was studied using a 600-μm resin bead tracer particle to simulate the bulk polypropylene powder with mean size 600 μm. Important differences were seen between particle flow patterns for wet and dry systems. Particle speed relative to blade speed was lower in the wet system than in the dry system, with the ratios of average particle speed to blade tip speed for all experiments in the range 0.01–0.25. In the axial plane, the same particle motion was observed around each blade; this provides a significant advance for modelling flow in ploughshare mixers. For the future, a detailed understanding of the local velocity, acceleration and density variations around a plough blade will reveal the effects of flow patterns in granulating systems on the resultant distribution of granular product attributes such as size, density and strength.     

Analysis of non-spherical polydisperse particle growth in a two-dimensional tubular reactor

Polydisperse aggregate particle growth considering coalescence, coagulation, generation and spatial transport processes is studied in a two-dimensional reactor for the first time. Effects of two-dimensional spatial transport processes, such as convection, diffusion, deposition and thermophoresis as well as nucleation, coagulation and coalescence are of primary interests. An efficient particle dynamics model based on two sets of coupled sectional equations (J. Aerosol Sci. 32 (2001) 565) is used to facilitate the severe computation loads for analyzing the growth of non-spherical polydisperse particles in an axi-symmetric two-dimensional geometry. Fluid dynamics calculations indicate the existence of non-uniform distributions of temperature and flow fields in the radial direction as well as in the axial direction inside the reactor. Particle dynamics simulations also demonstrate the significant inhomogeneous spatial distributions of the characteristics of aggregate particles. The present two dimensional calculations for reactor temperatures and particle size distributions are in agreement with the previous experimental data. The validity of simplified one-dimensional analysis is also evaluated against the present two-dimensional analysis. While the one-dimensional analysis agreed well with the spatially two-dimensional one for the cases of low flow rates, it resulted in significant errors for high flow rates.     

基于正交设计的旋流组合式喷嘴雾化性能实验

为寻求旋流组合式喷嘴雾化性能影响因素间的优化匹配方案,在分析和总结的基础上,选取旋流器的组合方式、喷头构型、进气流量和进气方式等作为主要影响因素,通过正交设计理论,安排试验方案,采用相位多普勒粒子分析仪（PDPA）对雾化性能的关键评判因素——喷雾场粒径进行了采集测量。实验结果的极差分析和方差分析表明,旋流器的组合方式对雾化粒径的影响最强,水流量次之,再次为喷头构型,而进气方式的影响最弱;此外,旋流器组合方式与喷头的交互作用产生的影响不应被忽略。     

Synthesis of polydiphenylamine with tunable size and shape via emulsion polymerization

The emulsion polymerization process was used in the synthesis of polydiphenylamine (PDPA) to obtain new morphologies, and the effects of surfactant types ? anionic, cationic, non‐ionic ? and surfactant concentrations were investigated with the roles of a template and a dopant. Scanning electron microscopy images indicated different PDPA morphologies depending on the surfactant type. The new morphological structures of the obtained PDPA were leaf‐like, coral‐reef‐like and red‐blood‐cell‐like, which have not been synthesized or seen before. The agglomeration of each nanoparticle is in the range of 50 nm to 500 nm depending on the surfactant type. The structure characterizations carried out by Fourier transform infrared spectroscopy, X‐ray diffractometry and UV?visible spectroscopy confirm the incorporation of surfactant in the PDPA. The electrical conductivity values of the PDPA with surfactants are higher than that without a surfactant by four orders of magnitude and are consistent with the resultant smaller particle sizes and narrower optical band gap as calculated from UV?visible data. To induce higher electrical conductivity of PDPA, various dopants were used. However, the thermal stability of the PDPA is lower than that of conventional microscopic PDPA (cPDPA) due to the larger surface area of PDPA which can decompose more easily. © 2014 Society of Chemical Industry     

Particle and bubble behaviour and velocities in a large-particle fluidized bed with immersed obstacles

A stereo-photogrammetric technique supplemented by cine-photography was used to study particle and bubble behaviour in a two-dimensional bed of large spherical particles whose U_mf was 79.4 cm/sec. The bed was equipped with immersed objects that simulated horizontal tubes. Single obstacles of several shapes as well as obstacles in array were studied. A detailed and accurate mapping of particle velocities, particularly in the neighbourhood of the obstacles, was done. At fluidizing-air velocities of 80 – 90 cm/sec, bubble velocities of up to 39 cm/sec were measured. Particle caps above the obstacles and stagnant air bubbles attached to the bottom of the obstacles were observed and their size and behaviour for various obstacles and arrays were noted.