顺流串联流化床流动特性研究

针对攀枝花钛资源钙、镁含量高的特点，研究了快速流化床—湍流床—快速流化床三级串联组成的顺流串联流化床的流动特性。采用光导纤维测速仪和压力计，研究了固相的停留时间和流动形态。对快速流化床的流化速度、湍流床的轴向和径向浓度分布以及抗粘结能力进行了考察。用功率谱密度函数表征床层的活跃程度，定性地说明了湍流床抗粘结能力提高的幅度。     

DSMC-LES方法数值模拟鼓泡流化床内气泡和颗粒流动行为

基于稠密气体分子动力学和气固两相流体动力学,建立流化床稠密气固两相离散颗粒运动-碰撞解耦模型,采用直接模拟蒙特卡罗方法(DSMC)模拟颗粒间的碰撞,采用考虑颗粒脉动流动对气相湍流流动影响的大涡模拟(LES)研究气相湍流,单颗粒运动满足牛顿第二定律,颗粒相和气相相间作用的双向耦合由牛顿第三定律确定.数值模拟流化床中颗粒流动以及气泡的生成、长大和破碎过程,获得颗粒轴向和径向速度的概率密度分布,及颗粒浓度分布.计算结果表明床内气泡的形成造成床内颗粒的循环,使得流化床内颗粒具有不同的轴向和径向脉动速度,颗粒分速度分布近似服从高斯分布.颗粒温度随颗粒浓度增加,达到最大值后,随颗粒浓度增大而下降.流化床颗粒浓度脉动主要是低频部分,高频分量较低,表明在流化床内颗粒浓度脉动频率低,能量高,颗粒浓度脉动主频率为0.4～1.0Hz,其值与Pain et al.获得的颗粒浓度脉动主频率基本吻合.     

提升管内气固两相双组分颗粒流动的离散颗粒硬球模型的模拟

基于离散颗粒(DPM)硬球模型,数值模拟提升管内双组分颗粒气固两相湍流流动行为。应用Vreman的亚格子尺度（SGS）模型模拟气体湍流,建立考虑不同颗粒加速度效应的两颗粒碰撞最小时间计算模型。数值模拟预测了大颗粒和小颗粒的速度和浓度分布。研究结果表明小颗粒具有高的轴向速度和脉动速度,而大颗粒具有低的轴向速度和脉动速度。在床中心区域,小颗粒轴向速度分布出现3个峰值,对于大颗粒轴向速度仅出现两个峰值。在壁面区域大颗粒和小颗粒速度均出现两个峰值。沿床径向方向呈现床中心颗粒浓度低、壁面区域颗粒浓度高的环核流动结果。随着表观气速的增大,颗粒浓度沿径向和床高分布趋于均匀。在床中心区域模拟计算轴向颗粒速度、颗粒浓度和RMS速度与文献实验结果相吻合。在提升管内气体湍流对小颗粒流动具有一定的影响,颗粒间碰撞作用对颗粒相流动的影响大于气相湍流的影响。     

倒置液固流化床内液固两相流动特性的数值模拟

基于欧拉-欧拉双流体模型,数值模拟倒置液固流化床内液固两相流动行为.数值模拟预测了床内颗粒的速度、浓度分布以及空隙率的变化.研究结果表明颗粒在床内分布呈现非均匀分布,床内形成局部高空隙率的流体团;随着床层高度增加,颗粒轴向速度增大:数值模拟床内空隙率与Renganthan等的实验结果相吻合.     

稠密固液循环流化床内流体湍流脉动对颗粒分散的影响

通过计算流体动力学模拟研究了固液循环流化床内流体湍流对高浓度颗粒的扩散作用。根据湍流机制下高浓度颗粒在液体中的分散机理,建立了同时考虑颗粒碰撞、流体拖拽和流体湍流扩散输运的欧拉-欧拉双流体模型。利用该模型对稠密固液循环流化床提升管内颗粒的分散运动进行了数值模拟,预测出颗粒轴向速度和体积浓度的径向分布,与相应条件下的实验数据符合很好。表明考虑流体湍流扩散输运的理论模型更能精确预测高浓度颗粒在循环流化床提升管内的运动情况;也表明即使针对以颗粒碰撞为主的稠密固液湍流体系,尺度较大的流体湍流涡也会因促使颗粒扩散输运,影响颗粒空间分布。工作为稠密固液循环流化床内两相流体动力学分析奠定了基础。     

用于四氯化钛生产的组合式流化床的模拟

组合式流化床是一种将提升管和湍床串联使用的新型反应器,适合于所需单程反应时间较长且需颗粒间、气固间作用力较大——防黏结、提高传质效率等的气固反应体系.通过数学模型模拟研究了提升管预热方式、氧气初始浓度、初始炭矿比对用于四氯化钛生产的组合式流化床的反应特征和反应性质的影响,其中颗粒沿轴向的粒径分布变化通过粒子数平衡模型进行描述.模拟指出：富钛料主要的转化在湍床中进行;焦炭颗粒的燃烧反应存在“着火”温度(约873K）;氧气初始浓度和富钛料初始含量的增加能够增大富钛料的转化量,但氧气初始浓度达到一定程度（3.0mol•m^-3）后已不能有效增加富钛料转化量;氧气和氯气初始浓度高于某一数值时,在合适的氯化温度范围内（973～1373K）,湍床才存在稳定的操作温度点.     

下行床气固两相流动计算流体力学模拟

基于颗粒相动力学理论 ,对层流机制表达的气固两相流体力学模型采用Reynolds平均的方法获得气固两相流的湍流模型描述 .其中 ,气相湍流行为以k -ε模型描述 ;颗粒相的碰撞行为以颗粒流的动力学模型表达 ;而湍流行为以kp 模型描述 .因此建立的k -ε -Θ -kp 模型综合考虑了气相和颗粒相的湍流运动以及颗粒的碰撞行为 .依据此模型建立了三维流体力学求解程序并对下行床气固两相流动行为进行了模型预测 .讨论了恢复系数的选取及壁效应假设 ,从机理上分析并考察了 3种模型的预测能力 .针对内径 1 40mm、高 7m的下行床冷态设备 ,在较宽的操作范围内 ,对比了详细的颗粒浓度和速度径向分布以及轴向参数分布 ,并对下行床的放大行为进行了预测 .     

新型液固循环床提升管颗粒速度径向分布的实验研究

新型液-固循环流化床与常规液-固循环流化床的区别在于提升管底部入口结构和顶部出口结构的不同.实验装置为φ80×8000 mm有机玻璃床,新结构可在较高表观液速和较高颗粒循环速率下操作.利用光纤速度测量仪测量床内颗粒速度径向分布,得到了颗粒速度径向分布规律.通过对实验结果分析发现,新型循环流化床颗粒速度径向分布与较高的表观液速和颗粒循环速率以及由此引发的较大的边壁效应密切相关.     

分布板气量分布对CFB上升管流动行为的影响研究

在高8.5 m大型循环流化床上升管中,使用两种类型的气体分布板,通过双探针电容探头,调查了上升管底部区域和上部稀相区域水平向颗粒浓度和颗粒速度分布.上升管底部,水平方向中心区域颗粒体积浓度较低,颗粒体积浓度在靠近床壁明显增大,最大颗粒体积浓度接近堆积状态下颗粒浓度值.表观气速相同时,高压降分布板颗粒浓度大于低压降气体分布板颗粒浓度.分布板压降对稀相区颗粒体积浓度和颗粒速度曲线没有影响.研究同时发现,分布板压降对稀相区轴向颗粒浓度和颗粒循环量无影响.     

宽粒体系液固流态化随机理论数学模型

用快速切割流化床研究了宽粒级液固流态化的轴向混合和分离,测定了粒度分布、平均粒径和空隙度沿床高的变化.证实了颗粒的运动有随机性.用马尔柯夫过程建立了一个随机游走模型,描述了流化床中宽粒体系的混合和分级特性.对钛铁矿和石英砂(粒径0.04～0.40mm)进行了检验.结果表明,体系的初始流态化速度、膨胀性质、粒度分布以及平均粒径和空隙度沿床高的变化的测定结果,同模型的预测值很好符合.     

Extraction into a flow of a fluid with a velocity gradient

Unsteady extraction from a system of semi-infinite capillaries to the flow of a fluid with a linear velocity gradient is studied. An assumption that the diffusion in the flow is a quasi-steady-state process is taken to obtain a linear equation for the local mass flux from the pore space, which involves fractional derivatives with respect to time and flow coordinate. Limiting solutions for the total diffusion flux at small and large times that cover the entire time interval are found.     

Electrolytes: From a Thorn Comes a Rose,and from a Rose,a Thorn

In this article we take a stroll through the metaphorical rose garden, part of the flower garden, that is electrochemical storage systems. We take a closer look at batteries as the center‐pieces – the roses – and especially at the system component of batteries, the electrolyte and its development, throughout history. Just as a rose can only develop its unique beauty when taken good care of and provided with clean water and suitable nutrients, a battery cell cannot function without its electrolyte; the seemingly trivial component that has to juggle a multitude of requirements in order to make batteries truly bloom.     

Propagation of a burning front over a condensed material from a focus

Measured propagation speeds are given for the combustion front in a blind gap in a condensed substance, which are related to gap height and mean pressure. The front may propagate monotonically, which is characteristic of relatively high pressures and wide gaps, or as a result of additional burning foci arising at a certain distance from the main front. At low pressures and particularly with small gap heights, the front propagates in an unstable fashion over the surface.Moscow. Translated from Fizika Goreniya i Vzryva, Vol. 28, No. 4, pp. 49–53, July–August, 1992.     

Mesomorphic transitions in a mixture of a flexible and a semi-rigid polymer

Phase studies on a mixture of two polymers are presented, one of which is mesomorphic. We have systematically examined the influence of the molecular weight of the flexible polymer (including the oligomers) and of the semi-flexible polymer. In addition to the effect of the molecular weight, specific interactions are important for compatibility and formation of a homogeneous mesomorphic phase. The nature of this phase is demonstrated to be cholesteric and the pitch is determined.     

When is a Beam a Plate?

Formulas associated with simple beam or plate theories are used extensively in structural design, to determine You's modulus, and to determine fracture strength of brittle nonmetallic materials. The question may arise as to whether the proper ratio of beam-width-to-beam-depth is such that the bent structural element can be considered as a beam and, if not, what is the correction factor that should be used with the simple beam formula. These questions are answered for a range of structural metallic and brittle nonmetallic materials.     

Laminar flow deformation of a droplet adhering to a wall in a channel

We study the deformation of oil droplets of varying viscosity adhering to a solid, rigid wall in a rectangular channel induced by a pressure-driven, laminar flow of water. Our experimental investigation involves the systematic study of the effects of initial droplet volume, flow rate and viscosity ratio on the various modes of droplet motion and deformation; this is performed via direct visualisation of the flow in a glass cell using a high-speed camera. Our results are used to construct flow maps that delineate the critical conditions for droplet ‘sliding’, ‘crawling’ and detachment from the channel wall as a function of system parameters. Comparisons of our experimental results with numerical predictions obtained using a procedure based on the diffuse-interface method yield reasonably good agreement for certain flow regimes.     

Detonation of a Column of a Chemically Active Bubbly Medium in a Liquid

The problem of a detonation wave propagating in a cylindrical column of a chemically active bubbly medium screened by a liquid from the tube walls is formulated and numerically solved within the framework of the Iordanskii–Kogarko two-phase model with allowance for energy dissipation due to acoustic radiation of bubbles. The wave structure of the reaction zone and the detonation velocity of the bubbly medium column are calculated. It is found that the self-sustaining wave can propagate with a velocity greater than the velocity of one-dimensional bubble detonation by a factor of 1.5–2.5.