INTERACTION OF GRAVITY AND ELECTROSTATIC EFFECTS IN PIPE FLOW OF A GAS-PARTICLE SUSPENSION

ABSTRACT

The interaction of gravity and electrostatic effects in isothermal, fully developed, horizontal turbulent pipe flow of dilute suspensions has been examined. Experimental study has validated the fact that, in the presence of gravity, increased space charge associated with increased local concentration due to gravity accentuates the asymmetry in mass flux and particles density distributions in the vertical plane passing through the pipe centerline. The space charge effect on the particle mass flux distribution near the pipe bottom is enhanced by increased particle density. Measurements were made with air suspensions of monodispensed particles of alumina and latex with non-uniform particle charge in pipes of 51 mm and 127 mm diameters.     

AN ELECTROSTATIC INDUCTION PROBE FOR MEASURING PARTICLE VELOCITY IN SUSPENSION FLOW

A probe for measuring particle velocity in pipe flow of a gas-solid suspension has been developed. A solid particle such as a 100 µm latex particle in suspension typically carries an electrostatic charge of say 10^-13 Coulomb via charge separation by surface contacts in normal handling. The tubular cylindrical probe makes use of the principle of electrostatic induction by a charged solid particle during its passage. This probe, which is insulated from ground by a teflon sleeve, converts the induced charge to voltage signals of sharp rise as the charged particle enters and a steep dip in voltage as it departs from the cylinder. Between the entering peak and the later dip at departure, the time of flight of the particle through the probe can be accurately measured and hence the particle velocity.     

A STUDY OF PARTICLE MOTION IN TURBULENT SHEAR FLOW OF A SUSPENSION

A report is made on the measurement of turbulent shear flows of a two-phase suspension of particles in a carrier fluid by the recently developed laser-Doppler anemometry particle sizing techniques, one for small particles (smaller than 240 μm) and one for large particles (larger than 240 μm). A good deal of insights of the dynamics at the individual particle level has thus been gained which defy the explanations offered by the conventional macroscopic theories.

These new experimental findings have stimulated the development of a series of new theoretical approaches which are based on the individual particle's dynamical frequency response characteristics in a turbulent flow. These new theories provide explanations to the measured peculiar features of flow behavior as well as a better understanding of the physics of such flows.     

A STUDY OF PARTICLE MOTION IN TURBULENT SHEAR FLOW OF A SUSPENSION

ABSTRACT

A report is made on the measurement of turbulent shear flows of a two-phase suspension of particles in a carrier fluid by the recently developed laser-Doppler anemometry particle sizing techniques, one for small particles (smaller than 240 μm) and one for large particles (larger than 240 μm). A good deal of insights of the dynamics at the individual particle level has thus been gained which defy the explanations offered by the conventional macroscopic theories.

These new experimental findings have stimulated the development of a series of new theoretical approaches which are based on the individual particle's dynamical frequency response characteristics in a turbulent flow. These new theories provide explanations to the measured peculiar features of flow behavior as well as a better understanding of the physics of such flows.     

管道内旋转细长梁的固液耦合方法研究

管道内旋转细长梁是石油钻采工程中的特有结构,旋转细长梁不仅与管道内壁产生随机多向碰撞,还与细长梁内外管道和环空流体耦合,是一个复杂的非线性固液耦合系统,迄今还未见该方面的研究文献.该文考虑管道内旋转细长梁的结构和工作状态,将结构动力学方程、流体连续方程和动量方程耦合,推导了界面力和界面位移的计算公式、迭代格式及收敛准则...     

INTERACTION BETWEEN PRESSURE DROP OF GAS AND FLOW OF MEDIUM IN A MOVING GRANULAR BED FILTER

Gradually increasing pressure drop, which ultimately leads to a rapid increase, is a problem encountered in moving granular bed filters when gas velocity is elevated during dust collection from the top gas of a blast furnace. The relationship between dust collection and pressure drop was mathematically simulated, and then a half-size test model moving granular bed filter was used to examine the conditions under which the medium can flow. The increase in gas pressure drop proceeds as a circular chain of interrelated events. When gas velocity is increased and the gas pressure gradient exceeds a certain critical value, the medium flow stalls along the gas discharge side of the bed. Dust accumulates in the stalled medium, raising the pressure gradient even further. The growth in pressure drop is thus accelerated, finally resulting in a rapid and undesirable increase that prevents further operation.     

悬索桥主缆变形及重力刚度新算法

为分析悬索桥主缆在活载下的变形,必须考虑在初始恒载下主缆所获得的重力刚度。利用缆索线形与简支梁弯矩图之间的比拟关系,并通过活载在竖向变位上所作的外力功等于缆索重力势能的改变这一功能原理,推导了主缆在活载下的竖向变形和内力的计算公式,以及重力刚度的解析表达式。最后通过算例分析,表明该文公式较现有其它公式具有更好的计算精度。     

圆管流动的二次转捩

利用直接数值模拟方法求解N-S方程来研究空间发展的圆管转捩,计算中雷诺数Re选定为3000。在局部壁面引入的周期性吹吸(PSB)扰动作用下,圆管中首先出现了塞流结构,并向下游迁移,同时有稳定的流向条带结构形成;在塞流结构离开计算域后,随着扰动的不断发展,流向条带结构逐渐破裂失稳,圆管流动出现了第二次转捩,这是一种新的转捩形式,我们称之为“二次转捩”。     

新型平板热管流动与传热特性的理论分析

提出了一种新型平板热管，这种热管整体成矩形平板状，其内部结构由许多并列的小矩形长条单元组成。对这种热管的流动特性和传热特性进行了理论建模分析，得到了热管蒸气腔内的速度分布，压力分布及温度分布的解析表达式。     

PREDICTION OF HEAT TRANSFER IN A TURBULENT GAS-SOLID PIPE FLOW USING A TWO-FLUID MODEL

The dynamic and thermal behaviour of a turbulent gas-solid flow in a vertical pipe has been numerically studied by means of an original two-fluid approach which includes the effects of particle-particle and particle-wall collisions as well as particle-turbulence interactions. A k-ε-k_p model for the flow dynamics has been combined with the energy balances of each phase. Comparisons have been carried out with available experimental data, first for the dynamic validation, and then for the thermal portion of the problem, in the case of rather large panicles (200 to 500 µm). Heat transfer from wall to suspension is seen to be strongly affected by particles. As a consequence, a suspension Nusselt number decrease of 20% may be observed at loading ratio smaller than two. Further increase is possible if more panicles are injected. Predictions had excellent agreement with experimental data for 500 µm particles. Slight discrepancies appear for smaller particles, probably due to more complex, partially understood panicle-turbulence interactions.     

HYDRODYNAMIC PRESSURE EFFECTS OF VISCOUS FLUID FLOW IN A FATIGUE CRACK

Abstract— The influence of hydrodynamic pressure on fatigue crack growth rates has been investigated. It was shown that the effects were small but beneficial, effectively reducing the stress intensity range. A theoretical model has been developed which successfully predicted the trends and approximate magnitudes of reductions in fatigue crack growth rates for a range of test conditions.     

挤管用螺旋芯模机头内熔体流动分析

本文以B.Procter的简化模型(方法Ⅰ)为基础,考虑流动指数与剪切速率的关系(方法Ⅱ)和垂直于轴的截面上的压力平衡(方法Ⅲ),用迭代法分配计算单元的轴向和沿螺旋流道方向的体积流率。编制了模拟螺旋芯模机头内熔体流量、压力降和剪切速率分布的计算机程序。模拟结果表明,根据漏流分布曲线的特性选择几何参数的螺旋芯模机头对熔体的分配效果不受更换物料和改变机头温度及挤出速率的影响。用高密度聚乙烯进行挤管实验时测定的机头压力降和管材壁厚偏差介于用方法Ⅱ和方法Ⅲ模拟结果之间,实验测定结果与用方法Ⅰ模拟结果的差别最大。高密度聚乙烯管的内、外表层的结晶不同,其差别随挤管时的牵引速度的提高而降低。     

有气相注入的管内气液分层流数值模拟

管内气液两相分层流是管道输运和水平井采油过程中重要的研究课题之一,而气液界面是研究的重点内容,尤其是有气泡穿过界面的分层流是水平井采油过程中从有壁面注入时不可回避的流动现象,也是数值计算的难点所在.本文利用VOF方法^[1]捕捉气液界面,应用有限体积方法和重正化κ-ε湍流模式^[2]计算圆管内三维非定常雷诺平均方程,得到了典型的界面上有质量交换时的分层流的流场、界面形状和界面上阻力变化的结果.     

丙烯酸钠的反相悬浮聚合及吸水性能研究

以环乙烷为连续相，司班６０为分散剂，Ｎ，Ｎ－亚甲基双丙烯酰胺为交联剂，过硫酸钾为引发剂，采用后期添加聚合单体的办法反相悬浮聚俣合成粒径增大的高吸水性聚丙烯酸钠树脂。研究了分散剂、引发剂、交联剂用量，后期添加单体量、搅拌速度以及链转移剂对吸液性能和树脂粒径的影响。制得的树脂吸去离子水率为１７００ｍＬ／ｇ以上，吸０．９％ＮａＣｌ溶液１００ｍＬ／ｇ以上。     

CHARACTERISTICS OF A HORIZONTAL SWIRLING FLOW PNEUMATIC CONVEYING WITH A CURVED PIPE

ABSTRACT

In order to prevent flow blockage phenomenon and to reduce the impact of particles on the wall of the bend, an experimental study of the swirling flow pneumatic conveying system with a horizontal curved pipe was carried out in this work. The experiment was performed in a 90-deg pipe bend with pipe diameter 75 mm and centerline curvature ratio 12. The straight pipes with 75 mm inside diameter at the upstream and downstream of the bend were 1.3 m and 4.0 m in lengths, respectively. The initial swirl number was varied from 0.22 to 0.60, the mean air velocity from 10 to 20 m/s, and the solid mass flow rate from 0.07 to 0.68 kg/s. It is found that in the lower air velocity range, the overall pressure drop of the swirling flow pneumatic conveying shows a lower tendency than that of axial flow pneumatic conveying. The minimum air velocities can be decreased by using the swirling flow pneumatic conveying. From the visualization of particle flow patterns, the impact of particles on the wall of the bend can be reduced using the swirling flow.     

CHARACTERISTICS OF A HORIZONTAL SWIRLING FLOW PNEUMATIC CONVEYING WITH A CURVED PIPE

In order to prevent flow blockage phenomenon and to reduce the impact of particles on the wall of the bend, an experimental study of the swirling flow pneumatic conveying system with a horizontal curved pipe was carried out in this work. The experiment was performed in a 90-deg pipe bend with pipe diameter 75 mm and centerline curvature ratio 12. The straight pipes with 75 mm inside diameter at the upstream and downstream of the bend were 1.3 m and 4.0 m in lengths, respectively. The initial swirl number was varied from 0.22 to 0.60, the mean air velocity from 10 to 20 m/s, and the solid mass flow rate from 0.07 to 0.68 kg/s. It is found that in the lower air velocity range, the overall pressure drop of the swirling flow pneumatic conveying shows a lower tendency than that of axial flow pneumatic conveying. The minimum air velocities can be decreased by using the swirling flow pneumatic conveying. From the visualization of particle flow patterns, the impact of particles on the wall of the bend can be reduced using the swirling flow.     

弹塑性海床上的管土相互作用分析

海底管线的在位稳定性问题是海底管线设计中的关键问题之一,为对海底管线的设计提供理论依据,采用大型通用有限元软件ABAQUS对管土系统进行分析。土体的本构模型采用动态的Ramberg-Osgood弹塑性模型,通过改变管道的水下重、环境载荷等参数进行计算。计算结果表明,由于土体侧向隆起而形成的楔形与试验结果相比吻合,管道的水下重、环境载荷对管道的稳定性都有一定程度的影响,并得到了管道侧向失稳的判别准则。     

A NUMERICAL MODEL FOR THE TURBULENT FLUCTUATION AND DIFFUSION OF GAS-PARTICLE FLOWS AND ITS APPLICATION IN THE FREEBOARD OF A FLUIDIZED BED

A numerical model for the turbulent fluctuation and diffusion of gas-particle flows is presented. This model is based on the idea of treating a turbulent gas flow field as a set of k-ε equations, and of modeling the turbulent fluctuation velocity of gas flow as a random Fourier series based on the fluctuation frequency and spectrum. The particle properties (trajectory and velocity) are described by a Lagrangian approach. Hence this model is known as the fluctuation-spectrum-random-trajectory () model. Finally, particle movements in the freeboard of a fluidized bed and in a turbulent gas-particle-laden jet are analyzed to illustrate the applicability of the model.     

考虑边缘效应的微镜静电力学性能分析

该文基于计及边缘效应的矩形平行板静电力计算公式,建立了扭转微镜的非线性静力学模型,分析了边缘效应对微镜静态特性和吸合特性的影响,并通过与实验数据的比较,证明该文所建立的模型更接近于实际。数值分析表明,微镜的激励电压、微镜电极的几何尺寸等参数都会影响微镜的边缘效应,从而使微镜的静态响应产生较大的误差。因此,在某些情况下分析微镜力学性能时必须考虑边缘效应的影响。     

微管道内湍流转捩的实验研究

研究旨在确定微管道内流动从层流到湍流转捩的临界雷诺数。利用微观粒子图像测速技术(Micro-PIV)研究了去离子水在内径为230μm的圆形截面玻璃微管道内的流场结构,得到了从层流到充分发展湍流各流动状态下的轴向平均速度分布和湍流度分布,实验雷诺数为1020~3145,同时研究了微管道内的流动阻力特性。平均速度场和脉动速度场的实验结果表明微管道内从层流到湍流的转捩发生在Re=1800~1900左右,与流动阻力的测量结果一致,与宏观流动比较,并未发现微管道内的流动转捩有明显提前。实验结果还显示,当Re>2700时,微管道内的平均流速分布和相对湍流度分布呈现典型的充分发展湍流状态特征。