SV型静态混合器湍流阻力的初步研究

为了获得流体在SV型静态混合器中湍流流动时的流动阻力规律,提出一种新的含有SV型静态混合器重要几何结构参数的流体阻力计算模型。对于不可压缩流体,将其在SV型静态混合器中的运动分解成沿管壁与轴线方向平行和沿混合元件凹槽方向的直线运动。运用流体力学理论,分别求解出流体作2种运动时所产生的湍流流体阻力的计算式,并计入相邻混合元件交接部分的局部阻力,然后进行叠加得到流体阻力理论计算式。以水为实验介质,对SV型静态混合器流体湍流阻力进行了实验测量,与理论结论进行比较分析,得出摩擦因子λ与Re-0.2呈线性关系的结论。     

流体粘度对离心泵能量损失的影响

根据叶轮和蜗壳内部时均流动的ＬＤＶ测量结果和性能实验数据,研究了被输送流体粘度对离心泵能量损失的影响。主要讨论了水力损失、容积效率和圆盘摩擦损失与流体粘度的关系。指出随着流体粘度增高,泵内部流动可能为层流。     

SK型静态混合器流体湍流阻力的研究

为了获得流体在SK型静态混合器中湍流流动时的流动阻力规律,提出一种新的流体阻力的计算模型。在流体不可压缩的假设前提下,将流体在SK型静态混合器中的螺旋形运动分解成轴向直线运动和环向旋转运动。在流体作湍流流动时,运用流体力学理论,分别求解出流体作2种运动时所产生的流体阻力的计算式,然后进行叠加得到SK型静态混合器湍流时流体阻力理论计算式。以水为实验介质,对SK型静态混合器流体湍流阻力进行了实验测量,回归出实验公式。与理论结论进行比较分析,得出流动摩擦系数与雷诺数的负0.25次幂呈线性关系的结论。     

关于机械能衡算式若干问题的探讨

本文就机械能衡算式推导及应用中涉及的两个问题提出了不同的解释，认为流体流动过程中的阻力损失中只有一部分转化为热量，另一部分转化为振动能等形式的能量；离开管路出口的流体还有流速，因此也就还有动力，克服出口阻力损失的能量大部分来自动能的损失，少部分来自静压的损失。     

基于CFD模拟的聚丙烯环管反应器非稳态分析

聚丙烯环管反应器中颗粒的非均匀流动现象是引发轴流泵功率波动的重要原因。基于CFD非稳态模拟,研究了环管反应器管内液固两相流体在时间尺度上的非均匀流动特性,并对比了颗粒粒径对非均匀流动的影响。模拟发现,颗粒粒径越大,环管出口处颗粒浓度及非均匀度的波动幅度和波动频率越大,越不利于轴流泵的稳定操作。此外,液固两相流体在经过环管反应器的弯头后,颗粒团聚物等结构会导致固相体积分数出现新的周期行为(脉动频率约为10 Hz),这使得流场的湍动程度加剧、颗粒-颗粒及颗粒-壁面间的摩擦碰撞加剧以及能量耗散加快。     

相似准则和量纲分析在高聚物流变学中的应用

用相似准则、量纲分析和π定理分析了可压缩的非等温和非牛顿流体流动的相似性。当π１，π２，．．．，πｎ与所对应的各准数基本相等时，可认为这两种流体的流动是相似的。     

低渗透岩心启动压力测试研究

随着国内油气藏的开发,低渗透油藏所占比重逐渐增大,而低渗透油藏存在启动压力。启动压力的产生是由于边界层的存在和流体的塑性流动。文章采用稳态法和非稳态法测定了低渗透油藏岩心启动压力梯度。实验表明,在同一粘度情况下,启动压力梯度随岩心渗透率的增大而减小;稳态法较非稳态法易实现。     

基于气流均匀分配的大型袋式除尘器布风风道的几何特性

以大型袋式除尘器为对象,研究其布风风道的气流分配不均匀性,以解决由此导致的除尘效率低、压降偏高及运行成本上升等问题;分析了表征布风风道内流体流动特性的不可压缩恒定流能量方程的相关参数,重点研究了布风风道流动摩擦阻力系数λ、局部阻力系数ζ的影响因素及量化方法,确定了风道的几何结构;采用数值模拟方法分析了布风风道内气流分配均匀性.结果表明,该风道内气体流动处于紊流第IV区,可用阿里特苏里公式确定风道摩擦阻力系数λ;当布风风道结构参数ψ一定时,局部阻力系数ζ与风速比C相关,C2.155时ζ的变化呈指数规律增大,C2.155时ζ的变化区间为1.51～1.57,逐渐趋于稳定;改进前后布风风道内流体流动分配的不均匀系数U分别为0.70和0.93,表明改进后布风风道内流体流动分配均匀性显著提高.     

化工系统工程讲座(六)

<正> 4.典型化工过程的数学模型 (1) 流体流动过程的数学模型 从广义来说,流体流动包括液体和气体的流动状态。液体和气体不同,前者是不可压缩流体,后者可则是压缩流体。流体流动的数学模型要描述包括有输送、贮存,混合、分解等操作的流动系统的特性,因此它将会涉及到泵、鼓风机、压缩机、输送管道、阀门     

T型反应器内流动、混合及界面反应特征

利用平面激光诱导荧光（PLIF）技术和酚酞显色反应,对不同Reynolds数（20<Re<420）下T型反应器内的复杂流动结构及界面反应进行了可视化研究。随着入口Re的增加,反应器内依次出现分离流、稳态吞噬流、非稳态吞噬流及非稳态对称流等流动模式。重点考察了不同流动模式下T型反应器内的界面反应特征,结合流动模式对混合效果、产物浓度分布及时间演化进行了分析,揭示了反应器内复杂流场对混合及界面反应的影响机理。结果表明,吞噬流三维旋涡结构使流体相互卷吸缠绕,通过折叠拉伸形成层状的流体界面,极大增加了反应物的界面接触面积,混合及反应程度显著提升,产物浓度较高且分布均匀。     

UNSTEADY MAGNETOHYDRODYNAMIC NON-NEWTONIAN FLOW DUE TO NON-COAXIAL ROTATIONS OF DISK AND A FLUID AT INFINITY

An analysis is carried out to study the flow generated in a semi-infinite expanse of an incompressible second-grade fluid bounded by a porous oscillating disk. The flow is due to non-coaxial rotations of a disk and a fluid at infinity. The fluid is electrically conducting in the presence of a uniform transverse magnetic field. The solutions of the developed flow are obtained for the cases when the angular velocity is greater than, smaller than, or equal to the frequency of oscillation. The velocity field is found analytically by a Laplace transform technique. It is found that for uniform suction and blowing at the disk, shear oscillations are confined to the Ekman-Hartmann layer near the disk for all values of the frequencies.     

UNSTEADY MOTION OF A SPHERE IN A NEWTONIAN FLUID: I. VELOCITY BOUNDARY CONDITIONS

Using linear operator techniques a general framework is developed in order determine the time dependent velocity and pressure fields of an incompressible Newtonian fluid in the creeping flow limit, when the velocity and/or pressure fields are specified on the boundary. For spherical boundaries detailed eigenfunction expansions are determined for several flow situations, including the motion of a spherical particle in an arbitrary, time dependent velocity field. When the sphere's motion is rectilinear and the external velocity field is uniform, the traditional solution due to Basset (1888) is recovered.     

STOKES FLOW BETWEEN TWO CROSSED AND SINUSOIDALLY CORRUGATED PLATES

The flow space formed between two wavy surfaces when the wave directions are mutually orthogonal is a model for flow through a porous medium. The model allows for both tortuosity and connectivity of flow channels but contains surfaces that are described by simple continuous functions. Characteristics of the creeping motion of an incompressible Newtonian fluid in such a flow space are presented. Results from a boundary integral solution to the equations of motion compare well with those obtained from a perturbation expansion valid for a slowly varying distance between channel walls. It is found that under certain conditions one or more recirculation eddies exist in the cavities formed by wall corrugations transverse to the flow direction.     

Motions of a fluid drop in linear and quadratic flows

A theoretical analysis is presented of the flow field near a spherical fluid drop immersed in an incompressible Newtonian fluid which, at large distances from the drop, is undergoing an undisturbed flow. The undisturbed flows considered here are relevant to studies of drop motions near a phase boundary, and to some aspects of the coalescence of liquid drops. Exacl solutions in closed form have been found using the harmonic function expansion in spherical coordinates. Calculation of the hydrodynamic force on the drop leads to a generalization of Faxen’s law to afluid particle in anarbitrary undisturbed creeping-flow. The solutions are then expressed in terms of she fundamental singularity solutions for Stokes flow in anticipation of future analysis of the drop coalescence. In addition, the deformed shapes are determined for a fluid drop freely suspended in an axisymmetric Poiseuillian flow.     

ANALYTICAL SOLUTION FOR FLOW OF A DUSTY FLUID IN A CIRCULAR PIPE WITH HALL AND ION SLIP EFFECTS

Unsteady flow of a dusty electrically conducting incompressible viscous fluid in a circular pipe is studied considering ion slip. A constant pressure gradient in the axial direction and a uniform magnetic field directed perpendicular to the flow direction are applied. The particle phase is assumed to behave as a viscous nonconducting fluid. A series solution for the governing equations of both fluid and particle phases is obtained for the whole range of physical parameters.     

Modelling laminar pulsed flow for the enhancement of cleaning

A Green function method is presented which enables computation of laminar flow of an incompressible Newtonian fluid in circular and annular pipes, subject to an arbitrary forcing periodic pressure gradient, in terms of Bessel functions. The response to a step change in pressure gradient in an annular pipe is presented. The method allows direct calculation of wall shear stress and flow rates generated by pulsed flows, which are of interest in fouling mitigation and cleaning-in-place systems.     

LOSS COEFFICIENTS IN ENTRANCE REGION FLOWS OF NEWTONIAN AND NON-NEWTONIAN FLUIDS IN ECCENTRIC ANNULI

Loss coefficients for laminar flow of an incompressible Newtonian and non-Newtonian fluids flowing in an eccentric annulus are calculated by modelling an eccentric annulus as a slit of variable height. While the loss coefficients for a power-law fluid are smaller than those for a Newtonian one, the reverse is true for a Bingham fluid. In the limiting case of a concentric annulus, the results are found to be in good agreement with those reported in the literature.     

ANALYTICAL SOLUTION FOR FLOW OF A DUSTY FLUID IN A CIRCULAR PIPE WITH HALL AND ION SLIP EFFECTS

Unsteady flow of a dusty electrically conducting incompressible viscous fluid in a circular pipe is studied considering ion slip. A constant pressure gradient in the axial direction and a uniform magnetic field directed perpendicular to the flow direction are applied. The particle phase is assumed to behave as a viscous nonconducting fluid. A series solution for the governing equations of both fluid and particle phases is obtained for the whole range of physical parameters.     

PERISTALTIC MOTION OF AN OLDROYD-B FLUID WITH INDUCED MAGNETIC FIELD

The problem of peristaltic flow in a channel is solved using the incompressible and magnetohydrodynamic (MHD) Oldroyd-B fluid. The induced magnetic field effects are incorporated in the mathematical modeling. Computations are performed for the small wave number. The obtained mathematical results show that the induced magnetic field effects taken into account in the model substantially affect the flow quantities. It is found that relaxation and retardation times have opposite effects on the flow quantities such as velocity and pressure rise. Moreover, it is observed that induced magnetic field and current density are larger for Oldroyd-B fluid than for the viscous fluid. The salient features of the emerging flow parameters are examined by graphs.     

ON THE EFFECTIVENESS OF UNIFORM SUCTION OR INJECTION ON TWO-DIMENSIONAL STAGNATION-POINT FLOW TOWARDS A STRETCHING SURFACE WITH HEAT GENERATION

An analysis is made of the steady laminar flow of an incompressible viscous fluid impinging on a permeable stretching surface with heat generation. A uniform suction or injection is applied normal to the plate, which is maintained at a constant temperature. Numerical solution for the governing nonlinear momentum and energy equations is obtained. The effect of the uniform suction/injection velocity, the surface stretching velocity, and the heat generation/absorption coefficient on both the flow and heat transfer is presented and discussed.