基于弯曲振动粘度测量的能耗研究

采用科氏流量计弯曲振动测量粘度其关键在于准确得到粘性力消耗的能量与粘度的关系.采用微元分析方法,系统分析了测量管中轴向无流速时弯曲振动中液体粘性力造成的能量损耗,推导出测量管谐振时消耗功率与粘度的数学模型,并用实验进行了验证.     

输流管道弯曲和振动的有限元分析

基于Timoshenko梁理论,利用虚功原理严格地建立了输流管道弯曲和振动的有限元方程.利用加速度合成定理推导了流体横向加速度的表达式,计算了两端简支和悬臂两种边界条件下管道受到重力和流体作用时的挠度和转角,分析了流体流速对其影响.两端简支条件下将预应力效应整合到管道应变能中,并讨论了轴向预应力与弯曲挠度的关系.给出了两种边界条件下管道自由振动的前三阶固有频率与流体流速的关系,分析了两端简支条件下管道轴向预应力对振动固有频率的影响.结果表明：两端简支边界条件下,流体速度增大则挠度和转角相应增大,预应力使得挠度和转角减小;前三阶固有频率随流速增大而减小,预应力增大则导致各阶固有频率增大.悬臂边界条件下,流体速度增大则挠度和转角减小,前三阶固有频率随流速增大而减小.     

基于科里奥利质量流量计的流体粘度测量分析

介绍了科里奥利质量流量计的工作原理,并从管内流体运动及内摩擦力耗能情况入手,针对影响粘度测量的密度变化因素,对流量计测量粘度的方法进行了改进,通过流体弯曲振动模型的分析,建立了流体粘度与流量计振动参数之间的关系.实验验证了该方法的正确性,并对其应用局限进行分析.该方法简单实用,拓展了科里奥利质量流量计的应用范围.     

分析两端扭转弹簧约束下简支输流管道的动力特性

研究了两端受扭转弹簧约束的简支输流管道的固有频率特性和静态失稳临界流速.根据梁模型横向弯曲振动模态函数,由端部支承和约束边界条件得到了其模态函数的一般表达式.根据动力方程的特征方程,具体分析了约束弹性刚度、流体压强、流速和管截面轴向力等参数对管道固有频率特性和静态失稳临界流速的影响.数值分析表明,约束弹性刚度的增大使管道的固有频率和失稳临界流速明显提高;流体流速、压强和管截面受到的轴向压力的增加使管道的固有频率和失稳临界流速降低.当管道的固有频率和失稳临界流速较低时,可以通过增加端部约束的方法来提高.     

弯曲柔性立管段塞流致振动实验研究

随着深海战略的推进,海洋油气开采向深海挺进,越来越多的海洋立管投入使用.因油气输量的变化及海底地形起伏的影响,立管中经常出现气液两相段塞流,段塞流动的周期性变化使立管受到不稳定的流体力作用从而激发振动,造成立管的疲劳损伤.本文在气液两相流循环实验系统中开展了水动力段塞流诱导的悬链线型柔性立管振动响应测试,利用高速摄像非介入测试方法同步捕捉了柔性立管的振动位移与管内的段塞流动细节,研究了气液混合流速和气液比两个流动参数对柔性立管振动响应的影响,分析了振幅与振频的时空分布、管内液塞长度、压力波动的变化规律及它们间的内在联系.发现固定气液比时,随着混合流速的增大,柔性立管的振幅逐渐增大,但振动模态始终由一阶主导.液塞长度随混合流速的增大变化不明显,但压力波动随混合流速的增大愈发剧烈.固定气液混合流速时,随着气液比的增大,立管振幅逐渐增大,气塞和液塞长度也逐渐增大,进出口压差波动加剧,但压差平均值逐渐减小.     

基于ZLJ-C系列科里奥利质量流量计的流体粘度测量技术研究

采用ZLJ-C系列科里奥利质量流量计进行流体粘度检测的技术与方法;将流体及传感器敏感管(以下简称传感器管)置于柱坐标下对流体动力粘度和科里奥利质量流量计振动时的参数进行了系统分析;提出了一种新的粘度检测方法;利用量纲分析法对相关结论进行了验证.实际实验数据表明该方法是可行的.该技术简单、有效,可在不改变科里奥利质量流量计原有结构的条件下实施.     

突扩管中磁性流体二维流动的模拟

数学模拟可以用来预测流体在突扩管中的流动并更好使用和优化产品制造。使用Herschel-Bulkley(H-B)作为本构方程。在没有磁场的条件下,通过改变参数,我们获得了不同磁性流体的流动过程并分析了回流区长度与参数之间的关系。     

差压式流量测量技术问答(三)

15 均速管流量计的取压孔位皿是如何确定的? 从流体在管道的流动状态来看,可分为充分发展状态下速度分布和非充分发展状态下速度分布的两种状态.对于充分发展状态下速度分布,可以在速度分布中找到一点平均速度,也就很容易测出流体的流量.均速管只适应非充分发展状态下速度分布的流量测量.由于非充分发展状态下速度分布影响因素较多,如管壁的粗糙度、雷诺数、流体粘度等,均速管测量总压的四个取压孔位置能否正确反映流体流速分布规律,所以取压孔位置的确定出现很多方法.     

管内流体诱导锥螺旋弹性管束振动分析

弹性管束换热器通过流体诱导弹性管束振动实现强化换热。弹性管束设计时,需兼顾强化换热和疲劳寿命。对管内流体诱导锥螺旋弹性管束的振动响应进行了研究。通过ANSYS CFX软件仿真分析了锥螺旋弹性管束的固有模态和管内流体流速对弹性管束振幅的影响,并搭建管内流体诱导锥螺旋弹性管束振动试验台。利用加速度传感器,测试了锥螺旋弹性管束监测点的振动加速度信号,对其进行快速傅里叶变换并分析了锥螺旋弹性管束的振动位移响应特性,将数值分析结果与试验值进行了对比分析,验证了数值分析结果的正确性。分析结果表明:锥螺旋弹性管束的振动形式主要表现为纵向振动;管内流体在0.05~0.6 m/s流速范围内,随着流速的增加,管束的振动主频保持不变;振幅随流速增加而增大且振幅增加值逐渐减小。该研究结果为锥螺旋弹性管束的设计提供了依据。     

两端固定输流管振动实验研究

通过实验的方法对简谐激励和脉动流作用下的两端固定输流管的动力学行为进行振动测试分析.设计并制作了两端固定输流管的振动实验装置,为确保实验结果翔实可靠,选取三种不同材料的管分别进行了三次实验,研究了管内流体流速、激振力振幅和脉动流频率对两端固定输流管振动特性的影响.结果表明,流体流速和激振力幅值对两端固定输流管的一阶共振特性和振动幅值有着显著影响,在脉动流作用下,两端固定输流管存在混沌运动,并且随着脉动频率的增大,管道平均振幅减小.     

Three-dimensional deformation analyses of the ultra-thin liquid film surface (linearized analyses for the steady state)

Long wave theory, which is the time evolution equation for the shape and deformation of thin liquid films and includes surface tension and surface forces such as van der Waals forces, was used to examine steady and three-dimensional deformations of ultra-thin but continuous liquid films. As liquid film deformations caused by gas pressures and shear stresses at the gas–liquid interface are usually very small, the linearized long wave equation, which is obtained for infinitesimal deformations, was employed to predict the steady-state liquid surface deformations produced by gas pressures and shear stresses. As the velocity of the solid increases and the liquid film thickness decreases, the deformation decreases and is nearly constant along solid running direction almost everywhere except at the applied position of the pressure and shearing stresses. The results obtained using the linearized equation agrees well with those obtained using the nonlinear equation and the calculation time is greatly reduced.     

Nanoparticle transportation through a permeable duct with Joule heating influence

Microsystem Technologies - Nanofluid radiation in a semi permeable duct is analyzed in existence of Lorentz forces. Lorentz forces impact on energy equation are involved. Last ODEs were solved via...     

The FEM based liquid transfer model in gravure offset printing using phase field method

The velocity control of a roller is crucial in gravure offset printing for determining the quality of the printed images such as width and thickness of an electric circuit. The velocity control also affects mass printability, especially when using micro-scale liquid of high conductivity ink. In this work, a liquid transfer model for gravure offset printing is developed using the phase field method to investigate interfacial dynamics. As a numerical scheme, the finite element method is used for discretization of the partial differential equation. The interfacial layer governed by the phase field variable is embodied by the Cahn–Hilliard equation for a convection–diffusion problem. The numerical results are compared with those from the literatures for their validation. The results were found to be in good agreement with both analytical and experimental results in the literatures. After the validation, the effects of several key factors in gravure offset printing, such as velocity, gravity, surface tension and viscosity on liquid transfer are studied with respect to the contact angle of the upper plate. The ranges of the velocity and contact angle are varied from 0.01 to 0.25?m/s and from 30° to 70°, respectively. Also, the values of the surface tension and viscosity are changed from 0.5 to 1.5?N/m and from 0.05 to 0.15 N?s/m², respectively. The simulation result showed that at α?=?β?=?60° regardless of gravity, the liquid transfer rate (R _%) is increased as the velocity of the upper plate is increased at velocities below 0.01?m/s for liquid with low density, whereas the liquid transfer rate is decreased as the velocity is increased for liquid with high density. Also, the liquid transfer rate is increased as the surface tension is increased until the contact angle (α?≤?β?=?60°) approached 60°. Whereas the liquid transfer rate is decreased as the surface tension is increased until the contact angle (α?≤?β?=?60°) is increased to 60°.     

Linearized analysis of the deformation of ultra-thin lubricant films under gas pressures by the long wave equation

Long wave theory was employed to examine the deformations of ultra-thin but continuum liquid films produced by applied pressures and shearing stresses. Long wave theory is based on the time-evolution equation for the shape and deformation of thin liquid films and includes surface tension and surface forces such as van der Waals forces. As the deformations caused by gas pressures are usually very small, the linearized long wave equation, which is applicable to infinitesimal deformations, was derived and employed to predict the steady-state liquid surface deformations of a non-polar lubricant produced by concentrated or distributed gas pressures. It was found that the results obtained using the linearized equation agree well with those obtained using the nonlinear long wave equation.     

Nonlocal vibration and instability analysis of carbon nanotubes conveying fluid considering the influences of nanoflow and non-uniform velocity profile

In this article, the influences of non-uniform velocity profile attributable to slip boundary condition and viscosity of fluid on the dynamic instability of carbon nanotubes (CNTs) conveying fluid are investigated. The nonlocal elasticity theory and the Euler–Bernoulli beam theory are employed to derive partial differential equation of nanotubes conveying fluid. Furthermore, a dimensionless momentum correction factor (MCF) is obtained as a function of Knudsen number (Kn) so as to insert the effects of non-uniform velocity profile into the equation of motion. In continuation, complex eigen-frequencies of the system are attained with respect to different boundary conditions, the momentum correction factor, slip boundary condition and nonlocal parameter. The results delineate that considering the effects of non-uniform velocity profile could diminish predicted critical velocity of flow. Therefore, the divergence instability occurs in the lower values of flow velocity. In addition, the MCF decreases through enhancement of Kn; hence, the effects of non-uniform velocity profile are more noticeable for liquid fluid than gas fluid.     

Controlling capillary-driven surface flow on a paper-based microfluidic channel

This paper describes two methods for controlling capillary-driven liquid flow on microfluidic channels. Unlike flow driven by external forces, capillary-driven flow is dominated by interfacial phenomena and, therefore, is sensitive to the channel geometry and chemical composition (surface energy) along the channel. The first method to control fluid flow is based on altering surface energy along the channel through regulation of UV irradiation time, which enables adjusting the contact angle along the fluid path. The slowing down (delay) of the liquid flow depends on the stripe length and its position in the channel. Using this technique, we generated flow delays spanning from a second to over 3 min. In the second approach, we manipulated the flow velocity by introducing contractions and expansions in the channel. The methods used herein are inexpensive and can be incorporated to the microfluidic channel fabrication step. They are capable of controlling liquid flow with precise time delays without introducing the foreign matter in the fluidic device.     

Lagrangian particle model for multiphase flows

A Lagrangian particle model for multiphase multicomponent fluid flow, based on smoothed particle hydrodynamics (SPH), was developed and used to simulate the flow of an emulsion consisting of bubbles of a non-wetting liquid surrounded by a wetting liquid. In SPH simulations, fluids are represented by sets of particles that are used as discretization points to solve the Navier-Stokes fluid dynamics equations. In the multiphase multicomponent SPH model, a modified van der Waals equation of state is used to close the system of flow equations. The combination of the momentum conservation equation with the van der Waals equation of state results in a particle equation of motion in which the total force acting on each particle consists of many-body repulsive and viscous forces, two-body (particle-particle) attractive forces, and body forces such as gravitational forces. Similar to molecular dynamics, for a given fluid component the combination of repulsive and attractive forces causes phase separation. The surface tension at liquid-liquid interfaces is imposed through component dependent attractive forces. The wetting behavior of the fluids is controlled by phase dependent attractive interactions between the fluid particles and stationary particles that represent the solid phase. The dynamics of fluids away from the interface is governed by purely hydrodynamic forces. Comparison with analytical solutions for static conditions and relatively simple flows demonstrates the accuracy of the SPH model.     

Langevin Particle: A Self‐Adaptive Lagrangian Primitive for Flow Simulation Enhancement

We develop a new Lagrangian primitive, named Langevin particle, to incorporate turbulent flow details in fluid simulation. A group of the particles are distributed inside the simulation domain based on a turbulence energy model with turbulence viscosity. A particle in particular moves obeying the generalized Langevin equation, a well known stochastic differential equation that describes the particle's motion as a random Markov process. The resultant particle trajectory shows self‐adapted fluctuation in accordance to the turbulence energy, while following the global flow dynamics. We then feed back Langevin forces to the simulation based on the stochastic trajectory, which drive the flow with necessary turbulence. The new hybrid flow simulation method features nonrestricted particle evolution requiring minimal extra manipulation after initiation. The flow turbulence is easily controlled and the total computational overhead of enhancement is minimal based on typical fluid solvers.     

Improved drag force model and its application in simulating nanofluid flow

The circumferential distribution of the surrounding particles contribution to the drag force for the reference particle is firstly proposed and analyzed. A new formula for the drag exerted on a given particle under the interaction between particle clouds and fluid is derived. Analysis shows that even for spherical particles with symmetric shape, as the particle dispersion is nonsymmetric and the direction of the particle velocity differs from the reference particle, the direction of the drag and the particle velocity is not parallel; therefore, it increased the complexity of evolution process for the particle concentration. Due to special feature of nanoparticle surface adsorption, this study presents analysis of the radial viscosity distribution in the vicinity of liquid layer for the first time. The increasing in the viscosity of the nanolayer is considered a contributing factor to the viscosity of nanofluids as the experimental result is larger than the theoretical prediction. Considering the effect of multi-particles interaction and the characteristics of liquid layer, the new drag force model is constructed and applied to simulate the nanofluid flow. Comparison is made for computed drag force on particle between the traditional and present models. The trajectory and distribution of the nanoparticles, as well as the velocity contours of the fluid, are presented. The physical meanings of these results have been discussed.