垂直管气液两相环状流界面扰动波频率特性

气液两相环状流的相界面存在扰动波,波动频率是描述环状流界面扰动波特性的关键参数,对环状流的传质传热研究有重要参考价值。利用近红外光的吸收特性,设计了液膜检测装置,采用垂直对射光路设计,并通过置入式导光管屏蔽一侧液膜和气芯夹带液滴,实现了对环状流局部液膜的非接触式检测。在此基础上对界面扰动波进行了频域分析,运用功率谱密度估计,对50 mm管径竖直上升管环状流界面扰动波波动频率进行了定量研究,得到0.1～0.8 MPa不同压强条件下,共70个流动条件的环状流界面扰动波频率值。利用实验结果对现有模型进行验证分析,在此基础上利用Strouhal数描述液相流动条件的影响,利用Froude数描述气相流动条件的影响,建立了预测环状流界面扰动波波动频率的St-Fr模型,经实验数据验证预测的平均绝对误差（MAE）为11.42%。     

环形狭缝通道内气液两相环状流流动特性

建立了环形狭缝通道内气液两相环状流的理论模型 ,该模型计及环状流气芯流动的可压缩性、气液两相间的相滑移、气相对液滴的夹带作用等因素 .考察了两相流质量流量和干度对压降、液滴速度相对变化和狭缝喉部气芯通流面积的影响 .用建立的理论模型对空气 -水两相环状流通过环形狭缝的两相压降进行预测 ,预测值和试验值吻合良好     

垂直及倾斜上升管内气液两相弹状流壁面切应力的模拟

用VOF模型对垂直及倾斜上升管内弹状流壁面切应力进行数值模拟。计算结果表明,垂直上升流动时,液膜厚度始终小于对应位置倾斜上升弹状流的液膜厚度,壁面切应力从气弹头部至尾部逐渐增大至恒定不变,在尾流区呈杂乱无章状态。倾斜上升流动时,气泡头部顶点偏向管中心线上方,倾角越小,相同轴向位置处测得的液膜厚度越大。当FrTB较小时,倾斜管内弹状流上管壁面的切应力曲线在液膜区有明显波动,而下管壁面在对应区域的切应力分布则比较光滑。随着FrTB的增大,上下壁面切应力分布曲线越来越靠近。     

水平管内气液两相泡状流进口段壁面切应力

利用TSI-1268W热膜探头对内径为35 mm的水平管内气液两相泡状流的壁面切应力进行了直接测量,得到了进口段不同截面上沿周向不同位置处的壁面切应力数据,通过分析实验段进口段的壁面切应力沿管长的变化来确定进口段的长度.结果表明,液相中加入气泡后增加了壁面切应力数据的离散程度.在实验参数范围内,测量的壁面切应力进口段的长度在52D～65D之间,并且壁面切应力进口段随着液流Reynolds数和截面含气率的增大而增大.液相中加入气泡后在不同的测量角度壁面切应力的变化呈现不同的特征.     

基于分相流模型的气液两相流流量测量

从伯努利方程出发,基于分相流模型,推导出气液两相流流过文丘里管的流量公式.在分析了两相流通过节流装置的实际流动情况后,作者认为气液两相滑移比是影响流量公式误差的一个重要因素.在理论与实验研究的基础上,作者提出了气液两相流流过文丘里管的滑移比经验关联式.利用作者提出的滑移比经验关联式和分相流模型的流量公式测量两相流流量,体积流量误差的均方根小于5.1%,表明该方法适用流过文丘里管的两相流流量测量,尤其对于两相流动激烈的两相相互作用区域,流量误差满足测量的要求.     

垂直同心环形管内上升气液两相环状流含气率与压降预测

对垂直同心环形管内上升气液环状流的截面含气率及压降预测进行了研究.根据Kelessidis有关团状流向环状流转换的思路以及Wallis有关圆管内环状流积分分析的方法,考虑环形管的结构特征及环状流的流型特征,通过两相动力学理论建立了新的预测截面含气率及总压降的模型.将新模型及现有模型与实验数据的分析比较表明新模型对于总压降的预测效果较好.     

超声多普勒测速仪在液-固和气-液两相流测量中的应用

引　言多相流反应器在化工、环境、生化过程中得到了广泛的应用[1,2 ] ,但是由于多相流的复杂性 ,还需要进行大量深入的研究 .虽然计算流体力学在多相流领域的应用取得了一定的进展 ,但是实验研究在目前仍是多相流研究的主要手段 .多相流测量领域已经开展了大量的工作 ,但仍是一个具有挑战性的研究领域[3] .多相流中需要测量的量主要有局部颗粒浓度、颗粒速度、气含率、液体速度、气泡行为[3] .固体催化剂浓度的分布[4 ] 和气泡行为[5]对反应器性能有着重要的影响 .同时测得气液两相的速度对于更好地表征气液两相的相间作用 ,提高ＣＦＤ模型…     

T形微通道内环状气液两相流相分离

以氮气为气相工作介质,以不同表面张力的液体（纯水、0.01%SDS溶液、0.5%SDS溶液、乙醇）为液相工作介质,对矩形截面为100 μm×800 μm的T形微通道内的气液环状流进行了相分离可视化实验。实验结果表明：环状流液相在侧支管中采出占优势。液相采出分率主要集中在0.25～0.65之间;气相采出分率在0.1～0.8,液相采出分率的增长幅度随着气相采出分率增加而变大。当气相表观速度一定时,液相采出分率随着两相流液体速度的增加而降低;当液体表观速度一定时,气体速度变化对液相采出分率影响不大;当两相的表观速度一定时,液相采出分率随着液体的表面张力降低而减小。所得实验数据与其它尺寸的数据进行比较,发现管径尺寸对环状流相分离有较大影响。     

气/液-固两相流中的粒子速度

通过实验研究和理论分析,考察了提升管中颗粒相的质量守恒;发现在传统的两相流研究中,对颗粒速度的时间平均和算术平均存在着误用。在传统理论中,由于引入了颗粒相的体积分率项,实际上是对离散的颗粒进行了连续化的假设。由此不可避免地造成颗粒速度时间平均和算术平均的混淆。在微观尺度上对气/液-固两相流中颗粒速度时间平均的物理意义进行了分析,给出了计算非连续流场中颗粒时均速度的表达式,并提出了分析颗粒相质量守恒的方法。     

管内相分隔双压差在多相流双参数测量中的应用

应用管内相分隔技术可以产生沿管道横截面的径向压差和沿管壁变化的轴向压差,研究表明,径向压差与两相流的总流量和相含率呈一定函数关系,若轴向压差与两相流的总流量和相含率也呈一定的函数关系,那么就可以通过双压差(轴向压差和径向压差)的联立实现多相流双参数的测量。以油水两相流为例,系统研究了基于管内相分隔产生的轴向压差在多相流测量的理论机理,并结合径向压差进行了实验验证。结果表明,在管内相分隔状态下,旋流器下游某两截面之间的轴向压差与油水两相流的总流量和体积含油率呈一定的函数关系,两者的实验值和理论值之间的相对误差分别在±1.05%和±9.84%以内;通过双压差的联立,可以求出某一状态下两相流的总流量和相含率,两者的实验值和理论值之间的相对误差分别在±1.13%和±6.89%以内,验证了基于管内相分隔双压差在多相流双参数测量应用的可行性。     

Effect of Inlet Type on Shear Stress and Mixing in an Annular Photobioreactor Involving a Swirling Decaying Flow

Improvement of mixing can lead to an enhancement of photobioreactors productivity, provided that the adverse effect of shear forces is kept below the fragility‐ threshold of cells. Implementation of a swirling decaying flow induced by a tangential inlet in an annular photobioreactor was investigated. The study focused on a compromise solution between the mixing and the resulting shear stress, and various hydrodynamical characteristics were measured for five types of tangential inlets and three Reynolds number values. Comparison with a pseudo‐axial flow induced by a radial inlet indicates that swirling flows are suitable in the particular application of microalgal cultures.     

Application of the Electrodiffusion Method to Measure Wall Shear Stress: Integrating Theory and Practice

The electrodiffusion method has been used in fluid dynamic research for the past 50 years. It allows the measurement of wall shear stress, a crucial parameter, e.g., for the cleaning of membrane modules used in water filtration. Various authors have published articles dealing with the theory behind this technique. But no paper collects all the knowledge assembled over five decades of application. Here, comprehensive summary of the theory of steady flow, unsteady flow, and transient voltage step experiments is given. Factors influencing the accuracy of the measurements are discussed. Furthermore, a new approach to calibrate the system from voltage step experiments is introduced, and practical issues related to its application in flow measurements are discussed for an exemplary signal response to a near‐wall flow.     

基于热示踪法的井下流量测量系统设计

根据热示踪方法的流量测量原理,采用C8051F360单片机、热源发生器及温度传感阵列等器件,设计一种基于热示踪方法的井下流量测量系统。该系统利用热源发生器对井下流体加热,当加热的流体经过传感器阵列时即可根据热示踪方法测出油水两相流的流量,并将数据传输给由LabVIEW设计的井上上位机系统,实现了井上地面计量站对井下数据的实时监控,解决了井下流量测量难、实时监测难、数据量大的问题。     

Interfacial Shear Stress of Stratified Flow in a Horizontal Pipe

Experimented data are presented for the void fraction aud the shear stresses of stratified gas-liquid flow in a pipe, A new technique was used to measure the interface shear strew. The interfacial shear stress was determined by using two methods: a momentum balance of gas and an extrapolation of the Reynolds shear stress prone at the gas-liquld interface. A new formula ,relatiog to the interfacial friction factor with the void fraction and superficiol gas Rcynold number, was dewloped to predict the interface shear stress. The predicted values are in good agreement with experimental data.     

Jenike型剪切测试仪在颗粒物料流动性测试中的应用

流动性测试能够准确地获得颗粒物料的相关特性,为设计颗粒物料处理工艺及设备提供准确可靠的依据。介绍了颗粒物料流动性的描述方法,以及用Jenike型剪切测试仪进行颗粒物料流动性测试的方法,分析了该测试试验存在的问题,并提出了解决方法,为颗粒物料流动性测试提供指导。     

聚合物剪切流动取向应力-应变关系实验研究

采用熔体流动速率(MFR)仪研究了聚丙烯(PP)材料在剪切流动中大分子链取向应力与应变关系模型。通过测定口模挤出物胀大比,依据Poiseuille定律计算得出材料在不同条件下的第一法向应力差;引入相关聚合物充模取向力学行为理论模型,考虑到相关模型表征了聚合物充模的瞬态过程,简化起见,以材料MFR代替模型中的应变张量;采用最小二乘与数据拟合理论求得相关模型常量,得出PP材料的流动取向应力–应变定量关系式。实验验证结果显示,线弹性模型和高弹性模型的应力最大平均理论误差分别为11.57%和10.95%,最小平均误差分别为9.60%和5.68%,均具有较好的适配性,为后续相关模型理论的定量表征提供了实验依据。     

Investigation of Wall Shear Stress in Cardiovascular Research and in Clinical Practice—From Bench to Bedside

In the 1900s, researchers established animal models experimentally to induce atherosclerosis by feeding them with a cholesterol-rich diet. It is now accepted that high circulating cholesterol is one of the main causes of atherosclerosis; however, plaque localization cannot be explained solely by hyperlipidemia. A tremendous amount of studies has demonstrated that hemodynamic forces modify endothelial athero-susceptibility phenotypes. Endothelial cells possess mechanosensors on the apical surface to detect a blood stream-induced force on the vessel wall, known as “wall shear stress (WSS)”, and induce cellular and molecular responses. Investigations to elucidate the mechanisms of this process are on-going: on the one hand, hemodynamics in complex vessel systems have been described in detail, owing to the recent progress in imaging and computational techniques. On the other hand, investigations using unique in vitro chamber systems with various flow applications have enhanced the understanding of WSS-induced changes in endothelial cell function and the involvement of the glycocalyx, the apical surface layer of endothelial cells, in this process. In the clinical setting, attempts have been made to measure WSS and/or glycocalyx degradation non-invasively, for the purpose of their diagnostic utilization. An increasing body of evidence shows that WSS, as well as serum glycocalyx components, can serve as a predicting factor for atherosclerosis development and, most importantly, for the rupture of plaques in patients with high risk of coronary heart disease.     

Impact of Fluid Flow Shear Stress on Osteoblast Differentiation and Cross-Talk with Articular Chondrocytes

Bone cells, in particular osteoblasts, are capable of communication with each other during bone growth and homeostasis. More recently it has become clear that they also communicate with other cell-types; including chondrocytes in articular cartilage. One way that this process is facilitated is by interstitial fluid movement within the pericellular and extracellular matrices. This stimulus is also an important mechanical signal in skeletal tissues, and is known to generate shear stresses at the micron-scale (known as fluid flow shear stresses (FFSS)). The primary aim of this study was to develop and characterize an in vitro bone–cartilage crosstalk system, to examine the effect of FFSS on these cell types. Specifically, we evaluated the response of osteoblasts and chondrocytes to FFSS and the effect of FFSS-induced soluble factors from the former, on the latter. This system will ultimately be used to help us understand the role of subchondral bone damage in articular cartilage degeneration. We also carried out a comparison of responses between cell lines and primary murine cells in this work. Our findings demonstrate that primary cells produce a more reliable and reproducible response to FFSS. Furthermore we found that at lower magnitudes , direct FFSS produces anabolic responses in both chondrocytes and osteoblasts, whereas higher levels produce more catabolic responses. Finally we show that exposure to osteoblast-derived factors in conditioned media experiments produced similarly catabolic changes in primary chondrocytes.     

新型涡流分级机分级区流场特性数值模拟研究

为获取新型涡流分级机分级区流场分布情况,在分析涡流分级机空气流动特性的基础上,采用计算流体动力学软件ANSYS CFX14.5对不同转速下环形区和转笼两区域各速度与转笼转速间关系进行了模拟.通过模拟可得:转笼转速大小影响环形区速度场稳定,并将导致转笼叶片间产生惯性反旋涡现象,存在一定范围的转速可使分级区的气流场稳定,从而使分级机的分级效率提高,最后,通过物料实验表明,模拟结果与实验结果相吻合.数值模拟对选择分级机合理的操作参数控制提供了一定的理论依据.     

移动床径向反应器的催化剂颗粒层中应力分布和贴壁现象产生的条件

本文应用散料力学理论,分析了移动床径向反应器颗粒床层内的应力,得到了在有气体径向流动情况下床内正应力和剪切应力沿径向分布的解析解,并由此得到了计算颗粒产生贴壁时的气体流量和床层总压降的计算方法,讨论了各种因素对产生贴壁现象的影响。最后将本模型的计算结果与文献中提供的实验结果进行了比较。