Effect of IR Transceiver orientation on gas/liquid two-phase flow regimes

Multiphase flows play a vital role in many industrial and naturally occurring processes. Recent trend of miniaturization in mini/micro fluid reactors, compact heat exchangers and micro thrusters requires a thorough knowledge on multiphase flow phenomena in mini/micro channels. The present work is focused on the effect irradiation behavior of infrared rays (IR) during gas liquid two phase flow consisting of thin liquid films inside a mini channel. The influence of size and shape of the slug regime and liquid film thickness on IR rays is analyzed with COMSOL Multi physics package. Experiments are carried out in a 2.5 mm diameter borosilicate glass tube with wall thickness of 0.3 mm. The refraction and transmittance behavior of IR rays on slug and bubbly flow is studied by analyzing the Current-time output of an IR photodiode kept at different angles with the test section. The results are found to be in good agreement with experimental image processing technique and COMSOL results. The results obtained will be useful for designing of IR sensor arrays sensitive to multiphase flows. It can also be used for measurement of liquid film thickness with proper calibration.     

Inertia effects in laminar radial flow of power law fluids

An approximate expression for the pressure distribution for the radial flow of a non-Newtonian fluid (power law) between two parallel disks is obtained by using the momentum and energy integral methods. It is shown that inertia has a significant effect on the pressure distribution especially for those fluids with a power law index, n 1.     

微小尺度下平板间气体流动机理及压力特性分析

基于平板间气膜内气体分子运动和碰撞的规律,提出气膜分层理论,将板间气膜内的气体划分为近壁层、稀薄层、连续流层。给出了划分稀薄层和连续流层的依据,建立分层物理模型并提出每层的控制方程,验证了分层理论的合理性。通过大规模原子/分子大型并行模拟器仿真板间气膜内气体流态并计算沿高度方向的压力,得出了如下结论：随着板间气体流速的增大,板间气膜有效压力减小,连续流层的厚度增大,稀薄层的厚度减小;当气体流速到达一定值时,气膜内压力不再分层,速度滑移现象可以忽略。     

A new hydrodynamic instability in ultra-thin film flows induced by electro-osmosis

A new hydrodynamic instability is identified for a nanofluidic flow. The flow analyzed is an electro-osmotic flow of a thin liquid layer, bounded below by a solid substrate and above by an inert gas. The Debye-Hûckel approximation is used for the potential distribution, and the interface with the gas is treated as a moving boundary. The stability analysis shows that the flow is always unstable to small-wavenumber disturbances, and the instability is accompanied by interface deformations. Neutral stability bounds due to the capillary cut-off are presented in parametric spaces for the electric field strength and the Debye length of the electrolyte.     

Non-newtonian squeeze films in spherical bearings

Non-newtonian behaviour which occurs in various lubrication problems is studied using a power law model. The geometry considered is that of squeeze films in spherical bearings. The Reynolds equation is given separately for the negative and positive pressure gradient regions. Various bearing characteristics are obtained in the form of integrals. The load capacity increases with the flow behaviour index n. Newtonian results are obtained by taking n = 1.     

Investigation on the swirlmeter performance in low pressure wet gas flow

Wet gas flow is a subset of gas-liquid two-phase flow, and the swirlmeter has been used in wet gas flow metering more and more recently. The swirlmeter performance in low pressure wet gas flow was investigated. It is found that the entrained liquid present in a gas stream tends to induce a negative bias in the gas flow rate reading of swirlmeter comparing with equal gas flow rate. When the Lockhart-Martinelli parameter X, which is closely related to the liquid fraction, is bigger than a threshold value, the swirlmeter will not properly work due to the disappearing of vortex precession. It is also found that the liquid-induced gas flow rate reading errors of swirlmeter are dependent on X and the gas densiometric Froude number Fr_g. A correlation for swirlmeter in low pressure wet gas flow is proposed, and it corrects the liquid-induced gas flow rate errors to an accepted accuracy under the tested conditions. It implies that the swirlmeter with the proposed correlation and the known liquid fraction may be used to meter the gas flow rate in wet gas applications with a relatively low liquid fraction.     

Performance model evaluation of turbine flow meter in vertical gas-liquid two-phase flows

Aiming at the need for flow measurement of gas-liquid flows in domestic gas well production, this paper proposes a measurement method based on the combination of the turbine flow meter (TFM) and a rotating electric field conductance sensor (REFCS). In experiments, the REFCS is used for the measurement of the gas holdup. To verify the applicability of the TFM models investigated in the previous study, for the modeling part, the mass, momentum and torque models are evaluated in vertical upward gas-liquid two-phase flows. In our model test, the meter factor model of TFM considers the effects of the slip ratio between the gas and liquid phases and flow patterns. In particular, the gas holdup involved in calculating the slip ratio in the model evaluation is obtained from the REFCS measurements. Model test results show the torque model has better volumetric flow rate prediction accuracy than the mass and momentum models. In the present study, the ranges of the liquid and gas phases are Q_w = 2–30 m³/d and Q_g = 1–16 m³/d, it was found that the average absolute deviation (AAD) in the predicted volume flow rate is equal to 1.23 m³/d and the average absolute percentage deviation (AAPD) is equal to 7.69%. The evaluated results presented in this paper will allow better estimates of the volumetric flow rates of gas-liquid flows based on the combined TMF and REFCS measurements during the monitoring of gas well production.     

On the Fluid Flow and Thermal Analysis of a Compliant Surface Foil Bearing and Seal

Foil gas bearings have been applied successfully to a wide range of high-speed rotating machinery such as air cycle machines (ACMs) and auxiliary power units (APUs). The performance of these bearings are based on the high pressure gas in a very thin layer between the journal and the bearing governed by the Reynolds equations. Generation of heat in these bearings especially at high journal rotating speed and high loads or at high ambient temperature directly affect their performance. Thermal and fluid flow analysis of an advanced compliant foil journal bearing/seal are presented. The side flow (known as leakage) and the approximate temperatures are the results of this analysis. The result of preliminary analysis shows that the major portion of the heat is carried through conduction and using the modified Couette flow approximation for the present working fluid, air, helped in analysis of the temperature magnitude, which can be related to the gas viscosity behavior and thin gas film thicknesses.     

Velocity distribution of liquid phase at gas-liquid two-phase stratified flow based on particle image velocimetry

Horizontal gas-liquid flows are commonly encountered in the production section of the oil and gas industry. To further understand all parameters of the pipe cross-section, this paper use particle image velocimetry to study the circular pipe cross-section liquid velocity distribution rule. Firstly the focus is on the software and hardware combination of image correction system, to solve the influence of different refractive indexes of medium and pipeline curvature caused by image distortion. Secondly, the velocity distribution law of the corrected stratified flow (the range of liquid flow of 0.09-0.18 m³/h, and gas flow range of 0.3-0.7 m³/h) cross-section at different flow points of the pipeline cross-section at x=0 and in the Y direction at the maximum liquid velocity is studied. It is found that these distribution laws are caused by the influence of the interphase force of the gas-liquid interface and the resistance of the pipe wall. The current measurements also produce a valuable data set that can be used to further improve the stratified flow model for gas-liquid flow.     

A study on the relationship between upstream and downstream conditions in swirling two-phase flow

Inline fluid separation is a concept, which is used in the oil and gas industry. Inline fluid separators typically have a static design and hence changing inlet conditions lead to less efficient phase separation. For introducing flow control into such a device, additional information is needed about the relationship of upstream and downstream conditions. This paper introduces a study on this relationship for gas/liquid two-phase flow. The downstream gas core development was analyzed for horizontal device installation in dependence of the inlet gas and liquid flow rates. A wire-mesh sensor was used for determining two-phase flow parameters upstream and a high-speed video camera to obtain core parameters downstream the swirling device. For higher accuracy of the calculated void fraction, a novel method for wire-mesh sensor data analysis has been implemented. Experimental results have shown that void fraction data of the wire-mesh sensor can be used to predict the downstream behavior for a majority of the investigated cases. Additionally, the upstream flow pattern has an impact on the stability of the gas core downstream which was determined by means of experimental data analysis.     

微尺度下空气静压支撑在滑移区的承载特性实验研究

为了阐释空气静压导轨气膜间隙处在微小尺度所体现的特性,引入努森数(Kn),计算了不同工况下气膜内压力和不同气膜厚度下Kn数的变化关系。引入支撑区气膜分层假设,与分子动力学相结合,对气膜内不同流态层的刚度进行了实验和分析。通过ANSYS仿真和实验数据相结合得出了结论:气膜内稀薄效应的增强,可以一定程度上提高气浮支撑的静承载能力。气浮支撑的刚度特性和气膜内部分层情况有关:以分子碰撞运动为主的稀薄层主要起容性效应,实现分子间动量的传递和转化,因此该层所体现出来的刚度较差;以惯性力驱动的连续流层内部分子运动比较稳定,特别是在垂直方向不存在显著的动能和压力能之间的转化,因此该层的刚度特性较强。实验证明,气膜厚度在1~10 μm时,气膜的刚度先增大后减小,也间接论证了静压支撑的刚度特性主要由气膜内连续流层决定。     

气流聚焦静电喷雾喷射行为实验研究

为提高射流喷射的稳定性和薄膜成型效率,设计开发了具有气流聚焦功能的静电喷雾装置。仿真研究了喷雾空间电场和气体流场的分布特性,开展了静电喷雾实验研究,分析了喷雾射流喷射行为,讨论了静电喷雾薄膜沉积面积和纳米颗粒直径的控制规律。结果表明,辅助气流的加载能够有效提高喷嘴处射流的喷射速度,促进射流拉伸细化,对减小纳米颗粒直径、提高颗粒均匀性都具有很好的促进作用。     

Numerical approach for cocurrent stratified steam water flow in a horizontal configuration

The present study deals with the one-dimensional numerical approach in predicting the local flow properties for cocurrent stratified steam-water flow in a horizontal configuration. The turbulence-centered model, developed principally for gas absorption, has been modified and introduced for the condensation heat transfer coefficient using interfacial parameters, such as turbulent velocity and length scales. The calculated condensation rates, pressures and mean water layer thicknesses are in good agreement with Lim’s experimental data obtained from cocurrent stratified steam flow on a fairly thick layer of water. In addition, the approach was applied to the case of relatively thin liquid films, and the results were compared with Linehan’s experimental data. The comparison indicates that the one-dimensional numerical approach with the present condensation heat transfer correlation developed from the thick liquid data can be applicable to the prediction of the flow properties for thin liquid films.     

磁致伸缩薄膜动态驱动特性的研究

提出一种新的磁致伸缩薄膜动态驱动特性的研究方法,其原理是以磁致伸缩薄膜复合梁的等效形变为基础,将磁致伸缩驱动应力转换为等效驱动力矩,建立磁致伸缩薄膜的强迫振动动态模型,通过受迫振动理论来研究磁致伸缩薄膜的动态特性。对该模型进行了仿真计算和试验验证,表明该模型可以描述磁致伸缩薄膜的动态行为。该方法对薄膜驱动器的运动分析与结构优化。最终实现基于磁场自感知的超磁致伸缩薄膜驱动器的闭环控制具有参考意义。     

An automated measurement setup for studying the dependences of the thermal conductivity and rheological characteristics of non-Newtonian fluids on the shear rate

An experimental setup designed for studying the rheological characteristics and thermal conductivity of liquid materials is described. The presented measurement and experimental-data-processing technique allows determination of the thermal conductivity of liquids as a function of the shear rate with allowance for the heat released in the studied material layer due to dissipation of the mechanical energy during a shearing motion and helps to find the consistence factor and the flow index for liquids that obey the power rheological law. The results of experiments on the determination of the thermal conductivity as a function of the shear rate of a 10% aqueous solution of polyoxyethylene and synthetic caoutchouc doped with nanostructural elements (carbon nanotubes and nanofibers) at different temperatures are presented. The thermal-conductivity measurement error is ≤10%, while the measurement errors for the consistence factor and the flow index are <7%.     

Adiabatic solutions for a misaligned journal bearing with non-Newtonian lubricants

Adiabatic solutions are presented for a finite width, hydrodynamic, misaligned journal bearing with non-Newtonian lubricants, obeying the power law model. The film viscosity is taken to be an exponential function of temperature. The performance characteristics of a misaligned journal bearing with slenderness ratio of unity are obtained for various values of non-Newtonian power law index n in the range 0.4 to 1.2, eccentricity ratio in the range 0.2 to 0.8, and misalignment angles of 0.0001 and 0.0002 rad. The adiabatic solutions show that the load-carrying capacity is greatly reduced when compared with that given by the isothermal solutions. In addition, thermal effects are found to be more pronounced for higher values of flow behaviour index n, higher eccentricity ratios and larger misalignment angles.     

Flow behavior control in immersion lithography

Over the past decade, immersion lithography has been the primary technology for exposure process in semiconductor manufacturing. Compared with traditional dry lithography method, this technology improves the exposure resolution greatly by inserting a high index liquid into the gap between lens and wafer surface. Keeping the immersion liquid pure and uniform as well as avoiding residual droplets during high speed scanning motion are two challenges faced by the development of immersion lithography. Contaminations, particles, bubbles, heating and stress in the liquid will destroy the continuity of the refractive index. High speed motion of the wafer during scanning may break the meniscus stability on the interface between the liquid and the gas surrounding it, and then generate residual droplets on the wafer. All above phenomena will affect the exposure performance of immersion lithography and corresponding flow behavior control methods are required to solve the problems. This paper gives a review of the studies on flow behavior control in immersion lithography, which contains two parts: studies for liquid purity and uniformity and studies for meniscus stability. In each part, the mechanism and character of the flow behaviors as well as their effects to exposure performance are presented firstly. Then, control approaches adopted by now, including material and surface modifications as well as immersion head utilization, are introduced. In addition, the challenges faced in future studies are also pointed out. The purpose of this review paper is to help the researchers to understand the flow control problems in immersion lithography and to provide better control approaches for exposure performance improvement.     

指数型粘度修正模型的提出及实用分析

根据吸附理论和分子间能量的变化规律来确定表面相互作用程度 ,以此可定义吸附层 ,得出吸附层厚度的分析计算公式。根据分子相互作用的基本理论及流体力学的基本定义得出指数型粘度修正的表达式 ,用于确定微小间隙内流体粘度的变化规律 ,用此修正模型对薄膜润滑条件下轴承的性能计算 ,同时与实验比较 ,得到比较吻合的效果     

大攻角下平面串列叶栅的试验研究

本文应用附面层控制的基本思想,对液力变矩器导轮串列叶栅进行风洞试验研究,分析了其内部的流动损失机理及特点,并与导轮单列叶栅的流动损失进行了比较。在S 1流面上计算了串列叶栅内部的流场及叶片表面的附面层参数。理论计算与试验结果分析表明,串列叶栅的应用为显著提高变矩器效率提供了一种大有希望的途径。     

真实事故中通过制动控制降低人地碰撞损伤的潜在效益及时空约束

为研究制动控制在降低人地碰撞损伤方面的潜在效益及其时空约束,首先从前期积累的事故数据库中筛选出139例真实的人车碰撞事故,利用PC-Crash对所有事故进行再现,再通过控制车辆制动以降低人地碰撞损伤,最后采集人体各部位损伤、头车与头地碰撞位置及制动控制过程中的时空约束等信息。分析结果显示,在真实事故中人车首次接触后车辆完全制动与否不会对人体损伤造成显著影响;通过制动控制能够显著降低头、臀与地面碰撞所致损伤,并能降低头车、头地碰撞位置的重合率,且不会加重车辆所致损伤;但要求车辆在较短时间内做出判断以正确控制车辆,且8.4%的案例在现实中未有足够空间让车辆实施制动控制。