测量两相流中颗粒特性的相位多普勒方法理论模型

本文在几何光学近似Ｍｉｅ散射理论的基础上建立了一种计算激光多普勒信号中相左与粒径关系的数学模型。对几种常用的相对折射率情况下的相差一粒径特性进行了计算,分析并给出了光学系统的最佳配置。计算结果与Ｍｉｅ散射理论的计算结果进行了对比,有限好的一致性。     

气液两相流理论与气幕降噪

气液两相流是广泛存在于工业过程中的复杂现象。本文将就气液两相流的理论、声学特性等方面进行综述,并对其在降噪方面的应用前景进行展望。     

气液两相流中气泡运动速度场的PIV分析与研究

粒子图像测速技术（PIV）作为一种无扰、瞬态、全场速度测量方法，已被广泛应用于液体或气体的单相流流速场测定。对于两相流PIV技术，目前还处于起步阶段，本文应用PIV技术的基本原理，对静止液体中的气泡运动速度进行了分析，并对有关气液两相流测量问题进行了探讨。     

气泡-水流两相流的激光多普勒法测量

为区分激光多普勒稀态两相流动测量中出现的流体相信号和颗粒(气泡、液滴)相信号,本文提出可见度和基座的复合判别法,并设计了专用的信号预处理器,此预处理器能将原始多普勒信号分为两路,分别代表两相,并可用计数型信号处理器测量每路的速度及其它统计量。使用本方案对矩形管道內低速气泡-水两相流的实验和测量表明,对两相的区分和测量是成功的。文中给出了两相速度、湍流度和气泡滑移速度的测量结果。     

气液两相流压力波传播速度研究

将双流体模型用于绝热无相的管道气液两相流,依据小扰动线化分析原理,导出了压力波波数Ｋ方程通过对不同空隙率下肉体上压力波小随角频率变化的计算,研究了虚拟质量力和狭义相间阻力对压力波波速及其人色散性的影响。对泡状流和弹状流压力波波速的计算结果与前人的测量结果作了比较,两者符合良好。     

微重力气/液两相泡状流的摩擦压降

针对微重力条件下气／液两相泡状流动特征,建立了其摩擦压降的半理论模型：ｆＴＰ＝ＡＲｅ＾－１ＴＰ,并利用献报道的微重力实验数据,确定了模型参数Ａ的数值。     

气液两相绕流柱体时的涡街特性研究

本文以水空气两相流体为工质，研究了两相流体横向冲刷准三角形柱体时的涡街生成特性．试验段管子内径５０ｍｍ，水流速度２．２０ｍ／ｓ－３．７４ｍ／ｓ截面含气率为０．０２－０．３．得出了两相流体中涡街发生频率，水流量和截面含气率三者之间的相互关系。     

瞬态通用固液两相流模型及其在动态井眼清洁模拟中的应用

为准确了解岩屑在井眼中的实时运移、积累过程及其变化规律,基于质量守恒和动量守恒方程,考虑岩屑运移流型和流型转换条件,建立了适应流型变化的瞬态通用固液两相流模型;并将其应用于一口窄密度窗口井的动态井眼清洁模拟过程中,实时模拟整个钻井过程中岩屑沿井筒分布情况.研究结果表明:岩屑对环空压力分布有重要影响;成功钻穿窄安全密度窗口井的关键是实时监测岩屑对井筒压力剖面的影响,通过洗井作业清理岩屑,将井底压力控制在安全密度窗口之内.本文结果能够为洗井间隔设计提供理论依据.     

高浓度固液两相流压力测量

本文介绍了确定水煤浆流动阻力的试验装置,应用膜片或传压器的传感器,可用来测定高浓度固液两相流压力。     

两相流场粒子成像测速技术(PTV-PIV)初探

在单相ＰＴＶ－ＰＩＶ研究基础上,研究液固两相流场粒子成像图像数字测速技术．首次用ＰＴＶ技术得到直槽道中液固两相流场二维瞬时全场两相流速分布．初步探讨了两相ＰＴＶ－ＰＩＶ技术中与单相ＰＴＶ－ＰＩＶ测速技术的关键不同之处,提出两相ＰＴＶ－ＰＩＶ测速采样的两相相容性准则．为深入研究两相流场粒子成像测速技术奠定了基础．     

Measurements of thermally-induced convection in a model porous medium

The velocity field generated by thermal convection in a model porous medium is experimentally determined by means of both PIV and LDA techniques. Details of matching refraction index under non isothermal conditions are given. Fields are measured in the empty parallelepipedic cell and in a model medium made of parallel circular bundles. Results are in good agreement. Moreover, by an averaging technique, we are able to measure seeping velocity profiles.     

应用二维激光测速系统研究面流消能的紊动特性

本文应用二维激光测速系统对面流消能工下游典型流态的紊动特性进行了系统的试验研究,得到了不同来流条件下面流的时均流速、紊动强度及雷诺应力等沿主流与回流区的分布特征;计算并绘制了流线图,由此分析了淹没面流时底旋滚长度和佛劳德数的关系。对紊动能量的转换过程及耗散特征进行了计算分析,初步探明了消能机理。     

Pumping of a fluid through a microchannel by means of a bubble driven by a light beam

A new method of pumping a fluid through a microchannel device using a gas bubble-piston, set in motion by the thermocapillary force induced by a light beam, is proposed. To demonstrate the method, a model micropump has been assembled. The model consists of two reservoirs connected by two channels with a bubble-piston driven by a light beam. The pumping rate and the volume per piston stroke are evaluated experimentally. The method proposed is compared with known microfluid pumping methods. Some advantages of the new method are indicated.     

The Motion of Long Bubbles in a Network of Tubes

The motion and interaction of discrete bubbles in porous materials is studied numerically using a network model. The goal is to extend analytical results for the motion of bubbles through a single straight tube to a more realistic geometry for porous materials, modeled here as a planar network of straight tubes of different radii. The problem is characterized by two dimensionless parameters, the capillary number (Ca) and the volume fraction of bubbles (); results are characterized by determining the effective permeability of the network and the mean residence time of bubbles in the material. The simulations indicate that at low volume fraction most of the bubbles follow a limited number of high-flow pathways through the network. In this case the predictions of our simulations can be approximated by a simple analytical model. Bubbles interact with each other because their presence changes the local resistance to flow in individual tubes. As increases, interactions between individual bubbles become important resulting in a wider range of residence times in the porous material.     

An experimental investigation of outflow of liquids from single-outlet vessels

This paper considers the outflow of a liquid from a single outlet vessel, i.e. a vessel in which the outflowing liquid is displaced by another fluid which enters the vessel through the same opening. The simplest possible arrangement is investigated: a sealed axisymmetric cylindrical vessel with an outlet in its base, in which water is displaced by air.

It is shown experimentally that the average liquid discharge velocity is independent of the liquid level in the vessel and the shape of the outlet for the range of outlets employed; it increases weakly with both the diameter of the vessel and the diameter of the outlet.     

Dynamic fluid flow behaviour of a tank draining through a vertical tube

This paper describes the unsteady draining of a sealed tank partially filled with water. The water discharges via a vertical tube into an open tank at atmospheric conditions. The air inflow, compensating for the volume of the discharged liquid, enters the system in an oscillatory manner, much like the “gulping” seen in an upended beer bottle. A mathematical model, based closly on that derived by Dougall & Kathiresan [Chem. Engng Commun. 8, 289–304 (1981)], has been applied to predict the pressure fluctuations in the closed tank. The rate of water discharge from the tank has been predicted and gives a much closer agreement with experimental results than a prediction based on a steady counter-current flooding limitation approach. A drift flux model has been used to describe the two-phase flow effect in the tube and the Wallis flooding criterion has been modified for use in the slug flow regime to describe the boundary conditions at the bottom of the tube. The pressure fluctuations in the sealed tank have been measured and compared with results obtained from the mathematical prediction for a variety of tube diameters.     

Modulation of homogeneous turbulence seeded with finite size bubbles or particles

The dynamics of homogeneous, isotropic turbulence seeded with finite sized particles or bubbles is investigated in a series of numerical simulations, using the force-coupling method for the particle phase and low wavenumber forcing of the flow to sustain the turbulence. Results are given on the modulation of the turbulence due to massless bubbles, neutrally buoyant particles and inertial particles of specific density 1.4 at volumetric concentrations of 6%. Buoyancy forces due to gravity are excluded to emphasize finite size and inertial effects for the bubbles or particles and their interactions with the turbulence. Besides observing the classical entrapment of bubbles and the expulsion of inertial particles by vortex structures, we analyze the Lagrangian statistics for the velocity and acceleration of the dispersed phase. The turbulent fluctuations are damped at mid-range wavenumbers by the bubbles or particles while the small-scale kinetic energy is significantly enhanced. Unexpectedly, the modulation of turbulence depends only slightly on the dispersion characteristics (bubble entrapment in vortices or inertial sweeping of the solid particles) but is closely related to the stresslet component (finite size effect) of the flow disturbances. The pivoting wavenumber characterizing the transition from damped to enhanced energy content is shown to vary with the size of the bubbles or particles. The spectrum for the energy transfer by the particle phase is examined and the possibility of representing this, at large scales, through an additional effective viscosity is discussed.     

An analytic solution of dense two-phase flow in a vertical pipeline

According to a mathematical model for dense two-phase flows presented in theprevious paper,a dense two-phase flow in a vertical pipeline is analytically solved,and theanalytic expressions of velocity of each continuous phase and dispersed phase arerespectively derived The results show that when the drag force between two phases dependslinearly on their relative velocity,the relative velocity profile in the pipeline coincides withDarcy’s law except for the thin layer region near the pipeline wall,and that the theoreticalassumptions in the dense two-phase flow theory mentioned are reasonable.     

Three-dimensional flow in axial flow fans of non-free vortex design

Three-dimensional laser Doppler anemometer (LDA) measurements were carried out downstream of isolated axial fan rotors of non-free vortex design in order to investigate the role of radial velocity components in design. The structure of secondary flows due to non-free vortex operation was studied in detail. It is pointed out that the tangential gradient of radial velocity at midspan is nearly in direct proportion with the spanwise gradient of ideal total head rise prescribed in design. Design criteria have been established for the neglect of torsion of stream surface segments inside the blading. A linear relationship was proposed in order to estimate the pitch-averaged radial velocities at the rotor exit. Using this relationship, a proposal has been put forward for taking the radial velocity components into account in non-free vortex design with the assumption of conical stream surfaces through the blading.