水平矩形管内气液两相流界面波特性

<正>气液两相流中界面波的存在对传热、传质、阻力特性及稳定性都有很大影响。前人有关界面波的研究大多偏重于两相流中界面波的类型及其转变,而对其特征参数变化规律(如振幅、波长、频率和速度等)的研究则很少。但界面波对气液两相流流动阻力和流动结构影响机理的深入研究必须以了解界面波的各特性参数为前提,同时界面波有关特性参数的深入研究也可为气液两相流的数学理论化提供实验基础。 本文以气、水为工质,系统研究了水平矩形管内气液两相流的界面波特性。根据界面波在时域、幅域内的不同特征区别出了各种类型的波并给出了相应的波形和流型图。着重研究了界面波各特征量随气液两相流量变化的变化规律。     

BASIC EQUATION OF TURBULENCE AND MODELING OF INTERFACIAL TRANSFER TERMS IN GAS-LIQUID TWO-PHASE FLOW

Turbulence is one of the most important phenomena in analyzing thermohydrodynamic characteristics of gas-liquid two-phase flow. For the purpose of accurate prediction of the turbulence phenomena, a basic conservation equation of Reynolds stress was derived based on the local instant formulation of mass and momentum conservations of two-phase flow. In this equation, interfacial transfer terms of turbulence appear as source terms. Detailed considerations on these transport terms were carried out. It was shown that they consist of a viscous damping term due to small scale interfacial structures, a drag induced turbulence generation term due to large scale interfacial structures and a term representing the exchange between surface energy and turbulence. Based on the mechanistic modeling and turbulence modulations, carried out were physical interpretations of interfacial area concentrations of small and large scale interfacial structures, a viscous damping term due to small scale interface and turbulence generation term due to large scale interface.     

INTERFACIAL INTERACTIONS AND SECONDARY FLOWS IN STRATIFIED TWO-PHASE FLOW

In this paper are analysed the interactions between a surface wave field and the kinematic structures above and below the waves, in gas-liquid stratified flow in a rectangular cross sectional channel. The analysis is based on experimental data both on the local structure of the flows and on the deformation of the gas-liquid surface. The basic phenomena that have been observed are: on the one hand, the waves that propagates over the liquid surface can exhibit a crosswise distribution of amplitude; on the other hand, secondary flows can be generated both in the gas and in the liquid. A theoretical attempt is developed to explain the distribution to wave amplitude: in fact, the waves propagate over a non uniform liquid current. On the one hand, the wave field interact with the liquid current to generate secondary flows below the waves. On the other hand, the wave amplitude distribution interacts with the gas flow; the wave distribution can be considered as a non uniform interfacial roughness which generates Prandtl second type secondary flows above the waves. These physical mechanisms which are based on the analysis of experimental results are also validated with numerical simulations.     

MEASUREMENT OF LIQUID-LIQUID INTERFACIAL SHEAR VISCOSITY: THE UNSTEADY STATE DEFORMATION OF AN INTERFACE IN A CYLINDRICAL CELL

The theoretical background of a new method for the measurement of liquid-liquid interfacial shear viscosities is presented. The method is simple in design and conducive to routine measurements. Liquid-liquid interfacial shear viscosities are measured by observation of the unsteady state deformation of the interface after a slowly rotating cylindrical cell containing the liquids is abruptly halted. The deformation is established with tracer particles located at the interface between two liquids. Presented here are correlations which relate the traversed angle of the panicles to the interfacial shear viscosity, the viscosities and densities of the bulk phases, and the cup dimensions. Correlations show that the method is sufficiently sensitive to allow measurements of interfacial shear viscosities ranging from 0.001 to 1.0 surface poise (sp). Preliminary data showing good agreement between theoretical predictions and experimental observations for a system expected to show negligible interfacial shear viscosity are also provided.     

MODELING AND ANALYSIS OF CHANNEL-TO-CHANNEL INSTABILITIES IN BOILING SYSTEMS

An analysis has been performed for the instability modes of unventilated boiling parallel channels and an associated hydraulic loop. This analysis was based on a one-dimensional space-dependent model, using linearized equations of boiling system dynamics. Experimental verification of the model is shown. The relationship between classical parallel channel instabilities, channel-to-channel in stabilities, and loop instabilities has been investigated. The theoretical considerations are illustrated with numerical calculations in both the time and frequency domains.     

预制整体模塑料在流道内的延伸流动及其影响

理论分析了BMC(预制整体模塑料 )在注射喷嘴收敛流道内的延伸应变速率分布 ,引入延伸应变速率积来衡量BMC熔体中玻璃纤维断裂破坏及其对制品强度影响的程度。结果表明 ,延伸应变速率和延伸流道长度是喷嘴收敛流道影响制品强度的 2个因素 ,而这 2个因素与流道收敛角有密切的关系 ;延伸应变速率积越大 ,制品的强度相应地越低 ;为尽可能提高BMC注射制品的机械强度 ,最后理论结合实验找出较合适的注射喷嘴收敛半角范围为 2 0～ 3 5°。     

AN EXPERIMENTAL STUDY OF AN INCLINED BUOYANT PLANE TURBULENT AIR JET

An experimental study of the effects of buoyancy forces resulting from temperature differences on the mean flow and turbulence characteristics of a plane turbulent jet discharged at an angle to the horizontal has been undertaken. The jets were generated by discharging air through a rounded nozzle which was 10 mm wide by 580 mm long. The discharged air could be heated and tests were undertaken with discharge temperatures of 20° and 40°C above the ambient air temperature at a single nozzle discharge velocity which gave a discharge Reynolds number of approximately 1700. Tests were undertaken with angles of jet discharge to the horizontal of 0°, 30°, 60° and 90°. Velocity and temperature measurements were undertaken using hot wire anemometers. Measurements of the mean velocity and temperature, the turbulence normal and shear stresses, the temperature fluctuation intensity and the two components of the turbulence heat flux were obtained. Profiles of these quantities were measured at six equally spaced positions to a distance of approximately 60 nozzle widths from the discharge plane. Measurements at much more closely spaced intervals were also taken along the jet “centre-line”, this being defined as the locus of the point of maximum velocity in the jet.     

非流态化气固流通过斜管与孔口的动力学

应用散料力学与多相流理论研究非流态化气体-颗粒两相流通过垂直与倾斜管道及孔口的动力学,建立了动力学方程,用以预测各种条件下的颗粒物料通过孔口的流率.方程的计算结果与各种条件下取得的大量实验数据相吻合,从而使颗粒物料通过孔口流率的计算由经验关联逐步上升为理论预测.     

INTERFACIAL FRICTION FACTORS IN COUNTERCURRENT STRATIFIED TWO-PHASE FLOW

Interfacial shear stresses have been determined for a countercurrent stratified flow of air-water in a nearly-horizontal rectangular channel based upon measurements of pressure drops, gas velocity profiles and mean film thicknesses. The interfacial friction factors of air-water flow were of the same order of magnitude as those of steam-water flow in the three-dimensional wave regime. A new dimensionless intensity of wave height fluctuation, which may be regarded as an effective roughness of the interface, was proposed. It showed that this dimensionless parameter has a unique relationship with the equivalent roughness for the gas-liquid interface calculated using the Nikuradse equation for both air-water and steam-water data. In addition, an empirical correlation of the interfacial friction factor for air-water and steam-water flows has been developed for practical application.     

WATER MIST FLOW IN A SUPERCONDUCTING MAGNET INCLINED AT VARIOUS ANGLES

Water mist (diamagnetic) flow in a superconducting magnet of 10 T at various angles is studied experimentally and numerically. Water mist is produced by ultrasonic atomizers and fed into a cylindrical Plexiglas pipe (inner diameter, 90 mm) placed in a bore space of an inclined superconducting magnet. The water mist is found to stop at some locations in the magnet at inclined angles ψ ≤ π/6. At ψ ≥ π/4, the amount of mist flowing out of the other opening of the pipe increases with an increase in inclined angle. In the computation of this phenomenon, water mist is simulated with 1000 water droplets of 3 μm diameter. Brownian motion is considered and the Langevin equation is solved. The numerical results show that at ψ ≤ π/6, most of the water droplets accumulate above the magnetic coil. However, at ψ ≥ π/4, with an increase in inclined angle, the number of water droplets passing through the magnetic coil increases.     

WATER MIST FLOW IN A SUPERCONDUCTING MAGNET INCLINED AT VARIOUS ANGLES

Water mist (diamagnetic) flow in a superconducting magnet of 10 T at various angles is studied experimentally and numerically. Water mist is produced by ultrasonic atomizers and fed into a cylindrical Plexiglas pipe (inner diameter, 90 mm) placed in a bore space of an inclined superconducting magnet. The water mist is found to stop at some locations in the magnet at inclined angles ψ ≤ π/6. At ψ ≥ π/4, the amount of mist flowing out of the other opening of the pipe increases with an increase in inclined angle. In the computation of this phenomenon, water mist is simulated with 1000 water droplets of 3 μm diameter. Brownian motion is considered and the Langevin equation is solved. The numerical results show that at ψ ≤ π/6, most of the water droplets accumulate above the magnetic coil. However, at ψ ≥ π/4, with an increase in inclined angle, the number of water droplets passing through the magnetic coil increases.     

AN ANALYSIS OF FLOW FILM BOILING OVER AN INCLINED SURFACE EMBEDDED IN POROUS MEDIA

The rate of heat dissipation during flow film boiling from inclined surfaces embedded in porous media is investigated both theoretically and experimentally. The theoretical model relies on the well established Darcy model for the flow both inside the vapor layer and inside the forced convection layer surrounding the vapor film. The main focus is to study the effects of wall temperature, liquid subcooling, wall suction, and orientation of the heated surface on the heat transfer phenomenon. The resulting similarity equations are integrated numerically by use of the fourth-order Runge Kutta method. Systematic “shooting” is required to satisfy the boundary conditions at the liquid-vapor interface and at infinity. Results are reported for the behavior of the vapor film thickness and both the local and average heat transfer coefficients as a function of vapor superheat and liquid subcooling. Experiments were conducted in Freon-113 and a porous medium consisting of 2.8 mm glass beads to verify the theoretical findings, and excellent agreement was found between theory and experiments.     

INTERFACIAL TRANSPORT OF ENERGY IN LAMINAR OPEN CHANNEL AND FILM FLOWS

A new dispersion theory applicable to interfacial transport is used to analyze unsteady two-dimensional thermal pollution in laminar open channel and film flows. A strip source across the width of the flow at a variable depth is considered. The unsteady state temperature distribution depends on three time variable coefficients which are the convection, dispersion and exchange coefficients and expressions for these coefficients are derived from first principles. The exchange coefficient in the theory depends on time, the thickness and position of the source and the interfacial transport rate. Furthermore, the convection and the dispersion coefficients are affected substantially by interphase transport. The results, which are relevant to reactor design and such separation processes as chromatography, are discussed in physical terms and are compared to those for laminar flow in tubes. The theory can be applied readily to turbulent flow systems but computing the coefficients is a more formidable job.     

INTERFACIAL TRANSPORT OF ENERGY IN LAMINAR OPEN CHANNEL AND FILM FLOWS

A new dispersion theory applicable to interfacial transport is used to analyze unsteady two-dimensional thermal pollution in laminar open channel and film flows. A strip source across the width of the flow at a variable depth is considered. The unsteady state temperature distribution depends on three time variable coefficients which are the convection, dispersion and exchange coefficients and expressions for these coefficients are derived from first principles. The exchange coefficient in the theory depends on time, the thickness and position of the source and the interfacial transport rate. Furthermore, the convection and the dispersion coefficients are affected substantially by interphase transport. The results, which are relevant to reactor design and such separation processes as chromatography, are discussed in physical terms and are compared to those for laminar flow in tubes. The theory can be applied readily to turbulent flow systems but computing the coefficients is a more formidable job.     

水平管内油气两相弹状流的产生

<正>近几十年来,水平管内气水两相弹状流发生的研究已引起各研究者的注意.Koldyhan＆a[什1970年）首先采用了古典的线性稳定分析方法研究了弹状流发生的初始条件,并得到了其发生     

波纹流道中流体流动特性的数值与实验研究

引　言翅片是紧凑式热交换器和化工设备的基本元件之一 ,对传热传质过程的强化起着重要作用[1～ 4].本文研究的波纹型翅片是翅片型式的一种 ,它是在平直翅片的基础上压成一定的波纹 ,横截面形状类似于平直翅片 .这种波纹形结构导致了很复杂的流动 ,使流体在弯曲流道中不断地改变流动方向 ,以促进流体的湍流 .有关波纹型翅片方面的研究报道很少 .波纹型流道的计算比较复杂 ,文献 [5,6]采用不同的方法、不同的网格生成技术对波纹形流道充分发展段的层流流场和温度场进行了数值模拟 .本文运用ＳＩＭＰＬＥ算法对波纹形流道的流场分布进行模拟计…     

INFLUENCE OF AN INDUCED MAGNETIC FIELD ON PERISTALTIC TRANSPORT IN AN ASYMMETRIC CHANNEL

In this study, we investigate the effects of an induced magnetic field on the peristaltic transport of a Phan-Thien-Tanner (PTT) fluid in an asymmetric channel. Asymmetry in the flow is induced because of wave trains with different amplitudes and phases. Development of mathematical analysis is made under long wavelength and low Reynolds number approximations. Explicit expressions of stream function, pressure gradient, magnetic force function, axial induced magnetic field, and current density are derived. Computation of pressure rise is based upon numerical integration. The obtained expressions are carefully analyzed through physical interpretation.     

螺旋管内油-水液液两相流流型

在两种不同放置位置螺旋管内进行了油 -水液液两相流流型的实验研究 ,定义了各种不同流动条件下油-水两相流的流型 ,给出了螺旋管内液液两相流的流型图 .进而讨论了各流型之间转变的机理 ,并考察了螺旋管结构尺寸及放置方式对油水两相流流型及相转变特性的影响 .     

INTERFACIAL TEMPERATURE RISE AND MULTIPLICITY IN NONISOTHERMAL GAS-LIQUID CSTRs

For exothermic gas-liquid reactions.the interfacial temperature affects the gas-solubility, interfacial reaction rate, mass transfer rate and the bulk temperature of the reactor. An overall heat balance on the reaction-diffusion 'film' relates the interfacial temperature to the bulk variables (temperature, concentration), and the interfacial variables (enhancement factor, etc.). While the interfacial balance shows (apparent) multiplicity of interfacial temperature for a given bulk temperature, uniqueness results when the interfacial balances are solved together with the mass and energy balances for the reactor bulk. It is shown that the state of interface and bulk are intimately related, and thus, consideration of interfacial temperature does not increase the multiplicty of a gas-liquid CSTR. Simple a priori estimates are derived for the interfacial temperature. All of the results are found to be rather independent of kinetic details. The interfacial temperature rise is encouraged by low interfacial heat and mass transfer coefficients, by small liquid residence time in the bulk and by increased heat losses from the reactor bulk.