A CONTRIBUTION TO THE PREDICTION OF PHASE SEPARATION IN BRANCHING CONDUITS

A phenomenological model for phase separation in branching conduits (Hwang el al., 1988) has been extended and improved. These modifications involve new models for the phase distribution at the inlet of a branching junction corresponding to four different flow regimes, and a correction for flooding in vertical junctions. This mechanistically-based model gives good agreement when compared with representative experimental data.     

Hydrodynamic properties of a turbulent confined solid-liquid jet evaluated using PIV and CFD

Particle image velocimetry is used to evaluate liquid and solid velocities and turbulence levels in the developing region of a confined solid-liquid jet. The measurements are conducted utilizing the method of matching refractive indices together with digital phase separation. The diameters of the solids are and the maximum mean volume fractions for which measurements can be performed is 1.9%, a number estimated from image analysis. The experimental results are compared with those from numerical simulations using the mixture, dispersed and per-phase realizable k-ε models together with two models for the drag force. The results show that the differences in axial velocity between the two phases are small and the axial RMS velocities generally increases with increasing volume fraction and are larger for the dispersed phase compared to the continuous phase. The numerical simulations capture the flow structure well, but generally, the continuous-phase centreline velocities are underestimated close to the inlet and overestimated further downstream. Regardless of solid loading, the per-phase turbulence model in combination with a drag force modified by a correction factor as to take into account the turbulence of the carrier phase provides the best numerical results.     

非流态化流体—颗粒流

本文应用多相流理论与颗粒介质力学研究非流态化流体—颗粒两相流动力学。建立了一系列动力学方程式,将流体压力、颗粒间接触压力、床层空隙率与颗粒和流体的性质、床的几何结构、操作条件相关联。这些方程的计算结果与大量实验数据相吻合。本文还归纳了垂直非流态化两相流的十三种操作状态,绘制了垂直移动床流体颗粒流动相图,定量地指明了各种操作状态存在的条件及其相互关系,并对理想料封状态进行了重点讨论。     

VAPOR-LIQUID FLOW THROUGH SPRING LOADED RELIEF VALVES

The behavior of a relief valve with a short throat has been studied. Measurements of discharge rates when the unit was fed with a two-phase mixture have been made at moderate pressure differentials. These experiments show that the valve behavior is similar to that of an orifice and that flashing does not occur until downstream of the flow restriction. Design techniques which enable valve discharge rates to be computed under these conditions are developed

Other data show that, when fed with a two-phase mixture and subject to high pressure differentials, relief valves with longer throats exhibit critical flow rates close to these preducted by the homogeneous-equilibrium model (HEM). Additional data are needed in order to define the transition between orifice-like and HEM choking behavior.     

Gas-assisted displacement of a viscoelastic fluid in capillary geometries

The effect of fluid viscoelasticity on the fraction of liquid deposited on the walls of capillary geometry and the pressure drop at the capillary static region are theoretically investigated using the Criminale-Ericksen-Filbey (CEF) constitutive equation to describe a non-Newtonian fluid displaced by the pressurized gas in a capillary. The singular perturbation method is used to determine the residual liquid film thickness of a viscoelastic fluid on the walls of a circular tube or a rectangular channel when displaced by another immiscible fluid. Inner and outer expansions are developed in terms of both a small parameter Ca^1/3 and a small parameter De/Ca^1/3. The method of matched asymptotic expansion is used to match the inner and outer solutions by means of a transition region between the advancing meniscus and the entrained film where the fluid rheology has its greatest effect. A detailed analysis indicates that the residual liquid film thickness of the viscoelastic fluid tends to decrease and the pressure drop across the bubble front tends to increase as the fluid becomes more viscoelastic. The theoretical results presented in this paper are in agreement with some of the experimental data and theoretical analyses available in the literature.     

LNG管道内气液相变流动传热理论的研究现状及趋势

针对液化天然气管道内流动传热理论的研究现状及趋势进行相关调研,结果表明管道内液化天然气的相变问题十分严峻,严重影响着管道的运输能力和运输安全性。为缓解这些问题的发生,主要从液化天然气的管道运输特点、液化天然气相变机理与特性以及液化天然气流型与传热三个方面进行分析比较,指出了存在的问题以及未来的发展前景,对液化天然气管道内相变流动传热的研究提供理论基础。     

Measurements of the flow of supercritical carbon dioxide through short orifices

This paper describes the methods used to measure flow rate of supercritical and two-phase CO₂ through short orifices. Orifices with diameters of 1 millimeter and orifice length-to-diameter ratios of 3.2 and 5 were tested. Flow rates through these orifices were measured over a broad range of inlet conditions in the supercritical region with orifice inlet pressures ranging from 5 MPa to 11 MPa and inlet densities ranging from 86.5 kg/m³ to 630 kg/m³. The data were compared to the isentropic real gas model for expansion of a fluid through a nozzle in order to observe the behavior of the discharge coefficient. For a given orifice inlet condition, the single-phase discharge coefficient was found to be between 0.81 and 0.87 and was independent of the pressure ratio. The discharge coefficient increased as the pressure ratio decreased when two-phase CO₂ was present with orifice inlet pressures of 7.7 MPa and 9 MPa. The critical mass flow rate and critical pressure ratio were determined for each test. The raw data from this investigation are available on the internet.This paper describes the methods used to measure flow of supercritical and two-phase CO₂ through short orifices. Orifices with diameters of 1 millimeter and orifice length-to-diameter ratios of 3.2 and 5 were tested. Flow rates through these orifices were measured over a broad range of inlet conditions in the supercritical region with orifice inlet pressures ranging from 7.7 MPa to 11 MPa and inlet densities ranging from 111 kg/m³ to 630 kg/m³. The data were compared to the isentropic real gas model for expansion of a fluid through a nozzle in order to observe the behavior of the discharge coefficient. For a given orifice inlet condition, the single-phase discharge coefficient was found to be between 0.81 and 0.87 and was independent of the pressure ratio. The discharge coefficient increased as the pressure ratio decreased when two-phase CO² was present with orifice inlet pressures of 7.7 MPa and 9 MPa. The critical mass flow rate and critical pressure ratio were determined for each test. The raw data from this investigation are available on the internet.     

Phase separation and phase inversion of polyurethane networks

A series of polyurethane networks were prepared from MDI (4,4¹-diphenyl methane diisocyanate), ethylene glycol and a polyoxyethylene-tipped polyoxypropylene triol. The phase separation and phase inversion phenomena of these polyurethane networks were investigated by differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA) and measurement of their tensile properties. The DSC and DMA data indicate that the segmented copolyurethanes possess a two-phase morphology comprising soft and hard segments. It can be found from DSC data that the polyether soft segments exhibit a T_g (glass transition temperature) of –60 °C, and the aromatic hard segments display a T_g of about 128 °C. Two T_gs corresponding to the comprised segments can also be found by DMA for some segmented polyurethanes. Varying the content of aromatic hard segments over the range from 0 to 80 wt% changes the material behavior from a soft rubber through a highly extensible elastomer to a brittle semi-ductile glassy material. Based on the property-composition plots, phase inversion appears to occur at a hard segment content of about 50 wt%.     

Structural disorder effect on the structural and magnetic properties of Pr0.4Re0.1Sr0.5−yBayMnO3 manganites (Re = Pr,Sm, Eu,Gd, Dy and Ho)

The influence of the A-site cation size-disorder σ² on the structural and magnetic properties of the polycrystalline Pr_0.4Re_0.1Sr_0.5−yBa_yMnO₃ (Re = Pr, Sm, Eu, Gd, Dy and Ho) samples with a constant average ionic radius <r_A> = 1.2445 Å, is investigated. All samples were synthesized using the solid-state reaction. Rietveld refinement of the X-ray diffraction patterns shows that the substitution generates a structural transition from tetragonal to orthorhombic symmetry. The temperature dependence of magnetization indicates a weakening of ferromagnetism by the increase of σ². The large difference between the field cooled and zero field cooled magnetization below Curie temperature suggests the presence of an inhomogeneous mixture of a ferromagnetic and antiferromagnetic domains at low temperature. The maximum of the magnetic entropy change decreases with increasing the mismatch effect. However, several peculiarities were observed in the magnetic behavior indicating that σ² is not the only factor controlling the physical properties; the nature and the magnetic moment of the substituent should be taken in consideration.     

Self-stratifying coatings containing barrier and active anticorrosive pigments

The influence of decorative and anticorrosive pigments on the distribution of pigments and protective properties of self-stratifying epoxy/acrylic coating systems was investigated. The separation of pigments was determined basing on their properties and the type of additives used and was expressed as a factor determining the separation of the pigments between the upper and bottom layer. The pigment distribution coefficient was calculated basing on the colour difference between the upper and bottom layer as well as by means of the XRF method.     

搅拌釜内流场三维数值模拟及功率预测

大型搅拌釜,尤其是涉及传热或两相介质搅拌的容器,其搅拌效果和功率往往难以预测。针对大型搅拌釜的搅拌器设计、流场结构模拟和功率预测等问题,采用CFD数值模拟技术,对搅拌釜内部的三维流场进行了数值计算。分析了搅拌釜内的流动结构,计算了不同曝气量时的搅拌功率,获得了详细的流场信息和各项特性参数。     

Multiferroic (Nd,Fe)-doped PbTiO3 ceramics with coexistent ferroelectricity and magnetism at room temperature

We report the structural, dielectric, elastic, ferroelectric and ferromagnetic properties of multiferroic (Nd, Fe)-doped PbTiO3 perovskite ceramics with composition (Pb_0.88Nd_0.08)(Ti_0.94Fe_0.04Mn_0.02)O₃, prepared by different solid state reaction methods: the first one based on a single-stage calcination (Method I) and the second based on a double-stage calcination (Method II). Structural, dielectric and anelastic measurements evidenced a double phase transition for samples prepared by Method I, which has been attributed to phase separation. This phase separation has been confirmed also by TEM and HRTEM investigations. Samples prepared by Method II showed a single phase transition from paraelectric to ferroelectric phase. We found coexistent ferroelectric and ferromagnetic properties, also at room-temperature, but only for ceramics prepared by Method II. The crucial role of calcination process for avoiding phase separation and obtaining homogeneous structures with ferroelectric and ferromagnetic order is underlined.     

Droplet–Droplet Interactions in Spray Drying by Using 2D Computational Fluid Dynamics

A 2D axisymmetric model of the spray drying process is presented. The two-phase flow theoretical model is based on a combined Eulerian-Lagrangian approach and takes binary interactions (coalescence or bouncing) between spray droplets into consideration. Validation of the model (incorporated in FLUENT 6.3.26) demonstrated good agreement and consistency with the literature data. The results of transient simulations showed that droplet–droplet interactions displace the region of heat and mass transfer from the central core toward the periphery of the drying chamber. It was also found that insulation of the spray dryer can substantially affect temperature and humidity patterns, whereas its influence on the velocity flow field is less marked.     

Droplet-Droplet Interactions in Spray Drying by Using 2D Computational Fluid Dynamics

A 2D axisymmetric model of the spray drying process is presented. The two-phase flow theoretical model is based on a combined Eulerian-Lagrangian approach and takes binary interactions (coalescence or bouncing) between spray droplets into consideration. Validation of the model (incorporated in FLUENT 6.3.26) demonstrated good agreement and consistency with the literature data. The results of transient simulations showed that droplet-droplet interactions displace the region of heat and mass transfer from the central core toward the periphery of the drying chamber. It was also found that insulation of the spray dryer can substantially affect temperature and humidity patterns, whereas its influence on the velocity flow field is less marked.     

Design Criteria for Oilfield Separators Improved by Computational Fluid Dynamics

Oilfield separator data ranging from light‐oil conditions to heavy‐oil conditions were incorporated into suitable two‐phase and three‐phase computational fluid dynamics (CFD) models to provide improved design criteria for separator design methods. The CFD simulation results revealed that the most important affecting parameters are vapor density and oil viscosity. In contrast with the classic design methods, noticeable residence times were required for liquid droplets to penetrate through the fluid interfaces. Moreover, it was indicated that the Abraham equation should be used instead of the Stokes' law in the liquid‐liquid separation calculations. The velocity constraints caused by re‐entrainment in horizontal separators were also studied and led to novel correlations.     

Numerical simulations of gas–liquid flow in thermal sorption processes

Thermal storage systems, used, e.g., for domestic heating, must be able to compensate the mismatch between supply and demand. The most efficient techniques for thermal storage are based on sorption storage processes. Usually in sorption, the adsorption process occurs in combination with a solid state adsorbent, whereas absorption takes place in a liquid/gas system. During such sorption processes the flow behavior of the carrier medium is crucial for the efficiency of a falling film absorber. In this work the hydrodynamics of the falling liquid film in two geometrical setups, namely on an inclined plane and over two horizontal parallel tubes, is studied. For the simulation the Eulerian–Eulerian model of the software ANSYS CFX and the interFoam application of the open source software OpenFOAM were used. The numerical results of the two geometries were compared with each other and also with existing data from literature to predict the performance of a sorption storage regarding the specific wetted area and the needed height for gravity driven film absorption.     

Study on the solid–liquid suspension behavior in a tank stirred by the long-short blades impeller

We investigated the solid–liquid suspension characteristics in the tank with a liquid height/tank diameter ratio of 1.5 stirred by a novel long-short blades(LSB) impeller by the Euler granular flow model coupled with the standard k–ε turbulence model. After validation of the local solid holdup by experiments,numerical predictions have been successfully used to explain the influences of impeller rotating speed,particle density, particle size, liquid viscosity and initial solid loading on the soli...