涡街流量计测量气液混相流的不确定度

涡街流量计可用于部分混相流的测量，但迄今为止有关混相流对涡街流量计测量特性的影响还缺少理论研究和实践经验。在体积含气率为2．0％-15．0％的范围内，评定了用涡街流量计测量气液混相流的不确定度，提出涡街流量计测量气液混相流的不确定度计算式。实验以空气和水为介质产生气液混相流，涡街信号通过管壁差压法采集，涡街频率通过功率谱分析获得。结果表明在保持涡街流量计一定测量准确度的前提下，涡街流量计相对扩展不确定度随气液混相流流量及其体积含气率的分布比较均匀；在涡街频率测量的不确定度分量中，由重复性和复现性引起的相对标准不确定度随流量的变化呈现出较强的随机性，而由频率分辨率引起的相对标准不确定度则随着流量的增加而减小。在本研究的流量与体积含气率范围内，由气液混相流引起的涡街流量计附加相对不确定度小于2．0％。这一研究为分析气液混相流对涡街流量计测量特性的影响提供了有益的借鉴。

气-液混相流在静态混合器中流体力学性能的探讨

静态混合器是一种新型高效的化工单元操作设备.本文通过对其流体力学特性的研究,以简易的实验方法,提出气-液混相流在静态混合器中压力损失的关联式.其误差仅为10%左右.对于工程设计和计算具有实际意义.

内混式二相流喷嘴流量特性

结合相关理论,以水、润滑油和十二烷基硫酸钠(SDS)溶液作为液体介质,详细研究了操作参数(气液比)和液体物性(粘度、表面张力)对一种典型的内混式二相流喷嘴流量特性的影响,通过对实验数据的分析得出了一些重要结论。随着液体介质粘度的增加,气液压力要随之增加,而表面张力的增加,气液压力基本上保持不变。根据大量的实验数据,回归出了内混式雾化喷嘴的液体流量系数的经验关联式。

三相循环流化床蒸发器防除垢机理

A model of "mixed phase flow" for preventing and cleaning fouling on inside tube wall by increasing three phase flow shearing stress was presented.The model can be used to study the mechanisms of preventing and cleaning fouling in the three phase circulating fluidized bed evaporator.The individual effects of operational parameters on three-phase flow shearing stress were studied.A saturated bittern solution was chosen as the work material.The fouling period of the saturated bitten could be prolonged effectively by increasing the amount of solid particles.

基于分相技术的油气计量系统探讨

针对目前深海油气田水下生产系统中油气分离和计量的技术要求,文章从T型三通的相分离原理出发,根据T型管分支管路流量低于临界值时,分流系数与入口两相流干度呈线性关系的规律,结合传感器、单片机和串口通讯技术提出了一种进行混相计量的方法,并初步设计了基于T型管分相的油气计量系统。

三维可压缩Navier-Stokes-Allen-Cahn方程组Cauchy问题的适定性

研究了一类刻画具有扩散界面的非混相两相流模型,即可压缩Navier-Stokes-Allen-Cahn方程组的Cauchy问题。在初始小扰动的条件下,通过能量估计的方法证明了三维Navier-Stokes-Allen-Cahn方程组全局强解的存在唯一性。

Chaotic Study in a Large Jetting Fluidized Bed with a Vertical Nozzle

The pressure fluctuation in a large jetting fluidized bed with a vertical nozzle was examined based on deterministic chaos theory. The effects of the jetting gas velocity and the static bed height on the correlation dimension were investigated. The correlation dimension increased with increasing jet gas velocity. At the same jet gas velocity, the higher the static bed height, the greater the correlation dimension is. The variations of correlation dimension and standard deviation of pressure fluctuation with gas jet velocity exhibited a similar shape and trend.

Numerical Investigation on Mixing Efficiency and Exponential Fluid Stretching in Chaotic Mixing

The stretching and folding of fluid element during chaotic mixing field is studied using numerical method. The chaotic mixing process is caused by periodic secondary flow in a twisted curved pipe. Using the nonlinear discrete velocity field as the dynamical system, the present study connects the fluid particle's stretching along its trajectory in one period to a linearized time-varying variational equation. After numerical approximation of the variational equation, fluid stretching is calculated on the whole cross section. The stretching distribution shows an exponential fluid stretching and folding, which indicates an excellent mixing performance.

Study on Liquid-Phase Axial Dispersion in Converging Taper Liquid-Solid Fluidized Beds

It is found analytically that the parabolic radial profile of liquid velocity in cylindrical liquid-solid fluidized bed (LSFB) causes particles to circulate around some radial position. This is the main reason for liquid-phase axial dispersions. The liquid-phase axial dispersion is depressed as the liquid velocity presents a flatter Bessel radial profile in a converging taper LSFB. The void fraction increases with axial distance in converging taper LSFB. The behavior produces less liquid-phase axial dispersion. Experimental results show good coincidence.

Gas-Liquid Two-Phase Axial Backmixing Through Structured Packing at Elevated Pressure

An experimental study of the extent of axial backmixing in both gas and liquid phases was conducted in a 150 mm ID column packed with Mellapak 250Y corrugated structured packing. The column was operated at pressures ranging from 0.3 MPa to 2.0MPa with nitrogen and water flowing countercurrently through the packing. The amount of axial backmixing was experimentally evaluated by the pulse response techniques using hydrogen in gas phase and an aqueous solution of NaCl in liquid phase as inert tracers. The response of the tracer was monitored by means of thermal conductivity in the gas phase and electrical conductance in the liquid phase. The experimentally determined residence time distribution (RTD) curves were interpreted in terms of the diffusion-type modei. The results indicated that the axial backmixing in the gas increased notably with gas flowrate and slightly with operating pressure and liquid flowrate. The liquid-phase axial backmixing was an increasing function of both gas and liquid flowrates and insensitive to pressure. Various correlations were developed for reproducing the experimental mixing data. The agreement between experimental and correlated data appeared to be acceptable and within ±20% of difference.

Numerical Simulation of Enhanced Oil-Water Separation in a Three-Stage Double-Stirring Extraction Tank

Numerical simulation of enhanced fluid flow characteristics in a three-stage double-stirring extraction tank was conducted with the coupling of an Eulerian multiphase flow model and a Morsi-Alexander interphase drag force model. Results show that the addition of a stirring device into the settler can efficiently reduce the volume fraction of out-of-phase impurity in the outlet, and accelerate the settling separation of oil-water mixture. Such addition can also effectively break down the oil-water-wrapped liquid droplets coming from the mixer, inhibit reflux from the outlet, and improve the oil-water separation. The addition of a stirring device induces ignorable power consumption compared with that by the mixer, and can thus facilitate the commercialized promotion of this novel equipment.

Prediction of Phase Behavior for Styrene/CO2/Polystyrene Mixtures

A lattice fluid model, Sanchez-Lacombe equation, is used to predict the phase behavior for a styrene/CO2/polystyrene ternary sys-tem. The binary parameters involved in the equation were optimized using experimental data. Phase diagrams and the distribution coefficients of styrene between polymer phase and fluid phase are obtained over a wide range of pressure, temperature and composition. The analysis of ter-nary phase diagrams indicates that this system at relatively high pressure or low temperature may display two-phase equilibrium, and at low pressures or high temperatures three-phase equilibrium may appear. The distribution coefficients of styrene between the fluid phase and the polymer phase increase asymptotically to unity when the concentration of styrene increases. The results provide thermodynamic knowledge for further exploitation of supercritical carbon dioxide assisted devolatilization and impregnation.

Comparison of the Reynolds-averaged Turbulence Models on Single Phase Flow Simulation in Agitated Extraction Columns

The flow field of liquid phase (water) of agitated extraction columns is simulated with the help of computational fluid dynamics (CFD). Four kinds of Reynolds-averaged turbulence models, i.e. the standard k-ε model, the RNG (renormalization group) k-s model, the realizable k-ε model and the Reynolds stress model, are compared in detail in order to judge which is the best model in terms of the accuracy, less CPU time and memory required. The performance of the realizable k-s model is obviously improved by reducing the model constant from C2 = 1.90 to C2 = 1.61. It is concluded that the improved realizable k-e model is the optimal model.

Mixture temperature prediction of waxy oil–water two-phase system flowing near wax appearance temperature

Temperature sensitivity of waxy crude oils makes it difficult to study their flow behaviour in the presence of water especially near their wax appearance temperature （WAT）. In this study a method was proposed and implemented to mitigate such difficulties which was applied in predicting mixture temperatures （Tin） of a typical Malaysian waxy crude oil and water flow in a horizontal pipe. To this end, two analytical models were derived firstly from calorimetry equation which based on developed two correlations for defining crude oil heat capacity actualized from the existed specific heat capacities of crude oils. The models were then applied for a set of experiments to reach the defined three predetermined Tm （26 ℃, 28 ℃ and 30 ℃）. The comparison between the predicted mixture temperatures （Tin,1 and Tin,2） from the two models and the experimental results displayed acceptable absolute average errors （0.80% 0.62%, 0.53% for model 1; 0,74%, 0.54%, 0.52% for model 2）. Moreover, the average errors for both models are in the range of standard error limits （4-0,75Z） according to ASTM E230. Conclusively, the proposed model showed the ease of obtaining mixture temperatures close to WAT as predetermined with accuracy of ± 0.5 ℃approximately for over 84% of the examined cases. The method is seen as a practical reference point to further study the flow behaviour of waxy crudes in oil-water two-phase flow system near sensitive temperatures.

分汊河道分沙的三维数值模型

为分析汊道口门处水流结构对悬移质分沙的影响,采用带旋流修正的k-ε双方程紊流模型,对分汊河道分流口门处的三维水流结构进行精确计算,并在此基础上,采用可考虑相间滑移的混相流模型对不同形态分汊河道的悬移质分沙进行计算。计算结果显示了分汊口门处表底层水流的差异及横向环流的存在等现象,与前人的实验值吻合良好。计算结果表明,分汊口门处的环流强弱和悬移质垂线分布是影响汊道分沙比与分流比关系的主要因素。

Mixing Characteristics of Pulsed Air-assist Liquid Jet into an Internal Subsonic Cross-flow

Penetration depth,spray dispersion angle,droplet sizes in breakup processes and atomization processes are very important parameters in combustor of air-breathing engine.These processes will enhance air/fuel mixing inside the combustor.Experimental results from the pulsed air-assist liquid jet injected into a cross-flow are investigated.And experiments were conducted to a range of cross-flow velocities from 42～136 m/s.Air is injected with 0～300kPa,with air-assist pulsation frequency of 0～20Hz.Pulsation frequency was modulated by solenoid valve.Phase Doppler Particle Analyzer(PDPA) was utilized to quantitatively measuring droplet characteristics.High-speed CCD camera was used to obtain injected spray structure.Pulsed air-assist liquid jet will offer rapid mixing and good liquid jet penetration.Air-assist makes a very fine droplet which generated mist-like spray.Pulsed air-assist liquid jet will introduce additional supplementary turbulent mixing and control of penetration depth into a cross-flow field.The results show that pulsation frequency has an effect on penetration,transverse velocities and droplet sizes.The experimental data generated in these studies are used for a development of active control strategies to optimize the liquid jet penetration in subsonic cross-flow conditions and predict combustion low frequency instability.

Direct Numerical Simulation of Gas-Solid Two-Phase Mixing Layer

In this paper, the spatially evolving of the higher Reynolds numbers gas-solid mixing layer under compressible conditions was investigated by a new direct numerical simulation technology. A high-resolution solver was performed for the gas-phase flow-field, particles with different Stokes numbers were traced by the Lagrangian approach based on one-way coupling. The processes of the vortex rolling up and pairing in the two-dimensional mixing layer were captured precisely. The large-scale structures developed from the initial inflow are characterized by the counter-rotating vortices. The mean velocity and the fluctuation intensities profiles agree well with the experimental data. Particles with smaller Stokes numbers accumulate at the vortex centers due to the smaller aerodynamic response time; particles with moderate Stokes numbers tend to orbit around individual streamwise vortices and in the periphery of paring vortices; particles with larger Stokes numbers disperse less evenly, showing a concentration distribution in the flow field.

Research on the control method for voltage-current source hybrid-HVDC system

The hybrid-HVDC topology,which consists of line-commutated-converter(LCC)and voltage source converter(VSC)and combines their advantages,has extensive application prospects.A hybrid-HVDC system,adopting VSC on rectifier side and LCC on inverter side,is investigated,and its mathematic model is deduced.The commutation failure issue of the LCC converter in the hybrid-HVDC system is considered,and a novel coordinated control method is proposed to enhance the system commutation failure immunity.A voltage dependent voltage order limiter(VDVOL)is designed based on the constant DC voltage control on the rectifier side,and constant extinction angle backup control is introduced based on the constant DC current control with voltage dependent current order limiter(VDCOL)on the inverter side.The hybrid-HVDC system performances under normal operation state and fault state are simulated in the PSCAD/EMTDC.Then,system transient state performances with or without the proposed control methods under fault condition are further compared and analyzed.It is concluded that the proposed control method has the ability to effectively reduce the probability of commutation failure and improve the fault recovery performance of the hybrid-HVDC system.

Influence of wall motion on particle sedimentation using hybrid LB-IBM scheme

We integrate the lattice Boltzmann method(LBM) and immersed boundary method(IBM) to capture the coupling between a rigid boundary surface and the hydrodynamic response of an enclosed particle laden fluid. We focus on a rigid box filled with a Newtonian fluid where the drag force based on the slip velocity at the wall and settling particles induces the interaction. We impose an external harmonic oscillation on the system boundary and found interesting results in the sedimentation behavior. Our results reveal that the sedimentation and particle locations are sensitive to the boundary walls oscillation amplitude and the subsequent changes on the enclosed flow field. Two different particle distribution analyses were performed and showed the presence of an agglomerate structure of particles. Despite the increase in the amplitude of wall motion, the turbulence level of the flow field and distribution of particles are found to be less in quantity compared to the stationary walls. The integrated LBM-IBM methodology promised the prospect of an efficient and accurate dynamic coupling between a non-compliant bounding surface and flow field in a wide-range of systems. Understanding the dynamics of the fluid-filled box can be particularly important in a simulation of particle deposition within biological systems and other engineering applications.