旋流器内气液两相流动的理论分析

气-液旋流分离过程是气-液两相的三维强旋流运动。以漂移流动模型和颗粒轨迹方程为基础,采用欧拉-拉格朗日方法建立一种新的气液两相流动机理模型。该模型可以用来直接计算气液旋流分离器内部流场中连续相、分散相(液滴)的速度分布,通过计算能够预测旋流器内部的浓度分布,并通过对影响气液分离效率的主要原因——出口气体中的液滴夹带进行分析计算,预测旋流器的分离性能。     

油水旋流分离器内部流场的CFD模拟

采用计算流体力学数值模拟方法研究油水旋流分离器的内部流场,模拟出分离器内轴向速度变化规律,得到钻井液气液旋流器内部流场的特征。分析油水旋流分离器内部油相体积浓度分布,得到了油水旋流分离器内部流场的分布规律和油水两相流的分离特性,为油水旋流分离器的工艺设计提供了参考依据。     

柱状气液旋流器压力场和速度场模拟分析

利用计算流体动力学(CFD)方法,采用流体力学软件FLUENT,针对柱状气液旋流分离器进行了内部流场、压力场和气相浓度的分析,得到了柱状气液旋流分离器的压力降分布特性和速度分布特性。揭示了入口位置及溢流口直径对柱状气液旋流分离器分离性能的影响。经研究发现:要使柱状气液旋流分离器具有低压力损失和高分离效率的综合性能,需要将入口位置和溢流口直径控制在一定范围。     

旋流干燥器流场模拟研究

旋流干燥器(SMTD)作为一种新型的干燥装置,其结构简单、干燥效率高、处理量大,成为气固二相流干燥研究的新方向.文中用流体力学软件Fluent对旋流干燥器内部的流场进行了数值模拟研究,采用雷诺应力模型(RSM)模拟气相流动,模拟结果表明:旋流干燥器各干燥事内气流主要做旋转运动,穿过旋流板时,主要做返混运动;切向速度分布...     

万吨片碱分离装置性能研究

分离器是万吨质量分数72%片碱生产系统中重要设备之一,采用数值模拟方法研究分离器的压力分布,分析了旋流板式分离器内部的三维二相流场,气相采用RNG湍流模型,液相采用离散相模型,选择SIMPLE算法进行计算,讨论了不同入口气速对旋流板式分离器性能的影响.计算结果表明:在入口气速为3-13 m/s时,旋流板式分离器的分离压...     

旋流分离器流动机理及流动影响因素简介

旋流分离器是一种利用相间的密度差产生不同的离心力,进而完成气-液、液-液、气-固等分离的设备,具有结构紧凑、分离效率高、环境适应性强等优点,在石油、化工、矿山、煤炭等行业应用广泛。旋流分离器的流动机理研究在整个旋流分离器的研究过程中占据重要地位,其内部流场属于三维强旋湍流,流动复杂,对分离器流场进行充分的研究是指导分离器设计、提高分离性能的前提。本文将对旋流分离器的流场结构进行详细介绍,并就国内外学者关于分离器结构变化对流场分布的影响关系进行总结概括。这对加深对旋流分离器的认识,指导其优化设计具有重要的辅助作用。     

气液旋流分离器排气管结构优化的数值模拟

利用FLUENT提供的RSM模型和DPM模型对采用扩散锥形排气管的切流式气液旋流分离器内部气相流场和液滴轨迹进行了数值模拟,模拟结果显示锥角在0²0°范围内,随着锥角的不断增大,压降小幅度减小,当达到临界角度时压降略高于传统型排气管压降,但分离效率提高了9.2%,因此扩散锥形排气管应用到切流式气液旋流分离器内既可以保持压降基本不变又能提高分离效率。     

导流板对旋风分离器内非轴对称流动的影响

采用雷诺应力模型(Reynolds Stress Model,RSM)对环形空间设有导流板的旋风分离器内的气相流场进行模拟研究,分别考察了导流板径向、周向位置和导流板半径、数目对旋风分离器内气相流动的影响。结果表明:导流板半径和导流板数目对气相流动的影响最大;导流板数目为2时,可有效抑制非轴对称流动,但导流板数目进一步增多会使流场的轴对称性变差;导流板半径越大,流场的轴对称性越好;外旋流区的切向速度越大,越有利于提高分离器的性能。     

轴流式气液旋流分离器内气相流场的数值研究

应用RSM湍流模型对内径100mm的轴流导叶式气液旋流分离器内气相流场进行了数值研究,计算得到的气流时均速度分布和压力分布与实验测量结果基本吻合。根据分离器内气相流动分布的特点可知:(1)气流旋转强度与导向叶片出口角有关,出口角越大,切向速度越小;(2)排气管下口区域存在明显的短路流分布,容易卷吸夹带液滴进入排气管逃出,造成分离效率下降;(3)排气口和排液口附近的区域气流湍流脉动强度高,容易造成液滴破碎,直径减小,从而影响分离效率。以上研究结果为轴流导叶式气液旋流分离器的结构优化,进一步提高分离性能奠定了基础。     

气液分离器的结构设计与流场分析

设计了一种新结构气液旋流分离装置,并介绍了该装置的结构特点、尺寸参数和工作原理。基于计算流体动力学软件Fluent,采用雷诺应力模型,模拟仿真了新型气液旋流分离器的内部流场分布。同时分析了不同分流比变化对分离器内气相浓度分布、压力和速度的影响规律。气-液分离器分离效率达到80%,说明新型气-液旋流分离器的除气处理效果优越。     

DEM‐simulation of the magnetic field enhanced cake filtration

Using the discrete element method, we simulate numerically the cake formation and growth in magnetic field enhanced cake filtration to give further insight on the mechanisms of the structuring of the filter cake due to the interaction of magnetic, hydrodynamic, and mass forces. The motion of the discrete particles is obtained by applying the three‐dimensional Newton's equations to individual particles, allowing for both external forces (gravity, applied magnetic field) and particle–particle interactions calculated using the modified DLVO‐theory. Continuous liquid phase flow is assumed as one‐dimensional. The simulation results compare favorably with reported experimental data, 1 and can be used to delineate the regimes associated with different liquid flow and magnetic field effects that are observed experimentally. © 2012 American Institute of Chemical Engineers AIChE J, 2012     

伞罩型湿式脱硫除尘器气液固三相流数值模拟

从数值模拟和试验研究的角度对新型脱硫除尘装置——伞罩型湿式脱硫除尘器气液固三相的除尘特性进行研究。利用FLUENT软件在Euler坐标系中考察气固二相,采用欧拉模型来表述气固二相的相互关系;同时在Lagrange坐标系中考察液滴的运动,并把液滴对气固二相的影响耦合于欧拉模型中,提出了气液固三相的Euler/Euler/Lagrange模型。分析了气相速度场、气相压力场、固相速度场以及液滴质量浓度等的分布情况,得到了除尘情况下装置内气液固三相的分布规律。数值模拟结果与试验结果吻合良好,对装置运行及其优化设计有一定的理论指导意义。     

Local measurements of fluid and particle velocities in a stirred suspension

An experimental approach is proposed for the measurement of the local behaviour of continuous and dispersed phases in a stirred suspension at low particle concentrations (0.5 vol.%). The basic principle involves the simultaneous measurement of the local velocity and particle size with a phase Doppler velocimeter and the separation of the data obtained from large particles (representing the dispersed phase) and very small particles (representing the motion of the continuous liquid phase).This technique was applied to the investigation of a fully baffled cylindrical vessel, with a flat bottom, stirred by an industrial axial propeller. The diameters of the vessel and the propeller and the vertical clearance were 0.3 m, 0.14 m and 0. l m respectively. The liquid was water and spherical glass particles were used as the dispersed phase.In the absence of particles, the circulation pattern created by the propeller in the middle plane between two baffles revealed a major circulation loop in the lower part of the vessel and a minor contra-rotative loop in the wall surface corner. The calculated pumping coefficient, circulation flow number, non-dimensional time of renewal and circulation time were 0.62, 0.89, 11.76 and 8.15 respectively. The tangential velocities remained at values of less than 15% of the impeller tip velocity in the plane of the measurements.Axial, radial and tangential mean and root-mean-square velocities for the carrier liquid phase and particles were measured in the two-phase flow, using particles with a mean diameter of 253 μm. These measurements showed that the particles lagged behind the liquid phase in the upward parts of the flow field, but were ahead in some downward parts. The root-mean-square axial velocities obtained for the particles were always greater than these obtained for the continuous phase. Non-homogeneities in the suspension were observed by the local mean diameter field. The effects of the stirring rate and size of the particles were also checked in the upward part of the flow in the vessel.     

离散单元法数值研究水平管中密相栓流气力输送

在对密相栓流气力输送过程中气固两相运动的特点和气固两相流的数值模拟方法进行分析的基础上,将广泛应用于岩土力学中的离散单元法引入以模拟多个颗粒之间长时间的相互作用,同时考虑颗粒与流体间的相互作用(双向耦合),建立了密相栓流气力输送过程中两相流的数学模型.对多个栓的密相栓流气力输送过程进行数值模拟,结果再现了栓的滑落、形成和运动过程,与实验观察到的现象基本一致,预示离散单元法在密相气固两相流数值模拟研究中具有广阔的应用前景,为密相栓流气力输送的进一步研究提供了基础.     

Motion of a magnetic flow follower in two‐phase flow — application to the study of airlift reactor hydrodynamics

A low‐cost and simple magnetic particle tracer method was adapted to characterize the hydrodynamic behavior of an internal‐ and an external‐loop airlift reactor (ALR). The residence time distribution of three magnetic particles differing in diameter (5.5, 11.0 and 21.2 mm) and with a density very close to that of water was measured in individual reactor sections. The measured data were analyzed and used to determine the velocity of the liquid phase. Validation of the experimental results for liquid velocity was done by means of the data obtained by an independent reference method. Furthermore, analysis of the differences found in the settling velocity of the particle in single‐liquid and gas‐liquid phases was carried out, using a simplified 3D momentum transfer model. The model considering particle‐bubble interaction forces resulting from changes in the liquid velocity field due to bubble motion was able to predict satisfactorily the increase in the particle settling velocity in the homogeneous bubbly regime. The effective drag coefficient in two‐phase flow was found to be directly dependent on particle Reynolds number to the power of ? 2 but independent of gas flow‐rate for all particle diameters studied. Based on the experimental and theoretical investigations, the valid exact formulation of the effective buoyancy force necessary for the calculation of the correct particle settling velocity in two‐phase flow was done. In addition, recommendations concerning the use of flow‐following particles in internal‐loop ALRs for liquid velocity measurements are presented. Copyright © 2006 Society of Chemical Industry     

G-LISR不同气相入口流速对流场特性的影响

为了提高气液撞击流反应器(G-LISR)的混合性能,找到合适气相入口速度的操作参数,采用ANSYS Workbench中的Geometry模块,基于欧拉·拉格朗日法建立G-LISR气液两相流动数学模型。在加速管对置距离为400mm,液相入口速度为5m/s,三种不同的气相入口速度(10,15,20m/s)条件下,用数值模拟软件Fluent分析模拟出了不同气相入口流速下反应器内流场的分布特征。模拟结果表明:随着气相入口初始流速的增大,反应器内湍流强度有所增加,在压力波动最为剧烈的撞击面中心点处,压力急剧增大。增大气相初始流速,将降低反应器中的液滴的浓度分布,减少了液相在反应器中的停留时间。从能量损耗和气液两相在反应器中的混合效果来看,气相初始流速不宜过大,10m/s为较佳。     

A fluid-dynamically based model of bubble column reactors

A heterogeneous fluid dynamic model has been developed to describe the complex flow structure of two-phase in bubble columns. The equation of continuity and momentum balances form the basis of the model. Coupling of the two phases occurs via an interaction force, deduced by a force balance around a single rising bubble. Multiphase flow mixing processes are taken into consideration by introducing turbulent viscosities of the two phases involved. The Simulation program was extended to reactive system, taking into account the mass balances of a second order gas-liquid chemical reaction as well as the different absorption/reaction regimes. The gas phase concentration profiles show pronounced axial and radial dependences, while the liquid phase can be regarded as a CSTR with respect to the liquid component. With reference to the gaseous component, which is being absorbed in the liquid phase, the degree of back mixing does not show CSTR behaviour as the influence of different absorption conditions in different axial and radial reactor positions is superposed on that of turbulent motion of the liquid carrier of the dissolved gaseous component.     

鼓泡塔气液两相流内部流场的流体力学特性

采用计算流体力学CFD软件对鼓泡塔内部4种表观气速下内部流场的流体力学行为进行模拟。分析了鼓泡塔内部整体气含率及轴截面处（X=0）液相速度随时间的变化情况;并且对比了在不同表观气速下局部气含率和液相速度在不同高度处的径向分布情况。模拟结果表明,随着时间的增大,整体气含率增大速度比较快,到达稳定时间,整体气含率不再增大。在同一高度处局部气含率随着表观气速的增大而增大。H/D<3时,液相循环流动表现为单相循环流;当H/D=3时,表现为双循环流,流型较单相复杂。     

Numerical Simulation and Assessment of a Two‐Stage Gasifier Modified from an Opposed Multi‐Burner Gasifier

An opposed multi‐burner (OMB) entrained‐flow gasifier with coal water slurry feeding is developed by the East China University of Science and Technology. A 3D model is employed to numerically simulate the gas flow field, motion of char particles, and distributions of temperature and gaseous components in an OMB gasifier and in a conceptual two‐stage gasifier modified from the OMB gasifier (TS‐OMB gasifier). Results show that the TS‐OMB gasifier produces higher concentration and productivity of the effective gases (CO+H₂) with a slightly higher carbon conversion than the OMB gasifier. The reasons for the differences between these two types of gasifier are discussed by means of numerical simulation. This information is valuable for guiding the design of an advanced OMB gasifier.     

A double-k-ε and multi-δ pdf model for turbulent gas-liquid reacting flows

The gas-liquid reacting two-phase flow of a gaseous SF₆ jet submerged in liquid metal Li is numerically simulated by a two-fluid model. To describe the changes of the flow pattern in the two-phase flow, a double-k-ε two-phase turbulence model is developed and adopted. A multi-δ-pdf model is proposed and applied to simulate the turbulent combustion of gaseous SF₆ with liquid metal Li. The gas and liquid velocities, void fraction, shape of the penetrating region (the region containing the gas phase) and the mixture fraction related to gas temperature and species concentration are predicted. Comparison with the results using a single-fluid model shows that current predictions are reasonable in reflecting the influence of velocity slip between the two phases and capable of predicting Li/SF₆ submerged combustion.