A mechanistic model for roll waves for two‐phase pipe flow

A new two‐phase roll wave model is compared with data from high pressure two‐phase stratified pipe flow experiments. Results from 754 experiments, including mean wave speed, wave height, pressure gradient, holdup and wave length, are compared with theoretical results. The model was able to predict these physical quantities with good accuracy without introducing any new empirically determined quantities to the two‐fluid model equations. This was possible by finding the unique theoretical limit for nonlinear roll amplitude and applying a new approach for determining the friction factor at the gas‐liquid interface. © 2009 American Institute of Chemical Engineers AIChE J, 2009     

A multidimensional model for annular gas-liquid flow

A finite volume method-based CFD model has been developed to simulate steady, turbulent, two-dimensional annular gas-liquid flow in a duct. The gas flow is treated as being equivalent to flow through a rough-walled duct. The effect of the liquid film on the gas phase is included in the form of modified wall functions which incorporate the well-known triangular relationship (Annular Two-Phase Flow, Pergamon Press, Oxford, 1970) that exists among wall shear stress, film flow rate and film thickness in annular flow. The presence of droplets is accounted for by solving an additional scalar transport equation for the mass fraction of the droplets. Entrainment and deposition of droplets are included as source term and boundary condition, respectively, in the mass fraction equation. It is shown that the resulting model, while retaining simplicity of formulation, gives good predictions of the literature data of annular flow parameters under equilibrium and non-equilibrium conditions.     

水平管气液二相分层流移动壁面模型的改进

针对基于Standard k-ε湍流模型的移动壁面模型在预测水平管气液二相分层流气相封闭关系时的不足,利用Launder-Spalding和Launder-Sharma低雷诺数k-ε湍流模型对移动壁面模型进行改进,其中湍流黏度和湍流雷诺数由修正湍流耗散率替代原定义的耗散率。通过数值模拟结果拟合出新的气壁和界面摩擦因子Blasius形式公式,计算结果发现,湍流模型的选择对固定壁面和移动壁面剪切的预测都有明显影响,其中Launder-Spalding低雷诺数k-ε湍流模型得到的气相封闭关系预测精度最高,在气、液相雷诺数9 000≤ReG≤50 000和20 000≤ReL≤30 000,压降预测相对均根误差为10.6%,为理论和实验研究提供了有价值的参考。     

水平管道气液两相段塞流参数计算的精确模型

分析了水平管内气液两相段塞流的运动特性和形态特征以及段塞单元内部的速度分布规律,建立了水平管路气液两相段塞单元的物理模型。将一个完整的段塞流单元分为液相段塞区和液层/气泡区,建立了液相段塞区的质量和动量守恒方程,计算了其压降和持液率;对液层区,模型考虑液层厚度分布不均(坡状液层)对参数计算的影响,通过建立局部控制方程,推导了液层高度随流动方向坐标变化的表达式,并将持液率和湿周写成液层高度的函数。通过与实验和其他模型的计算结果对比,本文建立的模型可以对压降和持液率有更准确的预测结果。     

摇摆对气液并流模式立体旋流筛板压降的影响研究

以空气-水为实验介质,在喷淋密度78～182 m³·(m²·h)^-1、气相动能因子1.19～2.77 m·s^-1·(kg·m^-3)^0.5、摇摆幅值Θ=5°～15°、周期T=8～20 s的条件下,测定了气液并流模式下立体旋流筛板(TRST)的压降,考察了气液通量、塔板数量、位置和方式对压降的影响,并与直立和倾斜工况对比。结果表明：增加倾斜及摇摆角度干板压降略微下降;摇摆时的湿板压降介于直立和倾斜之间,受摇摆角度影响较大,基本不受周期影响;增大气量有利于抵抗倾斜及摇摆的影响,而增大液量会使倾斜及摇摆的影响作用加剧。整体上,塔板顺、逆向安装时的湿板压降分别在100 Pa和170 Pa以内,而逆向安装的变化率约为顺向的2倍,这是由于逆向安装下改变了气液流动方向,增大了能量损失。建立了气液并流摇摆工况下TRST的湿压降预测模型,相对误差在15%以内。     

复杂地形条件下气液两相混输工艺水力模型建立

随着普光气田的开发,关于复杂地形条件下的气液混输工艺计算模型,特别是湿气集输工艺计算模型成为研究的关键问题。针对低含液复杂地形条件,建立了水力计算模型,提出了气液界面的凹面湿壁分数、剪切应力以及摩擦因子计算闭合关系式。开展了室内实验,验证了压力与持液率计算模型的准确性,收集了普光气田的现场生产压力和清管积液量数据,计算的压降结果与生产数据之间的误差在±5%以内,积液量的预测结果误差在±10%以内,吻合较好,建立的模型可以用于该条件的工艺计算。     

基于Chisholm模型的V锥流量计气液分层流测量新模型

针对V锥流量计应用Chisholm模型测量气液分层流时误差较大的问题,采用节流比分别为0.55、0.65和0.75的三个V锥流量计,实验研究了高含气率（体积含气率>95%）气液分层流条件下,气、液相流量、压力以及节流比对Chisholm模型修正因子C的影响规律,并建立气液分层流测量模型。结果表明,修正因子C随Lockhart-Martinelli参数X_LM的增大而单调递减,但基本不受压力和气体密度Froude数的影响,而节流比变化则对C有一定影响;建立了C随X_LM变化的测量模型,获得了不同节流比的V锥流量计气液分层流测量新模型。对于节流比为0.55和0.65的V锥流量计,分别在94.6%和88.6%置信水平下,新模型预测的气相流量相对误差不超过±3.0%;节流比为0.75时,在91.7%置信水平下,预测的气相流量相对误差不超过±4.0%。     

基于段塞流的通用气液两相流模型的建立与验证

气液两相混输流动中,由于段塞流与其他流型均有联系,从段塞流出发建立模型可以使不同流型下的计算模型得到统一。基于段塞流建立气液两相流动量方程和连续性方程,完善模型对气泡和液滴夹带的处理。建立模型的闭合关系式,对关键参数(壁面及气液相间水力摩阻系数、液塞平移速度、平均液塞长度)的计算闭合关系式进行优选,得到适用于模型的闭合关系式,同时,对液滴和气泡的夹带给出夹带条件及相关参数计算式,最终建立基于段塞流的通用气液两相流模型。使用3组不同来源的实验数据验证了模型计算压降和持液率的准确性,实验数据分别来自中国石油大学(华东)、大庆油田实验基地的气液两相流实验以及国外研究人员的实验研究,包含各个气液流型。模型具有较高的计算精度,优于未经关系式完善和优化的原始模型,大部分压降及持液率参数的计算误差在±15%以内。     

A semi-empirical model of the forward roll coating flow of newtonian fluids

A theory of the forward roll coating flow of Newtonian fluids has been developed recently by Greener and Middleman [1] utilizing the usual lubrication approximations and some very simple physical notions regarding the region in which the total flux through the nip splits into two films. These basic notions restricted the validity of their model to the simple case of two rolls of equal rotational speeds and equal radii. Their analysis resulted in an expression for the dimensionless total flux through the nip λ as a weak function of a modified capillary number N.The aim of this paper is to extend the model presented by these workers [1] by introducing to it experimental evidence of the flux distribution [2] and thus generalizing its applicability to operations involving rolls of different diameters rotating at different speeds. The results of this extended model give the dimensionless total flux λ as a function of the modified capillary number N, the speed ratio r_s, and the radius ratio r_r. This function is a weak one over the range of N, r_s, and r_r, normally encountered in forward roll coating operations and is in good agreement with experimental data [2].     

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。     

Experimental validation of a simple model for gas-liquid slug flow in horizontal pipes

In this work, the simple submodel of Taitel and Barnea (Chem. Eng. Sci. 45 (1990) 1191) for horizontal gas-liquid slug flow has been reformulated. An additional source of pressure loss suggested by Cook and Behnia (Chem. Eng. Sci. 55 (2000) 4699) was incorporated in the model, thus improving its predictive accuracy. The proposed model was tested extensively against 12 pressure gradient and eight liquid holdup data sources for both air-water and air-oil slug flow in smooth and rough pipes over a wide range of operating conditions. The very good agreement between the predicted and experimental results substantiates the general validity of the model.     

A dual-scale turbulence model for gas-liquid bubbly flows☆

A dual-scale turbulence model is applied to simulate cocurrent upward gas–liquid bubbly flows and validated with available experimental data. In the model, liquid phase turbulence is split into shear-induced and bubble-induced turbulence. Single-phase standard k-εmodel is used to compute shear-induced turbulence and another transport equation is added to model bubble-induced turbulence. In the latter transport equation, energy loss due to interface drag is the production term, and the characteristic length of bubble-induced turbulence, simply the bubble diameter in this work, is introduced to model the dissipation term. The simulated results agree well with experimental data of the test cases and it is demonstrated that the proposed dual-scale turbulence model outperforms other models. Analysis of the predicted turbulence shows that the main part of turbulent kinetic en-ergy is the bubble-induced one while the shear-induced turbulent viscosity predominates within turbulent vis-cosity, especially at the pipe center. The underlying reason is the apparently different scales for the two kinds of turbulence production mechanisms:the shear-induced turbulence is on the scale of the whole pipe while the bubble-induced turbulence is on the scale of bubble diameter. Therefore, the model reflects the multi-scale phe-nomenon involved in gas–liquid bubbly flows.     

基于EMD和ICA的AR模型在两相

为了对气液两相流流型进行准确识别,提出了一种基于经验模态分解（EMD）和独立成分分析（ICA）的AR模型的流型识别方法。该方法首先提取气液两相流动态差压信号,通过EMD技术对其进行分解,对分解出来的高频模态进行小波包消噪,然后通过ICA技术实现原始信号的降维处理。对通过ICA得到的独立分量建立AR模型,将模型参数和残差方差作为特征向量,建立不同流型的模板向量。计算未知流型信号的特征向量与模板特征向量的综合Mahalanobis距离,通过比较各判别距离的大小得到流型识别的结果。对40 mm水平管气水两相流进行实验,利用文丘里管采集动态差压信号,采用上述处理过程可以对泡状流、弹状流、塞状流进行有效识别,识别率达94.3％。该方法受环境条件影响小,可以有效滤除信号中的噪声成分,识别率高,易于工程实现。     

Flow regimes for adiabatic gas-liquid flow in microchannels

The patterns forming during adiabatic gas-liquid flows in single microchannels are reviewed and the parameters influencing pattern transitions are discussed. Six major patterns were identified: the surface tension dominated bubbly and Taylor flows, the transitional churn and Taylor-annular flows, and the inertia dominated dispersed and annular flows. From the various parameters that have been studied in the literature, channel size, phase superficial velocities, liquid phase surface tension, wall wettability and inlet conditions were found to affect the flow pattern formed while channel cross sectional geometry affected the patterns but to a lesser degree. Liquid viscosity and flow orientation with respect to gravity also seemed to play some role but the results were not conclusive. A universal flow regime map does not seem to exist and this is attributed to a lack of consistency in the inlets used in the various studies as well as to the effects of wall properties, such as wettability, contamination and roughness which are not usually varied systematically or reported. From the different flow regime maps suggested, those using U_GS-U_LS as coordinates represented better the transitions between patterns.     

A two-scale model for discrete cell gravure roll coating

A two-dimensional model for predicting the fluid pickout and coated film thickness characteristics of a discrete cell direct gravure roll coater operating in reverse mode is derived. A novel multiscale approach is adopted for this purpose and the resulting equations solved numerically for inertia-less flow conditions. A system of stiff ordinary differential equations is found to be sufficient to capture the major gross flow features, while at the cell level the analysis is based on a finite element solution of the momentum and continuity equations. It represents the first such predictive model of its kind, with particular interest placed on the nature of both the pressure distribution and web-to-roll gap profile spanning the coating bead. The effect of key operating parameters, web-to-roll speed ratio, web-tension, wrap-angle, capillary number and cell-geometry, on the degree of fluid pickout from gravure cells and the coated film thickness is explored. Although an idealised model, the trends observed show qualitative agreement with existing experimental data collected on a small-scale gravure coating rig and point the way forward to the eventual formulation of a full three-dimensional predictive model of the process.     

基于EMMS模型的搅拌釜内气液两相流数值模拟

采用欧拉-欧拉模型对搅拌釜内气液两相流进行了三维CFD模拟,重点研究了采用不同曳力模型时CFD模拟对搅拌桨附近排出流区两相流动的预测能力。模拟结果表明CFD能准确地预测排出流区的液相速度分布,但采用传统的Schiller-Naumann曳力一定程度上低估了排出流区的气液相间曳力,导致在完全扩散区CFD预测的分布器和桨叶下方区域气含率偏小,而基于气液非均匀结构和能量最小多尺度（EMMS）方法得到的DBS-Global曳力模型能更准确地描述完全扩散区气液搅拌釜内流动情况。与传统曳力模型相比,采用DBS-Global曳力模型能显著提高对气含率的预测。     

Two-phase gas-liquid flow in rectangular channels

The results of investigation of hydraulics in a two-phase gas—liquid flow in vertical and horizontal rectangular channels have been presented in the paper.Flow regime maps have been worked out and a method for calculating the pressure drop in a two-phase mixture flow has been proposed.The methods applied in a two-phase flow in pipes have been used to describe the results of investigations, after adopting the correction for the difference between the flow in rectangular channels and that in pipes.     

微通道内气-液传质研究

以CO₂-H₂O为模型体系，实验考察了当量直径为667 μm的单通道和16个并行通道内的气-液传质行为.实验发现，液体表观速度增加，单通道内液侧体积传质系数明显提高;同一液体表观速度下，液侧体积传质系数随气体表观速度增加而增加;在实验数据基础上关联了液侧体积传质系数与气-液两相流参数间的关系.微通道内的液侧体积传质系数较常规尺度气-液接触设备至少高1～2个数量级.并讨论了并行微通道内气-液两相流分配特性对整体传质性能的影响，表明合理设计气、液流动分布结构，可保证微通道内优异的传质特性.