预测水平管气-液环状流周向液膜厚度分布的理论模型

针对水平环状流液膜厚度沿周向分布的不对称性 ,用 5组双平行电导探针测量了水平管内气液环状流沿周向的瞬态液膜厚度 ,得到了平均液膜厚度沿周向的分布规律 .分析了液膜向上输送的机理 .为更为准确地预测液膜厚度 ,综合考虑了扰动波抽吸作用机理、气体二次流机理及液滴沉降和携带机理 ;通过量级比较和应力平衡的方法 ,提出了一个预测液膜厚度沿周向分布的理论模型 .数值模拟结果表明预测值与实验测量结果符合较好     

环状流起始点初始携带份额的分析计算

目前大多数研究采用液膜干涸模型预测气液两相环状流的临界热通量,其中确定环状流起始点、起始点和平衡状态的携带份额、携带现象的发生条件、液滴沉积率以及携带率对模型的计算精度都起着决定性的作用。通过大量研究目前已经得到了适用于不同条件下的经验关联式来预测此模型中的大多数参数,然而环状流起始点的初始携带份额至今仍需通过假设来确定。本文对蒸气-水为工质,压力为0.18～0.27 MPa条件下得到的实验数据进行了分析,通过计算值与实验值的对比提出了初始携带份额的经验关联式。比较结果表明,计算值与实验值的偏差在20%以内。     

环形狭缝通道内气液两相环状流流动特性

建立了环形狭缝通道内气液两相环状流的理论模型 ,该模型计及环状流气芯流动的可压缩性、气液两相间的相滑移、气相对液滴的夹带作用等因素 .考察了两相流质量流量和干度对压降、液滴速度相对变化和狭缝喉部气芯通流面积的影响 .用建立的理论模型对空气 -水两相环状流通过环形狭缝的两相压降进行预测 ,预测值和试验值吻合良好     

基于截面气含率的文丘里湿气压降模型

运用两相流理论对湿气中的气相与液相流动进行分析,在分层流与环雾状流的条件下推导了两相流通过水平标准文丘里流量计的理论模型.通过分别考虑截面气含率、相间摩擦以及液滴夹带等因素,在文丘里轴向对湿气流动中的气相动量方程进行求解.通过对水平直管中的截面气含率公式进行修正,建立了适用于收缩管道的截面气含率模型,并在此基础上模拟了湿气流经标准文丘里时其两个取压孔之间的轴向静压分布.实验证实,使用修正后的截面气含率公式将使模型对文丘里压降的预测准确度明显提升,其相对误差在15%以内.该模型以湿气两相流在水平文丘里中的流动形态为依据,具有较充分的物理背景,而且在推导过程中较少依赖特定实验装置与数据,为建立具有一定普适性的文丘里湿气计量模型奠定了基础.     

THEORETICAL SIMULATION OF HIGHLY EFFECTIVE COOLING WITH AN EVAPORATING ANNULAR FLOW IN A VERTICAL TUBE

A new concept is proposed for the highly effective cooling of a polymer electrolyte membrane fuel cell (PEMFC) using the downward annular two-phase flow of high-speed air and subcooled water in a small vertical tube. Numerical simulations based on the two-phase flow boundary layer model are performed to investigate the heat and mass transfer characteristics of the annular flow with uniform heat flux at the tube wall. The coupled heat transfer due to evaporation and convection and the effects of various relevant parameters on the temperature profiles on the wall and of the gas core are studied. It is shown that annular two-phase flow of air and subcooled water in a small vertical tube can provide high heat transfer rate through the evaporation of the water film, while still maintaining low wall temperature. This cooling method is found to be encouraging for use in the highly effective cooling of PEMFC.     

冷却表面影响高湿气流局部凝雾及成膜现象

采用气液两相湍流k-ε模型,通过引入局部冷凝推动力实现两相传热传质的耦合,对冷表面作用下高湿气流的冷凝过程进行了模型研究,并应用CFD方法对模型进行了数值模拟.对恒壁温冷凝管外混合气体在环形空间湍流冷却冷凝的温度分布、湿度分布及其凝雾区间分布的模拟结果显示,凝雾的产生受蒸汽过饱和度控制,而其分布受过程传热推动力影响.基于体系整体不饱和、局部过饱和的热力学非平衡状态,冷凝区间前端主要发生雾状冷凝,在x*＝0.7附近,随着凝雾在冷表面上逐渐积聚成膜,凝雾过程过渡为膜状-雾状冷凝协同作用.相同工况下,由本模型计算得到的冷凝量与高湿气流冷却冷凝现场实验数据的相对误差为±9%,验证了本文的模型与数值模拟.     

竖直管外气液逆流环状降膜速度与温度分布

建立了竖直管外环状降膜气液逆流传热传质条件下稳态层流降膜一维速度分布和二维温度分布模型,以及膜厚和降膜表面热通量的数值计算方法。表面热通量的模型计算值与实验值在气体Reynolds数Re_g<1200的范围内吻合较好,表明基于界面摩擦因子求解模型的方法在两相均为层流条件下是可靠的。模型显示了降膜速度分布和温度分布的非线性特征,降膜表面附近陡降的温度梯度表明,减小膜厚是强化降膜传热传质过程的有效途径。     

利用U形管测量低压环雾状流与液束环状流体积含气率

由能量方程出发,根据U形管垂直上升段与下降段的重位压降与摩阻压降的大小及方向之间的关系求得体积含气率测量模型,并通过实验研究了体积含气率测量误差的影响因素,利用体积含气率测量误差与流动密度测量值之间的线性关系对体积含气率进行了修正,使测量精度明显提高,并通过独立实验进行了验证。最后分析了U形管测量低压气液两相流体积含气率的适用范围。     

高湿度工业废气冷凝脱湿模型研究与数值模拟

针对高湿度工业废气冷凝脱湿进行模型研究和数值模拟,引入分配系数α表征雾状冷凝和膜状冷凝并存的权重.恒壁温冷凝管外混合气体在环形空间湍流冷却冷凝的温度分布、湿度分布及其梯度（传热传质推动力）分布的模拟结果显示,雾状冷凝的控制机理是冷壁面附近温度梯度与湿度梯度协同作用下传热传质产生的局部过饱和;膜状冷凝从冷壁面移出大量冷凝潜热,促使气相主体传热传质过程更迅速,脱湿效果更好.实际过程介于二者之间.DAP尾气冷却冷凝现场实验传热传质数据,在水汽冷凝减量34%～57%的范围内,与α＝0.2的数值模拟结果相当吻合,验证了本文的模型与数值模拟.     

垂直管气液两相环状流界面扰动波频率特性

气液两相环状流的相界面存在扰动波,波动频率是描述环状流界面扰动波特性的关键参数,对环状流的传质传热研究有重要参考价值。利用近红外光的吸收特性,设计了液膜检测装置,采用垂直对射光路设计,并通过置入式导光管屏蔽一侧液膜和气芯夹带液滴,实现了对环状流局部液膜的非接触式检测。在此基础上对界面扰动波进行了频域分析,运用功率谱密度估计,对50 mm管径竖直上升管环状流界面扰动波波动频率进行了定量研究,得到0.1～0.8 MPa不同压强条件下,共70个流动条件的环状流界面扰动波频率值。利用实验结果对现有模型进行验证分析,在此基础上利用Strouhal数描述液相流动条件的影响,利用Froude数描述气相流动条件的影响,建立了预测环状流界面扰动波波动频率的St-Fr模型,经实验数据验证预测的平均绝对误差（MAE）为11.42%。     

垂直管气液两相环状流的界面扰动波速度

在气液两相环状流中,界面波是两相间质量、动量和能量转移的重要载体,对其特性参数（波速、波频和波幅）的研究具有重要意义。首先根据气液两相流界面波分类,对其特征进行了定性描述。针对现有的界面剪切力推导了界面扰动波速度预测模型,考虑了气核中夹带液滴引起的密度增量及气核与液膜表面相对速度的影响,得到了改进的垂直管环状流扰动波速预测模型。针对工业现场工况压力较高现状,设计了基于近红外吸收衰减技术和互相关原理的界面波波速测量传感器,在五种压力（0.2～0.9 MPa） 154个界面波波动速度条件下进行了实验。结果表明,改进后模型预测效果良好,相对误差在±10%左右,在不同系统压力条件下具有一定外推性。     

A new mechanistic model to predict gas–liquid interface shape of gas–liquid flow through pipes with low liquid loading

Devising a new mechanistic method to predict gas–liquid interface shape in horizontal pipes is concerned in this article. An experiment was conducted to find the pressure gradients of air–water flow through a 1‐in. pipe diameter. Comparing results of model with some experimental data available in the literature demonstrates that the model provides quite better predictions than existed models do. This model also predicts flow regime transition from stratified to annular flow better than Apparent Rough Surface and Modified Apparent Rough Surface models for both 1‐ and 2‐in. pipe diameters. The model also leads to reliable predictions of wetted wall fraction experimental data. Although one parameter of new model was evaluated based on air–water flow pressure loss experimental data for 1 in. pipe, it was considerably successful to predict pressure drop, liquid holdup, stratified‐annular transition and wetted wall fraction for other gas–liquid systems and pipe diameters. © 2014 American Institute of Chemical Engineers AIChE J, 61: 1043–1053, 2015     

Atomization of Liquids by Two‐phase Gas‐liquid Flow through a Plain‐orifice Nozzle: Flow Regimes inside the Nozzle

Liquids or suspensions are divided into sprays of small droplets by atomization of two‐phase gas‐liquid mixtures. In this way either an equal distribution of the droplets or the generation of large surface areas of the liquid phase are accomplished, leading to increased heat‐ and mass‐transfer. The spatial and time dependency of the mean droplet diameter is a function of the total pressure upstream of the nozzle, the volumetric flow rate of the liquid and the gas, as well as on the flow regime in the nozzle. Thus the radial and axial profile of the void fraction inside the nozzle are measured with an electrical measurement technique. In addition, the flow in the nozzle is imaged by a high‐speed camera. Three flow regimes are identified. These are bubbly flow, plug flow and annular flow. A continuous flow of the emitting spray is observed for bubbly flow and annular flow only. The distribution of the dispersed bubble phase is given by ratio of the isothermic compression energy needed to pressurize the gas mass flow rate from atmospheric pressure up to the total pressure in front of the nozzle, and the potential energy of the supplied liquid mass flow rate.     

Z法气体超声波流量计湿气测量的虚高预测模型

引言湿气通常是指气相为连续相,液相为离散相的气液两相流。美国机械工程师学会ASME将其界定为Lockhart-Martinelli参数(L-M参数)X<0.3的气液两相流[1]。湿气普遍存在于自然界与工业现场中,如常规天然气田井口产出气(湿天然气)、煤层气、湿饱和蒸汽以及页岩气等均属湿气。随着工业生产的发展,对湿气不分离计量的要求越     

管内稠密气固两相流数值模拟计算:颗粒动力学方法

基于稠密气固两相流流体动力学模型、颗粒动力学的颗粒湍动能模型 (KTGF)和气体湍动能模型(SGS) ,模拟计算结果得到了实验研究所揭示的环 -核流动结构 .模拟计算与Miller和Gidaspow的实验结果进行了比较 ,颗粒相浓度、速度和颗粒相动力黏性系数分布与实验值基本吻合 .     

旋流型管壁取样分配器整流特性分析

为克服管壁取样测量气液两相流体流量方法中环状流不均匀稳定的缺点,在旋流叶片下游采用整流元件将旋流形成的环状流整改成液膜厚度均匀稳定的环状流型,增强取样的代表性,并在整流器下游增设了两个取样位置,以确定装置最佳取样位置。分析表明,在取样位置1处形成的环状流比较均匀稳定;随着流量的增大,均匀环状流稳定流动的时间延长。本实验装置存在最小正常工作范围:气相折算速度为30.50 m/s,液相折算速度为0.08 m/s。当流量超过这一特定值时,流型整改效果良好。     

Liquid film thickness in annular flow

An analytical solution relating the mass flow rate to the film thickness and other flow parameters have been developed for the general case of gas—liquid two-phase annular flow in a horizontal pipe line for power-law fluids. The equation developed reduces to the equation derived for the Newtonian fluid when the flow index is equated to unity. In the absence of a detailed knowledge of the flow dynamics, the data were interpreted tentatively in terms of superficial gas—liquid mass flow rate.     

Hydrodynamics and local mass transfer characterization under gas–liquid–liquid slug flow in a rectangular microchannel

Gas–liquid–liquid three-phase slug flow was generated in a glass microreactor with rectangular microchannel, where aqueous slugs were distinguished by relative positions to air bubbles and organic droplets. Oxygen from bubbles reacted with resazurin in slugs, leading to prominent color changes, which was used to quantify mass transfer performance. The development of slug length indicated a film flow through the corner between bubbles and the channel wall, where the aqueous phase was saturated with oxygen transferred from bubble body. This film flow results in the highest equivalent oxygen concentration within the slug led by a bubble and followed by a droplet. The three-phase slug flow subregime with alternate bubble and droplet was found to benefit the overall mass transfer performance most. These results provide insights into a precise manipulation of gas–liquid–liquid slug flow in microreactors and the relevant mass transfer behavior thereof.     

Evaporative Heat Transfer of Annular Two-phase Flow of Air-water in a Small Vertical Tube

The evaporative heat transfer of the non-boiling annular two-phase flow of air-water in a small vertical tube with uniform wall heat flux was studied both theoretically and experimentally. A simplified two-phase flow boundary layer model was used to calculate the thickness of the water film attached to the wall, and from the liquid film thickness the evaporative heat transfer coefficients of the annular two-phase flow were obtained. Theoretical equations and semi-theoretical equations were proposed for predicting the evaporative heat transfer of the annular two-phase flow of air-water in a small vertical tube. The semi-theoretical prediction agrees well with the experimental data. The mechanism of the heat transfer enhancement is the evaporation of the thin liquid film attached on the wall.     

An experimental study of gas void fraction in dilute alcohol solutions in annular gap bubble columns using a four-point conductivity probe

The influence of alcohol concentration on the gas void fraction in open tube and annular gap bubble columns has been investigated using a vertical column with an internal diameter of 0.102 m, containing a range of concentric inner tubes, which formed an annular gap; the inner tubes had diameter ratios from 0.25 to 0.69. Gas (air) superficial velocities in the range 0.014–0.200 m/s were investigated. Tap water and aqueous solutions of ethanol and isopropanol, with concentrations in the range 8–300 ppm by mass, were used as the working liquids. Radial profiles of the local void fraction were obtained using a four-point conductivity probe and were cross-sectionally averaged to give mean values that were within 12% of the volume-averaged gas void fractions obtained from changes in the aerated level. The presence of alcohol inhibited the coalescence between the bubbles and consequently increased the mean gas void fraction at a given gas superficial velocity in both the open tube and the annular gap bubble columns. This effect also extended the range of homogeneous bubbly flow and delayed the transition to heterogeneous flow. Moreover, isopropanol results gave slightly higher mean void fractions compared to those for ethanol at the same mass fraction, due to their increased carbon chain length. It was shown that the void fraction profiles in the annular gap bubble column were far from uniform, leading to lower mean void fractions than were obtained in an open tube for the same gas superficial velocity and liquid composition.