阶梯式T型微通道内液滴、气泡分散规律

采用高速摄像仪对嵌入毛细管的阶梯式T型微通道内液滴和气泡的分散规律进行研究。考察了两相流量、黏度、表面活性剂浓度等因素对分散流型及分散尺寸的影响规律。结果表明,对于液滴分散过程,表面活性剂的浓度和连续相流量决定了分散流型,随二者增大,流型从dripping流向jetting流转变。对于气泡分散过程,实验范围内仅存在squeezing、dripping流型,表面活性剂的加入对气泡分散过程影响可忽略。嵌入毛细管的阶梯式T型微通道内获得的液滴、气泡直径小于微通道直径,根据实验结果基于两相流量和毛细管数分别建立了计算液滴、气泡分散尺寸的半经验模型,模型与实验结果符合良好。     

气液两相在毛细管内作活塞流运动时的阻力计算

本文着重研究了毛细管中的气泡大小对流动阻力的影响,由实验确定了多个气泡相继运动时气泡的阻力系数,最终给出了流动阻力的计算公式。     

光电毛细管探头法测量搅拌槽中气泡大小分布的研究

本文以提供搅拌槽中气泡大小分布的测定方法为目的,对用光电毛细管探头法测量气泡大小分布过程中存在的关键问题:如何由毛细管内光电检测处的气泡长度正确地反映出搅拌槽中取样微元内的气泡大小分布,提出了较为合适的解决方法,具体包括:(1)保证进入取样微元内的大小气泡全被抽进毛细管;(2)避免气泡在毛细管的喇叭口内合并;(3)准确计算毛细管内轴向流体压力分布和气泡周围的液膜厚度。     

聚丙烯发泡体系的挤出胀大和泡孔平均直径预测模型

利用改进后的毛细管流变仪研究了温度、发泡剂与碳酸钙含量对聚丙烯发泡体系挤出胀大和泡孔直径的影响。综合胀大比与毛细管数的关系，提出了聚丙烯发泡体系挤出胀大和泡孔平均直径的预测模型。与实验结果相比，发泡体系挤出胀大的预测值与实验测量结果的误差在5％左右，气泡平均直径的预测值与实验测量值的误差在10％左右，表明所提出的预测模型能正确预测实验值。     

板式塔降液管中高气含率两相流研究

设计了盐水－空气系统试验装置模拟高压塔降液管中高气含率的两相流，采用毛细管光电检测技术测定了降液管中气含率分布和气泡直径分布，并与水－空气系统非高气含率的分布作了比较。实验结果与按上升气泡速度所预测的气含率相符合。     

PE微孔形成微气泡及其理论研究

微气泡制造技术的改进与提高是气浮技术广泛应用的关键。研究了PE微孔膜管在剪切流剪切作用下形成微气泡的条件,从气泡形成机理上分析了膜管孔径大小、气体流量、剪切流流速和表面张力对气泡粒径分布的影响。实验采用静态显微摄像技术对气泡粒径分布进行了表征。实验结果表明,利用PE微孔膜管形成的气泡粒径在40～80μm之间,气泡平均粒径在44.3～60.5μm之间。膜管孔径大小、气体流量、剪切流流速、液相流体的表面张力是影响气泡粒径分布的主要因素。     

泡载分离器的研究——泡载分离器内微气泡的分布规律

利用H_2O-CO_2体系,对溶气法产生气泡的分布规律进行考察。实验结果发现,微气泡的分布呈非对称拖尾分布。从气液传质、能量转换和气泡动力学的角度,对气泡形成饥理进行分析。提出了描述气泡拖尾分布的Γ函数分布,并讨论其分布函数中参数m的物理意义。     

被动式DMFC阳极通道气泡行为的实验研究

将被动式DMFC阳极通道内气泡形成过程简化为CO2气体注入充满静态甲醇溶液中形成气泡的过程。利用可视化实验研究了气体垂直注入静态甲醇溶液中形成气泡以及气泡脱离的过程,考察了气体流量、液层高度、孔径大小、甲醇浓度对气泡形成及长大脱离过程的影响。结果表明：在气泡的生长过程中,接触角先是快速下降后又迅速上升,然后趋于稳定值直...     

PE微孔形成微气泡及其理论研究

微气泡制造及微化技术的改进与提高是气浮技术广泛应用的关键.研究了利用PE微孔膜管在高速剪切流剪切作用下形成微气泡的条件,从气泡形成机理上分析了膜管孔径大小、气体流量、剪切流流速和表面张力对气泡粒径分布的影响.实验采用静态显微摄像技术对气泡粒径分布进行了表征.实验结果表明,利用PE微孔膜管形成的气泡粒径在40～80μm之间,气泡平均粒径在44.3～60.5μm之间.膜管孔径大小、气体流量、剪切流流速、液相流体的表面张力是影响气泡粒径分布的主要因素.     

毛细管内多相脉动流动的格子-Boltzmann模拟

基于伪势模型理论,建立毛细管内汽液两相工质脉动流动的等温格子-Boltzmann模型。将利用该模型取得的静态液滴形态以及表面张力、大空间和窄空间内气泡浮升运动时的形态模拟结果与文献的研究结果进行对比,验证了模型的可靠性。对毛细管内泡状流和柱塞流两种流型在边界正弦压力波作用下绝热脉动流动情况进行了数值模拟。通过模拟研究了毛细管内不同压力波振幅下液相Reynolds数和气泡位移幅度周期性变化规律;获得了汽液界面形态在脉动过程中的变化;观察到在边界液相速度方向发生改变时,边界附近区域的Reynolds数振荡现象;分析了重力对脉动运动过程的影响。模拟结果为分析以毛细管为主要构件的脉动热管内汽液两相工质的工作过程提供了一定依据。     

Hydrodynamics of slug flow inside capillaries

Understanding the motion of long gas bubbles (gas slugs) inside capillaries is a challenging problem that is relevant in many processes of chemical and biological interests. It has been proved by many workers that such long gas bubbles can be used successfully in enhancing mass and heat transfer in many chemical and biological processes. In order to quantify and understand this enhancement a light was shed on the hydrodynamics of such a flow pattern. The volume of fluid method implemented in the commercial CFD package, Fluent, is used for this numerical study. Velocity and bubble profile were obtained as functions of capillary number. Computed values of the bubble velocity and diameter were in excellent agreement with published experimental measurements. The detailed velocity field around the bubble was also computed and compared favourably with those experimental results reported in literature.     

Modeling of pressure losses for the slug flow of a gas–liquid mixture in mini- and microchannels

In addition to the previously constructed model of the hydrodynamics of a gas-liquid slug flow, a mathematical model is developed that describes pressure losses taking into account the rearrangement of a velocity profile in liquid slugs and energy losses on the formation and renewal of interfacial area during the motion of bubbles. The contribution of different forms of pressure losses in capillaries is analyzed. It is shown that in microchannels tangential stresses on the surface of a bubble substantially affect the total pressure losses. It is found that the length of bubbles does not affect the rate of surface formation and respective pressure losses if bubbles have the same velocity. The results of modeling are in satisfactory agreement with experimental data of other researchers.     

牛顿及非牛顿流体中的气泡生成与对比

采用激光成像结合CCD摄像技术分别对牛顿及非牛顿流体(甘油和羧甲基纤维素钠水溶液)中的气泡生成行为进行了研究,对2种流体气泡生成过程中气泡形状和体积变化进行了比较。分析了非牛顿流体的弹性效应对气泡生成过程气泡形状的影响。实验结果表明,在实验条件范围内,甘油中,气泡生长初期,气泡体积增加较快,到了后期,增加幅度减缓,气速对气泡生长过程气泡体积影响很小;羧甲基纤维素钠(CMC)水溶液中,气泡生长初期,气泡缓慢生长,气速对气泡体积影响很小,到了后期,气泡体积增加幅度变大,气泡体积随着气速的增大而增大。     

Influence of fluid properties on bubble formation,detachment, rising and collapse; Investigation using volume of fluid method

Numerical simulations have been carried out to investigate the formation and motion of single bubble in liquids using volume-of-fluid (VOF) method using the software platform of FLUENT 6.3. Transient conservation mass and momentum equations with considering the effects of surface tension and gravitational force were solved by the pressure implicit splitting operator (PISO) algorithm to simulate the behavior of gas-liquid interface movements in the VOF method. The simulation results of bubble formation and characteristics were in reasonable agreement with experimental observations and available literature results. Effects of fluid physical properties, operation conditions such as orifice diameter on bubble behavior, detachment time, bubble formation frequency and bubble diameter were numerically studied. The simulations showed that bubble size and bubble detachment times are linear functions of surface tension and decrease exponentially with the increase in liquid density. In contrast, only a small influence of the fluid viscosity on bubble size and detachment time was observed. Bubble collapse at a free surface simulation with VOF method was also investigated.     

A Simplified Correlation for Bubble Volume Estimation

In order to propose a simplified correlation to predict the detached bubble volume without considering the gas velocity, an experimental work has been performed to measure the detached bubble volume through a micro‐hole submerged in liquid. Several micro‐holes with diameters of 60, 90, 126, 220, 580, and 1200 µm are respectively used for bubble formation, while liquid in a test chamber is continuously drained at a constant rate of 0.006 ml/s. The predicted results by the present simplified correlation agree well with the measured values. Predictions of the detached bubble volume from previously published correlations using a model to compute the gas velocity are also compared with experimental data.     

Formation of Small Bubbles in an Electric Field

Abstract

The formation of gas bubbles injected into an insulating liquid was studied under the influence of a nonuniform electric field. The electrode configuration used consisted of a charged capillary opposite a grounded ring, and gas bubbles were formed at the capillary tip. The experimental part of the investigation afforded insight into the mechanism of bubble formation, which is influenced by the existence of corona discharge. Based on the balance of forces at bubble detachment, a theoretical model was developed to predict the variation in bubble sizes. The theory agrees closely with experimental results over a range of applied voltages where the corona discharges were absent.     

BUBBLE FORMATION FROM AN ORIFICE SUBMERGED IN LIQUIDS

The phenomena of the bubble formation from an orifice submerged in a liquid is classified according to their formation mechanisms and the estimation expressions of the bubble volume are reviewed

The revised two-stage model of bubble formation accompanied by the pressure fluctuation in the gas chamber is presented and the results computed by this model are compared with the experimental results obtained for relatively wider range of gas chamber volume. Effects of some factors on the bubble volume, such as, gas chamber volume, orifice diameter, physical properties of gas and velocity of surrounding liquid are discussed     

毛细管中泰勒流液侧传质特性及其强化机理的CFD模拟

采用计算流体力学（CFD）的方法,研究了圆管中泰勒流的液侧传质特性,分析了泰勒气泡上局部传质特性,并研究了气泡上升速度、液膜长度和液栓长度对液膜处和气泡半球帽处平均传质系数的影响。结果表明,泰勒气泡表面局部传质系数存在3个峰值,液膜处的平均传质系数随气泡上升速度增大显著增大,随液膜长度增大而减小,而半球帽处的平均传质系数随气泡速度和液膜长度的增大变化较小,即膜接触时间增加时,液膜处的传质系数降低,而半球帽处传质系数变化较小。另外,引入场协同原则对单元胞内速度场和浓度场进行分析,解释了局部传质特性及强化机理。最后,给出了分别预测短和长膜接触时间下泰勒流液侧体积传质系数的关联式,该式在较宽的管径尺度范围（0.25～3 mm）内的预测误差在±20%以内。     

CFD simulations of wall mass transfer for Taylor flow in circular capillaries

Computational fluid dynamics is used to investigate the mass transfer from the liquid phase to the channel wall for Taylor flow of bubbles rising in circular capillaries. The separate influences of the Taylor bubble rise velocity, unit cell length, gas holdup, and liquid diffusivity on mass transfer were investigated for capillaries of 1.5, 2 and 3 mm diameter. A correlation is proposed for estimation of the wall mass transfer coefficient and this correlation has been tested against published experimental data.