微通道内浆料体系中的气泡生成特性及尺寸预测

利用高速摄像仪对T型微通道内浆料体系中的气泡生成频率和气泡尺寸进行了研究。以氮气作为分散相,含0.35%(质量分数)表面活性剂(SDS)不同浓度玻璃珠的甘油-水溶液为连续相。实验考察了弹状流下气液两相流量、颗粒浓度以及浆料表观黏度对气泡生成频率及气泡尺寸的影响。结果表明:在弹状流下,当分散相流量一定时,随着连续相流量的增大,气泡的生成频率增大而气泡尺寸减小。当连续相流量一定时,随着分散相流量的增大,气泡生成频率和气泡尺寸均增大。随着颗粒浓度的增大,浆料的表面张力减小,表观黏度增大,气泡生成频率增大而气泡尺寸减小。提出了T型微通道内浆料体系中生成气泡尺寸的预测模型,模型具有良好的预测精度。     

双通道气流式喷嘴雾化特性实验研究

以清水和空气为实验介质,对同轴双通道气流式喷嘴雾化特性进行了实验研究,分析了喷淋量对雾化角及径向流通量分布的影响,分别考察了气速和喷嘴轴向位置对液滴索特平均直径(SMD)的影响。研究结果表明,喷嘴径向流通量分布随着雾化气量的升高而趋于集中,当气体流量高于1500 L/min时,雾化角随着气量升高而降低;喷口处气速与喷嘴轴向位置均是影响液滴SMD与粒径分布的重要因素,液滴SMD随着气速增大逐渐减小,当气速超过150 m/s时其下降趋势变缓,粒径分布均匀度显著提高;随着喷嘴轴向距离增大液滴SMD逐渐减小,当距离大于300 mm时其变化不再显著,但粒径分布均匀度显著提高。     

适用于液-液快速反应的三喷嘴IS-RPB微观混合性能研究

采用碘化物-碘酸盐平行竞争反应体系对三喷嘴IS-RPB微观混合性能进行了研究,考察了超重力因子β、入口雷诺数Re_(in)、入口流速u_(in)、喷嘴间距d_1、d_2、体积流量VB等因素对离集指数X_S的影响,结果表明增大超重力因子、入口雷诺数、入口流速都有利于微观混合效果的改善,表现为X_S显著减小;X_S随着体积流量的增大显著减小,但是随着体积流量比的增大而增大;d_16 mm时,X_S随喷嘴间距d_1的增大而减小;d_16 mm,增大d_1使X_S增加;较小的喷嘴间距d_2有利于微观混合。对比研究表明三喷嘴IS-RPB离集指数约为0.006,为传统IS-RPB的1/2,三喷嘴IS的1/3,显示出了优越的微观混合性能。     

静止非牛顿流体中气泡生成过程的传质

气泡生成过程中气液传质是气液接触设备的设计、优化的重要参考指标。以二氧化碳气泡在羧甲基纤维素钠(carboxymethyl cellulose,CMC)溶液中生成过程中的传质为研究对象,分别考察了气速、CMC溶液浓度、针头直径对气泡生成过程气液传质的影响,采用具有CCD显微相机的动态接触角分析仪测量了气泡形状、表面积和体积的变化,进而获得气泡生成过程气液传质系数k_l。实验结果表明,CMC浓度从0.2%增加到0.8%,黏度逐渐增大,传质系数随CMC浓度的增大而增大;针头直径从2.5 mm增加到4 mm,传质系数也随之增大;气速从1 ml·min^-1增加到9 ml·min^-1,传质系数也逐渐增大。     

Experimental investigation on bubbling behavior in anode channel of passive DMFC

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,然后趋于稳定值直到脱离。随着气体流量的增加,脱离时气泡的直径变化甚微,脱离时间先下降较快后趋于稳定。随着液层高度的增加,气泡的脱离直径变小,产生的频率加快,脱离时间先是减小后趋于稳定;气体流量在此条件下对脱离时间的影响减弱。随着孔径的增加,气泡的脱离直径增加,产生气泡的频率减慢,气泡的脱离时间减小。随着甲醇浓度的增加,气泡的脱离直径变小且波动明显,气泡产生的频率变快,脱离时间先是减小后趋于稳定,对低浓度的溶液影响较为明显。     

气泡直径对溶剂气浮分离废水中乙酸丁酯的影响

采用溶剂气浮法,以正壬烷为上层捕收溶剂,对0.40%(j)乙酸丁酯模拟废水进行分离,考察了气浮时间、气体流量、油水相体积比等对乙酸丁酯溶剂气浮分离效率的影响,特别是不同尺度气泡对溶剂气浮过程的影响. 结果表明,当油水体积相比为1:25时,平均直径为0.6 mm的气泡采用的通气流量为20 mL/min、平均直径为0.2 mm的气泡采用的气流量为1.67 mL/min的最终分离效率均可达60%,但分离时间、总气量及溶剂对水相的二次污染均有较大差别.     

不同管口浸没方式下气泡生成行为特性

对三种管口浸没方式下气泡生成行为过程进行可视化实验和三维数值模拟。对比分析了管口浸没方式、管口直径、气体流量等因素对气泡生成形态、气泡脱离直径、气泡膨胀脱离时间以及气液流场速度的影响。实验与数值模拟取得较为一致的结果。研究发现,气泡生成过程可分为单气泡生成和双气泡生成聚并两种模式,两者之间存在明显的气泡脱离形态转折点;三种管口浸没方式下,气泡脱离直径均随着管径和气体流量的增大而增大;气泡膨胀脱离时间随管径的增大而增加,而随气体流量的增加先急剧下降然后趋于平缓;在底吹和侧吹方式下,气泡长短轴比C值分别在0.75和1.1附近波动,其最终脱离形式均接近于球形;而顶吹方式下,C值在1.5附近波动,气泡脱离形态为椭球形。     

泡载分离器的研究——高压溶气水减压释气过程

本文研究了用于泡载分离过程、由高压饱和溶气水减压产生微小气泡过程的流体力学特性。实验采用CO_2-H_2O体系,考察了0.1～0.3MPa压力(表压)下,饱和CO_2水溶液通过三个不同长径比的喷嘴,减压产生的气体流量、气泡直径以及溶液中气泡浓度的变化规律,并对这些规律作了理论分析和经验关联。     

基于PLIF的浸没撞击流反应器的混合特性

利用平面激光诱导荧光技术对水平两喷嘴液-液撞击流反应器内的浓度场进行定性和定量分析,用离析度(IOS)评价时均混合效果,得到不同操作条件下IOS值沿径向射流方向的变化规律,并与三喷嘴的情况进行对比. 结果表明,喷嘴间距L、喷嘴直径D和进口流量Q对反应器混合效果有重要影响,在水平两向撞击流中,当喷嘴直径和流量一定时,随喷嘴间距增大,IOS下降速度加快,最佳间距为L/D=3;当喷嘴间距和流量一定时,随喷嘴直径增大,IOS下降更快,下降到IOS=0.05所需距离不断减小,最佳喷嘴直径D=12 mm;当喷嘴直径和喷嘴间距一定时,随流量增加,IOS下降速度先增加后减小,最佳流量Q=500′10-3 m3/h. 三喷嘴撞击流与两喷嘴变化趋势一致.     

不同管口浸没方式下气泡生成行为特性

对三种管口浸没方式下气泡生成行为过程进行可视化实验和三维数值模拟。对比分析了管口浸没方式、管口直径、气体流量等因素对气泡生成形态、气泡脱离直径、气泡膨胀脱离时间以及气液流场速度的影响。实验与数值模拟取得较为一致的结果。研究发现,气泡生成过程可分为单气泡生成和双气泡生成聚并两种模式,两者之间存在明显的气泡脱离形态转折点;三种管口浸没方式下,气泡脱离直径均随着管径和气体流量的增大而增大;气泡膨胀脱离时间随管径的增大而增加,而随气体流量的增加先急剧下降然后趋于平缓;在底吹和侧吹方式下,气泡长短轴比C值分别在0.75和1.1附近波动,其最终脱离形式均接近于球形;而顶吹方式下,C值在1.5附近波动,气泡脱离形态为椭球形。关键词:气液两相流;气泡;数值模拟;浸没方式;脱离直径     

应用激光成像系统研究非牛顿流体中的气泡生成

A self-developed laser image measurement system was established to study the behavior of bubble formation at a single orifice in non-Newtonian polyacrylamide （PAAm） solutions. Images of bubbles were captured by a CCD camera and volumes of bubbles were digitally analyzed online. The effects of rheological property of PAAm solution, orifice, reservoir, and gas flowrate on bubble formation were studied experimentally. It is found that the volume of bubble increases with the concentration of PAAm solution, the diameter of the orifice, and the gas flowrate, respectively, whereas little effect of reservoir is observed in experiments.     

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。     

非牛顿流体中的两并行运动气泡周围流场及气泡间相互作用的PIV研究

The flow fields surrounding two parallel moving bubbles rising from two identical orifices submerged in non-Newtonian fluid of carboxymethylcellulose (CMC) solution of three different mass concentration were measured experimentally by the use of particle image velocimetry (PIV). The influences of gas flowrate, solution mass concentration, orifice interval and the angle between two bubble centers line and vertical direction on the flow field surrounding bubbles were discussed respectively by analyzing the velocity vector, velocity contours as well as individual velocity components. The results show that the liquid velocity both in front of two bubbles and behind increases with gas flowrate duo to shear-thinning effect of previous bubbles, whereas decreases with the increase of CMC concentration due to the increase of drag force acting on bubbles. The effect of the orifice interval on the flow field around two moving bubbles becomes gradually obvious as the interval becomes closer. Moreover, two adjacent side-by-side bubbles repulse each other during rising, leading to the practical interval between them increased somewhat above the orifice interval. When the distance between bubbles is less than the orifice interval l0 mm, the interaction between two neighboring bubbles changed from mutual repellence to attraction with the decrease of the angle of the line of linking two bubble centers to the vertical direction.     

吹气发泡法制备闭孔泡沫铝发泡过程的三维数值模拟

吹气发泡法制备闭孔泡沫铝的过程实质上是搅拌流场中复杂的两相流动过程,应用计算流体力学方法分析由倾斜轴倾斜叶片引起的发泡熔池内气液两相强旋湍流流动过程. 在双流体模型基础上引入多重参考系法描述搅拌两相流场,通过分析相间相互作用及湍流模型进行封闭. 解气泡数密度函数的输运方程来分析气泡聚合和破碎引起的气泡尺寸变化. 应用体积积分的方法,计算平均及局部气含率及气泡直径. 考察了桨叶转速及气体流率对气泡直径及其分布的影响. 结果显示,气含率随桨叶转速和气体流率增加而增大;气泡直径随气体流率增加而增大,随桨叶转速增大而减小.     

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     

拟塑性非牛顿流体中在线气泡聚并规律

以拟塑性羧甲基纤维素钠(CMC)水溶液作为非牛顿流体,对在线上升气泡的聚并规律进行了研究。利用光电信号采集系统测定了不同高度的气泡聚并分布规律,分析了气体速度及流体性质等因素对聚并规律的影响。结果表明,在测量高度和实验气速范围内,随着高度升高,在高气速下,气泡聚并率减小,在低气速下,则先增大后减小。2种情况下,达到一定高度后均趋于恒定;在一定高度下,达到一定气速后,气泡聚并率变化较小;中低气速下,聚并率随CMC质量分数增大而减小,而在高气速下,CMC质量分数变化对聚并率影响较小。     

温度与压力对单孔气泡形成过程的影响

温度压力对进气管孔口气泡的生成具有重要影响。以氮气-水、氦气-水、氮气-十四烷为研究体系,采用高速摄像法,观察了恒速流下孔口气泡的形成过程,考察了孔口气速（0~1500 cm/s）、温度(293~393 K)、压力（0~6 MPa）、孔径（1.12, 2.5 mm）、气体类型（N₂、He）对气泡生长过程的影响。实验表明：随着压力增加,气泡直径减小,纵横比增加;温度升高一方面导致黏度、密度和表面张力降低,使气泡直径减小,另一方面加剧了液体汽化,使得气泡直径增大。根据实验结果修正了Gaddis提出的气泡直径模型,引入饱和蒸气压贡献项,得出新的适用于高温高压条件下气泡直径的估算式。     

Bubble Volume and Aspect Ratio Generated in Non‐Newtonian Fluids

Bubble formation from an orifice submerged in quiescent polyacrylamide aqueous solution was investigated numerically with a sharp‐interface coupled level‐set/volume‐of‐fluid method based on the rheological characteristics of the fluid. In both non‐Newtonian fluids and Newtonian fluids, the numerical approach was able to capture accurately the deformation of the bubble surface, validated by comparison with experimental results. The effects of orifice diameter, solution mass concentration, and gas flow rate on bubble volume and aspect ratio were evaluated. Both the instantaneous and detached volume decrease with the orifice diameter but increase with mass concentration and gas flow rate. The aspect ratio at the departing point tends to rise with the orifice diameter and mass concentration and falls with the gas flow rate.     

微曝氧化沟气液两相传质模型构建及传质影响因素分析

基于ANSYS Fluent软件建立了微曝氧化沟气–液两相流动和溶解氧输运模型,对比不同工况下氧体积传质系数的实验测量值和模拟结果,误差在7%以内。采用验证可靠性的模型模拟研究了气泡直径、曝气量和横向流动速度对微曝氧化沟内氧传质的影响。结果表明,气泡直径由1.5 mm增至3 mm时,氧体积传质系数由15.80 h?1降低至5.83 h?1;曝气量由0.5 m3/h增大至2 m3/h时,氧体积传质系数由4.21 h?1增至14.15 h?1,减小气泡直径和增大曝气量能明显提高氧体积传质系数。微曝氧化沟内气–液相间传质及溶解氧的分布受横向流动影响,开启单台和两台推流泵时,氧体积传质系数分别比无横向推流工况增大27.7%和42.4%,横向流动能有效提高气泡羽流内的气含率,增强氧传质效果。     

Bubble formation in cocurrently upward flowing liquid

The effects of liquid velocity, nozzle diameter, gas chamber volume and gas flow rate on volumes, shapes and growth curves of bubbles formed at a nozzle submerged in a cocurrently upward flowing liquid in a bubble column were experimentally investigated. The bubble volume decreases with increasing liquid flow velocity. The effect of liquid flow velocity on the volume of bubble increases with an increase in the gas flow rate. To simulate bubble formation at a nozzle submerged in cocurrently upward flowing liquid, a revised non-spherical bubble formation model was proposed. Bubble volumes, bubble growth curves and shapes experimentally obtained in this study, as well as in previous experimental studies, are well predicted by the present model.