Lightnin静态混合器内气泡分散流体动力学特性实验研究

以Lightnin静态混合器（LSM）内水-空气气液两相体系为研究对象,在连续相水表观速度U_L=0.071~0.127 m/s和离散相空气表观速度U_G=0.007~0.042 m/s的条件下,研究内径100 mm的LSM内气液两相湍流流动阻力与气泡分散水动力学行为。使用分辨率为1920×1080的高速相机Revealer-2F04M采集混合器内不同轴向窗口的气泡群演化过程。结果表明：当U_L<0.085 m/s和U_G=0.025~0.042 m/s时,LSM内的流型为泡状流。随着气泡群流经混合元件数的增加,气泡群的Sauter平均直径d₃₂逐渐减小。当液体表观速度U_L≤0.085 m/s时,Sauter平均直径d₃₂随气体表观速度的增加先减小后增大;U_G =0.028 m/s时d₃₂达到局部最小值,53%的气泡直径d_B/D₀在0.02~0.05范围内。Sauter平均直径、内径与无量纲停留时间τ之间的关系满足d₃₂/D₀=0.031τ^-0.14We^-0.41。平均气含率α的增大显著增加了单位体积内气泡数量密度,加剧气泡与元件表面碰撞频率,增大旋涡二次流强度,导致摩擦系数显著降低;采用Lockhart-Martinelli方法对实验数据回归,得到气液两相流压降预测常数C的关联式：C=5.26×10⁵U_G^-0.91/Re^0.74。     

Lightnin静态混合器内气泡分散流体动力学特性实验研究

以Lightnin静态混合器（LSM）内水-空气气液两相体系为研究对象,在连续相水表观速度U_L=0.071~0.127 m/s和离散相空气表观速度U_G=0.007~0.042 m/s的条件下,研究内径100 mm的LSM内气液两相湍流流动阻力与气泡分散水动力学行为。使用分辨率为1920×1080的高速相机Revealer-2F04M采集混合器内不同轴向窗口的气泡群演化过程。结果表明：当U_L<0.085 m/s和U_G=0.025~0.042 m/s时,LSM内的流型为泡状流。随着气泡群流经混合元件数的增加,气泡群的Sauter平均直径d₃₂逐渐减小。当液体表观速度U_L≤0.085 m/s时,Sauter平均直径d₃₂随气体表观速度的增加先减小后增大;U_G =0.028 m/s时d₃₂达到局部最小值,53%的气泡直径d_B/D₀在0.02~0.05范围内。Sauter平均直径、内径与无量纲停留时间τ之间的关系满足d₃₂/D₀=0.031τ^-0.14We^-0.41。平均气含率α的增大显著增加了单位体积内气泡数量密度,加剧气泡与元件表面碰撞频率,增大旋涡二次流强度,导致摩擦系数显著降低;采用Lockhart-Martinelli方法对实验数据回归,得到气液两相流压降预测常数C的关联式：C=5.26×10⁵U_G^-0.91/Re^0.74。     

喷吹搅拌系统中气液动力学行为的混沌识别

以底吹熔池熔炼过程为研究对象搭建水模型实验平台,捕获气体喷吹系统内气泡流型的彩色图像,对彩色图像进行灰度化,去噪及二值化操作后得到贝蒂数,以贝蒂数来表征气液二相混沌效果,引入0-1测试法并通过数值模拟验证该方法的有效性。运用回归方法和关联方法的0-1测试法检测贝蒂数时间序列的混沌特性,考察了喷枪倾角及数目对本系统混沌特性的影响。研究结果表明:模拟数据验证了0-1测试法在区分系统混沌特性方面的有效性;6组工况均表现出混沌特性;对每组工况的贝蒂数时间序列分别基于回归方法和关联方法进行了0-1测试,显示关联方法较回归方法更为显著,且渐近增长率Kc中值在一定程度上反应了各工况的混沌强弱程度。此研究为强化流体混沌混合提供了直观简便的测试方法。     

轻重相交替进料筛板萃取塔中的传质性能研究

针对间歇操作萃取工艺生产能力低,而逆流连续操作萃取工艺返混严重等问题,研究提出了轻重相交替进料操作的萃取工艺,并对轻重相交替进料筛板萃取塔中的传质性能进行了研究。以煤油-苯甲酸-水为萃取体系,采用单个液滴的传质模型来计算萃取塔的分散相总传质系数,并研究了分散相流速、连续相流速、液滴上升速度以及塔板间距对分散相总传质系数的影响。实验得到分散相总传质系数Kod的数值在3.49?10?5~5.47?10?5 m?s?1,总分散相存留分数在1.63%~4.37%。结果表明轻重相交替进料筛板萃取塔的分散相总传质数高于Kühni搅拌萃取塔、脉冲萃取塔和振动挡板塔,并且流量变化对Kod的影响小,返混效应弱,总分散相存留分数小,不易液泛。     

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。     

基于改进0-1测试的多相宏观混合效果混沌表征

针对多相搅拌混合效果的量化特征提取提出一种新思路:利用改进型0-1混沌测试方法表征多相混合过程贝蒂数时间序列的混沌特性,并优化混合效果与评价特征值之间定量协调关系。研究发现,将贝蒂数时间序列的渐进增长率Kc的中值作为混沌检测依据,可更加精确地表征不同混合过程中混沌度的差异性变化。贝蒂数混合效果评价方法表明,零维贝蒂数β0与一维贝蒂数β1之间存在相关性,经验证β0时序的Kc中值和β1时序的Kc中值之间也存在较强的正相关性,理论上更加符合β0和β1的代数拓扑学意义。在此基础上进一步发现基于混沌检测的渐进增长率Kc中值与表征混合效果的贝蒂数指标之间具有相关关系,相关系数为0.645,并且Kc中值表征混合效果的有效性由水动力学实验得到了验证。本研究对于拓展和丰富贝蒂数混合效果评价方法具有重要意义。     

旋流筛板式气固挡板流化床内压力脉动特性

在表观气速Ug=0.04~1.14 m/s时,采用旋流筛板构型的挡板式内构件,通过对比分析旋流筛板式气固挡板流化床与自由床内流动现象、压差脉动标准偏差和压力脉动标准偏差等参数,确定了旋流筛板式气固挡板流化床能有效破碎气泡的流动与操作条件。结果表明,构件下方区域颗粒随表观气速增加而不断转移至构件上方床层,造成构件下方区域密相床层高度持续降低,该区域出现3种流动状态并直接决定构件是否能破碎气泡。当Ug<0.44 m/s时,构件下方区域密相床层料位较高,形成下部为密相床层、上部为密相与大气泡交替通过构件的鼓泡床,此时构件具有抑制气泡生长并破碎气泡的作用,全床压差脉动及压力脉动标准偏差低于相同条件下的自由床;当0.44≤Ug<0.66 m/s时,密相床层料位较低,形成下部为密相床层、上部为单一稀相的湍动床,此时构件不再直接抑制气泡生长或破碎气泡,但构件下方密相床层的存在能降低构件下方及构件上方一定高度内床层的压力脉动强度;当Ug≥0.66 m/s后,密相床层完全消失,形成气体为连续相的稀相流化状态,构件不能破碎气泡、降低床层压力和压差脉动强度。     

同向环流萃取装置的存留分数和液泛研究

在直径0.1 m,孔径3 mm的一种同向环流萃取装置中,针对煤油-水和30%磷酸三丁酯(TBP)/煤油-水两种体系,采用体积置换法和观察法分别对分散相存留分数和液泛速度进行了研究。实验结果表明了分散相存留分数随两相表观速度的增大而增大,且分散相速度的影响大于连续相速度。得出了在这两种体系下,连续相的流量范围分别为0～29和0～34 L×h~(-1),分散相的流量范围分别为10～166和16～125 L×h~(-1)。同时,采用无因次数群法拟合出存留分数和液泛速度的经验关联式。两个经验关联式都能在实验范围内很好地对存留分数和液泛速度进行预测,为工业过程放大和工程设计提供了重要的计算依据。     

聚醚砜超滤膜乳化法制备乳化柴油

采用平均孔径为25 nm的聚醚砜超滤(UF)膜,以去离子水为分散相,以0#柴油为连续相,分别以Tween-20和Span-80为分散相及连续相的乳化剂,采用膜乳化法制备W/O型乳化柴油。UF膜乳化法制备的乳液比传统乳化方法稳定时间提高2～2.5倍,而相同条件下乳化剂用量减少了50%～65%。此外,考察了UF膜法制备乳化柴油过程中的各工艺参数对乳液液滴大小、分布及稳定性的影响规律,结果表明:当乳化剂质量分数高于0.5%,连续相流速在2.0～5.0 m/s范围内,跨膜压差为0.02 MPa时,乳液分散系数α达到0.12～0.3,液滴尺寸为30～65 nm。     

直接接触式沸腾换热过程气泡混合均匀度评价

针对直接接触式沸腾换热过程中气泡群扰动的多相流体混合性能评价问题,提出一种基于图像处理技术与像素偏差理论量化混合复杂流体流型均匀性的精确检测与度量新方法。通过气泡群RGB图像的灰度矩阵进行偏差计算,精确地定量描绘了直接接触式换热过程中的气-液混合状态,其值大小反映了气泡群的分布状况,而不同工况下混合均匀时间的差异反映了不同多相体系的均匀性差异;对偏差序列进行正态性检验,发现其近似符合正态分布;运用混沌检测方法对序列进行混沌特征分析,发现整个混合过程是混沌的。通过一个简单的指标实现了复杂条件下气泡群的量化和表征,为多相流流型识别提供了新的分析思路并指导换热过程的混沌强化。     

附加惯性力作用下竖直矩形流道内过冷流动沸腾的数值模拟

摇摆条件下附加惯性力的作用会对两相流动的压降及汽泡受力产生影响。考虑相变能量和质量输运,采用流体体积(VOF)多相流模型对附加惯性力条件下竖直矩形流道内过冷流动沸腾进行了数值模拟。汽液界面位置通过分段线性插值(PLIC)的方法获得。模拟结果获得了孤立汽泡周围压力、速度、温度分布以及二次流动现象,分析了汽泡聚合过程汽泡形态及内部速度矢量的演变过程,模拟结果与文献中结论吻合良好。附加惯性力作用使得流动压降比静止条件下要大,过冷流动沸腾压降由于汽相产生会在单相流动的基础上产生波动,且热通量越大,压降波动幅度越大。摇摆产生的附加惯性力相对汽泡所受的其他力而言可以忽略不计,而摇摆导致的流量波动会改变汽泡受力大小,进而影响沸腾换热。     

高气液密度比的传热相变复合模型

为研究两相流动中热量传递机制,基于格子Boltzmann热模型及大密度比模型,将相变源项引入到控制两相密度分布函数中,来描述温度场对气液相变的影响,提出了一个可以描述气液密度比达到2778的传热相变复合模型。通过对压力速度分布函数的回归修正克服了气液密度比过大造成的数值不稳定问题。模拟了溴化锂水溶液中双气泡的上升运动过程及周围的温度场分布,研究发现：双气泡上升时,碰撞前上方气泡温度高于下方气泡,碰撞时,两气泡间液桥打开,发生热量传递,气泡内部温度变得均匀;双气泡体积先减小再增大,碰撞时体积达到最大值,在融合成一个气泡后体积逐渐缩小,最终趋于稳定;初始气泡的体积越大,气泡上升过程中的速度越大。     

Influence of bubble column diameter on local heat transfer and related hydrodynamics

Heat transfer coefficients measured in a 0.15 m ID bubble column are compared with similar studies in larger diameter columns to identify influence of column diameter. Gas phase used is oil free compressed air and its flow rate is varied from 0.03 to 0.35 m/s. Tap water is the liquid phase and the solid particles used are 49 μm glass beads and their concentration is varied up to 20 vol%. The observed increase in heat transfer coefficients can be related to increase in liquid circulation velocity with column diameter which in turn is related to increase in large bubbles rise velocity. A simplified scale-up procedure is presented based on available data and suitably modified literature correlations for heat transfer coefficient.     

Distribution of the gas flow in fluidized beds with a slugging behaviour

Capacitance probe measurements of the visible bubble flow rate have been made in a pressurized fluidized bed burning coal. The bed, of 0.3 × 0.3 m cross-section, was operated at pressures between 1.0 and 2.0 MPa and at temperatures between 750 and 900°C. The fluidizing velocity was 0.95 m/s and the mean particle diameter was 0.9 mm. Based on the experimental results, a model of the gas distribution between the bubble phase and the particulate phase in fluidized beds with a slugging behaviour was developed. The model accounts for the lack of bubble flow obtained if the two-phase theory is employed. In order to verify the model, simultaneous measurements of the visible bubble flow rate and of the gas flow rate through the bubbles were carried out in a bed of similar geometry but operating at ambient conditions. In this bed the fludizing velocity was varied between 1.6 and 2.7 m/s and the mean particle diameter was 1.0 mm. The through-flow of gas was measured with the aid of pressure probes. Evaluation of the experimental results using the model showed that this gas through-flow in the bubble phase subsequently increases the superficial gas velocity in the particulate phase between the vertically aligned bubbles (slugs), and that this gas velocity in excess of the incipient fluidization velocity is responsible for the large deviation from the two-phase theory. The associated increase of the particulate phase voidage was calculated via the Ergun equation.     

Formation dynamics and size prediction of bubbles for slurry system in T-shape microchannel

The bubble formation dynamics and size manipulation in the slurry of polystyrene microspheres in the microfluidic T-junction were visually investigated by a high-speed camera. Based on the evolution of the bubble neck with time, the formation process of bubbles is divided into three stages: filling, squeezing and pinch-off. The particle concentration has an obvious effect on the squeezing stage, while less impact on the filling and pinch-off stages. In the squeezing stage, the evolution of the dimensionless minimum neck width of bubbles with time could be described by a power-law relationship. The increase of the particle concentration or continuous phase flow rate could lead to the increase of body flow of the continuous phase and the enhancement of the squeezing force acted on the bubble neck, correspondingly, the power-law index α in the squeezing stage enlarges. Moreover, the bubble size increases with the increase of the gas phase flow rate and the decrease of the particle concentration and continuous phase flow rate. However, the effect of the particle concentration on the bubble size weakens with the increase of the continuous phase flow rate. In addition, a new prediction correlation of the bubble size for the slurry system in a T-shape microchannel was proposed with good prediction accuracy.     

基于群体平衡原理的蒸汽发生器汽液两相流动与沸腾数值模拟

基于相似原理建立了耦合四叶梅花形支撑板的蒸汽发生器“单元管”三维物理模型。采用考虑汽泡聚合与破碎效应的MUSIG （multiple-size-group）模型描述二次侧汽泡尺度分布和水力特性,热相变模型计算二次侧汽液两相沸腾相变过程,对大亚湾蒸汽发生器汽液两相流动与沸腾过程进行数值研究。模拟结果表明,支撑板位置处汽、液相流速均急剧升高,产生射流,在离开支撑板孔口时迅速形成回流。两相邻支撑板间出现明显的汽泡由小到大的周期性变化过程,冷、热端沿程汽泡最大直径缓慢减小。二次侧平均传热系数与Rohsenow经验关联式的计算结果吻合较好。     

特征时间对剪切稀化流体气泡上浮特性的影响

非牛顿气液两相流广泛存在于工农业生产中,气泡和液相间的接触非常复杂,对相间的传递效率具有重要的影响。为了理解气泡在非牛顿流体中的运动特性,基于连续表面张力模型与Carreau本构模型,本文运用volume of fluid（VOF）法研究了单气泡在剪切稀化流体内自由上浮的运动特性。研究发现：气泡的动力学特性与液相的特征时间λ密切相关,液相的剪切稀化程度越强（流变指数n越小）或表面张力越小（Eo数越大）时,特征时间λ对气泡变形和尾涡的影响越大。在给定的剪切稀化程度和表面张力下,λ越大,气泡终端速度越大,其尾涡强度和尺度也越大,导致气泡周围液相高剪切速率区和低表观黏度区的范围越宽。此外,当液相的表面张力较小时,在气泡尾部出现了黏度盲区;并且随着λ的增大,黏度盲区逐渐脱离气泡尾部并破碎;黏度盲区的出现减小了气泡周围液相低表观黏度区的面积,增大了气泡上浮过程的摩擦阻力,降低了气泡的终端速度。     

Mass transfer with chemical reaction from spherical one or two component bubbles or drops

Unsteady state mass transfer between a one or two component bubble (or drop) and the continuous phase with a chemical reaction occuring either in the continuous or in the dispersed phase is examined. The main assumption for binary bubbles is that the rate determining step is diffusion in the continuous phase. Two limiting velocity fields. Hadamard flow (Re?:1) and potential flow (Re?:1) are used in the calculations.     

The modifications of a plane mixing layer by condensed bubbles

Injecting superheated water vapour bubbles into a sub-cooled shear flow will induce heat and mass transfer in the form of condensation. Of particular interest is finding the characteristic role that the large-scale vortex structures play on bubble condensation. Because the heat transfer and condensation take place mainly due to convection, the bubble is expected to collapse at an earlier stage because of the trapping by large-scale vortices. The aim of this paper is to investigate two-way thermal and momentum interaction between bubbles and the large-scale coherent structures in a plane turbulent shear layer, focusing on the effect of bubble condensation on large-scale vortex structures embedded in plane, free shear layers. The parameters such as initial bubble temperature, bubble injection location, and carrier fluid temperature have been chosen to examine their effects on the condensation and dispersion of bubbles. Because superheated vapour bubbles immersed within a sub-cooled shear flow field experience heat transfer, the gas phase will certainly condense into liquid if these bubbles remain surrounded long enough by this same sub-cooled liquid. Accordingly, bubble condensation is evident within the shear layer and bubble dispersion is influenced by the large-scale vortex structures. The main driving force behind complete bubble condensation was the difference in temperature between the bubble vapour and the carrier fluid. It was revealed that the effect of the large-scale vortex structures is that the condensed bubbles acquire a larger dispersion than bubbles that were not subject to thermal coupling.     

Y聚焦型微通道内磁流体液滴的生成与调控

利用高速摄像仪研究了截面为400 μm×400 μm Y聚焦型微通道内磁流体液滴在矿物油中的生成过程。以水基磁流体EMG 807为分散相,含4%表面活性剂Span-20的矿物油为连续相。实验观察到了3种流型：弹状流、滴状流和喷射流。分别考察了两相流量、连续相毛细数及磁感应强度对液滴尺寸及生成过程的影响。结果表明：可通过改变两相流量及磁场调控液滴尺寸。当分散相流量不变时,液滴尺寸随着两相流量比的增加而减小。液滴尺寸随着连续相毛细数及磁感应强度的增加而减小,随着分散相流量的增加而增加。以两相流量比、连续相毛细数和磁Bond数为参数提出了一个液滴尺寸的关联式,预测值与实验值吻合良好。