非牛顿流体中的气泡行为

非牛顿流体广泛存在于各学科领域（如化工、食品和生物医学等）,也与许多工业过程及人类的生命过程密切相关。非牛顿流体中的气泡行为直接影响流体传质、传热及化学过程的快慢。因此,了解和研究非牛顿流体中的气泡行为具有重要意义。本文分别从气泡生成、聚并和破裂3个方面对非牛顿流体中气泡行为的研究进展进行评述。     

Computational Fluid Dynamics Simulation of Generation and Coalescence of Bubbles in Non‐Newtonian Fluids

The successive generation and coalescence behaviors of bubbles from two parallel nozzles in non‐Newtonian fluids were numerically simulated by using the volume of fluid (VOF) method. Three flow patterns for bubbles and the related flow regime transition lines were obtained. Two critical nozzle intervals exist: one for the bubble coalescence before pinch‐off, and another for alternating bubble formation then in‐line coalescence under different conditions. Two correlations were proposed to predict the dimensionless critical nozzle intervals for the transition of bubble‐flow patterns. The influences of nozzle diameter, gas flow rate, nozzle interval, and rheological properties of fluid on bubble‐flow patterns were investigated systematically.     

低温气液两相流中Taylor气泡的合并

在自建的低温气液两相流实验平台的基础上,通过高速相机获得16 mm内径管路中30o~90o倾角下Taylor气泡之间的合并过程. 结果表明,已有的常温气液两相流中Taylor气泡的合并公式普遍高估了跟随气泡和领先气泡的速度比,与实验结果的最大误差为14.6%,对低温气液两相流不再适用. 新建的Taylor气泡合并过程速度拟合公式可将最大误差减小至4.7%. 此外,气泡间最小稳定距离在60o倾角附近最小,此时气泡间合并趋势最弱.     

淋降塔内非牛顿流体的传质研究

本文研究非牛顿幂律流体传质过程,实验采用淋降塔装置,测定高聚物溶液的传质速率.实验结果表明传质速率随温度和溶液流量增加而增大,还随压力和溶液稠度系数下降而增加.并应用相似论原理分析非牛顿幂律流体传质过程,得到柯尔本因子与雷诺数关系式j_m=BRe~B_1,由实验数据经线性回归得到B=2.2708×10~(-5),B_1=-0.7013相关系数0.99.     

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.     

聚合物流体入口收敛流动的数值模拟

聚合物流体从大截面流道进入小截面流道时产生的入口收敛流动,是工业中常见的流型之一。基于聚合物流体入口收敛边界流线方程,应用MATLAB对入口收敛流动进行了数值模拟,讨论了Bagley校正因子(e)、非牛顿指数(n)、流道收缩比(λ)等因素对入口收敛流线和入口自然收敛半角(α0)的影响。结果表明:在一定的条件下,入口收敛边界流线的半径r随着e的增加而增大,但随着n的增加而减小,而λ对入口流型的影响不明显;另外α0随着e的增加而减小,但随着n的增加而增大,α0与λ之间呈非线性关系。模拟结果与实验观测较为接近。     

非牛顿流体在搅拌槽内的传热

基于搅拌桨旋转扭矩和搅拌槽内所有壁面的平均扭矩近似相等的关系,引入流况系数,提出了计算非牛顿流体表观粘度的剪切速率模型.并对内蛇管、外蛇管和直管以及不同几何尺寸的MIG、透平、三叶后掠式、板式、锚和半椭圆片桨组成的多种搅拌体系,用该模型关联夹套侧和冷却管侧的给热系数,分别得到了统一不同几何尺寸搅拌桨的给热系数关联式.该模型适用于不同冷却构件.不同类型、不同几何尺寸的搅拌桨、过渡域和湍流域以及夹套侧和冷却管侧的非牛顿流体给热系数关联.另外,对多种剪切速率模型进行了比较和讨论.     

Numerical Study on Interaction Between Two Bubbles Rising Side by Side in CMC Solution

A numerical simulation was performed to investigate the interaction of two bubbles rising side by side in shear-thinning fluid using volume of fluid (VOF) method coupled with continuous surface force (CSF) method. By considering rheological characteristics of fluid, this approach was able to accurately capture the deformation of bubble interface, and validated by comparing with the experimental results. The rising of bubble pairs with different configurations, including horizontal alignment and oblique alignment, was simulated by the method. The influences of the bubble initial distance and the bubble alignment were studied by analyzing the bubble deformation, rising paths and flow fields surrounding bubbles. The results indicate that within certain initial bubble spacing of S^* 3.3 (S^* S_I/D, S_I initial distance between bubbles, and D bubble diameter), the dynamic interaction between two bubbles aligned horizontally shows repulsive effect that decreases with the increase of initial bubble spacing, but weakens to certain degree by the shear-thinning properties of fluid. However, the interaction between two bubbles aligned obliquely presents a repulsive effect for the small angle involved but an attractive impact for the large one, which is yet strengthened by the rheological characteristics of fluid.     

Coalescence Characteristics of Side-by-Side Growing Bubbles in Carboxymethyl Cellulose Solutions

New experimental data are presented on the coalescence dynamics of twin bubbles at two adjacent nozzles in carboxymethyl cellulose (CMC) solutions. The coalescence process was recorded by using a fast video technique and the images were then analyzed to evaluate the regime, efficiency, and patterns of bubble coalescence. The results reveal that the coalescence process contains the four periods of spherical expansion, rapid mergence, overall growth, and instant departure. The coalescence efficiency always passes through five stages with the gas flow rate; it grows with the CMC solution concentration, but decreases with the surfactant concentration, except at very low gas flow rates. The bubble coalescence pattern strongly depends on the nozzle spacing, but conditionally on the gas flow rate and the solution properties.     

粘弹性流体层流自然对流传质的研究

本文以求解微分方程组为手段,得到了此问题的近似解,其中选用Oldroyd三参数模型作为流体的本构方程.其理论结果已经电化学实验数据验证,经拟合发现两者较好地吻合,并且发现粘弹性流体的弹性对传质过程肯定有影响.     

一串上升气泡周围流体的湍动特性(英文)

The turbulence behavior of gas-liquid two-phase flow plays an important role in heat transfer and mass transfer in many chemical processes. In this work, a 2D particle image velocimetry (PIV) was used to investigate the turbulent characteristic of fluid induced by a chain of bubbles rising in Newtonian and non-Newtonian fluids. The instantaneous flow field, turbulent kinetic energy (TKE) and TKE dissipation rate were measured. The results demonstrated that the TKE profiles were almost symmetrical along the column center and showed higher values in the central region of the column. The TKE was enhanced with the increase of gas flow and decrease of liquid viscosity. The maximum TKE dissipation rate appeared on both sides of the bubble chain, and increased with the increase of gas flow rate or liquid viscosity. These results provide an understanding for gas-liquid mass transfer in non-Newtonian fluids.     

Efficiency of the Entrainment of Rodlike Particles by Rising Bubbles

The efficiency of the entrainment of rodlike particles by rising bubbles was determined experimentally. The observed and calculated data are in a satisfactory agreement.     

Coalescence of Two Viscous Cylinders by Capillarity: Part II, Shape Evolution

The theoretical geometry of the creeping plane-flow coalescence of two viscous cylinders driven by surface tension is described. Normalized results are given for initial diameter ratios D = (1, 2, 5, 20, ∞) Typical shapes are displayed. Time-dependencies of geometric features, and interrelationships between them, are presented graphically. The following features are noted: The relationships between reduced time and most dimensions depend rather weakly on D . There is no undercutting at the neck. Two-dimensional Frenkel theory is seriously incorrect. The theory describes experiments accurately for small times, but differences eventually appear. Their sources are uncertain.     

A General Correlation for the Rise Velocity of Single Gas Bubbles

A correlation for the terminal rising velocity of a single gas bubble in an infinite Newtonian fluid is proposed. The model is an extension to high Reynolds numbers of a model developed recently by the author (Rodrigue, 2001a). This new equation, which is explicit in velocity, is able to predict the velocity for any bubble volume in any Newtonian fluid.     

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.