Effect of mixer geometry and operating conditions on mixing efficiency of a non-Newtonian fluid in a twin screw mixer

The effect of mixer speed, fluid inflow rate, and paddle angle was examined in a shortened geometry. 3D FEM simulation of non-Newtonian 2 g/100 mL carboxymethyl cellulose aqueous solution in the mixing region of a Readco continuous mixer was performed. Data gathered included velocity vectors, shear rate, and mixing index. Increasing mixer speed increased velocity magnitudes in the horizontal and vertical directions. Fluid inflow rate had little impact on velocity in the horizontal and vertical directions, but increased velocity in the axial direction and elongational contribution to the mixing index. All configurations showed areas of simple shear flow where the fluid experienced high shear rates. Staggering paddles increased the maximum axial velocity and shear rate. When successive paddles on the same screw are parallel, a zone was seen between the center of the paddle and the barrel wall which demonstrated efficient dispersive mixing.     

Pulsatile flow of discotic mesophases

This paper presents an analysis using computational and scaling methods of pulsatile capillary Poiseuille flow of a model anisotropic viscoelastic discotic liquid crystalline material. The analysis shows that pulsatile pressure drops applied to anisotropic materials can result in flow-rate enhancement or reduction, defined as the relative flow-rate change with respect to the steady-state flow rate, for a given average pressure drop, amplitude, and frequency. It is found that flow-rate modification in pulsatile flow is a direct result of orientation-dependent viscosity. The role of average pressure drop, oscillation amplitude, and frequency on flow enhancement is characterized and explained. The new mechanism of flow-enhancement in liquid crystals subjected to pulsatile pressure is expected to be useful to the fundamental understanding of pulsatile flows of anisotropic suspensions and anisotropic biological fluids.     

GAS ABSORPTION INTO WAVY AND TURBULENT NON-NEWTONIAN FALLING LIQUID FILMS IN A WETTED-WALL COLUMN

Average Him thickness and liquid-side mass transfer coefficient for the absorption of oxygen in wavy and turbulent power-law model falling liquid films are measured. Considerable reduction in (he film thickness with resulting increase in the mass transfer coefficient are obtained as compared to that predicted by the theoretical laminar flow equation assuming no slip at the wall.     

基于FLUENT的SK型静态混合器的数值模拟

为提高混合器的优化设计水平和工程应用的速度,应用商业CFD软件—FLUENT,分析了聚酯在SK型静态混合器的混合流动。采用FLUENT中的Carreau模型描述了非牛顿流体聚酯的黏-温特性,得出了混合器的压力降及出口混合温度。     

幂律流体的二维层流自由射流

应用层流边界层方程,导出幂律流体二维层流自由射流的常微分方程,对该微分方程求数值解。结果表明,在相同的x处,n>1的流体的最大射流速度较n=1时增加,而射流宽度减小,n<1时则相反;并且,n值偏离1愈远,这种增加或减小愈甚。计算表明,射流宽度与x~(2/3n)成正比。     

Flow around individual Taylor bubbles rising in stagnant CMC solutions: PIV measurements

The flow around single Taylor bubbles rising in non-Newtonian solutions of Carboxymethylcellulose (CMC) polymer was studied using simultaneously particle image velocimetry (PIV) and shadowgraphy. This technique made it possible to determine the correct position of the bubble interface. Solutions of polymer with weight percentage varying from 0.1 to 1.0 wt% were used to cover a wide range of flow regimes. The rheological fluid properties and pipe dimension yielded Reynolds numbers between 4 and 714 and Deborah numbers for the higher concentration solutions between 0.001 and 0.236. The shape of the bubbles rising in the different solutions was compared. The flow around the nose of the bubbles was found to be similar in all the studied conditions. Velocity profiles in the liquid film around the bubble were measured and different wake structures were found. With increasing solution viscosity, the wake flow pattern varied from turbulent to laminar, and a negative wake was observed for the higher polymer concentration solutions.     

Gas-holdup distribution and energy dissipation in an ejector-induced downflow bubble column: the case of non-Newtonian liquid

A precise knowledge of gas-holdup distribution and energy dissipation is essential for designing gas-liquid contactors. A semi-theoretical approach has been presented to obtain the axial distribution of gas holdup through the column for gas-non-Newtonian liquid two-phase flow system. The whole column is distinguished to have three zones based on gas holdup, viz. top, middle and bottom. The middle section where significant accumulation of bubbles takes place, contributes higher gas holdup towards the total compared to the other two sections. Energy dissipation in the column have been calculated from two-phase gas-liquid frictional losses. A comparative study shows that substantial gas holdup are observed in the present system with considerably lower energy losses. The experimental data of gas holdup have been correlated in terms of pressure drop by the modified Lockhart-Martinelli equation.     

稠油油藏注水渗流特性与改善开发效果研究

稠油油藏原油的非牛顿流体流变特性和在注水开发中的渗流特性是影响采油速度和原油采收率的重要因素。根据对三个油田稠油样品的实验研究结果,表明稠油的非牛顿流体流变特性主要受原油组份、含气饱和度、温度和渗流速度的影响;在注水开发中的渗流特性由于受到多孔介质内吸附、凝结和堵塞作用影响,导致流度明显降低,直接影响开发效果。     

A macroscopic model for shear-thinning flow in packed beds based on network modeling

The flow of non-Newtonian fluids in packed beds and other porous media is important in several applications such as polymer processing, filtration, and enhanced oil recovery. Expressions for flowrate versus pressure gradient are desirable for a-priori prediction and for substitution into continuum models. In this work, physically representative network models are used to model the flow of shear-thinning fluids, including power-law and Ellis fluids. The networks are used to investigate the effects of fluid rheology and bed morphology on flow.A simple macroscopic model is developed for the flow of power-law and Ellis fluids in packed beds using results from the network model. The model has the same general functionality as those developed using the popular bundle-of-tubes approach. The constant β, which appears in these models, is often directly derived from the tortuosity and a simple representation of the porous media. It is shown here that this can lead to incorrect and ambiguous values of the constant. Furthermore, the constant is a weak function of the shear-thinning index, indicating that no single bundle-of-tubes could ever properly model flow for a wide variety of shear-thinning fluids.The macroscopic model is compared to experimental data for shear-thinning fluids available in the literature. The model fits the data well when β is treated as an experimental parameter. The best-fit values of β vary, which is expected because even the constant C in the Blake-Kozeny equation varies depending on the source consulted. Additionally, physical effects, such as adsorption and filtration, as well as rheological effects such as viscoelasticity may affect the value of β. We believe that in the absence of these effects, β equals approximately 1.46 for packed beds of uniform spheres at relatively moderate values of the shear-thinning index (>0.3).     

Fluidization with viscoelastic polymer solutions in the transition flow region

Fluidization of spherical and non-spherical particle beds with shear thinning viscoelastic polymer solutions was investigated experimentally in the transition flow region. It was observed that the influence of elasticity on the anomalous expansion course weakens with the increasing value of Reynolds number. After exceeding a critical value of Reynolds number, which depends on the measure of liquid elasticity, the effect of elasticity vanishes and the expansion curves have the same linear shape as for fluidization with Newtonian (or purely viscous non-Newtonian) fluids. Semi-empirical equations based on the Carreau viscosity model were proposed for predicting the critical value of Reynolds number and the bed expansion in the region of diminishing elasticity effects.