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CTAC表面活性剂水溶液圆盘减阻及其流变特性的实验研究
论文作者:童鞋论文网  论文来源:www.txlunwenw.com  发布时间:2019/9/3 9:53:07  

摘要:诸如离心泵、水轮机、船用螺旋桨等旋转机械在实际工程过程中均因湍流摩擦阻力的存在而消耗大量的能量。虽然表面活性剂的加入能够抑制湍流涡、减少叶片表面的湍流摩擦阻力,起到节能减阻的效果,但是直至目前表面活性剂溶液减阻机理仍不清晰,为此本文使用减阻与流变相结合的方法对表面活性剂溶液减阻开展了深入的研究。首先利用旋转圆盘减阻装置研究了浓度、温度和雷诺数对表面活性剂溶液减阻的影响;然后利用MCR302流变仪研究了浓度、温度和剪切速率对减阻表面活性剂溶液流变特性的影响;最后基于减阻溶液的减阻现象和流变特征,分析总结了减阻与流变的内在关系。从目前的研究结果,可以得到以下结论:

(1) CTAC/NaSal溶液的最大减阻率与其雷诺数、温度和浓度密切相关;在不同的雷诺数范围内,CTAC/NaSal减阻溶液最大减阻率所对应的温度是不同的;CTAC/NaSal减阻溶液黏性阻力和胶束结构转变直接影响其减阻效果的好坏。

(2) 低浓度CTAC/NaSal减阻溶液的剪切黏度随时间可分为4个阶段,其诱导时间随剪切速率的升高不断减小,并符合幂律函数关系y=axb;对于中等浓度的CTAC/NaSal减阻溶液,不会出现剪切增稠现象,意味着胶束初始结构对剪切作用的依赖不大。

(3) 对于低浓度的CTAC/NaSal减阻溶液,当浓度相对较高而剪切速率较大时,黏度曲线在高温处出现“平台”或短暂增稠的现象;在中等浓度的CTAC/NaSal减阻溶液中,胶束会出现分支现象,分支胶束的出现是减阻变差的原因之一。

(4) 在双对数坐标下,所有浓度减阻溶液的流动曲线均符合线性规律;当浓度C>2.5000mmol·L-1时,剪切增稠现象消失,同时其黏度和流动曲线的演变区域由3个减小到2个。

(5) 低浓度CTAC/NaSal减阻溶液的剪切增稠是因剪切诱导结构的形成引发的,而剪切诱导结构的形成正是其减阻的主要原因;当浓度C≥2.5000mmol·L-1时,在静态下形成的大胶束网络结构则是溶液减阻的主要原因。

ABSTRACT: Rotating machinery such as centrifugal pumps, turbines and marine propellers consume a lot of energy due to the existence of turbulent frictional resistance in the actual engineering process. Although the addition of surfactants can restrain turbulent vortices, reduce turbulent friction on blade surface, reduce energy consumption and play the effect of energy saving and drag reduction, the mechanism of drag reduction of surfactant solution is still unclear up to now. In this paper, drag reduction of surfactant solution by combining drag reduction and rheology is studied in depth. Firstly, the effects of concentration, temperature and Reynolds number on the drag reduction of surfactant solution were studied by using a rotating disk drag reduction device. Then the effects of concentration, temperature and shear rate on rheological properties of drag-reducing surfactant solution were studied by MCR302 rheometer. Finally, based on the drag reduction phenomena and rheological characteristics of drag reduction solution, the internal relationship between drag reduction and rheology is analyzed and summarized. From the current research results, the following conclusions can be drawn:

(1)The maximum drag reduction rate of CTAC/NaSal solution is closely related to its Reynolds number, temperature and concentration. In different Reynolds number range, the maximum drag reduction rate of CTAC/NaSal drag reduction solution corresponds to different temperatures. Viscous resistance and micelle structure transition of CTAC/NaSal drag reduction solution directly affect its drag reduction effect.

(2)The shear viscosity of low concentration CTAC/NaSal drag reduction solution can be divided into four stages with time. The induction time decreases with the increase of shear rate, and conforms to power law function y=axb. For medium concentration CTAC/NaSal drag reduction solution, shear thickening does not occur, which means that the initial structure of micelles does not depend much on shear.

(3)For the low concentration CTAC/NaSal drag reduction solution, when the concentration and the shear rate is relatively high, the viscosity curve appears "platform" or temporary thickening phenomenon at high temperature; in the medium concentration CTAC/NaSal drag reduction solution, micelles appear branching phenomenon, and the appearance of branching micelles is one of the reasons for the poor drag reduction.

(4)In logarithmic coordinates, the flow curves of all concentration drag reduction solutions conform to linear law. When the concentration of C>2.5000mmol·L-1, the shear thickening phenomenon disappeared, and the evolution area of viscosity and flow curve decreased from 3 to 2.

The shear thickening of low concentration CTAC/NaSal drag reduction solution is caused by the formation of shear-induced structure, which is the main reason for its drag reduction. When the concentration of C>2.5000mmol·L-1, the large micelle network structure formed under static state is the main reason for drag reduction.

关键词:表面活性剂;圆盘减阻;流变特性;温度;浓度;剪切速率

KEYWORDS: Surfactant; Disk drag reduction; Rheological properties; Temperature; Concentration; Shear rate

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