一种新的Couette流变仪的精度校核

利用新研制的外筒旋转可调压可视化Couette流变仪,开展了强剪切流的空化试验,发现剪切力矩及瞬态温度对剪切空化的影响非常明显。通过传感器温度阶跃响应试验数据,求得温度传感器在静止液体内受阶跃温度变化时的表面传热系数。采用柱坐标系,基于试验获得的纯剪切力矩和瞬态传热微分方程,由数值计算方法求出不同时刻强剪切Couette流的瞬态温度,理论计算值与试验结果较为吻合,表明新的外筒旋转可调压可视Couette流变仪获得的纯剪切力矩和瞬态温度的准确性,以及间隙的均匀性。利用文献[9]的初步估算方法,也可求出强剪切Couette流的温度变化值。对比分析结果表明,所提方法校核精度高且适用范围广。     

论多相流中单流体模型与多流体模型的统一性

本刊发表的“多相流的随体导数和基本方程”,一文认为对多相流的随体导数必须重新研究、定义,以使单流体模型和多流体模型能获得统一,并提出了一套建立随体导数的方法。本文作者认为[1]文的分析不仅在概念上有许多混淆之处,而且所提出的随体导数有些牵强附会,缺乏明确的物理意义,结果并没有使单流体模型和多流体模型真正统一。本文就随体导数的本来含义进行推导、分析,指出单流体模型和多流体模型的统一性。     

PDMS在大振幅剪切流动中的壁面滑移

本文采用旋转流变仪研究了聚二甲基硅氧烷(PDMS)在两平行板间的大振幅剪切流动,其中的关键参数是应变幅值和角频率.随应变幅值增加,依次观察到没有波形畸变→明显的波形畸变→波形畸变减弱直至消失,对应着熔体与壁面之间的粘附→弱滑移→粘附/滑移→强滑移.同时角频率增加,样品的非线性增加,滑移也增强.从应力的间距依赖性和波形畸变等力学响应角度讨论了大振幅剪切流中的壁面滑移现象,同时使用应力分解的方法对大振幅剪切流中样品的非线性强弱进行了度量,提出了PDMS在大振幅剪切流中的动力学图谱.     

非牛顿特性对偏心圆筒内流体混沌混合的影响

Effect of fluid elasticity and shear-thinning viscosity on the chaotic mixing between two alternately rotating cylinders has been studied. The h-p finite element method is used to obtain high accurate solutions of the steady flow. The unsteady, periodic flow is simulated using the piecewise-steady approximation. Characteristics of the chaotic mixing axe analyzed by examining the asymptotic coverage of a passive tracer and the lineal stretching ofthe fluid elements in the annulus. For the viscoelastic fluids modeled by the upper-convected Maxwell constitutive equation (UCM), our computation predicts little effect of the fluid elasticity on the mixing patterns. On the other hand, the shear-thinning viscosity, modeled by the Carreau equation, has a large impact on the advection of a passive tracer and the distribution of lineal stretching. We find that the zones of the lowest stretching match remarkably well with the regular zones in the tracer-coverage plotting. Our study reveals the vital importance of reducing the discretization errors of the velocity field in the numerical simulation of chaotic flows.     

空气在二甲基硅油和液压油中扩散系数的测量

A piston-cylinder apparatus was established to measure the solubility and diffusivity of air in dimethyl silicone oils and in hydraulic oils based on the PVT state equation of air and the solution of unsteady one-dimensional diffusion equation. The measured diffusivity-temperature relation can be well fitted by the Arrhenius equation for engineering applications. The correlation between the solute diffusivity D and solvent viscosity  is examined. In terms of Eyring’s activation theory, the activation in the air-silicone-oil diffusion process is quite different from that in the momentum transport of the silicone oil: the activation entropy of the former is positive while that of latter is negative. However, the activation enthalpies of the two processes are in the same order of magnitude, which leads to the observation that D/T is roughly constant.     

混沌混合中流体指数拉伸与混合效率的数值研究

The stretching and folding of fluid element during chaotic mixing field is studied using numerical method. The chaotic mixing process is caused by periodic secondary flow in a twisted curved pipe. Using the nonlinear discrete velocity field as the dynamical system, the present study connects the fluid particle‘s stretching along its trajectory in one period to a linearized time-varying variational equation. After numerical approximation of the variational equation, fluid stretching is calculated on the whole cross section. The stretching distribution shows an exponential fluid stretching and folding, which indicates an excellent mixing performance.     

可调压可视化微间隙Couette流变仪的研究及应用

采用精密的机械加工和独特的气动旋转密封技术,研制出可调压可视化微间隙Couette流变仪。外圆筒旋转内圆筒静止的特点,使该流变仪能产生剪切速率高达105/s数量级稳定的纯剪切流。利用商业旋转流变仪,测量试验用中、低粘度硅油在低剪切速率和不同温度下的粘度,应用粘温关系,推算出高剪切速率下粘性热使粘度下降的量,其值与微间隙Couette流变仪的测量结果较为吻合。在一定的切应力下,观察到淡水和中低粘度硅油在微间隙中发生剪切空化的现象,发现剪切空化的发生还强烈依赖于流体中气体的相对溶解量。     

交叉导流式微型混沌混合器

针对微尺度混合的特点,提出了一种以玻璃湿法刻蚀加工技术为基础,基于混沌对流混合机理的三维静态微混合器.微通道内,周期排列的导流块在轴向的压力梯度作用下产生了横向的速度分量,可以诱发混沌对流,同时实现微通道内流体的快速混合.运用流场可视化实验和计算流体动力学（CFD）方法研究了微混合器的混沌混合行为.混合试验表明,SOR微混合器在低Reynolds数和高Reynolds数条件下都可以获得好的混合效果.     

基于Couette流变仪的0.1～0.5MPa压力下液体粘度测量方法

为了研究使用Couette流变仪在0.1 MPa～0.5 MPa压力范围内测量液体粘度的方法,首先对流变仪进行了强度校核,结果表明流变仪在低于4.2 MPa压力下可以安全工作.然后对如何通过电机输出力矩得到流变仪工作段力矩的问题做出了研究;最后,根据推导出的工作段力矩与所测液体粘度成正比的关系,总结出了通过工作段力矩间...