【作者】 苏伟；

【导师】 吴大诚；

【作者基本信息】 四川大学 ， 材料学， 2007， 硕士

【摘要】 纤维悬浮流是含有较小的细长圆柱状固态的纤维粒子包含在液体或气体中而形成的混合流，在化工、纺织、复合材料、医药机械、造纸、环保等领域都有广泛的应用，纤维悬浮流的研究还涉及多个学科分支，具有重要的学术研究价值。本论文对较大长径比下的亚浓相纤维悬浮体系的流变性质做了详细研究，并对比和分析了纤维／硅油悬浮体系与纳米炭黑／硅油悬浮体系的流变性能。论文首先利用RV—2型共轴圆筒旋转粘度仪研究了纤维／硅油体系的流变行为。将尼龙长丝（11×12tex）切成长径比分别为40、100、200、400的短纤维，并配制成质量浓度为1mg/mL-6mg/mL的悬浮液，悬浮液均处于亚浓相。测定了不同温度和不同剪切速率下各体系的粘度。硅油是一种性能稳定的牛顿流体，添加了纤维以后，悬浮体系表现出一定的非牛顿性。实验表明，长径比较大的纤维亚浓悬浮体系，其粘度在低切变速率下的变化较明显。体系粘度在低剪切速率时随剪切速率的增加而增加，中等剪切速率水平时出现剪切变稀，最后在高剪切速率时逐步达到稳定值。长径比较小的纤维悬浮体系粘度随剪切速率的增加变化不是很明显。体系粘度随纤维浓度的增加而增加，在低切变速率时表现最明显。同等纤维浓度下，纤维的长径比越大，体系粘度增加越多。体系粘度随温度的增加而降低，但不同浓度的粘流活化能变化不大。研究了纤维／PVA水溶液悬浮亚浓体系的流变性能。制备了浓度为10％的PVA（聚乙烯醇）水溶液，并进行了流变测量实验。纤维／PVA水溶液是非牛顿体系，体系粘度对剪切速率的依赖性强，符合幂律模型：η=kγ^n-1。在20℃和30℃时表现出很明显的剪切变稀行为，粘度随剪切速率的增加下降很快，40℃以上和高剪切速率时体系粘度才趋于稳定，接近牛顿流体的性质。体系粘度随纤维质量浓度的增高而增加，小长径比的纤维悬浮体系对浓度依赖性更强，大长径比的纤维体系由于更容易出现剪切变稀，使得高剪切速率时纤维质量浓度高的体系粘度反而低于纤维质量浓度低的体系的粘度。悬浮体系的粘度随温度的变化符合Arrhenius方程，随温度升高，粘度以指数形式降低。纤维质量浓度高的体系粘流活化能较大，但由于体系均为亚浓相，总体变化并不大。最后一章研究了纳米流体-炭黑／硅油悬浮体系的流变性能，并与纤维悬浮体系的流变行为做了比较。在炭黑质量浓度不高的情况下，炭黑／硅油悬浮体系对剪切速率的依赖性不强，表现为准牛顿流体的性质。这是因为炭黑粒子粒径较小，粒子与流体的作用力较小，粒子间距较大，粒子间相互作用的机会和时间比较小（少），对流体粘度贡献小，故同等浓度下，炭黑悬浮液的粘度比纤维悬浮液的粘度小，也较稳定。炭黑悬浮体系对温度的敏感性更强，其粘流活化能较同等条件下的纤维悬浮体系略大。更多还原

【Abstract】 Fiber suspensions refer to the mixed flows containing suspending fiber particles of slender cylindrical body in fluids or airflows. They are widely appeared in nature and used in many fields of industry such as chemical engineering, textile, paper making, environment protecting and so on. Researches of fiber suspensions involve many branches of subjects and have great academic values. This thesis studied the rheological properties of a semi-dilute fiber suspension with high aspect ratios in comparison with another kind of suspension with nanoparticles (carbon black).First rheological properties of fiber/silicone oil suspension were measured by a coaxial geometry (RV-II). The fibers used in the suspension were made by cutting Nylon filaments (11 X 12 tex) and the resulted short fibers had different aspect ratios: 40, 100, 200 and 400. The fiber/silicone oil suspension was prepared in different mass concentrations of 1-6 mg/ml, which were in the semi-dilute region. Its dynamic viscosity was measured at different shear rates and temperatures. Silicone oil is a Newtonian fluid, which performed non-Newtonian character after adding fiber to it. The experimental results showed when the aspect ratio was high the viscosity of the suspension was obviously changed at low rate of shear. The value of viscosity was increased with increasing the shear rate at the lower shear level, and then appeared shear thinning at the middle shear level, while at the higher shear level the suspension viscosity was reached at a steady-state. The viscosity of suspension with fibers of the lower aspect ratio was changed slightly with increasing shear level. Higher concentration led to a higher viscosity, especially at the region of lower rate of shear. At the same fiber concentration, higher aspect ratio and lower temperature could lead to a higher viscosity.The rheological behavior of the fiber/polymer solution suspension was studied. A solution of PVA (polyvinyl alcohol) at the mass concentration of 10% was made for further measurement. Fiber/PVA solution suspension is a non-Newtonian fluid and its viscosity had a strong dependence on the rate of shear according to the power law model. The suspension showed obviously shear thinning at lower than 40℃, and its viscosity decreased rapidly as the shear rate increasing. The system was similar to Newtonian fluid when the rate of shear was high enough and the temperature was above 40℃. High fiber concentration in suspension increased its viscosity. For suspension with fibers of lower aspect ratio the viscosity depended mainly on the concentration, while for suspension with fibers of higher aspect ratio the shear thinning was more frequently. This leads to that the viscosity for higher concentration suspension with higher aspect ratio even lower that for lower concentration suspension with lower aspect ratio at the high shear region. The temperature dependence of the viscosity was characterized by the activation energy of viscous flow, which was derived from Arrhenius equation. The activation energy of viscous flow became higher at higher concentration, but it is not changed obviously in this semi-dilute concentration region.The rheological properties of a nanofluid—carbon black/silicone oil suspension were studied in the last chapter. The suspension of carbon black acted as a Newtonian fluid and depended slightly on the shear rate when the concentration was not high, because its particle was much smaller than that of the fiber suspension. The distance between particles was much larger than the diameter of the carbon black, so the interaction between particles was scale. At the same mass concentration, the viscosity of. carbon black suspension was lower than that of the fiber suspension, and the system was more stable. Carbon black suspension was more sensitive to tempareture, and its activation energy of viscous flow was higher than that of the fiber suspension at same conditions.更多还原