| 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.
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