涂布白纸板涂料流平粘度

从流平学角度，研究了影响流平时间的流平粘度。实验结果表明，涂布白纸板涂料在低剪切速率下呈明显的剪切稀化特性，特性指数为０．５９７；存在小屈服值，约５ｄｙｎ／ｃｍ；涂料在低剪切速率下流平粘度低，流平时间短。流平过程剪切应力与剪切速率关系符合Ｈｅｒｓｃｈｅｌ－Ｂｕｌｋｅｙ方程τ－τ＿０＝ＫＤ￣ｎ（ｎ＜１）。

Improvement of Prandtl mixing length theory and application in modeling of turbulent flow in circular tubes

In order to correctly predict tube cross section time-smoothed velocity distribution, friction factor and mass transfer behavior, two models for turbulent flow in circular tubes based on classical Prandtl mixing length theory and a modified mixing length were established. The results show that the modified mixing length includes the introduction of a damping function for the viscous sublayer and the second-order derivative to approximate eddy velocity. The calculated dimensionless time-smoothed velocity from the model based on Prandtl mixing length is much better than the result from the concept of eddy viscosity. The calculated eddy viscosity from the model based on modified mixing length is much better than the result from the model based on the classical Prandtl mixing length theory. And the friction factor calculated from the model based on the modified mixing length agrees well with the reported empirical relationships.