润滑脂在圆管内流动速度及粘度分布规律

The law of velocity distribution and viscosity distribution of lubricating grease during pipeline flow

润滑脂在管内流动的速度、粘度是影响润滑脂输送的重要因素,深入研究不同温度、流变指数、屈服应力对润滑脂在输送过程中的速度分布、粘度分布具有重要意义.文中首先采用旋转流变仪对润滑脂的流变行为进行实验研究,得到润滑脂的本构方程;然后基于Herschel-Bulkley模型,运用CFD对润滑脂的流动进行数值模拟.结果表明:温度和剪切速率对润滑脂的流变行为均存在较大影响,在低温下,润滑脂存在较大的屈服应力,且润滑脂输送性能较差;随着温度的升高,其流速增大,润滑脂表现出更好的流动性,且在管内中心,粘度分布均呈峰形;随着屈服应力增加,流速降低,粘度增加,当屈服应力从1 200 Pa升高到1 500 Pa时,流核区速度降低了65%,且中心处粘度升高了24%;流性指数对润滑脂在管内的粘度分布影响较小,而对速度分布影响较大,随着流性指数增大,润滑脂速度明显降低,当流性指数从0.19增加到0.79时,流核区速度降低了69%,而粘度分布基本保持一致.

The velocity and viscosity of the lubricating grease are the important factors that affect the lubricating grease in the process of transportation. It is important to investigate the influence of temperature,rheology exponent,and yield stress on the velocity and viscosity distributions of grease in its transporting. First,the rheological behavior of the grease is studied by the rotational rheometer to get the constitutive equation of the grease.Then,based on the Herschel-Bulkley model,we apply the CFD numerical simulation to the flow of grease. The results shows that temperature and shear rate have great influence on the rheological behavior of the grease. Under low temperatures,the lubricating grease has larger yield stress and poor grease transportability. With the temperature increasing,grease shows higher velocity and liquidity,and in the center of the pipe,the viscosity distribution is in peak shape. As the yield stress increases,the velocity decreases and the viscosity increases.When the yield stress is increased from 1 200 Pa to 1 500 Pa,the flow rate and viscosity become decreased by 65% and increased by 24%,respectively. The rheology exponent has little influence on the viscosity distribution of grease in the pipe,but has great influence on the velocity distribution. With the rheology exponent increasing,the grease velocity is obviously decreased,while the viscosity distribution remained the same. When the rheology exponent is increased from 0. 19 to 0. 79,the flow rate decreased by 69%.