易沉降悬浮液流变性测试时流体循环的理论分析

Theoretical Analysis on the Fluid Circulation in Measuring the Rheo-parameters of Easy Settling Suspensions

易沉降悬浮液流变性测试中必须考虑固相颗粒的沉降问题,而解决这一问题的有效途径是实现被测流体的循环。通过对流变仪转子壁面上受力状况的分析证明:流体在内外筒的环形间隙循环时,应尽量使由于循环而引起的流体运动速度只存在轴向分量并且在整个环形截面上均匀分布,如此则可保证旋转流变仪对易沉降悬浮液流变参数的准确测定。但考虑到实际操作的方便,本文推导了简单循环方式下即循环流体只进入环形截面的部分区域,且存在切向、径向、轴向的速度分量时流变参数测定的相对误差表达式,证明其与流体性质及转子角速度无关,此结果证明了流体循环方法在理论上的正确性,并已为此前的实验所证实。

The sedimentation of solid particles must be taken into account when the rheo-parameters of a solid-liquid suspension were determined with a coaxial cylinder rheometer, and a possible approach to the problem was the circulation of the measured fluid. In this paper, it was drawn by analyzing the stress on the rotor wall in theory that the circulation fluid should be forced to pass through the space with only axial velocity and with no radial and tangential flow, in addition the fluid should be dispersed impartially on the whole circulation cross-section. If these conditions were satisfied, the rheo-parameters of the easy settling suspensions could be obtained effectively with a coaxial cylinder viscometer. In practice, an easily operational circulation unit where the measured fluid was circulated through partial area and with three-dimensional velocity could be used, and a correction coefficient was derived. The coefficient was proved to be independent to beth the rheological parameters and the rotor speed. This makes the practical operation feasible and was verified by previous experiments.