刮膜蒸发器内非牛顿流体流场特性数值模拟

刮膜蒸发器是通过旋转刮板强制成膜,可实现高黏度非牛顿流体类物料平稳蒸发的新型高效蒸发器.蒸发器内流体的流动、分布与传输机制直接决定了蒸发器的蒸发效率与功耗.不同于现有研究主要基于牛顿流体开展,本文针对不同黏度的非牛顿流体,建立蒸发器三维计算流体动力学模型,系统研究了蒸发器内的流场分布特性和成膜机理.结果表明:低黏非牛顿流体的流场分布特性和牛顿流体类似,物料可在壁面形成均匀且连续的液膜;随着黏度的增加,液膜的均匀性和连续性逐渐变差.通过对流场分布与传输形式的研究,结合液膜分布、速度分布、剪应变率分布,以及黏度分布进行对比分析发现,蒸发器内部结构与运行状态形成的剪切场与黏度分布是蒸发器良好成膜的关键.此外,提出对刮板前缘进行弯折可辅助高黏流体液膜铺展,并对最佳弯折角度进行探索.本研究为刮膜蒸发器的设计和应用提供了理论指导与依据.

Numerical simulation of flow pattern for non-Newtonian flow in agitated thin film evaporator

Agitated thin film evaporator(ATFE)is a new type of high-efficiency evaporator where a film is forced to form through a rotating scraper and the high-viscosity non-Newtonian flow materials can be evaporated smoothly.The flow distribution and transmission mechanism of the material in the evaporator directly determine the evaporation efficiency and power consumption of the evaporator.Unlike previous study that was based mainly on Newtonian flow,this paper establishes a three-dimensional computational fluid dynamics model of ATFE for non-Newtonian flow with different viscosities,and systematically probes the flow field distribution characteristics and film forming mechanism in the evaporator.The results show that the flow field distribution characteristics of low-viscosity non-Newtonian flow are similar to those of Newtonian flow,the material can form a uniform and continuous liquid film on the wall;as the viscosity increases,the uniformity and continuity of the liquid film gradually deteriorate.Through studying the flow field distribution and transmission form of the materials,and combining the liquid film distribution,velocity distribution,shear strain rate distribution,and viscosity distribution,it is found that the shear field and viscosity distribution formed by the internal structure and operating state of the evaporator are the key to the good film formation.In addition,it is proposed that the bending of the leading edge of the scraper can assist the spreading of high viscous fluid liquid film,and the best bending angle is explored.This research provides theoretical guidance and basis for the design and application of ATFE.