搅拌槽内气液传质数值模拟以及宏观不稳定现象研究

发布时间：2018-03-07 17:27

本文选题：搅拌槽　切入点：组合桨　出处：《南京理工大学》2015年硕士论文　论文类型：学位论文

【摘要】：本文选用聚醚多元醇(PPG)作为研究介质,采用数值模拟方法从宏观和介观两个尺度对多层组合桨反应器进入了深入研究。并且初步探究搅拌槽内存在的一种大尺度、低频率的宏观不稳定现象,重点考察了搅拌转速、桨叶类型、离底高度等因素对聚醚多元醇体系宏观不稳定频率的影响,为反应器的优化设计提供参考。1.对组合桨1(下层六叶半椭圆管涡轮桨+中层四宽叶翼型上提桨+上层四宽叶翼型上提桨)和组合桨2(下层六叶半椭圆管涡轮桨+中层六斜叶圆盘涡轮桨+上层六斜叶开启式桨))搅拌釜内液相PPG流场进行了计算流体力学(CFD)研究。结果表明,组合桨1中桨和上桨流体形成一个整体轴向循环有利于混合,组合桨2速度与湍流动能小于组合桨1。组合桨1更适用于聚醚多元醇体系的工业生产中。2.采用群平衡模型(PBM)与CFD相耦合的方法,研究多层组合桨搅拌槽内空气-PPG两相混合的气液传质特性,探究不同网格划分对局部气含率、气泡直径大小、传质系数的影响,结果表明,液相宏观流场分布受到网格划分影响,局部气含率与气泡直径呈现双峰分布,Grid 2总体气含率模拟结果与实验结果吻合较好。说明Grid 2网格划分适用于聚醚多元醇-空气体系的气液混合,为进一步计算提供了参考。3.搅拌槽内的流体的流动是非稳态的,采用信号处理方法对搅拌槽内宏观不稳定现象进行压力信号分析,功率谱估计可以有效的分析低频信号。结果表明,对于单层与双层桨,宏观不稳定性频率频率主要分布在0.3-0.5Hz范围内。转速增加,搅拌槽内流体整体脉动增强,监测点的位置对于宏观不稳定频率近似无关。研究结果有助于了解流体混沌混合现象,避免搅拌槽内机械劳损。
[Abstract]:In this paper, polyether polyol (PPG) was chosen as the research medium, and the numerical simulation method was used to study the multilayer combined paddle reactor from macroscopic and mesoscopic scales. The effects of stirring speed, blade type and bottom height on the macroscopic instability frequency of polyether polyol system were investigated. Reference for the optimal design of the reactor. 1. Combined propeller 1 (upper lift propeller with upper four wide blade airfoils of lower six-blade half elliptical tube turbine impeller) and combined propeller 2 (lower six-leaf semi-elliptical tube turbine propeller). The liquid phase PPG flow field of the upper hexagonal blade open propeller in the middle hexagonal disk turbine impeller has been studied by computational fluid dynamics (CFD). The results show that, An integral axial cycle of the fluid between the propeller and the upper propeller in the combined propeller 1 is favorable for mixing. The velocity and turbulent kinetic energy of combined propeller 2 are smaller than that of combined propeller 1.Combinatorial propeller 1 is more suitable for industrial production of polyether polyol system. The gas-liquid mass transfer characteristics of air-PPG two-phase mixing in a multi-layer combined propeller stirred tank are studied. The effects of different mesh generation on local gas holdup, bubble diameter and mass transfer coefficient are investigated. The distribution of macroscopic flow field in liquid phase is affected by meshing. The local gas holdup and bubble diameter show a bimodal distribution. The simulation results of total gas holdup are in good agreement with the experimental results. It shows that Grid _ 2 mesh is suitable for gas-liquid mixing of polyether polyol and air system. This paper provides a reference for further calculation. 3. The flow of fluid in stirred tank is unsteady. The pressure signal of macroscopic instability in agitating tank is analyzed by signal processing method. The power spectrum estimation can effectively analyze the low frequency signals. The results show that the frequency of macroscopic instability is mainly distributed in the range of 0.3-0.5Hz for single-layer and double-layer propellers, and the whole pulsation of the fluid in the stirred tank increases with the increase of the rotational speed. The location of the monitoring point is almost independent of the macroscopic unstable frequency. The results are helpful to understand the chaotic mixing phenomenon of the fluid and to avoid the mechanical strain in the mixing tank.
【学位授予单位】：南京理工大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TQ051.72

【参考文献】