转子导程及偏心率对面团混合器混合流场及效率影响分析  

Analysis on influence of rotor lead and eccentricity on mixing flow field and efficiency of dough mixer

作　　者：朱向哲[1] 高鹤[1] 刘俭 Zhu Xiangzhe;Gao He;Liu Jian(School of Mechanical Engineering,Liaoning Shihua University,Fushun 113001,China)

机构地区：[1]辽宁石油化工大学机械工程学院,抚顺113001

出　　处：《农业工程学报》2018年第20期305-314,共10页Transactions of the Chinese Society of Agricultural Engineering

基　　金：国家自然科学基金项目(51473073; 50903042);辽宁省高等学校创新人才支持计划项目(LR2016022)

摘　　要：为了探究偏心螺旋转子扰动下面团混合器的混沌混合机制,明确偏心转子系统的关键几何参数对混沌混合机制的影响,从三维Lagrangian的新视角,利用有限时间Lyapunov指数(finite-time lyapunov exponent, FTLE)和拉格朗日拟序结构(lagrangian coherent structure, LCS),结合经典Poincaré截面,对面团混合器的流体输运和混合机理进行了深入研究。利用LCS的准边界特性,分析了混合器的混沌和非混沌区域分布规律;研究了转子偏心率对混沌尺度和非混沌区粒子运动特性的影响规律。利用剪切速率、对数拉伸、瞬时混合效率和平均时间混合效率等,分析了转子导程和偏心率对混合器混合效率的影响。结果表明,双曲LCS将混合器流域划分为两个不同动力学特性的区域:内回转区和外螺旋区。随着转子偏心率逐渐增大,外螺旋区流体的混沌混合强度增大,内回转区混合强度逐渐较低,当偏心率较小时,流体混合以内回转区运动为主;由于转子扰动减小,减小了混合器的轴向物质输运。从拉伸流动混合效率角度可知,当导程l=120 mm、偏心率ε=0.67时,混合器的具有相对较高的拉伸混合效率;当导程l=60 mm、偏心率ε=0.33时,混合器的拉伸混合效率相对最低,但其剪切混合效率相对最高。该文为食品及其它混合设备的设计和优化提供了新的研究思路和理论依据。The chaotic food mixer with an eccentric spiral rotor is a new type of food processing device,in which the food fluids with long molecular chains can not be damaged by high shear stresses,such as traditional twin screw extruders.In fact,the previous researches had demonstrated that the food melt with high viscosity flowing in the food mixer has the nature of chaotic mixing.However,as a dynamic system of flow,the traditional Euler methods is difficult to distinguish the chaotic manifolds,which is a barrier for better understanding the mixing mechanism in the internal mixer.From a new viewpoint of 3D Lagrangian,the objective of our study is to explore the chaotic mixing mechanism in this new kind of food mixer under the disturbance of eccentric spiral rotor,to visually locate the poor and well mixing regions in the mixer and optimize the key geometric parameters of the eccentric spiral rotors.Firstly,a numerical simulation of the three-dimensional flow field in the food mixer is carried out using the mesh superposition technique(MST)and CFD code of Polyflow without considering the re-meshing for the periodical geometric changes.The Carreau-Yasuda constitutive model was used to describe the rheological behavior of the food material.Based on the transient velocity distributions,the finite time Lyapunov exponent(FTLE),Lagrangian coherent structure(LCS)and Poincarésection were calculated to analyze the fluid transport and mixing in the new chaotic food mixer with helical eccentric rotors.The LCS from the ridges of FTLE as a boundary was adopted to reveal the chaotic and regular zones in the mixer.And the particle tracking was used to illustrate the different fluid motions in the flow dynamic system based on the fourth-order Runge-Kutta scheme.Then the effects of rotor eccentric ratio on the chaos scale and particles motions in the regular of the mixer were studied,respectively.Moreover,based on the quantitative mixing measures,such as mixing shear rate,logarithmic of stretching,instantaneous mixing efficiency and aver

关 键 词：混合器 食品加工 流场 偏心螺旋转子 有限时间Lyapunov指数 拉格朗日拟序结构 POINCARÉ截面 

分 类 号：S224.23[农业科学—农业机械化工程] TS203[农业科学—农业工程]