【作者】 罗云峰；

【导师】 刘跃进；

【作者基本信息】 湘潭大学 ， 工业催化， 2008， 硕士

【摘要】 搅拌釜反应器由于其外加机械搅拌,液相湍动剧烈,具有混合效果好、相接触面积大、传热和传质效率高等特点而在化工、生物、食品、制药等工业过程中有着非常广泛的应用。然而,与其有关的理论及计算方法却仍不完善,许多还是处在半经验半理论阶段。因而,越来越多的学者利用计算流体力学(Computational Fluid Dynamics,CFD)方法可以对搅拌过程进行数值模拟,使得流场可视化,给人们以清晰的认识。在湍流模拟方面,主要可分为直接数值模拟(DNS)、大涡模拟(LES)、雷诺平均方法(RANS)三种。脱体涡数值模拟(DES)是近年来出现的一种结合了雷诺平均方法(RANS)和大涡数值模拟(LES)两者优点的湍流模拟方法,可以被用来有效且快速的模拟大范围分离的湍流流动。据此,本文首次利用脱体涡数值分析方法(Detached eddy simulation, DES)研究了Rushton涡轮桨搅拌釜内的流动特性,并将模拟结果与RANS、LES模型及文献实验数据进行了比较。结果表明:DES方法可获得搅拌釜内的瞬态流场;对桨叶区时均速度及湍流动能的预测与实验数据较吻合,比RANS模型计算结果有明显改进,所需的运算时间比LES模型要少。另外考虑到传统经验关联式在工程上的简单易用性,而Rushton气液搅拌釜反应器通气时的搅拌功耗又是其设计与放大最重要的参数之一,国内外虽报道了不少关联式,但当通气速率很小时就会失去其合理性。所以本文对通气功率进行了探讨,首次提出将其分为两个部分考虑,建立了较为合理,且高精度的新型Weibull功率模型,具有一定的现实意义。更多还原

【Abstract】 Stirred tank reactors are extensively used in a variety of industries like the paper and pulp, pharmaceutical, fine chemicals, food industry, petroleum chemical engineering, pharmacy and biochemical engineering etc. However, the correlative theories and computational methods are not mature, and most of which are even semiempirical and semitheoretical. So there are more and more scholars using Computational Fluid Dynamics(CFD) simulate the mixing process and make the flowing of fluid visualizatation, which gives a clear understanding to people.There are three methods to simulate the turbulence in CFD: DNS, LES and RANS. Detached-Eddy Simulation (DES) is a new approach to treatment of turbulence appeared several years ago. It combines the advantages of Reynolds-Averaged Navier-Stokes(RANS) method and Large-Eddy Simulation method (LES), and it is aimed at the prediction of massively separated flows at a manageable cost in engineering.Accordingly, in this study, it is the first time that the hydrodynamic characteristics in a baffled Rushton impeller stirred tank were investigated by using Detached eddy simulation(DES), and then we compared the results with RANS and LES models and experimental data. The results show that DES approach can predict the transient flow field in the stirred tank. Velocity and turbulent kinetic energy obtained by DES modle are in good agreement with the experiment and much better than that predicted by the RANS model, also needs much less time to compute than the LES modle.In addition, considering the user-friendliness of the traditional empirical correlation equations in idustry, and furthermore, the aerated power consume is the most important factor of its design and scale up, there are many models have been reported, but they will lose the rationality when the gas rate is low. So in this study, the power consume has been divided into two parts in the first time, then establishs a Weibull power model which is reasonable and high precision. From the applied point of view, it has some valves.更多还原