【作者】 黄莹；

【导师】 刘春江；

【作者基本信息】 天津大学 ， 化学工程， 2006， 硕士

【摘要】 规整填料在反应,分离及混合等领域有着广泛的应用,填料内部流体的流动结构对相关设备的运行效率,如传质效率和混合效率等有重要的影响,但规整填料内流体流动情况的基础研究文献报道很少。因此对规整填料特征单元内流体的流动情况,及其混合能力进行深入的研究具有重要的意义。早期对规整填料内流动的研究集中在宏观流动分布方面,目前则集中在填料内部及更小尺度的流动描述上,而且采用CFD方法研究填料内部的流动成为一种趋势。本文针对Mellapak 350Y型规整填料特征单元内的流动及混合现象,利用计算流体力学(Computational Dynamics Fluid, CFD)的方法模拟了单元内的液相单相流流动,并结合脉冲示踪法对其混合行为进行了研究,考察了特征单元在不同流速下的返混系数。为选取合适的计算流体力学模型,首先进行了实验测量,建立了相应的实验装置,在室温下以甘油水溶液(65%,wt)为测试液体,利用激光多普勒测速仪(Laser Doppler Velocimeter, LDV)测量不同雷诺数下规整填料单元内的流场分布。利用该实验结果表明RNG(Renormalization group)k-ε模型最适合描述规整填料内流体的流动。再利用该模型进行多个特征单元的计算模拟,发现有良好的重复性,说明特征单元的选取是合理的。为了定量地研究流体在规整填料内的返混现象,利用选取的RNG k-ε模型研究了不同流动参数下的轴向返混系数。在流场模拟计算稳定以后,在填料单元其中一个入口(inlet1)处注入示踪剂,使用非稳态计算模型计算NaCl示踪剂在填料单元内的传递过程,得出单元出口处示踪剂的RTD曲线,利用RTD曲线求得返混系数,结果发现表观液速对轴向返混系数影响较大,并随着表观液速的增大而增大,而且流体在不同出口的轴向返混系数基本一致。另外为了更好地了解在填料单元内不同出口的浓度分配情况,在填料单元其中一个入口(inlet1)处连续注入示踪剂。计算其在单元内的浓度分配,并分别在两个出口处计算溶液中示踪剂的浓度分率。计算结果表明不同物系在不同出口的浓度分配呈现完全不同的规律。更多还原

【Abstract】 Hydrodynamics of the fluid is of great importance in determining the reaction or mass transfer efficiency for chemical process carried out in static mixer or distillation column which using structured packing as their internals. Up still now, very few reports have been found in literature to investigate the flow behavior, mixing behavior in the structured packing from representing unit scale.Because of the complicated structure in structured packing, it will definitely be unattained to simulate the fluid flow of the whole column with structured packing on the present conditions. In this paper, computational fluid dynamics (CFD) method was used to simulate the velocity distribution in the typical unit of structured packing. Commercial CFD package, FLUENT, was used to solve the proposed model where the special configurations of the structured packing was considered and multi-block body-fitted mesh was used. A single-fluid CFD model, based on Navier-Stokes equation, was used to numerically predict the velocity distribution inside the structured packing unit. Experimental data for liquid flow in a represent unit of the structured packing was collected using Laser Doppler Velocimetry (LDV) method. In the experiment, glycerol aqueous solution was selected as the tested liquid to minimize the refractive effects of Plexiglas packing. Different turbulent models were compared and the RNG k-εmodel was found in good agreement with experimental data. It has a lot of similarities when we investigated several units with this model.The dispersion characteristics of the structured packing unit can be determined reasonably well with RNG k-εmodel. Comparison of the RTD measured in the two different outlets with different inlet velocities lead to the conclusion that superficial velocity has great effects on axial dispersion coefficient without regard to the different outlets.更多还原