搅拌槽内中粘体系气液分散的数值模拟

发布时间：2018-03-26 22:06

本文选题：搅拌　切入点：数值模拟　出处：《北京化工大学》2015年硕士论文

【摘要】：气液反应器在化工领域是一种常用的反应器,搅拌槽是气液反应器中的一种。搅拌的方式中最传统的方式是机械搅拌。机械搅拌的原理概括起来就是槽内液体通过搅拌轴及搅拌桨的带动,在搅拌槽内做旋转运动。对于气液两相的混合,评价气液两相的好坏也是由多方面因素构成的。从宏观上看,包括搅拌功率、平均气含率、气液两相的流型,从介观上看,包括局部气含率、气泡尺寸分布等因素。若搅拌槽内有反应或传热等更复杂的现象,还需要考虑气液相界面积、气液相比热等参数的影响。在本论文中,主要考虑了转速、通气量、搅拌桨型、搅拌桨层间距、气体分布器直径对气液分散效果的影响。本论文借助CFD数值模拟,对气液两相在搅拌槽内的情况进行了研究,并通过模拟得到的数据与实验数据进行对比。论文选取的主要流体是粘度0.12 Pa-s的甘油水溶液,其他粘度的溶液还包括水、0.01Pa·s和0.05 Pa·s的甘油水溶液。具体得到结果如下：对于桨型的选择,论文选取了两种搅拌桨型,分别是InterMigDU和InterMigUD,在相同的通气量和搅拌转速下,InterMigUD会有更好的效果,InterMigUD消耗的功率小且有较大的平均气含率。从气泡分布方面来看,InterMigUD气泡分布的不均匀度大于InterMigDU,但是InterMiguD有更大的传质系数。对于层间距的讨论选取了三种层间距,分别是0.36D,0.5D和0.69D。由于整体的液位是1.49T,因此对于层间距的选择,本文建议△/D不宜过大。层间距为0.36D时,整体气含率居中,但是有较高的容积传质系数,气泡尺寸的均匀性也是三者中最好的。层间距为0.5D时,整体气含率最大,容积传质系数和均匀度略小于0.36D时的层间距。对于不同直径的气体分布器来讲,文中选取了五种不同直径的气体分布器,分别是0.3T、0.4T、0.55T、0.65T、0.75T,结果发现,随着气体分布器直径的增大,气液混合效果越来越好,整体气含率增加,均匀度趋于良好,容积传质系数逐渐增大。因此,对于气液搅拌,适当的增大气体分布器直径是有益处的。文中选取了水和三种甘油水溶液,以水作为基础比对,发现随着粘度的增加,功率消耗增加,整体气含率也呈递增趋势,平均气泡尺寸变大,容积传质系数呈递减趋势,由于所模拟的范围均处于过度流及湍流下,因此液相的流型并没有太大的差异。以上结果的部分数值与实验数据进行了对比,二者吻合良好,因此文中的其他模拟条件均采用了相同的模拟方法进行计算,并认为此种模拟方法可以推广到类似的中粘体系中,为工业生产提供参考。
[Abstract]:The gas-liquid reactor is a kind of commonly used reactor in the chemical industry. The mixing tank is one of the gas-liquid reactors. The most traditional way of stirring is mechanical agitation. The principle of mechanical stirring is that the liquid in the tank is driven by the mixing shaft and the impeller. For the mixing of gas-liquid two-phase, the evaluation of gas-liquid two-phase is also made up of many factors. From the macroscopic view, including mixing power, average gas holdup, gas-liquid two-phase flow pattern, from the mesoscopic point of view, These factors include local gas holdup and bubble size distribution. If there are more complicated phenomena such as reaction or heat transfer in the stirred tank, the influence of the boundary area of gas and liquid, the ratio of gas to liquid heat should be taken into account. In this paper, the rotational speed is mainly considered. The effects of aeration volume, impeller type, pitch between impeller layers and diameter of gas distributor on the gas-liquid dispersion effect are studied in this paper by means of CFD numerical simulation. The main fluid selected in this paper is glycerol aqueous solution with viscosity of 0. 12 Pa-s. Other viscosity solutions include glycerol aqueous solution of 0.01 Pa s and 0.05 Pa s. The results are as follows: for the selection of propeller type, two kinds of agitator type are selected in this paper. InterMigDU and InterMigUD have better effect under the same aeration rate and stirring speed, the power consumed by InterMigUD is smaller and the average gas holdup is larger than that of InterMigUD. In terms of bubble distribution, the inhomogeneity of intermigUD bubble distribution is greater than that of InterMigDUD, but InterMiguD is more effective than InterMigUD. There is a larger mass transfer coefficient. For the discussion of interlayer spacing, three kinds of interlayer spacing are selected. Because the whole liquid level is 1.49T, it is suggested that the selection of interlayer spacing should not be too large. When the interlayer spacing is 0.36D, the overall gas holdup is in the middle, but the volumetric mass transfer coefficient is higher. The uniformity of bubble size is also the best of the three. When the interlayer spacing is 0.5D, the overall gas holdup is the largest, and the volumetric mass transfer coefficient and uniformity are slightly less than 0.36D. for gas distributors with different diameters, Five kinds of gas distributors with different diameters are selected in this paper. The results show that the gas-liquid mixing effect increases with the increase of the diameter of the gas distributor, the gas holdup increases and the uniformity tends to be good. The volumetric mass transfer coefficient increases gradually. Therefore, for gas-liquid stirring, it is beneficial to increase the diameter of the gas distributor properly. In this paper, water and three kinds of glycerol aqueous solutions are selected and compared on the basis of water, it is found that with the increase of viscosity, With the increase of power consumption, the overall gas holdup tends to increase, the average bubble size increases and the volumetric mass transfer coefficient decreases. Therefore, there is not much difference in the flow pattern of liquid phase. Some of the above results are compared with the experimental data, which are in good agreement with each other, so the other simulation conditions in this paper are calculated by the same simulation method. It is considered that this simulation method can be extended to similar meso-viscous systems and provide a reference for industrial production.
【学位授予单位】：北京化工大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TQ027.2

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