【作者】 李红星；

【导师】 金志江；

【作者基本信息】 浙江大学 ， 化工过程机械， 2013， 硕士

【摘要】 气液反应器广泛应用于石油化工、生物化工和废水处理等工业过程中。气液反应过程的强化、反应装置的大型化趋势对于气液两相反应器的设计提出了新的要求。而在这些工业过程中使用的流体介质大部分为中高黏度流体,有别于水和空气体系。在粘性流体中气液混合状态是目前研究的重点和难点,也对反应器的设计提出更多的要求。本文首先提出了一套完整的实验设备设计方案,包括环状气体分布器设计和相关的实验设备的实验原理。然后利用水和18～59.5mPa·S的糖浆混合溶液对不同的操作条件下气液分散状态进行研究,该黏度范围覆盖工业生产的黏度范围,具有较强实用性。实验结果表明：溶液黏度增大,大气泡比例增大,气泡分布的不均匀程度加大,溶液传质能力明显降低；但溶液固气能力加强,整体气含率增加。同时借助于CFD的模拟结果显示,黏度增大,死区减小,整体气含率分布更为均匀；由于雷诺数的变化,涡心和桨叶排出端位置发生变化,某一处的局部气含率不一定随着黏度增大而增大,也可能降低。通过将不同的桨叶下的气液分散状态对比,调整不同的下部桨叶比较发现,含有涡轮圆盘的径流式搅拌桨更容易延缓气体的上升,较大的桨叶尖端速度对于气泡的粉碎和局部气含率的增大作用显著,圆盘斜凹叶桨(PCBDT)表现性能最好。粘性溶液中,气泡聚并和破裂速率均下降,便于大气泡产生,但是聚并速率仍然占主导；搅拌转速相对通气量而言,对局部气含率的影响更加明显,对于气泡分布的均匀化和传质方面明显优于通气量的增加。溶解氧和操作条件的结果显示,压强使溶氧上升作用最显著；温度升高,溶氧量略有上升。本文的CFD模拟结果显示,操作条件和溶液性质的变化容易导致桨叶排出段和涡心位置的变化,从而影响局部气液混合状态；轴-径流桨组合中,整体流场取决于下桨叶,且气体的上升对液相流场干扰较大。实验和模拟数据对比显示,上部数据拟合较好,但是下部(下桨叶排出段)数据拟合较差,这主要是小孔喷射效应和气泡模型导致。更多还原

【Abstract】 Gas-liquid reactors are widely applied in many process industries, for instance, petrochemical, biochemical and sewage treatment process. With the intensification of gas-liquid reaction process and the scale-up of equipment, new requirements for optimizing the existing reactors or designing novel reactors with high performance are appearing. And the viscosity of most fluid is moderate or high in these process industries, which is different from the water-air system. The gas-dispersion in viscous fluid is the important and difficult points, which proposes more new requirements for designing of reactors.Firstly, proposing and designing a set of experiment equipment are conducted, including the designing of ring gas distributor and the theory of relative experiment, in this paper. Then did research on the gas-dispersion in water and mixture between water and malt syrup, whose viscosity ranges from18～59.5mPa·S and contains the viscosity interval. So this project is practical. The results show that the proportion of larger bubbles and extent of nonuniformity of bubble size are both grow larger as the viscosity of fluid boosts, while the mass transfer rate is opposite. For the ability of detaining bubble boosts, the whole average gas volume fraction turns more. Meanwhile, by means of CFD numerical simulation, the result reveals that the dead zone decreases and the distribution of local gas volume fraction turns more homogenization. Since the centre of vortex and the location of impeller discharge zone change, the local gas volume fraction does not always turn larger as the viscosity of fluid boosts.Through the comparison of gas-liquid dispersion with different lower impeller, the result reveals that the radial-flow impeller with turbine disc has a good performance in hindering from the escaping of bubbles and decreasing bubble size. For the larger impeller tip velocity has a significant influence in decreasing the bubble size and boost the transfer rate, the PCBDT impeller has the best performance among the three impellers in experiment. In the viscous fluid, the rate of bubble coalescence and break-up both decrease, but the bubble coalescence rate is still prevailing. Compared to the gas inflation rate, the speed of agitator has a better performance. Because strengthening it is beneficial for boosting the local gas volume fraction and decreasing the nonuniformity of bubble size. The DO experiment reveals that the pressure above the liquid level has the best performance in promoting the rising of DO; while DO is also slightly boost as the liquid temperature becomes higher.The result of CFD show that the change of operating conditions or the properties of fluid can easily lead to the centre of vortex and the location of impeller discharge zone change, which is a main reason for the change of local gas volume fraction. In the combination of axial-radial impeller, the whole flow field is dependent on the lower impeller. Meanwhile the rising velocity of bubbles has a significant influence on the liquid flow field. The matching between the experimental and simulative result is good in the upper zone while bad in the lower zone, which is induced by the reason of injection effect from tiny hole and bubble models.更多还原