Abstract:

The commercial bubble column reactors are normally operated under the conditions of pressurized state and churn turbulent bubbly flow which the superficial gas velocity always exceeded 0.1 m·s^-1.However, most of the published literatures are focus on the cold model experimental investigation of the flow field characteristics in pressurized churn-turbulent bubble columns, and the empirical or semi-empirical correlations which were on the basis of the cold model experimental data to quantitatively estimate the characteristic parameters.Therefore, it is lack of the systematic study on the flow characteristics in the pressurized turbulent bubble columns by the hydrodynamic models with interactions between bubbles and liquid phase.In this work, a steady 2-D axisymmetric hydrodynamic two-fluid model of pressurized bubble column was developed on the platform of FLUENT 15.0 with the UDF sub-models which described the bubble swarm interface forces.The numerical investigations upon the flow field characteristics of pressurized churn turbulent bubble column with the operation pressure varying from 0.5 MPa to 2.0 MPa, and superficial gas velocity from 0.2 m·s^-1 to 0.31 m·s^-1 were performed.Moreover, the comparisons between the simulation results and cold model experimental data were implemented.The comparisons indicated that, the model with the bubble swarm interface forces including improved bubble swarm drag force model, lateral force balance model, and wall lubrication force model, is able to reflect the influences of operation pressure and superficial gas velocity upon flow pattern, that is, the elevating operation pressure leads to increase of time averaged gas holdup and decrease of time averaged axial gas phase velocity, whereas for the ascending superficial gas velocity, the gas holdup and gas phase velocity are both raising.Consequently this mathematical model could correctly predict the basic gas-liquid flow pattern in the turbulent pressurized bubble columns, and simulation results are in good agreement with the experimental data.

Key words: bubble column, gas-liquid flow, computational fluid dynamics, bubble swarm drag force model, lateral-force balance model, wall lubrication force model

摘要：

目前，多数文献报道了冷态加压湍动鼓泡塔内流动特征，并且通过实验数据回归相关经验关联式。然而，此类关联式适用范围有限，难以直接外推到工业鼓泡塔反应器条件。因此，在FLUENT平台上建立了基于气泡群相间作用力的、动态二维加压鼓泡塔计算流体力学模型。通过数值模拟考察了操作压力为0.5~2.0 MPa，表观气速为0.20~0.31 m·s^-1，内径0.3 m鼓泡塔内流场特性参数分布，并且与冷态实验数据进行比较。结果表明，采用修正后的气泡群曳力模型、径向力平衡模型以及壁面润滑力模型描述气泡群相间作用力，能够较为准确地反映平均气含率和气含率径向分布随操作压力和表观气速变化的规律。

关键词: 鼓泡塔, 气液两相流, 计算流体力学, 气泡群曳力模型, 径向力平衡模型, 壁面润滑力模型