共轴反转型生物反应器内流场数值模拟与性能分析

doi:10.11949/0438-1157.20200190

摘要/Abstract

摘要：

使用生物可降解塑料是解决白色污染的有效手段，然而在生物反应器中生产可降解塑料过程中会面临气体传质能力不足和能耗过大等问题，导致生产成本居高不下。为解决这些问题，提出了一种共轴反转型机械搅拌式生物反应器，并通过数值模拟对新型反应器内两相流场进行了仿真及定量分析。通过模拟气泡羽流、鼓泡塔及搅拌器系统内流场，并与实验结果对比，在双流体模型中引入了曳力、升力及湍流扩散力以及基于Troshko-Hassan模型的两相湍流模型，验证了双流体模型在该问题中的有效性。对新设计的反应器内流场模拟结果表明，两相作用力模型对模拟准确性影响较大，而共轴反转能够在流场中形成更好的剪切效应，增强气体分散能力，从而提高整体气含率及相对功率准数。

关键词: 生物反应器, 数值模拟, 气液两相流, 气含率, 传质

Abstract:

The use of biodegradable plastics is an effective means of solving white pollution. However, the production of degradable plastics in bioreactors will face problems such as insufficient gas mass transfer capacity and excessive energy consumption, resulting in high production costs. To solve these problems, a new design of bioreactor with coaxial contra-rotating propellers is proposed as well as according flow analysis based on numerical simulation. To verify our numerical models, three different benchmarks including bubble plume, bubble column and stirred tank are performed. Drag force, lift force and turbulent dispersion force are included in our two-phase model. Standard k- $ε$ method is modified via Troshko-Hassan model to consider bubble induced turbulence. Additionally, sliding grid method is employed to simulated rotating turbine. The results show that phase interactions in two-fluid method have a significant influence on accuracy of simulation. Our final result agrees well with experiments and previous literature. As for new bioreactor, it is shown that shear force is enhanced between two turbines. Gas hold-up, dispersion capabilities and RPD(relative power demand) are improved in new bioreactor compared with traditional design.

Key words: bioreactor, numerical simulation, gas-liquid two-phase flow, gas hold-up, mass transfer

中图分类号:

TQ 022

杨光,王沫然. 共轴反转型生物反应器内流场数值模拟与性能分析[J]. 化工学报, 2020, 71(11): 5188-5199.

Guang YANG,Moran WANG. Numerical simulation and performance analysis of flow field in coaxial contra-rotating bioreactor[J]. CIESC Journal, 2020, 71(11): 5188-5199.

图/表 18

图1 典型机械搅拌式反应器设计

Fig.1 Typical design of stirred tank reactor

表1 湍流模型参数数值

Table 1 Coefficient value of turbulent model

C_μ	C₁_ε	C₂_ε	C_VM	C_ke	C_td	σ_k	σ_ε
0.09	1.44	1.92	0.5	0.75	0.5	1	1.3

图2 求解问题几何与轴对称近似下边界条件设置

Fig.2 Size and structure of bubble plume problem and boundary condition of axisymmetric situation

图3 气泡羽流气体体积分布情况

Fig.3 Gas volume fraction distribution of bubble plume

图4 两种曳力模型对比：气体体积分数（a）及气体速度（b）沿中心分布

Fig.4 Comparison of two drag model: gas volume fraction(a) and gas velocity(b)

图5 气体体积分数沿径向的分布

Fig.5 Gas volume fraction along radial direction

图6 二维轴对称模拟与三维模拟对比：气体体积分数（a）及气体速度（b）沿中心分布

Fig.6 Comparison of 2D axial-symmetric result and 3D result: gas volume fraction(a) and gas velocity(b)

图7 鼓泡塔几何尺寸与边界条件示意图

Fig.7 Geometry and boundary condition of bubble column

图8 中心截面处51.5 s时气体体积分数云图（a）和液体速度矢量图（b）

Fig.8 Gas volume fraction (a) and liquid velocity vector map(b) of center section at 51.5 s

图9 高度z/H=0.63，y=0.075 m截面上气相（a）与液相（b）速度沿x方向变化

Fig.9 Velocity of gas(a) and liquid(b) along x axis at height z/H=0.63 and depth y=0.075 m

图10 两相搅拌体系验证算例几何结构

Fig.10 Structure of two-phase stirred tank benchmark

图11 两相旋转机械内气体体积分数云图

Fig.11 Gas volume fraction of two-phase stirred tank reactor

图12 液相径向速度(a)与轴向速度(b)

Fig.12 Radial velocity(a) and axial velocity(b) of liquid phase

图13 气相径向速度(a)与轴向速度(b)

Fig.13 Radial velocity(a) and axial velocity(b) of gas phase

图14 两桨叶反应器几何结构

Fig.14 Structure of dual turbine stirred tank benchmark

图15 单相时反应器流线图：转动方向相反（a）和转动方向相同（b）

Fig.15 Streamline of single phase reactor: contrarotating(a) and corotating(b)

图16 单相情况功率随时间步变化情况

Fig.16 Power consumption of single phase at different time step

图17 气体体积分数：转动方向相反（a）和转动方向相同（b）

Fig.17 Gas volume fraction: contrarotating(a) and corotating(b)

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