Biotechnol Prog. 2014 Jan-Feb;30(1):48-58. doi: 10.1002/btpr.1790.
According to recent experimental studies on sparged bioreactors, significant cell damage may occur at the gas inlet region near the sparger. Although shear stress was proposed to be one of the potential causes for cell damage, detailed hydrodynamic studies at the gas inlet region of gas–liquid bioreactors have not been performed to date. In this work, a second-order moment (SOM) bubble–liquid two-phase turbulent model based on the two-fluid continuum approach is used to investigate the gas–liquid hydrodynamics in the bubble column reactor and their potential impacts on cell viability, especially at the gas inlet region. By establishing fluctuation velocity and bubble–liquid two-phase fluctuation velocities correlation transport equations, the anisotropy of two-phase stresses and the bubble– liquid interactions are fully considered. Simulation results from the SOM model indicate that shear and normal stresses, turbulent energy dissipation rate, and the turbulent kinetic energy are generally smaller at the gas inlet region when compared with those in the fully developed region. In comparison, a newly proposed correlation expression, stress-induced turbulent energy production (STEP), is found to correlate well with the unusually high cell death rate at the gas inlet region. Therefore, STEP, which represents turbulent energy transfer to a controlled volume induced by a combination of shear and normal stresses, has the potential to provide better explanation for increased cell death at the sparger region.
根据最近关于喷射生物反应器的实验研究，在靠近喷射器的气体入口区域可能会发生显著的细胞损伤。虽然剪切应力被认为是细胞损伤的潜在原因之一，但迄今为止，尚未对气-液生物反应器的气体入口区域进行详细的流体动力学研究。在这项工作中，基于双流体连续介质方法的二阶矩（SOM）气泡-液体两相湍流模型用于研究鼓泡柱反应器中的气-液流体动力学及其对细胞活力的潜在影响，特别是在气体入口区域。通过建立脉动速度和气泡-液体两相脉动速度相关输运方程，充分考虑了两相应力的各向异性和气泡-液体相互作用。SOM 模型的模拟结果表明，与完全发展区域相比，气体入口区域的剪切和法向应力、湍流动能耗散率和湍流动能通常较小。相比之下，新提出的应力诱导湍流动能产生（STEP）相关式与气体入口区域异常高的细胞死亡率很好地相关。因此，STEP 代表了剪切和法向应力共同作用下将湍流动能传递到控制体的过程，它有可能为喷射器区域增加的细胞死亡提供更好的解释。
