Davidson Kyle M, Sushil Shrinivasan, Eggleton Charles D, Marten Mark R
Department of Mechanical Engineering, 1000 Hilltop Circle, University of Maryland, Baltimore County, Baltimore, Maryland 21250, USA.
Biotechnol Prog. 2003 Sep-Oct;19(5):1480-6. doi: 10.1021/bp025580d.
Nonideal mixing in many fermentation processes can lead to concentration gradients in nutrients, oxygen, and pH, among others. These gradients are likely to influence cellular behavior, growth, or yield of the fermentation process. Frequency of exposure to these gradients can be defined by the circulation time distribution (CTD). There are few examples of CTDs in the literature, and experimental determination of CTD is at best a challenging task. The goal in this study was to determine whether computational fluid dynamics (CFD) software (FLUENT 4 and MixSim) could be used to characterize the CTD in a single-impeller mixing tank. To accomplish this, CFD software was used to simulate flow fields in three different mixing tanks by meshing the tanks with a grid of elements and solving the Navier-Stokes equations using the kappa-epsilon turbulence model. Tracer particles were released from a reference zone within the simulated flow fields, particle trajectories were simulated for 30 s, and the time taken for these tracer particles to return to the reference zone was calculated. CTDs determined by experimental measurement, which showed distinct features (log-normal, bimodal, and unimodal), were compared with CTDs determined using CFD simulation. Reproducing the signal processing procedures used in each of the experiments, CFD simulations captured the characteristic features of the experimentally measured CTDs. The CFD data suggests new signal processing procedures that predict unimodal CTDs for all three tanks.
在许多发酵过程中，非理想混合会导致营养物质、氧气和pH值等出现浓度梯度。这些梯度可能会影响发酵过程中的细胞行为、生长或产量。接触这些梯度的频率可以通过循环时间分布（CTD）来定义。文献中CTD的例子很少，而且CTD的实验测定充其量是一项具有挑战性的任务。本研究的目的是确定计算流体动力学（CFD）软件（FLUENT 4和MixSim）是否可用于表征单叶轮搅拌槽中的CTD。为实现这一目标，通过用单元网格划分搅拌槽并使用kappa-epsilon湍流模型求解Navier-Stokes方程，利用CFD软件模拟了三种不同搅拌槽中的流场。在模拟流场内的一个参考区域释放示踪粒子，模拟粒子轨迹30秒，并计算这些示踪粒子返回参考区域所需的时间。将通过实验测量确定的CTD（显示出不同特征，如对数正态、双峰和单峰）与使用CFD模拟确定的CTD进行比较。CFD模拟重现了每个实验中使用的信号处理程序，捕捉到了实验测量的CTD的特征。CFD数据表明了新的信号处理程序，可预测所有三个搅拌槽的单峰CTD。
