基于均龄理论模拟搅拌式反应器的混合时间

Numerical Simulation of Mixing Time in Stirred Reactors Based on Mean Age Theory

利用计算流体力学(CFD)模拟搅拌式反应器内生物的平均年龄分布,并建立了以平均年龄(均龄理论)为基础的混合时间模拟方法。通过比较混合时间的预测值与实验值结果,表明当反应器的高径比低于1.5∶1时,模拟结果和实验值的吻合度较高,平均误差在10%以内。对比单层四斜叶上翻桨(PBTU)和四斜叶下压桨(PBTD),PBTD的模拟结果都在实验值范围内,而PBTU的模拟结果都比实验值高,最大误差达14%。同时研究表明,模拟得到的N·θ准数不受反应器规模的影响。

A mixing time simulation method based on mean age theory is established.This method is suitable for industrial stirred reactors for computing their resource saving.The simulation process is as follows:simulation of the velocity field of bioreactor using computational fluid dynamics (CFD);simulation of the mean age distribution using CFD steady-state calculation;mixing time simulation through volume integration process performed on the histogram of the mean age distribution.To get accurate mixing time,three conditions are required:unstructured mesh element number should ensure that the power calculated by energy dissipation rate is exceed 80% of the power calculated by the torque;inlet flux should be two orders lower in magnitude than the impeller pumping flow rates;number of mean age groups should be more than 12 500 for Matlab post-processing.When the ratio of height to diameter of the reactor is lower than 1.5∶1,the simulation results are in good agreement with the experimental values,and the average error is within 10%.When the ratio is higher than 1.5∶1 with a Reynolds number less than 2.1×105,the differences between the simulation results and the experimental values become higher,and the error is 12%.Upon comparing the cases of the pitch blade turbine pumping down (PBTD) and the pitch blade turbine pumping up (PBTU),it is found that the simulation results of PBTD completely fall in the experimental data range,while the simulation results of PBTU are higher than the experimental values,the maximum error is up to 14%.In addition,many mixing time empirical formulas are absence of considering the volume factor.On the basis of the present work,it is found that N·θ number obtained by simulation is not affected by the scales of reactors.