旋转床内微观混合与反应过程的特性

Characteristics of micromixing and reaction in a rotating bed

对旋转床内微观混合的研究有助于建立其内部微观尺度上的混合与反应机制。在以往研究工作的基础上,依据数值模拟与实验结果的对比,间接确定了旋转床内的液膜厚度范围;对液膜速度模拟进行合理修正,通过流体流动、传质及反应过程的数值模拟,得到离集指数、湍流耗散率、停留时间以及微观混合时间的变化。实验结果和数值模拟表明:不同转速下的离集指数、混合时间、湍流动能耗散率等均表现出一定的多尺度现象。研究结果丰富了旋转床内微观混合与反应的认识,将为后续研究提供坚实的基础。

Rotating packed bed （RPB） is a new highly effective contact device, which can strengthen the mixing and mass transfer. The exploration on the microscale transport phenomena in RPB is of significance to understand the mechanism of microscale mixing and chemical, reaction therein. On the basis of previous studies, numerical simulation is carried out and the numerical results are compared with the experimental results to indirectly determine the thickness of the liquid film. Appropriate modification on the rotational velocity component of the liquid film is proposed and the numerical result is in reasonable agreement with the experimental result. The fluid flow and mass transfer with a parallel reaction are studied to obtain the evolution of segregation index, turbulence dissipation rate, resident time and micromixing time with the rotational speed. Based on the analysis on mixing and reaction in the RPB, the physical models about the mixing and mixing-reaction coupling process are obtained. With the structure characteristics of packing space and packing wire mesh, the rectangular equation is used to describe the packing space and the polar coordinate equation is used to describe the flowing process on the wire mesh. The numerical simulation gives the change of reactant concentration, reaction product concentration and the integrating index at different film thickness, volume ratios and feeding concentrations. The obtained residence time, turbulence dissipation rate, and micro-mixing time are consistent with the experimental values. It is evident that there exist different regions of micromixing at different rotating speeds, so a multi-scale phenomenon is clarified.It leads to a two-region theory and more understanding for the micromixing in RPB and will provide a solid base for further study.