网板柱塞流电化学反应器流动特性及传质性能的研究

发布时间：2018-09-06 11:05

【摘要】：柱塞流电化学反应器(PFER)是一种可以提高电流效率,降低处理成本的新型电化学法处理技术。网板柱塞流电化学反应器(MPE-PFER)因阴阳电极面积相同且垂直于流体流动方向,电极为棱形网孔结构,可解决传统柱塞流电化学反应器电流分布不均、流体速度分布不均、湍流强度不均等不足,有利于污染物的传质和分解。计算流体力学(CFD)可有效模拟反应器内部流场、粒子图像测速技术(PIV)可直观观测反应器内部流场,结合这两种技术可为反应器的性能研究和结构优化提供可靠的依据。本文采用CFD与PIV相结合的方式,分别模拟和测试了不同进口方式(轴向、径向和切向)对反应器的影响,分析了反应器进口区域的速度场和整个反应器的压强降等水力特性。结果显示,模拟结果与测试结果基本一致,进口区域属流体流动的过渡区域,受进口方式的影响较大。相比其他两种进口方式,切向进口的速度分布均匀,没有大的速度梯度,没有回流死区,电极表面流速也比较适合,且压降最小。其次,通过DPM模型,分析了不同气泡直径和质量流量对反应器内部流场的影响。模拟结果表明,气泡对连续相流场的影响随着气泡直径的增大而增大,气泡直径较小时,气泡增强湍动且使流场分布变得均匀,而直径较大时,反应器上下部分湍动强度分布不均匀,上端湍动剧烈,而下端出现低湍动区;当气泡量少时,连续相流动起主导作用,气泡对湍动强度的影响不明显,随着气泡的增多,气泡效应越来越明显,流场分布变得越来越均匀。最后,分别从流场分布和传质性能两方面对比分析了MPE-PFER和PFER的性能。从流场来看,MPE-PFER中流场受进口区域影响小,流场可以更早达到稳定,稳定后径向流速分布更加均匀,在网孔处达到速度峰值;PFER中电极间流场呈抛物线型分布,流场受进口区域影响较大。通过对两种反应器传质半经验公式的分析发现,由于网板电极的存在,MPE-PFER的传质性能明显高于PFER,MPE-PFER的传质关联式是PFER的23.061.4?u倍,在相同的流量变化下,MPE-PFER传质系数提高的是PFER的两倍。
[Abstract]:Plunger flow electrochemical reactor (PFER) is a new electrochemical treatment technology which can improve current efficiency and reduce treatment cost. Because of the same area of cathode and positive electrode and perpendicular to the direction of fluid flow, the electrode of MPE-PFER is a prism mesh structure, which can solve the problem of uneven current distribution and uneven fluid velocity distribution in traditional plunger flow electrochemical reactor (MPE-PFER). The uneven turbulence intensity is favorable to the mass transfer and decomposition of pollutants. Computational fluid dynamics (CFD) can effectively simulate the flow field in the reactor. Particle image velocimetry (PIV) can directly observe the flow field in the reactor. The combination of these two techniques can provide reliable basis for the performance research and structural optimization of the reactor. In this paper, the effects of different inlet modes (axial, radial and tangential) on the reactor were simulated and tested by using CFD and PIV, respectively. The velocity field in the inlet region of the reactor and the hydraulic characteristics of the whole reactor such as pressure drop were analyzed. The results show that the simulation results are in good agreement with the test results, and the inlet region is a transition region of fluid flow, which is greatly affected by the inlet mode. Compared with the other two methods, the velocity distribution of tangential inlet is uniform, there is no large velocity gradient, there is no reflux dead zone, the electrode surface velocity is more suitable, and the pressure drop is minimum. Secondly, the influence of different bubble diameter and mass flow rate on the flow field in the reactor was analyzed by DPM model. The simulation results show that the effect of bubbles on the continuous phase flow field increases with the increase of bubble diameter. When the bubble diameter is small, the bubble increases turbulence and makes the flow field distribution more uniform. The turbulent intensity distribution of the upper and lower parts of the reactor is uneven, the upper end of the reactor is intense, and the lower end of the reactor has a low turbulent zone, when the amount of bubbles is small, the continuous phase flow plays a leading role, and the effect of bubbles on the turbulent intensity is not obvious, with the increase of bubbles, The bubble effect becomes more and more obvious, and the flow field distribution becomes more and more uniform. Finally, the performance of MPE-PFER and PFER are compared and analyzed in terms of flow field distribution and mass transfer performance. From the point of view of the flow field, the flow field in MPE-PFER is less affected by the inlet region, the flow field can be stabilized earlier, the radial velocity distribution is more uniform after stabilization, and the flow field between the electrodes in the PFER reaches the peak velocity at the mesh. The flow field is greatly affected by the inlet area. Through the analysis of the semi-empirical formula of mass transfer in two reactors, it is found that the mass transfer performance of MPE-PFER is obviously higher than that of PFER by 23.061.4u, and the mass transfer coefficient of MPE-PFER is twice that of PFER under the same flow rate.
【学位授予单位】：浙江工业大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：X703

【共引文献】