Simulation of the mixing process in a straight tube with sudden changed cross-section  

作　　者：Yangcheng LU Shan Zhu Kai Wang Guangsheng Luo 

机构地区：[1]State Key Laboratory of Chemical Engineering, Department of Chemical Engineering, Tsinghua University, Beijing 100084, China

出　　处：《Chinese Journal of Chemical Engineering》2016年第6期711-718,共8页中国化学工程学报（英文版）

基　　金：Supported by the National Natural Science Foundation of China(21176136,21422603);the National Science and Technology Support Program of China(2011BAC06B01)

摘　　要：In this work, we revised the expression of mixing intensity to describe the mixing output through a cross section in a flow system by considering heterogeneity of flow field, and carefully investigated the mixing process along a straight tube with expanding/contracting cross section by simulation method. The simulation results show that a sudden expansion of cross section has remarkable mixing intensification effect within a limited period(on the sub-second scale) or tube-length(on the millimeter scale), corresponding to the generation of considerable local vortices determined by both the flow capacity and the ratio of cross section change; a sudden contraction of cross section has instantaneous but weak mixing intensification effect; through introducing a local expansion structure with proper length, as the combination of sudden expansion and sudden contraction, their mixing intensification effects could be superposed. Besides, the rationality and importance are experimentally verified to explore the time profile of mixing intensity and carry out the vortex analysis by simulation for enhancing the selectivity of a complicated reaction system. These progresses may lead to more meaningful quantitative description of mixing process in a flow microreactor for some specific chemical processes.In this work, we revised the expression of mixing intensity to describe the mixing output through a cross section in a flow system by considering heterogeneity of flow field, and carefully investigated the mixing process along a straight tube with expanding/contracting cross section by simulation method. The simulation results show that a sudden expansion of cross section has remarkable mixing intensification effect within a limited period （on the sub-second scale） or tube-length （on the millimeter scale）, corresponding to the generation of considerable local vortices determined by both the flow capacity and the ratio of cross section change; a sudden contraction of cross section has instantaneous but weak mixing intensification effect; through introducing a local expansion structure with proper length, as the combination of sudden expansion and sudden contraction, their mixing intensification effects could be superposed. Besides, the rationality and importance are experimentally verified to explore the time profile of mixing intensity and carry out the vortex analysis by simulation for enhancing the selectivity of a complicated reaction system. These progresses may lead to more meaningful quantitative description of mixing process in a flow microreactor for some specific chemical processes.

关 键 词：MixingIntensificationSimulationSudden change in cross-sectionVortex 

分 类 号：TQ027.1[化学工程] TU323.01[建筑科学—结构工程]