Study On Flow Type Transition And Micromixing Performance Of Spinning Disk Reactor Enhanced By Surface Microstructure

The spinning disc reactor is as a new type of high gravity process intensification equipment.It uses the jet impacting on a spinning wall to form a high gravity film flow,which has the advantages of high heat transfer rate,high mass transfer capacity,excellent micromixing performance,easy to scale up and continuous production,etc.It is widely used in precipitation,crystallization,polymerization and photocatalysis and other mixing sensitive reaction fields.Micromixing is controlled by the viscous convective deformation and molecular diffusion of the liquid film on the reactor surface,and high rotational speed can promote the mixing process within a certain flow rate range,but the product quality cannot be significantly improved,and faces problems such as sharp increase in specific energy consumption,structural stability and safety.Therefore,in this dissertation,we improve the reactor surface structure to regulate the liquid film flow behavior and enhance the microscopic mixing at lower rotational speed,and explain the intrinsic mechanism to provide guidance for enhancing the reaction process.Based on the visualization spinning disc reactor experimental platform,this dissertation investigates the influence of operating conditions and media physical parameters on the flow characteristics of liquid film on the reactor surface and micromixing performance for five micro-groove spinning disc structures,and draws the following main conclusions:(1)The influence of micro-groove arrangement forms(circumferential,radial,and number of micro-grooves)on the distribution of liquid film flow type on the surface of the spinning disc was investigated,and six typical flow types were summarized,including incomplete wetting type,smooth spiral linear type,smooth spiral serrated type,smooth spiral broken type,irregular stacked type and irregular broken type,and the typical characteristics and existence range of each flow type were explained.Relative to the smooth disk,no transition flow and reverse spiral wave structure appear,and the smooth spiral region expands,especially the broken region.(2)A phase diagram of the liquid film flow structure transition is plotted.The form of micro-groove arrangement,operating conditions and media properties do not significantly affect the existence range of incomplete wetting flow type.For the same micro-groove structure,the transition of smooth spiral flow type is mainly influenced by the rotational speed,and with the increase of rotational speed,the smooth spiral serrated and smooth spiral broken flow types will be experienced in turn;the irregular flow type is mainly influenced by the flow rate,and with the increase of rotational speed,it gradually changes from stacked to broken type.For different micro-groove structures,the number of micro-grooves increases and the distribution range of unpaved flow type is larger;compared with circumferential micro-grooves,the arrangement of micro-grooves in radial direction leads to a relatively smaller range of irregular flow type existence and is more likely to appear broken flow type,while the smooth spiral flow type exists in a wider range and is more regular,which can effectively regulate the existence range.(3)Based on digital image processing,the initial formation position of the spiral wave is quantified by using the occurrence radius factorη,and the variation rule ofηis summarized.ηdecreases with the increase of rotational speed and decrease of flow rate;the decrease of medium surface tension leads to the increase ofη,and the low viscosity fluid The radius of occurrence is more influenced by the micro-groove;the relationship between the radius of occurrence and the synchronization radius as well as the local Ekman number is analyzed.For low viscosity fluids,the circumferential micro-groove distribution area increases,and the radius of occurrence first decreases sharply with increasing rotational speed and then flattens out;there is instability in the radius of occurrence with increasing rotational speed as the density of circumferential micro-grooves increases,and the radius of occurrence of radial micro-grooves decreases significantly at higher rotational speeds compared with that of circumferential micro-grooves.(4)The micromixing performance of the reactor was characterized using the iodide-iodate parallel competition system.It was found that the micro-mixing performance was significantly improved for both micro-groove discs compared with smooth discs;the micromixing effect increased with the increase of micro-groove distribution range;the circumferential micro-groove density had little effect on the disaggregation index;the radial micro-groove micro-mixing enhancement was more significant compared with circumferential micro-grooves.The micromixing characteristic time t_m was estimated based on the agglomeration model,and the t_m range was between 0.04-2.19ms under the experimental conditions of this dissertation,and was compared and analyzed with related studies.