The Research For Macroscopic Dispersion In Liquid-continuous Impinging Streams Reactor

The problems of mass transfer or dispersive mixing in Chemical equipment havegreat effect on the plant efficiency and product quality, especially for the reactor. TheLiquid-continuous impinging streams reactor(LISR) is a new type of reactor, which isproposed in recent years and mainly used to strengthen the decentralized byimpinging stream mixing technology that can be applied to the reactor. A series ofexperiments results show that the reactor is not only displaying the well mixeddispersion and the promotion of good reaction characteristics, but also cansignificantly improve product quality. It is necessary to pay close attention to themixing and diffusion processes in LISR. However, the characteristics of fluid flowstructure and dispersion in LISR, in particular the macroscopic fluid dispersioncharacteristics, affects the efficiency of fluid dispersion mixing greatly. In time order,the macro-dispersed have precedence over the micro-dispersed, and the time requiredby macro-dispersion is much greater than the micro-dispersed, reducing themacroscopic dispersion time can greatly reduce the total fluid mixing time. Besides,the researches on macroscopic dispersion are very few; most of them only study fluidmixing performance through the experiment.In this paper, it is based on the LISR. First of all, the physical model, referring tothe size of the existing experimental model, can be simplified and approximateprocessed. And its geometry and mesh model are established by using softwareGAMBIT. Then, under a different structure and operating parameters, themacroscopic fluid flow field in LISR is simulated by using computational fluiddynamics software FLUENT, it can be concluded that the macroscopic fluiddispersion law is changing with parameter.The main results are as follows: With the blade angle increases, the fluid velocity,pressure fluctuations and changes in the value of shear stress all show the maximumin the middle of the blade; But the changing angle of the blades does not change macroscopic mixing time and only results in the discrepancies component of themaximum difference for each section; When the blade speed is1500r/min, theaverage of the maximum pressure is12.097Pa and the maximum pressure fluctuationis0.889Pa; The increases of paddle speed do not affect the spatial distribution of shearstress, but to make the impact zone spatial average shear stress increase and the fluidshear dispersing more intense; In addition, with the blade speed increases, themacroscopic mixing time decreases. When the speed is added to a certain, mixingtime does not change the macro time or less; With the impact distance increases, themaximum speed of the fluid increase firstly and then it decrease, but overall it showslittle change; The average pressure value which is stable in pressure moments firstlydecreases and then increases. When the impact distance is40mm, the minimumaverage pressure is12.0972Pa in its stable time, but the pressure fluctuations is in thevalue of the maximum and reach0.8895Pa; Meanwhile, the variable impact distancedoes not affect the symmetry of the spatial distribution of the intensity of pressurefluctuations. With the impact distance increasing, the impact area range also increasesso that the fluid shear stress and spatial average maximum shear stress in the impactzone are reduced. And macroscopic mixing time also increases, but the change is notobvious and always around2.5s.Analysis of these results indicate that, as the blade angle increase, the active areaof the fluid in the axial direction of the blades increase, but the fluid force on theblade is continuously reducing. Under the joint action of two factors, the blade at theintermediate angle of inclination of45degrees, the fluid component uniformly isdispersed and mixed; as the collision distance of impinging zone increase, it results inthat the volume of impinging zone is gradually increasing. but the impact of thecollision of the fluid per unit volume weaken, leading to poor dispersion ofmacroscopic fluid; Nevertheless, As the collision distance increase, it can promote theflow of fluid circulating which is in favor of the fluid component fraction uniformlydistributed throughout the reactor. When the collision distance is40mm, the overalldispersion of the components is the best; with the impact velocity increases, the fluidof rotation in the draft tube is enhanced. It strengthens the interaction between the two fluids in the impact zone, which has a catalytic role for macroscopic fluid dispersion,so as to promote both macroscopic fluid moment dispersed. Meanwhile, from theenergy point of view, increasing the impact velocity can promote the fluid energy toincrease, and then more energy is used in the fluid dispersion. But when the energy isincreased to a certain extent, the energy for the fluid dispersion reach the saturationlevel and the dispersing effect weaken. To sum up, when the impeller speed is1500r/min, the blade angle is45degrees and the impact distance is40mm, the effectof dispersion is the best of all.