Study On Preparation Of Microdroplets In Ultra-high Gravity Environment And Application In Fenton Oxidation Process

On the advantages of small size,large specific surface area,short diffusion distance,etc.,microdroplet has been widely used in many fields such as biomedicine,material science,food processing and microelectronic engineering.The high-throughput and controllable generation of microdroplets is the key to its application.Therefore,it is of great significance to develop and design an efficient microdroplet preparation device.In this study,a novel microdroplet preparation device is designed based on ultra-high gravity environment.Firstly,the characteristics of the microdroplets prepared by the said device were fundamentally studied using laser diffraction technology,and the effects of rotational speed,initial liquid velocity,viscosity,surface tension,and pore size of packing on the average diameter and diameter distribution of the generated droplets were investigated respectively.The device was further applied to the treatment of organic wastewater.Fenton reagent was used to the degradation of Rhodamine B simulated wastewater,and the effects of different operating conditions on the degradation efficiency and apparent reaction rate constant of Rhodamine B were investigated.The main findings are shown as follows:(1)The average diameter of the droplets decreases with the increase of rotational speed,viscosity,and filler pore size,increases with the increases of liquid surface tension,and slightly increases with the increase of the initial liquid velocity.The dimensional analysis method is used to correlate the average diameter of droplets under different conditions,and the error between the predicted value and the experimental value is within±15%.In the range of rotational speed of 4000-12000 r/min,the average diameter of the generated droplets is 25-63 μm.At the same time,the droplet size can be adjusted by changing the rotational speed and the filler pore size.The diameter distribution of droplets conforms to the R-R distribution model.Compared with the rotating cup and disk,in the same rotational speed range,the average diameter of droplets in this study is smaller.(2)The Fenton oxidation process was intensified by changing the addition method of the Fenton reagents,i.e.using H2O2 droplets to collide wastewater film.The purpose is to increase the generation rate and utilization ratio of hydroxyl radicals,so as to realize the on-demand supply of H2O2.The degradation efficiency increases and then stabilizes with the increase of rotational speed.The rotational speed has no obvious effect on the apparent reaction rate constant.The initial pH of the solution,the concentration ratio of Fe2+to H2O2,and the concentration of H2O2 have important influence on the degradation efficiency and apparent reaction rate constant.The degradation efficiency and apparent reaction rate constant increase with the decrease of the initial pH value of solution,and increase with the increase of concentration ratio of Fe2+to H2O2,the concentration of H2O2,and the temperature.Reducing the pore size of the packing is beneficial to improve the degradation efficiency.In this research,the optimal operating conditions are as followed:the rotational speed is 5000 r/min,the initial pH of solution is 3,the concentration ratio of Fe2+to H2O2 is 1:1,the concentration of H2O2 is 0.24mmol/L,and the temperature is 20℃.Further,compared with other Fenton processes,the dosage of H2O2 in this study is less in the same processing time.