A Study On Characteristics And Mechanism Of Single Drop Breakup In Jet Flow

Liquid-liquid system generally exists in the chemical mixing,absorption,extraction,separation and other operations.The properties and behaviors of these systems depend heavily on the drop size distribution(DSD)of the dispersed phase.The drop size distribution can affect the interface area of the two phases,the mass and heat transfer in the system,and finally the effect of the mixed reactor.Droplet size distribution is the result of a series of complex processes occurring simultaneously on a single drop.It is of great significance to further understand the mechanism of droplet breakage and improve the model of droplet breakage.At the same time,it can provide theoretical support for optimizing the industrial reactor.In this study,the characteristics of drop breakup in the jet flow field were studied experimentally and numerically.The jet fields in this study included simple laminar and transitional flow,turbulent jet and more complex blade jet.The breaking conditions,breaking probability and droplet distribution of binary breakup,ternary breakup and multiple breakup were studied in different jet fields.With the help of particle image velocimetry(PIV),the characteristics of flow field in the process of drop breakup were studied,and the effects of viscosity and inertia on the process of drop breakup were analyzed.In the experiment of liquid drop breakup in laminar and transitional flow,the critical Reynolds number of binary breakup is determined accurately.In a narrow range of Reynolds number,the probability of the drop breakup changes from 15%to 85%.When the Reynolds number exceeds a critical value,the probability of the drop breakup is close to 100%.The volume of daughter drops changes regularly with Reynolds number.The breakup time decreases with the increase of Reynolds number.The average flow field plays an important role in the process of drop breakup.The deformation from micro scale to mesoscale is caused by viscous shear,and the deformation from mesoscale to macro scale is caused by inertial impact,which leads to binary drop breakup.The critical capillary number and Weber number is 0.17 and 32,respectively.In the turbulent jet flow field,the probability of binary breakup decreases from nearly 100%to 6.3%as the Reynolds number increases from Re=2727 to 4825;the probability of ternary breakup increases from 0%to about 33%,and decreases to about 10%;and the multiple breakup increased from 0%to 83.3%.The total probability of three kinds of breakup is close to 100%.The expected of daughter drop number ranges from 3.59 to 7.65 within the range of Re studied.With the combination of drop breakup results and single-phase 2D PIV data,the following transformation conditions can be estimated:Ca from 0.17 to 0.27 and We from 55 to 111.In the complex turbulent blade jet,with Reynolds number ranging from 8950 to 13930,the probability of drop breakup increases from 17%to 73%.The binary breakup decreases from 100%to 31%,and the multiple breakup increases from 0%to 69%.The expected of daughter drop number ranges from 2.63 to 5.66 within the range of Re studied.The phase average velocity of the flow field is mainly distributed in the jet area at the right of the blade,which is slightly close to the upper side of the blade.The flow field shows Reynolds similarity.The dimensionless turbulent kinetic energy(TKE)is almost the same under different Reynolds numbers.The peak value of TKE is about 0.1 under phase-averaged condition and 0.12 under phase-resolved condition.The peak value of Ca ranges from 0.038 to 0.095,and We ranges from 7.0 to 18.8.In the section of numerical simulation of single-phase jet,the shape and velocity distribution of jet are basically consistent with the experimental results.However,there is still deviation between the experimental and simulation results of the velocity attenuation at the core area of the jet.This is also a deficiency of the model itself for simulation at the transformation from laminar to transitional flow.In the simulation of drop breakup,the deformation and breakup,the volume of daughter drops corresponds well with the experiment results.The coupling of the velocity field and the droplet deformation is very important for the analysis of deformation and breakup process.It provides a visual guidance for the analysis of the role of viscous and inertial forces in the process of drop deformation and breakup.It is also important for analyzing the breakup mechanism of drop.However,there are still some shortcomings in the current numerical simulation study.The Re deviation between simulation and experition results is about 8%.