Characteristics Of Flash Boiling Atomization In Injector

Ejectors have many advantages over other traditional static mixers such as higher mixing effect and mass transfer coefficients.Therefore,ejectors have been widely used in many fields such as chemical engineering,machinery,environmental protection.The performance of ejector is determined by the process of jet atomization.In other words,it is determined by the droplet size and distribution.Although there are quite a few studies on the flash boiling atomization,due to the diversity of operating conditions,the influencing factors are not fully studied and the parameters used to indicate the influencing factors are not convenient.So based on the computational fluid dynamics simulation,the relationship of nozzle structure and flow patterns was discussed,the new model of judgment of flow pattern was obtained,then the relationship of operation condition and characteristics of flash boiling atomization was analyzed.At last,the difference between traditional and flash boiling atomization was analyzed.The results were obtained as follows.First,using the CFD method,the relationship of the injection pressure,the ratio of nozzle length and nozzle diameter(L/d),the ratio of nozzle radius of the entrance and nozzle diameter(r/d)and change of flow patterns was studied,the results are as follows:The study shows that it is easier to form cavitation zone when the injection pressure is larger and r/d is small.Hydraulic flip can change to cavitation by increasing L/d.At present,there are defects in judgment of flow pattern with empirical model.The model established in this paper is more accurate than the empirical model to judge the change of flow pattern.The new model is helpful to modify the existing empirical model.In addition,according to the relationship,we can use the method of reasonably adjusting the relationship between the nozzle structure and operating conditions to avoid the generation of hydraulic flip,and to get better atomization effect.Secondly,the characteristics of flash boiling atomization were studied by using CFD,the results are as follows:Under other conditions are the same,the greater the vaporization rate of the jet,the smaller SMD,the more narrow droplet distribution.The greater the vaporization rate of the jet liquid,the greater the impact force on the droplet,the quality of atomization is enhanced by increasing the vaporization rate of liquid.With the increase of the surface tension of the droplet,the SMD value of the droplet is increase,the droplet distribution range becomes larger,the droplet distribution is more uniform.The effect of density on droplet atomization characteristics is opposite to that of surface tension.With the increase of droplet density,the SMD value of droplets is decreased,and the distribution range becomes narrow.In the simulation of this paper,the effect of viscosity change on atomization characteristics is small when viscosity value less than 0.01 kg/(m�s),but the greater the viscosity,the greater the value of SMD when the viscosity value larger than 0.01 kg/(m�s).The effect is similar to that of surface tension,which is to prevent the breakup of droplets.The difference between traditional and flash boiling atomization was analyzed.Under the same injection rate and injection pressure,the droplet size SMD of flash boiling atomization is reduced compared with the traditional atomization,the droplet breakup effect is enhanced,and the droplet distribution is more uniform.