Experimental Investigation And Theoretical Calculation On Electrospray Characteristics With Different Electrode Structures

The droplet size and velocity were measured by a Phase Doppler Anemometer in single electrode structure and combined electrode structure.Compared with single electrode structure,the droplet size in combined electrode structure is smaller and the velocity is slower at same spraying mode.Meanwhile the spraying in combined electrode structure is more stable than it in single electrode structure due to its smaller RMS velocity.The axial electric field intensity was theoretically calculated respectively in the two spraying systems.It is found that electric field intensity of two electro-spraying systems decreases rapidly around the position where z=0.0mm.It is inferred that the effect of electric filed force on ethanol droplet is strongest around nozzle.The current caused by the electrospray was measured and the specific charge was calculated.It is found that specific charge of single electrode structure is close to that of combined electrode structure at the same spraying mode on the whole.It means that ring electrode has little effect on specific charge of droplet.Simultaneously,the nozzle voltage of combined electrode structure is lower than that of single electrode structure at the same spraying mode.The reason for this phenomenon is that the ring electrode plays an important role on the breakup of ethanol droplet.The differences of droplets size,axial velocity and axial RMS(root mean square)velocity in different conditions are compared.Under the experimental conditions in this paper,many rules are found.Droplets size and velocity are smaller and spraying is more stable when flow rate reduces.The ring electrode can reduce the droplet size and velocity obviously.Droplet size becomes smaller and spray becomes more stable when ring electrode voltage is 1.30 kV.Droplets size decreases under the effect of evaporation and droplets velocity decreases under the effect of air viscous resistance when the distance between steel mesh and nozzle outlet increases.Better spraying performance can be achieved under the conditions of the spacing between the nozzle and ring electrode is 1mm.The theoretical values of corona charge were calculated using classical formulas in the two spraying systems.It is found that the calculated specific charge generated by corona charging is close to the experimental specific charge in two spraying systems.Thus,it can be inferred that the main source of surface charge comes from the corona charging process.Theoretical analysis is performed based on the Rayleigh limit model,and it is found that the Rayleigh limit coefficient is between 0.4 and 0.6 at Cone-jet mode,but it is between 0.2 and 0.4 at Pulsed-jet mode and Skewed cone-jet mode,and it is below 0.2 at Multi-jet mode.According to the Weber number model,the critical specific charge decreases with the increasing of the droplet velocity.Meanwhile,with the droplet radius decreasing,the critical specific charge increases intensely,and the range of droplet velocity expands.