New regimes and their spraying characteristics of electrohydrodynamic atomization

Electrohydrodynamic (EHD) atomization is a highly useful regime of EHD spraying, which has been applied to the production of three-dimensional ultra-thin membrane structures and also the removal of high heat flux called electrospray cooling. However, the rapidly changing liquid atomization behavior under the impact of a high electrostatic potential is so complicated that many aspects of the atomization morphology are not completely comprehended. In this work, we conducted an experimental study on EHD atomization under three key operating parameters including applied voltage, flow rate, and nozzle height, where nozzle height is a variable that was barely investigated in previous EHD spraying work. Seven distinct spraying regimes, namely Spindle, Pulsating Jet, Rotating Atomization, Pulsating Atomization, Stable Atomization, Tilted Atomization, and Oscillating Jet are observed, where Rotating Atomization and Pulsating Atomization are two newly discovered regimes that have not been discussed before. We use the electric Bond number and dimensionless flow rate to analyze and explain the variations of spraying profile and regime, Taylor cone profile, liquid jet breakup length, liquid jet rotating and pulsating frequency, liquid jet atomization angle and atomization area of the atomization process. Especially, the characteristics of the two newly discovered atomization regimes are comprehensively examined and compared with those of the Stable Atomization regime, which provide some new insights into the complex and variable EHD atomization phenomena.