An experimental study on the transition of electrohydrodynamic spraying process and regime

Abstract

Electrohydrodynamic (EHD) spraying based manufacturing techniques are remarkably useful for the fabrication of micro/nanoscopic multi-functional devices but also quite complicated owing to their highly changeable spraying behavior and regime. For the propose of gaining more knowledge about different EHD spraying process and regime, this paper carries out an experimental study on EHD spraying of ethanol under a wide range of three key operating parameters: applied voltage ($\Phi$ = 1500– 4000 V), flow rate ($Q$ = 0.05, 0.1, 0.2, 0.3 mL/min), and nozzle height ($H$ = 5, 10, 20, 30 mm), while nozzle height was a variable that was barely investigated in previous EHD spraying studies. Six distinct spraying regimes, namely Dripping, Spindle, Atomization, Spindle + Atomization, Whipping, and Oscillation are discovered, whose dependences on these three parameters are demonstrated and explained. Besides, as a significant part of the EHD spraying process, the variations of the spraying period and morphology with these three parameters are also discussed. Moreover, the variations of the spraying regime, spraying frequency, and nondimensionalized Taylor cone length with the electric Bond number and dimensionless flow rate are analyzed, which signifies the close correlation between these dimensionless variables and liquid spraying behaviors. The findings in this work can be used for promoting the understanding of EHD spraying process and achieving more accurate regulation of EHD spraying based manufacturing techniques.