Electrospray modes of liquids in electrohydrodynamic atomization: A review

Liquid is sprayed from a capillary tube and further disperses into fine drops in various means, when subjected to an externally electric field, where the process of liquid jet formation and breakup into drops is usually named as electrohydrodynamic atomization or electrospray (ES). Electrospray has been extensively applied into many fields because uniform and highly charged drops, easy controllability in size and motion, and various ES modes are available to match the requirements of various applications. In present work, recent progresses in theory and numerical work to explain electrospray structure and drop formation were summarized. According to the geometry of liquid ejection and its further disintegration, main ES modes including dripping, micro-dripping, spindle, cone-jet, multi-jet, and simple-jet have been designated. The transformation of ES modes due to variation of electric potential, liquid flow rate, and physical parameters, the formation of curved liquid surface, and jet fragmentation behavior in these ES modes were also reviewed, as well as generated drops dynamics. In a rational range of flow rate, dripping, micro-dripping, spindle, cone-jet, multi-jet modes successively emerge with an increase in electric potential, and otherwise, an irregular instability may occur. In addition, the simple jet mode occurs in a relatively large flow rate. The insight into ES modes may fully understand mechanism and technology of electrospray and further promote more extensive application in industrial fields.