Development of electrohydrodynamic (EHD) jet technology

Formation of micro and nanometer-sized droplets from an electrostatic nozzle is an interesting problem. It is useful in a number of different fields including ink-jet printing, electrospray for mass spectroscopy, processing of biomaterials, electrohydrodynamic atomization, and other applications. This process can be considered as a branch of fluid mechanics concerned with electrical force effects. The variety of variables affecting electrohydrodynamic ejection often makes it difficult to investigate and predict its operation, for instance, the difficulty in getting an exact formulation of the dependence of droplet size with other parameters such as applied voltage, flow rate, size of capillary nozzle, electrode configuration, and chemical properties of liquid such as viscosity, electric conductivity, and relative permittivity. Among these effects, the electrospray can be classified into many modes such as dripping, micro-dripping, pulsating, cone-jet and instability of cone-jet including varicose, kink and multi-jet. This classification is important to consider and define main factors to establish controlling equation of droplet size. However, it is still lacking in detailed analysis of the transition dynamics of this process.